Digital Wireless Basics

This article discusses digital wireless basics. It covers wireless history along with basic radio principles and terms. Digital building blocks like bits, frames, slots, and channels are explained along with details of entire operating systems. Building on my analog cellular article, digital cellular gets treated along with the newest service: personal communication services or PCS.

Where we are now?

Wireless has gone digital, enabling services that analog couldn't easily provide. Like better eavesdropping protection, increased call capacity, decreased fraud, e-mail delivery, and text messaging. But digital has its drawbacks, especially poor coverage and often bad audio quality.We'll compare newer digital systems like GSM and PCS1900 with systems like analog and early digital cellular. We'll better understand where wireless is today and where it's headed.

New and existing wireless services share much in common. They all provide coverage using a cellular like network of radio base stations and antennas. They all use mobile switches to manage that network, allowing calls, arranging handoffs between cells, and so on. They all use use one of two microwave frequency bands. Sometimes both. They all use digital to some extent. But aside from providing basic voice and data handling, the many services differ greatly in features and how they provided. Here's a quick, completely oversimplified list to get us going. More information follows:

AMPS: Advanced Mobile Phone service. Conventional cellular service. Mostly analog, with some digital signals providing call setup and management. A first generation service, now only installed in remote regions.

IS-95: All digital cellular using CDMA, a spread spectrum technique. Sprint PCS uses this technology. Sometimes called by its trade name of PCS 1900. A second generation or early digital service.

IS-136: D-AMPS 1900. Feature rich cellular. Mostly digital, although backward compatible with analog based AMPS. AT&T uses it for their nationwide cellular network. Uses time division multiple access or TDMA. Incorporates the old standard IS-54, an early second generation system at the time. IS-136 operates at either 800 Mhz or 1900 Mhz. AT&T is moving to a transitional technology whereby three standards, in some form, will work together: IS-136, GSM, and the newer General Packet Radio Service or GPRS. Eventually AT&T will stop using IS-136, replace it with GSM, and eventually replace that with a wideband CDMA system.

GSM. European cellular come to North America at 1900 Mhz. Fully digital with advanced features. Each mobile has intelligence within the phone, using a smart card. Uses TDMA. Among others, Pacific Bell uses GSM. Will migrate in a few years to a wideband CDMA technology.

iDEN: Proprietary cellular scheme devised by Motorola and used nationwide by NEXTEL. Combines a cell phone with a business radio. TDMA based.

We'll look soon at each service. For right now, though, to give us some orientation, let's go over recent mobile telephone history. It is quite a L-O-N-G history, so feel free to skip over that series and go on to the next topic, which is about standards.

Click here for this free chapter from Professor Noll's book described below, the selection is an excellent, simple introduction to cellular. (32 pages, 204K in .pdf)

More info on Introduction to Telephones and Telephone Systems (external link to Amazon) (Artech House) Professor A. Michael Noll

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Here's my latest writing on mobile telephone history. 9,000 words, concentrating on developments after World War II. It's much easier to get into than this article if you're just interested in the cellular radio era. You can download it in .pdf format (internal link) or as a Word document (internal link). The .pdf is illustrated. Both versions have dozens of references. Comments are always welcome. Thanks, Tom

Digital wireless and cellular roots go back to the 1940s when commercial mobile telephony began. Compared with the furious pace of development today, it may seem odd that mobile wireless hasn't progressed further in the last 60 years. Where's my real time video watch phone? There were many reasons for this delay but the most important ones were technology, cautiousness, and federal regulation.

As the loading coil and vacuum tube made possible the early telephone network, the wireless revolution began only after low cost microprocessors and digital switching became available. The Bell System, producers of the finest landline telephone system in the world, moved hesitatingly and at times with disinterest toward wireless. Anything AT&T produced had to work reliably with the rest of their network and it had to make economic sense, something not possible for them with the few customers permitted by the limited frequencies available at the time. Frequency availability was in turn controlled by the Federal Communications Commission, whose regulations and unresponsiveness constituted the most significant factors hindering radio-telephone development, especially with cellular radio, delaying that technology in America by perhaps 10 years.

In Europe and Japan, though, where governments could regulate their state run telephone companies less, mobile wireless came no sooner, and in most cases later than the United States. Japanese manufacturers, although not first with a working cellular radio, did equip some of the first car mounted mobile telephone services, their technology equal to whatever America was producing. Their products enabled several first commercial cellular telephone systems, starting in Bahrain, Tokyo, Osaka, and Mexico City.

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Communicating wirelessly does not require radio. Everyone's noticed how appliances like power saws cause havoc to A.M. radio reception. By turning a saw on and off you can communicate wirelessly over short distances using Morse code, with the radio as a receiver. But causing electrical interference does not constitute a radio transmission. Inductive and conductive schemes, which we will look at shortly, also communicate wirelessly but are limited in range, often difficult to implement, and do not fufill the need to reliably and predictably communicate over long distances. So let's see what radio is and then go over what it is not.

Weik defines radio as:

"1. A method of communicating over a distance by modulating electromagnetic waves by means of an intelligence bearing-signal and radiating these modulated waves by means of transmitter and a receiver. 2. A device or pertaining to a device, that transmits or receives electromagnetic waves in the frequency bands that are between 10kHz and 3000 GHz."

Interestingly, the United States Federal Communications Commission does not define radio but the U.S. General Services Administration defined the term simply:

1. Telecommunication by modulation and radiation of electromagnetic waves. 2. A transmitter, receiver, or transceiver used for communication via electromagnetic waves. 3. A general term applied to the use of radio waves.

Radio thus requires a modulated signal within the radio spectrum, using a transmitter and a receiver. Modulation is a two part process, a current called the carrier, and a signal which bears information. We generate a continuous, high frequency carrier wave, and then we modulate or vary that current with the signal we wish to send. Notice how a voice signal varies the carrier wave below:

This technique to modulate the carrier is called amplitude modulation. Amplitude means strength. A.M. means a carrier wave is modulated in proportion to the strength of a signal. The carrier rises and falls instantaneously with each high and low of the conversation.The voice current, in other words, produces an immediate and equivalent change in the carrier.

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As we can tell already, and as with the telephone (internal link), a radio is an electrical instrument. A thorough understanding of electricity was necessary before inventors could produce a reliable, practical radio system. That understanding didn't happen quickly. Starting with the work of Oersted in 1820 and continuing until and beyond Marconi's successful radio system of 1897, dozens of inventors and scientists around the world worked on different parts of the radio puzzle. In an era of poor communication and non-systematic research, people duplicated the work of others, misunderstood the results of other inventors, and often misinterpreted the results they themselves had achieved. While puzzling over the mysteries of radio, many inventors worked concurrently on power generation, telegraphs, lighting, and, later, telephones. We should start at the beginning.

In 1820 Danish physicist Christian Oersted discovered electromagnetism, the critical idea needed to develop electrical power and to communicate. In a famous experiment at his University of Copenhagen classroom, Oersted pushed a compass under a live electric wire. This caused its needle to turn from pointing north, as if acted on by a larger magnet. Oersted discovered that an electric current creates a magnetic field. But could a magnetic field create electricity? If so, a new source of power beckoned. And the principle of electromagnetism, if fully understood and applied, promised a new era of communication.

In 1821 Michael Faraday reversed Oersted's experiment and in so doing discovered induction (internal link). He got a weak current to flow in a wire revolving around a permanent magnet. In other words, a magnetic field caused or induced an electric current to flow in a nearby wire. In so doing, Faraday had built the world's first electric generator. Mechanical energy could now be converted to electrical energy. Is that clear? This is a very important point. The simple act of moving ones' hand caused current to flow. Mechanical energy into electrical energy. But current was produced only when the magnetic field was in motion, that is, when it was changing.

Faraday worked through different electrical problems in the next ten years, eventually publishing his results on induction in 1831. By that year many people were producing electrical dynamos. But electromagnetism still needed understanding. Someone had to show how to use it for communicating.

In 1830 the great American scientist Professor Joseph Henry transmitted the first practical electrical signal. A short time before Henry had invented the first efficient electromagnet. He also concluded similar thoughts about induction before Faraday but he didn't publish them first. Henry's place in electrical history however, has always been secure, in particular for showing that electromagnetism could do more than create current or pick up heavy weights -- it could communicate.

In a stunning demonstration in his Albany Academy classroom, Henry created the forerunner of the telegraph. Henry first built an electromagnet by winding an iron bar with several feet of wire. A pivot mounted steel bar sat next to the magnet. A bell, in turn, stood next to the bar. From the electromagnet Henry strung a mile of wire around the inside of the classroom. He completed the circuit by connecting the ends of the wires at a battery. Guess what happened? The steel bar swung toward the magnet, of course, striking the bell at the same time. Breaking the connection released the bar and it was free to strike again. And while Henry did not pursue electrical signaling, he did help someone who did. And that man was Samuel Finley Breese Morse.

From the December, 1963 American Heritage magazine, "a sketch of Henry's primitive telegraph, a dozen years before Morse, reveals the essential components: an electromagnet activated by a distant battery, and a pivoted iron bar that moves to ring a bell."

In 1837 Samuel Morse invented the first practical telegraph, applied for its patent in 1838, and was finally granted it in 1848. Joseph Henry helped Morse build a telegraph relay or repeater that allowed long distance operation. The telegraph united the country and eventually the world. Not a professional inventor, Morse was nevertheless captivated by electrical experiments. In 1832 he had heard of Faraday's recently published work on inductance, and was given an electromagnet at the same time to ponder over. An idea came to him and Morse quickly worked out details for his telegraph.

As depicted below, his system used a key (a switch) to make or break the electrical circuit, a battery to produce power, a single line joining one telegraph station to another and an electromagnetic receiver or sounder that upon being turned on and off, produced a clicking noise. He completed the package by devising the Morse code system of dots and dashes. A quick key tap broke the circuit momentarily, transmitting a short pulse to a distant sounder, interpreted by an operator as a dot. A more lengthy break produced a dash.

Telegraphy became big business as it replaced messengers, the Pony Express, clipper ships and every other slow paced means of communicating. The fact that service was limited to Western Union offices or large firms seemed hardly a problem. After all, communicating over long distances instantly was otherwise impossible. Morse also experimented with wireless, but not in a way you might think. Morse didn't pass signals though the atmosphere but through the earth and water. Without a cable.

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On October 18, 1842, Morse laid wires between Governor's Island and Castle Garden, New York, a distance of about a mile. [For a complete description click here] Part of that circuit was under water, indeed, Morse wanted to show that an underwater cable could transmit signals as well as a copper wire suspended on poles. But before he could complete this demonstration a passing ship pulled up his cable, ending, it seemed, his experiment. Undaunted, Morse proceeded without the cable, passing his telegraph signals through the water itself. This is wireless by conduction.

Over the next thirty years most inventors and developers concentrated on wireline telegraphy, that is, conventional telegraphy carried over wires suspended on poles. Few tinkered exclusively with wireless since basic radio theory had not yet been worked out and trial and error experimenting produced no consistent results. Telegraphy did produce a good understanding of wireless by induction (internal link), however, since wires ran parallel to each other and often induced rogue currents into other lines. University research and some field work did continue, though, with many people making contributions.

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In 1843 Faraday began intensive research into whether space could conduct electricity. In April,1846 he reported his findings in a speech called "Thoughts on Ray-vibrations." He continued work in this area for many years, with inventors and academicians closely following his discoveries and theories. James Clerk Maxwell, whom we today would call a theoretical physicist, pondered constantly over Faraday's findings, translating and interpreting these field results into a set of mathematical equations. Maxwell often wove these equations into the many papers he published on electricity and magnetism. Scientists knew that light was a wave but they didn't know what made it up. Maxwell figured it out.

In 1864 Maxwell released his paper "Dynamical Theory of the Electromagnetic Field" which concluded that light, electricity, and magnetism, were all related, all worked hand in hand, and that these electromagnetic phenomena all traveled in waves. As he put it "[W]e have strong reason to conclude that light itself -- including radiant heat, and other radiations if any -- is an electromagnetic disturbance in the form of waves . . ." Maxwell found further. If electricity rapidly varied in amount then electromagnetic waves could be produced at will; they would radiate in waves to a distant point. At least he said so. There was no method yet to prove that "other radiations" existed, to demonstrate that waves other than light occurred. How could one see, produce, or detect an invisible wave?

Visible light is only one small part of the omnipresent electromagnetic field or spectrum, that great, universal energy force that constantly washes over and through us. (Illustration, 244K) All matter is in fact a wave (internal link) Radio waves as well as infrared waves lie below the visible spectrum. Things like X-Rays lie above. And because light is a radiated electromagnetic emission, lasers and all things optical qualify, strictly speaking, as a radio transmission.

Maxwell's equations also stated that radiation increased dramatically with frequency, that is, many more radio waves are generated at high frequencies than low, given the same amount of power. Experimenting with generating high frequency waves thus began. This wasn't an easy task since it isn't until 90,000 cycles per second, or 9kHz, that radio begins. The familiar A.M. radio band starts around 560 kHz, or 560,000 cycles a second, with all present day radio-telephone services far, far above this. If you want to define radio, generating a rapidly oscillating, high frequency electromagnetic wave is certainly a prerequisite.

Radio spectrum not to scale, Diagram above modified from here: http://www.jsc.mil/images/speccht.jpg (519K) external link)

Need a different perspective on the spectrum? I have archived a nice NASA diagram. Click here (internal link)

Got Java enabled in your browser? Most folks do. Then try this URL for an excellent demonstration of an electromagnetic wave, it correctly portrays how electric and magnetic fields travel at right angles to each other:

http://micro.magnet.fsu.edu/primer/java/electromagnetic/index.html

Blue stands for the electric field and red for the magnetic field. An electrical current or signal always has a magnetic field associated with it, either in a wire or out in space when it is radiated from an antenna. This modulated signal does NOT go straight up, rather, these big and small loops of electrical energy, depending on how low or high the frequency, are whipped out 360 degrees from an omnidirectional antenna such as the one above. Or focused like a light beam from a directional antenna.

Let's review before we look at how early radio developers developed high frequency waves. At the top of this page we saw how Morse used conduction, to wirelessly pass a signal without using the atmosphere. The second way is to do wireless is by induction, where one wire induces current to flow in another. The third way is radiation, where high frequency, rapidly moving waves get generated by electricity and radiate from a fixed point like an antenna. I want to cover induction just a bit more, to better let us understand the difference between this method and what we now know as true radio.

Don't be put off with phrases like "lines of force" and "electro-magnetic fields." The above is a simple bar magnet with its lines of force. Wrap some wire around it, connect the wire to a battery and you will have an electromagnetic field. Communications often use complex words for simple subjects. For an excellent, authoratative look at electricity and magnetism, visit the IEEE site below:

http://www.ieee.org/organizations/history_center/general_info/lines_menu.html#eandm

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We can define radio as the transmission and reception of signals by means of high frequency electrical waves without a connecting wire. And as we noted before, true radio requires that a signal modulate a carrier wave. Early induction schemes operated at low frequencies and possessed no modulating signal. As I stated above induction was well known to telegraphy, since signals often jumped from one line to another. This same tendency is known as "cross talk" in telephone lines, where one conversation may be heard on another line. In this case the wires are not physically crossed with each other, rather, induction induces one signal to travel on the wire of a nearby line.

An experiment in electromagnetic induction: Two separate but closely set coils of wire are wrapped around a nail. The coils are insulated from the nail itself by several pieces of paper, which you cannot see in the drawing. When the battery is connected current steadily flows in one direction and no sound is produced. Remove a lead from the battery and a clicking noise sounds from the receiver. Current in one wire has been induced to flow in the second wire. Only when the current is turned on or off do you get a change in the electromagnetic field and, consequently, a corresponding click. This is induction.

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In 1865 the dentist Dr. Mahlon Loomis of Virginia may have been the first person to communicate wirelessly through the atmosphere. Between 1866 and 1873 he transmitted telegraphic messages a distance of 18 miles between the tops of Cohocton Mountain and Beorse Deer Mountain, Virginia. Perhaps taking inspiration from Benjamin Franklin, at one location he flew a metal framed kite on a metal wire. He attached a telegraph key to the kite wire and sent signals from it. At another location a similar kite picked up these signals and noted them with a galvanometer. No attempt was made to generate high frequency, rapidly oscillating waves, rather, signals were simply electrical discharges, with current turned off and on to represent the dots and dashes of Morse code. He was granted U.S. patent number 129,971 on July 30, 1872 for an "Improvement in Telegraphing," but for financial reasons did not proceed further with his system.

The text of this sign reads: "T-11: Forerunner of Wireless Telegraphy. From nearby Bear's Den Mountain to the Catoctin Ridge, a distance of fourteen miles, Dr. Mahlon Loomis, Dentist, sent the first aerial wireless signals, 1866-73, using kites flown by copper wires. Loomis received a patent in 1872 and his company was chartered by Congress in 1873. But lack of capital frustrated his experiments. He died in 1866. Virginia Conservation Commission 1848."

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Over the next thirty years different inventors, including Preece and Edison, experimented with various induction schemes. You can read about many of them by clicking here (internal link). The most succesful systems were aboard trains, where a wire atop a passenger car could communicate by induction with telegraph wires strung along the track. A typical plan for that was William W. Smith's idea, contained in U. S. Pat. No. 247,127, which was granted on Sept 13, 1881. Edison, L. J. Phelps, and others came out later with improved systems. In 1888 the principle was successfully employed on 200 miles of the Lehigh Valley Railroad. Now, let's get back to true radio and Maxwell's findings, which lead to intense experimenting.

Maxwells' 1864 conclusions were distributed around the world and created a sensation. But it was not until 1888 that Professor Heinrich Hertz of Bonn, Germany, could reliably produce and detect radio waves. Before that many brushed close to detecting radio waves but did not pursue the elusive goal. The most notable were Edison and David Edward Hughes, who became the first person to take a call on a mobile telephone.

On November 22, 1875, while working on acoustical telegraphy, a science close to telephony, Thomas Alva Edison noticed unusual looking electro-magnetic sparks. Generated from a so called vibrator magnet, Edison had seen similar sparks from other eclectric equipment before and had always thought they were due to induction. Further testing ruled out induction and pointed to a new, unknown force. Although unsure of what he was observing, Edison leapt to amazing, accurate conclusions. This etheric force as he now named it, might replace wires and cables as a way to communicate. Under deadline to complete other inventions Edison did not pursue this mysterious force, although in later years he returned to consider it. Edison's vibrating magnet had in fact set up crude, oscillating electromagnetic waves, although these were too weak to detect at much distance. [Josephson]

An on-line Edison bioghrapy which touches on this subject is here. It is a 376K(!) file: http://www.bookrags.com/books/ehlai/PART32.htm (external link)

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From 1879 to 1886, London born David Hughes discovered radio waves but was told incorrectly that he had discovered no such thing. Discouraged, he pursued radio no further. But he did take the first mobile telephone call. Hughes was a talented freelance inventor who had at only 26 designed an all new printing telegraph (internal link). Like Edison and Elisha Gray he often worked under contract for Western Union. He went on to invent what many consider the first true microphone, a device that made the telephone practical, a transmitter as good as the one Edison developed.

Hughes noted many unusual electrical phenomena while experimenting on his microphone, telephone, and wireless related projects. The telephone, by the way, had been invented in 1876 and plans for constructing them had circulated around the world. Hughes noticed a clicking noise in his home built telephone each time he worked used his induction balance, a device now often used as a metal detector.

From the illustration and explanation on the previous page we know that turning current on and off to an induction coil can produce a clicking sound on another wire. It would seem then that Hughes was receiving an inductively produced sound, not a signal over radio waves. But Hughes noticed something more than just a click. In looking over the balance Hughes saw that he hadn't wired it together well, indeed, the unit was sparking at a poorly fastened wire. What would Sherlock Holmes have said? "Come, Watson, come! The game is afoot."

The spark we see isn't the radio signal, instead, it is light from energy released by excited or charged atoms between the spheres. And the spark does not indicate a single current flowing in one direction, but rather it is a set of oscillating, back and forth currents, too fast to observe.

Fixing the circuit's loose contact stopped the signal. Hughes correctly deduced that radio waves, electromagnetic, radiated emissions, were produced by the coil of wire in his induction balance and that the gap the spark raced across marked the point they radiated from. He set about making all sorts of equipment to test his hypothesis. Most ingenious, perhaps, was a clockwork transmitter that interrupted the circuit as it ticked, allowing Hughes to walk about with his telephone, now aided by a specially built receiver, to test how far each version of his equipment would send a signal.

At first Hughes transmitted signals from one room to another in his house on Great Portland Street, London. But since the greatest range there was about 60 feet, Hughes took to the streets of London with his telephone, intently listening for the clicking produced by the tick, tock of his clockwork transmitter. Ellison Hawks F.R.S., quoted and commented on Hughes' accounting, published years later in 1899:

"He obtained a greater range by setting 'the transmitter in operation and walking up and down Great Portland Street with the receiver in my hand and with the telephone to my ear.' We are not told what passers-by thought of the learned scientist, apparently wandering aimlessly about with a telephone receiver held to his ear, but doubtless they had their own ideas. Hughes found that the strength of the signals increased slightly for a distance of 60 yards and then gradually diminished until they no longer could be heard with certainty." [Hawks]

Since Hughes moved his experimenting from the lab to the field he had truly gone mobile. Although these clicks were not voice transmissions, I think it fair to credit Hughes with taking the first mobile telephone call in 1879. That's because his sparking induction coil and equipment put his signal into the radio frequency band, thus fulfilling part of our radio definition. Modulation, the act of putting intelligence onto a carrier wave such as the one he generated, would have to wait for others. This was an important first step, though, even though his clockwork mechanism signaled simply by turning the current on and off, like inductance and conductance schemes before.

Hughes' experimenting was profound and well researched, it was not accidental discovery. Click here to see a picture of all his radio apparatus.

Now, we can signal using a spark transmitter without a coil. This would be just like a car spark plug. When spark plugs fire up they spew electrical energy across the electromagnetic spectrum; this noise wreaks havoc in nearby radios. It's typical of all unmodulated electrical energy called, appropriately enough, RFI, for radio-frequency interference. Light dimmers, electrical saws, badly adjusted ballast in fluorescent light bulbs, dying door bell transformers, and so on, all generate RFI. If you turn the source of RFI on and off you could communicate over short distances using Morse code. But only by interfering with true radio services and causing the wrath of your neighbors. By contrast to spuriously generated electrical noise, Hughes deliberately formed electromagnetic waves which easily travelled a great distance, were tuned to more or less a specific frequency, and were picked up by a receiver designed to do just that.

Beginning in 1879 Hughes started showing his equipment and results to Royal Society (external link) members. On February 20, 1880 Hughes was sufficiently confident in his findings to arrange a demonstration before the president of the Royal Society, a Mr. Spottiswoode, and his entourage. Less knowledgeable in radio and less inquisitive than Hughes, a Professor Stokes declared that signals were not carried by radio waves but by induction. The group agreed and left after a few hours, leaving Hughes so discouraged he did not even publish the results of his work. Although he continued experimenting with radio, it was left to others to document his findings and by that time radio had passed him by.

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Resources

[Hawks] Hawks, Ellison, Pioneers of Wireless Arno Press, New York (1974) 172. This is a reprint of the original work which was published by Methuen & Co. Ltd. in London in 1927.

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The coil Hughes used raised the audio frequency signal on his line to the lower end of the radio band, providing an essential element of our radio definition. How was the frequency raised? Voice, conversations, music, and all other acoustic sounds reside in the the audio frequency band, far below the radio frequency band. Our range of hearing extends to perhaps 20,000 cycles a second, whereas the radio band starts around 100,000 cycles per second, with normal radio frequencies much higher. Let's stop right here to make a distinction between audio or acoustic signals and radio waves.

Sound waves are acoustic waves, with no electrical component. They are simply vibrations in the air, a physical pressure made by the utterance of a speaker or other sound source. Sounds in the audio and radio band both travel in waves but otherwise they are completely dissimilar. Acoustic waves are sounds made manifest by a physical distrubance, electromagnetic or radio waves are the product of radiated electrical energy. Go to this page to read more about acoustic sounds. And this external link from NASA to learn more about radio waves and the entire electromagnetic spectrum:

http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html

When put on a wire a sound occupies the frequency it would normally take up if not on the wire, that is, if a normal conversation is taking place at around 500Hz, then the conversation would naturally set up at 500Hz if put on a wire. That's a simple example, of course, since the telephone system for several reasons limits this baseband or voice band channel on a telephone wire to around 300Hz to 3,000Hz.

As the diagram above show a wire laid flat exhibits only a simple electromagnetic field when current flows. But if you scrunch it together, start running dozens of feet of wire around a core, spacing each loop nearly on top of each other, well, now you've really changed the dynamics of that line. You might have 25 feet or more of wire on a five inch core.

Have you ever seen an A.M. radio antenna in an old style radio? All that wire, wrapped around a ferrite core, is designed to tune frequencies from around 560,000 cycles per second, to about 1,600,000 cycles per second. The length of the wire tries to represent the length of the radio wave itself, although in practice it may be a quarter wavelength in size or less. The closer in size your antenna comes to the size of the wavelength you want to listen to, the better your chances are of receiving it. If you took that same antenna, no core needed, and wired it into a telephone line, you will probably raise the signal on the baseband channel into the low end of the radio band.

Modern radios don't use this principle to produce a high frequency carrier wave, of course, but the point I am making is that an induction coil to produce electromagnetic radio waves was an element which distinguished Hughe's work from more primitive schemes.

So who did complete the first radio telephone call using voice? None other than Alexander Graham Bell, the man who invented the telephone and of course made the first call on a wired telephone to Thomas Watson. Bell was also first with radio, although in a way you probably wouldn't imagine.

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Inductive reactance is the proper term for opposition to current flow through a coil. Resistance of a circuit and inductive reactance, both measured in Ohms, makes up impedance. The other confusing term in radio is AC.

In many radio discussions AC does not mean the alternating current that powers your appliances, rather, it means the way audio signals alternate in a wave like fashion. Huh? As we've just seen above and on the on the previous page , we need a change in current flow through a coil to get radiation. Current must go on and off to release the electromagnetic energy stored within the coil.

AC in radio means the natural alternating current of a voice signal, that is, the normal up and down waveform of the analog signal. In this case the rise and fall of a signal above a median point, that is, the top and bottom of a wave. Alternating current. Get it? A battery powered walkie talkie illustrates the difference between AC signaling current and AC power current.

