Predistortion as an effective technique for linearisation of basestation amplifiers in a mobile radio cellular system

Abstract

Linearisation of a radio basestation amplifier using a third order and a fifth order predistortion scheme is studied. Adaptive predistortion using a third order predistorter improved the amplifiers intermodulation distortion by between 6.5 dB and 30 dB as measured by a two-tone test. The variation in improvement is due to changes in the input power level. The improvement increases as the input power is backed off from the 1 dB compression point. A fifth order predistorter will give an IMD improvement of between 9 dB and 48 dB if properly adjusted. For a nine-tone test (with uniformly distributed random phase), a fifth order predistorter, if properly adapted will give an IMD improvement of between 8.5 dB and 40 dB from the worst IMD level, provided by the raw nonlinear amplifier.