Improved opportunistic beamforming in Ricean channels

In order to improve the performance of opportunistic beamforming in Ricean channels, we propose an improved opportunistic beamforming scheme which forms beams intelligently to the users. First, a new concept of the generalized Ricean distribution is introduced. On the basis of this theory, we propose a maximum-likelihood (ML) estimator of the directions of arrival of the users, and we derive the Cramer-Rao lower bound to evaluate the performance of the ML estimator. Furthermore, the generalized Ricean K-factors are estimated by a moment-based method. With the same pilot overhead in the downlink and with the same feedback overhead in the uplink, the improved scheme considerably outperforms conventional opportunistic beamforming.