Mobile-assisted scheduling for downlink multibeam phase-sweep transmit diversity (PSTD) with partial feedback

In this paper, we consider a wireless access network with K mobile devices and an access point with n_T transmit antennas. We shall propose a novel mobile-assisted scheduling algorithm for the multibeam phase-sweep transmit diversity (MB-PSTD) systems. We consider the downlink system performance with respect to maximal-throughput and proportional-fair utility functions. We show that the MB-PSTD scheme could significantly enhance the downlink system performance compared to the conventional PSTD schemes by fully utilizing the n_T degrees of freedom in the system. With the mobile-assisted scheduling algorithm, the feedback requirement is substantially reduced. The beam-sweeping facilitates the multiuser selection diversity between slow mobility users while the multibeam fully utilize the intrinsic system degree of freedom. As we increase n_T, the MB-PSTD system performance is gradually limited by the multibeam interference because it more and more difficult to find a set of users perfectly aligned with the n_T orthogonal beams. Yet, the multibeam interference could be reduced by increasing the number of active users (K) in the system. Asymptotically at large n_T and K, we show that the system capacity scales linearly instead of logarithmically with respect to the transmitted power.