| The development of video monitoring system has experienced from the first generation--analog monitoring system to the third generation, which is supported by network and with the compression, transmission, storing and playing of digital video as core. The third generation of video monitoring system has developed rapidly by virtue of the Internet spreading far and fast and the high performance of video compression algorithm. It has been widely used in many fields, such as military, commerce and civil spheres. Restricted by the cost and layout of wired monitoring, it has great practical significance to study wireless network camera. The appearance of high performance video compression algorithm and the development of radiocommunications make it possible for us to achieve real-time video transmission in wireless environment.H.264, which is the latest international standard of digital video coding, is established by VCEG (Video Coding Experts Group) of ITU-T and MPEG (Moving Picture Experts Group) of ISO/IEC. It has the characteristics of strong network adaptability and high coding efficiency, and it can real-timely transmit high quality video flow at a low bit rate in the different network.CDMA 2000 1X develops from IS-95 which is the early standard of CDMA, and it can transmit data with a speed of 153.6kbit/s. Because of its wide coverage, it can easily achieve video monitoring under the circumstances of long-distance and great extent. The monitoring system adopting CDMA 2000 has the distinctions of low networking costs, small volume, installing simply, upgrading conveniently and so on.In this article, a network video monitoring system based on wireless environment has been carried out, combining the latest video coding standard H.264 with data transmission technology of CDMA 2000 1x. Firstly, the writer briefly introduces the CDMA 2000 1X physical channel, TCP/IP protocol, PPP protocol and the standard of H.264, then gives the solution to the the following key problems :(1)The hardware design of wireless transmission:Design PCB adopting MG815 module of ZTE, and build the hardware platform used for transmitting. (2)The software design of transmission:To make full use of the CDMA bandwidth, we abandon the TCP/IP protocol stack in the module and achieve it on a microprocessor. Where, the TCP adopts microminiature uIP protocol stack. Meanwhile, the UDP protocol and the protocol of data link layer based on PPP are achieved by programming. By using coding, working pattern of parallel transmission and cycle queue buffer strategy, the efficiency of coding and transmission has been improved greatly.(3)The design of image transmission strategy:The assignment of the transport layer protocol,writing programmes referring to the Central transmission server,making system communication protocol.The forwarding pattern gateway program is carried out. The video data adopts UDP protocol, control commend words adopt TCP protocol and a semireliable strategy for missing packets resending is established which refers to RTP protocol. The relinking of disconnection, waving of channel bandwidth and improvement of user subjective impression are all dealed with effectively. |
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