On the Optimal Number of Cooperative Base Stations in Network MIMO

Abstract: We consider the multi-cell uplink (network MIMO) where M base-stations (BSs) communicate simultaneously with M user terminals (UTs). Although the potential benefit of multi-cell cooperation increases with M, the overhead related to learning the uplink channels will rapidly dominate the uplink resource. In other words, there exists a non-trivial tradeoff between the performance gains of network MIMO and the related overhead in channel estimation for a finite coherence time. We use a close approximation of the ergodic capacity to study this tradeoff by taking some realistic aspects into account such as unreliable backhaul links and different path losses between the BSs and UTs. Our results provide some insight into practical limitations as well as realistic dimensions of network MIMO systems.