Optimized Multi-User Beamforming with Channel Tracking Based on a Low Rate Feedback

Opportunistic beamforming exploits multi-user diversity by introducing a varying beamformer independent of the channel realizations. This choice of the beamformer is only optimal for a very large number of users. In this paper a new multi-user beamforming and scheduling technique is proposed. It uses the channel state information available at the transmitter in the form of a quantized feedback to track the users channels. Then it transmits to (schedules) the user with the best channel conditions using optimal beamforming weights and thus improving the system spectral efficiency. The performance enhancements result from the ability to reconstruct the different users channels based on a low rate feedback that quantizes the equivalent single transmit antenna channel seen by each user. In comparison to opportunistic beamforming, the proposed technique keeps the receiver simple with minor additional complexity at the base station. Simulation results show important improvements.