Energy Efficient Resource Allocation in NOMA-Sectored Heterogeneous Network

Non-orthogonal multiple access (NOMA) and heterogeneous network (HetNet) have been regarded as two promising technologies in 5G, which can support massive connectivity. Integrating NOMA technology into HetNet is an inevitable trend to achieve better spectral efficiency. However, interference control becomes more complicated due to the combination of these two technologies and the optimization of energy efficiency comes at the expense of spectral efficiency. Therefore, we develop a novel network scenario, which exploits the benefits of sectorization. In this paper, we aim to maximize the energy efficiency of the entire small cells in an uplink underlaying two-tier NOMA heterogeneous network with sectorization. Since this energy efficiency maximization problem is a mixed integer non-linear programming (MINLP) problem which is difficult to solve, it is decomposed into two subproblems. Firstly, we use the Lagrange dual method and Karush-Kuhn-Tucker (KKT) optimal conditions to obtain the closed-form power allocation solution. Secondly, a low-complexity subchannel allocation algorithm based on the greedy strategy is proposed. Simulation results show that our proposed scheme obtain significant energy efficiency gain and is superior to other existing schemes.