Advantages of Wireless Network Video Surveillance System

Wireless video surveillance technology is used in many security areas. For example, the use of the subway safety guard system is an important equipment to ensure the smooth running of the subway and the safety of transportation. In the metro video surveillance system, there is the use of wireless video surveillance technology. It has the following advantages and characteristics.

Flexibility Urban traffic intersections have a wide distribution and geographical dispersion. With the lack of flexibility in the use of wired networks, the need for future development must be considered as much as possible, which necessitates the presupposition of a large number of information points with low utilization. After the wireless network is established, the wireless terminal station can be set up at any position within the coverage area of ​​the wireless signal, and the network access can be realized with high flexibility.

Strong scalability When it is necessary to increase service points, there is no need for large-scale network transformation. As long as wireless devices at monitored points are increased or decreased, the increase or decrease of monitored points can be completed.

Installation and construction facilitate the use of wireless networks, which avoids or reduces the workload of network cabling without destroying the original environment facilities, and has the characteristics of short construction period and high cost performance.

The greatest advantage of enabling rapid coverage of wireless network systems is the ability to achieve rapid coverage. With the point-to-multipoint wireless communication method, generally only one or more wireless central station devices need to be installed, and a broadband wireless access network system covering the entire urban area can be established.

The wireless video surveillance system consists of three parts: the video information acquisition point, the wireless transmission system, and the traffic control center.

Intersection video image collection points According to the specific conditions of each city, corresponding surveillance cameras (color or black and white, fixed or active pan/tilt, fixed focus, or zoom) and software systems are installed at each traffic intersection. One or several surveillance cameras can be installed at each traffic intersection, and each is equipped with a pan/tilt head, a protective cover and a PTZ controller. Each video capture point matches a video codec. Surveillance cameras are used to collect real-time traffic status video signals of all roads in cities, mainly monitoring vehicles within a certain range of traffic intersections. The PTZ can be controlled by the computer in the control center. The user can perform horizontal 360°, vertical 90° and zoom control on the camera.

The video codec is responsible for converting the camera's analog video signal into a digital signal, compressing it at the same time, and also transmitting control signals. The video codec has a built-in 10/100M network card and is connected to a wireless monitoring device via a network cable. The code is compressed after processing. The monitoring information is collected through the wireless network to the traffic monitoring and management center. The monitoring center can see the conditions of the roads and intersections under its jurisdiction. The monitoring personnel can remotely view the video images and the remote control heads through the monitoring center LAN or the Internet.

In order to fully ensure the bandwidth of each monitoring point, the MPEG4 coding standard is adopted, the bandwidth is occupied less, and high-quality transmission and storage of images can be realized, and the transmission distance is relatively long, which is suitable for monitoring in a wide area of ​​the city.

The wireless video transmission system adopts a point-to-multipoint method to establish a wireless broadband network covering an urban intersection through a wireless broadband access device. A wireless bridge Sunet 5800 (central station) is installed at the center point, and a Sunet 5800-RU (remote station) is installed at the remote monitoring point. The central station chooses to install at the commanding heights of the city, such as high-rise buildings, iron tower tops, high mountain tops, etc., in order to ensure that they can receive the signal transmitted from each branch point.

One central point and several distributed access points are connected, and each distributed access point shares the total channel bandwidth provided by the central point in a shared manner, and the sharing mode may allocate the total bandwidth according to the real-time needs of the access users. The system adopts the 802.11a protocol standard. The total system bandwidth is 54Mbps, the effective bandwidth is 22Mbps, and the number of wireless remote monitoring points connected to each central station is 3-5. The effective access bandwidth of each distributed access point is generally 4Mbps. Both the Sunet5800 remote station and the central station equipment provide 10/100BaseT Ethernet interfaces. The switches, video decoders, and cameras in the monitoring center can be directly connected to the 10/100BaseT Ethernet interface of the Sunet5800 device in twisted pair.

The traffic control center security monitoring center is mainly composed of a video codec, a matrix video wall, a monitoring server, a hard disk recorder, etc. It can complete the reception and display of the on-site scene images, storage, retrieval, playback, backup, and recovery of the video.

The video codec encodes and decodes the video signal collected by the front-end surveillance point camera transmitted via the wireless network, passes it to the monitoring and control center LAN video monitoring server, and then is transmitted to the customers of various related departments or personnel through the internal LAN through the switch. end.

The user can view the images of multiple monitoring sites on the site through the multi-channel video wall in the center. The matrix video wall display mode can display 9/16 camera images at the same time.

The control commands issued by the wireless monitoring center for pan-tilt, lens, etc. are transmitted to the monitoring point through the wireless device. The user can control the pan/tilt, lens aperture, focal length and zoom of any point on the spot through the PTZ control device located at the monitoring center; PTZ's up, down, left, right, automatic or auxiliary control of the remote power supply, camera switch Wait.

The video images transmitted from the scene are converted into digital signals and stored on the hard disk video recorder. The data can be stored, updated, searched and backed up conveniently and quickly, providing the basis for law enforcement such as traffic violation handling.

Since a large number of 2.4GHz spread spectrum communication products have been deployed in urban areas and the interference in the 2.4GHz frequency band is severe, the wireless network products operating in the 5.8GHz frequency band can achieve better signal noise than the 2.4GHz wireless network products. In contrast, a stable network link can be established.

Therefore, products with 5.8GHz band should be used as far as possible in product selection. At the same time, 5.8GHz products can also provide higher bandwidth (54Mbps).

Between the site and the monitoring center, due to being blocked by the building, it is invisible. To ensure the monitoring center's image receiving effect, it is also possible to find out the third point that the monitoring site and the center can see. The wireless relay device is installed for transmission.

Equipment needed to build the system: The center station uses Sunet5800-AU high-speed wireless bridge, adopts OFDM technology, the rate is 54Mbps, supports point-to-multipoint wireless communication; the remote station adopts Sunet5800-RU, adopts OFDM technology, and the speed is 54M, supporting point-to-point wireless Communication. The central station uses a plate sector antenna with 18 dBi gain, and the remote station uses a parabolic directional antenna with 24 dBi gain. Other accessories include lightning arresters, feeders, and patch cords.

The video uses MPEG4 ACE compression algorithm, the amount of data is much smaller than the MEPG1 and MPEG2 algorithms, saves disk space, is suitable for network transmission, can provide users with high-speed video images, each video stream speed can reach 30 frames per second, can be for users Provides smooth image effects.