Channel estimation for DS-CDMA downlink with aperiodic spreading codes

Synchronous code-division multiple-access (CDMA) techniques possess intrinsic protection against cochannel interference when orthogonal spreading codes are used. However, in the presence of multipath propagation, the signals lose their orthogonality property, leading to increased cross correlation. In these cases, channel estimation may be needed in order to improve detection. We propose and compare several algorithms for channel estimation of a synchronous CDMA point-to-multipoint link (downlink) that uses aperiodic spreading waveforms. We compare by simulation and analysis a subspace approach, a pilot-aided approach, and a decision-based approach.