Joint Uplink and Downlink User Association for Energy-Efficient HetNets Using Nash Bargaining Solution

In heterogeneous networks (HetNets), due to transmit power disparity between macro and pico base stations (BSs), the conventional strongest downlink (DL) reference signal received power (RSRP) based user association results in high uplink (UL) interference. Such interference degrades the UL performance especially in terms of energy efficiency. In this paper, we propose Joint Uplink and Downlink User Association (JUDUA) that takes both the UL and DL energy efficiencies into consideration when deciding the serving BS for user equipments (UEs). JUDUA formulates user association optimization problem as a Nash bargaining problem aiming to maximize the sum of log-scale UL and DL energy efficiencies among all UEs. Simulation results demonstrate that JUDUA improves UL and DL energy efficiencies of UEs, which in turn boosts UL and DL system capacity, reduces UL transmit power compared with the conventional user association schemes.