Mobile-assisted scheduling for downlink multibeam phase-sweep transmit diversity (PSTD) with partial feedback
21 March 2004
In this paper, we consider a wireless access network with K mobile devices and an access point with nT 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 nT 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 nT, 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 nT orthogonal beams. Yet, the multibeam interference could be reduced by increasing the number of active users (K) in the system. Asymptotically at large nT and K, we show that the system capacity scales linearly instead of logarithmically with respect to the transmitted power.