The signal multiplexing technology used in the Advanced Mobile Phone Service (AMPS) analog version of cellular phone technology. Frequency Division Multiple Access (FDMA) is one of three methods used for allocating channels to users over the shared wireless communications medium in cellular phone communication; the others are Time Division Multiple Access (TDMA) and Code Division Multiple Access (CDMA).
FDMA is implemented at the media access control (MAC) layer of the data-link layer in the Open Systems Interconnection (OSI) reference model for networking protocol stacks. FDMA is based on the frequency-division multiplexing (FDM) technique used in wireless networking. In FDMA, the user is assigned a specific frequency band in the electromagnetic spectrum, and during a call that user is the only one who has the right to access the specific band. In the AMPS cellular phone system, these frequency bands are allocated from the electromagnetic spectrum as follows:
Two different frequency bands are used to allow full-duplex communication between base and mobile stations. Both of these bands are then divided into discrete channels that are 30 kHz wide in bandwidth.
Graphic F-21. Frequency Division Multiple Access (FDMA).
One way to understand FDMA is to imagine different people in the same room communicating in voices with different pitches, some high and some low; they would all be able to talk simultaneously and (more or less) understand one another. This is similar to the way FDMA works. FDMA is used by traditional AM and FM radio bands to allow broadcast by individual stations.