A battery powered radio transmitter uses direct current to do all things. Including converting your voice, through the microphone, into a signal it can transmit. But the signal it transmits is not called a DC signal but an AC signal. That's because the radio rapidly oscillates (or alternates) the original signal. This is the needed step to get the signal high enough in the frequency band so that it will radiate from the antenna. AC, in this case, is not the power coming out of a wall outlet, it is the alternating current formed by waves of acoustical energy in the voice band converted into electrical waves by the radio circuitry. These terms get clearer as you read more. But if you are really mystified, read this little tutorial on how basic radio circuits work. I think it will help you a great deal and you can always come back here to continue.

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On February 22,1880 Alexander Graham Bell and his cousin Charles Bell communicated over the Photophone, a remarkable invention conceived of by Bell and executed by Sumner Tainter. [Grosvenor] This device transmitted voice over a light beam. A person's voice projected through a glass test tube toward a thin mirror which acted as a transmitter. Acoustical vibrations caused by the voice produced like or sympathetic vibrations in the mirror.

Sunlight was directed onto the mirror, where the vibrations were captured by a parabolic dish. The dish focused the light on a photo-sensitive selenium cell, in circuit with a telephone. The electrical resistance of the selenium changed as the strength of the received light changed, varying the current flowing through the circuit. The telephone's receiver then changed these flucuating currents into speech.

Although not related to the mobile telephony of today, Bell's experimenting was a first: radiated electromagnetic waves had carried the human voice. Despite Bell's brilliant achievement, optical transmission had obvious drawbacks, only now being overcome by firms like TeraBeam. Most later inventors concentrated instead on transmitting in the radio bands, with the period from 1880 to 1900 being one of tremendous technological innovation.

For ruminations on the Photophone and how to improve it go here: http://jefferson.village.virginia.edu/~meg3c/id/id_edin/ph/ph1.html

For a fascinating look at how ham radio operators can communicate optically click here

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Resources

[Grosvenor] Grosvenor, Edwin S. and Morgan Wesson. Alexander Graham Bell : The Life and Times of the Man Who Invented the Telephone Abrams, New York (1997) p.102.
Editor's note: The Photophone photograph that accompanies the text is from Grosvenor's excellent book. I never take pictures from books still in print but I have been unable to find any accurate picture of the Photophone on the net. I will immediately remove this image once I do.

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In 1888 the German Heinrich Hertz conclusively proved Maxwell's prediction that electricity could travel in waves through the atmosphere. Unlike Hughes, the extensive and systematic experiments into radio waves that Hertz conducted were recognized and validated by inventors around the world. Now, who would take take these findings further and develop a true radio?

Dozens and dozens of people began working in the field after Hertz made his findings. It is a miserable job to decide what to report on from this period, with people like Tesla, Branly, and yes, even folks like Nathan B. Stubblefield (external link), claiming to have invented radio. Typical of these events is Jagadis Chandra Bose (external link -- 817K!) demonstrating in 1895 electromagnetic waves "by using them to ring a bell remotely and to explode some gunpowder." While not inventing radio, any more than Edison invented the incadesent light bulb, Marconi did indeed establish the first successful and practical radio system. Starting in 1894 with his first electrical experiments, and continuing until 1901 when his radio telegraph system sent signals across the Atlantic ocean, Marconi fought against every kind of discouragement and deserves lionizing for making radio something reliable and useful.

Don Kimberlin (internal link) now questions Marconi's 1901 claim. It seems likely Marconi did not make a transatlantic radio reception that year. Read Kimberlin's page or download the .pdf file discussing this by clicking here.

Ships were the first wireless mobile platforms. In 1901 Marconi placed a radio aboard a Thornycroft steam powered truck, thus producing the first land based wireless mobile. (Transmitting data, of course, and not voice.) Arthur C. Clarke says the vehicle's cylindrical antenna was lowered to a horizontal position before the the wagon began moving. Marconi never envisioned his system broadcasting voices, he always thought of radio as a wireless telegraph. That would soon change.

Visit Arthur C. Clarke's Time Line of Communication at http://www.acclarke.co.uk/1900-1909.html This link no longer seems to be working.

On December 24, 1906, the first radio band wave communication of human speech was accomplished by Reginald Fessenden over a distance of 11 miles, from Brant Rock, Massachusetts, to ships in the Atlantic Ocean. Radio was no longer limited to telegraph codes, no longer just a wireless telegraph. This was quite a milestone, and many historians regard the radio era as beginning here, at the start of the voice transmitted age.

Coils of wire, induction at work, changing the frequency of a line, crystal receivers demonstrate many electrical principles. I've built small crystal sets myself and you can find the kits in many places. They are fascinating, operating not off of a battery but only by the energy contained in the captured radio wave. Just the power of a received radio wave, nothing more.

As Morgan put it, "Radio receivers with sensitive, inexpensive crystal detectors, such as this double slide tuner crystal set, appeared as early as 1904, and were used by most amateurs until the early Thirties, when vacuum tubes replaced crystals. An oatmeal box was a favorite base upon which to wind the wire coils." (Click here for a much clearer, larger image.)

Visit this site soon, plans to build, kits to buy, good information on crystal radios:
Crystal Radio Connections: blending art and science

http://www.crystalradio.org.uk/ (external link)

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From 1910 on it appears that Lars Magnus Ericsson and his wife Hilda regularly worked the first car telephone. Yes, this was the man who founded Ericsson in 1876. Although he retired to farming in 1901, and seemed set in his ways, his wife Hilda wanted to tour the countryside in that fairly new contraption, the horseless carriage. Lars was reluctant to go but soon realized he could take a telephone along. As Meurling and Jeans relate,

"In today's terminology, the system was an early 'telepoint' application: you could make telephone calls from the car. Access was not by radio, of course -- instead there were two long sticks, like fishing rods, handled by Hilda. She would hook them over a pair of telephone wires, seeking a pair that were free . . . When they were found, Lars Magnus would crank the dynamo handle of the telephone, which produced a signal to an operator in the nearest exchange." [Meurling and Jeans]

Thus we have the founder of Ericsson (external link), that Power of The Permafrost, bouncing along the back roads of Sweden, making calls along the way. Now, telephone companies themselves had portable telephones before this, especially to test their lines, and armed forces would often tap into existing lines while their divisions were on the move, but I still think this is the first regularly occurring, authorized, civilian use of a mobile telephone. More on mobile working below.

Around the middle teens the triode tube was developed, allowing far greater signal strength to be developed both for wireline and wireless telephony. No longer passive like a crystal set, a triode was powered by an external source, which provided much better reception and volume. Later, with Armstrong's regenerative circuit, tubes were developed that could either transmit or receive signals. They were the answer to developing high frequency oscillating waves; tubes were stable and powerful enough to carry the human voice and sensitive enough to detect those signals in the radio spectrum.

More on ho w a triode works and its history is here

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Resources:

[Meurling and Jeans] Meurling, John and Richard Jeans. The Mobile Phone Book: The Invention of The Mobile Phone Industry Communications Week International, London, on behalf of Ericsson Radio Systems (1994) p. 43. ISBN Number 0952403102

More on mobile working: Johan Hauknes points out that "L.M. Ericsson had already developed telephones for military purposes in the field -- mobile -- I would guess of the same kind as Meurling and Jeans describes, tapping into fixed systems. That's according to according to Ericsson's Centennial History which is written in Swedish."

"LME [sold] a large number of transportable field telephones and so called cavalry telephones to South Africa during the Boer War from 1899 to 1902. Several types of transportable telephones for military purposes had been developed by LME during the 1890s, bought by the Swedish Military. This according to Messrs A. Attman, J. Kuuse, and U. Olsson, in LM Ericsson 100 år Band 1 Pionjärtid - Kamp om koncessioner - Kris - 1876-1932 (vol. 1 of 3), published. by LM Ericsson in 1976."

"Finally, the first transportable phone documented in the centennial volume is from 1889 - primarily for 'railroad and canal works, military purposes etc.' There's a facsimile of an ad of this in vol. 3: C. Jakobaeus, LM Ericsson 100 år Band III Teleteknisk skapandet 1876-1976.) Railroad related maintenance and repair work, such as for signbased telegraph systems, was a major source of income for LME in the first years."

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(Please note: treat this material with caution, I am revising the explanation.)

Armstrong's regenerative circuit fed back the input signal into the circuit over and over again, amplifying the signal far more than original designs, building great wireless and wireline transmission signal strength. The feedback circuit could also be overdriven, fed back so many times that supplying a small current to the circuit would develop in it an extremely high frequency, so high it could resonate at the frequency of a radio wave, letting the triode receive or detect signals, not just transmit them. You had a tunable electronic tuning fork, of sorts, a device which detected and amplified the rhythmic energy of the radio wave when set to the frequency desired.

In 1919 three firms came together to develop a wireless company that one day would reach around the world. Heavy equipment maker ASEA, boiler and gas equipment maker AGA, and telephone manufacturer LM Ericsson, formed SRA Radio, the forerunner of Ericsson's radio division. Svenska Radio Aktiebolaget, known simply as SRA, was formed to build radio receivers, broadcasting having just started in Scandinavia. (Aktiebolaget, by the way, is Swedish for a joint stock company or corporation.)

Much unregulated radio experimenting was happening world wide at this time with different services causing confusion and interference with each other. In many countries government regulation stepped in to develop order. In the United States the Radio Act of 1912 brought some order to the radio bands, requiring station and operator licenses and assigning some spectrum blocks to existing users. But since anyone who filed for an operating license got a permit many problems remained and others got worse.

In 1921 United States mobile radios began operating at 2 MHz, just above the present A.M. radio broadcast band. For the most part law enforcement used these frequencies. [Young] The first radio systems were one way, sometimes using Morse Code, with police getting out of their cars and then calling their station house on a wired telephone after being paged. As if to confirm this, a reader recently e-mailed me this paragraph. The reader did not include the author's name or any references, however, the content is quite similiar to Bowers in Communications for a Mobile Society, Sage Publications, Cornell University, Beverley Hills (1978):

"Until the 1920s, mobile radio communications mainly made use of Morse Code. In the early 1920s, under the leadership of William P. Rutledge, the Commissioner of Detroit Police Department, Detroit, Michigan police carried out pioneering experiments to broadcast radio messages to receivers in police cars. The Detroit police department installed the first land mobile radio telephone systems for police car dispatch in the year 1921. [With the call sign KOP!, ed.] This system was similar to the present day paging systems. It was one-way transmission only and the patrolmen had to stop at a wire-line telephone station to call back in. On April 7, 1928, the first voice based radio mobile system went operational. Although the system was still one-way, its effectiveness was immediate and dramatic."

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Resources:

Young, W.R. "Advanced Mobile Phone Service: Introduction, Background, and Objectives." Bell System Technical Journal January, 1979: 7

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A detailed article on the pioneering efforts of the Detroit Police Department with wireless mobile is here:

http://www.detroitnews.com/history/police/police.htm

Police and emergency services drove mobile radio pioneering, therefore, with little thought given to private, individual telephone use. Equipment in all cases was chiefly experimental, with practical systems not implemented until the 1940s, and no interconnection with the the land based telephone system.[FCC: (external link)] Having said this, Bell Laboratories (external link) does claim inventing the first version of a mobile, two way, voice based radio telephone in 1924 and I see nothing that contradicts this, indeed, the photo below from their site certainly seems to confirm it!

http://www.bell-labs.com/history/75/gallery.html

For the difficulty involved in dating radio history, consider this page: http://members.aol.com/jeff560/chrono1.html

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On September 25,1928, Paul V. Galvin and his brother Joseph E. Galvin incorporated the Galvin Manufacturing Corporation. We know it today as Motorola (external link)

In 1927 the United States created a temporary five-member Federal Radio Commission (external link), an agency it was hoped would check the chaos and court cases involving radio. It did not and was quickly replaced by the F.C.C. just a few years later. In 1934 the United States Congress created the Federal Communications Commission. In addition to regulating landline telephone business, they also began managing the radio spectrum. The federal government gave the F.C.C. a broad public interest mandate, telling it to grant licenses if it was in the "public interest, convenience, and necessity" to do so. The FCC would now decide who would get what frequencies.

Founded originally as part of Franklin Roosevelt's liberal New Deal Policy, the Commission gradually became a conservative, industry backed agent for the interests of big business. During the 1940s and 1950s the agency became incestuously close to the broadcasting industry in general and in particular to RCA, helping existing A.M. radio broadcasting companies beat off competition from F.M. for decades. The F.C.C. also became a plodding agency over the years, especially when Bell System business was involved.

The American government had a love/hate relation with AT&T. On one hand they knew the Bell System was the best telephone company in the world. On the other hand they could not permit AT&T's power and reach to extend over every part of communications in America. Room had to be left for other companies and competitors. The F.C.C., the Federal Trade Commission, and the United States Justice Department, were all involved in limiting the Bell System's power and yet at the same time permitting them to continue. It was a difficult and awkward dance for everyone involved. And as for cellular, well, the slow action by the FCC would eventually delay cellular by at least a ten years, possibly twenty.

The FCC gave priority to emergency services, government agencies, utility companies, and services it thought helped the most people. Radio users like a taxi service or a tow truck dispatch company required little spectrum to conduct their business. Radio-telephone, by comparison, used large frequency blocks to serve just a few people. A single radio-telephone call, after all, takes up as much spectrum as a radio broadcast station. The FCC designated no private or individual radio-telephone channels until after World War II. Why the FCC did not allocate large frequency blocks in the then available higher frequency spectrum is still debated. Although commercial radios in quantity were not yet made for those frequencies, it is likely that equipment would have been produced had the F.C.C. freed up the spectrum.

Mobile radio?! A marine radio telephone of 1937 recently up for bid on e-bay.com The seller thought it was a Harvey Wells, Model MR-10. This beast measures 20"X 11"X 8 1/2" and weighs close to 40 pounds. This was probably compact for its time. The tube based radio also needed a big and heavy power supply. The present day SEA digital radiotelephone, by comparison, is a far superior machine and weighs in at 9.1 pounds, and measures only 4" by 10.5" It draws just 13 volts. As is clearly evident, much progress in radio had to await microprocessors and miniaturization.

IMTS authority Geoff Fors checked in recently:

"Tom. Get this -- I just looked at some of your material on your website on early mobile phone history, and saw you have a photo of my Harvey Wells 1941 marine radio telephone! I bought that unit on eBay, I don't recall if anyone else even bid on it, it was very cheap. The seller just threw it in a box with some wadded newspapers, and when it arrived the microphone was smashed to bits along with the porcelain insulators and everything protruding from the rear panel, the cabinet was caved in on top, and there was a baggie with the smashed up knobs in it lying INSIDE the cabinet. I don't know how the knobs were shown in the photo on eBay but then wound up inside the cabinet for shipping. They were shot anyway. It does actually work, although the cabinet was painted a horrible yellow color and should have been wrinkle burgundy. I have already straightened, stripped and primed the cabinet and have a replacement mike lined up from a friend. There is some consternation whether the set is pre or post-war. It uses metal octal tubes, which suggests postwar use, although those tubes were available before 1946. It is definitely pre-1950, in any case."

(Editor's note: I don't mean to confuse you, but these are both principally short wave radios, able to place a phone call through an operator, but they aren't units dedicated to telephony. "Phone" is an old radio term for voice transmission, it doesn't mean, necessarily, that you have a radio-telephone. Photographs simply illustrate radio size.)

Early conventional radio-telephone development and progress towards miniaturization

Radio-telephone work was ongoing throughout the world before the war. This excellent photograph shows a Dutch Post Telegraph and Telephone mobile radio. As the excellent Mobile Radio in the Netherlands web site explains it:

"The NSF Type DR38a transmitter receiver was the first practical mobile radio telephone in Holland. The set was developed in 1937 from PTT specifications and saw use from 1939 onwards. It operates in the frequency range between 66-75 MHz having a RF power output of approximately 4-5 Watts. Change-over from receive to transmit is effected by the large lever on the front panel. The transmitter is pre-set on a single frequency while the receiver is tuneable over the frequency range." I do not know if this set actually connected to their public switched telephone network. It may have been called a radio-telephone, just like the marine radio-telephone described above.

More good details are here. Their page does take a long time to load:
http://home.hccnet.nl/l.meulstee/mobilophone/mobilophone.html

DuringWorld War II civilian commercial mobile telephony work ceased but intensive radio research and development went on for military use. While RADAR was perhaps the most publicized achievement, other landmarks were reached as well. "The first portable FM two-way radio, the "walkie-talkie" backpack radio," [was] designed by Motorola's Dan Noble. It and the "Handie-Talkie" handheld radio become vital to battlefield communications throughout Europe and the South Pacific during World War II." [Motorola (external link) For those researching this time period, see my comments for reading below.

In the July 28, 1945 Saturday Evening Post magazine, the commissioner of the F.C.C., E.K. Jett, hinted at a cellular radio scheme, without calling it by that name. (These systems would first be described as "a small zone system" and then cellular.) Jett had obviously been briefed by telephone people, possibly Bell Labs scientists, to discuss how American civilian radio might proceed after the war.

What he describes below is frequency reuse, the defining principle of cellular. In this context frequency reuse is not enabled by a well developed radio system, but simply by the high frequency band selected. Higher frequency signals travel shorter distances than lower frequencies, consequently you can use them closer together. And if you use F.M. you have even less to worry about, since F.M. has a capture effect, whereby the nearest signal blocks a weaker, more distant station. That compares to A.M. which lets undesired signals drift in and out, requiring stations be located much further apart:

"In the 460,000-kilocycle band, sky waves do not have to be taken into account, day or night. The only ones that matter are those parallel to the ground. These follow a line of sight path and their range can be measured roughly by the range of vision. The higher the antenna, the greater the distance covered. A signal from a mountain top or from an airplane might span 100 miles, by one from a walkie talkie on low ground normally would not go beyond five miles, and one from a higher powered fixed transmitter in a home would not spread more than ten to fifteen miles. There are other factors, such as high buildings and hilly terrain which serve as obstacles and reduce the range considerably."

"Thanks to this extremely limited reach, the same wave lengths may be employed simultaneously in thousands of zones in this country. Citizens in two towns only fifteen miles apart -- or even less if the terrain is especially flat -- will be able to send messages on the same lanes at the same time without getting in one another's way."

"In each zone, the Citizen' Radio frequencies will provide from 70 to 100 different channels, half of which may be used simultaneously in the same area without any overlapping. And each channel in every one of the thousands of sectors will on average assure adequate facilities for ten or twenty, or even more "subscribers," because most of these will be talking on the ether only a very small part of the time. In each locality, radiocasters will avoid interference with one another by listening, before going on the air, to find out whether the lane is free. Thus the 460,000 to 470,000 kilocycle band is expected to furnish enough room for millions of users. . . "

The article was deceptively titled "Phone Me by Air"; no radio-telephone use was envisioned, simply point to point communications in what was to become the Citizens' Radio Band, eventually put at the much lower 27Mhz. Still, the controlling idea of cellular was now being discussed, even if technology and the F.C.C. would not yet permit radio-telephones to use it.

In 1946, the very first circuit boards, a product of war technology, became commercially available. Check out the small board in the lower right hand corner. It would take many years before such boards became common. The National Museum of American History (external link) explains this photo of a 'midget radio set' like this: "Silver lines replace copper wires in the 'printed' method developed for radio circuits . . . One of the new tiny circuits utilizing midget tubes is shown beside the same circuit as produced by conventional methods." These tiny tubes were called "acorn tubes" and were generally used in lower powered equipment. Car mounted mobile telephones used much larger tubes and circuits.

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Resources

My comments for reading: The following three volumes chronicle American military radio development during World War II, focusing on the United States Army. They are indispensable for anyone researching radio, especially those looking at the beginning of F.M. for handheld and mobile operations. Part of a larger series, the United States' official chronicle of World War II, these should be available through any major university. Out of print, used copies exist, figure $25 to $30 a volume; I paid $80 for my set. They have been reprinted a number of times, any edition is serviceable. For used books try ABE below.

Terrett, Dulany. The Signal Corps: The Emergency (to December 1941). Washington, Office of the Chief of Military History, Dept. of the Army, 1956. xiii, 383 p. illus., ports. 26 cm. Series title: United States Army in World War II. Technical services

Thompson, George Raynor. The Signal Corps: The Test (December 1941 to July 1943), by George Raynor Thompson [and others] Washington, Office of the Chief of Military History, Dept. of the Army, 1957. xv, 621 p. illus. 26 cm. Series title: United States Army in World War II : The technical services

Thompson, George Raynor. The Signal Corps: The Outcome (mid-1943 through 1945), by George Raynor Thompson and Dixie R. Harris. Washington, Office of the Chief of Military History, U.S. Army;1966. xvi, 720 p. illus., maps, ports. 26 cm. Series title: United States Army in World War II. Technical services

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On June 17, 1946 in Saint Louis, Missouri, AT&T and Southwestern Bell introduced the first American commercial mobile radio-telephone service to private customers. Mobiles used newly issued vehicle radio-telephone licenses granted to Southwestern Bell by the FCC. They operated on six channels in the 150 MHz band with a 60 kHz channel spacing. [Peterson] Bad cross channel interference, something like cross talk in a landline phone, soon forced Bell to use only three channels. In a rare exception to Bell System practice, subscribers could buy their own radio sets and not AT&T's equipment.

A simplified picture of Radio Telephone Service -- A Non-Zoned System

The diagram above shows a central transmitter serving mobiles over a wide area. One antenna serves a wide area, like a taxi dispatch service. While small cities used this arrangement, radio telephone service was more complicated, using more receiving antennas as depicted below. That's because car mounted transmitters weren't as powerful as the central antenna, thus their signals couldn't always get back to the originating site. That meant, in other words, you needed receiving antennas throughout a large area to funnel radio traffic back to the switch handling the call.. This process of keeping a call going from one zone to another is called a handoff.

The 1946 Bell System Mobile Telephone Service in St. Louis -- A Zoned System
M: mobile R:receiver. PSTN: Public switched telephone network.

As depicted above, in larger cities the Bell System Mobile Telephone Service used a central transmitter to page mobiles and deliver voice traffic on the downlink. Mobiles, based on a signal to noise ratio, selected the nearest receiver to transmit their signal to. In other words, they got messages on one frequency from the central transmitter but they sent their messages to the nearest receiver on a separate frequency.

Placed atop distant central offices, these receivers and antennas could also "be installed in buildings or mounted in weather proof cabinets or poles." They collected the traffic and passed it on to the largest telephone office, where the main mobile equipment and operators resided. [Peterson2]

Installed high above Southwestern Bell's headquarters at 1010 Pine Street, a centrally located antenna transmitting 250 watts paged mobiles and provided radio-telephone traffic on the downlink or forward path, that is, the frequency from the transmitter to the mobile. Operation was straightforward, as the following describes:

How Mobile Telephone Calls Are Handled

Telephone customer (1) dials 'Long Distance' and asks to be connected with the mobile services operator, to whom he gives the telephone number of the vehicle he wants to call. The operator sends out a signal from the radio control terminal (2) which causes a lamp to light and a bell to ring in the mobile unit (3). Occupant answers his telephone, his voice traveling by radio to the nearest receiver (4) and thence by telephone wire.

To place a call from a vehicle, the occupant merely lifts his telephone and presses a 'talk' button. This sends out a radio signal which is picked up by the nearest receiver and transmitted to the operator.[BLR1]

The above text accompanies a Bell Laboratories Record illustration (346K), from the 1946 article that first described the system. It gives you a good idea of how the system worked. Click on the link to view this big, but slow to load graphic.)

Simple block diagrams can be hard to follow. Click here to see another MTS illustration; it is from Bell Labs and my cellular telephone basics article.)

One party talked at a time with Mobile Telephone Service or MTS. You pushed a handset button to talk, then released the button to listen. (This eliminated echo problems which took years to solve before natural, full duplex communications were possible.) Mobile telephone service was not simplex operation as many writers describe, but half duplex operation.

Simplex uses only one frequency to both transmit and receive. In MTS the base station frequency and mobile frequency were offset by five kHz. Privacy is one reason to do this; eavesdroppers could hear only one side of a conversation. Like a citizen's band radio, a caller searched manually for an unused frequency before placing a call. But since there were so few channels this wasn't much of a problem. This does point out greatest problem for conventional radio-telephony: too few channels.

Shortly after this cartoon appeared the July 1948 BLR reported that a taxi cab driver with a mobile phone reported a stuck car on a railroad crossing, thus saving the broken down car and its motorist from disaster. Possibly the first radio-telephone rescue of its kind. This incident happened at a "grade crossing of the Nickel Plate Railroad at Dunkirk, New York." Dr. Scott Savett has found a photograph on the web of a representative Dunkirk rail crossing. The Dr. says, "According to a source on the Web, there were about five grade crossings in Dunkirk, so there's no guarantee that the one shown above is actually the one where the call was made." Still, this photo gives you an idea of the country. Click here to view. I wonder if the county history museum knows of the crossing's place in mobile telephone history.

Art imitating life below. This cartoon is from the April, 1948 issue of The Bell Laboratories Record. It reads, "Hello, Mr. Bunting. I've changed my mind -- I'll take that accident policy!"

Things to come. "All equipped with telephones so that the minute you catch anything you can call all your friends and start bragging." From the September, 1950 Bell Laboratories Record.

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Resources:

Peterson, A.C., Jr. "Vehicle Radiotelephony Becomes a Bell System Practice." Bell Laboratories Record April, 1947: 137

Peterson2 ibid. 140

BLR1"Telephone Service for St. Louis Vehicles." Bell Laboratories Record July, 1946: 267

BLR2 ibid.

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The MTS system presaged many cellular developments. In December,1947 Bell Laboratories' D.H. Ring articulated the cellular concept for mobile telephony in an internal memorandum, authored by Ring with crucial assistance from W.R. Young. Mr. Young later recalled that all the elements were known then: a network of small geographical areas called cells, a low powered transmitter in each, the cell traffic controlled by a central switch, frequencies reused by different cells and so on. Young states that from 1947 Bell teams "had faith that the means for administering and connecting to many small cells would evolve by the time they were needed." [Young]The authors at SRI International, in their voluminous history of cell phones[SR1], put those early days like this:

"The earliest written description of the cellular concept appeared in a 1947 Bell Labs Technical Memorandum authored by D. H. Ring. [but see previous page, the key difference is that Ring describes true mobile telephone service, ed.] The TM detailed the concept of frequency reuse in small cells, which remained one of the key elements of cellular design from then on. The memorandum also dealt with the critical issue of handoff, stating "If more than one primary band is used, means must be provided for switching the car receiver and transmitter to the various bands." Ring does not speculate how this might be accomplished, and, in fact, his focus was on how frequencies might be best conserved in various theoretical system designs."

