Enhanced opportunistic beamforming for Jakes-correlated fading channels

In multiuser communication systems all users can estimate their instantaneous signal-to-noise ratio (SNR) and send this information to the base station (BS), which in turn decides to which user a data packet should be sent. For a large number of users, the channel conditions seen by different users vary independently and, consequently, it is likely that at any one time slot the scheduler will find at least one user whose channel is in favorable conditions (large SNR), yielding what is called multiuser diversity. In fading channels, where the fluctuation dynamics of the channel are limited, opportunistic beamforming (OBF) which employs multiple antennas at the BS can be used. By varying the antenna gains (power and phase) in a random manner, to induce faster and larger fluctuations in fading channels, OBF achieves multiuser diversity. In this paper we propose an enhancement of OBF to improve the overall throughput. By saving at the BS the sequence of antenna gains for each user, along with the corresponding SNRs, for as long as the channel time-coherence is significant, the proposed system can adopt for the selected user the most appropriate antenna gain in the memory, rather than the current gain, as in the original OBF approach. Computer simulation results for the Jakes-correlated fading channels indicate a favorable throughput performance. Moreover, the new approach requires only BS updates, facilitating its adoption.