Optimal Power Allocations for Relay-assisted NOMA-based 5G V2X Broadcast/Multicast Communications

Recently, as the benefit of its compelling applications, vehicle-to-everything (V2X) communications have attracted more and more attentions. Non-orthogonal multiple access (NOMA) provides a new solution for V2X services to ease traffic congestion and reduce latency. Different from existing works, we propose two NOMA-based schemes for V2X broadcasting and multicasting, and investigate the power allocation problems for them. The power allocation problems are formulated to maximize the minimum achievable vehicle rate for the purpose of fairness. In addition, we show that the formulated problem is neither convex nor concave. Fortunately, it is shown that the considered problem is quasi-concave, and hence we obtain the solution to the problem by a power allocation algorithm based on a bisection procedure. Simulation results demonstrate that the proposed scheme out-performs the scheme with fixed power allocation obviously and achieves a significant performance improvement with respect to a suboptimal fractional transmit power allocation (FTPA) method and the optimized time division multiple access (TDMA) scheme.