Research On Key Technoloties Of Quality Of Service For Streaming Media Transmission In Wireless Environment

With the development of wireless communication technologies, deploying steaming media services on wireless networks even in mobile environments is becoming reality. However, congestion of wired link and/or wireless link,high wireless error rate and time-varying and non-stationary characteristic of wireless channel,heterogeneity of network and client,low power consumption and portability of mobile terminals limited streaming media transmission in wireless environment. How to utilize resources with reason,control congestion and wireless error effectively,provide QoS for users as well as possible and increase the profit of service providers are key issues of QoS research of streaming media transmission in wireless environment.On the basis of the systemic analysis of streaming media characteristic,advantage and disadvantage of proposed QoS guarantee schemes, we propose an end-to-end QoS framework for video delivery over wireless networks. All main modules in this architecture are introduced. The congestion control scheme,the error control scheme and the QoS mapping algorithm in this framework are described in detail:1) Congestion control scheme. The traditional congestion control scheme judge all packet loss as congestion loss. To overcome the shortcoming of the traditional congestion control, we propose a more effective congestion control scheme. According to loss type, we adopt different control mode. If wireless error causes packet loss, then do nothing. If both network congestion and wireless error cause packet loss, then estimate the bottle link bandwidth according to the congestion loss ratio. The bandwidth estimation is more accurate, so the congestion control is more effective. At the same time, QoS parameters are mapping to bandwidth requirement. In this way, we can adapt the QoS requirement according to the bandwidth condition.2) Error control scheme. The traditional error control schemes usually add redundant packets according as packet loss ratio. This kind of schemes can cause network congestion at the same time of error control. Some error control schemes determine redundant packet number experiential and can not achieve preferable control result. The hybrid FEC/ARQ error control scheme has strict requirement of network condition and high algorithm complexity. The error control scheme in the thesis adjusts the number of data packets and redundant packets according to frame importance and network condition. The distribution scheme is then mapped to the distortion reduction. The error control result is the minimum distortion in the current network condition.3) QoS mapping algorithm. QoS is measured by different parameters in the different layers of transport protocol. The ultimate purpose of QoS support is to improve the user perceived QoS. The improvement of packet loss ratio,packet delay and delay jitter can improve the perceived QoS on a certain extent. However, the QoS improvement of the application layer is not related to the QoS of lower layers necessarily. So it is necessary to research the QoS mapping algorithm. The QoS parameters of lower layers are mapped to the improvement of distortion or PSNR. Another application of QoS mapping is translating QoS exponents in the link layer to the bandwidth requirement.