Multi-cell coordination in K-tier heterogeneous downlink cellular networks: Dynamic clustering and feedback allocation

We characterize the ergodic spectral efficiency of a cooperative type of K-tier heterogeneous networks (HetNets) with limited feedback. Specifically, a base station (BS) coordination set is formed by using dynamic clustering across the tiers, wherein the intra-cluster interference is mitigated by using multi-cell zero-forcing based on limited feedback. Modeling the network based on stochastic geometry, we derive analytical expressions for the ergodic spectral efficiency as a function of the system parameters. Leveraging the obtained expression, we formulate a feedback allocation problem and obtain a solution to improve the ergodic spectral efficiency. Simulations show the spectral efficiency improvement by using the proposed feedback allocation. One major finding in the obtained solution is that allocating more feedback to stronger intra-cluster BSs is efficient.