Frequency Division Multiple Access (FDMA)

Frequency Division Multiple Access (FDMA) is a channel access technique found in multiple-access protocols as a channelization protocol.

FDMA permits individual allocation of single or multiple frequency bands, or channels to the users. FDMA, just like any other multiple access system, harmonizes access between multiple users.

Some alternatives include Code Division Multiple Access (CDMA), Space Division Multiple Access (SDMA), or Time Division Multiple Access (TDMA). These protocols are used in different ways, at different stages of the theoretical Open Systems Interconnection (OSI) model.

FDMA is different from frequency division duplexing (FDD). While FDMA permits multiple users to simultaneously access a transmission system, FDD describes the way the radio channel is shared between the downlink and uplink.

FDMA is also different from Frequency-division multiplexing (FDM). FDM refers to a physical layer method that blends and transmits low-bandwidth channels via a high-bandwidth channel. FDMA, in contrast, is a channel access technique in the data link layer.

Main features:

• In FDMA, every user shares the frequency channel or satellite transponder simultaneously; however, every user transmits at single frequency.
• FDMA is compatible with both digital and analog signals.
• FDMA demands highly efficient filters in the radio hardware, contrary to CDMA and TDMA.
• FDMA is devoid of timing issues that exist in TDMA.
• As a result of the frequency filtering, FDMA is not prone to the near-far problem that exists in CDMA.
• All users transmit and receive at different frequencies because every user receives an individual frequency slot.

One disadvantage of FDMA is crosstalk, which can cause interference between frequencies and interrupt the transmission.