Research And Implement Of Wireless Stream Media System Based On Pocket PC

During recent years, there is great development in computer technology. Embedded system's core chip has been up to 400MHz, and the mobile device has some the Audio and Video codec ability. In wireless communication area, It have developed from GSM network that provided with 9600bps data channel, to 3G mobile network that provided with 2Mbps data channel bandwidth. The wireless LAN can provide up to 54Mbps bandwidth. Both the wireless network's channel quality and channel bandwidth are enough to allow a large amount of data's transmission. Meanwhile, the video compresses technology' progress from H.261 to MPEG-4, and then to H.264, has the ability to allow the transmission of high-quality video over the unstable wireless channel.For the limitations of bandwidth of the mobile network, the mobile devices can only offer the not real time multimedia service of low-quality. People hope urgently mobile devices can offer real-time stream media service or non-real-time and high-quality video, for instance IPTV, long-distance surveillance system etc. When 3G network be widespread, the mobile stream media will be in great demand.This issue is on the basis of the implement of wireless video surveillance system on Pocket PC, research wireless mobile stream media's video quality guarantee technology and transmission control strategy to a certain degree. For the wireless mobile stream media, must consider the characteristic of the wireless network and performance of mobile devices. As to the high channel bit error ratios of network, error control mechanism must be employed to protect coded video data to make the video decoder resume from error. For the limited bandwidth of the wireless network and the limited compute ability of mobile devices, the rate control must be employed in encoder and the mobile device perform the rate control based on receiver's packet loss ratio.At the last, the article put forward some suggestions about system's optimization and improvement. This system is developed for a series of digit network cameras, and has already passed confirmation. The system has proved its practicability.