Adaptive channel precoding for slowly fading channels

The bit error rate (BER) performance of a mobile or personal radio digital communications system at a high bit rate can be increased significantly by intersymbol interference (ISI) due to multipath propagation. In this paper, a novel adaptive channel precoder is proposed to improve the system performance with-out increasing the complexity of the portable unit. In the forward link, both the amplitude and phase of the signal carrier are predistorted at the transmitter of the base station, so that the signal received at the portable unit is ISI free (in the ideal case). The precoding is based on channel information estimated (from the reverse link) at the receiver of the base station. Computer simulation results demonstrate that, over a two-path Rayleigh fading channel, differential QPSK with the precoder has significantly lower BER values than those with a conventional decision feedback equalizer (DFE), because the precoder is not subject to error propagation.