Here we come to an important point, one that illustrates the controlling difference between conventional mobile telephony and cellular. Note how the authors describe handoffs, a process that Mobile Telephone Service already used. The problem wasn't so much about conducting a handoff from one zone to another, but dealing with handoffs in a cellular system, one in which frequencies were used over and over again. In a cellular system you need to transfer the call from zone to zone as the mobile travels, and you need to switch the frequency it is placed on, since frequencies differ from cell to cell. See the difference? Frequency re-use is the critical and unique element of cellular, not handoffs, since conventional radio telephone systems used them as well. [Discussion] Let's get back to Young's comments, when he says that Bell teams had faith that cellular would evolve by the time it was needed.

Important conventional mobile telephone handoff patents are: Communication System with Carrier Strength Control, Henry Magunski, assignor to Motorola, Inc. U.S. 2,734,131 (1956) and Automatic Radio Telephone Switching System, R.A. Channey, assignor to Bell Telephone Laboratories, Inc. U.S. 3,355,556(1967)

While recognizing the Laboratories' prescience, more mobile telephones were always needed. Waiting lists developed in every city where mobile telephone service was introduced. By 1976 only 545 customers in New York City had Bell System mobiles, with 3,700 customers on the waiting list. Around the country 44,000 Bell subscribers had AT&T mobiles but 20,000 people sat on five to ten year waiting lists. [Gibson] Despite this incredible demand it took cellular 37 years to go commercial from the mobile phone's introduction. But the FCC's regulatory foot dragging slowed cellular as well. Until the 1980s they never made enough channels available; as late as 1978 the Bell System, the Independents, and the non-wireline carriers divided just 54 channels nationwide. [O'Brien] That compares to the 666 channels the first AMPS systems needed to work. Let's back up.

In mobile telephony a channel is a pair of frequencies. One frequency to transmit on and one to receive. It makes up a circuit or a complete communication path. Sounds simple enough to accommodate. Yet the radio spectrum is extremely crowded. In the late 1940s little space existed at the lower frequencies most equipment used. Inefficient radios contributed to the crowding, using a 60 kHz wide bandwidth to send an signal that can now be done with 10kHz or less. But what could you do with just six channels, no matter what the technology? With conventional mobile telephone service you had users by the scores vying for an open frequency. You had, in effect, a wireless party line, with perhaps forty subscribers fighting to place calls on each channel. Most mobile telephone systems couldn't accommodate more than 250 people. There were other problems.

Radio waves at lower frequencies travel great distances, sometimes hundreds of miles when they skip across the atmosphere. High powered transmitters gave mobiles a wide operating range but added to the dilemma. Telephone companies couldn't reuse their precious few channels in nearby cities, lest they interfere with their own systems. They needed at least seventy five miles between systems before they could use them again. While better frequency reuse techniques might have helped, something doubtful with the technology of the times, the FCC held the key to opening more channels for wireless.

In 1947 AT&T began operating a "highway service", a radio-telephone offering that provided service between New York and Boston. It operated in the 35 to 44MHz band and caused interference from to time with other distant services. Even AT&T thought the system unsuccessful. Tom Kneitel, K2AES, writing in his Tune In Telephone Calls, 3d edition, CRB Books (1996) recalls the times:

"Service in those early days was very basic, the mobile subscriber was assigned to use one specific channel, and calls from mobile units were made by raising the operator by voice and saying aloud the number being called. Mobile units were assigned distinctive telephone numbers based upon the coded channel designator upon which they were permitted to operate. A unit assigned to operate on Channel 'ZL' (33.66 Mhz base station) might be ZL-2-2849. The mobile number YJ-3-5771 was a unit assigned to work with a Channel YJ (152.63 Mhz) base station. All conversations meant pushing the button to talk, releasing it to listen."

Also in 1947 the Bell System asked the FCC for more frequencies. The FCC allocated a few more channels in 1949, but gave half to other companies wanting to sell mobile telephone service. Berresford says "these radio common carriers or RCCs, were the first FCC-created competition for the Bell System" He elaborates on the radio common carriers, a group of market driven businessmen who pushed mobile telephony in the early years further and faster than the Bell System:

"The telephone companies and the RCCs evolved differently in the early mobile telephone business. The telephone companies were primarily interested in providing ordinary, 'basic' telephone service to the masses and, therefore, gave scant attention to mobile services throughout the 1950s and 1960s. The RCCs were generally small entrepreneurs that were involved in several related businesses-- telephone answering services, private radio systems for taxicab and delivery companies, maritime and air-to-ground services, and 'beeper' paging services. As a class, the RCCs were more sales-oriented than the telephone companies and won many more customers; a few became rich in the paging business. The RCCs were also highly independent of each other; aside from sales, their specialty was litigation, often tying telephone companies (and each other) up in regulatory proceedings for years." [Berresford External Link

As proof of their competitiveness, the RCCs serviced 80,000 mobile units by 1978, twice as many as Bell. This growth built on a strong start, the introduction of automatic dialing in 1948.]

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Resources

Bullington, Kenneth "Frequency Economy in Mobile Radio Bands." Bell System Technical Journal, January 1953, Volume 32: 42 et. seq.

Douglas, V.A. "The MJ Mobile Radio Telephone System." Bell Laboratories Record December, 1964: 383

Gibson, Stephen W., Cellular Mobile Radiotelephones. Englewood Cliff: Prentice Hall, 1987. 8

McDonald, Ramsey "'Dial Direct'" Automatic Radiotelephone System. IRE Transactions on Vehicle Communications July, 1958: 80 (back to text) As a courtesy to researchers I have scanned this article for you to download and review. These are very large files but they are readable and with some work will be decent for OCR. The first image is the title page for the IRE Transactions publication. The article starts at page 80:

http://www.privateline.com/IRE/IREfrontpiece.jpg
http://www.privateline.com/IRE/page80.jpg
http://www.privateline.com/IRE/page81.jpg
http://www.privateline.com.com/IRE/page82.jpg
http://www.privateline.com.com/IRE/page83.jpg
http://www.privateline.com.com/IRE/page84.jpg
http://www.privateline.com.com/IRE/page85.jpg

[McDonald2] ibid. 84

O'Brien, James "Final Tests Begin for Mobile Telephone System." Bell Laboratories Record July/August, 1978: 171

[SRI1] David Roessner, Robert Carr, Irwin Feller, Michael McGeary, and Nils Newman, "The Role of NSF's Support of Engineering in Enabling Technological Innovation: Phase II Final report to the National Science Foundation. Arlington, VA: SRI International, 1998.

[SRI2] ibid.

Young, W.R. "Advanced Mobile Phone Service: Introduction, Background, and Objectives." Bell System Technical Journal January, 1979: 7 (back to text) Messrs. Carr. Feller, McGeary, and Newman, of SRI, supra, cite the original memo describing cellular as follows: "Mobile Telephony -- Wide Area Coverage" Bell Laboratories Technical Memorandum, December 11, 1947.

[Discussion] Some might say conventional mobile telephones already employ frequency reuse since the same frequencies are used in radio-telephone service some distance away, in other cities perhaps seventy miles or more distant. Broadcast radio and television stations use this same approach to prevent interference, where the same frequencies are used throughout the country and where each station is separated by distance or space. In cellular, though, frequency reuse goes on within the fixed wide area of a cellular carrier, as part of an overall operating system. Within the coverage area of an AM or FM radio station, by comparison, no other station can use the frequency of that station. And there is no connection between other stations to act as a network.

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On March 1, 1948 the first fully automatic radiotelephone service began operating in Richmond, Indiana, eliminating the operator to place most calls. [McDonald] The Richmond Radiotelephone Company bested the Bell System by 16 years. AT&T didn't provide automated dialing for most mobiles until 1964, lagging behind automatic switching for wireless as they had done with landline telephony. (As an aside, the Bell System did not retire their last cord switchboard until 1978.) Most systems, though, RCCs included, still operated manually until the 1960s.

Some claim the Swedish Telecommunications Administration's S. Lauhrén designed the world's first automatic mobile telephone system, with a Stockholm trial starting in 1951. [http://www.telemuseum.se, link, now dead] I've found no literature to support this. Anders Lindeberg of the Swedish Museum of Science and Technology points out the text at the link I provide above is "a summary from an article in the yearbook 'Daedalus' (1991) for the Swedish Museum of Science and Technology http://www.tekmu.se/, link now dead]." He goes on to say, "The Swedish original article is much more extensive than the summary" and that "The Mobile Phone Book" by John Meurling and Richard Jeans, ISBN 0-9524031-02 published by Communications Week International, London in 1994 does briefly describe the "MTL" from 1951. But, again, nothing contradicts my contention that Richmond Telephone was first with automatic dialing.

On July 1, 1948 the Bell System unveiled the transistor, a joint invention of Bell Laboratories scientists William Shockley, John Bardeen, and Walter Brattain. It would revolutionize every aspect of the telephone industry and all of communications. One engineer remarked, "Asking us to predict what transistors will do is like asking the man who first put wheels on an ox cart to foresee the automobile, the wristwatch, or the high speed generator." Sensitive, bulky, high current drawing radios with tubes would be replaced over the next ten to fifteen years with rugged, miniature, low drain units. For the late 1940s and most of the 1950s, however, most radios would still rely on tubes, as the photograph below illustrates, a typical radio-telephone of the time.

Visit the Telecommunication Museum of Sweden!http://www.telemuseum.se/historia/mobtel/mobtfn_2e.html (link now dead)

Let's go to Sweden to read about a typical radio-telephone unit, something similar to American installations:

"It was in the mid-1950's that the first phone-equipped cars took to the road. This was in Stockholm - home of Ericsson's corporate headquarters - and the first users were a doctor-on-call and a bank-on-wheels. The apparatus consisted of receiver, transmitter and logic unit mounted in the boot of the car, with the dial and handset fixed to a board hanging over the back of the front seat. It was like driving around with a complete telephone station in the car. With all the functions of an ordinary telephone, the telephone was powered by the car battery. Rumour has it that the equipment devoured so much power that you were only able to make two calls - the second one to ask the garage to send a breakdown truck to tow away you, your car and your flat battery. . . These first carphones were just too heavy and cumbersome - and too expensive to use - for more than a handful of subscribers. It was not until the mid-1960's that new equipment using transistors were brought onto the market.Weighing a lot less and drawing not nearly so much power, mobile phones now left plenty of room in the boot - but you still needed a car to be able to move them around."

The above paragraph was taken from: http://www.ericsson.com/Connexion/connexion1-94/hist.html Ericsson has since removed this information from their website. You might try Alexa.com to do a Wayback Machine search.

In 1953 the Bell System's Kenneth Bullington wrote an article entitled, "Frequency Economy in Mobile Radio Bands." [Bullington] It appeared in the widely read Bell System Technical Journal. For perhaps the first time in a publicly distributed paper, the 21 page article hinted at, although obliquely, cellular radio principles.

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Resources

Bullington, Kenneth "Frequency Economy in Mobile Radio Bands." Bell System Technical Journal, January 1953, Volume 32: 42 et. seq.

Douglas, V.A. "The MJ Mobile Radio Telephone System." Bell Laboratories Record December, 1964: 383

Gibson, Stephen W., Cellular Mobile Radiotelephones. Englewood Cliff: Prentice Hall, 1987. 8

McDonald, Ramsey "'Dial Direct'" Automatic Radiotelephone System. IRE Transactions on Vehicle Communications July, 1958: 80 (back to text) As a courtesy to researchers I have scanned this article for you to download and review. These are very large files but they are readable and with some work will be decent for OCR. The first image is the title page for the IRE Transactions publication. The article starts at page 80:

http://www.privateline.com/IRE/IREfrontpiece.jpg
http://www.privateline.com/IRE/page80.jpg
http://www.privateline.com/IRE/page81.jpg
http://www.privateline.com.com/IRE/page82.jpg
http://www.privateline.com.com/IRE/page83.jpg
http://www.privateline.com.com/IRE/page84.jpg
http://www.privateline.com.com/IRE/page85.jpg

[McDonald2] ibid. 84

O'Brien, James "Final Tests Begin for Mobile Telephone System." Bell Laboratories Record July/August, 1978: 171

[SRI1] David Roessner, Robert Carr, Irwin Feller, Michael McGeary, and Nils Newman, "The Role of NSF's Support of Engineering in Enabling Technological Innovation: Phase II Final report to the National Science Foundation. Arlington, VA: SRI International, 1998.

[SRI2] ibid.

Young, W.R. "Advanced Mobile Phone Service: Introduction, Background, and Objectives." Bell System Technical Journal January, 1979: 7 (back to text) Messrs. Carr. Feller, McGeary, and Newman, of SRI, supra, cite the original memo describing cellular as follows: "Mobile Telephony -- Wide Area Coverage" Bell Laboratories Technical Memorandum, December 11, 1947.

[Discussion] Some might say conventional mobile telephones already employ frequency reuse since the same frequencies are used in radio-telephone service some distance away, in other cities perhaps seventy miles or more distant. Broadcast radio and television stations use this same approach to prevent interference, where the same frequencies are used throughout the country and where each station is separated by distance or space. In cellular, though, frequency reuse goes on within the fixed wide area of a cellular carrier, as part of an overall operating system. Within the coverage area of an AM or FM radio station, by comparison, no other station can use the frequency of that station. And there is no connection between other stations to act as a network.

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"In1954, Texas Instruments was the first company to start commercial production of silicon transistors instead of using germanium. Silicon raised the power output while lowering operating temperatures, enabling the miniaturization of electronics. The first commercial transistor radio was also produced in 1954 - powered by TI silicon transistors." Photo courtesy of Texas Instruments: http://www.ti.com/ (external link)

In 1956 AT&T and the United States Justice Department settled, for a while, another anti-monopoly suit. AT&T agreed not to expand their business beyond telephones and transmitting information. Bell Laboratories and Western Electric would not enter such fields as computers and business machines. The Bell System in return was left intact with a reprieve from monopoly scrutiny for a few years. This affected wireless as well. Bell and WECO previously supplied radio equipment and systems to private and public concerns. No longer. Western Electric Company stopped making radio-telephone sets. Outside contractors using Bell System specs would make AT&T's next generation of radio-telephone equipment. Companies like Motorola, Secode, and ITT-Kellog, now CORTELCO. Also in 1956 the Bell System began providing manual radio-telephone service at 450 MHz, a new frequency band assigned to relieve overcrowding. AT&T did not automate this service until 1969.

In this same year Motorola produces its first commerical transistorized product: an automobile radio. "It is smaller and more durable than previous models, and demands less power from a car battery. An all-transistor auto radio, [it] is considered the most reliable in the industry." [Motorola (external link)]

In 1958 the innovative Richmond Radiotelephone Company improved their automatic dialing system. They added new features to it, including direct mobile to mobile communications. [McDonald2] Other independent telephone companies and the Radio Common Carriers made similar advances to mobile-telephony throughout the 1950s and 1960s. If this subject interests you, The Independent Radio Engineer Transactions on Vehicle Communications, later renamed the IEEE Transactions on Vehicle Communications, is the publication to read during these years.

Mobile Phone Stuff! (1) Service cost and per-minute charges table / (2) Product literature photos / (3) Briefcase Model Phone / (4) More info on the briefcase model / (5) MTS and IMTS history / (6) Bell System (7) Outline of IMTS / (8) Land Mobile Page 1 (375K) / (9) Land Mobile Page Two (375K)

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Resources

Bullington, Kenneth "Frequency Economy in Mobile Radio Bands." Bell System Technical Journal, January 1953, Volume 32: 42 et. seq.

Douglas, V.A. "The MJ Mobile Radio Telephone System." Bell Laboratories Record December, 1964: 383

Gibson, Stephen W., Cellular Mobile Radiotelephones. Englewood Cliff: Prentice Hall, 1987. 8

McDonald, Ramsey "'Dial Direct'" Automatic Radiotelephone System. IRE Transactions on Vehicle Communications July, 1958: 80 (back to text) As a courtesy to researchers I have scanned this article for you to download and review. These are very large files but they are readable and with some work will be decent for OCR. The first image is the title page for the IRE Transactions publication. The article starts at page 80:

http://www.privateline.com/IRE/IREfrontpiece.jpg
http://www.privateline.com/IRE/page80.jpg
http://www.privateline.com/IRE/page81.jpg
http://www.privateline.com.com/IRE/page82.jpg
http://www.privateline.com.com/IRE/page83.jpg
http://www.privateline.com.com/IRE/page84.jpg
http://www.privateline.com.com/IRE/page85.jpg

[McDonald2] ibid. 84

O'Brien, James "Final Tests Begin for Mobile Telephone System." Bell Laboratories Record July/August, 1978: 171

[SRI1] David Roessner, Robert Carr, Irwin Feller, Michael McGeary, and Nils Newman, "The Role of NSF's Support of Engineering in Enabling Technological Innovation: Phase II Final report to the National Science Foundation. Arlington, VA: SRI International, 1998.

[SRI2] ibid.

Young, W.R. "Advanced Mobile Phone Service: Introduction, Background, and Objectives." Bell System Technical Journal January, 1979: 7 (back to text) Messrs. Carr. Feller, McGeary, and Newman, of SRI, supra, cite the original memo describing cellular as follows: "Mobile Telephony -- Wide Area Coverage" Bell Laboratories Technical Memorandum, December 11, 1947.

[Discussion] Some might say conventional mobile telephones already employ frequency reuse since the same frequencies are used in radio-telephone service some distance away, in other cities perhaps seventy miles or more distant. Broadcast radio and television stations use this same approach to prevent interference, where the same frequencies are used throughout the country and where each station is separated by distance or space. In cellular, though, frequency reuse goes on within the fixed wide area of a cellular carrier, as part of an overall operating system. Within the coverage area of an AM or FM radio station, by comparison, no other station can use the frequency of that station. And there is no connection between other stations to act as a network.

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"In 1958 Jack Kilby invented the integrated circuit at Texas Instruments. Comprised of only a transistor and other components on a slice of germanium, Kilby's invention, 7/16-by-1/16-inches in size, revolutionized the electronics industry. The roots of almost every electronic device we take for granted today can be traced back to Dallas more than 40 years ago." Photo courtesy of Texas Instruments.
http://www.ti.com (external link)

Also in1958 the Bell System petitioned the FCC to grant 75 MHz worth of spectrum to radio-telephones in the 800 MHz band. The FCC had not yet allowed any channels below 500MHz, where there was not enough continuous spectrum to develop an efficient radio system. Despite the Bell System's forward thinking, the FCC sat on this proposal for ten years and only considered it in 1968 when requests for more frequencies became so backlogged that they could not ignore them.

"Because it appeared that sufficient frequencies would not be allocated for mobile radio, the 1950s saw only low level R&D activity related to cellular systems. Nonetheless, this modest activity resulted in additional Technical Memoranda in 1958 and 1959, respectively, 'High Capacity Mobile Telephone System - Preliminary Considerations,' W.D. Lewis, 2/10/58; and 'Multi-Area Mobile Telephone System,' W.A. Cornell & H. J. Schulte, 4/30/59. These two memoranda discussed possible models for cellular systems and again recognized the critical nature of handoff. In the 1959 memo, the authors assert that handoff could be accomplished with the technology of the day, but they do not discuss in detail how it might be implemented." [SRI2]

Although the two papers cited above were chiefly limited to Bell System employees, it seems they were substantially reprinted in the IRE Transactions on Vehicle Communications the next year in 1960. This marked, I think, the first time the entire cellular system concept was outlined in print to the entire world. The abbreviated cites are: "Coordinated Broadband Mobile Telephone System, W.D. Lewis, Bell Telephone Laboratories, Incorporated, Murray Hill, New Jersey, IRE Transactions May, 1960, p. 43, and "Multi-area Mobile Telephone System, H.J. Schulte, Jr. & W.A. Cornell, Bell Telephone Laboratories, IRE Transactions May, 1960, p. 49.

In 1961 the Ericsson (external link) subsidiary Svenska Radio Aktiebolaget, or SRA, reorganized to concentrate on building radio systems, ending involvement with making consumer goods. This forerunner of Ericsson Radio Systems was already selling paging and land mobile radio equipment throughout Europe. Land mobile or business communication systems serviced towing, taxi, and trucking services, where a dispatcher communicated to mobiles from a central base station. These business radio systems were and continue to this day to be simplex, with one party talking at a time. SRA also sold to police and military groups.

In 1964 the Bell System began introducing Improved Mobile Telephone Service or IMTS, a replacement to the badly aging Mobile Telephone System. The IMTS field test was in Harrisburg, Pennsylvania, from 1962-1964. Improved Telephone Service worked full-duplex so people didn't have to press a button to talk. Talk went back and forth just like a regular telephone. It finally permitted direct dialing, automatic channel selection and reduced bandwidth to 25-30 kHz. [Douglas]

Some operating companies like Pacific Bell took nearly twenty years to replace their old MTS systems, by that time cellular networks were being planned. IMTS was not cut into service in Pacific Bell territory until mid-1982. It lasted until 1995 when the service was discontinued in favor of cellular. I am not aware that any American IMTS system operated after 1995, however, at least one in Canada remains, at least for another few months. Gerald Rose writes:

"As far as I am aware, the last IMTS/MTS mobile system left in North America is run by Bell/Aliant Telecom in Newfoundland, Canada. This system is also slated to be de-commissioned in August of 2002, thereby ending a long history of this technology. In conversation with a past IMTS supplier, Glenayre, a few years ago, they indicated that the only other IMTS system that they were aware of still in operation was in Asia (Cambodia or somewhere). Naturally, I stand to be corrected on this info."

"In Newfoundland, our mobile switch is a Glenayre GL1200 (6 side by side units) and the mobile units used were mostly a combination of Novatel VTR74, VTR84, and VTR2084 radios, Glenayre GL2020, 2040, 2021, and 4040 units. Being a landscape with some remote areas difficult to service with cellular, the old IMTS will be missed by some users."

You can read the paperwork Aliant filed to decommission this service by clicking here. It is in Word format and contains some operating details.

More on IMTS! (1) Service cost and per-minute charges table / (2) Product literature photos / (3) Briefcase Model Phone / (4) More info on the briefcase model / (5) MTS and IMTS history / (6) Bell System Outline of IMTS

Take a look at a company newsletter describing the 1982 cutover from MTS to IMTS:
Page One / Page Two / Page Three / Page Four

Across the ocean the Japanese were operating conventional mobile radio telephones and looking forward to the future as well. Limited frequencies did not permit individuals to own radio-telephones, only government and institutions, and so there was a great demand by the public. It is my understanding that in 1967 the Nippon Telegraph and Telephone Company proposed a nationwide cellular system at 800Mhz for Japan. This proposal is supposedly contained in NTTs' Electrical Communications Laboratories Technical Journal Volume 16, No. 5, a 23 page article entitled "Fundamental problems of nation-wide mobile radio telephone system," written by K. Araki. I have not yet seen the English version of the NTT Journal in question, but it does agree with material I will go over later in this article.

What is certain is that every major telecommunications company and manufacturer knew about the cellular idea by the middle 1960s; the key questions then became which company could make the concept work, technically and economically, and who might patent a system first.

In 1967 the Nokia group was formed by consolidating two companies: the Finnish Rubber Works and the Finnish Cable Works. Finnish Cable Works had an electronics division which Nokia expanded to include semi-conductor research. These early 1970s studies readied Nokia to develop digital landline telephone switches. Also helping the Finns was a free market for telecom equipment, an open economic climate which promoted creativity and competitiveness. Unlike most European countries, the state run Post, Telephone and Telegraph Administration was not required to buy equipment from a Finnish company. And other telephone companies existed in the country, any of whom could decide on their own which supplier they would buy from. Nokia's later cellular development was greatly helped by this free market background and their early research.

Back in the United States, the FCC in 1968 took up the Bell System's now ten year old request for more frequencies. They made a tentative decision in 1970 to do so, asked AT&T to comment, and received the system's technical report in December, 1971. The Bell System submitted docket 19262, outlining a cellular radio scheme based on frequency-reuse. Their docket was in turn based on the patent Amos E. Joel, Jr. and Bell Telephone Laboratories filed on December 21, 1970 for a mobile communication system. This patent was approved on May 16, 1972 and given the United States patent number 3,663,762. Six more years would pass before the FCC allowed AT&T to start a trial. This delay deserves some explaining.

Besides bureaucratic sloth, this delay was also caused, rightly enough, by the radio common carriers. These private companies provided conventional wireless telephone service in competition with AT&T. Carriers like the American Radio Telephone Service, and suppliers to them like Motorola, feared the Bell System would dominate cellular radio if private companies weren't allowed to compete equally. They wanted the FCC to design open market rules, and they fought constantly in court and in administrative hearings to make sure they had equal access. And although its rollout was delayed, the Bell System was already working with cellular radio, in a small but ingenious way.

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Resources

Douglas, V.A. "The MJ Mobile Radio Telephone System." Bell Laboratories Record December, 1964: 383

Paul, C.E. "Telephones Aboard the 'Metroliner'." Bell Laboratories Record March, 1969: 77

[SRI2] David Roessner, Robert Carr, Irwin Feller, Michael McGeary, and Nils Newman, "The Role of NSF's Support of Engineering in Enabling Technological Innovation: Phase II Final report to the National Science Foundation. Arlington, VA: SRI International, 1998.

http://www.sri.com/policy/stp/techin2/chp4.html (external link, now dead)

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In 1965 miniaturization let mobile telephony accomplish its greatest achievement to date: the fully mobile shoe phone, aptly demonstrated by Don Adams in the hit television show of the day, 'Get Smart.' Some argue that the 1966 mobile Batphone supra, was more remarkable, but as the photograph shows it remained solidly anchored to the Batmobile, limiting Batman and Robin to vehicle based communications.

For kids researching papers, this section is a joke! :-)

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In January, 1969 the Bell System made commercial cellular radio operational by employing frequency reuse for the first time. Aboard a train. Using payphones. Small zone frequency reuse, as I've said many times before, is the principle defining cellular and this system had it. (Some say handoffs or handovers also define cellular, which they do in part, but MTS and IMTS could use handovers as well; only frequency reuse within a local network is unique to cellular.) "[D]elighted passengers" on Metroliner trains running between New York City and Washington, D.C. "found they could conveniently make telephone calls while racing along at better than 100 miles an hour."[Paul] Six channels in the 450 MHz band were used again and again in nine zones along the 225 mile route. A computerized control center in Philadelphia managed the system." Thus, the first cell phone was a payphone! As Paul put it in the Laboratories' article, ". . .[T]he system is unique. It is the first practical integrated system to use the radio-zone concept within the Bell System in order to achieve optimum use of a limited number of radio-frequency channels."

