Real-time monitoring system for ocean-going vessels based on IDP satellite communication module

Aiming at the problem that there is no GPRS signal in the ocean and wireless communication cannot be carried out, a real-time monitoring system for ocean-going ships is designed based on the STM32F103VCT6 microcontroller and IDP satellite communication module. This system has the characteristics of high accuracy, strong real-time performance, and all-weather monitoring. The working principle, hardware design and software implementation method of the system are given, and the central control module, GPS positioning information acquisition module, and wireless communication module are analyzed in detail. The experimental results verify the feasibility of designing an ocean-going ship monitoring system using the STM32F103VCT6 microcontroller and IDP satellite communication module. Through this system, the geographical location information and other information of ocean-going ships can be monitored in real time to ensure the safety of ocean-going ships in shipping to the greatest extent.

introduction

This paper uses ARM chip as the control core and designs a real-time monitoring system for ocean-going ships based on GPS positioning module and satellite communication module. The system can upload the location information and heading information of ocean-going ships regularly according to user requirements, solves the problems in traditional ship positioning and rescue, and ensures timely, accurate and reliable dynamic monitoring of ships. At the same time, the system is convenient to expand other functions for wider application.

1 System overall design

The dedicated circuit board on board the ship collects the ship's position, speed, heading, SOS alarm and other information in real time. The dedicated circuit board processes the collected data and sends it to the maritime communication satellite through the satellite communication module. The maritime satellite transmits the data to the ground receiving station for users to use. The overall system block diagram is shown in Figure 1.

 

 

Figure 1 System overall block diagram

2 System Hardware Design

2.1 Overall hardware design

The hardware system adopts modular design, which is mainly divided into central processing module, GPS positioning module and satellite communication module, etc. The hardware structure is shown in Figure 2. Data processing and input/output control are completed by ST's STM32F103VCT6 processor. After receiving the GPS data, the processor processes the data and regularly uploads the processed positioning data to the ground receiving station. The GPS positioning module uses Globalsat's ET-314, which updates the GPS positioning data in real time. The satellite communication module uses Canada's Skywave's IDP satellite communication module, which uses the International Maritime Satellite (Inmarsat) to achieve all-weather, wide-area, and high-reliability two-way communication with the ground receiving station. In order to back up long-term positioning data, SST's SST25VF016B chip is used as an external Flash to realize the data storage function.

 

 

Figure 2 Hardware structure diagram

2.2 Central Control Module

This system uses the STM32F103VCT6 processor as the main control chip. The STM32F103VCT6 is a 32-bit processor with a Cortex-M3 core and a maximum operating frequency of 72 MHz.

The central control module STM32F103VCT6 is the core part of this system design, responsible for data collection, analysis, processing and data upload. The original GPS data will be transmitted to the serial port buffer of the MCU in real time. After verification by the MCU, it will be sent to the satellite communication module through the serial port. The SOS alarm information is sent to the MCU through the set GPIO port and uploaded to the ground receiving station through the satellite communication module. The hardware schematic diagram of this module is omitted - Editor's note.

2.3 GPS Positioning Module

The positioning module uses the Globalsat ET-314 chip from Globalsat to realize the position and speed collection of the ship. The Globalsat ET-314 module uses the SIRF III chip, which has the advantages of fast positioning, high positioning accuracy, short startup time and wide detection range. The functions achieved by using the Globalsat ET-314 module are as follows:

①Accurately collect geographic location information. The positioning accuracy of the Globalsat ET-314 module is 10 m.

②Accurately collect time information. The time collected by the Globalsat ET-314 module is synchronized with GPS time within 1μs.

 

 

Figure 3 GPS positioning diagram

The basic method of GPS positioning is spatial distance resection, which requires knowing the instantaneous position of the satellite. As shown in Figure 3, assuming that a GPS signal receiver is placed at the test location on the ground at time t, the time it takes for the GPS signal to reach the receiver here is determined to be △t, and the following four equations are determined based on other known conditions. The geographical coordinates of satellite 1, satellite 2, satellite 3, satellite 4 and the ground receiving station are (x1, y1, z1), (x2, y2, z2), (x3, y3, z3), (x4, y4, z4), (x, y, z); d1, d2, d3, d4 are measured pseudoranges; c is the speed of light;

dt is the satellite clock deviation; dT1, dT2, dT3, dT4 are the GPS receiving clock deviation items.

 

 

By combining these four equations, the geographic coordinates of the receiver can be obtained. The schematic diagram of the GPS positioning module is shown in Figure 4. The GPS communicates with the MCU through the serial port.

 

 

Figure 4 GPS module circuit schematic

2.4 Satellite Communication Module

The satellite communication module used is the IDP satellite communication module from Skywave, Canada. IDP's communication is based on international maritime satellites, and its global coverage is not limited by external factors. IDP also has the advantage of strong data transmission capability, with a single data transmission of up to 6,400 bytes and a single data reception of up to 10,000 bytes. IDP supports secondary development, making it convenient for users to connect IDP to other products. [page]

The International Maritime Satellite Communication System is the world's first global mobile satellite communication system. The Inmarsat communication system is basically composed of four parts, namely the space segment, the network coordination station, the satellite ground station (Land Earth Station) and the satellite ship station (Mobile Earth Station). IDP680 is a satellite ship station. The sent information is processed by the satellite ground station and forwarded to the user server through a dedicated gateway for user analysis and use. The terminal initiates the communication process as shown in Figure 5.

