## 4 Results and Analysis
### Angle Spread  
Figure 7 illustrates the AS for all the frequency bands in the industrial scenario. Firstly, the AS of the visible light band was much larger than that of the electronic wave bands. This was due to the different reflection patterns on the surface of metal reflectors for the visible light and electronic wave bands. There are two kinds of reflection patterns for visible light signals on non-smooth metal surfaces: specular reflection and Lambertian radiation. Meanwhile, electronic wave signals mainly undergo specular reflection. In specular reflection, the direction of the reflected signal is singular, while in Lambertian radiation, the direction of the received signal exists within the range of 0-360\({}^{\circ}\). Therefore, the AS for the visible light channel always maintains a high value. \begin{table}
\begin{tabular}{c c c c} \hline  & **Frequency/GHz** & \(\mu\) & \(\sigma\) \\ \hline \multirow{2}{*}{Sub-6 GHz} & 3.5 & \(-\)7.79 & 0.12 \\ \cline{2-4}  & 6 & \(-\)7.75 & 0.12 \\ \hline \multirow{2}{*}{mmWave} & 28 & \(-\)7.72 & 0.16 \\ \cline{2-4}  & 60 & \(-\)7.75 & 0.18 \\ \hline \multirow{2}{*}{THz} & 220 & \(-\)7.72 & 0.18 \\ \cline{2-4}  & 260 & \(-\)7.72 & 0.17 \\ \cline{2-4}  & 300 & \(-\)7.73 & 0.19 \\ \hline \multicolumn{4}{c}{VLC} & \(-\)7.93 & 0.23 \\ \hline \end{tabular}
\end{table} 
Table 4: Fitting parameters of lognormal distribution for RMS DS (log\({}_{10}\)(s)). Figure 6: CDF of the RMS DS. Moreover, in the electronic wave band, the AS slightly decreased with an increase in the frequency bands, and within each frequency band, the difference in the AS was not significant. For example, at a distance of 21.50 m, for the sub-6 GHz bands, the AS for 3.5 GHz and 6 GHz was 0.81 and 0.76 \(\log_{10}(^{\circ})\), respectively. For the mmWave bands, the AS for 28 GHz and 60 GHz was 0.73 and 0.72 \(\log_{10}(^{\circ})\), respectively. For the THz bands, the AS for 220, 260, and 300 GHz was 0.68, 0.68, and 0.69 \(\log_{10}(^{\circ})\), respectively. This is because as the frequency increases, the reflection ability of the signal decreases, and the power of the NLOS signals decreases, resulting in a decrease in the AS. Secondly, it can be observed that the AS for the electronic wave band channels experienced four stages as the transceiver distance increased. Firstly, at the receiver closest to the transmitter, the power of the LOS path accounted for a large proportion, and the AS was small, as shown in Figure 8a. As the transceiver distance increased to 2 m, the AS increased significantly with an increase in the transceiver distance. On the one hand, the number of NLOS components increased, which led to an increase in the AS. On the other hand, there was a metal instrument with a large size located at the position with a transceiver distance of 2 m, resulting in a series of strong NLOS signals. The strong NLOS signals caused by this large metal instrument can be clearly seen from the power angular spectrum (PAS), as shown in Figure 8b, which caused an increase in the AS by a large margin. Within the transceiver distance range of 2-5 m, the strong NLOS signals caused by this large metal instrument disappeared, and the AS suddenly decreased. Thirdly, as the transceiver distance increased from 5 m to 10 m, the power of the LOS component decreased greatly, and the NLOS components from the metal instruments on both sides gradually intensified, as shown in Figure 8d, resulting in a slow growth in the AS. Finally, when the transceiver distance was greater than 10 m, the AS decreased as the transceiver distance increased. It can be clearly observed from Figure 8e that the angle range of the received signal gradually converged towards the direction of the transmitter. Due to the lower height of the receivers, the blockage effect of the metal instruments on both sides caused the angle of the received signals to continue to be concentrated toward the transmitter, resulting in a continuous  
Figure 7: AS v.s. transceiver distance. decrease in the AS.