Joint user association and power minimization for a two-tier HetNet with Interference Coordination and QoS guarantees

This paper addresses the joint User Association (UA) and power minimization in the downlink of a two-tier Heterogeneous Network (HetNet). Macro Base Stations (MBSs) apply an enhanced Inter-Cell Interference Coordination (eICIC) technique via Almost Blank Subframes (ABSs) in which each MBS is muted for a certain ABS ratio to reduce the interference to the offloaded users. Also, MBSs can further reduce their transmit power on those protected subframes. Besides, we study the load coupling as well as the ABS ratio impact in the SINR expression. The defined optimization problems are then very challenging where we jointly maximize the number of satisfied users and minimize the total power consumption given the users' QoS requirements while optimising the ABS ratio and the MBSs transmit powers. The formulated problems are Mixed Integer Non linear Problems (MINLPs). Therefore, we propose to solve them in two phases: the joint UA and eICIC followed by the power minimization. In the first phase, a centralized algorithm is derived by relaxing the association constraints and using Lagrange dual decomposition method. The second stage is solved using a heurestic approach. Numerical results corroborate the performance enhancement achieved by the proposed scheme.