# Hybrid Cooperative Spectrum Sharing Protocols Based on OMA and NOMA in Cognitive Radio Networks
## 5 Numerical Results and Simulations
However, with the increase of the PU's transmit power,  
Figure 4: Throughput vs. transmit power (\(P_{P}=P_{\text{S}}\)). Figure 5: Throughput vs. PU’s transmit power \(P_{P}\) with different SU’s transmit power \(P_{\text{S}}\). the throughput of the SU first increases and then decreases. This is due to the successful transmission of the PU, and as a reward, the SU is transmitted in underlay OMA mode, so the throughput of the SU increases first. Moreover, the PU also transmits and interferes with the SU, which leads to the decrease of SU throughput. In addition, for a given transmit power of the PU, the throughput of the PU decreases with the increase of data rate in both OMA/NOMA protocol and pure OMA protocol. This is due to the increase of data rate would leads to the increase of the outage probability of the PU, and thus the performance of the PU decreases. For the SU, with the increase of transmit power, the SU has the optimal throughput. In this case, only with a small transmit power can the SU transmit successfully, thus increasing the opportunity for the SU to access the spectrum. Figure 7 demonstrates the impact of distance factor d on the throughput of the PU and SU. The throughput of the PU decreases with the increase of distance factor d in both OMA/NOMA protocol and pure OMA protocol. This indicates that the distance between PUs has a significant impact on performance. In real life, a similar concept can be found: the farther away from a base station, the worse the signal of a cell phone or other terminal will be. For the SU, however, with the increasing of distance, the throughput first increases and then decreases. This is due to the fact that in the cooperative CRNs, ST generally acts as a relay to help the PU, and the SU exists at an optimal distance from the PU to help the PU's transmission, while at the same time increasing the spectrum access rate. Figure 6: Throughput vs. PU’s transmit power \(P_{p}\) with different data rate \(R_{p}\) and \(R_{S}\). Figure 7: Throughput vs. distance factor. The impact of the power allocation factor and the transmit power on the throughput PU and SU are shown in Figures 8 and 9. It can be obtained from Figure 8 that increasing the transmit power of the PU will improve the performance of the hybrid OMA/NOMA protocol, while it has no effect on the performance of the pure OMA protocol. The main reason is that the power allocation factor is used in NOMA technology in overlay mode, resulting in the higher power allocated to the PU users, the higher the probability of the PU transmitting successfully, and therefore the better the performance. In the pure OMA protocol, there is no power allocation factor. Therefore, for the pure OMA protocol, the change of power allocation factor will not cause the performance change. In addition, when the power allocation factor is constant, the higher the  
Figure 10 shows the impact of the interference threshold on the system throughput. As can be seen from the figure, with the increase of the interference threshold, the throughput of the PU decreases while the throughput of the SU increases. This is because the higher the interference threshold, the higher the transmitting power of the SU, the higher the probability of successful transmitting of the SU, and therefore the best performance of the SU. For the PU, when the interference threshold is larger, the interference of the SU to the PU is larger, which leads to the degradation of PU performance. As shown in the figure, the throughput of the PU for the hybrid OMA/NOMA protocol is the same as that for the pure OMA protocol. This is mainly because the hybrid OMA/NOMA protocol and the pure OMA protocol distinguish between NOMA technology and OMA technology in overlay mode, but it is the same in the underlay mode. Therefore, the interference threshold has no effect on the throughput for the two protocols, and the throughput of the PU for the two protocols are consistent.