Phase Precoding for Frequency-Selective Rayleigh and Rician Slowly Fading Channels1

This paper presents a novel phase precoding (pre-equalization) technique to equalize frequency-selective Rayleigh and Rician slowly fading channels for personal communication systems using phase modulation. In order to achieve intersymbol interference (ISI)-free transmission, the precoding technique predistorts the signal transmitted from a base station to a portable unit. The novelty of the technique lies in using a spiral curve design i) to ensure the stability of the precoder even in equalizing a non minimum-phase channel, ii) to obtain an ISI-free received signal, and iii) to keep a constant transmitted signal amplitude. Using the precoder can improve the bit error rate (BER) transmission performance without increasing the complexity of the portable unit receiver. The BER performance of coherent quadrature phase-shift-keying (QPSK) with the channel pre-equalization is analyzed theoretically for both Rayleigh and Rician fading channels. Analytical and simulation results demonstrate that, coherent QPSK using the proposed channel precoder has a signiicantly lower BER than that using a conventional decision-feedback equalizer (DFE) because the precoder does not suuer from error propagation.