Improved subspace-based channel estimation algorithm for DS/CDMA systems exploiting pulse-shaping information

An improved subspace-based channel estimation algorithm for DS/CDMA system is presented. The proposed algorithm is based on the Torlak/Xu algorithm for asynchronous DS/CDMA systems. The aim is to incorporate knowledge of the pulse-shaping filter into the Torlak/Xu subspace algorithm with the objective of reducing the variance of the channel estimates. The improved algorithm is developed from a system model of a DS/CDMA system where the output is oversampled with respect to the chip rate. By oversampling the received signal, knowledge of the pulse-shaping filter is incorporated into the proposed channel estimation algorithm. It is shown that the variance of the channel estimate for the proposed subspace algorithm is less than the Torlak/Xu algorithm that does not exploit pulse-shaping filter information. A mathematical expression of the mean square error of estimation for the improved algorithm is also derived. It is shown that the analytical expression provides a good approximation of the actual mean square error for high SNR signals.