Predistort-linearisation method for future basestation amplifiers of cellular radio

Linearisation of a radio base station 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 (IMD) 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. 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.