Blind adaptive space-time block-coded receivers for DS-CDMA systems in multipath channels based on the constant modulus criterion

We present in this work blind adaptive linear multiuser receivers for direct sequence code division multiple access (DS-CDMA) systems using multiple transmit antennas and space-time block codes (STBC) in multipath channels. A code-constrained constant modulus (CCM) design criterion based on constrained optimization techniques and recursive least squares (RLS) adaptive algorithms are described for estimating the parameters of the linear receivers. The receiver is designed by exploiting the unique structure imposed by both spreading codes and STBC. A blind space-time channel estimation scheme for STBC systems based on the subspace approach is also proposed along with an efficient RLS algorithm for channel estimation. Numerical results for a downlink scenario assess the receiver structures and algorithms in several practical situations.