Channel estimation for asynchronous CDMA systems in time-varying multipath channels

A matching pursuit followed by a cancellation (MPC) algorithm is proposed for channel estimation in time-varying multipath channels for asynchronous CDMA. The algorithm has low computational complexity and consists of two steps. In the first step, a basic matching pursuit algorithm that identifies the strongest channel taps, and successively cancels them is used. The second step of the algorithm uses the already estimated channel taps to remove interference from the received vector in order to identify the channel coefficients more accurately. Analytical insights in terms of the Cramer-Rao lower bound are developed in order to understand the benefit of the MPC technique over the conventional least squares (LS) approach. The MPC algorithm is found to outperform the conventional LS technique when the channel is sparse with large delay spreads and/or the users are highly asynchronous. Our simulation results show that the proposed approach is highly robust against the number of users and it performs very well in rapidly fading channels.