Spatial-multiplexing phase-sweep transmit diversity (SM-PSTD) for multiantenna base stations with mobile-assisted scheduling and incremental rate feedback

Phase-sweep transmit diversity (PSTD) has been widely studied in 3G1X and Universal Mobile Telecommunications Systems (UMTS) for its performance gain and simplicity. However, conventional PSTD systems are designed based on asingle-sweeping beam, and only one user is selected for transmission at any time. Therefore, it fails to fully exploit the available spatial degree of freedom. In this study, a novel spatial-multiplexing phase-sweep transmit diversity (SM-PSTD) scheme with partial feedback mobile-assisted scheduling is being proposed. The downlink performance (system capacity and proportional fairness) of a multiantenna base station has been its focus. The spatial-channel sweeping facilitates the multiuser selection diversity between users, while the spatial multiplexing significantly enhances the system capacity. As the number of transmit antennas n_T is increased, the SM-PSTD system performance is gradually limited by the multiuser interference because it is more and more difficult to find a set of users perfectly orthogonal within the n_T spatial channels. Yet, the multiuser interference could be reduced by increasing the number of active users K in the system. Asymptotically, at large n_T and K, it shows that the system capacity scales linearly instead of logarithmically with respect to the transmitted power.