Green Base Station Assignment for NOMA-Enabled HCNs

In this paper, for the heterogeneous cellular networks (HCNs) with non-orthogonal multiple access (NOMA), we mainly concentrate on the design of green base station (BS) assignment integrating with power allocation. Note that the power allocation is mainly used for mitigating network interference and reducing energy consumption. To attain the goal of green communications, we take account of an optimization problem with maximizing the whole energy efficiency under users' signal-to-interference-plus-noise ratio (SINR) constraints, where such efficiency represents the ratio of the total throughput of users to the total power consumption of BSs selected by them. To solve the finally formulated problem in a nonconvex and nonlinear form, we first introduce an auxiliary parameter to convert it into a tractable one whose optimal solution can be found by employing an effective iterative algorithm. After that, the whole problem, being in a coupling form, can be broken into the BS assignment and power allocation subproblems that can be optimized alternately. To solve the former, a type of highly effective algorithm is designed according to a coalitional game. In addition, an approach based on a two-sided scalable (2.s.s.) function is developed for the latter. Then, we reveal the properties of these proposed algorithms, including computation complexity and convergence. In the simulation, we mainly investigate the impacts of densities of small BSs and users on the different performance indices of the designed and existing algorithms.