Constrained space-time spreading for MIMO-CDMA systems: Tensor modeling and blind detection

In this paper, we present a new space-time transmission framework for Multiple Input Multiple Output (MIMO) Code Division Multiple Access (CDMA) systems. A Constrained Space-Time Spreading (CSTS) model is proposed by using a tensor modeling formalism. The key feature of the CSTS model is the presence of two constraint matrices controlling the spatial spreading of the data streams and the reuse factor of the spreading codes across subsets of transmit antennas. The proposed CSTS model allows one to derive several multiple-antenna transmit schemes with different space-time spreading patterns by simply adjusting the structure of these two constraint matrices. Finite sets of CSTS schemes for 2, 3 and 4 transmit antennas are derived, which ensures the blind recovery of the transmitted data streams. Exploiting the constrained tensor model of the received signal, a joint blind detection using the alternating least squares algorithm is used for performance evaluation of several CSTS schemes.