Cellular Networks and Mobile Telephony
Mobile telephone systems can be categorized into generations. The first-generation systems are based on analog voice communication using frequency modulation. Due to the overwhelming popularity of the first-generation systems, systems that use the spectrum more efficiently became necessary to reduce congestion. This requirement was addressed by the second generation, which uses digital techniques and time-division multiple access (TDMA) or code-division multiple access (CDMA) for channel access. Advanced call-processing features are present as well. The most widely used second-generation system is GSM, described below. The third generation is evolving from a number of second-generation wireless systems.