Downlink cell association for large-scale MIMO HetNets employing small cell wireless backhaul

Downlink cell association (CA) is studied for cellular heterogeneous networks (HetNets) where large-scale antenna array is implemented at the macro base station (BS), while the opportunistically deployed small cells are single-antenna nodes, and they rely on over-the-air links to the macro base station for backhaul. The coupling constraint due to in-band wireless backhaul becomes another key criterion for cell association. A duplex and spectrum sharing scheme based on reverse timedivision duplex (TDD) is considered for interference management in the HetNet under the wireless backhaul constraint. A sum logarithmic-throughput maximization problem is formulated to balance throughput and fairness. By relaxing the binary cell association indicator variables, the optimization problem is shown to be a convex problem. Dual decomposition for relaxed optimization is employed to solve the integer nonlinear CA problem, which results in a distributed CA algorithm. Improved performance and fairness are achieved with the proposed algorithm under the wireless backhaul constraint, and more small cells implemented within the macro cell range achieves better load balancing. As no additional radio frequency hardware is required by the proposed scheme, it allows low-cost and fast implementation of wireless backhaul enabled cellular HetNets.