The core technology of vehicle DVR-Wireless network transmission technology

With the rapid development of wireless network technology, vehicle-mounted hard disk video recorder (Car DVR) It is no longer an isolated vehicle monitoring terminal, but an integral part of large-scale network monitoring. The wireless network monitoring command center can not only view the video images inside and outside the vehicle in real time, obtain GPS satellite positioning information, but also interact with the management personnel inside the vehicle through short messages or voice exchange. The wireless network shortens the space distance between the monitoring command center and the vehicle DVR, which is convenient for remote command and management of vehicles. Vehicle DVR products have been widely used in public transportation, police cars, environmental protection, special vehicle monitoring and other industries. The types of wireless network transmission, the wireless network transmission scheme suitable for vehicle DVR should meet the requirements of high-speed two-way data transmission, and the main technologies include the following categories: microwave data network transmission technology, satellite communication network transmission technology, operator-based wireless network transmission technology and wireless LAN network transmission technology. Among them, microwave data network transmission and satellite communication network transmission technology are limited to specific industries due to their high operating costs. The following is a detailed introduction to the latter two network transmission methods. The Comparison table of main network transmission technologies is shown in Table 1. Transmission mode, whether self-built base station is required, cost, operating expenses, microwave data network transmission, high requirements, no satellite communication network transmission, no very high requirements, based on operators' wireless network transmission, it does not need to be relatively low. Generally, it needs to be relatively low for wireless LAN network transmission. There is no wireless network transmission technology based on operators. The network transmission technology based on operators refers to using the existing network platform of wireless network operators to carry out network transmission, the main network transmission schemes include China Mobile's GPRS/EDGE and China Unicom's CDMA network. Several pairs of wireless network transmission mode rates based on operators are shown in Table 2. Transmission mode, theoretical uplink rate, actual test rate GPRS 85. 6Kbps 20 Kbps CDMA 153. 6Kbps 60 Kbps EDGE 128Kbps 50 Kbps currently, most of the vehicle-mounted DVR wireless network transmission applications adopt China Unicom CDMA network transmission scheme, with China Unicom CDMA network covering a wide range ( China Mobile EDGE covers only the urban areas of some major cities in China) , CDMA network speed is several times faster than GPRS network, and video or picture transmission can be carried out under low bandwidth. However, because its network bandwidth is still relatively low, the vehicle DVR can only transmit low frame rate (1-10 frames/sec)Video image; Moreover, due to the large fluctuation of wireless network bandwidth, the video image effect is not ideal when running at high speed. Common problems include long Image delay time, mosaic of images and incoherence of videos, unable to meet the needs of customers' senses. In order to solve the above problems, the manufacturer optimized the video coding scheme and network transmission protocol of the vehicle DVR. The video coding algorithm can automatically adapt to bandwidth fluctuations and automatically adjust parameters such as frame rate and code stream according to real-time network bandwidth; Through the analysis and research of the wireless network situation, we adjusted the structure of IP data packets in the network protocol to ensure the clarity and stability of the wireless video image network transmission. Car DVR products can not only use wireless network to transmit remote video images, but also complete the front-end capture function through DSP chips and transmit the images back to the command center. The captured image has not been processed by video coding, and the maximum resolution can reach D1 (704 × 576) The picture is clear and can distinguish the facial features of the person. The front-end capture function provides users with more solutions to obtain front-end information, which is suitable for customers with low real-time requirements. The main advantages of the wireless network transmission scheme based on operators lie in the low investment cost and wide coverage of the civil wireless data network, and there is no need to build a base station; It is estimated that after the 3G network license is issued in the second half of this year, the networks of various operators will be upgraded, the uplink bandwidth will be greatly improved, and the image quality and frame rate transmitted by the vehicle DVR wireless network will also be correspondingly improved, by then, the wireless network application of the vehicle DVR will be more extensive. Wireless local area network (WLAN)Wireless local area network (WLAN) It is a high-speed wireless network transmission scheme developed rapidly in recent years and adopts IEEE 802. 11 or 802. 16 (WIMAX) The network Physical Layer Protocol has the technical advantages of low cost and fast speed; However, due to the small network coverage, it is not suitable for high-speed driving of vehicles. At present, it is mainly used for data backup after vehicles return to the station and parking lot and video network transmission monitoring in fixed areas. Several major wireless LAN network transmission protocol pairs are shown in Table 3. Transmission mode, theoretical uplink rate, coverage cost, security 802. 11b 11Mbps low, low, generally 802. 11g 54Mbps is larger and lower, generally 802. 11n 300Mbps large, high, generally 802. 16 (WIMAX)34. 56Mbps is large and high. At present, the most widely used wireless LAN protocol is 802. 11g, the network transmission rate is fast, the terminal cost is relatively low, the network coverage is about 300, the cost performance is high, and it can meet the needs of ordinary customers. The following is an example of a wireless local area network (WLAN)802. 11g application: multiple wireless APs (Access point access point) The wireless network card is configured on the vehicle DVR. When the vehicle enters the area covered by the wireless AP, the wireless network card actively finds the wireless AP with the strongest signal and establishes a wireless network link, managers can back up data and manage on-board DVR through client software. 802. 11n transmission rate is very high, even faster than 100 megabytes of wired Ethernet, and the network coverage is wider; WIMAX has always been considered as the best wireless network transmission scheme to replace 3G. However, because the introduction of these two network transmission schemes is not long, the terminal price is relatively high, and the technology has yet to be further matured, it is the future development direction of vehicle DVR wireless LAN transmission. Conclusion in today's increasingly popular network video surveillance, vehicle DVR wireless network transmission, as an emerging technology, is being rapidly promoted and is also the focus of technical competition among major vehicle DVR manufacturers. With the progress of wireless network technology and the optimization of video network transmission technology by various vehicle DVR manufacturers, the wireless video network transmission scheme will be more perfect, it will certainly provide more convenient and perfect solutions for the promotion of vehicle DVR.