Radio Access Technology

The GSM Um interface applies the multiple access technology. With this technology, multiple subscribers can share the same public communication connection. Basically, there are three modes of channelization for multiple access,  the frequency, time and code division multiple access connections respectively. They are  frequency division multiple access (FDMA), time division multiple access (TDMA) and code division multiple access (CDMA)

FDMA-frequency division multiple access:

The frequency division is also called channelization sometimes. In this mode, the whole assignable frequency spectrum is divided into many single radio channels. Under the control of the system, each subscriber can be served by any one of these channels.

The analogue cell system, AMPS, is a typical example that uses the FDMA technology. The digital cell system can also use the FDMA. The difference is that it only uses the frequency division mode,but the GSM system uses the FDMA also.