A Design Of An Embedded System For Wireless Video Transmission Based On H.264

With the rapid development of mobile communication technology and multimedia technology,wireless transmission technology has been widely applied to the streaming direct broadcasting system. The technology of streaming video transmission over wireless channels has thus become the focus of study as well as a crux for researchers. Because of the properties of wireless channel, the transmission of date can be easily interfered by the Multipath effect and other environmental factors, leading to high bit error rate, high latency and jitter. The problem of how to transfer real video through the full-of-interference wireless channels has become a hotly-studied issue, and it is also the starting point of this study, too.This paper makes a comparative study, simulation and realization of related technologies for the real-time transmission of wireless networks video. The work that this author has completed consists of the following aspects:(1) As a variety of high-speed wireless transmission scheme have emerged in the market, this paper analyzes respective technological features of 3G, Wi-Fi and WiMAX, and makes a comparison of the said three kinds of wireless transmission technology under the background of wireless video transmission applications. It also compares three standards of 3G, namely WCDMA, CDMA2000, TD-SCDMA, in terms of technology and measured effect. Taking factors such as coverage, stability and cost into consideration, this author chooses CDMA2000 as the way to achieve wireless transmission.(2) According to the measured performance parameters of CDMA2000,this author has simulated 3G network transmission with the help of NS-2 software. On the basis of the output of simulations, the caps of video resolution and frame rate can thus be figured out. After analyzing, through NS-2 simulations, the advantages and disadvantages of UDP and TCP protocol for real video transmission, this author decides to apply the UDP/RTP mode to build a stable and efficient transmission channel.(3) This author then writes code to complete the video encoding module initialization, and transmits the H.264 NALU output from hardware-encoder to the RTP sending process through the System V share memory.(4) After an NS-2 analysis of the transmission performance in differently packaged RTP, the best RTP MTU is decided, and the NALU to be delivered is re-unpacked and packaged according to the RFC3984 protocol.(5) The real-time packet loss rate can be gained via RTCP the feedback of RTCP, and then the packet loss rate undergoes a filtering process to remove jitter. Because of the shortages of AIMD algorithm, this paper uses the Gilbert channel model to evaluate the bandwidth of actual wireless channel. Then the resolution rate and frame rate is adjusted based on the evaluated bandwidth, in order to ensure real-time video transmission and avoid network congestion.(6) To ensure the network's transparency and enhance network security, this author chooses P2P mixed-mode networking and applies the STUN mode to realize P2P NAT traversal.(7) Tests of video transmission quality are carried out respectively in the LAN and 3G modes. A further analysis of RTP package helps to achieve the optimal RTP MTU.