Distributed delay-energy aware user association in 3-tier HetNets with hybrid energy sources

With tremendous attention for green communications, base station (BS) which is powered by both the power grid and renewable energy sources, is regarded as a promising paradigm to reduce energy consumption as well as provide uninterrupted service. In this paper, we propose distributed Delay-Energy Aware (IDEA) user association in 3-tier HetNets with hybrid energy sources. IDEA user association aims to reduce on-grid power consumption by maximizing the utilization of green power harvested from renewable energy sources, as well as enhance network quality of service by minimizing the average traffic delay. To this end, a convex optimization problem is formulated which enables a flexible tradeoff between average traffic delay and on-grid power consumption. We prove that the proposed IDEA user association converges to the globally optimal solution. We then address admission control for the case where the traffic load is heavy to ensure IDEA user association works when network traffic demand is over network capacity. Simulation results indicate that the proposed IDEA user association is able to adjust the loads of BSs and RSs along with the distributions of green power, substantially reduces on-grid power consumption and achieves comparable average traffic delay compared with the existing algorithm which aims to minimize average traffic delay.