ON CHANNEL ESTIMATION AND SEQUENCE DETECTION OF INTERLEAVED CODED SIGNALS OVER FREQUENCY NONSELECTIVE RAYLEIGH FADING CHANNELS

Due to the receiver complexity introduced by interleaving, the impleme ntation of maximum likelihood (ML) decoding of interleaved coded signa ls transmitted over frequency nonselective Rayleigh fading channels ha s been shown to be practically impossible. As an alternative, a two-st age receiver structure has been proposed, where the channel estimation and sequence decoding are done separately. The channel estimation iss ue in a two-stage receiver is examined in detail in this paper. It is shown that although an optimum [maximum a posteriori (MAP)I channel es timation is not possible in practice, it can be approached asymptotica lly by joint MAP estimation of the channel and the coded data sequence . The implementation of the joint MAP estimation is shown to be an ML sequence estimator followed by an minimum mean square error (MMSE) cha nnel estimator. Approximate ML sequence estimation using pilot symbol interpolation is also studied, and through computer simulations, its p erformance is compared to receivers using ML sequence estimation. The effect of decision delay (DD), prediction order, and pilot insertion r ate (PIR) on the reduced complexity ML sequence estimation is investig ated as well. Finally, a practical receiver is proposed that makes the best compromise among the error performance, receiver complexity, DD, and power (or bandwidth) expansion due to pilot insertion.