# Bidirectional Atmospheric Channel Reciprocity-Based Adaptive Power Transmission
## 3 Simulation and Investigation
### The BER Performance of Proposed Adaptive Power Transfer Technique
However, when noise was added, as in Figure 6e,f, the channel was nearly completely overrun with noise, and noise was thus present in this situation. The signal was severely distorted, with MSE values as high as 0.634 and 0.863. In this channel situation, it was challenging to transmit signals even with effective anti-noise measures. The three techniques' performances for two turbulent transmission channels with background noise \(\mathrm{N_{b}}=30\) dB added are shown in Figure 7. In the turbulence transmission channel of \(\sigma^{2}=0.0596\), the channel reciprocity value was \(\rho=0.9912\), while in the turbulence transmission channel of \(\sigma^{2}=0.5250\), it was \(\rho=0.9986\). From Figure 7, it was evident that the channel was less impacted by background noise, the channel reciprocity was powerful, and the CR-APT technique's performance in the two channels was very nearly optimal. In Figure 7a, the ATD and CR-APT transmission performances were outstanding, while the BER of the FTD approach was high when traveling through the channel of \(\sigma^{2}=0.0596\). When going via the channel of \(\sigma^{2}=0.5250\) in Figure 7b, the FTD approach entirely lost its impact. The ATD technique, on the other hand, achieved \(1.5\times 10^{-4}\) at SNR = 30 dB. The CR-APT approach achieved a BER of \(5.8\times 10^{-5}\) at SNR = 20 dB, and after that, with a rise in the SNR, the BER was maintained at about \(2.3\times 10^{-5}\), which was a respectable performance. Figure 5: Ideal BER performance of the three techniques in two channels with different turbulence strengths. (**a**) \(\sigma^{2}=0.0596\), (**b**) \(\sigma^{2}=0.5250\). The measured channel reciprocity value in the turbulent transmission channel of \(\sigma^{2}=0.0596\) was \(\rho=0.9730\) and in the turbulent transmission channel of \(\sigma^{2}=0.5250\) was \(\rho=0.9954\), respectively, when \(\rm{N_{b}}=25\) dB. The CR-APT technique tended to be closer to the ATD technique than Figure 8a, although overall performance was marginally better. It is foreseeable that when background noise levels rise, channel reciprocity would fall and CR-APT's BER performance will decline. It was demonstrated in Figure 8b that the CR-APT technique had the same BER as the FTD technique at SNR = 30 dB in the turbulent transmission channel of \(\sigma^{2}=0.5250\). Figure 6: Time-domain performance of a signal through the turbulent channel of \(\sigma^{2}=0.0596\) with different background noises. (**a**) \(\rm{N_{b}}=30\) dB, (**b**) \(\rm{N_{b}}=25\) dB, (**c**) \(\rm{N_{b}}=20\) dB, (**d**) \(\rm{N_{b}}=15\) dB, (**e**) \(\rm{N_{b}}=10\) dB, (**f**) \(\rm{N_{b}}=5\) dB. Figure 7: BER performance of the three techniques in different turbulent channels when \(\rm{N_{b}}=30\) dB. (**a**) \(\sigma^{2}=0.0596\), (**b**) \(\sigma^{2}=0.5250\). At \(\rm{N_{b}}=20\) dB, Figure 9a showed that the BER performance of CR-APT technique was delimited by SNR = 18 dB. At SNR < 18 dB, the CR-APT technique outperformed the ATD and FTD techniques; at SNR \(\geq\) 18 dB, the ATD technique performed better and achieved the BER of \(1\times 10^{-7}\) at SNR = 22 dB. Reciprocity \(\rho=0.9214\) in the channel of \(\sigma^{2}=0.0596\) and reciprocity \(\rho=0.9857\) in the channel of \(\sigma^{2}=0.5250\) at \(\rm{N_{b}}=20\) dB. At \(\rm{N_{b}}=15\) dB, Figure 10a shows that the performance of the CR-APT technique was similar to that of the FTD technique with SNR = 20 dB as the demarcation, and the BER was much higher than that of the ATD technique. At SNR < 20 dB, the FTD technique outperformed the CR-APT; at SNR \(\geq\) 22 dB, the CR-APT technique performed better. And in turbulent channel \(\sigma^{2}=0.0596\), \(\rho=0.8\); in turbulent channel of \(\sigma^{2}=0.5250\), \(\rho=0.9570\). The channel reciprocity dropped to 0.8 in a mildly turbulent channel when the added background noise went from \(\rm{N_{b}}=20\) dB to \(\rm{N_{b}}=15\) dB, and the performance of the CR-APT technique suffered.