Non linear effects in FDMA:

In a FDMA system, many channels share the same antenna at the base station. The power amplifiers or the power combiners, when operated at or near saturation for maximum power efficiency are non linear. The nonlinearities cause signal spreading in the frequency domain and generate IM (Inter modulated) frequencies. IM is undesired RF radiations which can interfere with other channels in FDMA systems. Spreading of the spectrum results in adjacent-channel interference. Intermodulation is the generation of undesirable harmonics. Harmonics generated outside the radio band cause interference to adjacent services, while those present inside the band causes interference to other users in the mobile systems.