On Cell Association in Multi-Tier Full-Duplex Cellular Networks

This paper addresses the cell association problem in multi-tier in-band full-duplex (FD) networks. Specifically, we consider the case of decoupled cell association (DCA) in which users are not necessarily served by the same base station (BS) for uplink and downlink transmissions. Instead, users can simultaneously associate to different BSs based on two independent weighted path-loss cell association criteria for the uplink and downlink. We use stochastic geometry to develop a comprehensive modeling framework for the proposed system model where BSs and users are spatially distributed according to independent point processes. We derive closed-form expressions for the mean interference experienced at users and BSs as well as the overall mean rate coverage to evaluate the performance of the network. We also investigate the effect of interference in FD networks on legacy users with only half-duplex (HD) capabilities and how it can be mitigated by controlling the cell association weighting factors. In particular, we formulate and solve two optimization problems that aim at maximizing the mean rate of the legacy users as well as uplink and downlink mean rate by optimizing the cell association criteria. We show the effect of varying different network parameters such as the spatial density of BSs, receiver sensitivity, and weighting factors. In addition, we discuss several special cases and provide guidelines on the extensions of the proposed framework. Finally, we show that DCA outperforms coupled cell association (CCA) in which users associate to the same BS for both uplink and downlink transmissions.