Phase precoding for frequency-selective Rayleigh and Rician slowly fading channels

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 pre-distorts the signal transmitted from a base station to a portable unit. The novelty of the technique lies in using a spiral curve design: (1) to ensure the stability of the precoder even in equalizing a non-minimum-phase channel; (2) to obtain an ISI-free received signal; and (3) 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 significantly lower BER than that using a conventional decision-feedback equalizer (DFE) because the precoder does not suffer from error propagation.