Modified TH-precoding with constant amplitude for indoor wireless system using QPSK

This paper develops a new phase precoding technique to combat intersymbol interference (ISI) resulting from a frequency-selective slowly fading channel in an indoor personal communication system using quadrature phase-shift-keying (QPSK). The precoding technique predistorts only the phase of the transmitted signal to keep a constant transmitted signal amplitude. The stability of the precoder, even in equalizing a nonminimum-phase channel, is ensured by a new dimension partitioning. Computer simulation results demonstrate that, the system using the proposed channel precoder has significantly improved BER transmission performance when compared with that using a conventional decision-feedback equalizer (DFE), because the precoder is not subject to error propagation.