CDMA downlink channel estimation with aperiodic spreading

Abstract

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 properly 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 and compare several algorithms for channel estimation of a synchronous CDMA point to multipoint link (downlink) which uses aperiodic spreading waveforms. We compare by simulation and analysis a subspace approach, a pilot-aided approach, and a decision feedback approach.