## 4 Numerical Analysis  
In this section, we assume that the packet size is equal to 12,000 Bit, the maximum backoff state is 10, the minimum contention window is equal to 5, the propagation delay is 300 us, the transmission speed is 6 Mbps, a slot is 9 us, a DIFS is 34 us, a SIFS is 16 us, the transmission delay of a BSR frame is 200 us, the transmission delay of a TF frame is 400 us. The transmission delay of the MBA frame is 200 us. Then the system throughput, high-priority patient throughput, low-priority patient throughput, and channel utilization of this paper are compared with conventional OFDMA and DRA-OFDMA using MATLAB. In addition, the fairness of the protocol in this paper is illustrated. Figure 8 shows the relationship between system throughput and the number of low-priority patients. It can be seen that as the number of low-priority patients increases, the system throughput increases and then decreases. The main reason is that the number of patients successfully accessing the subchannel and transmitting data increases when the number of low-priority patients increases, but when the number of low-priority patients is large, the collision probability becomes particularly high, resulting in a smaller number of patients successfully accessing the subchannel. The difference between Figure 8a,b is the number of high-priority patients. As shown in Figure 8a, in the case of \(n_{1}=20\), the DRA-OFDMA can improve the performance of traditional OFDMA and increase system throughput, but CR-OFDMA can further improve system throughput. As shown in Figure 8b, in the case of \(n_{1}=5\), the system throughput of the DRA-OFDMA is similar to the conventional OFDMA. In contrast, the system throughput of the CR-OFDMA in this paper is significantly higher than the system throughput of the traditional OFDMA and DRA-OFDMA. Thus, the CR-OFDMA in this paper offers the best throughput performance, no matter the scenario. In Figure 9a, we observe that as the number of low-priority patients increases, the throughput of high-priority patients decreases. The main reason is that low-priority patients occupy the subchannel, which results in a smaller number of high-priority patients accessing the subchannel. In Figure 9b, we can see that as the number of low-priority patients increases, the throughput of low-priority patients increases and then decreases. It is due to the fact that the collision probability becomes higher when the number of low-priority patients is particularly large, resulting in a smaller successful access number of low-priority patients. In addition, from Figure 9, we can see that the high-priority patients' throughput of the CR-OFDMA is the same as the DRA-OFDMA and higher than the conventional OFDMA. The throughput of low-priority patients for the CR-OFDMA in this paper is higher than the DRA-OFDMA and the conventional OFDMA. As a result, the CR-OFDMA has the highest throughput performance of the three. Figure 10 shows channel utilization versus the number of low-priority patients. As can be seen from the figure, channel utilization increases and then decreases as the number of patients increases. As the number of low-priority patients increases, the number of  
Figure 8: (**a**) The system throughput versus the number of low-priority patients \(n_{2}\) for the cases \(n_{1}=20\), \(r=18\); (**b**) The system throughput versus the number of low-priority patients \(n_{2}\) for the cases \(n_{1}=5,\ r=18\). Figure 9: (**a**) The throughput of high-priority patients versus the number of low-priority patients \(n_{2}\) for the cases \(n_{1}=20,\ r=18\); (**b**) The throughput of low-priority patients versus the number of low-priority patients \(n_{2}\) for the cases \(n_{1}=20,\ r=18\). subchannels that can be effectively utilized increases. However, when the number of patients is particularly large, the collision probability is too high, resulting in subchannels not being utilized instead, therefore, channel utilization decreases.