Novel Tap-Wise LMMSE Channel Estimation for MIMO W-CDMA

In this paper, a tap-wise LMMSE channel estimator for MIMO W-CDMA is derived. Descrambling operations applied to delayed versions of the received signal whiten the input signal. The descrambling process thus breaks up the full channel autocorrelation matrix (including spatial and temporal correlation) into several independent, small autocorrelation matrices that include only spatial correlation. The problem of estimating the channel autocorrelation matrices is tackled by an "instantaneous" autocorrelation estimator that uses only one channel estimate (obtained by a very low complexity channel estimator) as input. Simulation results of a MIMO HSDPA system show that the tap-wise LMMSE estimator with instantaneous channel autocorrelation estimation yields performance gains of up to 0.85 dB over a correlation-based channel estimator. Even larger gains can be achieved with improved channel autocorrelation estimators.