Optimal subcarrier allocation for 2-user downlink multiantenna OFDMA channels with beamforming interpolation

We consider a 2-user multiantenna downlink OFDMA with limited feedback. Assuming perfect channel state information (CSI) at mobile stations, each mobile equipped with a single receive antenna quantizes and feeds back to a base station one optimal transmit beamforming vector for each subcarrier cluster. A base station then applies constant or linear interpolation methods to obtain all other beamforming vectors for each cluster. For given feedback rate and channel condition, we analyze the optimal cluster size, the number of clusters, and thus, subcarrier allocation for the two users. Numerical examples show that the optimized sum capacity can be significantly higher than a sum capacity with arbitrary system parameters.