Research on Coverage Enhancement and Sum Rate Maximization of 5G NOMA Network Based on Multiple IRSs

Intelligent reflecting surface (IRS) and non-orthogonal multiple access (NOMA) are new revolutionary technologies for the 5G and forthcoming wireless communication period. IRS is an effective means to improve weak coverage for that inadequate coverage will lead to signal quality degradation and low service transmission rate. In this paper, considering mobile users with variable location, to overcome the challenge that traditional IRS-assisted NOMA system with a single IRS cannot cover all mobile users, a new multiple IRS-assisted downlink NOMA network is proposed to improve system performance. The base station (BS) transmits overlay signals to multiple users with variable location through multiple IRSs reflecting elements. We maximize the sum rate by optimizing the phase shift matrix of IRSs. For the optimization problem is non convex, the semidefinite relaxation (SDR) and Gauss randomization methods are applied to solve it. The simulation results indicate that the multiple IRSs-NOMA system with optimal reflection phase can extend the coverage and improve the system performance.