Cluster based coordinated beamforming and power allocation for MIMO heterogeneous networks

Coordinated intercell interference management is essential in dense heterogeneous networks with limited backhaul capacity. This paper proposes a cluster-based hierarchical cooperative transmission and resource allocation scheme with proportionally fair objective in a cellular network where both the macro base station (BS) and the small cell access-points (SCAs) are equipped with multiple antennas and share the entire available bandwidth. As the first step, SCAs form clusters based on their pairwise distances where each cluster comprised of adjacent SCAs which are potentially strong interferers. Clustering enables intra-cluster coordinated transmission and inter-cluster coordinated resource allocation. Specifically, SCAs within each cluster form a network multiple-input multiple-output (MIMO) system, share the users´ data symbols, and cancel intra-cluster interference via zero-forcing spatial multiplexing. Further, a distributed power control scheme is devised for the purpose of mitigating inter-cluster interference without exchanging users´ data signals. We show that clustering facilitates intra-cluster coordination by enabling data exchange and channel training with reasonable backhaul communication within each cluster. We also show that the proposed inter-cluster power control scheme can further improve the network-wide utility.