Opportunistic scheduling and beamforming for MIMO OFDMA downlink systems with reduced feedback

Opportunistic scheduling and beamforming schemes with reduced feedback are proposed for MIMO OFDMA down link systems. Unlike the conventional beamforming schemes in which beamforming is implemented solely by the base station (BS) in a per subcarrier fashion, the proposed schemes take ad vantages of a novel channel decomposition technique to perform beamforming jointly by the BS and the mobile terminal (MT). The resulting beamforming schemes allow the BS to employ only one beamforming matrix (BFM) to form beams for all subcarriers while each MT completes the beamforming task for each subcarrier locally. Consequently, for a MIMO OFDMA system with Q subcarriers, the proposed opportunistic scheduling and beamforming schemes require only one BFM index and Q supportable throughputs to be returned from each MT to the BS, in contrast to Q BFM indices and Q supportable throughputs required by the conventional schemes. The advantage of the proposed schemes becomes more evident when a further feedback reduction is achieved by grouping adjacent subcarriers into exclusive clusters and returning only cluster information from each MT. Theoretical analysis and computer simulation confirm the effectiveness of the proposed reduced feedback schemes.