Basics of FDMA

Frequency Division Multiple Access (FDMA) assigns individual channels to individual users. The users is allocated a unique frequency band or channel. During the period of the call no other users can share the same channel. In Frequency Division Duplexing (FDD) systems the users are assigned a channel as a pair of frequencies; one frequency is used for forward channel, while other is used for reverse channel. The features of FDMA are as follows:

1. The FDMA channel carries only one phone circuit at a time.
2. If an FDMA channel is not in use, then it sits idle and cannot be used by other users to increase or share capacity. It is essentially a wasted resource.
3. The bandwidth of FDMA channels are very narrow (30 KHz in AMPS).
4. FDMA is used in Narrow band only.
5. The amount of intersymbol interference is low, thus no equalization is required for FDMA.
6. The complexity of the FDMA systems is much lower than TDMA.
7. FDMA systems have higher cell site system cost when compared to TDMA systems.
8. FDMA uses duplexers because both transmitter and receiver acts simultaneously in FDMA.
9. FDMA requires tight RF filtering to minimize adjacent channel interference.
10. In FDMA fewer bits are used for overhead purposes.

The Features of TDMA and CDMA are discussed separately click on respective Links for CDMA and TDMA features.