Modeling and analysis of Uplink-Downlink relationship in Heterogeneous Cellular Network

Small cell technology significantly improves the coverage and boosts the capacity in Heterogeneous Cellular Network. And Cell Range Expansion technology makes average rate nearly optimal in downlink. However, because of large transmit power disparities of different kinds of base stations, uplink and downlink need to be considered as two different networks. In uplink, the problem is that many user equipments have to be associated with suboptimal base stations due to old Uplink-Downlink relationship. So we propose a new Uplink-Downlink relationship under which user equipments can be associated with optimal (may not the same) base stations in both directions. Numerical results demonstrate that performance under new Uplink-Downlink relationship has impressive gain in uplink coverage probability and average rate. Besides, when user equipments are all associated with their optimal base stations, network interference will be effectively mitigated through controlling uplink transmit power.