The Application of Intelligent Reflecting Surface in Downlink NOMA Systems

Abstract

This paper investigates the downlink communications of the intelligent reflecting surface (IRS) assisted non-orthogonal multiple access (NOMA) systems. To maximize the system capacity, we formulate an joint optimization problem to deal with the decoding order, power allocation and reflection coefficients. To tackle this problem, a novel two-step iterative algorithm is proposed. Firstly, a low-complexity optimization algorithm is proposed for determining the decoding order. Secondly, for the given decoding order, a joint optimization algorithm is proposed for solving the power allocation and reflection coefficient optimization problem iteratively. Numerical results illustrate that: i) with the aid of IRS, the proposed algorithm for IRS assisted NOMA systems outperforms the conventional NOMA system without the implementation of IRS in terms of system capacity; ii) the proposed IRS assisted NOMA systems achieves higher system capacity than IRS assisted orthogonal multiple access (OMA) systems.