Coherent opportunistic beamforming in multi-user wireless systems

In this paper, we propose a beamforming scheme that exploits the advantages of opportunistic beamforming and coherent beamforming in multi-user environment. It is analytically shown that the proposed scheme achieves multi-user diversity gain and beamforming gain simultaneously, providing much better performance over the conventional ones. The performance of the proposed scheme is analyzed using an upper bound method. Although the proposed scheme involves an additional feedback delay, the analytical result implies that the use of the proposed scheme is quite effective unless the user mobility is too high. Finally, the analytic results are verified by computer simulation.