MMSE Optimisation for LS Channel Estimation in Wideband DS-CDMA Rake Receivers

It is well established that the quality of the channel estimate plays a crucial role in the performance of a DS-CDMA receiver. This paper addresses the problem of optimising the channel estimate for a wideband DS-CDMA rake receiver. A simplified adaptive least squares scheme is proposed as a channel estimator, with only one adjustable parameter, the averaging window size. Then, the mean squared error of the channel estimate is analytically extracted. The estimation error is found to consist of two antagonistic (with respect to the window size) components: a) the estimation noise (due to the transmission channel noise, inter-chip interference and multiple-access interference), and b) the estimation distortion (due to the limited ability of the adaptive algorithm to track the non-stationary channel). An MMSE channel estimator is finally proposed, exhibiting the best trade-off between the two antagonistic estimation error components