Opportunistic Beamforming with Partial Channel State Information

In a wireless network the channel fluctuations of the users can be exploited by means of multiuser diversity where the user transmissions are scheduled when they experience a high instantaneous SNR. When fading is slow, beamforming at a multiple antenna transmitter can be used to induce artificial temporal fading to ensure multiuser diversity in the network. Such a beamforming scheme is called opportunistic beamforming [1] since the transmitter sends random beamforming vectors to artificially induce opportunism in the network. Opportunistic beamforming requires a large number of users in the system in order to achieve the performance of the true beamforming that uses perfect channel state information (CSI). In this paper we investigate the benefit of having partial CSI at the transmitter. We show that opportunism is still exploited to increase the average throughput of the system. Numerical results show that with partial CSI at the transmitter performance close to that of true beamforming can be obtained with even fewer number of users in the system.