Joint Beamforming and Scheduling for SDMA Systems with Limited Feedback

On a multi-antenna broadcast (downlink) channel, simultaneous transmission to multiple users is capable of achieving very high throughput. Unfortunately, the optimal approach for such multi-user transmission, namely dirty paper coding, is highly complicated. Therefore, this paper proposes a practical joint beamforming and scheduling scheme that is enabled by feedback of quantized channel state information. In this approach, the base station generates multiple sets of orthogonal beamforming vectors and associates each vector with a specific user. Next, the base station selects one set of beamforming vectors and the associated users for downlink transmission such that the throughput is maximized. Unlike the optimal approach, the proposed scheme has computational complexity that increases only linearly with the number of users since it does not require an exhaustive search over all possible subsets of users. Compared with two recently proposed schemes by Sharif et al. and Choi et al., the present scheme achieves higher downlink throughput, avoids multi-user conflicts when selecting beamforming vectors, requires no broadcast of beamforming vectors, and facilitates feedback compression.