FDMA Frequency Division Multiple Access M.S.P.V.L Polytechnic College, Pavoorchatram

Introduction In FDMA the total bandwidth is divided among multiple simultaneous users (as shown in figure) such that each user is allocated a channel with a bandwidth of W FDMA = W/M Hz. The capacity of each channel is C FDMA = (W/M) log2 (1+S/N) = C/M M.S.P.V.L Polytechnic College, Pavoorchatram

Cont.., Where, C is the channel capacity in bits per second W is the bandwidth in Hz S is the mean signal power N is the noise variance M.S.P.V.L Polytechnic College, Pavoorchatram

Cont.., For a constant S/N, the capacity of the total bandwidth is divided among the users. In practice, each user occupies a bandwidth slightly narrower than W/M so that interference between channels will be acceptable in a system using realizable filters, which have a frequency response that does not go to zero abruptly outside the channel bandwidth. This approach is applicable to both digital and analog modulation formats. M.S.P.V.L Polytechnic College, Pavoorchatram

FDMA(Frequency Division Multiple Access) User 1 User 2 User 3 Time power 30kHz Frequency M.S.P.V.L Polytechnic College, Pavoorchatram

Assign different frequency bands to individual users or circuits – Frequency band(“channel”) assigned on demand to users who request service. – No sharing of the frequency bands: idle if not used. – Usually available spectrum divided into number of “narrowband” channels symbol time >> average delay spread, little or no equalization required. M.S.P.V.L Polytechnic College, Pavoorchatram

Cont.., Continuous transmission implies no framing or synchronization bits needed. Tight RF filtering to minimize adjacent band interference. Costly bandpass filters at base station to eliminate spurious radiation. Usually combined with FDD for duplexing. M.S.P.V.L Polytechnic College, Pavoorchatram

FDMA assigning different frequency bands to individual users Time Frequency F2’F2’ F2F2 F1F1 F1’F1’ F2’F2’ F1’F1’ F2F2 F1F1 M.S.P.V.L Polytechnic College, Pavoorchatram

Uses FDMA/FDD A channel is a pair of frequency duplexed simplex channels. Each simplex channel is 30 KHz. Simplex channels are separated by 45 MHz (allows cheap RF duplexers). Forward link MHz, reverse link MHz. Two carriers per market share the channels. M.S.P.V.L Polytechnic College, Pavoorchatram

Advantages Very simple to design. Narrowband (no ISI). Synchronization is easy. No interference among users in a cell. M.S.P.V.L Polytechnic College, Pavoorchatram

Disadvantages Narrow band interference Static spectrum allocation. Frequency reuse is a problem. High Q analog filters or large guard band required. M.S.P.V.L Polytechnic College, Pavoorchatram

The End.…. Thank You….. M.S.P.V.L Polytechnic College, Pavoorchatram