Wireless categories
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?
