Error Propagation Mitigation for Iterative Channel Tracking, Detection and Decoding of BICM-OFDM Systems

We present a novel method to reduce error- propagation in iterative receivers of BICM-OFDM systems under fast fading channels. The effect of symbols misdetection on channel tracking is studied and a novel solution to combat the performance degradation is suggested. In general, for blind channel tracking, the use of the detected symbols is required. However, as we show in this work, these decisions can be errornous and diverge the channel tracker from its true trajectory, even when coding is used. While most of the previous studies have ignored the error-propagation effect on channel tracking, counting on many pilot symbols, using coded systems or assuming that no misdetections occur, we challenge those methods and show that even in coded systems, error-propagation is a problem of great concern, particularly in iterative receivers where misdetections propagate faster. We propose a method to alleviate this problem, based on a new module, which estimates the reliability of each of the detected symbols. We design a criterion for using only reliable detections for the purpose of channel tracking, thus robustifying the channel tracker. We also provide an analysis of the effect of misdetections on the mean square error (MSE) of the channel tracker for different subcarriers and show how the MSE not only smears and affects subcarriers that are misdetected but also subcarriers that were detected correctly. Simulation results show that the proposed method reduces error-propagation to a large extent, reducing the MSE, which in turn, leads to better overall performance of the system in terms of bit error rate (BER).