Opportunistic vector channel estimation based on scalar feedback

Multi-user diversity exploits channel fluctuations by favouring the user with the best channel. In slow fading environments, channel fluctuations are artificially created by the use of random beamforming at the transmitter, a technique called opportunistic beamforming. One drawback of opportunistic beamforming is that, it needs large number of users to achieve the capacity of a true beamforming system. On the other hand, if partial channel state information is available at the transmitter, this can be used to reduce the necessary number of users to reach this capacity. Opportunistic beamforming systems require scalar feedback from users in the system instead of the complete channel vector to reduce the feedback load. In conventional systems, these feedback values are used for scheduling only. In this letter, we propose three channel estimation methods that solely rely on the scalar feedback already available at the transmitter. We also propose an accompanying scheduling method where these estimates are used to form the beamforming vectors. Although we use the same information available in a conventional opportunistic beamforming system, the proposed scheduling scheme in conjunction with channel estimation is able to achieve higher throughput and also achieve better fairness which is verified by simulations. Copyright © 2016 John Wiley & Sons, Ltd.