# Research on Hybrid Relay Protocol Design and Cross-Layer Performance Based on NOMA
## 4 Simulation Results and Analysis
### Simulation Results and Analysis  
Let \(P_{th}=4\times 10^{-10}\), \(\rho=10^{-9}\). Figure 3 compares the normalized throughput and packet loss performance of the system using NOMA transmission scheme under different channel parameters. It can be seen from the figure that under different channel fading conditions, the theoretical calculation is consistent with the simulation results, which verifies the accuracy of the theoretical cross-layer model and performance formula. With the increase of the total transmitting power of S-end, the normalized throughput of the system increases first and then decreases, and the packet loss decreases first and then increases. This is because for the cross-layer algorithm in this paper, the increase of transmitting power will reduce the outage probability of the physical layer and improve the reliability of the physical layer. On the other hand, the number of competing stations in the MAC layer will increase, and the probability of packet collision will increase. With the increase of transmitting power, the physical layer of the system receives a significant beneficial effect, which leads to the increase of system throughput and the decrease of the packet loss rate. However, when the transmitting power continues to increase, the MAC layer gradually becomes the dominant factor, and the significant increase of the number of competing stations leads to the decrease of system performance. The cross-layer algorithm in this paper analyzes the relationship between transmitting power and performance index more comprehensively and accurately, and then selects the optimal transmit power according to the channel quality, which can achieve the best performance of the system. Figures 4 and 5 show the comparison of normalized throughput and packet loss probability of the system using two-hop NOMA, two-hop OMA, and single-hop transmission  
Figure 3: System normalized throughput and packet loss probability curve with different channel parameters. \begin{table}
\begin{tabular}{l l} \hline \hline
**Parameter** & **Numerical Value** \\ \hline Slot Time (\(\sigma_{\text{pl}}\)) & 35.84 μs \\ Priority Resolution Slot (\(T_{\text{PRS}}\)) & 35.84 μs \\ Preamble (\(T_{\text{P}}\)) & 110.48 μs \\ Contention Interframe Space (\(T_{\text{CIFS}}\)) & 100 μs \\ Response Interframe Space (\(T_{\text{RIFS}}\)) & 140 μs \\ Acknowledgement frame (\(T_{\text{ACK}_{pl}}\)) & 110.48 μs \\ Extended Interframe Space (\(T_{\text{EIFS}}\)) & 2920.64 μs \\ \(T_{\text{AT}_{pl}}\) & \(T_{\text{ACK}_{pl}}\) + 60 μs \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Main parameters and values of MAC layer protocol of wireless communication of PLC. schemes under different channel average signal-to-noise ratios for wireless and power line channel fading coefficients \(m_{RD1}=1,m_{RD2}=2.5,\sigma_{RD1}=3.5,\sigma_{RD2}=2\). As can be seen from the figure, with the increase of channel average signal-to-noise ratio \(SNR\)--that is, the wireless and power line channel conditions become better--the system throughput of different transmission schemes increases, the packet loss probability decreases, and the system performance improves. By comparing the system performance of different schemes, it can be found that the two-hop NOMA scheme has the highest throughput and the lowest packet loss probability, and the performance of this scheme decreases more slowly with the change of transmitting power. This is because there is serious large-scale and small-scale fading in the wireless environment. Compared with single-hop, the two-hop NOMA scheme reduces the outage probability of physical layer by introducing relay nodes and improves the reliability of physical layer packet transmission. At the same time, NOMA allows multiple users to share a given channel resource at the same time, which reduces the probability of collision caused by the simultaneous transmission of data packets by the stations.