Commercial cellular telecommunications date from the early 1980s when
the first car telephone arrived on the market. Public acceptance grew
rapidly and the technology progressed through a sequence of “generations”
that begin with each new decade. The first generation systems in 1980 used
frequency division multiple access (FDMA) to create physical channels.
Digital transmission arrived in the early 1990s with the most popular systems
employing time division multiple access (TDMA) and others relying
on code division (CDMA). Third generation technology dating from 2000
uses code division whereas the next generation promises a return to frequency
division. As the preferred form of multiple access migrates through
the time-frequency-code space, the bandwidth of the transmission channels
steadily increases. The first systems transmitted signals in 25 or 30
kHz bands. Second generation Global System for Mobile (GSM) uses 200
kHz and the CDMA channels occupy 1.25 MHz. The channel spacing of
third generation wideband CDMA is 5 MHz and the next generation of
cellular systems will transmit signals in bandwidths up to 20 MHz.