Energy Efficiency and Spectral Efficiency Tradeoff in IRS-Assisted Downlink MmWave NOMA Systems

Abstract

In this letter, we investigate the energy efficiency (EE) and spectral efficiency (SE) tradeoff problem in intelligent reflecting surface (IRS)-assisted downlink millimeter wave (mmWave) non-orthogonal multiple access (NOMA) systems, where a quality of service (QoS) requirement-based decoding strategy is proposed to address the decoding uncertainty due to the impact of the IRS on channel gains. The EE-SE tradeoff problem is formulated as a multi-objective optimization problem through jointly optimizing power allocation, active precoding, and passive precoding. To handle the intractable problem, we first adopt the weighted-sum method to transform the original problem into a single objective problem. Then, we propose an iterative alternating optimization algorithm (IAOA) to effectively solve the single objective problem, as shown in simulation results. Moreover, the proof of the convergence and the complexity analysis of IAOA algorithm are given.