Energy-Efficient User Association and Power Control in the Heterogeneous Network

We consider a heterogeneous network (HetNet) containing primary users (PUs) and secondary users (SUs). Ordinary cellular users are characterized as PUs, while SUs are the unlicensed users, sensors, or some other Internet of Things equipments. The PUs occupy all the channels in the HetNet and the SUs try to reuse the channels of PUs. We consider two transmission modes for SUs, i.e., the SU can associate with the base station (BS) directly or through the help of its cooperative relay. The optimization of energy efficiency (EE) of SUs is considered. Particularly, we focus on user association (BS selection, channel allocation, and mode selection) and power control to optimize the uplink EE of the communication between the SU and the BS. The original problem is formulated as a non-convex and mixed-integer optimization problem. To get a tractable solution, we propose an iterative optimization algorithm. The alterative optimization method decomposes the original problem into three subproblems. In each iteration, the three subproblems are solved by using the sum-of-ratios programming algorithm, the parametric Dinkelbach algorithm, and convex optimization. Then, the proposed scheme repeats the iteration until convergence. Numerical results confirm that the proposed method can improve the uplink EE performance for SUs.