31.3 MOBILE COMMUNICATIONS STANDARDS

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The mobile communications systems deployed in various countries follow different standards, so universal mobility is still a problem. Nowdays, dual-band mobile handsets are available so that a user can use different mobile systems, particularly when moving from one country to another. The various systems deployed for mobile communications are:

Nordic Mobile Telephony (NMT 450) system, operating in 450MHz band since 1981.
Advanced Mobile Phone System (AMPS), operating in 800/900MHz band since 1983.
Total Access Communication System (TACS), operational since 1985.
Nordic Mobile Telephony (NMT 900), operating in 900MHz band since 1986.
American Digital Cellular (ADC) system, operational since 1991.
Global System for Mobile Communications (GSM), operational since 1991.

All these systems are operational in many parts of the world, though the analog systems-NMT, AMPS, and TACS-are now outdated. The drawbacks of these analog cellular systems are low calling capacity (about 55 calls/cell), limited spectrum, poor data communication support, and lack of privacy. Subsequently, a number of digital cellular systems were deployed, out of which GSM became the most widely deployed system in Europe, Africa, and Asia. In the whole world, at the end of the year 2002, GSM subscribers numbered about 787 million.

Over the last 30 years, a number of standards have been developed for cellular mobile communications. Presently predominant standards are GSM and ADC.

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