Direct decoding of uplink space-time block coded multicarrier code division multiple access systems

The uplink of a space-time block coded multicarrier code division multiple access (MC-CDMA) system endowed with a uniform linear array (ULA) at the base station of macrocell is studied. Transmission takes place over frequency-selective fading channels and the transmitted symbol of a user is encoded by Tarokh's rate 1 space-time block encoder, (V. Tarokh and H. Jafarkhani, July 1999) from real orthogonal design, with three transmit antennas. An algorithm is proposed to blindly estimate the data symbol sequence and the direction of arrival (DOA) of each user without determining the space-time vector channels. The algorithm employs an ESPRIT- like method (Y. Zeng et al.) to separate multiple co-channel users with different impinging DOAs, then exploits the structure of space- time block coding (STBC) in combination with the subspace method to estimate the original symbol sequences for multiple users. In particular, the theoretical analysis shows that the signal subspace defined by the received data covariance matrix can be separated by users' DOA, so the joint diagonalization step of many matrices due to the method presented by A. Swindlehurst (April 2002) is avoided, which saves large computations. Computer simulations illustrate the overall performances of the proposed algorithm.