How many types of mobile telephone systems are there?

     The main mobile telephone systems in the last twenty five years have been:

1981 Nordic Mobile Telephone (NMT); 1983 Advanced Mobile Phone System (AMPS); 1985 Total Access Communication System (TACS); 1991 American Digital Cellular (ADC); 1991 Global System for Mobile Communication (GSM); 1992 Digital Cellular System (DCS); 1994 Japanese Personal Digital Cellular (PDC); 1995 Personal Communications Service (PCS) - Canada; 1996 Personal Communications Service (PCS) – USA.

Mobile telephone systems are either analog or digital. In analog systems, voice messages are transmitted as sound waves. When you speak into an analog mobile telephone, your voice wave is linked to a radio wave and transmitted. In digital systems, voice messages are transmitted as a stream of zeroes and ones. When you speak into a digital mobile telephone, your voice wave is converted into a binary pattern before being transmitted.

     Mobile telephone system all utilize some method to allow multiple users to share the system concurrently. The three methods for doing this are: FDM  Frequency Division Multiplexing; TDMA Time Division Multiple Access; CDMA Code Division Multiple Access.

In a FDM system, the available frequency is divided into channels. Each conversation is given a channel. When the system runs out of channels in a given area, no more telephone calls can be connected. In this way, FDM operates much like the channel button on your television set. The AMPS and NAMPS mobile telephone systems utilize FDM.

     In a TDMA system, your encoded voice is digitized and then placed on a radio-frequency (RF) channel with other calls. This is accomplished by allocating time slots to each call within the frequency. In the D-AMPS (Digital AMPS) system, each 30kHz carrier frequency is divided into three time slots. In the GSM and PCS systems, each 200kHz carrier is divided into eight time slots. The D-AMPS, D-AMPS 1900, GSM, PCS and iDEN systems all utilize TDMA.

     In a CDMA system, your encoded voice is digitized and divided into packets. These packets are tagged with "codes." The packets then mix with all of the other packets of traffic in the local CDMA network as they are routed towards their destination. The receiving system only accepts the packets with the codes destined for it. Analog systems are FDM. Digital systems can utilize either TDMA or CDMA.

     FDM systems typically allow one call per 10Khz or 30Khz of spectrum. Early TDMA systems tripled the capacity of FDM systems. Recent advances in TDMA promise to provide forty times the carrying capacity of FDM systems. CDMA promises to improve on the results of TDMA.

Before there were cellular telephone systems, there was MTS (Mobile Telephone Service) and IMTS (Improved Mobile Telephone Service). These early systems have ceased operations.

Many mobile telephone systems exist outside the United States, including NMT, TACS/ETACS, and JTACS. New systems are constantly in development.

GSM (Global System for Mobile communication) is a digital mobile telephone system that is widely used in Europe and other parts of the world. GSM uses a variation of Time Division Multiple Access (TDMA) and is the most widely used of the three digital wireless telephone technologies (TDMA, GSM, and CDMA). GSM digitizes and compresses data, then sends it down a channel with two other streams of user data, each in its own time slot. It operates at either the 900 MHz or 1,800 MHz frequency band.

GSM is the de facto wireless telephone standard in Europe. GSM has over one billion users worldwide and is available in 190 countries. Since many GSM network operators have roaming agreements with foreign operators, users can often continue to use their mobile phones when they travel to other countries.

GSM together with other technologies is part of an evolution of wireless mobile telecommunication that includes High-Speed Circuit-Switched Data (HSCSD), General Packet Radio System (GPRS), Enhanced Data rate for GSM Evolution (EDGE), and Universal Mobile Telecommunications Service (UMTS).