# Hybrid Cooperative Spectrum Sharing Protocols Based on OMA and NOMA in Cognitive Radio Networks
## 5 Numerical Results and Simulations  
This section provides the MATLAB and Monte-Carlo simulation to simulate and analyze the performance of the proposed hybrid cooperative cognitive radio network based on NOMA and OMA, and to compare the proposed new protocol with the traditional OMA cognitive protocol. We assume the channel gains of all links experience Rayleigh effects with path loss exponent, \(v\), i.e., \(\lambda_{XY}=d_{XY}^{-v}\), where \(d_{XY}\) denotes the distance between the transmitter, \(X\), and the receiver, \(Y\)[5; 21]. Without loss of generality, we set \(v=4\), PT, ST, PR, and SR are located in two dimensions as \((0,0),(d,0),(2d,0)\) and \((d,d)\), respectively, where \(d\) is distance factor. The number of simulations in this paper is \(5\times 10^{5}\) times. In fact, \(10^{3}\) times of simulation are sufficient to achieve a good fit. For convenience, we use the spectrum sharing protocol based on pure OMA in Section 3 as a basis to compare the performance with the proposed hybrid NOMA/OMA spectrum sharing protocol. Figure 4 compares the impact of transmit power on throughput performance of the PUs and SUs with different protocols. As can be seen, with the increase of transmit power, the throughput of the PUs continues to increase, while the throughput of the SUs increases first and then decreases. This is because the increase of transmit power leads to the increase of the transmit success probability of the PUs, so the performance of the PUs is improved. However, the SUs opportunistically share the spectrum of the PUs when PUs have spectrum holes. In addition, the throughput of the SUs for the proposed hybrid cooperative cognitive radio network based on OMA and NOMA is better than that of the traditional OMA hybrid cooperative cognitive radio network. This shows that the proposed new protocol can make SUs share the spectrum of PUs opportunistically, on the premise of guaranteeing the performance of PUs. Figure 5 shows the influence of the transmit power of the PU on the throughput when the transmit power of the PU is 5, 10, and 25, respectively. It can be observed from Figure 5 that with the increase of the PU's transmit power, the throughput of the PU for the hybrid OMA/NOMA protocol is increasing, and the throughput of both the PU and the SU for the conventional OMA protocol is increasing, while the throughput of the  
SU for hybrid OMA/NOMA protocol increases first and then decreases. In the hybrid cooperative CRNs based on OMA/NOMA, as the power of the PU increases, the probability of the PU transmitting successfully increases, which results in the SU transmitting in underlay OMA mode, and therefore the throughput of the SU increases. This is attributed to the fact that the higher the power of the PU, the stronger the interference to the SU, resulting in lower throughput of the SU. In addition, when the transmit power of PU is constant, the throughput of PU and SU of the OMA/NOMA hybrid cooperation increases as transmit power of SU increases; the throughput of the PU and SU for the pure OMA hybrid cooperation remains constant. This is because when the transmit power of the PU is fixed, ST uses the NOMA principle to send the superimposed signal of the PU and SU in overlay NOMA mode. In this case, the higher the transmit power of the SU, the better the performance of the PU and SU. However, for the pure OMA hybrid cooperation, in overlay OMA mode, ST only forwards the packet from the PU. In this case, the change of the SU's transmit power has no effect on the performance of both the PU and SU. Figure 6 depicts the impact of the transmit power of the PU on the throughput of both PU and SU with different target data rates. As can be seen from the figure, regardless of whether the hybrid OMA/NOMA protocol or the traditional OMA protocol, with the increase of transmit power of the PU, the throughput of the PU shows an increasing trend. This is in line with the general principle that as the PU's transmit power increases, the throughput of the PU increases.