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. )