Blind multiuser receiver for space-time coded CDMA signals in frequency-selective channels

Blind detection of a desired user´s signal in a direct sequence code-division multiple-access (DS-CDMA) system using multiple transmit and receive antennas and space-time (ST) block coding is considered. We consider Alamouti´s ST coding scheme for two transmit antennas designed for flat-fading channels but allow the channel to be frequency selective. A (spreading) code-constrained inverse filter criterion (IFC)-based linear blind detector to detect a desired user´s signal for uncoded CDMA signals exploiting only a single transmit and single receive antenna was recently presented. The IFC method exploits the higher order statistics of the data. In ST-coded multiantenna CDMA systems, a user signal may be treated as the superposition of several virtual user signals derived from the same parent user. In particular, for Alamouti´s scheme, one has two virtual users for each user if the information symbols are real valued. The previously proposed code-constrained IFC-based detector is modified to detect a given virtual-user signal. The original user signal can then be recovered from the associated detected virtual user signals obtained by running two code-constrained IFC-based detectors in parallel. We also propose a novel approach combining the code-constrained IFC and a penalty function to simultaneously extract the two virtual user signals associated with a given user. Global minima of the proposed cost functions are analyzed. An illustrative simulation example is presented.