Weighted Sum Rate Maximization in Millimeter Wave Interfering Broadcast MIMO Channels

Abstract:
In this paper, we propose weighted sum rate (WSR) maximization in millimeter wave interfering broadcast channels in the general case where both transmitters and receivers have multiple antennas, multiple radio frequency chains, and employ hybrid beamforming. We show how to adapt the WSR algorithm to the hybrid beamforming case, aiming at a practical low complexity design that allow a split between the analog beam alignment (BA) phase and digital precoder optimization such that transmit power constraint only needs to be satisfied by the digital precoders. We model the BA phase, after which transmitters and receivers have access to only low dimensional partial channel state information (CSI), corresponding to the matrix product of the analog precoder, physical channel and analog receive filter. In the MIMO broadcast channel, the proposed method shows a large performance improvement compared to block diagonalization (BD) and regularized BD schemes applied after BA, even in the unweighted case. In the MIMO interference channel, the proposed method shows significant gains with respect to literature methods based on orthogonal matching pursuit (OMP), even when the latter are run with perfect CSI. This is due to the fact that the OMP method results in additional leaked interference with every precoder or receive filter approximation. The obtained gains in all cases are larger with more constrained analog beamforming such as discrete Hadamard transform beams.