Frequency-division multiple access

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Frequency Division Multiple Access or FDMA is an access technology that is used by radio systems to share the radio spectrum. The terminology “multiple access” implies the sharing of the resource amongst users, and the “frequency division” describes how the sharing is done: by allocating users with different carrier frequencies of the radio spectrum.

This technique relies upon sharing of the available radio spectrum by the communications signals that must pass through that spectrum. The terminology “multiple access” indicates how the radio spectrum resource is intended to be used: by enabling more than one communications signal to pass within a particular band; and the “frequency division” indicates how the sharing is accomplished: by allocating individual frequencies for each communications signal within the band.

In demand assigned multiple access (DAMA) systems, a control mechanism is used to establish or terminate voice and/or data links between the source and destination stations. Consequently, any of the subdivisions is used by any of the participating earth stations at any given time.

FDMA also supports demand assignment in addition to fixed assignment. Demand assignment allows all users apparently continuous access of the transponder bandwidth by assigning carrier frequencies on a temporary basis using a statistical assignment process. The first FDMA demand-assignment system for satellite was developed by COMSAT for use on the Intelsat series IVA and V satellites.

In contrast to FDMA, Time Division Multiple Access (TDMA) is an access technique whereby users are separated in time. Code Division Multiple Access CDMA is an access technology whereby users are separated by codes. Other access techniques include: SDMA – Space division multiple access, CSMA – Carrier sense multiple access, and MF-TDMA - Multi-Frequency TDMA

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