Application of CCTV Monitoring System in Rail Transit

1 Introduction

At present, in the overall planning of large and medium-sized cities, urban rail transit has gradually become the dominant direction of urban transportation facilities construction. In the next few years, my country's rail transit construction will usher in a period of rapid construction and development. The continuous development of information technology, network technology, advanced equipment manufacturing technology, and the combination and application of modular, standardized and open design concepts in the subway field have made the integration of various rail transit systems increasingly diverse, constantly improved and more flexible.

As an important part of the regional security system and production management system, the closed-circuit television (CCTV) monitoring system mainly realizes the management of relevant areas and key parts through the display of video images. It is an important means for subway operators to grasp the flow of personnel, materials and vehicles in each station (train) and key areas in real time. It is also an important tool for rail public security supervision departments to prevent in advance, discover during the event and deal with it afterwards.

Figure 1 Schematic diagram of station/parking lot CCTV monitoring system

2. Rail Transit CCTV Monitoring System Integration Solution

The construction of the closed-circuit television monitoring system for rail transit requires the use of the resources of the subway's dedicated transmission network system and wireless system, and the use of various advanced technical means to build an interactive and unified image monitoring system that meets the requirements of the rail transit monitoring center and other superior monitoring centers. Through unified authorization across the entire network, relevant image data can be remotely accessed and queried, realizing the functions of interconnection, intercommunication, mutual control, open interfaces, and platform resource sharing.

In addition to realizing the basic functions of video image control and monitoring, the construction of rail transit CCTV monitoring system should also make the system operation as simple as possible and maintenance as convenient as possible. Through system software and special software, the editing and modification of related functions as well as the interconnection, intercommunication and openness with external systems and interfaces can be flexibly realized.

Therefore, the integration and application of rail transit CCTV monitoring system should consider the following aspects:

(1) System design should fully consider the system characteristics of the distributed multi-level network of rail transit, follow the principle of giving equal importance to advanced, practical, mature and reliable technology, and form a complete set of overall solutions with full functions based on a full understanding of the technical equipment used in the transmission system.

(2) The system hardware and software design should be compatible with, access and control monitoring equipment such as video recorders, digital encoders, video controllers, control keyboards, cameras, etc. at the station level, depot and control center, achieve seamless connection, and be expandable.

(3) The system should have flexible and rich device control permission settings, and can configure the monitoring permissions of access units according to the actual needs of users to achieve multi-level distributed management functions.

(4) To meet the needs of system expansion and multi-level network image monitoring, the system network equipment should support network communication functions such as unicast, multi-point unicast and multicast, and achieve smooth and seamless operation with the transmission equipment of the communication transmission subsystem.

(5) The system should adopt a distributed intelligent mechanism to eliminate single point failures in the system and ensure that multiple (redundant) video servers and control keyboards can work simultaneously and independently without interfering with each other.

(6) The system should have the ability to detect the status of each operating device online to facilitate users to locate and eliminate faults, and have the function of automatic backup and manual restoration of relevant system parameters and records.

2.1 Station/Parking Lot Video Surveillance System

The station/parking lot TV closed-circuit television monitoring system consists of front-end video acquisition equipment, communication room transmission and control equipment, customer service center/fire room/police room terminal display and control equipment, etc. The system configuration is shown in Figure 1:

Each station/parking lot shall be equipped with fixed cameras and integrated cameras at the station hall level, platform level, entrances and exits, elevators, substations, etc. as needed.

All video images are transmitted to the communication machinery room through double-shielded video coaxial cables. The video signals transmitted over long distances are compensated and superimposed with characters through character superposition and video equalization equipment. The superimposed characters contain information such as station name (or station number), area number (or camera number), date, time, etc. Each video signal is input to the video encoding device through the video distribution device for analog-to-digital conversion and transmitted on the network in digital form; one channel is input to the station recording device for local video storage and remote video review; one channel is input to the picture synthesis device for 4/9 picture synthesis and then redistributed.

The digital video recorders installed in each station/parking lot record all video images 24 hours a day, and all stored video data can be backed up using CDs. At the same time, the digital video recorders automatically loop over outdated video files.

The video controller (server) is the core equipment of the station/parking lot monitoring system, which mainly includes the control of different users' access to video resources in the station and control center, selection of permissions, video network management and time synchronization, etc. At the same time, when the call button of the elevator intercom terminal, the alarm switch of the ticket office of each station, and the trigger switch of the access control device at each entrance in the corridor are pressed, they will send a persistent switch signal to the video controller for linkage, and the switch signal will drive the station customer service center to control the keyboard to beep and display the image of the corresponding area on the video monitor.

The station/parking lot customer service center, fire equipment room, and police room are equipped with color monitors and special control keyboards. The duty personnel can switch any video image of the station to the color monitor and control the integrated camera through the control keyboard. By switching the image synthesized by the 4/9 screen processor to the monitor, the function of viewing all video images of the station at the same time can be achieved. At the same time, the station duty personnel can also poll all monitoring images in a group on a monitor in a pre-set order within a set time interval.

The system can flexibly set the control authority of each operating terminal, and can set it in chronological order. That is, when a certain image is being controlled, other operating terminals cannot control the camera and can only passively watch the image resource screen. Only when the original control terminal stops control can it control the video resource.

