Increasing system throughput by time-varying beamforming in multiuser systems with slowly varying fading channels

We analyze a cellular communication system in which a base station or access point equipped with several antennas transmits packet data to several mobile data users by means of a TDMA scheme. A scheduler in the base station uses knowledge about the instantaneous channel quality (signal-to-noise ratio, SNR) of all users to allocate to the user the channel resource which maximizes a certain metric. By this means, the system exploits multiuser diversity, which increases system throughput (with constant quality of service) particularly if the rate of variation of the users´ SNR is fast. In cases when the underlying physical channel dynamic is insufficient, time-varying beamforming is employed in order to increase the effective channel dynamic. We analyze the implication of time-varying beamforming on coherent channel estimation, which is performed by all users for coherent detection, and discuss fundamental tradeoffs between system (and user) throughput and estimation performance.