Talking about the Application of Mobile Wireless Multifunctional Transmission System in Intelligent Transportation
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1. Background overview
As the capital of the motherland, Beijing is characterized by a large city area and a large number of motor vehicles. Especially in recent years, the number of motor vehicles has increased rapidly (see Chart 1), and the speed of road construction is far behind the rapid flow of vehicles and traffic. Growth, the traffic situation is very severe, especially the 2008 Olympic Games in Beijing will make Beijing traffic management face a huge test.
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The development of high and new technology such as electronic technology, communication technology, and computer technology has provided new ideas and new methods for solving problems for traffic management, and has improved the mobility, safety, and orderliness of traffic, and maximized the use of existing road systems. Provides technical support for the efficiency of traffic. It is a very effective means to strengthen the scientific management of traffic by using high technology such as traffic command and dispatch system, traffic vehicle information and driver information management system, and traffic image remote monitoring system. Although the existing traffic image remote monitoring system realizes unified monitoring of traffic image information in the public security traffic command center (see Figure 1), the existing traffic information service website facilitates the query and access of traffic information by the public and traffic management departments. However, the front-line traffic police, traffic patrol vehicles and command vehicles that most need this information have not yet efficiently and conveniently accessed these information means. Therefore, the role of these information resources is far from being brought into play.
Practice has shown that it has become an inevitable trend and a need for modern traffic management to provide traffic images and multimedia information resources to on-site traffic managers in a timely and efficient manner. The establishment of a mobile wireless multi-function transmission system is an extension and extension of the existing comprehensive information system for traffic management and a perfection of the wireless command and dispatch system.
2. Status quo at home and abroad
1. The status quo of Beijing’s 800M digital trunking TETRA system
Beijing’s 800M digital trunking network is built by Beijing Municipal Affairs Network Management Center and Beijing Zhengtong Network Communication Co., Ltd. At present, there are 172 base stations in the city. The outdoor coverage rate in the eight districts of the city has reached more than 90%, the wireless coverage rate of key indoor places has reached more than 95%, and the wireless coverage rate of suburban plain areas has reached more than 85%.
TETRA is currently the world’s advanced digital trunking system with powerful voice functions, but the current data capability of TETRA networks is very poor, and can only reach 7.2Kbit/s.
2. The status quo of Beijing’s terrestrial digital video broadcasting DVB-T system
Beijing Radio Film and Television Group built the Beijing Terrestrial Mobile Digital Television Broadcasting Network System for trial broadcast in May 2004, covering major traffic roads in downtown Beijing.
Beijing Mobile’s terrestrial digital TV broadcasting network system consists of a main transmitter station and two auxiliary transmitter stations. The main transmitter and the two auxiliary transmitters use the same frequency to form a single frequency network (SFN). The main transmitter is installed on the CCTV tower next to the West Third Ring Road, and the two auxiliary transmitters are installed in Beijing Jingguang Center and Beijing Celebrity Square, which can cover main roads and areas in the urban area.
The frequency resources of Beijing terrestrial TV broadcasting are very tight. It is impossible to apply for a frequency for traffic command alone. Therefore, the Beijing Municipal Public Security Bureau Public Security Transportation Administration shared the 1M bandwidth of Beijing terrestrial TV broadcasting network to solve the problem of mobile traffic image transmission. .
In summary, the completion and use of Beijing’s 800M digital trunking TETRA system and Beijing’s terrestrial digital television broadcasting DVB-T system provide basic conditions and technical guarantees for the development of mobile wireless traffic information transmission services of the Beijing Municipal Public Security Bureau’s Public Security Traffic Management Bureau .
In combination with the current situation of traffic management, we propose to build a multifunctional (vehicle) application terminal under mobile conditions using the TETRA network as a platform, which organically combines voice, data, images, and query information on one terminal to achieve a scientific combination of effective information.
3. System construction
1. Design principles
The design principle of the mobile wireless multi-function transmission system of the Beijing Municipal Public Security Bureau Public Security Traffic Management Bureau is to use existing equipment and network resources as much as possible to complete the transmission of different traffic information services in a mobile environment with the least investment.
2. System composition
The mobile wireless multifunctional transmission system (see Figure 2 for a schematic diagram of the structure) is mainly divided into two parts:
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The first part is the central part: it includes TETRA network access management server, service broadcast control management server, IP-DVB network management server and gateway, traffic information service server, switch, network security equipment, etc. It is mainly installed in the Beijing Municipal Public Security Bureau Public Security Transportation The communications equipment room of the Authority. The main task of the central part is to determine the type of service from the service application obtained from the TETRA network access terminal, and send the result back through the DVB-T network after accessing different service servers.
