Energy and spectrum efficient power allocation with NOMA in downlink HetNets.

This paper investigates the tradeoff between energy efficiency (EE) and spectrum efficiency (SE) in a downlink non-orthogonal multiple access (NOMA)-based heterogeneous networks (HetNets). The tradeoff problem is formulated as a multi-objective optimization problem (MOP). Under the constraints of maximum transmit power of small cell users (SUEs) and minimum rate requirements, both EE and SE are maximized. In order to make the MOP tractable, a weighted sum method is used to transform it into a single-objective optimization problem (SOP), which enables the network providers to dynamically tune the weight factor to adapt to different EE and SE design requirements. To solve the transformed SOP, a SUE allocation algorithm is proposed to determine the multiple SUEs for each sub-channel, based on which a power proportional factor determination algorithm for SUEs and a novel power allocation algorithm for sub-channels are proposed. Numerical results show the fast convergence property, and demonstrate that the EE and SE obtained by our algorithms are Pareto optimal solutions and superior to the conventional orthogonal multiple access scheme.