Leverage Weighted Decision Directed Channel Tracking for OFDM Systems

Decision directed channel tracking (DDCT) in OFDM systems can suffer from error propagation at high fade rates, due to the combined effect of rapid variation of the channel, long frame length and frequency selectivity of the channel. Conventional estimators like the 2D-minimum mean square error (MMSE) channel estimator and the expectation maximization (EM) based Kalman channel estimator [3] show poor performance when they are applied to DDCT over large frame lengths, due to the error propagation induced by wrong symbol decisions. The poor symbols decisions usually act like leverage points in the regression matrix, and can be identified using the hat matrix as a leverage diagnostic. We use extreme value theory (EVT) on the hat matrix to define a channel estimator, which, in addition to exploiting time and frequency correlation of the channel, downweighs leverage points before utilizing them in the estimator structure. The proposed EVT-leverage weighted (LW) estimator reduces error propagation in the frame since it downweighs possible wrong decisions before using them in the channel estimator structure. The proposed EVT-LW estimator has a significantly better error rate performance when compared to both the 2D-MMSE estimator [2] and the EM based Kalman estimator [3].