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

研究成果可分为以下四类。研究了无线局域网环境下支持切换的存储音视频传输的媒体同步质量问题。通过实验证明，基于重传的视频动态分辨率控制的差错恢复方案RVTR能够提高语音质量。我们提出了一种在PHS 64kbps尽力而为信道上连续媒体的流量控制方案，其传输容量根据网络条件在两个值之间变化。我们开发了两种类型的实验系统：一种仅在基站内改变容量，另一种通过在两个公共基站之间切换来切换容量。实验证明了该方案的有效性。对蓝牙局域网接入系统中服务器将存储的音视频流以点对点方式传输到终端时的媒体同步质量进行了实验评估。我们首先研究了来自直接序列扩频无线局域网系统的干扰和蓝牙分组类型对质量的影响。然后，我们研究了RFCOMM最大帧大小和基带分组有效载荷大小之间的差异对分段失配的影响。提出了一种根据网络状况自适应选择最佳报文类型的方案，并通过实验验证了该方案的有效性。在一个由基于路由器的IP网络和带有两个基站的无线局域网组成的有线和无线综合网络中，进行了目的地间同步控制的实验研究。有线网络中的服务器向执行从一个基站到另一个基站的切换的有线终端和无线终端多播一对音频和视频流。我们测量了目标间、流内和流间的同步质量。

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.