For a great, personal account of this, please click here. (internal link) John Winward remembers his work on the Metroliner

If you want another explanation of frequency reuse and how this concept differs cellular telephony from conventional mobile telephone service, click here to read a description (internal link) by Amos Joel Jr., writing taken from the original cellular telephone patent.

The brilliant Amos E. Joel Jr., the greatest figure in American switching since Almon Strowger. Pictured here in a Bell Labs photo from 1960, posing before his assembler-computer patent, the largest patent issued up to that date. In 1993 Joel was awarded The National Medal of Technology, "For his vision, inventiveness and perseverance in introducing technological advances in telecommunications, particularly in switching, that have had a major impact on the evolution of the telecommunications industry in the U.S. and worldwide."

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Resources:

Resources

Douglas, V.A. "The MJ Mobile Radio Telephone System." Bell Laboratories Record December, 1964: 383

Paul, C.E. "Telephones Aboard the 'Metroliner'." Bell Laboratories Record March, 1969: 77

[SRI2] David Roessner, Robert Carr, Irwin Feller, Michael McGeary, and Nils Newman, "The Role of NSF's Support of Engineering in Enabling Technological Innovation: Phase II Final report to the National Science Foundation. Arlington, VA: SRI International, 1998.

http://www.sri.com/policy/stp/techin2/chp4.html (external link, now dead)

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In 1971 Intel introduced their first microprocessor, the 4004. (4004B pictured here, courtesy of Intel: http://www.intel.com (external link) ) Designed originally for a desktop calculator, the microprocessor was soon improved on and quickly put into all fields of electronics, including cell phones. The original did 4,000 operations a second. According to the June, 2001 issue of Wired magazine, Gordon Moore described the microprocessor as "one of the most revolutionary products in the history of mankind." At the time Intel's chairman Andrew Grove was not so impressed. He reflected that "I was running an assembly line to build memory chips. I saw the microprocessor as a bloody nuisance." Motorola also did much to pioneer the microprocessor and semiconductor field, indeed, in their advertisements of the time, they rightly noted that Motorola circuits were on board each NASA mission since the American space program begain.

In a manuscript submitted to the IEEE Transactions On Communications on September 8, 1971, NTT's Fumio Ikegami explained that his company began studying a nationwide cellular radio system for Japan in 1967. Radio propagation experiments, measuring signal strength and reception in urban areas from mobiles, were ongoing throughout this time, first at 400Mhz and then at 900Mhz. [Ikegami] A successful system trial may have happened in 1975 but I am unable to confirm this. What I can confirm is that Ito and Matsuzaka wrote in late 1977 that "Field tests have been carried out in the Tokyo metropolitan area since 1975 and have now been brought to a successful completion." The two authors wrote this in a major article describing how the first Japanese cellular system would work. [Ito]

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Resources:

Ikegami, Fumio, "Mobile Radio Communications in Japan." IEEE Transactions On Communications Vol. Com-20 No. 4, August 1972: 744

Ito , Sadao and Yasushi Matsuzaka. "800 MHz Band Land Mobile Telephone System -- Overall View." IEEE Transactions on Vehicular Technology, Volume VT-27, No. 4, November 1978, p.205, as reprinted from Nippon Telegraph and Telephone's The Review of the Electrical Communication Laboratories, vol. 25, nos 11-12, November-December, 1977 (English and Japanese)

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In 1983 Texas Instruments introduced their single chip digital signal processor, operating at over five million operations a second. Though not the first to make a single chip DSP, Lucent claiming that distinction in 1979 (external link), TI's entry heralded the wide spread use of this technology. The digital signal processor is to cell phones what the microprocessor is to the computer. A DSP contains many individual circuits that do different things. A properly equipped DSP chip can compress speech so that a call takes less room in the radio bands, permitting more calls in the same amount of scarce radio spectrum. With a single chip DSP fully digital cellular systems like GSM and TDMA could make economic sense and come into being. Depending on design, at least three calls in a digital system could fit into the same radio frequency or channel space that a single analog call had taken before. DSP chips today run at over 35,000,000 operations a second. http://www.ti.com (external link)

In February, 1983 Canadian cellular service began. This wasn't AMPS but something different. Alberta Government Telephones, now Telus (external link), launched the AURORA-400 system , using GTE and NovAtel equipment. This so called decentralized system operates at 420 MHZ, using 86 cells but featuring no handoffs. As David Crowe explains, "It provides much better rural coverage, although its capacity is low." You had, in other words, a system employing frequency reuse, the defining principle of cellular, but no handoffs between the large sized cells. This worked well for a rural area needing wide area coverage but it could not deliver the capacity that a system with many more small cells could offer, since more cells means more customers served.

Visit this site for an excellent timeline on American cellular development: http://books.nap.edu/books/030903891X/html/159.html#pagetop

On October 12, 1983 the regional Bell operating company Ameritech began the first United States commercial cellular service in Chicago, Illinois. This was AMPS, or Advanced Mobile Phone Service, which we've discussed in previous pages. United States cellular service developed from this AT&T model, along with Motorola's analog system known as Dyna-TAC(external link), first introduced commercially in Baltimore and Washington D.C. by Cellular One on December 16, 1983. Dyna-Tac stood for, hold your breath, Dynamic Adaptive Total Area Coverage. Of course.

Analog or First Generation Cellular Systems

NB: Some systems may still be in use, others are defunct. All systems used analog routines for sending voice, signaling was done with a variety of tones and data bursts. Handoffs were based on measuring signal strength except C-Netz which measured the round trip delay. Early C-Netz phones, most made by Nokia, also used magnetic stripe cards to access a customer's information, a predecessor to the ubiquitous SIM cards of GSM/PCS phones. e-mail me with corrections or additions, I am still working on this table. Here is another look at an analog system table.

Before proceeding further, I must take up just a little space to discuss a huge event: the breakup of AT&T. Although they pioneered much of telecom, many people thought the information age was growing faster than the Bell System could handle. Some thought AT&T stood in the way of development and competition. And the thought of any large monopoly struck most as inherently wrong.

In 1982 the Bell System had grown to an unbelievable 155 billion dollars in assets (256 billion in today's dollars), with over one million employees. By comparison, Microsoft in 1998 had assets of around 10 billion dollars. On August 24, 1982, after seven years of wrangling with the federal justice department, the Bell System was split apart, succumbing to government pressure from without and a carefully thought up plan from within. Essentially, the Bell System divested itself.

In the decision reached, AT&T kept their long distance service, Western Electric, Bell Labs, the newly formed AT&T Technologies and AT&T Consumer Products. AT&T got their most profitable companies, in other words, and spun off their regional Bell Operating Companies or RBOCs. Complete divestiture took place on January, 1, 1984. After the breakup new companies, products, and services appeared immediately in all fields of American telecom, as a fresh, competitive spirit swept the country. The Bell System divestiture caused nations around the world to reconsider their state owned and operated telephone companies, with a view toward fostering competition in their own countries. But back to cellular.

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Resources:

Johann Storck recently checked in to make some comments:

"I've just read page 9 of "Mobile Telephone History" and found a picture I knew well ... the good old Ericsson GH 388 [code name Jane, ed.], one of the first really handy and still (from the size factor) small mobile phones. Just don't measure the weight! Well, you put a picture of the model 388 from 1996 on your page and I want to inform you that there was an earlier model, dating back to 1994 which had already the same size factor and nearly the same features (except SMS sending). I've included a picture of my own device manufactured in calendar week 44 in 1994. The phone measures 12.8cm (about 5 inches) in height, 4.8cm (about 1.9 inches) in width and the depth with the normal capacity battery is about 2.6cm (about 1 inch)."

"As for Ericsson getting out of the handset business, I think they were once the leading developer of mobile phones, back in the times when they made models like the 337. But they didn't learn from their design faults. Think of the small display the 337-owner had to deal with, they kept that size for several other models (377, 388 and even the latest phones like T-28 and the T-20). Or think of the fact that the menu structure was far too complicated and still is. From that point of view Ericsson could be better off giving away the mobile phone business to Flextronics because that could bring some innovations to their (technically very good) products."

"If you compare Ericsson to Nokia you see what can be done by listening to the consumer wishes. Nokia designed an easy-to-use graphical menu structure and (in some phones) eliminated the antenna to make the devices smaller and more robust. All these facts made the Nokia phones more mass-market compliant and, as a matter of fact, more people bought Nokia phones even when they weren't seen as having the same technical quality level (quality of speech transmission, battery life time, and so on, like the ones made by other companies."

Editor's note. I always liked Ericsson mobiles. They were rugged and worked. Their design philosophy seemed liked Porsche, you always knew an Ericsson phone when you saw one. There was a nice article on Ericsson design in the first issue of their publication On, once at this address: http://on.magazine.se/

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The Bahrain Telephone Company (Batelco external link) in May, 1978 began operating a commercial cellular telephone system. It probably marks the first time in the world that individuals started using what we think of as traditional, mobile cellular radio. The two cell system had 250 subscribers, 20 channels in the 400Mhz band to operate on, and used all Matsushita equipment. (Panasonic is the name of Matsushita in the United States.) [Gibson]Cable and Wireless, now Global Crossing, installed the equipment.

In July, 1978 Advanced Mobile Phone Service or AMPS started operating in North America. In AT&T labs in Newark, New Jersey, and most importantly in a trial around Chicago, Illinois Bell and AT&T jointly rolled out analog based cellular telephone service. Ten cells covering 21,000 square miles made up the Chicago system. This first equipment test began using 90 Bell System employees. After six months, on December 20th, 1978, a market trial began with paying customers who leased the car mounted telephones. This was called the service test. The system used the newly allocated 800 MHz band. [Blecher] Although the Bell System bought an additional 1,000 mobile phones from Oki for the lease phase, it did place orders from Motorola and E.F. Johnson for the remainder of the 2100 radios needed. [Business Week2] This early network, using large scale integrated circuits throughout, a dedicated computer and switching system, custom made mobile telephones and antennas, proved a large cellular system could work.

Picture originally from http://park.org:8888/Japan/NTT/MUSEUM/html_ht/HT979020_e.html

"The car telephone service was introduced in the 23 districts of Tokyo in December 1979 (Showa 54). Five years later, in 1984 (Showa 59), the system became available throughout the country. Coin operated car telephones were also introduced to allow convenient calling from inside buses or taxis." NTT

Worldwide commercial AMPS deployment followed quickly. An 88 cell system in Tokyo began in December, 1979, using Matsushita and NEC equipment. The first North American system in Mexico City, a one cell affair, started in August, 1981. United States cellular development did not keep up since fully commercial systems were still not allowed, despite the fact that paying customers were permitted under the service test. The Bell System's impending breakup and a new FCC competition requirement (external link) delayed cellular once again. The Federal Communication Commission's 1981 regulations required the Bell System or a regional operating company, such as Bell Atlantic, to have competition in every cellular market. That's unlike the landline monopoly those companies had. The theory being that competition would provide better service and keep prices low. Before moving on, let's discuss Japanese cellular development a little more.

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Resources:

Blecher, Franklin H. "Advanced Mobile Phone Service." IEEE Transactions on Vehicle Communications, Vol. VT-29, No. 2, May, 1980

[Business Week2]"Fewer busy signals for mobile phones" Business Week, Industrial Edition, August 7, 1978 Number 2546: 60B

Gibson, Stephen W., Cellular Mobile Radiotelephones. Englewood Cliff: Prentice Hall, (1987): 141, quoting information from the company Personal Communications Technology. You can view the table I cite from this book by clicking here for the low resolution version first (85K), and, if you are still interested, try your luck with the original TIFF image file, an astounding 2.2 megabytes!

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At the end of World War II Japan's economy and much of its infrastructure was in ruins. While America's telecom research and development increased quickly after the War, the Japanese first had to rebuild their country. It is remarkable that they did so much in communications so quickly. Three things especially helped.

The first was privatizing radio in 1950. No commercial radio or television broadcasting existed before then and hence there was little demand for receivers and related consumer electronics. Stewart Brand, writing in The Media Lab, quotes Koji Kobayashi in his book Computers and Communications: "Clearly the release of radio waves was a pivotal event that set off a burst of activity that revitalized postwar Japan. In this sense it is quite significant that every year on the first day of June a grand 'Radio Waves Day' takes place to commemorate the promulgation of the Radio Waves Laws." The second great help was Japan re-gaining its independence in 1952, allowing the country to go forward on its own path, arranging its own future. The third event was an easy patent policy AT&T adopted toward the transistor.

Fearing anti-monopoly action by the U.S. States Justice department, the Bell System allowed anyone for $25,000 to use its transistor patents. Although the first transistorized products were American, the Japanese soon displayed an inventiveness toward producing electronics that by the mid-1960s caused many American manufacturers to go out of business. This productivity was in turn helped by a third cause: a government willingness to fund research and development in electronics. Essner, writing in a Japanese Technology Evaluation Center report, neatly sums up most of the telecom situation:

"In 1944, there were 1 million telephone subscribers in Japan. By the end of the war, that number had been reduced to 400,000. NTT [Nippon Telegraph and Telephone] was established to reconstruct the Japanese telecommunication facilities and to develop the required technology for domestic use and production. Between 1966 and 1980, NTT went through an age of growth, introducing new communication services, and the number of subscribers exceeded 10 million by 1968. From 1981 to 1990, NTT became a world class competitor, with many of its technologies, including its optical communication technologies, being used throughout the world. In 1985, NTT was converted into a private corporation." [JTEC]

NTT produced the first cellular systems for Japan, using all Japanese equipment. While their research benefited from studying the work of others, of course, the Japanese contributed important studies of their own. Y. Okumura's "Field Strength and its Variability in VHF and UHF Land Mobile Service," published in 1968, is cited by Roessner et. al. as "the basis for the design of several computer-modeling systems." These were "[D]eveloped to predict frequency propagation characteristics in urban areas where cellular systems were being implemented. These computer systems (the two main cellular players, Bell Labs and Motorola each developed its own) became indispensable to the design of commercial cellular systems."[SR3]

Often thought of as the 'Bell Labs of Japan,' NTT did not manufacture their own products, as did Western Electric for the Bell System. They worked closely instead with companies like Matsushita Electric Industrial Co. Ltd. (external link) (also known as Panasonic in the United States), and NEC, originally incorporated as the Nippon Electric Company, but now known simply as NEC. (external link) As we've seen, Oki Electric was also a player, as were Hitachi and Toshiba. The silent partner in all of this was the Japanese government, especially the Ministry of International Trade and Research, which in the 1970s put hundreds of millions of dollars into electronic research. The Japanese government also helped their country by stifling competition from overseas, refusing entrance to many American and foreign built electronics.

The Ministry of International Trade and Research, otherwise known as MITI, controls the Agency of Industrial Science and Technology. That agency traces its roots to 1882, its Electric Laboratory to 1891. Many other labs were established over the following decades to foster technological research. In 1948, MITI Ministry folded all these labs into the presently named Agency of Industrial Science and Technology (external link). Funded projects in the 1970s included artificial intelligence, pattern recognition, and, most importantly to communications, research into very large scale integrated circuits. [Business Week3] The work leading up to VSLI production, in which tens of thousands of interconnected transistors were put on a single chip, greatly helped Japan to reduce component and part size. It was not just research, which all companies were doing, but also a fanatical quality control and efficiency that helped the Japanese surge ahead in electronics in the late early to mid 1980s, just as they were doing with car building.

On March 25, 1980, Richard Anderson, general manager for Hewlet Packard's Data Division, shocked American chip producers by saying that his company would henceforth buy most of its chips from Japan. After inspecting 300,000 standard memory chips, what we now call RAM, HP discovered the American chips had a failure rate six times greater than the worst Japanese manufacturer. American firms were not alone in needing to retool. Ericsson admits it took years for them to compete in producing mobile phones. In 1987 Panasonic took over an Ericsson plant in Kumla, Sweden, 120 miles east of Stockholm to produce a handset for the Nordic Mobile Telephone network. As Meurling and Jeans explained:

"Panasonic brought in altogether new standards of quality. They sent their inspection engineers over, who took out their little magnifying glasses and studied, say displays. And when they saw some dust, they asked that the unit should be dismantled and that dust-free elements should be used instead. Einar Dahlin, one of the original small development team in Lund, had to reach a specific agreement on how many specks of dust were permitted." [Meurling and Jeans]

America and the rest of the world responded and got better with time. Many Japanese manufacturers flourished while several companies producing cell phones at the start no longer do so. Other Japanese companies since entered the world wide market, where there now seems room for everyone. Many years ago Motorola started selling into the Japanese market, something unthinkable at the beginning of cellular. And the proprietary analog telephone system NTT first designed was so expensive to use that it attracted few customers until years later when competition was introduced and rates lowered. The few systems Japanese companies sold overseas, in the Middle East or or Australia, were replaced with other systems, usually GSM, after just a few years. But now I am getting ahead of myself.

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Resources

Blecher, Franklin H. "Advanced Mobile Phone Service." IEEE Transactions on Vehicle Communications, Vol. VT-29, No. 2, May, 1980

[Business Week2]"Fewer busy signals for mobile phones" Business Week, Industrial Edition, August 7, 1978 Number 2546: 60B

[Business Week3]"Japan's Bid to out-design the United States" Business Week, Industrial Edition, April 13, Number 2863: 123

Gibson, Stephen W., Cellular Mobile Radiotelephones. Englewood Cliff: Prentice Hall, (1987): 141, quoting information from the company Personal Communications Technology. You can view the table I cite from this book by clicking here for the low resolution version first (85K), and, if you are still interested, try your luck with the original TIFF image file, an astounding 2.2 megabytes!

This Bahrain date was confirmed on December 5, 2000 by Mr. Ali Abdulla Sahwan, Manager, Public Relations, of the Bahrain Telecommunications Company (Batelco) in a personal correspondence to myself, Tom Farley. There is contradictary if somewhat baffling evidence from the General Manager of C&W's radio division in Bahrain at the time, a Mr. Alec Sherman. He maintains that the system was not cellular but, well, read his own words and then tell me what you think.

[JTEC] Forrest, Stephen R. (ed.). JTEC Panel Report on Optoelectronics in Japan and the United States. Baltimore, MD: Japanese Technology Evaluation Center, Loyola College, February 1996. NTIS PB96-152202. 295 to 297

http://itri.loyola.edu/opto/ad_nonsl.htm (external link)

Meurling. John and Richard Jeans. The Ugly Duckling: Mobile phones from Ericsson -- putting people on speaking terms, Stockholm, Ericsson Radio Systems AB (1997) p.46 ISBN# 9163054523

[SRI3] David Roessner, Robert Carr, Irwin Feller, Michael McGeary, and Nils Newman, "The Role of NSF's Support of Engineering in Enabling Technological Innovation: Phase II Final report to the National Science Foundation. Arlington, VA: SRI International, 1998.

http://www.sri.com/policy/stp/techin2/chp4.html (external link, now dead)

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In 1983 Texas Instruments introduced their single chip digital signal processor, operating at over five million operations a second. Though not the first to make a single chip DSP, Lucent claiming that distinction in 1979 (external link), TI's entry heralded the wide spread use of this technology. The digital signal processor is to cell phones what the microprocessor is to the computer. A DSP contains many individual circuits that do different things. A properly equipped DSP chip can compress speech so that a call takes less room in the radio bands, permitting more calls in the same amount of scarce radio spectrum. With a single chip DSP fully digital cellular systems like GSM and TDMA could make economic sense and come into being. Depending on design, at least three calls in a digital system could fit into the same radio frequency or channel space that a single analog call had taken before. DSP chips today run at over 35,000,000 operations a second. http://www.ti.com (external link)

In February, 1983 Canadian cellular service began. This wasn't AMPS but something different. Alberta Government Telephones, now Telus (external link), launched the AURORA-400 system , using GTE and NovAtel equipment. This so called decentralized system operates at 420 MHZ, using 86 cells but featuring no handoffs. As David Crowe explains, "It provides much better rural coverage, although its capacity is low." You had, in other words, a system employing frequency reuse, the defining principle of cellular, but no handoffs between the large sized cells. This worked well for a rural area needing wide area coverage but it could not deliver the capacity that a system with many more small cells could offer, since more cells means more customers served.

Visit this site for an excellent timeline on American cellular development: http://books.nap.edu/books/030903891X/html/159.html#pagetop

On October 12, 1983 the regional Bell operating company Ameritech began the first United States commercial cellular service in Chicago, Illinois. This was AMPS, or Advanced Mobile Phone Service, which we've discussed in previous pages. United States cellular service developed from this AT&T model, along with Motorola's analog system known as Dyna-TAC(external link), first introduced commercially in Baltimore and Washington D.C. by Cellular One on December 16, 1983. Dyna-Tac stood for, hold your breath, Dynamic Adaptive Total Area Coverage. Of course.

Analog or First Generation Cellular Systems

NB: Some systems may still be in use, others are defunct. All systems used analog routines for sending voice, signaling was done with a variety of tones and data bursts. Handoffs were based on measuring signal strength except C-Netz which measured the round trip delay. Early C-Netz phones, most made by Nokia, also used magnetic stripe cards to access a customer's information, a predecessor to the ubiquitous SIM cards of GSM/PCS phones. e-mail me with corrections or additions, I am still working on this table. Here is another look at an analog system table.

Before proceeding further, I must take up just a little space to discuss a huge event: the breakup of AT&T. Although they pioneered much of telecom, many people thought the information age was growing faster than the Bell System could handle. Some thought AT&T stood in the way of development and competition. And the thought of any large monopoly struck most as inherently wrong.

In 1982 the Bell System had grown to an unbelievable 155 billion dollars in assets (256 billion in today's dollars), with over one million employees. By comparison, Microsoft in 1998 had assets of around 10 billion dollars. On August 24, 1982, after seven years of wrangling with the federal justice department, the Bell System was split apart, succumbing to government pressure from without and a carefully thought up plan from within. Essentially, the Bell System divested itself.

In the decision reached, AT&T kept their long distance service, Western Electric, Bell Labs, the newly formed AT&T Technologies and AT&T Consumer Products. AT&T got their most profitable companies, in other words, and spun off their regional Bell Operating Companies or RBOCs. Complete divestiture took place on January, 1, 1984. After the breakup new companies, products, and services appeared immediately in all fields of American telecom, as a fresh, competitive spirit swept the country. The Bell System divestiture caused nations around the world to reconsider their state owned and operated telephone companies, with a view toward fostering competition in their own countries. But back to cellular.

---------------------------------------------

Resources:

Johann Storck recently checked in to make some comments:

"I've just read page 9 of "Mobile Telephone History" and found a picture I knew well ... the good old Ericsson GH 388 [code name Jane, ed.], one of the first really handy and still (from the size factor) small mobile phones. Just don't measure the weight! Well, you put a picture of the model 388 from 1996 on your page and I want to inform you that there was an earlier model, dating back to 1994 which had already the same size factor and nearly the same features (except SMS sending). I've included a picture of my own device manufactured in calendar week 44 in 1994. The phone measures 12.8cm (about 5 inches) in height, 4.8cm (about 1.9 inches) in width and the depth with the normal capacity battery is about 2.6cm (about 1 inch)."

"As for Ericsson getting out of the handset business, I think they were once the leading developer of mobile phones, back in the times when they made models like the 337. But they didn't learn from their design faults. Think of the small display the 337-owner had to deal with, they kept that size for several other models (377, 388 and even the latest phones like T-28 and the T-20). Or think of the fact that the menu structure was far too complicated and still is. From that point of view Ericsson could be better off giving away the mobile phone business to Flextronics because that could bring some innovations to their (technically very good) products."

"If you compare Ericsson to Nokia you see what can be done by listening to the consumer wishes. Nokia designed an easy-to-use graphical menu structure and (in some phones) eliminated the antenna to make the devices smaller and more robust. All these facts made the Nokia phones more mass-market compliant and, as a matter of fact, more people bought Nokia phones even when they weren't seen as having the same technical quality level (quality of speech transmission, battery life time, and so on, like the ones made by other companies."

Editor's note. I always liked Ericsson mobiles. They were rugged and worked. Their design philosophy seemed liked Porsche, you always knew an Ericsson phone when you saw one. There was a nice article on Ericsson design in the first issue of their publication On, once at this address: http://on.magazine.se/

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Europe saw cellular service introduced in 1981, when the Nordic Mobile Telephone System or NMT450 began operating in Denmark, Sweden, Finland, and Norway in the 450 MHz range. It was the first multinational cellular system. In 1985 Great Britain started using the Total Access Communications System or TACS at 900 MHz. Later, the West German C-Netz, the French Radiocom 2000, and the Italian RTMI/RTMS helped make up Europe's nine analog incompatible radio telephone systems. Plans were afoot during the early 1980s, however, to create a single European wide digital mobile service with advanced features and easy roaming. While North American groups concentrated on building out their robust but increasingly fraud plagued and featureless analog network, Europe planned for a digital future.

The first portable units were really big and heavy. Called transportables or luggables, few were as glamorous as this one made by Spectrum Cellular Corporation. Oki, too, produced a briefcase model. Click here for free permissions rights and a higher res photo.

The United States suffered no variety of incompatible systems. Roaming from one city or state to another wasn't difficult like in Europe. Your mobile usually worked as long as there was coverage. Little desire existed to design an all digital system when the present one was working well and proving popular. To illustrate that point, the American cellular phone industry grew from less than 204,000 subscribers in 1985 to 1,600,000 in 1988. And with each analog based phone sold, chances dimmed for an all digital future. To keep those phones working (and producing money for the carriers) any technological system advance would have to accommodate them.

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Europeans saw things differently. No new telephone system could accommodate their existing services on so many frequencies. They decided instead to start a new technology in a new radio band. Cellular structured but fully digital, the new service would incorporate the best thinking of the time. They patterned their new wireless standard after landline requirements for ISDN, hoping to make a wireless counterpart to it. The new service was called GSM.

