Joint coding and decision feedback equalization for broadband wireless channels

This paper introduces a new approach for joint convolutional coding and dec ision feedback equalization (DFE). To minimize error propagation, the DFE u ses a combination of soft decisions and delayed tentative decisions to canc el intersymbol interference (ISI). Soft decisions are obtained by passing t he DFE output through a (soft) nonlinear device. This simple method is show n to perform almost as well as an optimum soft feedback approach on wireles s channels with diversity. Tentative decisions from the Viterbi decoder are used to cancel ISI due to multipath with large delays, remedying the incre asing effect of error propagation in channels with large delay spreads. We consider the use of this soft/delayed feedback DFE (S/D-DFE) technique in b roadband wireless channels (with delay spreads up to several tens of the sy mbol period) typical in high-bit-rate mobile data applications. Simulation results indicate that the proposed joint coding and S/D-DFE technique perfo rms to within 1-2 dB [in required signal-to-noise ratio (SNR)] of an ideal coded DFE without error propagation. When combined with antenna diversity a nd a reduced-complexity DFE concept with adaptive feedforward tap assignmen t, it provides high packet throughput against Rayleigh fading, severe delay spreads, and high Doppler rates.