When the station video controller receives operation instructions from the operation duty console and the public security console at the same time, it compares the control permissions according to the different operation and public security priority settings. The public security operator has a higher permission level for the cameras with public security priority, and the operation operator has a higher permission level for the cameras with operation priority.

All front-end video resources of the station can be replayed through the video playback terminal installed in the police station. All recorded images can be set with different permissions for real-time viewing locally (station/parking lot) and remotely (control center) as needed, and normal recording will not be affected during playback. The playback image is superimposed with the time, location and other information of the video, and the stored images can be imported into other external storage devices such as hard disks and optical disks.

2.2 Train Video Surveillance System Integration

Compared with the station video surveillance system, the train video surveillance system, in addition to the basic function of video surveillance inside the train, has higher requirements on the design and installation of on-board equipment hardware, on-board equipment performance (such as: earthquake resistance, fire protection, electromagnetic compatibility (EMC), impact resistance, mean trouble-free working time, etc.), and the network structure of the train video surveillance system.

The vehicle-mounted monitoring adopts an IP-based digital video monitoring system, which consists of vehicle-mounted cameras, video encoders, industrial Ethernet switches, vehicle-mounted video servers, vehicle-mounted network video recorders and other equipment.

Fixed cameras are installed in each carriage and the driver's cab as needed to monitor the images inside the carriage and the tunnel. The encoder corresponds to the camera one by one through a coaxial cable and is connected to the on-board switch through its 100M Ethernet port. In order to increase reliability, the on-board Ethernet switch forms a ring network through optical fiber connection. The video encoder adopts a small size, low power consumption and strong shock resistance device.

Redundant hot standby on-board video servers and on-board video recorders are installed at the front and rear of the train. The on-board video server completes the station video system management and maintenance functions, is responsible for monitoring the operating status of the train video equipment and the control center's access to the on-board images, and sends alarm information to the control center when the equipment is abnormal. The on-board network video recorder is connected to the on-board network through the Ethernet port, and all the analog videos of the train are recorded and stored after video encoding. The on-board video recorder uses a solid-state disk as the storage medium, which has extremely strong shockproof performance.

Figure 2 Schematic diagram of train video monitoring system

The composition of the train video monitoring system is shown in Figure 2.

2.3 Control Center Video Surveillance System Integration

The control center is also the monitoring center for various rail transit disciplines, managing the network and information resources of the entire system.

The video surveillance system of the control center consists of video decoders (groups), video distributors, (dispatching desk) video monitors, (dispatching desk) control keyboards, video playback workstations, video servers (dual-machine hot standby), network management servers, maintenance workstations, switches (including vehicle-ground wireless system access points) and other equipment, as shown in Figure 3.

Figure 3 Schematic diagram of the video surveillance system of the control center

Each dispatching desk in the control center can use the control keyboard to select single/multi-channel images of any station for monitoring, switch any image and control the integrated camera according to the authority, and can also switch the images of each station to the large screen in the dispatching hall at will.

Like the station-level operators, each dispatching seat in the control center can rotate and switch a considerable number of monitoring images in a pre-set time interval in a pre-set order. It can rotate and display partial camera images of a single station or different stations on one monitor, and can also display related images through 4/9 screen synthesis and project them onto a large screen as needed. Each dispatching seat can arbitrarily select images of different stations through different operation terminals, and can also display the same route of images at the same station. All operations are independent and do not interfere with each other.

The control center can flexibly set the control authority of each operating terminal, and play back all front-end video resources of the entire line's stations through the video playback terminal installed in the network management room.

2.4 Interface and expansion with external systems

Each station on the entire line can realize resource sharing such as mutual monitoring and mutual control of video sources with other existing and under-construction rail transit stations by adding video distribution and encoding and decoding equipment. The control center provides a communication interface with the upper network/public security center, through which it provides services to the upper network/public security center or obtains resources from the upper network/public security center.

The upper network/public security center sends switching and control instructions to the video server through the local video control terminal. After the instructions are parsed, prioritized and the destination address is determined by the video server of the control center, the station-level video server selects and controls the corresponding image and transmits the image to the designated output end of the decoder and monitor of the upper network/public security center through the transmission system. The access diagram of the control center and the upper network/public security center is shown in Figure 4.

Figure 4 Schematic diagram of access between the control center and the upper network/public security center

The upper network/public security center can use the same remote video playback workstation (Figure 4 upper network/public security center video management server) to play back all hard disk recorders in a software decoding manner. The playback image can display information such as time and location, and the video can be searched based on the time and location information.

The identity authentication of the upper network/public security center video user adopts the combination of device authentication and operator identity authentication. When the upper network/public security center user uses the resources of this line, the user's authority is first verified, and the operation is allowed only when the corresponding authority is possessed. When there are multiple conflicting operation requests for the same resource, the authority comparison method is used to compare and identify the authority of different operation initiators.

3 Conclusion

Through the organic combination with network technology and software technology, the integration and application of rail transit CCTV monitoring system provides timely and reliable monitoring image information for various background applications such as monitoring departments at all levels and leadership decision-making, command and dispatch, investigation and evidence collection. In addition, through the use of digital image processing technology, rail transit CCTV monitoring system can also realize intelligent video monitoring, intrusion detection, alarm linkage and other functions, thus providing more solid technical guarantee for the normal operation of rail transit, the handling of major emergencies, and the rapid response capability of anti-terrorist incidents.