-- An Evolution of Ericsson Handhelds, from Analog to Digital -- smaller and smaller, lighter and lighter (click on photograph to bring up a bigger image)
1987: Curt, a converted police radio design turned into an NMT 900 phone and later a ETACS mobile. The first Ericsson handheld. Known officially as the HotLine Pocket.	1989: Olivia. Introduced originally for NMT 900 networks, followed by versions for ETACS, AMPS, and eventually GSM. The first Ericsson GSM phone and consequently its first all digital mobile.	1991: Sandra, first version in NMT 900, then ETACS, D-AMPS/AMPS, and finally GSM in 1993.	1996: Jane, D-AMPS, GSM, DCS, PCS1900/GSM. A 'slim' version appeared in a D-AMPS 1900 model as well as a PDC version.

Special thanks to James Borup, Senior Press Officer, Corporate Communications for Ericsson, who provided the book The Ugly Duckling: Mobile phones from Ericsson -- putting people on speaking terms, from which the photographs and information above were taken. I did not put in the 'Sandra' or the 'Hotline Combi' phone. The code names above were mostly "girls names because they were so small and shapely." No, I am not making that up. And Jane is after Jane Seymour but that is another story . . .

And for a diagramatic look at NTT models, click here

GSM first stood for Groupe Speciale Mobile, after the study group that created the standard. It's now known as Global System for Mobile Communications, although the "C" isn't included in the abbreviation. In 1982 twenty-six European national phone companies began developing GSM. This Conference of European Postal and Telecommunications Administrations or CEPT, planned a uniform, European wide cellular system around 900 MHz. A rare triumph of European unity, GSM achievements became "one of the most convincing demonstrations of what co-operation throughout European industry can achieve on the global market." Planning began in earnest and continued for several years.

In the mid-1980s commercial mobile telephony took to the air. The North American terrestrial system or NATS was introduced by Airfone in 1984, the company soon bought out by GTE. The aeronautical public correspondence or APC service breaks down into two divisions. The first is the ground or terrestial based system (TAPC). That's where aircraft placed telephone calls go directly to a ground station. The satellite-based division, which came much later, places calls to a satellite which then relays the transmission to a ground station. AT&T soon established their own TAPC network after GTE.

In December 1988 Japan's Ministry of Posts and Telecommunications ended NTT's monopoly on mobile phone service. Although technically adept, NTT was also monolithic and bureaucratic, it developed a good cellular system but priced it beyond reach, and required customers to lease phones, not to buy them. With this atmosphere and without competition cellular growth in Japan had flatlined. With rivals cellular customers did increase but it was not until April,1994, when the market was completely deregulated, allowing price breaks and letting customers own their own phones, did Japanese cellular really take off.

In 1989 The European Telecommunication Standards Institute or ETSI (external link) took responsibility for further developing GSM. In 1990 the first recommendations were published. Pre-dating American PCS, the United Kingdom asked for and got a GSM plan for higher frequencies. The Digital Cellular System or DCS1800 works at 1.8 GHz, uses lower powered base stations and has greater capacity because more frequencies are available than on the continent. Aside from these "air interface" considerations, the system is pure GSM. The specs were published in 1991.

The late 1980s saw North American cellular becoming standardized as network growth and complexity accelerated. In 1988 the analog networking cellular standard called TIA-IS-41 was published. [Crowe] This Interim Standard is still evolving. IS-41 seeks to unify how network elements operate; the way various databases and mobile switches communicate with each other and with the regular landline telephone network. Despite ownership or location, all cellular systems across America need to act as one larger system. In this way roamers can travel from system to system without having a call dropped, calls can be validated to check against fraud, subscriber features can be supported in any location, and so on. All of these things rely on network elementscooperating in a uniform, timely manner.

In 1990 in-flight radio-telephone moved to digital. The FCC invited applications for and subsequently awarded new licences to operate digital terrestial aeronautical public correspondence or TAPC services in the US. GTE Airfone, AT&T Wireless Services (previously Claircom Communications), and InFlight Phone Inc. were awarded licenses. "[T]hese U.S. service providers now have TAPC networks covering the major part of North America. The FCC has not specified a common standard for TAPC services in the US, other than a basic protocol for allocating radio channel resources, and all three systems are mutually incompatible. Currently over 3000 aircraft are fitted with one of these three North American Telephone Systems (NATS). It is estimated that the potential market for TAPC services in North America is in excess of 4000 aircraft." [Capway (external link)]

-------------------------------

Resources:

Johann Storck recently checked in to make some comments:

"I've just read page 9 of "Mobile Telephone History" and found a picture I knew well ... the good old Ericsson GH 388 [code name Jane, ed.], one of the first really handy and still (from the size factor) small mobile phones. Just don't measure the weight! Well, you put a picture of the model 388 from 1996 on your page and I want to inform you that there was an earlier model, dating back to 1994 which had already the same size factor and nearly the same features (except SMS sending). I've included a picture of my own device manufactured in calendar week 44 in 1994. The phone measures 12.8cm (about 5 inches) in height, 4.8cm (about 1.9 inches) in width and the depth with the normal capacity battery is about 2.6cm (about 1 inch)."

"As for Ericsson getting out of the handset business, I think they were once the leading developer of mobile phones, back in the times when they made models like the 337. But they didn't learn from their design faults. Think of the small display the 337-owner had to deal with, they kept that size for several other models (377, 388 and even the latest phones like T-28 and the T-20). Or think of the fact that the menu structure was far too complicated and still is. From that point of view Ericsson could be better off giving away the mobile phone business to Flextronics because that could bring some innovations to their (technically very good) products."

"If you compare Ericsson to Nokia you see what can be done by listening to the consumer wishes. Nokia designed an easy-to-use graphical menu structure and (in some phones) eliminated the antenna to make the devices smaller and more robust. All these facts made the Nokia phones more mass-market compliant and, as a matter of fact, more people bought Nokia phones even when they weren't seen as having the same technical quality level (quality of speech transmission, battery life time, and so on, like the ones made by other companies."

Editor's note. I always liked Ericsson mobiles. They were rugged and worked. Their design philosophy seemed liked Porsche, you always knew an Ericsson phone when you saw one. There was a nice article on Ericsson design in the first issue of their publication On, once at this address: http://on.magazine.se/

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In 1990 North American carriers faced the question -- how do we increase capacity? -- do we pick an analog or digital method? The answer was digital. In March, 1990 the North American cellular network incorporated the IS-54B standard, the first North American dual mode digital cellular standard. This standard won over Motorola's Narrowband AMPS or NAMPS, an analog scheme that increased capacity by cutting down voice channels from 30KHz to 10KHz. IS-54 on the other hand increased capacity by digital means: sampling, digitizing, and then multiplexing conversations, a technique called TDMA or time division multiple access. This method separates calls by time, placing parts of individual conversations on the same frequency, one after the next. It tripled call capacity .

Using IS-54, a cellular carrier could convert any of its systems' analog voice channels to digital. A dual mode phone uses digital channels where available and defaults to regular AMPS where they are not. IS-54 was, in fact, backward compatible with analog cellular and indeed happily co-exists on the same radio channels as AMPS. No analog customers were left behind; they simply couldn't access IS-54's new features. CANTEL got IS-54 going in Canada in 1992. IS-54 also supported authentication, a help in preventing fraud. IS-54, now rolled into IS-136, accounts for perhaps half of the cellular radio accounts in this country.

I should point out that no radio service can be judged on whether it is all digital or not. Other factors such as poorer voice quality must be considered. In America GSM systems usually operate at a higher frequency than it does in most of Europe. As we will see later, nearly twice as many base stations are required as on the continent, leaving gaps and holes in coverage that do not exist with lower frequency, conventional cellular. And data transfer remains no higher than 9.6 kbs, a fifth the speed of an ordinary landline modem. Tremendous potential exists but until networks are built out and other problems solved, that potential remains unfulfilled.

Meanwhile, back on the continent, commercial GSM networks started operating in mid-1991 in European countries. GSM developed later than conventional cellular and in many respects was better designed. Its North American counterpart is sometimes called PCS 1900, operating in a higher frequency band than the original European GSM. But be careful with marketing terms: in America a PCS service might use GSM or it might not. All GSM systems are TDMA based, but other PCS systems use what's known as IS-95, a CDMA based technology. Sometimes GSM at 1900Mhz is called PCS 1900, sometimes it is not. Arrgh.

Advanced Mobile Phone Service contended well with GSM and PCS at first, but it has since declined in market share. While it was still vibrant, David Crowe put it like this:

"The best known AMPS systems are in the US and Canada, but AMPS is also a de facto standard throughout Mexico, Central and South America, very common in the Pacific Rim and also found in Africa and the remains of the USSR. In summary, AMPS is on every continent except Europe and Antarctica. . . due to the high capacity allowed by the cellular concept, the lower power which enabled portable operation and its robust design, AMPS has been a stunning success. Today, more than half the cellular phones in the world operate according to AMPS standards . . . From its humble beginnings, AMPS has grown from its roots as an 800MHz analog standard, to accommodate TDMA and CDMA digital technology, narrowband (FDMA) analog operation (NAMPS), in-building and residential modifications."

"Most recently, operation in the 1800 Mhz (1.8-2.2 GHz) PCS frequency band has been added to standards for CDMA and TDMA. All of these additions have been done while maintaining an AMPS compatibility mode (known as BOA: Boring Old AMPS). It might be boring, but it works, and the AMPS compatibility makes advanced digital phones work everywhere, even if all their features are not available in analog mode." Cellular Networking Perspectives (external link)

This excellent cellular handheld telephone timeline is of NTT models.

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We come to the early 1990s. Cellular telephone deployment is now world wide, but development remains concentrated in three areas: Scandinavia, the United States, and Japan. Telecom deregulation is occurring across the globe and the private market is offering a wide variety of wireless services. The leading technology in America is now IS-54 while GSM dominates in Europe and many other countries. Japan goes a slightly different direction, with Japanese Digital Cellular (or Personal Digital Cellular) in 1991 and the Personal Handyphone System in 1995. These early digital schemes all use time division multiple access or TDMA. Over the coming years many carriers will replace TDMA with CDMA to increase call capacity, while retaining the same service.

In 1991 Japan began operating their own digital standard called PDC in the 800 MHz and 1.5 GHz frequency bands. Based on TDMA, carriers hoped to eventually replace their three analog cellular systems with digital working and thereby increase capacity.

In July 1992 Nippon Telephone and Telegraph creates a wireless division called NTTDoCoMo, officially known as NTT Mobile Communications Network, Inc. It takes over NTT's mobile operations and customers. In March 1993 digital cellular comes to Japan. And as noted before, in April 1994 the Japanese market became completely deregulated and customers were allowed to own their own phones. Japanese cellular took off.

By 1993 American cellular was again running out of capacity, despite a wide movement to IS-54. The American cellular business continued booming. Subscribers grew from one and a half million customers in 1988 to more than thirteen million subscribers in 1993. Room existed for other technologies to cater to the growing market.

In August, 1993 NEXTEL began operating their new wireless network in Los Angeles. They used Motorola phones which combined a dispatch radio (the so called walkie talkie feature) with a cellular phone. NEXTEL began building out their network nation-wide, with spectrum bought in nearly every major market. The beginning did not go well. Their launch was delayed for several months when it was discovered by Mark van der Hoek (internal link) that they were causing massive interference to the B band carrier's receive band. Filtering was finally put in place that let them operate.

In 1994 Qualcomm, Inc. proposed a cellular system and standard based on spread spectrum technology to increase capacity. It was and still is called IS-95. It uses the AMPS protocol as a default, but in normal operation operates quite differently than analog cellular or the more advanced IS-54. Built on an earlier proposal, this code-division multiple access or CDMA based system would be all digital and promised 10 to 20 times the capacity of existing analog cellular systems. But although IS-95 did work well, the dramatic increase in capacity never proved out. There was enough increase, however, for CDMA based systems to become the transmission method of choice for new installations over TDMA.

Short but good introduction to IS-95 from the title below (10 pages, 275K, .in .pdf)

CDMA IS-95 for Cellular and PCS: Technology, Applications, and Resource Guide by Harte, et.al(external link to Amazon)

By the mid-1990s even more wireless channels were needed in America. Existing cellular bands had no more room. New services and many more frequencies were needed to handle all the customers. So a new block of frequencies. much higher in the radio spectrum, was licensed for wireless use. After much study the FCC began auctioning spectrum in the newly designated PCS band, from December 5, 1994 to January 14, 1997. [The FCC (external link)] A convoluted set of rules resulted in several carriers being licensed in each metropolitan area. The FCC at first thought this new competition to conventional cellular would lower rates overall. While competition was stimulated, lower prices did not occur. In many areas conventional cellular is now cheaper than PCS.

PCS or Personal Communication Services were all digital, using TDMA routines and also code division multiple access or CDMA. These were IS-136 and IS-95, respectively. The most notable offering was European GSM, brought to America at a higher frequency and sometimes dubbed PCS1900. It uses TDMA. The evolution of IS-54, IS-136, came into being shortly after these new spectrum blocks were opened up. Today some carriers use both 900 MHz and 1900 MHz spectrum in a single area, putting a mobile call on whatever band is best at the time.

As we look toward the future the demand for new mobile wireless services seems unlimited, especially with the mobile internet upon us. Existing voice oriented systems will continue and be updated. New systems such as 3G will arrive in America once additional spectrum is cleared for their use. These new services will combine data and voice, treating transmission in a different way. Packet switching is a fundamental, elemental change between how wireless was delivered in the past and how it will be presented in the future.

Conventional cellular radio and landline telephony use circuit switching. Wireless services like Cellular Digital Packet Data or CDPD, by contrast, employ packet switching. Wireless services now developing such as General Packet Radio Service or GRPS (external link), Bluetooth (external link), and 3G (external link), will use packet switching as well.

Circuit switching dominates the public switched telephone network or PSTN. Network resources set up calls over the most efficient route, even if that means a call to New York from San Francisco, for example, goes through switching centers in San Diego, Chicago, and Saint Louis. But no matter how convoluted the route, that path or circuit stays the same throughout the call. It's like having a dedicated railroad track with only one train, your call, permitted on the track at a time.

Footnote: Short Range Wireless Technologies

Cordless Phone Technologies

On July 1, 1995 the NTT Personal Communications Network Group and DDI Pocket Telephone Group introduced the Personal Handyphone System or PHS to Japan. Also operating at 1900 MHz, sometimes referred to as 1.9GHz, PHS is an extremely clever system, allowing the same phone at home to roam with you across a city. A cordless phone gone mobile. According to NTT, by November 1998, subscribers totaled 1,518,700. PHS features a fast 32kbps data transfer rate, commenced in April 1997. In December 1998 this rate was pushed to 64kbps in some limited areas. One can connect PDAs and notebooks through the personal handy phone mobile to the PHS network.

In this selection Nathan Muller writes a short pagragraph on PHS as well as early history of American PCS (6 pages, 274K in.pdf. )

Bluetooth: This link goes to my Blutetooth page

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This page discusses standards, uniform rules cellular systems follow. Learning standards teaches how cellular radio is organized. Unless a company foregoes the standards process, such as Motorola with their iDEN system, a radio technology will always have a single industry name and a standard to go with it. Learning about standards and the industry names that go with them, clears up much confusion.

A standard is an accepted or established rule or model. They are a set of agreed on principles and practices. Different industry standards specify everything from film roll speed to electrical outlet shapes. Most standards are voluntary but everything works better if manufacturers agree on them. Who wants a dozen credit card sizes? Rather than specifying the construction, size, or shape of cellular equipment, cellular standards more often mandate a process, they dictate how a system works. Many rule making groups produce standards.

TIA (external link) means the Telecommunication Industry Association, a group accredited by the larger American National Standards Institute or ANSI (external link). The TIA, along with the T1P1 Committee of the Alliance for Telecommunications Industry Solutions or ATIS , develop North American wireless standards. The IS means an interim standard, one still developing. The TR-45 committee within the TIA coordinates each standard's work, assigning sub-committees to specific projects. (Click here (external link) for a great overview of their work.) Lastly, spread spectrum or CDMA based PCS relies on TIA-IS- 95 as well as an ANSI standard: ANSI J-STD-00 (external link). The European Telecommunications Standards Institute or ETSI (external link) develops European standards. Like those for GSM.

Cellular standards set rules that mobiles, base stations, mobile switches, cellular databases, and other network elements follow to communicate with each other. Since wireless has many operating systems it has many standards. Some cover small details and others broad areas. North American cellular standards strive to make every mobile and every cell site across the hemisphere work together.

Network standards like TIA IS-41 specify how individual cellular systems communicate over the public switched telephone network or PSTN with every like cellular system and its associated resources. IS-41 provides a common operating framework for different technologies. Its full and telling name is "Cellular Radio telecommunications Inter-System Operations." IS-41 provides the connections to network resources that an AMPS, TDMA, or CDMA systems needs to work. So, IS-41 is not technology dependent, rather, all cellular systems, no matter what type, use the IS-41 protocol to permit calling.

As David Crowe puts it, "Automatic roaming with a cellular phone is made possible by the TIA/EIA-41 standard that provides intersystem handoff, call delivery, remote feature control, short message delivery, validation and authentication through an inter-system messaging protocol." [CNP (external link)] IS-41 makes everything go. Let's move now from a networking standard to a specific technology standard.

Radio or "air interface" standards like TIA IS-54, now rolled into IS-136, specify a technology's operating details. IS-136 is the time division multiple access or TDMA based cellular scheme we looked at briefly in the history section. It's what AT&T uses for their national cellular network; many local carriers use it as well. The IS-136 standard details frequencies, data formats, signalling requirements and other steps used to make a call. What we Americans call "the nitty gritty."

Global Engineering (external link) sells most wireless standards. The documents are expensive and obtuse, with little information relevant to the average telecom enthusiast. Unless you work in a field directly impacted by a standard I would not recommend buying them. Consult books, newsletters, and magazines instead that analyze the standards for you. Check out the files below, then read the informative comments from a telecomwriting.com reader who has actually worked on standards. You won't find such background on many other sites . .

For more on the cellular radio standards, check out this section from Understanding Digital PCS: The TDMA Standard, by Cameron Kelly Coursey (11 pages, 63K in .pdf)

More information on this title is here (external link to Amazon.com)

Need a quick overview of the different electronic associations? Click here for information from Travis Russell's Telecommunications Protocols, 2nd Edition (6 pages, 194K)

More information on this title is here (external link to Amazon.com)

More Discussion

Thanks to Bill Price for the insights below, he graciously took the time to send them in. He relates:

"Sales of standards documents fund the bureaucratic empires of the standardizing organizations, but do not fund any research or development activities."

"From 1978 through 1983 or 1984, I was heavily involved in standards-development efforts in IEEE, ANSI, and ISO arenas. In particular, I was an individual contributor at the Technical Subcommittee level (IEEE, ANSI) and Expert/Working Group (ISO), a company representative
at the Technical Committee level (ANSI), a Member Body Delegate at the ISO Technical Subcommittee level, and a Member Body Delegation Technical Advisor at the ISO Technical Committee level. Now, what does all that mean?"

"It may all sound grand and glorious, but being a US delegate to an ISO committee is no big deal. Anybody can do it. All you need is somebody to pay the bills--and it won't be the sales of any standard you might help to develop. In fact, your company not only gets to pay your expenses, but they also pay the standards-development organization for the license for them to participate. The license is usually called a Membership or Service fee, in the range of $50-$500 per year. This is supposed to cover office expenses of the Sponsoring Organization, which is usually a trade group."

"The formal requirement for membership in any standards group is 'willing and able to participate in the work.' The real meaning of this is that you've got to know something about the subject matter, and you have to have someone to pay your expenses to the meetings. Of all the people I worked with, about 200 in all, in this standards stuff, there was only one who was not paid for by a company or agency that either produced or consumed the stuff of the standard. That one was partially funded by a grant from the NBS (now NIST); the rest came from his own pocket."

"Organizations" can be producers and consumers: the companies that make the affected products, and companies or government agencies and the like that buy the affected products. On some standards, like those related to safety, some members are recruited (if necessary) to represent "the public interest," whatever that is. ANSI rules for accreditation expect a more-or-less balanced membership, but that's sometimes hard to get. On the other hand, IEEE rules are incredibly loose. Most ANSI-accredited committees have quarterly meetings, rotating around the country, to encourage participation by geography. Most IEEE committees that I've been involved with, for example, meet the third Thursday of each month at Ricky's Hyatt House in Palo Alto, California.

"A supplier participates so that its products will be acceptable in the market upon adoption of the standard. The company sends a representative (or more than one), chosen to best represent the company's interests in the personal/technical/corporate/international politics of the subject, as the company sees best. Because the company's interests have already influenced the hiring and job-assignment decisions, the people they send will already be in agreement with the company's goals."

"As to profiting by standards writing, there was a standard that IEEE wanted to develop because they saw it as a popular subject -- they were quite up-front in admitting that they lusted for the publication rights to the standard. A more mainstream group also wanted to develop the standard, and formed their committee first. The IEEE raised a fuss with ANSI, and as a final result the committees merged and IEEE got the publication rights. I was one of the participants in that fiasco: the merger worked because there was an almost complete overlap in membership between the IEEE committee and the mainstream committee."

"The benefits to participation in standards work are usually listed as a) influence over the content of the standard, and b) early knowledge of the content of the approved standard, before approval. The real meaning of the second point is that you, as a participant, already have all the information that will be in the expensive document. You will, of course, share this information within your company -- before committee action -- to get consensus from your coworkers and your management. Your company will start benefiting from the content of the standard before its publication, so it really doesn't need to buy anything from IEEE or from Global Engineering."

"It's not the participants that pay for the documents -- it's all of us poor slobs who didn't have the time, money, or timely interest to get into the development of the standard. Let me say in closing that the publication income consideration is not universal. For example, the American Plywood Association sponsors ANSI standards in its area of interest. APA publishes these standards on the web, freely available to anyone who can find their website."

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Four key components make up most cellular radio systems: the cellular layout itself, a carefully engineered network of radio base stations and antennas, base station controllers which manage several base stations at a time, and a mobile switch, which gathers traffic from dozens of cells and passes it on to the public switched telephone network. ...

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Four key components make up most cellular radio systems: the cellular layout itself, a carefully engineered network of radio base stations and antennas, base station controllers which manage several base stations at a time, and a mobile switch, which gathers traffic from dozens of cells and passes it on to the public switched telephone network.

All analog and digital mobiles use a network of base stations and antennas to cover a large area. The area a base station covers is called a cell, the spot where the base station and antennas are located is called a cell site. Viewed on a diagram, the small territory covered by each base station appears like a cell in a honeycomb, hence the name cellular. Cell sizes range from sixth tenths of a mile to thirty miles in radius for cellular (1km to 50km). GSM and PCS use much smaller cells, no more than 6 miles (10km) across. A large carrier may use hundreds of cells.

Each cell site's radio base station uses a computerized 800 or 1900 megahertz transceiver with an antenna to provide coverage. Each base station uses carefully chosen frequencies to reduce interference with neighboring cells. Narrowly directed sites cover tunnels, subways and specific roadways. The area served depends on topography, population, and traffic. In some PCS and GSM systems, a base station hierarchy exists, with pico cells covering building interiors, microcells covering selected outdoor areas, and macrocells providing more extensive coverage to wider areas. See the Ericsson diagram below.

The macro cell controls the cells overlaid beneath it. A macro cell often built first to provide coverage and smaller cells built to provide capacity.

Macario describes a business park or college campus as a typical situation. In those cases a macrocell provides overall coverage, especially to fast moving mobiles like those in cars. A microcell might provide coverage to slow moving people between large buildings and a piconet might cover an individual lobby or the floor of a convention center.

Steve Punter, of the excellent Steve's Toronto Area Cellular/PCS Site Guide, http://www.arcx.com/sites/ (external link) says that typically microcells are employed along the sides of busy highways or on street corners. Steve sent in pictures of two typical microcells in the Toronto area:

[Microcell 1 (70K)] [Microcell2 (71K)

Base station equipment by itself is nothing without a means to manage it. In GSM and PCS 1900 that's done by a base station controller or BSC. As Nokia puts it, a base station controller "is a high-capacity switch which provides total overview and control of radio functions, such as handover, management of radio network resources and handling of cell configuration data. It also controls radio frequency power levels in the RBSs, and in the mobile phones. Base station controllers also set transceiver configurations and frequencies for each cell." Depending on the complexity and capacity of a carrier's system, there may be several base station controllers.

These BSCs react and coordinate with a mobile telecommunication switching office or MTSO, sometimes called, too, a MSC or mobile switching center. With AMPS or D-AMPs, however, the mobile switch controls the entire network. In either case, the mobile switch interacts with distant databases and the public switched telephone network or PSTN. It checks that a customer has a valid account before letting a call go through, delivers subscriber services like Caller ID, and pages the mobile when a call comes in. Among many other administrative duties. Learn more about cellular switches by checking out this small graphic. Also, if you want to see pictures of a "mobile" mobile switching center, (a Motorola EMX 100 Plus Cellular Switch) go to Michael Hart's excellent site (external link)[Link not working right now]

How does this work out in the real world? Consider Omnipoint's PCS network for the greater New York city area. To cover the 63,000-square-mile service area, Ericsson says Omnipoint installed over 500 cell sites, with their attendant base stations and antennas, three mobile switching centers, one home location register, and one service control point. (The latter two are network resources.) The New York Times says the entire system cost $680 million dollars, although they didn't say if that included Omnipoint's discounted operating license. Now that we've seen what makes up a cellular network, let's discuss the idea that makes that makes those networks possible: frequency reuse.]

Dual band IS-136 Ericsson RBS 884 base station

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The heart and soul, the inner core, the sine qua non of cellular radio is frequency reuse. The same frequency sets are used and reused systematically throughout a carrier's coverage area. If you have frequency reuse you have cellular. If you don't, well, you don't have cellular. Frequency reuse distinguishes cellular from conventional mobile telephone service, where only a few frequencies are used over a large area, with many customer's competing to use the same channels. Much like a taxi dispatch operation, older style radio telephone service depended on a high powered, centrally located transmitter which paged or called mobiles on just a few frequencies.

Cellular instead relies on a distributed network of cells, each cell site with its own antenna and radio equipment, using low power to communicate with the mobile. In each cell the same frequency sets are used as in other cells. But the cells with those same frequencies are spaced many miles apart to reduce interference. Thus, in a 21 cell system a single frequency may be used several times. The lone, important exception to this are CDMA systems which we will cover later. In those, the same frequencies are used by every cell.

