Joint Power Control and User Association in Downlink Heterogeneous Network

As 5G aims to provide 1000-fold network capacity to mobile networks, heterogeneous networks (HetNet) have become a promising technology to deliver this goal. This thesis proposes a novel algorithm to maximize network utility of a downlink SISO HetNet jointly over user association and BS power control. The proposed problem formulation allows for investigation of a trade-off between network utility and network power consumption in the HetNet. Through finding the appropriate balance in the trade-off, the proposed algorithm forms a non-greedy heuristic to determine the appropriate activation of BSs under arbitrary total network consumption constraints. Greedy heuristics as motivated by those in literature are further used to compare with the proposed heuristic. Furthermore, this thesis considers the division of the downlink spectrum into multiple sub-bands and optimizes user association and BS powers independently over each sub-band. This provides an interesting alternative to the existing "soft frequency reuse" (SFR) scheme widely employed to maintain high network capacity while ensuring coverage for cell-edge users. Rate performances under various sub-band divisions are compared with the SFR scheme to examine the impact on user rates by considering a two-tier HetNet in a regular hexagonal deployment, where pico BSs are placed at known locations near the edges of macro-cells.