Vehicle dispatching system without blind spots based on GPS/Beidou satellite technology
The modern vehicle dispatching system is a high-tech project integrating global satellite positioning technology (GPS), geographic information technology (GIS) and modern communication technology . It transmits information such as the dynamic position (longitude and latitude), time and status of the moving target to the control center through the wireless communication link in real time , and then displays the moving track of the moving target on the electronic map with the geographic information query function. It also monitors and inquires parameters of interest to the user, such as the position, speed, direction of motion, and vehicle status of the target. At present, this type of system mainly uses GPS/GSM to complete the positioning and communication requirements. However, the pure GPS/GSM vehicle dispatching system cannot fully meet the needs of daily life, such as in remote western areas, deep mountains and old forests, etc. , a very acute problem is that there is no GSM signal , or when the GSM signal is covered, the vehicle dispatching system is completely ineffective. In addition, due to strategic considerations, the United States may turn off GPS satellite positioning signals in certain extraordinary periods (such as wars). If our system relies entirely on GPS, it will inevitably cause great losses. Due to the above problems, we have designed and developed a system design based on GPS/Beidou satellites, which can better solve these problems.
2 Introduction to the "Beidou" system
At the end of 2000, China established its own self-developed satellite positioning and navigation system - "Beidou-1" satellite positioning and navigation system. The system is an all-weather and all-weather regional navigation system that provides satellite navigation information, and will mainly provide positioning and navigation services for my country's transportation, transportation, maritime operations and other fields.
The same positioning system, my country's "Beidou" positioning system and the United States' Global Positioning System (GPS) are different. GPS is passive (broadcasting) and can be positioned after receiving a signal. The number of users is not limited, but communication cannot be achieved. function; while the "BeiDou" positioning system is active (responsive), and realizes the positioning function by establishing contact with the central station, and has a communication function at the same time. The "Beidou" positioning system has the ability to combine communication and navigation. Two-way information exchange can be carried out by using two synchronous real-point satellites. The uplink and downlink of the Beidou navigation and positioning satellite system support 200 positioning or short message services per second, which is much higher than the concurrency of Inmars at-C/OmniTrack and other systems . Processing capacity; the range covers all areas and sea areas in mainland China, and compared with the telecommunications cellular network , it is a true coverage without blind spots. The main system components of Beidou satellite navigation and positioning system are: (A) Beidou
satellite: composed of 2 geosynchronous satellites (1 in-orbit spare satellite); Clock , test subsystem and supporting equipment are composed of five parts; (C) User machine: the terminal for satellite navigation and positioning users, and the service scope is divided into two types: ordinary type and command type. Each command-type user machine can control 100 common-type user machines; the common-type user machines are divided into four types according to the mode of delivery: portable type, vehicle-mounted type, ship-borne type, and airborne type.
3 Overall System Architecture
The system is composed of vehicle-mounted terminal, communication link, central server and monitoring terminal. Its overall structure is shown in Figure 1. The vehicle-mounted terminal completes vehicle positioning, track storage and information transmission, the wireless communication link completes information interaction, the central server completes the connection and data storage with the vehicle-mounted terminal and monitoring terminal, and the monitoring terminal completes the monitoring of the vehicle.
Figure 1 Overall structure diagram of the system
3.1 System working principle
When the scheduling information appears, the vehicle-mounted GPS receiver receives the positioning data of the GPS satellites, calculates the longitude and latitude coordinates of its geographical location, and then sends the position, status, and alarm information to the control center through the GSM module of the vehicle-mounted station, and stores them in the database; When the GSM signal cannot be captured, the Beidou satellite positioning system is activated. This system has dual functions of positioning and communication, and sends information such as the position and status of the vehicle to the control center through the satellite system.
3.2 Vehicle-mounted unit introduction
The vehicle-mounted unit is divided into GPS part and "Beidou" part.
The GPS vehicle equipment adopts GSM/GPS all-in-one machine, equipped with a standard serial port, which can output NEMA-0183 standard GPS positioning data. In addition, the vehicle equipment can perform voice calls and data communications. Usually, the vehicle station communicates with the control center through GSM text messages. connect.
The "Beidou" part uses vehicle-mounted user terminals, and its technical indicators are:
beam width: pitch direction: 25°~90°; horizontal direction: 0°~360°;
frequency: use L/S band transmission/reception, anti-rain attenuation ability Strong, the attenuation for rain and fog is less than 0.3dB;
the number of receiving channels: ≥ 2;
the first capture time: ≤ 4 seconds;
the recapture time after losing the lock: ≤ 1 second; the bit error rate of received
signals: ≤ 10-5;
13 dBW;
Transmit frequency offset: ≤2×10-7;
Transmit signal power stability:
±0.5dB (one longest transmit signal cycle);
±1 Db (24 hours, working environment conditions);
Transmit signal carrier suppression: ≥30 dB;
power consumption: DC 10 ~ 32V ripple ≤ 1%, with power supply logic control function;
standby power consumption: 300mW;
average power consumption: ≤ 6W;
maximum transmission power: ≤ 20W
; Information (location and other requested service information) transmits GPS positioning information and sends messages through the GSM network; when the GSM signal cannot be received, the Beidou user machine installed on the moving target communicates to The positioning central station sends a positioning application, and the positioning central station calculates the longitude and latitude of the target position according to the received two satellite signals, and transmits it back to the user machine through the satellite, and the user machine obtains the position information. At the same time, the command to which the user machine belongs The machine also gets the location information. The command plane directly transmits the location information to the connected positioning data server and GIS server, and displays the vehicle location on the electronic map. The personnel in the monitoring center implement effective scheduling and monitoring of the vehicles according to the intuitive graphic information, and complete the data communication from the mobile vehicle to the user command and control center through the above process.
