# Research on Hybrid Relay Protocol Design and Cross-Layer Performance Based on NOMA
## 1 Introduction
In order to meet the requirements of quality of service, [PERSON] et al. [11] studied the design of a multi-user NOMA system for video transmission. By studying the semi-analytic rate distortion model of encoded video sequence and the physical layer model of multi-carrier NOMA network, the distortion-sensing power distribution problem was established to minimize the end-to-end distortion of the system. Ref. [12] studied the optimal delay uplink transmission of NOMA based on cross-layer design under block-fading channels. By using the constrained Markov decision process, a cross-layer optimization algorithm aiming at minimum average delay was established under the constraints of power and reliability. In order to improve the spectrum utilization rate and system capacity of wireless networks, ref. [13] applied NOMA technology to the unmanned aerial vehicle (UAV) auxiliary wireless networks to serve multiple users on the same spectrum at the same time, and proposed cross-layer resource allocation strategies, including UAV scheduling, user grouping, and power allocation. The above cross-layer algorithms focus on using resource scheduling and optimal allocation [8; 9; 10; 11; 12], optimal decoding sequence [8; 10], user pairing [13], and other methods to achieve tradeoff and optimization of system performance, but rarely in-depth analysis of the interaction mechanism between physical layer and MAC layer parameters and performance. In order to further elaborate the contribution of this paper, Table 1 summarizes the existing main literature based on NOMA technology in the past three years. The two-hop relay system can improve the reliability and coverage of data transmission, and the cross-layer research of the physical layer and MAC layer can realize the information exchange between the physical layer and MAC layer, and further optimize the network performance. Therefore, the cross-layer analysis and optimization of the two-hop hybrid communication system based on NOMA technology has important research value. In this paper, aiming at the hybrid relay system of wireless and power line communication based on NOMA, the cross-layer performance modeling, optimization, and simulation analysis of the combined physical layer and MAC are carried out. The influence of the power level of the physical layer used for information transmission on the bandwidth efficiency and reliability of the system is studied, and the optimal power distribution model based on multi-objective programming is established to maximize the performance of the system. The main contributions of this paper are as follows:  
* For the hybrid relay system of wireless and power line communication based on NOMA, the cross-layer performance analysis model of the combined physical layer and MAC layer is established. Based on the CSMA algorithm of IEEE 802.11 and IEEE 1901 standards [14; 15], a media access control scheme of two-hop NOMA is presented. By studying the influence of power control on physical layer and MAC layer, a cross-layer performance analysis model is established considering MAC layer retreat flow and physical layer channel conditions, and expressions such as normalized throughput, packet loss probability, and delay are derived. * For the hybrid relay system of wireless and power line communication, by studying the influence of power control on the transmission reliability of the physical layer and the number of competing nodes in the MAC layer, a cross-layer optimization model based on multi-objective programming is established to realize the combined optimization of the transmitted power at the source end and the power distribution factor among users, and the optimal power distribution factor under different parameters is determined by using a genetic algorithm and exhaustion method. * The model and algorithm performance are simulated through extensive Monte Carlo simulation.