Enhanced opportunistic beamforming scheme for practical broadcast systems

In multiantenna systems the optimisation of linear spatial precoding is severely hampered by the amount of feedback. A practical solution consists in the opportunistic beamforming (OB), which randomly generates the beamforming and schedules the user with the largest signal-to-noise ratio (SNR). In this paper we investigate the benefits that can be provided by the knowledge of the users spatial covariance at the transmitter. We enhance the OB scheme by matching the beamforming generation to the users channels spatial patterns. We analytically assess the performance of the proposed scheme, referred to as Cluster-Eigenbeamforming (Cluster-EB), both in ideal (perfect feedback) and in practical scenario (imperfect feedback). Cluster-EB is shown to outperform the conventional schemes and the performance gain increases in practical systems as Cluster-EB capitalises on the spatial covariance knowledge to reduce the sensitivity with respect to the feedback imperfections. Copyright © 2007 John Wiley & Sons, Ltd.