Optimality of Extended Maximum Ratio Transmission

In this paper, we investigate a general class of partial channel state information feedback strategies for communication over flat fading multiple antenna channels with t transmitters and r receivers. Specifically, we consider scenarios where the partial channel state information is sent back from the receiver to the transmitter in the form of n beamformer vectors with corresponding power allocations [1]. We show that, in order to maximize the channel capacity, a globally optimal strategy is to feedback the n dominant eigenvectors of HH .