Soft-Output Demodulation on Frequency-Selective Rayleigh Fading Channels Using AR Channel Models

This paper is a study of high-performance soft-output demodulation for slow or moderate frequency-selective and flat Rayleigh fading using an autoregressive (AR) channel model. For channel taps modeled as AR processes, the discrete-time-equivalent channel model is derived for a matched filter (matched to the transmit pulse) and symbol rate-sampled receiver front end. The optimum symbol-by-symbol demodulator is then derived and shown to consist of a joint data and Kalman filter (KF) channel estimator. Additionally, a symbol-by-symbol demodulator with an extended KF is proposed that jointly identifies and tracks the channel and the unknown parameters in AR channel models. A simulation study shows that the proposed algorithms offer significant advantages in performance or complexity compared to several previously proposed algorithms. The algorithms do not exhibit a significant error floor, provide soft-output metrics needed for interleaved coded modulation, provide high performance with a blind initialization, are capable of blind operation with fast acquisition though compatible with pilot-symbol-assisted modulation, and are robust to parameter mismatch.