Security Trends: Video Surveillance Technology Of Wireless Transmission - Video Surveillance,

Video surveillance access way into wireless by the cable is an inevitable trend

. Wireless video transmission to break the traditional coaxial and fiber optic image Monitoring Subject to the adverse situation of the hardware connections, with more flexibility and convenience of wireless network based video surveillance system came into being. Wireless video transmission Technology The development has the structure of the wireless mobile networks and protocols had a profound impact, but because of the limited wireless channel bandwidth, interference by many factors, but the video signal data volume, real-time requirements such problems.

Wireless video transmission technology status With the development of information society, people are increasingly demanding security surveillance, in addition to a concentration of party and government organs, enterprises and units, such as the sea, mountains, mines, basements, or other complex Environment Can not achieve erection of the local cable network. Need to achieve security video surveillance, which requires use of wireless video transmission technology.

Present, Market Most of the wireless video transmission technology using GPRS and CDMA technology. The GPRS bandwidth shortage, only a few frames per second video transmission, and emergency incidents occurred prone to break and the wireless receiver of the dead. CDMA transmission also exists for such failure, the upstream bandwidth is 153kb / s, upstream bandwidth is 70 ~ 80kb / s, transmission fluid and therefore the video is basically impossible. As the image is only a few frames to drawings in the form of transmission, and for the small screen size. Apparently, this can not satisfy the real-time video surveillance system applications. For the microwave (digital microwave, spread spectrum microwave), wireless local area network (WLAN, 802.11 (ab, g)) technologies and other high Wireless transmission Program, its implementation video encoding to MPEG-2 / 4, H.264, etc. mainly. However, many of them have a common problem, that can only be done through visual transmission, directional transmission, and difficult to support mobile transmission, thus limiting the application of video surveillance systems.

Monitoring system Generally low frame rate and ensure the transmission of clarity, because only the CIF MPEG-4 over the image resolution in order to meet the needs of investigation and evidence collection. Therefore, the wireless transmission technology to be fully in control system play an absolute advantage, should be met: visualization and in non-blocking environment applications; is suitable for high-speed wireless transmission of real-time moving images; suitable for transmission of high bandwidth, high streams, high-definition audio and video; have excellent anti-interference, anti-fading capability. In practice, wireless video transmission for two main concepts: first, the transmission of movement; Second, broadband transmission. Therefore, the development can be very wide-band high-definition video to an unlimited and stable video transmission systems, data transmission mechanism optimization is one of the key issues to be resolved, infinite link bandwidth resources are limited, this limitation handed down in the massive video especially reflected. Here, for wireless video transmission system fault tolerant data transfer mechanism to start the appropriate research, to solve the bandwidth wireless video transmission with limited resources and large amount of video data, this contradiction, full use of temporal correlation of video signal to save as brought unnecessary retransmission bandwidth waste of resources. Through the use of bandwidth, the concept of a distortion cost function to evaluate the wireless video transmission system. On this basis, further consideration is given based on the bandwidth of a distortion minimization, part of retransmission error control mechanism, thus improving bandwidth utilization, and the corresponding experimental analysis.

Wireless video transmission system analysis and fault-tolerant transmission technology

Reliable signal transmission channel aims to make full use of channel bandwidth; and unreliable channel for transmission in the focus of the study is to make full use of bandwidth resources to achieve reliable transmission, that is fault-tolerant transmission technology. Discussed here in the wireless channel on the video transmission system, its main research is fault-tolerant transmission control. Fault-tolerant transmission control technology under its control method can be divided into three categories: namely, the forward error control, ARQ, and based on the feedback of the joint source and channel coding. Forward Error Control (ForwardErrorControl, FEC), including the channel error correction coding, interleaving packaging technology and optimized packet scheduling mechanism. ARQ techniques based on feedback information including the use of multi-frame reference picture selection mechanism (ReferencePictureSelection, RPS) mechanisms, hybrid ARQ (Hybrid, HARQ) feedback mechanisms and ARQ-based error tracking. As the ARQ-based fault-tolerant transmission control technology has excellent performance, so this highlights the ARQ transmission control-related technologies, and discuss the existing fault-tolerant video transmission system weaknesses.

Forward error control coding using forward error correction method to overcome channel errors. Fluctuations in the channel error probability of more severe cases (such as existing mobile channel), in order to obtain a certain transmission quality, forward error correction coding must be present to increase the estimated worst-case redundancy check bits, which will lead to waste of bandwidth resources. On the already limited bandwidth wireless channel is concerned, obviously can not meet the requirements. To this end, consider the ARQ error control technology and to integrate the former, known as the HARQ technology. HARQ is divided into two types: I type HARQ, the transmitter should be the first to have some error-correcting coding capacity of the receiving end when an error is found, the first use FEC codes to correct errors. If the error is corrected, then the sender sends a packet reception success of the current feedback information (ACK), the contrary is received failed to send a message (NACK). If the transmitter received ACK, continued to send the next packet, otherwise, the re-issue of wrong packet. So I need a strong class of ARQ FEC, in applications where a lower error rate would result in waste of bandwidth resources, but the error rate in the environment can be better than other types of ARQ system throughput efficiency. Only the required class ARQ FEC error detection capability can have, according to error-correcting capability of channel coding theory known, it can play a role in saving bandwidth. When the receiver found in error, send a repeat request; the sending end only the error data transmission with error correction ability corresponding checksum. When the receiver received, if you still can not correct the error, then continue to send the retransmission request, the sender can choose the retransmission data and the overall error check code, you can also choose to send a stronger ability to check error-correcting codes, specifically for different control strategies can be adjusted. View of the wireless channel error rate, with the feedback channel usually used for wireless transmission of HARQ-I. Figure 2 shows use of HARQ-I of the wireless video transmission systems, the figure dashed box represents a transmission error control of the process. According to HARQ-I of the design principles, the receiver

by: gaga

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