# Optimization for an Indoor 6G Simultaneous Wireless Information and Power Transfer System
## 5 Conclusions  
In this paper, the millimeter-wave frequency band of the future sixth-generation mobile communication system is analyzed and presented. The impact of the actual environment on the millimeter wave band is taken into account by the ray-bouncing tracking method, and the frequency of 99-109 GHz is used for optimization analysis. The distance between the transmitter and the SWIPT as well as WPT nodes is considered for our study. SWIPT nodes need to consider the communication quality and the harvesting power simultaneously. On the other hand, WPT nodes only need to consider the harvesting power. To satisfy the bit error rate constraint--the basic power requirements for SWIPT nodes and WPT nodes--a special objective function is employed, and it is ultimately solved the by Self-Adaptive Dynamic Differential Evolution method. In summary, SWIPT can achieve basic communication quality and, in the meantime, can maintain the minimum harvesting power requirement by applying the multi-objective function algorithm. In the first scenario, the improvement in efficiency by power-splitting adjustment is affected by the total distance. Since the WPT can easily meet the constraint via SADDE with the designed objective function at a closer total distance, the power-splitting improvement is only 2.6%, but the improvement is 7.15% better at a greater total distance. Moreover, the second scenario's results show that when the WPT node is closer to the transmitter and the SWIPT node is farther from transmitter, the total harvesting power can be improved by 7.87% in the total long-distance case. However, the third scenario's results show that when the SWIPT node is placed closer to Tx, the total harvesting power can be improved by 86.7%. This is due to the fact that when the total distance is lower than that in the second scenario, the constraints are easy to achieve, and the power-splitting adjustment has more flexibility to improve the total efficiency. Finally, the system efficiency is improved overall, while the targeted bit error rate constraints can be met in all cases as well. However, our algorithm is very time-consuming. We intend to modify and speed up the algorithm in the future.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & **BER** & \
\begin{tabular}{c} **Harvesting** \\ **Power Ratio** \\ \end{tabular} &
\begin{tabular}{c} **Harvesting Power Ratio** \\ **Improvement** \\ \end{tabular} & \(\alpha\) \\ \hline Rx1 & O & 5.00 \(\times\) 10\({}^{-8}\) & & 0.5 \\ \hline Rx2 & & 1.80 \(\times\) 10\({}^{-7}\) & & \\ \hline Rx1 (\(\alpha\)) & O & 5.02 \(\times\) 10\({}^{-8}\) & & 0.55 \\ \hline Rx2 (\(\alpha\)) & & 1.81 \(\times\) 10\({}^{-7}\) & & \\ \hline \hline \end  
**Author Contributions:** Conceptualization, C.-C.C.; methodology, C.-C.C. and P.-H.C.; software, P.-H.C., Y.-T.C. and E.-L.C.; validation, P.-H.C.; formal analysis, H.J.; investigation, W.C.; resources, W.C.; data curation, W.C.; writing--original draft preparation, E.-L.C.; visualization, H.J.; supervision, C.-C.C.; project administration, Y.-T.C. All authors have read and agreed to the published version of the manuscript.  
**Funding:** Ministry of Science and Technology Taiwan: 110 WFD0410371.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Conflicts of Interest:** The authors declare no conflict of interest.