Electronic buoys are developed to address the environmental problems in the littoral sea caused by discarded fishing gears and fishing nets. The proposed system aims to check the location and status of fishing nets by connecting to a smartphone, which is different from the existing electronic buoys [6]. The system utilizes 890 MHz band of the WCDMA/LTE (band 8) cellular network frequencies and employs Advanced Encryption Standard (AES) encryption for data transmission in order to safeguard information pertaining to fishing activities. To lower power consumption, it is designed to minimize power consumption by blocking power after information is received. The system can also be used to check the location and status of fishing nets in real-time during fishing or shipboard activities, even when the onboard electronic chart display is not visible.

Research has been conducted to develop electronic buoys that utilize low-cost, non-toxic, and stable materials [7]. This system proposes the use of non-toxic and stable low-cost materials in electronic buoys, considering the marine environmental problems caused by toxicity of lithium and cobalt-based materials found in batteries in electronic buoys. In addition, a currentcounting-based SBMS (Seawater Batteries Management System) was introduced to identify the state of charge and discharge, thereby significantly extending the lifespan of seawater batteries.

Research has been conducted and proposed on drifting buoys capable of monitoring marine environmental information [8]. The focus of this research was to effectively configure a drifting buoy system using a Lagrangian Drifter for marine environmental monitoring and optimized device development. In addition, we developed a system to observe water temperature and salinity as a fundamental survey element of the marine environment. We also proposed a method for calibrating sensor gain to enhance precision of measured data.

An electronic buoy monitoring system developed to track the position of buoys by utilizing GNSS devices combined with Internet of Things (IoT) technology has been proposed [9]. The name of this system is BMS (Buoy Monitoring System), and a case study was conducted for all signals operating in the port of Taranto. The system that has been developed is primarily designed to ensure the safety of navigation and to continuously measure signal conditions. All Signals proposed an IoT-based method to collect and monitor maritime conditions, including buoys, nautical markers, and beacons.

To address problems of meteorological and oceanographic monitoring in the Adriatic Sea, an aluminum-plastic coated buoy is proposed [10]. The system is specifically designed to ensure reliable operation in the high waves and wind speeds that may occur in the Adriatic Sea. What was also suggested is the introduction of solar panels specifically designed to address buoy power, to ensure continuous operation of the buoy's electronic sensors.

The problem of pollution in the marine environment was noted, and a proposal was made to use an electronic buoy with advanced sensors to detect oil spills [11]. The designed system samples the air above water and generates data for classifying the overall level of contamination detected. The study also sought to tackle problems of classifying contamination levels from data generated using two artificial neural networks.

Figure 1 shows a block diagram of a data transmitter. It collects data via GNNS antennas and GNSS modules. GNSS refers to a network of multiple satellites, including the Global Positioning System (GPS), which provide location and time information around the world. The system provides various location information of fishing gears with high accuracy and updates location information in real-time.

Figure 1: 
Block diagram of an electronic buoy transmitter for fishing net surveillance

The electronic buoy transmitter for fishing nets utilizes a Low Power Wide Area Network (LPWAN) module to communicate with sensors and devices through Long Range (LoRa) transmission and reception technology. LPWAN is a wireless communication network technology primarily suited for long-distance and low-power device communication, offering low-power, wide-area communication [12].

LoRa transmission and reception technology use LoRa modulation for data transmission and reception, facilitated by a LoRa modem. This technology enables frequency spreading, multiple access, low-power operation, and transmits data using frequency modulation.

The electronic buoy transmitter for fishing nets enables low-power data communication between sensors and devices, while LoRa transmitting and receiving technology extends their coverage to a larger area. In addition, efficient data communication with onboard receivers can be achieved by combining LPWAN and LoRa technologies.

Sub-Ghz RF radio frequencies are used to optimize transmitter batteries. This provides the advantages of low power consumption and long distance communication. Sub-GHz radio frequency refers to the lower 1 GHz frequency band in wireless communications, and electronic buoys for monitoring fishing nets utilize it to demonstrate several advantages such as low power consumption, long-range communication, expandable networking capabilities, and cost-effectiveness.

Figure 2 depicts a block diagram of the power supply of an electronic buoy transmitter.

Low dropout (LDO) regulator is a type of linear voltage regulator that maintains stable operation even when the input voltage exceeds the output voltage. This allows for accurate voltage regulation while maintaining a stable output voltage with low variation. Low-dropout regulators generate less heat, making them ideal for small and lightweight designs, such as electronic buoys. Battery ICR18650-2S1P-3400mAh(7.2Vdc) is developed for low power and extended operation.

Figure 2: 
Block diagram of the power supply of an electronic buoy transmitter

Figure 3 depicts an onboard block diagram data receiver.

Figure 3: 
Block diagram of an electronic buoy receiver for fishing net surveillance

The data transmitted by transmitter communicates with a receiver onboard using a 442 Mhz frequency antenna. The 442 Mhz frequency is a commonly used low frequency in wireless communication. It is used to efficiently overcome obstacles and minimize power consumption [13]. These characteristics promote long-range communication between transmitters and receivers, ensuring an effective distance of communication between antennas.

