Design And Implementation Of PDA Audio-video Communications System Based On Satellite Transmission

With the video-conference technology becoming maturity and the increasing performance of PDA devices, embedded streaming media communication technologies become a hot research. At the same time, along with the development of satellite communications technology and the global coverage of satellite signals, the development of PDA audio-video communication system based on satellite transmission, which is used to respond to natural disasters and scientific exploration activities, has important practical significance.The design and implementation of PDA audio-video communications system based on satellite transmission is studied in this paper. After the satellites communication modes being studied, the International Maritime Satellite System is selected as the audio-video data transmission system. The PDA audio-video communications system is modular designed and is consist of audio-video communications control module, audio-video capturing and playing module, audio-video codec module, data real-time transmission module and quality of service (QoS) guarantee module. The TCP Socket technology is adopted to implement the control of audio-video communications. The Win32 API is called in PDA video capturing. The Waveln/WaveOut technology is used to capture and play voice. The G726 codec and the Xvid codec are chosen for audio-video codec. The JRTPLib technology is used to guarantee the real-time transmission of audio-video data. According to the satellite channel's characteristics, the solutions of the delay jitter control, the audio-video synchronization control and the packet loss rate control are studied and implemented in the QoS module. The system has been tested and run on the Marine Satellite Channel and it has met the system requirements.The PDA audio-video communications system based on satellite transmission has the following characteristics: (1) the system could communicate with the Control Center server anywhere of the Earth's surface by satellite; (2) the audio-video communications system can be bandwidth self-adaptive when the quality of satellite channel becomes poor, and the audio communication has priority ensure; (3) the system can run well in any IP-based wireless networks, including the satellite networks, the WiFi, the GPRS and the CDMA, etc.; (4) some open-source projects are used in system development, which is good for understanding and optimization in the future.