# Optimization for an Indoor 6G Simultaneous Wireless Information and Power Transfer System
## 4 Numerical Results  
Terahertz waves were deployed as the indoor communication system in our research. The frequency was set from 99 GHz to 109 GHz in a sixth-generation communication system with 48 antennas. The SWIPT node was Rx1. The power collection node was Rx2. Figure 4 shows the floor plan of the actual simulation environment. The Tx antenna was located at the center of the room (5, 5, 1 m). In order to investigate the performance against the location factor, three different distance scenarios were arranged between the receiving antennas Rx1 and Rx2 and the Tx antenna. The first scenario placed Rx1 farther away from Tx than Rx2. Here, Rx1 (9, 7, 1 m) and Rx2 (2, 6, 1 m) corresponded to the longer total distance (i.e., Rx1 to Tx plus Rx2 to Tx), while Rx1 (7, 2, 1 m) and Rx2 (3, 6, 1 m) corresponded to the shorter total distance. In the second scenario, Rx1 was placed closer to Tx than Rx2. Rx1 (5, 8, 1 m) and Rx2 (2, 2, 1 m) corresponded to the longer total distance,while Rx1 (6, 6, 1 m) and Rx2 (2, 5, 1 m) corresponded to the shorter total distance. In the third scenario, the distance of Rx1 and Rx2 from Tx was less than 1 m. Rx1 (9, 8, 1 m) and Rx2 (3, 1, 1 m) corresponded to the longer total distance, while Rx1 (7, 8, 1 m) and Rx2 (2, 7, 1 m) corresponded to the shorter total distance. In the first scenario, Rx1 was farther away from Tx than Rx2. Figures 5 and 6 show the SWIPT and WPT harvesting power, respectively, with and without \(\alpha\) adjustment, where \(\alpha=0.5\) (power allocation ratio) is preset for the case without optimization adjustment. It can be seen that the convergence was reached after 200 iterations. The harvesting power for the WTP node was slightly increased with the power-splitting adjustment. Table 1 shows the harvesting power ratio for the first group Rx1 (9, 7, 1 m) and Rx2 (2, 6, 1 m), in which the harvesting power ratio was increased by about 7.15% by \(\alpha\) adjustment. As long as the \(BER\) and minimum harvesting power requirement for Rx1 are met, the excess power can be efficiently allocated to Rx2 during the field adjustment process. Under this circumstance, the total power for Rx1 plus Rx2 is increased. Figure 4: Indoor environment layout. Figure 5: Harvesting power of the SWIPT node with and without power\(-\)splitting adjustment. (Scenario 1). Table 2 shows the harvesting power for the second group, Rx1 (7, 2, 1 m) and Rx2 (3, 6, 1 m). We can see that the harvesting power for Rx1 without (\(\alpha\) = 0.5) and with power-splitting adjustment (\(\alpha\) = 0.53) is the same. This is because the antenna pattern is changed when \(\alpha\) is being adjusted. In other words, the antenna gain towards Rx1 is decreased while the power-splitting ratio is increased. Moreover, when the antenna gain towards Rx2 is increased, the harvesting power for Rx2 is also increased. In the end, the total harvesting power of Rx1 plus Rx2 is increased by 2.6% compared with that of \(\alpha\) = 0.5. The random search for the first generation is used in the SADDE algorithm. The different random seed affects the convergence of our problem. However, if we use enough iterations, we can obtain an accurate result. In the second scenario, Rx2 is closer to Tx, and Rx1 is farther from Tx. Figures 7 and 8 show the SWIPT and WPT harvesting power, respectively, with and without \(\alpha\) adjustment, where \(\alpha\) = 0.5 (power allocation ratio) is prese \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 & \(6.61\times 10^{-8}\) & & 0.5 \\ \hline Rx2 & & \(2.54\times 10^{-7}\) & & \\ \hline Rx1 (\(\alpha\)) & O & \(5.00\times 10^{-8}\) & & 0.44 \\ \hline Rx2 (\(\alpha\)) & & \(2.93\times 10^{-7}\) & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Harvesting power ratios for Rx1 (9, 7, 1) and Rx2 (2, 6, 1).