Small cells on/off control and load balancing for green dense heterogeneous networks

This paper considers the joint small cells (SCs) on/off and load balancing (LB) design in dense heterogeneous networks (HetNets). We aim to maximize the network energy efficiency (NEE), defined as the network throughput divided by the total energy consumption (EC), subject to the rate fairness constraints among users. This problem is NP-hard and thus is difficult to solve. To overcome this issue, we propose a new optimization approach, in which the LB scheme is first optimized under the fixed SCs on/off pattern, and the SCs on/off pattern is then derived iteratively. For the LB design, we obtain the optimal user association and resource allocation algorithms by considering multi-homing access. Due to the difficulty of applying multi-homing access in practice, we also derive a suboptimal but delicate user access rule for single access criterions. Combined with the optimal LB design, we then propose an optimal SCs on/off algorithm, by using the observation that the NEE decreases or first increases and then decreases as a function of the number of off SCs. By exploiting the optimal solution structure, a practical suboptimal SCs on/off algorithm with linear computational complexity is also developed. Through simulations, we find that the suboptimal algorithm achieves a comparable performance, in terms of both the NEE and the network throughput, as the optimal one and outperforms the traditional algorithms.