Channel precoding for π/4-DQPSK and MSK over frequency-selective slow fading channels

This paper presents channel precoding schemes to combat intersymbol interference (ISI) over a frequency-selective slow fading channel in wireless communication systems using π/4 differential quadrature phase shift keying (π/4-DQPSK) or minimum shift keying (MSK). Based on the dimension partitioning technique, the precoders predistort the phase of the transmitted signals in the forward link to combat ISI, keeping the transmitted signal amplitude constant. The precoding schemes can (i) ensure the stability of the precoders even in equalizing a non-minimum-phase channel, (ii) achieve ISI-free transmission without increasing the complexity of the portable unit receiver and (iii) reduce the envelope variations of transmitted signals such that a power efficient nonlinear amplifier can be used without causing undue distortion. Theoretical and simulation results are presented to demonstrate that the proposed channel precoders can outperform DFE when the ISI is severe and the precoding scheme for π/4-DQPSK can achieve a smaller envelope variation than the standard π/4-DQPSK