The second part is the terminal part, which includes TETRA network and special data access equipment, management and display notebook computer equipment, etc., which are mainly installed in traffic command vehicles and patrol police vehicles. The main task of the dedicated data access equipment is to transmit business applications through the TETRA network, receive signals through the DVB-T network, and realize the query and display of various traffic information in a mobile state. Under mobile conditions, in addition to the general characteristics of the system, the receiving part must also consider characteristics such as DC power input, seismic structure, and anti-interference ability (electric ignition, etc.).
The basic process is: the terminal sends out service application data information, transmits it through the TETRA network, receives the service application information from the TETRA network access server, and then judges the service type through the broadcast control server, accesses different service periods, and passes through the IP-DVB gateway and network management The server performs flow control and conversion of IP data and DVB transport stream, and returns the result through DVB-T network transmission. The terminal receives signals through the DVB-T network, and realizes access, transmission, and display of various traffic information in a mobile state.
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3. System function
Two-channel dynamic video image on-site monitoring or playback function
Each channel of video adopts 384K bandwidth, MPEG-4 or H.264 video and audio coding standard, uses very narrow bandwidth, through frame reconstruction technology, data compression, in order to obtain the best image quality with the least data, and transmit to the system Not much pressure.
The two-channel dynamic video images are generally surveillance images of traffic road intersections, but also images of emergencies. There are two ways to play images: carousel and on-demand.
Carousel: Loop video images of key and important intersections.
On-demand: Select and switch video images according to the size of the user’s authority. For the convenience of selection, several selection methods are specially set, such as terrain icon mode, area mode, pinyin mode, etc.
File sending and receiving function
Handle the information requested by mobile users to retrieve and send and receive media files. Query and download related files (text files, data files, pictures, etc.) in the file server. If the sent information is important, the sender will be automatically notified that it has been received or read. The local information database is automatically archived after the message is read. All processed messages can be viewed in the form of drafts, receiving letters, and sending letters.
Dynamic traffic information function
Watch the real-time information released by the command center, which can be text or pictures.
On-site query function for vehicle files and driver files
This function provides the police on-site real-time inquiry function, which can quickly inquire the basic situation of the vehicle files, especially the abnormal state, such as the vehicle scrapped, stopped, theft, the court seized, the second place seizure and the non-annual inspection status, so as to provide the police law enforcement Reliable basis.
Real-time traffic report function
Each traffic detachment reports the traffic status of the main traffic arteries and intersections in the area through the terminal duty system every half an hour. The command center automatically receives the data reported by the terminal duty system to form a city-wide traffic status report, and automatically archives the received data. Various ways of statistical query can be performed on the archived road condition information.
After the command and control center receives the regular road condition reports from each detachment, it will automatically aggregate the city-wide road condition reports for that period.
Voice scheduling function
Supports all the functions of the TETRA network, the TETRA network terminal equipment is completely a TETRA radio terminal when there is no data request.
Police auxiliary database query function
Establish a variety of special document libraries to assist the on-site traffic police to deal with problems. Generally include the following content:
(1) Database of various laws and regulations.
(2) On-site task management.
(3) On-duty log.
(4) Regional database
Business monitoring station
As traffic police work on the scene for law enforcement and emergency handling, they have strong sensitivity and high principles, and need to implement background monitoring of key business and sensitive tasks. Therefore, the business monitoring station includes the following functions:
(1) User identity management:
Complete the user management of the system, you can register each user’s name, siren, unit, usable mobile terminal number, system ID number, system password and authority, and can complete functions such as adding, changing, deleting, querying, and statistics. .
(2) Usage management
Supervise the operation of the system and the use of each unit’s system: total use of the information query system; statistics on the use of the information query system by each unit; statistics on the use of the information query system by individual users.
Four, concluding remarks
With the rapid development of mobile terrestrial digital trunking technology, digital TV technology, and CDMA/GPRS, mobile communication of voice, data, and image information has become a reality, which can transmit real-time images, animations, sounds, charts and other forms of traffic business information. The realization of intelligent and information-based traffic management will eventually provide a powerful scientific and technological means to improve the level of road traffic management and ensure a good traffic environment in the capital.
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