3D position optimization for the UAV-assisted relay networks enhancing by NOMA and MRC

In this paper, we consider an unmanned aerial vehicle (UAV)-assisted relay network for B5G, where the UAV and the base station (BS) cooperated with each other to serve the cell-edge users. Aiming at this network, we propose a new decode-and-forward (DF) relay protocol incorporated with Non-orthogonal multiple access (NOMA) and maximum ratio combining (MRC), by which the coverage for the cell-edge users is enhanced. Theoretical analysis demonstrates that the proposed NOMA based relay protocol is superior to the traditional orthogonal multiple access (OMA) based relay protocol in terms of channel capacity. In order to make full use of the advantages of the proposed protocol, we formulate the 3D spatial position optimization problem of the UAV relay with the objective to maximize the sum-rate of all the cell-edge users. Based on the genetic algorithm, we propose an effective algorithm to solve the formulated problem. simulation results indicate that the proposed relay protocol greatly outperforms the traditional protocols, and the proposed algorithm achieves orders of magnitude speedup in computational time with only slight loss of performance.1