Coordinated beamforming in clustered HetNets: System design and performance evaluation

In this paper, we consider interference issues arising in HetNets where the small-cells are deployed in closely-spaced clusters. Such dense deployments pose an important challenge for scaling throughput proportional to the number of cells, since inter-cell interference becomes a key bottleneck for achieving high capacity. We examine key design issues around the use of coordinated beamforming (CBF) strategies for mitigating inter-small-cell interference in such clustered layouts. In particular, we show that system planning of the sounding reference signal (SRS), along with multi-user channel estimation approaches, are critical to realize the benefits of CBF. We also develop key notions of beneficiary sets and co-operative clusters for enabling such interference mitigation in cellular networks. Through extensive and detailed system simulations, we showcase the benefits of the proposed system designs for two use cases: (1) a dense urban Micro-cellular deployment, and (2) a clustered small-cell Stadium deployment. System parameter optimization of SRS power control and co-operative cluster size are also developed. Significant capacity gains are observed for both these deployments using the proposed system design in clustered small-cell topologies.