Each base station, in addition, controls a mobile's power output, keeping it low enough to complete a circuit while not high enough to skip over to another cell. (back to Cell Basics article)

The frequency reuse concept. Each honeycomb represents a cell. Each number represents a different set of channels or paired frequencies. A cellular system separates each cell that shares the same channel set. This minimizes interference while letting the same frequencies be used in another part of the system. This is frequency reuse. Note, though, that CDMA based systems can use, in theory, all frequencies in all cells, substantially increasing capacity . For review, a channel is a pair of frequencies, one for transmitting on and one for receiving. Frequencies are described by their place in the radio spectrum, such as 900mHZ, whereas channels are described by numbers, such as channels 334 through 666. Illustration from the CDC.

Click here to go to another frequency resuse explanation in my Cellular Baiscs Article -- it contains a large graphic from an early AT&T journal.

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Adding cells and sectoring cells allows cellular expansion. Don't have enough circuits in a crowded cell? Too many customers? Then add to that cell by providing smaller cells like micro and pico cells, underneath and controlled by the existing and larger macro cell. As Steve Punter puts it, "By placing these short-range microcells along busy highways or at busy street corners, you effectively reduce the strain on the primary macrosites by a substantial margin.

Splitting a single cell does not mean that it is broken into smaller cells, like a dividing amoebae, but rather into sectors. A previously omnidirectional base station antenna, radiating equally in all directions, is replaced by several directional antennas on the same tower. This "sectorizing" thus divides the previously homogeneous cell into 3 or 6 distinct areas (120 and 60 degrees around the site respectively). Each sector gets its own frequencies to operate on.

As Fernando Lepe-Casillas neatly puts it, "We sector cells to reduce interference between similar cells in adjacent clusters. Cell splitting is done to increase traffic capacity." Still confused by all of this? I understand. I give another, I think somewhat clearer, explanation at this link.

According to Telephony Magazine, AT&T began splitting their macrocell based New York City network in 1994. (They use IS-136 at both 800 and 1900 MHz.) Starting in Midtown Manhattan, the $30 million-plus project added 55 microcells to the three square mile area by 1997, with 10 more on the way. Lower Manhattan got a "few dozen." Microcells in lower Manhattan sought to increase signal quality, while Midtown improvements tried to increase system capacity. An AT&T engineer said "a macrocell costs $500,000 to $1 million to build, a microcell one-third as much and you don't have to build a room around it." AT&T used Ericsson base stations, with plans to use Ericsson 884 base stations as pictured above in the future. Camouflaged antennas got placed on buildings between 25 and 50 feet above street level.

---------------------------

Resources:

Keiser, Bernhard, and Eugene Strange. Digital Telephony and Network Integration. 2d ed. New York, 1995

Landler, Mark." Yipes! Invasion of the 9-inch antennas! A new form of
wireless phone service is in the works for New York City. (Omnipoint Communications to offer wireless personal communications services)" (Company Business and Marketing) New York Times v145 (August 19, 1996):C1(N), D1(L).

Luxner, Larry. "The Manhattan Project: AT&T Wireless invades the Big Apple with microcells" Telephony, Feb 24, 1997, 232(8):20. 1997

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The following table lists a few frequency allocations for common cellular and PCS services around the world. It's immediately clear why you can't easily use your cell phone while traveling: different countries use different frequencies. Today's mobiles can't tune themselves automatically to the frequencies they find, they need the right hardware, not just software, to use different frequencies. That's why you need a so called dual or triple band phone to use a mobile overseas; these units have additional circuitry built in to use the different frequencies in the countries you might travel to.

Dual mode phones, by comparison, are those few that operate in, say, a digital CDMA operating system, but use a non digital system like AMPS when no PCS signal is found. Sprint and others make these phones. The future promises more operating systems than today and far more different frequency allocations. A single wireless standard based on a common frequency and operating system will be nearly impossible to achieve. It makes sense then to build radios which accommodate different frequencies and protocols. "Smart" radios and "smart" antennas. But I am getting ahead of myself. Back to frequencies.

1. General frequency table

2. Wireless frequencies and the microwave band

United States cellular and PCS frequencies lie in the ITU (external link) recognized UHF or ultra high frequency band. That band runs between 300 MHz and 3000 MHz (3GHz). T.V. channels 14 to 70 also occupy this large band, ranging from 470 to 806 MHz. More specifically, cellular frequencies start at 824 MHz and end at 894 MHz. PCS broadband freqs go from1850 MHz to1990 MHz. The radio spectrum cellular and PCS occupy also places them in the arbitarily termed microwave band, encompassing frequencies between 1 GHz (1000 MHz) and 100 GHz. This means many things.

At these wavelengths radio frequencies behave like light. For the mobile, low powered light waves since the FCC lets mobile use just a few watts and, in actual practice, more often milliwatts. (The base station, by comparison, uses much more power. "PCS base stations put out more than 200 watts. A Motorola 800 MHz CDMA system is putting out more than twice that. In analog, we often used 100 watts per channel in rural areas." [Van Der Hoek] ) I digressed. I was trying to compare microwaves to lightwaves and the problems that causes.

To use Cannon and Luecke's analogy, microwaves act like narrowly focused flashlights: they travel short distances, are directional, work best in a straight line, and get reflected or absorbed by obstacles. Tall buildings, billboards, and even large trucks cause havoc. What Lee calls 'local scatterers.' Unless a system is properly engineered, especially one using 1900 MHz frequencies within a large city, dropped calls may frequently result. Omnipoint, for example, initially employed only 160 base stations for New York City, an inadequate number for the conditions. They now have over 500, with base stations nearly every ten blocks and some cells covering particular streets. [The New York Times]

3. Frequencies and bandwidth

Cellular and PCS occupy 50 megahertz and 140 MHz worth of radio frequency spectrum respectively. By comparison, the entire AM broadcast band takes up only 1.17 megahertz. That band, however, provides only 107 broadcast frequencies. Cellular provides thousands of frequencies to carry conversations and data. The many frequencies and their large channel width account for the large amount of spectrum used. Advanced Mobile Phone Service or AMPS uses 832 channels that are 30 kHz wide. Digital systems like IS-95 (CDMA) and the TDMA based IS-54B (now folded into IS-136), provide more channels in the same space. Let's back up a little.

I mentioned that a typical cell channel is 30 kilohertz wide compared to the ten kHz allowed an AM radio station How is it possible, you might ask, that a one to three watt cellular phone call takes up a path three times wider than a 50,000 watt broadcast signal? Power does not necessarily relate to bandwidth. A high powered signal might take up lots of room or a high powered signal might be narrowly focused. A wider channel helps with audio quality, that's what's important. An FM stereo station, for example, uses a 150 kHz channel to provide the best quality sound. A 30 kHz cellular channel gives you good sound almost automatically, nearly on par with the normal telephone network. We'll see later how TDMA puts three calls within a 30KHz channel, and describe the technological struggle to keep up sound quality.

4. Offsets: Transmit and Receive Frequencies

In AMPS, IS-54B, IS-36, and PCS 1900, 45 MHz speparates transmit and recieve frequencies. That keeps them from interfering with each other and allows simultaneous talking. For example, in the conventional cellular band, mobiles use frequencies 824.04 MHz to 848.97MHz and the base stations operate on 869.04 MHz to 893.97 MHz.

To see how this works, let's look at eight frequencies in a single cell of a single carrier. Assume for the moment that this is one of 21 cells in either an AMPS or or IS-136 system. For IS-136 at 1900 MHz and PCS the channel width (30KHz) remains the same but the offset is greater: 80 Mhz.

Cell#1 of 21 in Band A (The nonwireline carrier)

Channel 1 (333) Tx 879.990 Rx 834.990(The control channel in AMPS)

Channel 2 (312) Tx 879.360 Rx 834.360

Channel 3 (291) Tx 878.730 Rx 833.730

Channel 4 (270) Tx 878.100 Rx 833.100

Channel 5 (249) Tx 877.470 Rx 832.470

Channel 6 (228) Tx 876.840 Rx 831.840

Channel 7 (207) Tx 876.210 Rx 831.210

Channel 8 (186) Tx 875.580 Rx 830.580

etc., etc., etc.,

(Each cell has at least 15 frequencies or channels)

Get the idea of offsets? Check out the animated gif below, modified only slightly from Marshall Brain's award winning, very cool site. Note what we call these frequencies: the reverse channel and the forward channel. They're what makes talking at the same time possible. In the case of analog and TDMA systems the cellular carrier assigns each transmit and receive frequency for each cell in advance. The MTSO or base station controller then chooses from those frequencies for your call.

Frequency offsets and forward and reverse channels depicted. The base station transmits
on the forward channel and the mobile transmits on the reverse channel.

PCS frequencies as mentioned above are offset as well. One more thing. A transmit and receive frequency are often called paired frequencies. That seems logical enough since it takes two frequencies to pass information. Unfortunately, the forward and reverse channels refer to just a single frequency, making a channel definition muddy. For now, think of a channel as a communication path, no matter what form or frequencies make it up. Still following me? Good. Since we've been talking about frequencies, for the most detailed diagram of cellular and PCS frequencies on the web, click here or on the chart below. It's from the Webproforum.

Cell chart

American cell phone frequencies start at 824 MHz and end at 894 MHz. The band isn't continuous, though, it runs from 824 to 849MHz, and then from 869 to 894. Airphone, Nextel, SMR, and public safety services use the bandwidth between the two cellular blocks. Cellular takes up 50 megahertz total. Quite a chunk. By comparison, the AM broadcast band takes up only 1.17 megahertz of space. That band, however, provides only 107 frequencies to broadcast on. Cellular provides thousands of frequencies to carry conversations and data.

5. Frequency blocks and licenses
a. Cellular - 800 MHz

Now things get really dry. Hold on. As we'll see in detail later, North American cellular development got going in earnest after the Bell System breakup in 1984. To foster competition in a limited radio spectrum, the United States licensed two carriers in every large metropolitan area. One license went automatically to the local telephone company, the local exchange carriers or LECs. Or as telco talk puts it, the wireline carriers. Companies like Ameritech or Pacific Bell. The other went to an individual, a company or a group of investors who met a long list of requirements and who properly petitioned the FCC. The non-wireline carriers. Groups like Cellular One.

Each company in each area took half the spectrum available. What's called the "A Band" and the "B Band." The nonwireline carriers usually got the A Band and the wireline carriers got the B band. There's no real advantage to having either one. It's important to remember, though, that depending on the technology used, one carrier might provide three times the connections a competitor does with the same amount of spectrum. Now that we've gotten through the cellular band, let's move up the spectrum.

b. PCS-1900 MHz

From 1995 to 1997 the FCC licensed the so called PCS or Personal Communication Service spectrum, the area around 1900 MHz and some additional radio space around 900 Mhz. It's here where most TDMA based GSM systems are, as well as the CDMA based IS-95 system.

The FCC calls the two PCS spectrum blocks broadband and narrowband frequencies. To make things confusing, PCS licenses differ in bandwidth size from cellular licenses. PCS operators can have two different sized licenses: 30 MHz and 10 MHz, of which they are allowed to put together. Six PCS licenses exist for each market. It's said that "the real advantage for PCS is that the 30 MHz and 10 MHz licenses are contiguous, which cuts down on the cost of infrastructure and subscriber equipment. So, the advantages for PCS are more capacity, lower infrastructure cost, and lower subscriber costs." Speaking of the Personal Communications Service, the FCC divided it into two sections, which we should look at now.

6.The PCS band
a. Narrowband

Lower in the spectrum than wideband PCS, Narrowband PCS uses narrower frequency blocks. Less room means N-PCS is better suited for advanced paging services. Narrowband's spectrum falls into these frequency ranges: 901-902MHz, 930-931 MHz, and 940-941 MHz

50 kHz wide paired and unpaired channels make up narrowband's frequency ranges. 12.5 kHz response channels for existing paging licenses also exist. Besides paging services, something this spectrum isn't limited to by regulation, N-PCS can be used for telemetry, such as remotely monitoring gas and electric meters. Even keeping track of copier usage or vending machines. I won't discuss PCS narrowband very much because, quite honestly, I'm not that interested. I like voice communications, not data comms. In addition, each technology can differ widely from another. So little would be gained in understanding PCS in general by exploring paging system nuances. But feel free to go further by exploring these company websites: all external links: SkyTel, Paging Network, AT&T Wireless Services

b. Broadband

Broadband PCS belongs in the microwave band near 2GHz., utilizing 30 MHz wide frequency blocks. This room allows voice, data, and video. Of the 140 MHz allotted, 20MHz is reserved for "unlicensed applications that could include both data and voice services." [FCC external link] Broadband's spectrum falls into the frequency range of 1850MHz to 1990.

Within each range are scattered frequency blocks. The A, B, and C blocks are 30 MHz wide while the D, E, and F blocks are 10 MHz wide. Check out this illustration from the Cellular Development Group (external link).

MS means Mobile Station and BS means base station. Don't worry about remembering exact frequency allocations; it's enough to know that most voice based PCS telephony operates around 2GHz. To remember it by, GSM 1900 refers to 1900 MHz. And IS-136 is often called D-AMPS 1900. For a much more detailed look at the cellular and PCS spectrum, click here to go to Webforum's most excellent PCS primer: http://www.iec.org/online/tutorials/ (external link)

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Resources:

Don L. Cannon and Gerald Luecke. Understanding Communications Systems, (Indianapolis: Howard W. Sams & Co. 1984) p. 94

47 CFR24 Title 47--Telecommunication Chapter 1, FCC, Part 24 Personal Communications Services

Mark Van Der Hoek, personal correspondence. "Consider the differences in the antenna. The mobile has, typically, a unity gain (0 dB gain) antenna. The base station (PCS) will have 18 to 20 dBi gain. So the big signal put out by the base station is received by the puny little mobile's ears, while the puny little signal put out by the mobile is heard by the base station big ears."

Landler, Mark. "Yipes! Invasion of the 9-inch antennas! A new form of wireless phone service is in the works for New York City." (Omnipoint Communications to offer wireless personal communications services) (Company Business and Marketing) NewYork Times v145 (August 19, 1996):C1(N), D1(L).

Meyers, Jason. "To the point" Telephony, Aug 18, 1997,30-32. Intertec Publishing Corp 1997 Company Profile with some interesting operating details.

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Transmission in telephony means sending information on electricity or light from one point to another. Voice or data makes up the transmission. We call the device or matter that the information travels on, be it wires, cable, or radio waves, the transmission media.

FDM, TDMA, and CDMA are different transmission technologies. Wireless folks call them transport mechanisms or access technologies. Whatever. They make up part of the overall operating system a cellular carrier uses. No transmission scheme stands by itself, that is, these techniques are not by themselves operating systems. They are part of one. When someone asks, "Is IS-136 TDMA?" they usually mean, or should mean, "Is IS-136 TDMA based?"

American PCS operating systems use TDMA or CDMA, two different transmission technologies. Usually it is either IS-136, a TDMA system, or IS-95, a CDMA based system. Analog cellular might use conventional frequency multiplexing division. GSM only works in TDMA.

Wireless systems use many ways to transmit information. Here are some:

1. Frequency division multiplex or FDM, used in analog cellular;
where calls are separated by frequency

2. Time division multiple access or TDMA, used in digital cellular and PCS;
where calls are separated by time

3. Code division multiple access or CDMA, used mostly for PCS;
where calls are separated by code

2. Frequency Division Multiplexing

Analog cellular use frequency division multiplexing or FDM. It's simpler than its name suggests. As we've seen, a carrier's assigned radio spectrum is divided into specific frequencies, each separated by space. Like AM radio, which is divided into 10 KHz chunks. Radio station 810, 820, 830, and so on. That's all FDM is. Think of FDM as a single train running on a single track, pulling just one freight car. But what if you've run out of frequencies to handle your customers? What if you need more capacity? You can either separate your existing frequencies by narrower amounts or you can separate your calls over time.

Motorola's Narrowband Advanced Mobile Phone system or NAMPS, used precise frequency control to divide the 30 Khz AMPS channel into three subchannels. Each call takes up just 10Khz. But NAMPS had the same fading problems as normal AMPS, lacked the error correction that digital systems provided and it wasn't sophisticated enough to handle encryption or advanced services. To increase capacity most cellular carriers moved instead to a digital solution, one separating conversations by time or by code.

[Look to my cellular basics article for more information on the now defunct NAMPS.]

3. Time Division Multiple Access

In TDMA first digitizes calls, then combines those conversations into a unified digital stream on a single radio channel. Time division multiple access or TDMA divides each cellular channel into three time slots. In conventional cellular or AMPS a single call takes up 10Khz. In TDMA based D-AMPS or digital AMPS, three calls get put on that single frequency, tripling a carrier's system's capacity. GSM, D-AMPS, and D-AMPS 1900 (IS-136), and Motorola's iDEN all use or can use TDMA. This scheme assigns a specific time slot, a regular space in a digital stream, for each call's use during a conversation.

Think of a not so drunken cocktail party, with each person speaking in turn. Everyone gets to speak over time. Or think of a train pulling three freight cars. In a TDMA analogy, each caller puts their supplies or payload, their part of the conversation, on every third boxcar in a long train. No need for three separate frequencies like in FDM. With TDMA a single radio channel is not monopolized, rather, it efficiently carries three calls at the same time.

An anonymous writer summed TDMA like this, "Effectively, the IS-54 and IS-136 implementations of TDMA immediately tripled the capacity of cellular frequencies by dividing a 30-kHz channel into three time slots, enabling three different users to occupy it at the same time. Currently, systems are in place that allow six times capacity. In the future, with the utilization of hierarchical cells, intelligent antennas, and adaptive channel allocation, the capacity should approach 40 times analog capacity." Webproforum 40 times analog capacity! That's quite a hope. Almost as hopeful at the old, unrealized promises that CDMA would increase capacity 20 times.

4. Code division multiple access

CDMA is another transmission technology. Rather than separating frequencies by space as in FDM, or by time as in TDMA, CDMA separates calls by code. Every bit of every conversation gets tagged with a specific code. The system receives a call, seeming at first like so much radio hash, and reassembles the conversation from the coded bits. Like at a cocktail party with most people speaking English but two people speaking French. The French speakers can easily understand each other above the din of the English. That's because they are speaking in a different language or code. To further punish you with the railroad analogy, think of shipping companies filling every boxcar with packages seemingly at random. Their order doesn't really matter since they each have a unique label on them, like a shipping number, and thus can be sorted out accordingly at the other end.

Each face represents a conversation or a part of a conversation. With FDMA we put different calls on different frequencies, like broadcast stations are separated or divided by frequency. You know, A.M. station 560, 570, 580, 590, 600, 610 and so on. With time division multiple access we divide each call on a single frequency by time, like talking in turn. With CDMA we assign an identifying code to each call and put bits and pieces of different calls on different frequencies as the conversation continues. AT&T's national wireless network, as well as GSM, use TDMA. Sprint's PCS network uses CDMA.

CDMA's greatest benefit is that it can use all cellular frequencies in every cell. We saw how TDMA and FDM carefully assigns channels to each cell in advance to prevent interference. But CDMA codes are so specific that interfering radio signals are treated like noise and disregarded. So you can increase capacity, theoretically, by making all frequencies available at all times. We'll see why that promised capacity doesn't quite work out in practice later. For now, let's look at the operating systems these transmission technologies are placed in.

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I mentioned wireless operating systems: analog cellular, PCS, GSM, and so on. This page gives you an overall look at cellular radio before we concentrate on their details. Bookmark this page and go to the next topic if you don't find it relevant right now.

Wireless systems share many things in common. Here's a short pictorial of basic wireless elements:

The MS or Mobile Station 1. The mobile makes a call . . .	The Cell Site Antenna 2. A nearby cell site's antenna picks up the call from the mobile . . .
The BS or Base Station   3. The call is then routed through the base station's transceiver. In PCS and GSM several base stations may be controlled by a base station controller or BSC . . .	THE MSC OR MTSO 4. The mobile switching center or mobile telecommunications switching office gets the call next. This switch can be a normal landline switch like a 5ESS or an AXE or a dedicated one like a Motorola. Each MSC manages dozens to scores of cell sites and their attendant base stations. Large systems may have two or more MSCs. . .
THE HLR. VLR, AC, EIR 5. The mobile switch queries several databases before permitting a call. A dedicated server associated with the switch houses these databases. The Home Location Register (HLR), The Visited Location Register (VLR), the Authentication Center (AC), and the Equipment Identity Register (EIR) are some of these databases. . .	The PSTN  6. The call is processed and routed next to the telephone network at large, also known as the Public Switched Telephone Network. The switch communicates, too, with distant databases over the PSTN.
	This silly little spinning globe is supposed to represent the Public Switched Telephone Network at large.
The OMC 7. At all times an Operations and Maintenance Center monitors the network.

Simple block diagram of network elements

Now that we've seen the elements, let's put it into a block diagram and discuss some terms. We'll look at more complicated diagram after the terminology discussion below. Again, if this is more than you need to know about cellular radio, bookmark this page and move to the next topic.

The elements in depth

The Home Location Register and the Visitor Location Register work together – they permit both local operation and roaming outside the local service area. You couldn't use your mobile in San Francisco and then Los Angeles without these two electronic directories sharing information. Most often these these two directories are located in the same place.

The HLR and VLR are big databases maintained on computers called servers, often UNIX workstations. Companies like Tandem and DSC make the servers, which they simply call HLRs. These servers maintain more than the home location register, but that's what they call the machine. Many mobile switches use the same HLR.

The HLR stores complete local information. It's the main database. Signed up for cellular service in Topeka? Your carrier puts your information on its nearest HRL, or the one assigned to your area. That info includes your international mobile equipment identity number or IMEI, your directory number, and the class of service you have. It also includes your current city and your last known "location area", the place you last used your mobile.

The VLR or visitor location registry contains roamer information. Passing through another carrier's system? Once the visited system detects your mobile, its VLR queries your assigned home location register. The VLR makes sure you are a valid subscriber, then retrieves just enough information from the now distant HLR to manage your call. It temporarily stores your last known location area, the power your mobile uses, special services you subscribe to and so on. Though traveling, the cellular network now knows where you are and can direct calls to you.

The AC or AUC is the Authentication Center, a secured database handling authentication and encryption keys. (GSM, PCS 1900, and certain cellular systems support these features.) As we'll see later, authentication verifies a mobile customer with a complex challenge and reply routine. The network sends a randomly generated number to the mobile. The mobile then performs a calculation against it with a number it has stored and sends the result back. Only if the switch gets the number it expects does the call proceed. The AC stores all data needed to authenticate a call and to then encrypt both voice traffic and signaling messages.

The EIR or Equipment Identity Register is another database.The EIR lists stolen phones, fraudulent telephone identity numbers, and faulty equipment. It's one tool to deny service or track problem equipment.

The OMC or operation maintenance center is network control. It monitors every aspect of a cellular system. A maintenance center may monitor several carrier's systems. Every OMC is staffed twenty four hours a day.

Now let's look at the more complicated block diagram below. It's from Ericsson and it details a GSM or PCS system. I'm discussing this to familiarize you with block diagrams; to show network elements don't have to be mysterious.

A more complicated model

Much is familiar in the diagram below. Ericsson divides a system into several parts, such as a switching system, base station system, network management system and so on. Here's my quick guide below:

Base station system

Made up of a base station controller (BSC) and the individual base transceiver stations (BTS), which most people just call base stations. The radio base station 2000 (RBS) is Ericsson's newest base station. AXE stands for Automatic Exchange Electric, Ericsson's digital switch. Seeing AXE in a box means that element is tied or linked to the switch.

Gateway products

The service order gateway (SOG) means a service desk, where clerks access network databases. Operators enter and cancel accounts and do administrative chores. The billing gateway (BGW) is where customer and administrative billing information contacts the individual carrier.

Message Center

"Stores and forwards voice, fax and electronic mail, as well as short texts from paging networks."

MIN Network

MIN stands for mobile intelligent network. The service control point (SCP), The service management system (SMAS) provides service management functions. "800-number lookup services, calling card services, calling number identification, short message service, message waiting indicator, and debit card services" are all provided through databases linked to the cellular system by the much larger, countrywide MIN.

Operations support system

Operations support system (OSS) is another word for the operation and maintenance center we discussed above. EET stands for Ericsson engineering tool, a network planning device.

AXE: Automatic Exchange Electric: Ericsson's digital switch. They operate as either a landline or wireless switch. OSS: Operations support system EET: Ericsson engineering tool, network planning software. SOG: service order gateway BGW: billing gateway. MIN: Mobile intelligent network. SCP: service control point.

Familiar now or at least more comfortable with block diagrams? Good, let's end this discussion and move on. And those who want more, well, download this outstanding .pdf file of Levine, far more details on GSM and PCS and network elements than I will ever write.

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Here are the five main wireless categories:

1.) Personal Communications Services
2.) Cellular
3.) New or proposed services
4.) Paging
5.) Wireless Data

(Categories adopted from Quent Cassen of the IEEE Orange County Communications and Computer Society)

I find paging and wireless data boring and I don't write about them in this series. But I will provide a quick overview of them with a few links for going further.What follows then are quick snapshots of the different categories and their services. I'll have further information in later sections.

Before describing wireless communication types and what sets them apart, we must remember what they have in common. As we've discussed, and as we have seen, PCS, GSM, and conventional cellular systems use the following:

1. A distributed network of . . .

2. Cell sites, encompassing a low powered radio base station transceiver, a base station controller, and an antenna which . . .

3. Provide coverage in small geographical areas called cells . . .

4. Calls from those cells being managed by . . .

5. The base station controller and mobile switches, the . . .

6. Mobile switch and its connected databases providing an . . .

7. Interface between the wireless network and the wired or landline telephone network.

These systems, regardless of name, are all cellular radio. That broad, all-encompassing term best describes modern radio-telephony. Remember this as we discuss different terms. Let's look now at details and see how these mostly incompatible technologies provide similiar services in different ways.

(For a comprehensive treatment on cellular radio, including GSM/PCS, click here for Levine's most excellent 100 page .pdf file)

A. Personal Communications Services (PCS)

Personal communications services started as another choice to conventional cellular, and possibly as an improvement to it. As I noted in the history section, PCS started in America in the mid 1990s. The FCC first licensed only two cellular carriers in each metropolitan area. But by 1994 more channels were needed since many carriers were at system capacity. After much study the FCC began auctioning space in the newly designated PCS band, from December 5, 1994 to January 14, 1997. Convoluted rules resulted in several carriers being licensed in each metropolitan area. A new group of wireless offerings in the new, higher frequency band would allow more companies to compete for the mobile customer and possibly lower wireless rates.

