Double cancellation receivers for asynchronous CDMA systems in multipath channels

Low complexity receiver structures for CDMA systems in multipath channels with a large possible number of channel coefficients are studied. The channel estimator employs a matching pursuit followed by cancellation (MPC) algorithm that 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 estimate the channel coefficients more accurately. The data detector employs a partial parallel interference canceller (PIC). It is observed that a multipass structure consisting of an MP step and a C step followed by a single stage PIC performs nearly similar to a multipass structure where a multistage PIC is employed after the C step. Further, nonlinear clipped decisions, fed into both the channel estimator and PIC, are found to give good results.