Energy-Efficient Design for IRS-Empowered Uplink MIMO-NOMA Systems

In future wireless communication systems, intelligent reflecting surface (IRS) plays an important role since it is capable of dynamically reconfiguring the channel conditions. In this paper, we apply IRS to facilitate the communication of an uplink multiple-input multiple-output non-orthogonal multiple access system. The objective is to maximize the system energy-efficiency (EE), requiring a joint optimization of the active beamforming at the base station, passive beamforming at the IRS, and power allocation. An iterative method is proposed to solve the formulated multi-variable non-convex optimization problem. Moreover, a low-complexity user ordering method is provided. Numerical results verify the rapid convergence of the iterative optimization scheme and the effectiveness of the user ordering. In addition, a substantial gain can be obtained by employing the proposed scheme over the benchmark schemes without IRS and with orthogonal multiple access.

I. Introduction

Intelligent reflecting surface (IRS) represents a promising transmission technology for the next generation communication systems. [1], [2]. Comprising of a large number of passive reflecting components, IRS can reflect the impinging signal in a controllable way by finely adjusting its components’ phase and/or amplitude, such that the signal propagation environment can be changed on a macroscopic scale. On this basis, IRS owns great potential to boost the system spectral-efficiency (SE) and energy-efficiency (EE) by creating an additional communication link between transceivers [3].