# Stable Throughput Analysis of Heterogeneous Hybrid FSO/RF Networks with Cognitive Radio Capability
## 6 Numerical Results
However, REF surpasses the cooperative case with a higher \(\lambda_{\texttt{R}0}\) in the range of 0.875-0.905 of \(\lambda_{\texttt{H}yr}\). Beyond this point, the cooperative case regains a higher \(\lambda_{\texttt{R}0}\). \begin{table}
\begin{tabular}{c c c} \hline \hline
**RF Parameter** & **Symbol** & **Value** \\ \hline Antenna type & - & omnidirectional \\ \hline Carrier frequency & \(f_{RF}\) & 60 GHz \\ \hline Bandwidth & \(W\) & 250 MHz \\ \hline Transmit power & \(P_{RF}\) & 15 dBm \\ \hline Transmit antenna gain & \(G_{T}\) & 43 dBi \\ \hline Receive antenna gain & \(G_{R}\) & 43 dBi \\ \hline Noise variance & \(\sigma_{N0,RF}\) & \(-91\) dBm \\ \hline Receiver noise figure & \(N_{r,RF}\) & 5 dB \\ \hline Oxygen attenuation & \(\alpha_{oxy}\) & 15.1 dB/Km \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Simulation parameters for RF systems. Figure 4: Comparison of stable regions for stay-and-switching transmission for \(z=z^{I}=3000\) m.  
When \(\lambda_{\rm HY}<0.875\), there is a reduced chance of interference from the RF pair on the hybrid FSO/RF pair, leading to a greater opportunity to access the idle channel of \(f_{2}\). This results in a higher \(\lambda_{\rm HY}\) compared to REF. However, within the range of \(0.875<\lambda_{\rm HY}<0.905\), the likelihood of interference with the hybrid FSO/RF pair increases, diminishing the opportunity to access the idle channel of \(f_{2}\), which leads to a lower \(\lambda_{\rm HY}\) than REF. Once \(\lambda_{\rm HY}>0.905\), the hybrid FSO/RF pair in the REF case fails to reach a stable region. In contrast, the cooperative case enables the hybrid FSO/RF pair to achieve a stable region by accessing the \(f_{1}\) frequency. Under moderate rain conditions, the results indicate a lower \(\lambda_{\rm HY}\). The economic system presents an equal (in clear conditions) or smaller stable region than the REF across clear, haze, and moderate rain conditions. Figure 5 compares the stable regions for SAS with \(z=3000\) m and \(z^{I}=2500\) m. Under these conditions, we have \(s_{f_{1,\rm RQ}}=s_{f_{2,\rm RQ}}=s_{f_{1,\rm HY}}=s_{f_{2,\rm HY}}=0.6581\) and \(s^{I}_{f_{1,\rm RQ}}=s^{I}_{f_{2,\rm RQ}}=s^{I}_{f_{1,\rm HY}}=s^{I}_{f_{2, \rm HY}}=0.0141\). Despite the low probability of success with the interference signal, the REF does not cause any performance changes due to interference signals with each other. However, COG and ECO, which can generate interference signals, experience a slight performance degradation. When \(z^{I}=2500\) m, both COG and ECO show a decrease in \(\lambda_{\rm RQ}\) compared to the scenario where \(z^{I}=3000\) m, as the magnitude of the interference signal between RO and HY increases. This leads to a reduction in \(\lambda_{\rm RQ}\) of 0.007% to 1.47% across all tested FSO link environments compared to the \(z^{I}=3000\) m scenario. Consequently, under haze conditions, the area where the cooperative case yields \(\lambda_{\rm RQ}\) higher than REF is reduced to ranges of 0-0.870 and 0.905-0.952. Figure 6 illustrates the stability regions for the SMP with \(z=z^{I}=3000\) m. Under clear air conditions, the stability region of the cooperative and economic system decreases as \(\lambda_{\rm HY}\) increases. In the SMP, the hybrid FSO/RF pair within the cooperative and economic system seeks to access the \(f_{1}\) frequency for additional transmissions, even when the HY successfully sends packets through the FSO link. As a result, the stability region of the cooperative and economic system diminishes with increasing \(\lambda_{\rm HY}\) in clear air conditions. In the cooperative system, the RF pair can maintain stability with \(\lambda_{\rm RO}\leq 1\) as long as \(\lambda_{\rm HY}<0.335\). When \(\lambda_{\rm HY}<0.335\), the RF pair experiences less interference from the hybrid FSO/RF pair and has a greater chance of accessing the idle channel at \(f_{2}\).