Interference Management for IRS-NOMA Networks via Constructive Interference

Owing to the ability of reconfiguring wireless channels, intelligent reflecting surface (IRS) can help non-orthogonal multiple access (NOMA) to release its tremendous potential. However, the inter-user interference becomes the bottleneck of IRS-NOMA networks. To tackle this challenge, we propose two constructive interference precoding (CIP) based countermeasures for interference exploitation in IRS-NOMA networks. Specifically, the first scheme makes the interference from higher-order users (HUs) be constructive to lower-order users (LUs), so that the interference-free decoding can be achieved. While the second scheme utilizes the interference from LUs for the signal reception of HUs to avoid successive interference cancellation (SIC). The transmit power is mini-mized by jointly optimizing the BS active and the IRS passive beamformings for the two schemes. To solve each scheme, we apply successive convex approximation (SCA) and alternating optimization (AO) algorithm. Simulation results are presented to show the superiority and applicability of the proposed schemes compared to benchmarks.