Fair allocation of backhaul resources in multi-cell MIMO coordinated beamforming

Coordinated beamforming in multipoint MIMO networks has been introduced to increase the overall capacity of wireless networks. In coordinated beamforming, the channel state information between the different MIMO access points/base stations in one hand, and the mobile stations on the other hand, needs to be shared among the MIMO nodes. A "backhaul" between different MIMO access points is used to transfer the channel state information. The channel state information of different links is quantized with different quantization steps according to a specific optimization criteria. This information is then shared through the backhaul. In this paper, we study the problem of allocating the backhaul bandwidth among users in coordinated beamforming MIMO multipoint networks. First, we prove through mathematical analysis, that there are many allocations that can provide "near maximum sum rate". These different allocations vary significantly in fairness between users. A "fair" allocation is an allocation that provides a small variance between the rates of different users. Motivated by this finding, we introduce two novel, low complexity, backhaul bandwidth distribution schemes that can achieve a very close to maximum sum rate, and at the same time, offer throughput fairness among users. Simulation results show that, for the same sum-rate, the proposed schemes can achieve more fairness among users when compared to the conventional scheme, which gives all users the same share of bandwidth. Moreover, we show that one of the proposed schemes, namely the Equal SIR scheme, can achieve zero variance among users in a wide range of backhaul bandwidths while keeping a very close to maximum sum rate.