Joint base station operation and user association in cloud based HCNs with hybrid energy sources

This paper formulates a joint base station operation and user association optimization problem in the cloud based heterogeneous cellular networks with hybrid energy sources, where all the base stations are connected to the cloud computing center and powered by both on-grid power and renewable energy. The combinatorial optimization problem is decomposed into two subproblems based on the time scale separation. For the base station operation problem, a simple algorithm is designed to determine the active base stations using a Lagrange multiplier as the threshold, which is inspired by the submodularity maximization problem. For the user association problem, an iterative algorithm implemented by the user and base station side is proposed to achieve load balancing. Simulation results demonstrate that the proposed algorithm can reduce energy consumption, and enable a flexible tradeoff between energy consumption and load balancing.