In each area new services and new carriers did develop to compete against conventional cellular and its existing carriers. Prices did not lower, though, and in many areas conventional cellular is now cheaper than PCS. Personal communication services, though, had been born, the most different offerings being IS-95, a spread spectrum system, which Sprint PCS uses, and the European derived GSM, a smart card technology, which many carriers now use across the United States.

Most importantly, perhaps, most PCS services started from scratch, with no older phones or handsets to accomodate analog routines. They could be an all digital service from the start. Unlike existing cellular carriers which had to accomodate even the most simple analog phone, the PCS carriers didn't worry about servicing customers with older equipment. That's because there were no new customers yet. They could build a whole new network including handsets, exactly the way they wanted.

In the United States, therefore, personal communication systems or PCS means products or services using the Federal Communication Commission's two designated PCS radio bands. Equipment like multi-purpose phones, advanced pagers, "portable facsimile and other imaging devices, new types of multi-function cordless phones, and advanced devices with two-way data capabilities." [FCC (external link)]

By regulation the FCC says PCS are "Radio communications that encompass mobile and ancillary fixed communication that provide services to individuals and businesses and can be integrated with a variety of competing networks." [47 CFR 24.5 9] Just about, in other words, any high tech wireless gadget or service imaginable. PCS includes many present wireless services, too, like conventional cellular, modified for the higher, newly allotted PCS frequencies. An example is AT&T's PCS offering, "Pure Digital PCS", more precisely known as IS-136. It's the foundation for their digital one rate plan. Sprint uses a technology called IS-95, which is CDMA based.

Outside the United States, and sometimes even within, defining PCS further gets trickier. Mobility Canada says they "don't believe that PCS can be defined as a technology, a radio spectrum, or a market. It is whatever the wireless communications customer wants it to be." Perhaps. But their quote reminds me of Humpty Dumpty's exhortation that "When I use a word, it means just what I choose it to mean -- neither more nor less."

Calling something PCS is now sexy and it implies that your technology, however old and dusty it may be compared to the competition, is actually happening and cutting edge. AT&T, in fact, deliberately planned to "blur the distinction between cellular and PCS" when they called their cellular service PCS. This debate is not purely semantical, at least to lawyers. Roseville Telephone, now Surewest, and AirTouch Cellular were in a lawsuit hinging on the definition of PCS and Cellular.

Let's remember two things. One, that cellular radio best describes most modern radio-telephone systems, while names like AMPS and GSM refer to the operating system itself. Secondly, PCS in the States generally refers to digital cellular radio operating at a higher frequency. Those services can include different technologies, like IS-136, IS-95, and GSM.

a. The two PCS types or divisions

Two PCS types exist: narrowband and broadband. Narrowband does data and wideband does voice. Mostly. PCS narrowband uses 900 megahertz (MHz) frequencies for many advanced paging services. Broadband uses 2 gigahertz (GHz) frequencies for voice, data, and video services.

In general broadband PCS systems use higher frequencies, lower power, smaller cells and more of them, than conventional cellular at 800 MHz. That reflects the spectrum's properties: higher frequency waves are shorter, travel less distance than low frequency signals, and thus need more base stations spaced more closely together. Base station requirements are, in fact, 50% to 100% more than 800 MHz cellular. [IEEE-OCCS, external link, now dead] These characteristics, in turn, reflect the main problem with PCS systems: lack of coverage! Until PCS networks are completely built out in America, conventional cellular service will continue to lead in coverage and lack of dropped calls.

b. The five main PCS systems

David Crowe of the outstanding Cellular Networking Perspectives (external link), says five PCS systems exist, along with a smaller, more different group of three, which we won't discuss. By way of explanation, 'upband' means a wireless service operating at a higher frequency than it normally does.

PCS1900 Upbanded GSM (A TDMA system)
TIA IS-136 Upbanded TDMA digital cellular
TIA IS-95 Upbanded CDMA digital cellular
TIA IS-88 Upbanded NAMPS narrowband analog cellular (Now defunct)
TIA IS-91 Upbanded Plain old analog cellular

As anyone can see, the major players are all existing cellular radio systems put at higher frequencies. And since they are all cellular, it makes sense to discuss them in the cellular radio discussion. Am I clear on this? PCS in America is just cellular radio put at a higher frequency. Okay? Perhaps another diagram?

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Modulation means to vary or change. In wireless we first take a signal, say a telephone conversation, and then impress it on a constant radio wave called a carrier. Once done the voice signal varies or modulates this radio wave. The two go together over the air. A voice frequency in the audible or audio range, what we can hear, thus modulates or varies a constant frequency in the radio range, which we can't hear. That's an important point. Modulation makes voice band and radio band frequencies work together. Different modulation techniques, such as A.M., F.M., P.C.M. and so on, represent different ways to shape or form electromagnetic radio waves.

There are many reasons to modulate a signal in a particular way. Amplitude modulation, like that still used by Citizens' Band radios, produces a simple, robust wave that doesn't use much spectrum or radio bandwidth. It's plagued by noise though and requires high transmitting power. Frequency modulation, such as analog cell phones use, provides better sound but it needs more bandwidth to achieve that quality and is technically more complex to produce. And then there are modulation types just for transmitting digital information. GSM and IS-136 use these schemes.

Amplitude Modulation

Amplitude modulation means a carrier wave is modulated in proportion to the strength of a signal. The carrier rises and falls instantaneously with each high and low of the conversation. Check out the diagram below. See how the voice current produces an immediate and equivalent change in the carrier.

Low frequency commercial broadcast stations in the "A.M band" use amplitude modulation. Most C.B. or citizens band radios use it too. It's a simple, robust method to form a radio wave but it suffers from static and high battery power requirements, reasons enough that few personal communications devices use it.

Frequency Modulation

Frequency modulation confuses many people but it shouldn't. FM is not limited to the FM band. It is not frequency dependent, that is, it can be used at high or low frequencies. That's because it is a modulation technique, a way to shape a radio wave, not a service by itself. The word frequency in FM relates, instead, to the rate at which this method varies a carrier wave, not to any particular radio frequency it is used on. This will become more clear as we go on.

An FM signal quality is apparent by listening to the FM band: low distortion, little static, good voice quality and immunity from electrical and atmospheric interference. It's why television audio and analog cellular use it. FM also exhibits a capture effect, whereby the receiver seizes on the strongest signal and rejects any others. That's unlike A.M, with signals fading in and out. What's more, F.M. needs far less power to transmit a signal the same distance than A.M.

See the difference in the waveform on the right in the diagram below? You don't have the modulated carrier varying in amplitude, as with A.M., but in the number of cycles or rate. Although perhaps not obvious at first, the right hand side does differ from the left hand side.

This diagram above is courtesy of Douglas-Young's brilliant article on modulation. We have an unvarying carrier wave as we do with A.M. See that? But in F.M. the carrier wave is engineered to deliver a uniform output signal. When we impress upon the carrier a audio signal, such as a 440 hertz dial tone, things begin to happen.

Frequency modulation varies the carrier at a rate of 440 cycles per second, matching the original signal. This differs dramatically from A.M., where a wildly swinging sine wave would be produced instead. In F.M. a quick change in audio frequency results in a quick rate change to the carrier. Despite this seemingly complicated operating method, F.M. circuitry after sixty years is now well established, cheap, simple to make, and easily miniaturized.

Still confused? Understandable. Click here for an extended discussion on F.M.

The July, 1999 Popular Electronics outlined a simple F.M. transmitter kit. It used only one transistor, eleven other parts, and took up no more than a square inch or two. F.M. is now everywhere, developed largely by one man.

Time Out for History!

On January 31, 1954 a 64 year old man wrote a letter to his wife, dressed for work, and walked out of his 13th floor apartment window, plunging to his death. Colonel Edwin Armstrong, the father of modern radio, and the creator of the first F.M. system, had committed suicide. A brilliant but sensitive man, Armstrong allowed the U.S. military to use his patents royalty-free for the duration of World War II. Before that he played a crucial role in communications during the First World War. He believed, rightly so, that F.M. was a revolutionary operating system and that it should replace A.M. equipment for broadcasting. Tired and despondent after fighting one lawsuit after another against RCA and others, his personal fortune spent on promoting and defending F.M., Armstrong finally gave up and killed himself. Every modern radio has circuits Armstrong designed. And you thought modulation was boring. . .

Frequency shift keying, an F.M. variation

Conventional cellular makes much use of frequency shift keying modulation to send signaling and control messages. It's old technology, in fact, the earliest modems were built with this technique, but FSK works well for what it does. To explain its title, FSK means sending data by slightly shifting frequencies. Simple. Keying, by the way, simply means forming or creating a signal. When you "key up" a microphone you create a signal. You turn on

Frequency shift keying uses the existing carrier wave, say, 879.990 MHz. The data rides 8kHz above and below that frequency. It's just like the earliest modems. 0s and 1s. 0s go on one frequency and 1s go on another. They alternate back and forth in rapid succession. FSK gives you only two states to send information. There's a low limit, then, how much and how quickly you can send information. There is a more efficient way.

Phase Modulation

Three ways exists to modulate a signal: by amplitude, frequency or phase. And although there are dozens of modulation techniques, under the most confusing names possible, all of them will fit into one of these categories. We've looked at amplitude modulation, which changes the carrier wave by signal strength, and frequency modulation, which converts the originating signal into cycles. Now we look at phase modulation, which changes the angle of the carrier wave. Phase modulation is strictly for digital working and is closely related to F.M. Phase in fact enjoys the same capture effect as F.M. First, a note.

A digital signal means an ongoing stream of bits, 0s and 1s, on and off pulses of electrical energy. Like those signals running around the inside your computer. Well, how do we transmit that staccato beat of electrical pulses? Very good. We put it on a carrier wave.

A not to scale diagram of a digital signal

You might think you could send digital without a carrier wave, like the earliest wireless telegraphs but your results wouldn't be good. As Dwayne Rosenburgh, N3BJM, puts it, "Transmitting pure radio frequency energy, with no carrier, is like a spark gap transmitter. Very wideband, very inefficient, and with a limited data rate capacity." Ever had an AM radio on nearby by when you switched on a light dimmer? Blast! That's sort of how an old spark gap transmitter worked. Poorly. But new technology is bringing back an old idea.

Dwayne mentions that ultra wideband technology or UWB does now what old spark transmitters couldn't: transmit without a carrier wave. "UWB transmissions can use 'direct modulation' of the rf energy and transmit pulses without carrier modulation. Think of this as a spark gap transmitter that is controlled, with very low power, and spread across about 7 GHz of rf spectrum. Modern processing technology has been able to allow this type of communication using low rf power and efficient digital signal processing algorithms. Therefore, we can reduce the noise and inefficiencies associated with a spark gap transmitter and create UWB transmitters. Dwayne continues, "This ultra wideband technology exception aside, our radio technology is built on carrier waves. No matter how we transmit RF energy, there is always some type of 'carrier' involved."

Ever hear an A.M. radio station go silent for a minute or two? If they are off the air completely you'll hear static. But if they have simply lost audio for a while you'll hear a slight hum. That's the carrier wave.

For more on carrier waves: what they are, what they do, and why we need them, you may want to read my wireless history series from the start.

Let's get back to phase modulation. How does P.M. represent those on and offs?, those 0s and 1s? By playing with angles.

A continuous wave produced to transmit analog or digital information. The many phases or angles of a sine way give rise to different ways of sending information. More here under Digital principles

Quadrature phase shift keying

Let's discuss the awesomely titled quadrature phase shift keying or QPSK. This scheme, used by most high speed modems, allows quicker data transfer than FSK. And it gives at least four states to send information. There's a good chance you've heard this type as your modem makes a dial up connection. IS-136 uses this technology to enable its digital control channel, allowing PCS like services for conventional cellular. GSM uses a variation called Gaussian Minimum Shift Keying,

Quadrature phase shift keying changes a sine wave's normal pattern. It shifts or alters a wave's natural fall to rest or 0 degrees. By forcing changes in a sine wave you can convey information. You don't stop or abbreviate the sine wave, you change its shape or angle of attack. Check out the diagram below.

As an example, 90 degrees, 0 degrees, 180 degrees, and 270 degrees might be represented by binary digits 00,01,10, and 11 respectively.

You arrange a circuit so that at each point you wish to transmit a bit you force a shift in the sine wave. The receiver expects these shifts and decodes them in the proper sequence. Again, we are putting digital information on a carrier wave. We are shaping a carrier wave to do this, to carry more pulses more efficiently. That's why, confusing though it may be to visualize, we have the make and break, up and down pattern of digital, carried on the smooth, up and down shape of an analog looking wave.

This.pdf file is from Professor Noll's book; it is a short, clear introduction to signals and will give you background to what you are reading here.

Wireless services use amplitude, frequency, and phase modulation to send both analog or digital radio signals. But what converts an analog signal to digital in the first place? An encoding scheme. Pulse amplitude modulation first measures or samples the strength of an analog signal. Pulse code modulation encodes these plots into binary words, namely 0s and 1s. These binary digits are represented by on and off pulses of electrical energy.

A digital signal thus produced usually modulates the current carrying the signal within a landline. Modulation and pulses, therefore, get digital messages going. Once completed, the resulting digital signal can be sent over the air with another modulation technique for doing just that. We'll now go over some digital basics and then see in detail how pulse modulation works.

---------------------------------

Notes:

Modulation and Cellular Radio

A.M. or Amplitude Modulation Types

Quadrature amplitude modulation (QAM): Used in Motorola's iDEN system. Some argue that QAM is a hybrid system, not belonging to A.M., but a cross between A.M. and phase modulation.

F.M. or Frequency Modulation Types

Normal F.M.: Used in all analog cellular radio systems, such as AMPS, TAC, ETACS, NMT 900 and so on.

Narrowband F.M: Was used in the now defunct NAMPS cellular system.

Frequency shift keying (FSK): Used in AMPS for control signaling.

Gaussian minimum shift keying (GMSK): Used by GSM systems.

P.M. or Phase Modulation Types

Quadrature phase shift keying (QPSK): IS-95 and the coming Universal Mobile Telephone System.

Differential quadrature phase shift keying (DQPSK): Used by IS-54, the first North American digital cellular system. I'm not sure if it is now incorporated into IS-136.

Pi/4 differential quadrature phase shift keying: IS-136, Japanese Handy Phone and the European TETRA systems.

Extended discussion on F.M. The word frequency in an F.M. discussion confuses many people. That's because this word is used in three separate but related contexts. Here are the subjects; I describe them separately and then discuss them together after that:

1. Frequency and the original audio signal. Usually our voice, this is the message we want to put on a carrier wave. This is what varies the carrier. The audio signal varies in two ways: strength or amplitude and in frequency. Let's concentrate on the audio. Being in the voice band, an audible frequency might range from, say, 300 to 3,000Hz. I used a dial tone at 440Khz as an example before. For our discussion, let's call this signal the voice frequency.

2. Frequency and the the carrier wave. Easily understood. A radio frequency. For an example, let us use 94.5MHz, something in the F.M. band. A carrier wave stays roughly on the same frequency, give or take, no matter if it is modulated by amplitude, frequency, or phase. This is the radio frequency.

3. Frequency and Frequency Modulation. Whereby our signal is put on or merged with the carrier wave. This is the modulation technique.

Okay, let's take a slight time-out. Look again at our friendly F.M. waveform diagram below. See the channel width an F.M. signal occupies? You have a median point, say 880 Mhz, represented here by 0. With an analog FM cellular signal the radio channel is 30Khz wide. That allows 15Khz of room or deviation above and below its assigned frequency. Following this so far?

"The amplitude (volume) of the input or audio signal (Beethoven's 5th, or whatever) produces the AMOUNT of deviation. More volume, more deviation from the original carrier frequency. The FREQUENCY of the input signal is contained in the RATE of deviation. The faster the signal deviates in frequency, the faster audio is output from the FM detector. Hmm. That makes sense - faster = frequency. Amount = amplitude."

Did you get that explanation from Mark van der Hoek? We have two steps here, amount of deviation and rate of deviation. Let's first discuss amount or amplitude or strength. Whatever.

1) Amount of deviation: The diagram doesn't portray signal strength and FM very well. At first glance the output signal looks uniform. Which it is. But we know that no conversation is of uniform strength. What happens, and I know this is difficult to understand, the carrier frequency moves slightly up up or down to reflect the audio signal strength. That is, the carrier frequency itself deviates slightly from the median line or 0 when modulated. So the radio channel width and the output signal remain uniform, it's just that the carrier frequency deviates within the channel assigned it. Got it?

2) Rate of deviation. Back to simple stuff. This is as depicted above, with the carrier modulated by the audio signal at a rate in lock step to the frequency of the original signal. A higher audio frequency? A quicker rate. A lower frequency signal? A lower rate.

As Mark says in summing all this up, "With F.M. the radio frequency does change, slightly, within a window defined by the information that is pressed onto the carrier wave. Both the amount of deviation and the rate of deviation carry information. The original audio signal varies both in amplitude and in frequency. The rate of deviation in the FM signal carries the frequency info, and the amount of deviation carries the amplitude of the original audio signal." Mark van der Hoek.

Modulation (sung to the tune of the French childrens' song of Frere Jacques)

Modulation, tricky modulation

Modulation, I will soon know you

Modulation is a term

Something I will quickly learn

Tricky term, quickly learn

Tricky term, quickly learn

Ah! (repeat)

(NB: Here, play it on your touch tone phone: 1231, 1231, 369, 369, 9*9631, 9*9631, 111, 111)

Resources:

Douglas-Young, John, Illustrated Encyclopedic Dictionary of Electronics, Parker, West Nyack, N.Y. (1981) p.385

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Okay, we've finished with the easy material. Now that you've read the introduction, something on digital history, modulation, a bit about standards, it's time to learn the basics: digital basics. Digital allows features analog schemes can't easily provide. Things like encryption, calling number identification, extension phone service and messaging. It's just a matter of adding more 0s and 1s to the data stream running between the mobile and the base station. Analog based systems by comparison can't easily expand.

But aside from more services for customers, the carrier also benefits. Calls use less bandwidth once digitized and compressed, allowing greater capacity in an already cramped radio spectrum. And an all digital wireless system promises complete compatibility with the landline telephone network. Before understanding how digital communications works we must first look at what makes it up.

A.Turning speech into electrical impulses

Speech is sound in motion. Talking produces acoustic pressure. Speaking into the can of a string telephone, for example, makes the line vibrate, causing sound waves to travel from one end of the stretched line to the other. A telephone by comparison, reproduces sound by electrical means. What the Victorians called "talking by lightning." A standard dictionary defines the telephone as "an apparatus for reproducing sound, especially that of the voice, at a great distance, by means of electricity; consisting of transmitting and receiving instruments connected by a line or wire which conveys the electric current."

Electricity works the phone itself: operates the keypad, makes it ring. Electricity provides a path, too, for voice and data to travel over wires. This gets confusing. Electric current doesn't really convey voice; sound merely varies the current. It's these electrical variations, analogs of the acoustic pressure originally spoken into the telephone transmitter or microphone, that represent voice. Get it? To sum up: 1) electrical current operates the telephone and 2) that electric current is varied by the telephone to communicate. More below.

The telephone is an electrical instrument. Speaking into the handset's transmitter or microphone makes its diaphragm vibrate. This varies the electric current, causing the receiver's diaphragm to vibrate. This duplicates the original sound. Take a look at this image to make this point much clear.

Speaking into an older telephone's transmitter causes the diaphragm, a thin metal sheet, to vibrate, varying the electric current. This up and down current, in turn, causes the receiver's diaphragm to vibrate, reproducing the original sound. Modern phones use electret microphones for transmitters and piezoelectric transducers (external link) for receivers but the principle is the same.

In wireless technology, a coder inside the mobile telephone converts sound to digital impulses on the transmitting side. On the receiving side it converts these impulses back to analog sounds. A coder or vocoder is a speech analyzer and synthesizer in one. Vocoders are in every digital wireless telephone, part of a larger chip set called a digital signal processor. Sound gets modeled and transmitted on one end by the analyzer part of the vocoder. On the receiving end the speech synthesizer part interprets the signal and produces a close match of the original. Keep following along.

Once converted by the telephone to electricity, normal speech, music, or tones, are all analog signals. Their electrical waveforms are like or 'analogous' to the sounds they represent. These sounds vary a telephone circuit's resistance, electrically representing speech with a continuous electromagnetic wave. But along with the good comes the bad. Analog voice transmission amplifies distortion along with the original signal. Like when you make a tape of a tape or a photocopy of a photocopy. Digital systems don't have that problem. Digital signals, for the most part, remain stable for the length of their travel. Why is that?

Digital signals are a mathematical or numerical representation of sound, with each sonic nuance captured as a binary number. Reproducing sound is as easy as reproducing the numbers. Extensive error checking schemes ensure that a wireless digital link stays intact, even when transmitted through the air. Let's see how digital signals are made and then later compressed.

B. Converting electrical impulses to digital signals -- voice coding

Converting sound to digital used to be easy to describe, however, with the newest techniques it's getting tougher. So let's first look at the old fashioned way of digitizing, before we complicate matters.

You've probably seen an analog signal wave. It's a rise and fall pattern, like what you see on an oscilloscope. By plotting its coordinates on graph paper, you know, A-2 , B-4, C-3, and so on, we could record its shape in a numerical or digital form. And the more coordinates we plotted the more accurate the record would become. Well, if we wrote down those plots and gave them to someone else, they could easily redraw the waveform and eventually reproduce the sound. And if we have digital signal processing technology, which we do, our coordinates of A-2, B-4, and C-3 could easily be converted to binary. See what I mean below?

The diagram above and the similiar one that follows are conceptual, don't worry about the plus and the minus, any plot, no matter above or below the median, can be converted to binary. The beautiful, stylized sine wave is from Jessica Koeppel's site: http://gratuitous.com/~jessica/

In T-1, the backbone of long distance telephone service, a caller's voice gets measured or sampled 8,000 times a second! That produces a highly accurate speech record, at least enough for landline telephones. In making a CD, by comparison, music gets sampled 44,000 times a second. Get what we mean by sampling? We take a numerical record of sound, with T-1, 8,000 times a second, and with a CD, 44,000 times a second. The more samples the more accurate our record.

As an aside, I find it odd that some audiophiles claim they can hear the difference between a song on a phonograph record and that same song recorded on a CD. How is it possible to distinguish between an analog record and a CD when sampling occurs at 44,000 times a second? Okay, and since I am rambling, how about that phonograph record? It is the perfect analog example: an entire song recorded in a single, long, continuous groove. No stops and starts or sampling like in digital. Even in silent periods the groove continues on, recording. See how the groove sort of resembles an actual sine wave? A record groove thus represents a continuous and ever varying wave. Analog!

See how a record grove represents a varying, continuous wave? This is totally different from digital. This graphic was from :http://members.chello.se/christer.hamp/phono/poliak.html

Back to sampling. This first step in digitizing is called pulse amplitude modulation or PAM.Amplitude refers to a signal's strength, the relative rise and fall that PAM takes measurements of. These levels, ranging from 0 to 256 in T-1, are plotted against time. How's that? To have a coordinate like those below you must have two magnitudes. The signal strength and the time it occurred. Once you have those you have a plot that can be put into binary.

>img src="http://www.privateline.com/PCS/images/blacksinewavetime.gif">

After PAM takes its measurements, each sample gets converted to an 8 bit binary code word. Let's say one piece of conversation, a fraction of a second's worth, actually, hits a strength level of 175. It's now put into binary, transmitted by turning on or off an electrical current or light wave. Like sending Morse code. The bits 10101111, for example, represent 175. Voltage turned on or off. Since this second step encodes the previous information, it is called pulse code modulation or PCM. That's what the code in PCM stands for.

Putting the measured strength or amplitude into 8 bit code words is also called quantization. A name for both steps is called voice coding. And every code word generated is time stamped so it can be put back together in the order it was made. The result? The bottom line? Old fashioned pulse code modulation needs 64,000 bits (64kbs) every second to represent speech. Better ways exist for wireless. Oh, and make sure you don't confuse the sampling rate with the bit rate we just mentioned. A sampling of 8,000 times a second might result in a 64,000 bit a second signal but it all depends on what follows next.

STOP! Don't rush through. Do you really understand, at least enough to proceed with this article, PAM, PCM, voice coding, and quantization? If not, go back. Take five minutes. You'll learn better.

Does this help you visualize quantization better? It's another kind of waveform coding, different from PCM although similar. This and many other outstanding graphics are at Ericsson's site.

1. Better voice coding: VSLEP

PCM, invented decades ago, isn't efficient for digital wireless working. Radio frequencies are limited in number and size, yet demand for them keeps growing. Data must be sampled and then compressed more effectively to conserve bandwidth. In IS-54, now IS-136, the digital system we will look at later, voice traffic gets coded and compressed at the same time using a technique called VSELP. That stands for, hold your breath, Vector Sum Excited Linear Predictive speech compression. Of course. Voice is compressed down to 7.95 KBits/s, almost one sixth PCM's size. The circuit that does both the initial sampling and compression is called, as we mentioned briefly above, a voice coder, again, part of the digital signal processor or DSP. There's a number of tricks the DSP uses to crunch down speech and conserve bandwidth.

With VSELP, the coder models a speech waveform every 20 milliseconds. That helps immediately, at least compared to T1, which samples every 125 microseconds, piling up a lot of needless bits. And rather than copying the entire sound, VSLEP digitizes the voice's essential elements. It's used with digital sound processing techniques, along with proprietary algorithms owned by the chip maker. If modeling, rather than copying doesn't sound magical enough, hold on. "[I]f a speech segment gets lost over the radio channel, the VSELP decoder (on the receiving end) can 'repair' the effect through speech extrapolation."

In explaining how a GSM mobile encodes speech, Nathan Muller, in the Mobile Telecommunications Factbook, described the related technology called RPE-LPC. He says that "information from previous samples, which does not change very quickly, is used to predict the current sample. The difference between the predicted and actual signal, represent the signal." To put it another way, there's not much change between samples, since each takes place every 20 milliseconds. So, instead of transmitting full full samples each time, the digital signal processor sends only the change between samples. Get it? There's a little more, and then we'll move on.

Many coders support digital speech interpolation or DSI, which gains compression by filling in the gaps during speech pauses. It's said that silence makes up 60% of a conversation, consequently, DSI transmits only during voice spurts. Another active channel then uses the bandwidth during silent periods. Very efficient unless, as David Crowe points out, that speakers don't talk over each other. Don't get overwhelmed by the terminology. Just remember that coders and DSP make up a vital part of any digital wireless system, converting an analog signal to digital and back to analog again.