 

 

Figure 5: Terminal initiated communication diagram

IDP680 provides users with 4 configurable I/O ports and 1 RS232 and 1 RS458 serial ports for easy integration. The interface definition diagram is omitted - Editor's note.

Configure the satellite communication module to use the interrupt mode to receive the data transmitted from the MCU through the serial port. After the verification is correct, the satellite communication module executes the data sending function. The satellite communication module receives the remote command sent by the user and transmits it to the MCU through the serial port. The MCU uses the interrupt mode to process the data transmitted from the serial port. After the verification is correct, the corresponding command action is executed.

2.5 Data Storage Module

The data storage uses a 1M x 16-bit SST25VF016B chip. The uploaded positioning data packet is 27 bytes, which can store a total of (2x 1 024×1 024)/27=77 672 positioning data. According to the frequency of storing one positioning data per minute, a total of 77 672/(60×24)=53 days of positioning data can be stored.

3. System software design

3.1 Overall software design

After the system hardware design is completed, the software design is required. The software also adopts a modular design concept. The software mainly includes the main program module, GPS positioning data acquisition module and wireless communication module. The satellite communication module has secondary development function, and the satellite communication module needs to be specially designed. The system software operation process is shown in Figure 6.

 

 

Figure 6 Overall software flow chart

 

 

Figure 7 Startup process diagram

3.2 STM32F103VCT6 startup/UART usage process

The STM32F103VCT6 chip uses the Cortex-M3 core, and the firmware library provided by ST includes the startup file "stm32f10x_vector.s". After the Cortex-M3 core is reset, it will automatically fetch the reset interrupt entry vector from the next 32-bit space of the starting address and jump to execute the reset interrupt service program. The startup of the STM32F103VCT6 mainly includes initializing the heap and stack, defining and transferring the vector table, initializing the interrupt register, and jumping into the main function. The process is shown in Figure 7.

The use of the serial port of STM32F103VCT6 mainly includes starting the peripheral clock, configuring NVIC, configuring the GPIO port, configuring the serial port, initializing the serial port, enabling the sending and receiving interrupts, and enabling the serial port. The process is shown in Figure 8. [page]

 

 

Figure 8 Usage diagram

3.3 Satellite communication module software design

The serial port configuration of the satellite communication module is as follows: the baud rate is set to 9600 bps; the data bit is 8; the check bit is set to "None"; and the stop bit is 1.

The satellite module is developed using Lua language. Lua is a small scripting language. This language is designed for embedded applications and can provide flexible expansion and customization functions for applications. Lua is small in size and fast in startup, making it suitable for embedding in other programs.

Part of the source code of the satellite communication module developed using the LUA language is omitted - Editor's note.

3.4 Information Software Platform Design

CS monitoring platform is an information software platform for user equipment and monitoring center. The monitoring software platform can dynamically display the real-time position of the ship and manage the ship at the same time.

The CS software platform mainly plays the following roles: tracking and locating ships to understand the ship's operating conditions; querying the specific geographical conditions at a certain point on the nautical chart, including sea depth, tidal height, etc.; and distance measurement.

4 Test Results

This paper uses 5 locations in Shenzhen as test samples for verification test experiments. The positioning accuracy and long-term return data stability are used to evaluate the performance of the design. During verification, the system is allowed to work for at least 1 day at each location.

At the same time, the accuracy of real-time data upload and the accuracy of data stored in Flash are tested. The accuracy of positioning is now explained by taking part of the positioning data of location 1 received by the server as an example, as shown in FIG9 .

 

 

Figure 9 Test data screenshot

Extract one of the data for analysis. The hexadecimal data is as follows: 1 5 18 CE C9 F1 46 BD 60 00 00 00 00 00 00 00 00 00 00 4A A1 78 67 F0 35.

The corresponding ASCII code represents the data as follows: 1518CEC9F1FBD0000000000JA1xgF05 According to the protocol, latitude is a signed integer, which is represented by the two's complement code. After converting to a decimal value, it is divided by 60 000 to get the latitude value. Among them, positive numbers represent north latitude, and negative numbers represent south latitude. Pay attention to the existence of the sign bit when converting. Longitude is a signed integer, which is represented by the two's complement code. After converting to a decimal value, it is divided by 60 000 to get the longitude value. Among them, positive numbers represent east longitude, and negative numbers represent both longitudes. Pay attention to the existence of the sign bit when converting.

In this example, latitude = (146BD6)h/(60 000)d = 1 338 326/60 000 = 22.30543°. When calculating longitude, the last 25 digits are taken: 000011001111111000000110101)b = 6811701d, longitude = 6 811 701/60 000 = 113.528 35°. After analysis, it is known that this location is exactly the test site 1 in Majialong Industrial Zone, Nanshan District, Shenzhen, and the error with the actual location is within 15 m. After analyzing the test data of the five locations, they are all within the error range.

After at least one week of testing, the data transmitted back from each test point was stable and continuous, with no data loss, proving the long-term working stability of the system.

Conclusion

The ocean-going vessel monitoring system has made the shipping industry's demand for ocean-going vessel monitoring a reality, laying the foundation for marine informatization. The system research results will effectively promote the scientific and technological progress of my country's shipping industry and greatly accelerate the informatization process of the marine transportation industry.

The system's real-time online monitoring mode has greatly improved the safety monitoring and search and rescue capabilities of ocean-going fleets, thereby significantly reducing the probability of maritime accidents and reducing the losses caused by maritime accidents; the system's results can be promoted and applied to ship energy conservation and emission reduction, marine environmental protection and other aspects, promoting the sustainable development of the shipping industry.