Study On Some Key Technologies And Design For Wireless Video Conferencing Systems

Wireless video conferencing system is a multimedia application in Wireless Broadband Communication Systems (WBCS), and has gained increased interest in the videoconferencing field during the last few years. Most multimedia services tend to be high-data-rate, real-time in nature and have the property of multimedia quality. But on the other hand, wireless channel is band-limited, multipath-flatting, high-error-rate etc. This implies the need to develop techniques both of video signal and wireless channel. To these issues, we develop a video conferencing system based on the OpenH323 protocol stack and study the synchronization technology of OFDM that is a basic technique of WBCS.In this paper, we present and study the realization principle and method of video conferencing systems, the basic principle of ActiveX control, the characteristic of H.323 protocol and the whole pattern of OpenH323 protocol stack. And we provide the main design idea, systematic structure and realization method. Moreover, we analyze the mixing technique of MCU audio and video in the multi-point conference. At last, the video conferencing system control runfor its performance detection in wired LAN. The results show that utilized RTP/RTCP of the media streaming transmission protocol can improve real-time transmission with some QoS guarantees for video conferencing system, which provide valuable reference for the system running in wireless network.OFDM technique maybe applied in future broadband mobile wireless communications and wireless LAN. The synchronization method is one of key technologies of OFDM systems. In this paper, an optimum algorithm by combining received signal energy (RSE) detection and delay-and-correlate algorithm for packet detection is presented for the synchronization system of OFDM. By estimating the SNR of received signals, it is easy to set an optimum threshold to decide when a new packet is coming, and to dynamically track the change of channels, so that the packet synchronization is more exactly. The new algorithm is simulated in the IEEE 802.11a system. Simulation results show that the performance of new algorithm is better than that of original delay-and-correlate algorithm.