Joint Rate and SINR Coverage Analysis for Decoupled Uplink-Downlink Biased Cell Associations in HetNets

摘要

Load balancing by proactively offloading users onto small and otherwiselightly-loaded cells is critical for tapping the potential of denseheterogeneous cellular networks (HCNs). Offloading has mostly been studied forthe downlink, where it is generally assumed that a user offloaded to a smallcell will communicate with it on the uplink as well. The impact of coupleddownlink-uplink offloading is not well understood. Uplink power control andspatial interference correlation further complicate the mathematical analysisas compared to the downlink. We propose an accurate and tractable model tocharacterize the uplink SINR and rate distribution in a multi-tier HCN as afunction of the association rules and power control parameters. Jointuplink-downlink rate coverage is also characterized. Using the developedanalysis, it is shown that the optimal degree of channel inversion (for uplinkpower control) increases with load imbalance in the network. In sharp contrastto the downlink, minimum path loss association is shown to be optimal foruplink rate. Moreover, with minimum path loss association and full channelinversion, uplink SIR is shown to be invariant of infrastructure density. It isfurther shown that a decoupled association---employing differing associationstrategies for uplink and downlink---leads to significant improvement in jointuplink-downlink rate coverage over the standard coupled association in HCNs.