## 6 Numerical Results
### Transmission Rate  
Figure 3 shows the transmission rate with different numbers of relay nodes, where \(Q=15\) dB and \(P_{T}=30\) W. From it, we can find that the transmission rate increases as the number of relay nodes increases. When the number of relay nodes increases, a better SR\({}_{\text{b}}\) can be selected, thus increasing the transmission rate. Furthermore, when compared with the BRS, the transmission rates under EEAB-SWIPT, the EEAB, and the AB are enhanced, and EEAB-SWIPT obtains the highest transmission rate. For example, when the relay node's number is 5, the transmission rates under BRS, AB, EEAB, and EEAB-SWIPT are 2.27 bps, 2.65 bps, 2.96 bps, and 3.72 bps, respectively. This is because the EEAB-SWIPT combines the SWIPT technique, the adaptive transmission, and the OPA, thus realizing the highest transmission rates. BRS only makes the best relay node selection with consideration  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Notation** & **Description** & **Values** \\ \hline \(\sigma^{2}\) & Noise power & \(1\) W \\ SNR & Signal-to-noise ratio & \([-10,25]\) dB \\ Q & Interference threshold & \((0,15]\) dB \\ \(\eta\) & Energy conversion efficiency & 0.6 \\ \(\rho\) & PS factor & 0.5 \\ \(\tau\) & Path loss factor & \([2,4]\) \\ \(SR_{k}\) & Relay number & \([1,10]\) \\ \(P_{T}\) & Total transmit power & \([0,60]\) W \\ \hline \hline \end{tabular}
\end{table}
Table 2: Simulation parameters.  
of the part channel gain, and it also does not consider the adaptive transmission; thus, it has the lowest transmission rate.  
Figure 4 shows the transmission rate with different total transmit powers, where \(Q=15\) dB and the number of relay nodes is 5. From it, we can find that the transmission rate increases with the total transmit power increases. But when the total transmit power increases to a certain level, the increases in transmission rate become slow, which means the influence of the total transmit power becomes weak. Meanwhile, from Figure 4, the transmission rate of the EEAB-SWIPT is higher than that of any other transmission strategies. This is because our EEAB-SWIPT realizes adaptive transmission between the BRT and BDT based on the total transmit power to obtain a higher total transmission rate, which corresponds to the definition of function \(f(P_{T})\). At the same time, our EEAB-SWIPT introduces the energy-constrained relay node to harvest energy so that a higher transmission rate can be obtained, which corresponds to Equation (3). In addition, our EEAB-SWIPT optimizes each node's power, thus increasing the transmission rate with the same total transmit power. With Figures 3 and 4, it can be found that the designed EEAB-SWIPT transmission strategy can effectively improve the network transmission rate.  
Figure 5 shows the transmission rate of EEAB-SWIPT and AB-SWIPT with a different PS coefficient \(\rho\). The AB-SWIPT is our AB with SWIPT and without OPA. From it, we can  
Figure 4: The transmission rate vs. the total transmit power.  
Figure 3: The transmission rate vs. the number of relay nodes.  
find that no matter whether the total transmit power is 15 W or 20 W, the transmission rate first increases and then decreases. At the same time, the maximum transmission rate is achieved at around \(\rho=0.8\). Because the energy harvested by the SR\({}_{\text{b}}\) increases with \(\rho\), while the SNR at the SR\({}_{\text{b}}\) decreases with \(\rho\), when \(\rho\) increases to a certain level, the transmission rate decreases with the increases in \(\rho\). In addition, when compared with AB-SWIPT, EEAB-SWIPT obtains a higher transmission rate with the OPA. Furthermore, from Figure 5, for the same transmission strategy, the transmission rate increases with the total transmit power increases. This phenomenon corresponds to Figure 4.