3.3 Control Center Introduction
This system adopts the working mode of C/S structure combined control of main control center + reception desk. The main control center is composed of a database subsystem, a communication subsystem, and a call acceptance subsystem; the reception desk includes a communication subsystem, a GIS subsystem, a main control center, and each reception desk form a computer network through a dedicated line to exchange data and share information with each other, realizing group Scheduling, network alarm, and absolute guarantee of high safety requirements.
The structure of the control center is shown in Figure 2.
Figure 2 Structural block diagram of the control center
3.4 Main functions of the system
Vehicle tracking and monitoring:
track and monitor the position (including longitude and latitude) of the driving vehicle, and visually display the vehicle running position on the electronic map of the monitoring area. The positioning interval can be set independently.
Command and dispatch:
The monitoring center can implement voice or digital command and dispatch to the vehicle through the call handle of the vehicle equipment.
Alarm reception:
When the vehicle alarms, the monitoring center will receive the sound and light alarm prompt, and at the same time, the alarm vehicle will be automatically tracked on the screen, and the distance mark centered on the alarm vehicle will be displayed. According to the vehicle archives, various parameters of the alarm vehicle will be displayed , such as serial number, model, license plate, color, owner, etc.
Vehicle control:
Take relevant technical measures. After the vehicle is stolen, the monitoring center can make the vehicle unable to drive by remote control to cut off the power of the vehicle, or make the vehicle send out audible and visual distress signals.
Vehicle management:
Combined with vehicle location information and status information, it can effectively record and count the working conditions of vehicles and drivers.
Data report output:
daily and monthly alarm table record output, alarm location map, user usage report, login logout table output. The monitoring center can check the daily login or logout information of the vehicle, as well as the vehicle file, and can print out the daily monitoring report.
Vehicle track playback:
The monitoring center can playback the past driving route of the controlled vehicle at any time.
Network management:
network management of the main control center and reception desk.
Information deployment:
the control center has all user information, and the geographical information and auxiliary information of all service areas can schedule the system resources of the whole network, and allocate the number of users who can realize various tracking at the same time among the user monitoring centers.
4 System software design
The main modules of the software system include target positioning and scheduling, data transmission, trajectory playback, and basic information management of moving targets. The system adopts C/S structure, utilizes technologies such as Windows Sockets, large-scale database, TCP/IP network and MapX, realizes the integration of "Beidou" system and GPS, and expands the scope of application. Its software flowchart is shown in Fig. 3.
In system software design, we have used some mainstream technologies, making our system an open system, fully considered in terms of compatibility and scalability. In the realization of network data transmission, we mainly use Windows Sockets technology, and use the very popular TCP/IP protocol to transmit data. In the design of GIS system, use MapInfo to make electronic map and call MapX secondary development tool to complete various operations of electronic map. In terms of accessing the database, we use the ADO data interface under the Microsoft ODBC standard to access the database.
5 Database management design
In consideration of the system's performance-price ratio, MS SQLSERVER2000 database is adopted after demonstration. System databases include GIS databases and system databases. According to the user's login information to operate different permissions, set multiple levels of identities such as ordinary operator level, commander level, system management personnel level, system maintenance personnel level, etc. Users of different levels can have different access rights.
The GIS database stores geographic information, including map information and its spatial relationship; the system database includes positioning information tables, vehicle information tables, communication information tables, vehicle status information tables, and abnormal information tables.
6 Conclusion
This system has established a mobile target dispatching system with complete functions using "BeiDou" as a means of positioning and communication, which can effectively locate, track, communicate, command, and dispatch management of moving targets in real time. The integration of the mobile target dispatching system has expanded the dispatching range of the mobile target dispatching system; the positioning and communication function of the Beidou satellite system has been fully applied, so that the dispatching, navigation and communication of the moving target dispatching system are integrated, which improves the overall integration of the system and facilitates the dispatching center to move the target. Scheduling management.
The positioning part of today's mobile target dispatching system is based on the GPS of the United States or Russia's GLO NAS S, and there is basically no mobile target dispatching system based on the Beidou satellite navigation system developed by China. By fully drawing on past experience, the vehicle dispatching system established in this paper takes into account the particularity of the "Beidou" system and the functions required for moving target vehicle dispatching. The system has been successfully applied to the 120 emergency system, which has won the support and recognition of users and laid a foundation for the application of the "Beidou" system in other fields.