Synchronous DS-CDMA downlink with frequency selective fading

Synchronous code-division multiple-access (CDMA) techniques possess intrinsic protection against co-channel interference due to the orthogonal spreading codes used. However, in the presence of multipath, the signals lose their orthogonality property, leading to increased cross correlation. In these cases, channel estimation may be needed in order to improve the detection of the desired symbols. We propose a subspace-based algorithm for blind channel estimation of a synchronous CDMA downlink. We compare the channel estimation accuracy with the Cramer-Rao bound, and we show that the estimation accuracy can be increased considerably using a decision feedback approach.