  We propose blind adaptive multi-input multi-output (MIMO) linear receivers
for DS-CDMA systems using multiple transmit antennas and space-time block codes
(STBC) in multipath channels. A space-time code-constrained constant modulus
(CCM) design criterion based on constrained optimization techniques is
considered and recursive least squares (RLS) adaptive algorithms are developed
for estimating the parameters of the linear receivers. A blind space-time
channel estimation method for MIMO DS-CDMA systems with STBC based on a
subspace approach is also proposed along with an efficient RLS algorithm.
Simulations for a downlink scenario assess the proposed algorithms in several
situations against existing methods.
