A Low-Complexity Constructive Interference Exploitation Scheme in IRS-NOMA Systems

In this paper, we study the symbol-level precoding design problem in an intelligent reflecting surface (IRS)-assisted downlink non-orthogonal multiple access (NOMA) system. Conventional symbol-level design schemes perform symbol-by-symbol design, which can incur high computational complexity, limiting their practical applications. To address this, we propose a low-complexity symbol-level design scheme for the IRS-NOMA system. Specifically, the proposed scheme consists of two steps. The first step performs block-level design to obtain the precoders and reflection matrix, which are reused across all symbols. In the second step, we design an individual coefficient for each user based on the obtained precoders and reflection matrix to guarantee that the interference signal fall within the decoding region of desired signal. This approach significantly reduces computational complexity, as the block-level design is performed once for multiple symbols, and a simple problem is solved for each symbol to optimize the coefficients. Simulation results demonstrate the efficacy of the proposed scheme.