## 2 Materials and Methods
### 4G Mobile Communication Network Module  
Stable data communication is essential for the real-time transmission of data collected by underwater ROV and other sensing equipment to the central system. In this architecture, the mobile communication module serves as the communication backbone of the multiple remote control system, ensuring that data can be transmitted quickly and reliably. The system employs 4G mobile communication networks for data transmission, leveraging the extensive coverage provided by 4G mobile communication network base stations to facilitate remote operations. The underwater ROV, along with its connected buoy or shore-based station, is equipped with a 4G mobile communication network data terminal that includes a SIM card for connectivity to land-based 4G base stations. This communication setup enables the real-time uploading of data collected underwater by the ROV, including sensor readings and camera images, to a cloud server or control center. Additionally, it allows for the transmission of control commands from the multiple remote control system to the ROV. This research focuses on Chunghwa Telecom's (Taipei, Taiwan) 4G mobile communication network, primarily due to its extensive base station coverage in Taiwan's coastal regions. Field surveys indicate that Chunghwa Telecom boasts the densest distribution of base stations in Taiwan, with coverage in near-sea areas significantly surpassing that of other telecommunications operators. This characteristic is essential for maintaining stable communication connections in maritime aquaculture farms. The technical architecture of the communication system includes the following:  
1. 4G Mobile Communication Network Module: This module supports multi-frequency band operation, ensuring stable connections across various regions. It provides the essential communication foundation required for multiple remote control applications. Actual measurements in maritime environments indicate that the communication system maintains average download speeds of 5-10 Mbps and upload \begin{table}
**Sensor Model** & **Measurement Range** & **Technology** & **Sensitivity** \\ \hline CS4751 Dissolved Oxygen Sensor & 0–40 mg/L & Polarography method & Current output 400 nA \\ \hline CS1529 pH Sensor & pH 0–14 & \begin{tabular}{p{85.4 pt} p{113.8 pt}} Glass electrode with SNEX reference system and double salt bridge \\ \end{tabular} & \
\begin{tabular}{p{85.4 pt} p{113.8 pt}} Approximately 59 mV/pH \\ (standard value for glass electrodes) \\ \end{tabular} \\ \hline CS3740 Salinity Sensor & 0.01–500 mS/cm &
\begin{tabular}{p{85.4 pt} p{113.8 pt}} Four-pole conductivity measurement, graphite electrodes \\ \end{tabular} & Cell constant K = 0.4 cm\({}^{-1}\) \\ \hline \end{tabular}
\end{table} 
Table 1: Introduction to water quality sensor specifications. Figure 5: Deployment and power configuration of communication modules in the ROV system. (a) Deployed buoy system serving as communication relay; (b) Close-up of ROV communication module with integrated solar panel. speeds of 3-8 Mbps, fully meeting the demands of underwater ROV control and data transmission. 2. High-Gain Antenna: This external high-gain antenna is optimized for long-distance environments, significantly enhancing communication capabilities. It effectively addresses maritime signal attenuation issues, ensuring that commands from multiple control devices can be reliably transmitted to deep-sea areas. Actual deployment tests demonstrate that with high-gain antennas, the system can maintain stable connections in offshore environments up to 2 km from shore. 4G Mobile Communication Hardware Specifications--ASUS 4G-AX56 Router (ASUS Computer Inc., Taipei, Taiwan):  
1. Wireless Standard: IEEE 802.11 ax (Wi-Fi 6) [23]
2. Maximum Data Rates: 2.4 GHz: 574 Mbps, 5 GHz: 1201 Mbps
3. LTE Category and Speeds: Cat.6, Maximum Download Speed: 300 Mbps, Maximum Upload Speed: 50 Mbps
4.