Intelligent Reflecting Surface Assisted Hybrid Access Vehicular Communication: NOMA or OMA Contributes the Most?

Vehicular communications have witnessed remarkable achievements throughout the last few years on the way of providing reliable, safe, and affordable travel experience. Such achievements have not only skyrocketed the demand to the current services of vehicular communications, but also exploited many new services. To meet different Quality-of-Service (QoS) requirements of vehicular communications services, we assume the adoption of the hybrid OMA/NOMA-enabled access scheme as well as deploying intelligent reflecting surface (IRS) in such highly dynamic environments. We focus on maximizing the total system sum rate via jointly optimizing the transmit power allocation, the IRS's phase shift, and the vehicle active beamforming under different QoS levels, in terms of reliability and rate constraints of vehicles. To tackle such an optimization problem, we divide the original problem into three subproblems, and propose an efficient iterative suboptimal algorithm. Specifically, the successive convex approximation (SCA) approach is applied to turn this original nonconvex problem into separate power allocation, IRS phase shift, and active transmit beamforming optimization subproblems. Simulation results demonstrate that the proposed algorithm converges fast, and the proposed design can enhance the total system sum rate through enhancing the rate within cell-edge zones regardless of the vehicle speeds.