The received data is modulated using LoRa technology in LPWANM1 and M2. RS-232 is a standard protocol and hardware interface specification for serial communication, providing a continuous transmission method of data bits [14]. This is commonly used as a standard for simple communication between terminal devices, sensors, and computers.

The RS-232 interface is used in electronic buoys for monitoring fishing nets to ensure reliable data transmission and enable long-range communication with fewer wires. In addition, the RS-232 has the advantage of being able to operate reliably in unfavorable installation environments, such as fishing boats.

ST-Link, developed by STMicroelectronics, is an integrated tool used for programming and debugging microprocessors and microcontrollers [15]. The ST-Link enables users to monitor and debug behaviors of a developed software in real-time. A program developed using the ST-Link is used to display the data transmitted by an electronic buoy for monitoring fishing nets.

Figure 4 depicts a block diagram of the power supply of an electronic buoy receiver.

Figure 4: 
Block diagram of the power supply of an electronic buoy receiver

Line filters are connected in power circuits in electrical and electronic devices to control and filter noise and electrical waves [16]. The line filter removes noise from power entering circuits. This improves the performance of an electronic buoy and helps maintain electrical stability.

DC-DC Converter Isolation is used in power supply circuits primarily for converting and isolating power between various voltage levels [17]. This maintains an electrically isolated circuit to prevent any noise or problems encountered during power conversion from propagating to other parts of electronic buoys. Maintaining isolation, especially particularly between high- and low-voltage circuits, is crucial for protection of electronic buoys.

The type, size, and storage of the data received are shown in Table 1.

The types of data received are ID, latitude, longitude, battery level, and check-sum. Data is 10 bytes in size and consists of 22 bits of ID, 24 bits of latitude and longitude, 2 bits of battery level, and 8 bits of check-sum. Data storage method is ID; important data is stored in the internal flash memory, and other data is stored in the internal RAM.

Based on the design, a transmitter and receiver of the electronic buoy for monitoring fishing nets were developed. The developed transmitter, shown in Figure 5, is waterproof and can float on the sea surface. The average transmit power is 2 watts, with a range of 1 to 2.4 watts. The occupied frequency bandwidth is set to 8.5Khz or lower. The neighboring channel leakage power is set to 60 Dbc or higher.

The developed receiver is shown in Figure 6. The receiver in put voltage is DC24V. The receiving antenna is set to MRF120 C.

Figure 5: 
Electronic buoy transmitter device for monitoring fishing nets

Figure 6: 
Electronic buoy receiver device for monitoring fishing nets

The data received from the developed electronic buoy for monitoring fishing nets is shown in Figures 7(a) and 7(b).

Figure 7: 
(a) Electronic buoy for monitoring fishing nets, (b) Display for electronic buoy for monitoring fishing nets

Data loss rate is evaluated using the Received Signal Strength Indicator (RSSI), which is a metric that measures strength of signal received in wireless communications. The signal quality is typically expressed in dBm, and the higher it is, the better the quality of the signal.

In the experiment, the size of RSSI sensitivity and transmits were checked once per minute, and checks data for an hour to determine the amount of data transferred. This allows monitoring the amount of data transmitted through wireless communication and generating statistics. Figure 8 shows the data received. It stores the buoy's ID, latitude and longitude, received signal strength, and SNR. The buoy that transmits data is set at 35 kilometers, as shown in Figure 9. At 35 kilometers, the maximum reception strength was measured to be -87 and the minimum reception strength to be -106.

Figure 8: 
Receive data and server-stored data

Figure 9: 
Buoy data transmission location

Comparative experiments were conducted on transmitting antennas we built in order to increase a communication distance for both transmission and reception in the 442Mhz band.

Figure 10 shows the reception sensitivity by transmit antenna of the many antennas, antenna number 19 has the lowest sensitivity, which is represented by -102. The antennas with the second lowest sensitivity are numbers 6 and 18, which have sensitivities of -110 and -111, respectively. The experimental results demonstrate the difference in reception sensitivity among the antennas, aiding in the selection of antennas for optimizing transmission and reception distances in communication.

Figure 10: 
Reception sensitivity by transmit antenna

Figure 11 shows the results of an experiment where the length of the C4 antenna coil was varied in order to enhance the communication distance. The experiment utilized three antenna configurations consisting of 22 PCB + 91 nH, 24 PCB + 43 nH, and 27 PCB + 27 nH, with reception sensitivity measured for each antenna length. The reception sensitivity has the lowest value of -65.44 at 22 PCB + 91 nH when the antenna is 90 mm long. When the antenna is 24 PCB + 43 nH, and its length is 80 mm, the reception sensitivity reaches its lowest value of -54.50. The reception sensitivity has the lowest value of -51.47 at 27PCB + 27nH when the antenna is 120 mm long.

Figure 11: 
C4 reception sensitivity by antenna coil length

The experimental results demonstrate the impact of antenna length on communication distance and indicate that optimal performance is attained at a specific length.