Low complexity resource allocation scheme for IRS-assisted downlink non-orthogonal multiple access systems

A low complexity resource allocation method is proposed for downlink non-orthogonal multiple access system assisted by intelligent reflecting surface (IRS). Firstly, an optimisation problem is formulated to minimise power consumption, with power allocation and IRS phase shifts as variables. Then, the joint optimisation problem of power allocation and IRS phase shifts is transformed into the optimisation of IRS phase shifts, which is further decomposed into multiple single variable sub-problems, the solutions to which can be obtained by using the function extremum method. Next, based on these sub-problems, one-level iterative algorithm is developed to optimise IRS phase shifts. Finally, the minimum power required by each user is calculated based on the IRS phase shifts obtained through iteration. Simulation results show that the proposed scheme is better than the existing schemes in the same scenario under the same rate requirement in terms of computational complexity and power consumption.