An iterative decoding scheme for pilot-assisted modulation in fading channels
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Turbo coding is one of the most powerful techniques for enhancing the performance of next-generation wideband systems. In time-variant wireless fading channels, pilot symbol assisted modulation (PSAM) is a useful method that enables coherent demodulation. In this paper, we develop an iterative joint channel-data estimation receiver structure for coded PSAM systems in a fading environment, which exploits the power of both techniques. The key innovation in the proposed receiver is a low-complexity soft channel estimator, which divides a processing block into overlapped cells and performs maximum a posteriori (MAP) sequence estimation and MMSE filtering based on the received signal and extrinsic information delivered by the soft channel decoder. Moreover, the refined channel extrinsic information obtained in one cell is passed to subsequent cells to enhance estimation of the fading process. During iterations, code extrinsic information is sent to channel estimator by soft channel decoder and updated channel estimation is sent back to soft channel decoder to achieve successively refined estimate of the users' signal. The soft channel estimator has a complexity of O(2 W /W) per bit, where W is the cell size. Simulation results demonstrate that for turbo-coded PSAM systems under time-variant fading, the proposed receiver, at a low complexity, i.e. W7, offers significant performance gains over the non-iterative receiver and two other estimation schemes.