Downlink Multi-IRS Aided NOMA System with Second-Order Reflection

The performance of non-orthogonal multiple access (NOMA) system can be enhanced by the incorporation of intelligent reflecting surface (IRS), which has the capability of reconfiguring each user's channel condition according to the demands. In this letter, we aim to design a transmission scheme with low power consumption for downlink multi-IRS assisted NOMA system with the consideration of second-order reflection. To this end, a joint transmit power and phase shift optimization problem is formulated. By leveraging the relationship between the phase shifts and each user's required transmit power, the joint minimization problem is simplified as a pure phase shift optimization problem. To further address the transformed non-convex problem, a successive phase-rotation method is proposed to determine the phase shifts sequentially. Simulation results show that the proposed scheme performs better than extensive benchmarking schemes in terms of total transmit power.