## 1 Introduction
### Literature Review  
Looking at the existing literature, a number of works have been reported on channel characteristics and modeling at multiple bands in the industrial scenario, as shown in Table 1. In the following subsection, we will review the progress of industrial scenario channels according to frequency bands. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Frequency Band** & **Frequency Point** & **Modeling Approach** & **Channel Characteristics** & **Influence Factors** & **Ref.** \\ \hline \multirow{4}{*}{Sub-6 GHz} & 2.4 GHz & Channel measurement & Path loss & Transceiver distance & [7] \\ \cline{2-5}  & 4.145 GHz & Channel measurement & Path loss, RMS DS & Environmental density & [8] \\ \cline{2-5}  & 4.1 GHz & Channel measurement & Path loss, RMS DS & \begin{tabular}{c} Transceiver distance, \\ LOS and NLOS cases \\ \end{tabular} & [9] \\ \hline \multirow{4}{*}{mmWave} & 28 GHz & Channel measurement & Path loss, RMS DS, AS & Antenna height & [6] \\ \cline{2-5}  & 28 GHz & Ray-tracing-based simulation & Path loss, LOS probability & Environmental density & [10] \\ \cline{2-5}  & 28 GHz & Channel measurement & Path loss & \begin{tabular}{c} Transceiver distance, \\ LOS and NLOS cases \\ \end{tabular} & [11] \\ \cline{2-5}  & 28 GHz & Channel measurement & Path loss, RMS DS, AS & LOS and NLOS cases & [12] \\ \cline{2-5}  & 105 GHz & Channel measurement & \
\begin{tabular}{c} PDP, RMS DS, temporal PDP \\ correlation coefficient \\ \end{tabular} & Time-varying channel & [13] \\ \cline{2-5}  & 142 GHz & Channel measurement & Path loss, RMS DS, AS & Polarization characteristics & [14] \\ \cline{2-5}  & 142 GHz & Channel measurement & Path loss, RMS DS, AS & Antenna transmission pattern, \\ \cline{2-5}  & 142 GHz & Channel measurement &
\begin{tabular}{c} A 3-D omnidirectional multipath \\ channel model based on clusters \\ \end{tabular} & LOS and NLOS cases & [15] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Research progress in channel characteristics at multiple bands in industrial scenarios. With respect to the sub-6 GHz band, the existing channel research on the industrial scenario mainly concentrates on the path loss and root mean square (RMS) delay spread (DS), and the reference distance (CI) model is mainly used for path loss modeling. In [7], the author investigated the multi-wall-multi-floor (MWF) model of the industrial environment, and measurements were conducted at 2.4 GHz in the multistoried building. By comparing the MWF model with the path loss obtained through measurements, it was found that the MMF model can accurately characterize the path loss in industrial scenarios. In [8], the author presented channel measurements at 4.145 GHz in both a sparse industrial environment with a normal size and a dense industrial environment with an extra-large size. It was found that the line-of-sight (LOS) path loss exponents (PLEs) of the CI model were 1.24 and 1.5, and the RMS DS was 22 and 83.2 for the sparse environment and dense environment, respectively. This indicates that the path loss and RMS DS are dependent on the industrial environment. In [9], the CI path loss model and the RMS DS were investigated at 4.1 GHz in both LOS and non-line-of-sight (NLOS) scenarios. The PLEs for the LOS and NLOS cases were 1.96 and 2.72, and the majority of the RMS DSs for the LoS and NLoS cases were 172 ns and 204 ns, respectively. However, due to the lack of detailed descriptions of the measurement scenario and measurement setting in [9], it is difficult to explain why there were significant differences in the channel characteristic parameters between [8] and [9]. Moreover, research on the spatial domain is still lacking. Regarding the mmWave band, channel research for the industrial scenario mainly focuses on 28 GHz [6; 10; 11; 12] and 142 GHz [14; 15; 16], which is also known as the sub-THz frequency band.