Frequency division Multiple Access (FDMA) is a technology whereby the total amount of spectrum is divided in a number of channels. Each channel can be assigned to a different user. FDMA is commonly used in analog mobile radio, including analogue cellular mobile telephone systems like AMPS, NMT and TACS.
|The principle of FDMA.|
Between the different used frequency channels is a small amount of bandwidth not used. This space is called a guard band. This bandwidth is necessary to cater for instability of the sender, frequency shifts due to movement (the Doppler effect) and no-ideal filtering.