Optimal user association for delay-power tradeoffs in HetNets with hybrid energy sources

In wireless networks, it is of great significance to balance power consumption and network quality of service (QoS). In this paper, we propose an optimal user association algorithm for delay and power consumption tradeoffs in HetNets with hybrid energy sources. In the considered HetNets, all the base stations (BSs) are assumed powered by a combination of power grid and renewable energy sources, in order to achieve both reliable and green communications. The proposed user association algorithm aims to enhance network QoS by minimizing the average traffic delay, as well as reduce on-grid power consumption by maximizing the utilization of green power harvested from renewable energy sources. To this end, a convex optimization problem is formulated to minimize the weighted sum of cost of average traffic delay and cost of on-grid power consumption. We have proved that the proposed user association algorithm converges to the global optimum which enables a flexible tradeoff between average traffic delay and on-grid power consumption. Simulation results indicate that the proposed user association algorithm substantially reduces on-grid power consumption with limited sacrifice on average traffic delay, compared with the existing user association algorithm which aims to minimize the average traffic delay.