Blind multi-user detection of space-time block coded signals in a CDMA system

A blind multi-user detection algorithm for space-time block coded signal is proposed based upon subspace and constant modulus algorithms. The subspace method is used to determine decorrelating filter required for the mitigation of multi-user interference and to coherently combine multi-path signals. We show that this subspace method for STBC could however solve this problem only up to a matrix ambiguity and this matrix in structure looks like a channel matrix obtained for a single user STBC system with frequency non-selective channel. Hence the remaining problem has been shown to be equivalent to blind equalization of single user STBC in flat fading channel, and we propose a tap constrained constant modulus algorithm to solve this. Simulation result shows superior performance of the proposed method over a conventional matched filter.