【作者】 房胜； 李旭健； 梁永全； 钟玉琢；

【Author】 FANG Sheng1+, LI Xu-Jian1, LIANG Yong-Quan1, ZHONG Yu-Zhuo2 1(Department of Computer Sci. & Tech., Shandong University of Sci. & Tech., Qingdao, 266510, China) 2(Department of Computer Science and Technology, Tsinghua University, Beijing 100084, China)

【机构】 山东科技大学计算机科学与技术系； 清华大学计算机科学与技术系；

【摘要】 MANET的链路容量随干扰、节点移动等因素的变化而变化。本文从链路容量角度出发研究MANET中流媒体传输机制。提出一种简单的基于接收方无线链路容量测试方法RWLCM的无线adhoc流媒体传输机制,利用成对数据包的发送间隔和接收间隔计算当前无线链路容量,发送方根据接收方反馈的链路容量对基于UDP的无线流媒体传输进行粗粒度码率调整。在802.11b环境下的模拟实验结果表明了提出的方法简单、反应快速而又不失稳定性,并且流媒体解码质量得到了较大改善。更多还原

【Abstract】 Pervasive computing needs the edge networks around us to be wireless and to be able to handle multimedia traffic in an effective way. From the viewpoints of mobile ad hoc networks(MANET), the scheme for media streaming over MANET should be simple, response fast and remain stable. Note the fact that the packet loss rate or congestion is a reflect of the relation of link capacity and traffic rate, this paper studies how the media streaming over MANET can be implemented directly based on the link capacity measurement, not on a complicated response function like TFRC protocol. A simple scheme of media streaming based on a receiver-based wireless link capacity measurement (RWLCM) approach was proposed. The RWLCM approach made use of the dispersion of the one-way packet pair to estimate the link capacity. In order to reduce the influence of fluctuation, which couldn’t be omitted owing to the nature of wireless techniques, the sum of one-way end-to-end delay of the transmitted packet pair was used to eliminate the fluctuated estimation. The reason was that the sum of delay of the packet pair transmission is less sensitive to fluctuation than the dispersion of the packet pair. In the presence of cross traffic the results of the RWLCM reflects the available bandwidth of the current link path. After the receiver computed the current end-to-end link capacity, it fed back the estimation to the source sender. So the sender adjusted the sending rates according to the estimated link capacity or available bandwidth. The simulations under NS software were performed to verify the validity of the proposed scheme. First the RWLCM approach was tested in 802.11b ad hoc networks, and the simulation results show that the curves of the estimated link capacities under the different link paths are in accordance with the analytical results and the transmitted video rate-distortion curves. Then the scheme of media streaming based on the RWLCM approach was simulated in a topology with moving nodes. After the topology was changed, the sending rate was adjusted according to the new acquired link capacity with a low latency. This process produces a higher decode video quality than the constant bit rate traffic. During the whole transmission even there exist some sharp fluctuations, the scheme never produced error action to adjust sending rates. All above simulation results show that the proposed simple method could adjust media streaming rates with a coarse grade fast and stable in the 802.11b MANET.更多还原