A Study on Preservation and Recovery Mechanisms of Temporal Structure of Continuous Media in Mobile Multimedia Communications

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The research results can be classified into the following four categories.1. We have studied the media synchronization quality for stored audio-video transmission in a wireless LAN environment with handover. By experiment, we have demonstrated that a retransmission-based error recovery scheme RVTR with dynamic resolution control of video can improve the voice quality.2. We have proposed a traffic control scheme for continuous media over a PHS 64kbps best-effort channel, whose transmission capacity changes between two values according to network conditions. We developed two types of experimental systems : one changes the capacity only within a base station, and the other switches it by handover between two public base stations. The experiment showed the effectiveness of the scheme.3. Experimental assessment of the media synchronization quality in a Bluetooth LAN access system has been made when a server transfers stored audio and video streams to a terminal with point-to-point communication. We first examined the effects of the interference from DSSS wireless LAN systems and Bluetooth packet types on the quality. We then studied the effect of segmentation mismatch caused by the difference between the RFCOMM Maximum Frame Size and the baseband packet payload size. We also proposed a scheme that adaptively selects the best packet type according to the network condition and showed its effectiveness by experiment.4. An experimental study on inter-destination synchronization control has been done in an integrated wired and wireless network that consists of a router-based IP network and a wireless LAN with two base stations. A server in the wired network multicasts a pair of audio and video streams to a wired terminal and a wireless terminal which performs handover from one base station to the other. We measured the synchronization quality of inter-destination as well as intra-stream and inter-stream.