On Cooperative Double-IRS Aided Downlink NOMA System with Multiple Channels

Both intelligent reflecting surface (IRS) and non-orthogonal multiple access (NOMA) are advocated as the promising technologies to support high spectrum/energy efficiency for future wireless communications. In this paper, we investigate the effect of cooperative-IRS on transmission power consumption for downlink NOMA communication system with multiple channels. To this end, we formulate a power minimization problem for double-IRS aided downlink NOMA system with multiple channels, taking into account the constraint of each user's minimum signal-to-interference-plus-noise-ratio (SINR). In order to solve the non-convex optimization problem brought by double-IRS, we first establish the relation between the transmit power and the phase shifts, and then develop an alternative optimization algorithm to determine the optimal phase shift. Simulation results show that the performance of deploying double-IRS is significantly better than that of deploying a centralized-IRS when there are sufficient number of reflecting elements. Besides, compared with various benchmarking schemes, the proposed joint optimization algorithm can significantly reduce the transmit power consumption.