FDMA

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.