A new semi-blind channel estimation technique is proposed for space-time coded wideband CDMA systems using aperiodic and
possibly multirate spreading codes. Exploiting the subspace structure of the WCDMA signaling and the orthogonality of the space-time code, the proposed algorithm provides the least squares channel estimate in closed form. Using a decorrelating matched filter, the proposed method projects the received signal into subspaces from which channel parameters and data symbols can be estimated jointly. A new blind identifiability condition is established. The mean square error of the estimated channel is compared with the Cram´er-Rao bound, and bit error rate (BER) is assessed through Monte Carlo simulation.