Sparse Beamforming Design for Network MIMO System with Limited Backhaul

Sparse Beamforming Design for Network MIMO System with Limited Backhaul Binbin Dai Master of Applied Science Graduate Department of Electrical and Computer Engineering University of Toronto 2014 This thesis considers a downlink multicell cooperation model in which the basestations (BSs) are connected to a central processor via rate-limited backhaul links and each scheduled user is cooperatively served by a potentially overlapped cluster of BSs. Two different problem formulations are considered respectively: optimal tradeoff between the total transmit power and backhaul capacity under fixed user rate constraints, and utility maximization for given per-BS power and backhaul constraints. Motivated by the compressive sensing literature, we propose to approximate the backhaul rate as a function of the weighted `2-norm square of the beamformers. This novel idea allows the optimal tradeoff to be converted into a weighted power minimization problem, which then can be solved efficiently using the well-known uplink-downlink duality approach; it also makes the utility maximization problem solvable through a generalized weighted minimum mean square error approach. The effectiveness of the proposed algorithms is justified through numerical simulation results.