Reducing Feedback Requirements of the Multiple Weight Opportunistic Beamforming Scheme via Selective Multiuser Diversity

Opportunistic beamforming (OB) relies on the transmission of channel state information (CSI) in the form of instantaneous signal to noise ratio (SNR) from mobile stations (MSs) back to the base station (BS) for scheduling purposes that increase throughput and/or maintain resource allocation fairness. OB is employed in environments of low mobility and low scatter, artificially inducing channel fluctuations that can better exploit multiuser diversity (MUD). Multiple antennas at the BS randomly alter the channel´s response and generate peaks in gain where users can be scheduled on, maximising system throughput. Additional gains are achieved by transmitting multiple weighting vectors from the BS, but their use can significantly increase the load of the feedback channel and mitigate MUD gains. Selective multiuser diversity (SMUD) has been proposed for the original beamforming scheme as a technique that reduces feedback requirements substantially without any significant throughput degradations. This paper considers the joined use of multiple weights and SMUD in opportunistic beamforming, aiming to increase capacity while reducing feedback overhead. Results show that with an appropriate use of threshold levels, not only average throughput can be increased through the use of multiple weighting vectors but also a notable decrease in feedback load requirements compared to the conventional OB with SMUD design is achieved.