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Wireless video transmission technology
2011-02-28 08:59:34
Video transmission wireless broke the traditional coaxial cables, and fiber images monitored subject to the adverse situation of hardware connections, provides greater flexibility and convenience, wireless network-based video surveillance system came into being. Development of wireless video transmission technology for wireless mobile network architecture and Protocol has had a profound impact, but due to the limited wireless bandwidth resources, interference, and the volume of video data, real-time high problem.

Wireless video transmission technology

Signal transmission on the purpose of the study is fully reliable channel using the channel bandwidth resources; for unreliable channels, transfers in the focus of the study is to make full use of bandwidth resources to achieve the reliable transmission, that is, fault-tolerant transmission technology. Video transmission over wireless channels on the mechanisms discussed here, the main points of research is fault-tolerant transmission control. Fault-tolerant transmission control technology according to the different control methods can be divided into three main categories: forward error control, based on the feedback of joint source-channel coding and ARQ. Forward error control (Forward Error Control,FEC) including channel error correction coding weave technology, packaging technology and optimized packet scheduling mechanisms. Based on feedback mechanism of ARQ technique including the use of multiple frames of reference reference picture selection (Reference Picture Selection,RPS) hybrid ARQ mechanism, (Hybrid,HARQ) based on ARQ feedback mechanisms and error tracking technology. Because of ARQ-based fault tolerant transmission control technology with superior performance, so this focuses on ARQ-related transmission control technology and discusses the deficiencies of the existing video a fault-tolerant transmission mechanism.

Forward error control ways to overcome the channel using forward error correction coding errors. In the more severe cases channel error probability wave (such as existing mobile channels), in order to obtain a certain degree of transmission quality, forward error correction coding must be based on the current estimated worst case to increase redundancy check bit, which may result in waste of bandwidth. Wireless channel that is inherently limited bandwidth resources, apparently does not meet the requirements. For this reason, consider combining ARQ error control technique and forward called HARQ technique. HARQ fall into two categories: class I HARQ, sender of forward error correction encoding must have a certain capacity when the receiver after an error is found, forward error correction coding first used to correct the error. If the error is correct, then transmit a current package to the sender to receive feedback for success (ACK), while sending and receiving a failure message (NACK). Send port if you receive an ACK, then sends the next packet, otherwise the packet is sent wrong. So I type ARQ needs strong forward error correction coding, in applications with low error rates can result in waste of bandwidth, but in environments with high error rates can get better throughput than any other type of ARQ mechanism efficiency. Only requires forward error correction coding in class ⅱ ARQ with error detection capability, based on channel coding theory of error correcting ability, which can play a role in saving bandwidth. When the receiver after an error is found, send a retransmission request; send port only transmitted corresponds to the error data parity-check codes with error correction capability. When upon receipt, the receiving end, if you still cannot correct the error, you continue to send requests for retransmissions, the sender can choose to retransmit the overall error data and parity-check code, you can also choose to send more error correction ability of parity-check code, specific control strategies can be adjusted. In view of the wireless channel error rate is high, with feedback channel wireless transmission is usually HARQ-I. Figure 2 shows the wireless video transmission system using HARQ-I, dotted boxes in the figure represent the process of transmission error control. According to the design principles of HARQ-I, the receiving end after an error is found, first of all for forward error correction (first barrier layer error in the figure), if not correct and current time delay system meets the limit, it sends an ACK request sent duanzhong out of the wrong part of the data (the second barrier layer error). Such retransmission can be duplicated to the receiver receives the correct time delay of data or the retransmission delay exceeds the system limit so far. If you still do not receive the correct data retransmission after the end of the package, will be at the receiving end using error concealment for error recovery (third layer error barrier). As can be seen, which is the basic idea of using ARQ technique as far as possible to restore error after error, so here is named as "best" ARQ mechanism (Best Effort ARQ,BEA,RQ).

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