Digital AMPS - History

History

The evolution of mobile communication has been almost wholly in 3 different geographic regions. The standards that were born in these regions were quite independent. The 3 regions are North America, Europe and Japan. The earlier mobile or wireless technologies were wholly analog and are collectively known as 1st Generation (1G) technologies. In Japan, the 1G standards were Nippon Telegraph and Telephone (NTT) and the high capacity version of it (Hicap). The European systems were not common and the ‘European Union’ viewpoint that is visible in the later technologies was absent. Various 1G standards that were in use in Europe include C-Netz (in Germany and Austria), Comviq (in Sweden), Nordic Mobile Telephones/450 (NMT450) and NMT900 (both in Nordic countries), NMT-F (French version of NMT900), Radiocom 2000 (RC2000) (in France), and TACS(Total Access Communication System) (in the United Kingdom and Ireland). North American standards were Advanced Mobile Phone System (AMPS) and Narrow-band AMPS (N-AMPS).

Out of the 1G standards, the most successful was the AMPS system. Despite the Nordic countries' cooperation, European engineering efforts were divided among the various standards, and the Japanese standards did not get much attention. Developed by Bell Labs in the 1970s and first used commercially in the United States in 1983, AMPS operates in the 800 MHz band in the United States and is the most widely distributed analog cellular standard. (The 1900 MHz PCS band, established in 1994, is for digital operation only.) The success of AMPS kick-started the mobile age in the North America.

The market showed an increasing demand because it had higher capacity and mobility than the then existing mobile communication standards. For instance, the Bell Labs system in the 1970s could carry only 12 calls at a time throughout all of New York City. AMPS used Frequency Division Multiple Access FDMA which meant each cell site would transmit on different frequencies, allowing many cell sites to be built near each other.

However, AMPS had many disadvantages too. Primarily, it did not have the potential to support the increasing demand for mobile communication usage. Each cell site did not have much capacity for carrying higher numbers of calls. It also had a poor security system which allowed people to steal a phone's serial code to use for making illegal calls. All of these triggered the search for a more capable system.

The quest resulted in IS-54, the first American 2G standard. 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 N-AMPS, an analog scheme that increased capacity by cutting down voice channels from 30 kHz to 10 kHz. IS-54, on the other hand, increased capacity by digital means using TDMA protocols. This method separates calls by time, placing parts of individual conversations on the same frequency, one after the next. TDMA tripled call capacity.

Using IS-54, a cellular carrier could convert any of its system's 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 co-exists on the same radio channels as AMPS. No analog customers were left behind; they simply could not access IS-54's new features. IS-54 also supported authentication, a help in preventing fraud.