Leveraging the Coupling of Radio Access Network and mmWave Backhaul Network: Modeling and Optimization

Capable of supporting the on-demand high-rate connection towards the core network, wireless millimeter wave (mmWave) backhaul becomes an appealing solution with the growing deployment of small cell base stations (BSs). However, the application of wireless backhaul would impose great limitations on the admission of BSs and the access rate, resulting in a tight coupling between backhaul and radio access network (RAN). In this light, we comprehensively investigate the performance of small cell networks (SCN) in terms of network spatial throughput (ST), supposing that backhaul is conveyed from gateways to BSs through mmWave links. Our results show that the coupling effect makes network ST in the RAN greatly dependent on gateway density lambda(G) and suffer exponential degradation with over-provision of backhaul. It manifests that, if excessive backhaul capacity is provided by deploying more gateways, the exacerbating BS-generated interference deteriorates spatial reuse gain, thereby degrading network ST. Thus, leveraging the coupling between backhaul and RAN, we further conduct a joint optimization of BS and gateway densities to improve network ST. Remarkably, the optimization could mitigate the dependence of network ST on lambda(G) and brings a 2-fold increase in network ST, which is inversely proportional to mmWave beamforming beamwidth.