Energy Efficiency Optimization with SINR Constraints in Downlink MIMO-NOMA Systems

Abstract

In downlink multiple-input, multiple-output, (MIMO) and non-orthogonal multiple access (NOMA) systems, the inter-cluster interference can be cancelled by optimizing pre-coding and detection matrices. Thus, the MIMO-NOMA channel is decomposed into multiple single-input, single-output and (SISO)-MOMA channels. Then, we formulate an energy efficiency (EE) optimization problem subject to the signal-to-interference-plus-noise ratio (SINR) constraints which is non-convex. To solve the problem, we propose the algorithm based on one-dimensional linear search and first-order Taylor expansion. Moreover, as in conventional communication systems, EE and spectrum efficiency (SE) cannot always be improved simultaneously. Thus, the trade-off between EE and SE is investigated based on the formulated problem. Numerical analyses and simulation results verify the proposed algorithm. In addition, the performance in terms of EE and the EE-SE trade-off can be improved by optimizing the user pairing method.