To wrap this up, let's make totally sure we understand the difference between a digital signal and an analog one. Sampling or quantization takes a lot of measurements. But it is not continuous, even at a hundred or a thousand times a second. There are always small gaps. These breaks, these starts and stops, differ an analog signal from a digital one. A digital signal is made up of discrete units but an analog signal is a continuous unit. Like the record I mentioned, remember?

(I know this animated GIF is annoying but I needed to show a continuous wave)

Digitized speech is a representative model of speech done in near real time. Let's discuss how digital transmission sends information -- inside frames.

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Frames, slots, and channels organize digital information. They're key to understanding cellular radio. And discussing them gets really complicated. So let's back up, review, and then look at the earliest method for organizing digital information: Morse code.

We saw in the last page how information gets converted from sound waves to binary numbers or bits. It's done by pulse code modulation or some other scheme. This binary information or code is then sent by electricity or light wave, with electricity or light turned on and off to represent the code. 10101111, for example, is the binary number for 175. Turning on and off the signal source in the above sequence represents the code.

Early digital wireless used a similar method with the telegraph. Instead of binary, though, they used Morse code. Landline telegraphs used a key to make or break an electrical circuit, a battery to produce power, a single line joining one telegraph station to another, and an electromagnetic receiver or sounder that upon being turned on and off, produced a clicking noise.

A telegraph key tap broke the circuit momentarily, transmitting a short pulse to a distant sounder, interpreted by an operator as a dot. A more lengthy break produced a dash. To illustrate and compare, sending the number 175 in American Morse Code requires 11 pulses, three more than in binary code. Here's the drill: dot, dash, dash, dot; dash, dash, dot, dot; dash, dash, dash. Now that's complicated! But how do we get to wireless?

Let's say you build a telegraph or buy one. You power it with, say, two six volt lantern batteries. Now run a line away from the unit -- any length of insulated wire will do. Strip a foot or two of insulation off. Put the exposed wire into the air. Tap the key. Congratulations. You've just sent a digital signal. An inch or two. The line acts as an antenna, conducting electrical energy. And instead of using a wire to connect to a distant receiver, you've used electromagnetic waves, silently passing energy and the information it carries across the atmosphere.

Transmitting binary or digital information today is, of course, much more complicated and faster than sending Morse code. And you need a radio transmitter, not just a piece of wire, to get your signal into the practical radio spectrum. But transmission still involves sending code, represented by turning energy on and off, and radio waves to send it. And as American Morse code was a logical, cohesive plan to send signals, much more complicated and useful arrangements have been devised.

We know that 1s and 0s make up binary messages. An almost unending stream of them, millions of them really, parade back and forth between mobiles and base stations. Keeping that information flowing without interruption or error means keeping that data organized. Engineers build elaborate data structures to do that, digital formats to house those 1s and 0s: frames, slots, and channels. Frames hold slots which in turn hold channels. These elements all act together. We'll discuss these in turn. Here's the heiarchary again:

Frames

Slots

Channels

A frame is an all inclusive data package. A sequence of bits makes up a frame. Bit stands for binary digit, 0s and 1s that represent electrical impulses. (Go back to the previous discussion if this seems unclear.) A frame can be long or short, depending on the complexity of its task and the amount of information it carries. A frame carries conversation or data as well as information about the frame itself. More specifically, a frame contains three things:

1. Control information, such as a frame's length, its destination, and its origin;

2. The payload or content, the actual call or data;

3. A error checking routine, known as "error detection and correction bits." These help keep the data stream intact while the mobile moves about.

Slots hold individual call information within the frame, that is, the multiplexed pieces of each conversation as well as signaling and control data. With TDMA, used in IS-136, and most GSM systems, each user occupies a radio frequency for a predetermined amount of time in an assigned time slot. Calls are combined or multiplexed into a digital stream by the base station. It assigns these chopped up bits and pieces into an efficient order by putting that information into the right time slots at the right time. Most TDMA based systems use two slots out of a possible six.

Multiplexing combines several different calls into one coherent digital stream.

Channels handle call processing, the actual mechanics of a call. Don't confuse these data channels with radio channels. Two radio frequencies make a cellular radio channel. One frequency to transmit on and one to receive. In digital working, however, we call a channel a dedicated time slot within a data or bit stream. We'll go over this again soon. A channel sends particular messages. Things like pages, for when a mobile is called, or origination requests, when a mobile is first turned on and asks for service.

We'll discuss frames, slots and channels further by looking at representative diagrams of different digital communication systems. I'm not trying to depict every digital cellular or PCS format. I'm trying instead to give you enough terms and ideas that so that you can understand the basics and so that you can go further.

1. Frames

Generic frame with time slots

In the diagram above we look at the basis of time division multiplexing. As we've discussed, TDMA or time division multiple access, places several calls on a single frequency. It does so by separating the conversations in time. Its purpose is to expand a system's carrying capacity while still using the same numbers of frequencies. In the exaggerated example above, imagine that a single part of three digitized and compressed conversations are put into each frame as time goes on.

In IS-136 each radio channel is 30 KHz wide, just as with conventional cellular. Frequencies and control channels are the same, in fact, the whole system is compatible with AMPS, since, at least with IS-136, call setup is done using the AMPS protocol. The difference is that voice traffic is digitized, compressed, and multiplexed to save space or bandwidth. This is true with all digital schemes and bears repeating. With digital, voice traffic is digitized, compressed, and multiplexed to use as little bandwidth as possible.

2. Slots

IS-54B, IS-136 frame with time slots

TDMA puts each time segment into 6 slots. Two slots make up one voice circuit. Like slots 1 and 4, 2 and 5, or 3 and 6. The data rate is 48.6 Kbits/s, less than a 56K modem, with each slot transmitting 324 bits in 6.67 ms. How is this rate determined? By the number of samples taken, when speech is first converted to digital. Remember Pulse Amplitude Modulation? If not, go back. Let's look at what's contained in just one slot of half a frame in digital cellular.

IS-54B time slot structure (Part of the digital traffic channel)

All numbers refer to the amount of bits. Note that data fields and channels change depending on direction. G: Guard time. Keeps one time slot or data burst separate from the others. R: Ramp time. Lets the transmitter go from a quiet state to full power. DATA: The data bits of the actual conversation. DVCC: Digital verification color code. Data field that keeps the mobile on frequency. RSVD: Reserved. SACCH: Slow associated control channel. Where system control information goes. SYNC: Time synchronization signal. Full explanations on next page.

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Now that we've looked at frames and time slots, let's look more closely at channels. They have many definitions. Borrowing heavily from the good folks at Webopedia, a channel is a "communications path between two computers or devices." Most commonly a channel describes a pair of radio frequencies, one to receive on and one to transmit. They link the mobile to the nearest base station. 879.360 Mhz might be a transmit frequency and 834.360Mhz might be the receive frequency. Those paired radio frequencies make up a channel. Find out more by skipping ahead.

In a digital discussion, however, a channel is also a communications path within a data stream. A specified place in that train of 1s and 0s going back and forth between the mobile and the computerized base station transceiver. In IS-54, now IS-136, voice traffic is digitized and put within the digital traffic channel as you see below.

Different data channels in a bit stream go beyond the base station to a mobile telephone switch and out to the greater telephone network at large. These bits convey voice, signaling, and administrative information. It's fascinating: if you talk to another digital phone user on your mobile then the entire conversation has gone digital from one end of the telephone system to the other. Let's look again at the D-AMPS digital traffic channel. It carries data, voice, and some signaling:

The Digital Traffic Channel in Digital-AMPS)

A conversation's data bits makes up the DATA field. Six slots make up a complete IS-54 frame. DATA in slots 1 and 4, 2 and 5, and 3 and 6 make up a voice circuit. DVCC stands for digital verification color code, arcane terminology for a unique 8-bit code value assigned to each cell. The DVCC acts like a digital marker, similar to the supervisory audio tone in AMPS, keeping a mobile on frequency.

G means guard time, the period between each time slot. As you might guess, RSVD stands for reserved. SYNC represents synchronization, a critical TDMA data field. Each slot in every frame must be synchronized against all others and a master clock for everything to work.

(1) How the Digital Traffic Channel Works

Let's see how these strange terms and abbreviations come together by describing handoffs -- what happens when you go from one cell to another. Again, this is an AMPS discussion. If you want call processing in GSM you should download Levine's GSM/PCS .pdf file. First things first. As we'll see in call processing, the mobile idles on the analog control channel or ACC waiting for a call. That's a radio channel, usually the first in a cell's set of frequencies.

Click here for my GSM call processing article

Once a call comes in the mobile switches to a different pair of frequencies; a voice radio channel which the system carrier has made analog or digital. This pair carries the call. If an IS-54 signal is detected it gets assigned a digital traffic channel if one is available. The mobile stays there for the call, returning to the ACC only after the conversation is done. The fast associated channel or FACCH performs handoffs during the call, with no need for the mobile to go back to the control channel. As shown above the fast associated channel is embedded within the digital traffic channel. The DTC is in turn carried on a radio channel. Got it?

The slow associated control channel or SACCH does not perform handoffs but conveys things like signal strength information to the base station. The SACCH runs together with the slot's voice traffic. It's called an associated channel since it is "associated" with the slot that carries the voice. In other words, signaling and voice traffic smoothly together.

The fast associated control channel or FACCH, on the other hand, runs in a blank and burst mode. It transmits during handovers or when the slow associated channel can't send information quickly enough.. Like when entering a tunnel or possibly when a large truck gets in front of you. At that point the data link might be broken so the FACCH acts quickly. As an engineer puts it, "The FACCH overrides the voice payload, degrading speech quality to convey control information." This keeps Mr. Mobile linked to the base station.

All of this goes on while retaining a backward compatibility with analog phone service or AMPS. Don't have digital service in your area? No problem. Your IS-136 phone will still work, just in analog mode and without the fancy features. Speaking of features, IS-136 is now the standard TDMA cellular technology. It adds a digital control channel to the bit stream., enabling features that IS-54 doesn't have, and presenting true competition for Personal Communication Services. So let's keep discussing channels.

SACCH Life in the slow lane . . .   The slow associated control channel. A sub channel of the Digital Traffic Channel. Puts messages in the same slot containing error correction and digitized voice.

FACCH   Number 5 and barely alive . . .   The fast associated control channel. Another sub-channel of the DTC. Sends messages in a hurry, if needed, using a blank and burst routine. Like when handoffs occur. Voice traffic in a slot is "blanked out" while a "burst" of data gets sent through.

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We just looked at the digital traffic channel in IS-54, now IS-136. Now let's look at the digital control channel in IS-136, which, again, is the most prominent TDMA based cellular system in America. At least for now, with AT&T saying they will convert their networks to another TDMA technology, GSM, in the years ahead. IS-136's most important feature is the digital control channel.

The DCCH handles only signaling but it is not the only routine in IS-136 handling signaling. Does that make sense? Other parts handle other signaling tasks. The digital traffic channel in IS-136, for example, uses sub-channels to signal things associated with it. Like messages needed to hand over an active call from one cell to the next. The digital control channel, on the other hand, uses signals for administrative work and providing services. Such as sending cell system information to mobiles or relaying text messages.

The digital control channel builds on IS-54 practices, to some extent, but includes many new things. Among the possibilities:

Caller ID
E-mail

Sleep mode
Voicemail message waiting indicator
Text paging (2-way short messaging)
Normal paging
Advanced fraud protection
International mobile station identification

Blah, blah, blah, blah!

The DCCH also permits properly equipped IS-136 mobiles to act as extended cordless phones in private systems, small wireless networks for in-building and on campus use. How are all these new features achieved? A different kind of modulation.

Click here for wonderful information on IS-136. It's from IS-136 TDMA Technology, Economics, and Services, by Harte, Smith, and Jacobs (1.2mb, 62 pages in .pdf)

Book description and ordering information (external link to Amazon.com)

Modulation

A different modulation scheme provides more capability. Modulation means putting information on a telephone wire or a radio wave. (Here's more on modulation) How that's done has a big impact. AMPS uses frequency shift keying or FSK to send control information. FSK sends data by slightly shifting frequencies. Frequency shift keying uses the existing carrier wave, say, 879.990 MHz. The data rides 8kHz above and below that frequency. Just like early modems. 0's and 1's. 0's go on one frequency and 1's go on another. They alternate back and forth in rapid succession. FSK gives you only two states to send information.

The DCCH transmits data not with frequency shift keying, but rather with the awesomely titled differential quadrature phase shift keying or DQPSK. This scheme, used by most high speed modems, allows quicker data transfer than FSK. It gives you four states to send information.

Differential quadrature phase shift keying changes a sine wave's normal pattern. It shifts or alters a wave's natural fall to rest or 0 degrees. By forcing changes in a sine wave you can convey information. You don't stop or abbreviate the sine wave, you change its shape or angle of attack. Ever watch Star Trek? And seen someone who is supposed to be out of phase? They appear ghostly, with much of their body set off at an angle. That's out of phase.

With the digital control channel we're discussing a fully digital system. That means bits, 0's and 1's, on and off pulses of electrical energy. This staccato beat of electrical pulses pulses gets sent through the atmosphere on radio waves. What might not be clear is how or why we need an analog like looking wave to send digital information. We form the wave to carry digital information. A carrier wave. The original signal, which are electrical pulses, doesn't have anything to do with the way we shape the carrier wave which actually transports the signal. Get the difference?

Remember the digital basics page? A normal landline digital phone call after sampling takes up 64,000 bits. And how better techniques for wireless exist, which reduce bandwidth to 7,500 bits. That's efficient. Similarly, differential quadrature phase shift keying is more efficient than FSK, with at least four possible states to carry information in every wave.

A continuous wave produced to transmit analog or digital information. The many phases or angles of a sine permit different ways to modulate

To review, and to quote someone I cannot now remember, three modulations schemes exist:

"Three methods of digital signal modulation. A digital signal, representing the binary digits 0 and 1 by a series of on and off amplitudes, is impressed onto an analog carrier wave of constant amplitude and frequency."

"1) In amplitude-shift keying (ASK), the modulated wave represents the series of bits by shifting abruptly between high and low amplitude."

"2) In frequency-shift keying (FSK), the bit stream is represented by shifts between two frequencies."

"3) In phase-shift keying (PSK), amplitude and frequency remain constant; the bit stream is represented by shifts in the phase of the modulated signal."

Don't be put off by the many abbreviations and strange concepts; PCS and GSM use related techniques so what you learn here will definitely help later. These modulation types work in either the 800 MHz cellular or the 1900 MHz PCS band. They are not frequency dependent. IS-136, though, is backward compatible with analog AMPS service. You can buy a dual mode phone, dual band phone, for example, that hunts for an IS-136 signal at 1900 Mhz, moves to 800 Mhz if not found, and then uses analog service as a last resort. Coverage gets improved, even if you don't have all features in every territory. It's what AT&T's "nationwide" Digital One Rate Service is based on.

Maintaining backward compatibility with existing services while adding new ones was a major task. But IS-136 lets TDMA cellular carriers offer advanced wireless services to compete against rival and incompatible PCS systems. GSM uses similarly elaborate data structures to provide its features.

We've looked at how frames, slots and channels make up what goes in a bit stream. In IS-136 frames are organized into hyperframes, an extended collection of frames, all working together to provide the extra information IS-136 needs. Don't worry about the complexity. I'll cover the highlights and you can go further elsewhere (external link). The example below depicts a hyperframe and its time slots. Two so called superframes make it up.

IS-136 hyperframe and super frame structure

To repeat our previous discussion, one slot happens every 6.67 seconds. Six slots make up a frame. A frame happens every 40 milliseconds.

Complex, eh? It gets more complicated. Sorry. What makes up the individual digital control channel within a time slot is amazingly complex. Sub-channel upon sub-channel run together, like a layer cake with swirls. To describe this data structure engineers use an artificial construct, a framework of ideas called a layered model. What's known as the OSI model. (OSI discussion at the bottom of this page.) While layers and how they work are beyond the scope of this article, we can first look at what these sub-channels do. And then in the call processing article we'll see how they work.

The diagram below is based on one from a PCS article at the Web Proforum, the best wireless writing on the web:http://www.iec.org/online/tutorials/ (external link)

Click here for wonderful information on IS-136. It's from a chapter in IS-136 TDMA Technology, Economics, and Services, by Harte, Smith, and Jacobs (1.2mb, 62 pages in .pdf)

IS-136 Digital Control Channel

Q. What are the frequencies for the control channel in IS-136 and EDGE?

Mark van der Hoek (internal link):

"The control channels for IS-136 would be the same as for AMPS. In theory they could be any set of 21 channels, but in practice they are 334-354 for the B side carriers, and 333 to 313 for the A side. EDGE should follow the GSM control channels, although GSM is not my strong point. Some IS-136 handsets are dual mode compatible and so would seek only digital control channels."

"Professor Levine (internal link) explains more below. He describes what happens after an IS-136 mobile is booted up and finds that technology available in its area. My understanding is that the mobile (being AMPS compatible) will first scan the AMPS control channels. Once it locks onto and decodes the AMPS control channel, it looks to see if another technology is available. If it sees that, I forget the proper name right now, call it the Advanced Technology Bit, is set, then it goes into its TDMA scan mode. This will get clearer as you read . . ."

Professor Levine:

"Mark and Tom: In contrast to TIA-553 (analog) and IS-54 (dual mode digital- analog cellular), IS-136 standards have no pre assigned carrier frequency/ies for control/setup channels. The system operator/installer can choose any frequency in each cell for this purpose, and can even change that setup channel frequency from time to time if so desired. Since there is no pre-determined carrier frequency for the control channel, the base station transmits the 'carrier number' as a binary code value, contained in the last 12 bits of the TDMA time frame on EVERY downlink carrier frequency in that cell. (That corresponding bit field is all zeros in IS-54. Also, I may be wrong about 12 bits since I am quickly typing this from memory. There may be 11 bits and an extra bit for another purpose. If I recall properly, this is called the 'pointer' value.)"

"Therefore, when a power-on but non-conversation IS-136 mobile station enters a cell and is first scanning the various carrier frequencies in a cell, as soon as it receives a good and sufficiently strong carrier from a base station, it quickly finds the proper frequency for the setup/control channel of that particular cell, and does not need to exhaustively scan all the carrier frequencies in that cell to find the setup channel frequency."

"The IS-136 handset stores all the valid control frequencies in a FIFO (first in, first out) memory list, and on subsequent entries to a new cell while not in conversation, it tries just the frequencies in this FIFO list first. If they don't work (prove not to contain a setup time slot channel) the handset goes back to scanning and looking for the 'pointer' in every downlink carrier frequency. The standard does not call for a FIFO list or this process, but all handset manufacturers do this (copied from the similar process in GSM described in the next paragraph)."

"EDGE follows a method similar to GSM. The operator may assign 'setup' channels to any arbitrarily chosen carrier in the cell. Mobile stations scan all the carriers in 'carrier number' order (e.g., starting from carrier 1, then carrier 2 and so on up to 124 for 900 MHz band GSM/GPRS."

"When a new GSM handset with a brand new SIM chip (just out of the box) is first turned on, it scans all the carrier frequencies that it can receive. Note that due to less carrier frequencies (and more TDM channels per carrier) an exhaustive scan of all 124 carriers in 900 MHz band GSM takes much less time than scanning 416 carriers (from one of the two licensees in the 850 MHz band) in IS-136. The mobile recognizes a 'beacon' frequency that contains setup (broadcast, etc.) channels due to the distinctive presence of the 'frequency correction time burst' on such assigned carrier frequencies (that type of frequency correction burst does NOT occur on a carrier that is used only for traffic channels."

"In a city with multiple GSM service providers intermixed on the same radio band (like Paris or Frankfurt, on the 900 MHz band, in contrast to segregating different service providers into different subbands of the 1900 MHz band in North America) the mobile station also checks to ensure that the broadcast channel indicates a base station Mobile Network Identity (MNI) number that is in the list of those that the SIM chip indicates have a roaming agreement with the home service provider, and of course the home service provider itself. (There is more to this aspect of the process that I am not describing here for brevity.)"

"These carrier code numbers, as found, are stored in the SIM chip, so as the mobile station moves around the city, it automatically accumulates a list of 'acceptable MNI beacon frequencies' in a FIFO list stored in the SIM chip. In a base installation using a 7-frequency cell plan, this is typically only 7 beacon frequencies, although there are some exceptions to this. If you take your GSM handset (or your SIM chip) to another city, it will automatically update the FIFO list of beacon frequencies using actual scan data from the new city. Once a FIFO list is in place, each time you turn on your handset, it scans just the 7 or so frequencies in the FIFO list. This gets your handset up and ready for service very quickly. If none of these frequencies have an acceptable MNI in the broadcast setup channel, then it is likely that you have carried your SIM chip to another city and turned it on there, so it then goes through an exhaustive scan just as it did when it was first powered up (as explained in previous paragraphs)."

"Sorry to be so verbose, but it takes quite a few words to explain what's going on, but I hope this is clear. The most complete source on this is the GSM specifications, but I can't tell you which part from memory -- you may need to read several diverse sections and then put the pieces in order mentally to find out what you need. There is also a simpler but not highly detailed verbal explanation in the book GSM Superphones by Lawrence Harte and myself."

Regards, Richard Levine

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IS-136 migrating to GSM

A major change in the United States cellular radio landscape began on Thursday, July 19th, 2001 in Seattle, Washington. AT&T began a transition from the technology they invented, IS-136, to GSM, a technique originally European that has now gone global.

Both IS-136 and GSM are digital or second generation cellular systems. Both are TDMA based. But AT&T has progressed beyond second generation to 2.5G, since their newest offering includes GPRS or Global Packet Radio Service. GPRS is an advanced packet switched data network that promises more services and higher data transfer rates than the original Cellular Data Packet Data or CDPD technology common across America.

The official name then for AT&T's new service is GSM/GPRS. In a confusing press release short on facts, AT&T left many questions unanswered. I want to know how the GSM/GPRS system will co-exist with the existing IS-136/CDPD service which AT&T will continue to support. One good GPRS report is here: http://www.cisco.com/warp/public/cc/so/neso/gprs/gprs_wp.htm (external link)

Is the OSI model important to understanding cellular radio?

OSI stands for for Open System Interconnection, a standard defining rules communication networks should follow. Seven levels or layers make it up. It was first thought system designers following the OSI model could make their different communication systems more compatible. But for many reasons the OSI model was never fully implemented in every network scheme. Computer networks use it most, radio systems least. Here's an excellent link if you want to know more, a funny, stylish web page: http://routergod.com/ccnabootcamp/osi.html

Graphic from http://www.lightreading.com/ (external link)

The OSI model reminds me of Esperanto, that failed universal language. It promises a way for all Western people to communicate but its promise cannot overcome its impracticality and lack of appeal. (As an aside, a more difficult but far more applicable language has emerged as the world's universal tongue: broken English. ) Similiary, text books do not realistically describe the OSI model's actual, limited use. They stress its universality, its possibilities. Not its problems. Beginning students think that if mastered a knowledge of the OSI model will help them understand dissimilar communication networks by considering them through a common, uniform framework. Each will relate to the other since the OSI model applies to them all. Which is, of course, not the case. Learning is about not only picking certain subjects up, but leaving others down.

Professor Richard Levine (internal link) responds to a recent question from a reader:

"The OSI model is a theoretical structure used for description and documentation of certain communication protocols. Some protocols, particularly those that were developed before the original papers on the OSI model were published (in the 1970s) do not 'fit' or agree with the OSI layers, or there have been several alternative ways to describe what some protocols do in which different authors choose to place different parts of the same protocol in different 'layers.'"

"There are also several instances in which the original authors of the descriptive articles on OSI made the wrong assignment of layers for various purposes, probably due to lack of knowledge of how some specific systems work. For example, many systems have no explicit presentation layer. Some authors place encryption, if used, in the presentation layer."

"But most military systems (and also GSM air Um interface) actually puts encryption at a lower level (like level 2 or 3) which does not correspond to a unique layer (that is, in the Um GSM air interface, all the bits except for those that establish frame synch (the training bits) and time slot boundaries are encrypted in most (not all) types of GSM logical air interface channels."

"It is not always possible or meaningful to try to analyze real systems, such as cellular base station processes, in accordance with the OSI seven layer model. Don't be worried or concerned about it. Sometimes the OSI model is not the best or the appropriate way to describe some communication protocols. "

Regards, Richard Levine

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Click here for my GSM call processing article

This is the last page of the digital basic series. There's much more on radio in my cellular telephone basic series and in my radio series. If you think you've understood most of what I have written, and you want to learn more, download and read R.C. Levine's comprehensive, somewhat easy to read work on cellular and PCS by going here. It's a 368K download in .pdf format. About 100 pages for you to print out. It deals with PCS/GSM better than I can and in more detail than a web site permits. If you want something less extensive on PCS/GSM, but just as good, try the WebProforum at this link here: http://www.iec.org/online/tutorials/ (external link). It's a great read and you will soon be a PCS wizard.

I describe AMPS call processing in the cellular basics series I just mentioned. GSM or PCS call processing, unfortunately, is too difficult for any beginning article. The chart below, reprinted with permission from Clint Smith's Wireless Telecom FAQs, gives you an idea of the GSM complexity. This is chart one of two from his call processing article in his latest wireless book.

PLMN: Public land mobile network. BCCH: Broadcast Control Channel, FCB: Frequency control bursts. BSIC: Base station ID code. Reproduced by permission.

See how complex things get? And you have to translate his terms into something you are familiar for the chart to make sense. Best to go to the library to search for his book. Here is a review I wrote for McGraw Hill. I hope you enjoyed the series and if you know of something less complex on GSM/PCS call processing on the web, let me know.

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The nifty table below is built, somewhat, upon the good work from the folks at:

http://mobileoffice.co.za/celltech.htm (external link)

Editor's note: Many links won't work. Webmasters constantly pull good files off of servers when they re-do their websites. Please don't blame me if these external links fail, try the search engine at the top of this page to look for something else.

Analog Cellular Technologies

Click here for another analog cellular table. Many more links!

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I didn't make this chart. It is archived on this server for your convenience only; if you want to read some of the best writing about wireless anywhere, go to the source: http://www.iec.org/online/tutorials/

And here's my presentation of the cellular frequencies:

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