On remote radio head selection for the downlink of backhaul constrained network MIMO systems

A relevant architecture to enable network MIMO in cellular systems consists of a central unit that is connected to remote radio heads (RRHs) via a shared wireless backhaul link. This letter studies the impact of RRH selection in this system under the two extreme scenarios of perfect and stale channel state information (CSI) at the central unit. It is shown that in both cases, RRH selection based on the instantaneous conditions or the long-term statistics of the backhaul links and of the access channels (i.e., from RRHs to mobile stations) significantly improves the sum-rate performance. The presented results also demonstrate that, in the presence of shared backhaul limitations, the classical precoding design based on the maximization of the number of degrees of freedom (DOFs) on the access channels leads to strictly suboptimal performance even when the access channels operate in the high SNR regime.