Reasearch On Key Points For Multimedia Communications In Wireless Multihop Networks

With the latest developments in multimedia coding technology and fast deployment of end-user wireless connections, real-time media applications become increasing interesting for both private users and businesses. However, most of current wireless networks remain a best-effort service network unable to guarantee the stringent requirements of the media application, in terms of high, constant bandwidth, low packet loss rate and transmission delay. Therefore, efficient scheduling mechanism must be derived in order to bridge the application requirements with the transport medium characteristics. Up to now, multimedia communications over wireless multi-hop networks is still an open problem. In this dissertation, we study some key technical points about this topic and propose some practical and efficient resolution from the following aspects:Within a cross-layer design framework, we first address the problem optimal mulpath routing. Here, we invest the combination of the routing and rate control in a united convex optimization formulation, and propose a distributed joint solution based on cross-layer design. We first develop a distortion model which captures both the impact of encoder quantization and packet loss due to network congestion on the overall video quality. Then, the optimal joint rate control and routing scheme is realized by adapting its rate to the time-varying traffic and minimizing the overall network congestion.Next, we address the problem of joint authentication-coding mechanism. In this part, we propose a framework for jointly authenticating and coding multimedia to be transmitted over wireless networks. We firstly provide a novel graph-based authentication scheme which can not only construct the authentication graph flexibly but also trade-off well among some practical requirements such as overhead, robustness and delay. And then, a rate-distortion optimized joint source-channel coding (JSCC) approach for error-resilient scalable encoded video is presented, in which the video is encoded into multiple independent streams and each stream is assigned forward error correction (FEC) codes to avoid error propagation.Furthermore, we consider integrating authentication with the specific JSCC scheme to achieve a satisfactory authentication results and end-to-end reconstruction quality by optimally applying the appropriate authentication and coding rate.Robust resolution-enhancement scheme problem is addressed next in our thesis. We propose a coordinated application of ER (Error-Resilient) and SR (Super-Resolution) to enhance the resolution of image transmitted over wireless networks. In order to combat error propagation, a flexible multiple description coding method based on shifted 3-D SPIHT (3-D Set Partitioning in Hierarchical Trees) algorithm is presented to generate variable independent descriptions (sub-streams) according to the network condition. And then, a novel unequal error protection strategy based on the priority level is provided to assign a higher level of error protection to more important parts of bit-stream. Moreover, a robust SR algorithm is proposed in the presence of different kinds of packet loss rate to enhance the image resolution.Finally, we describe the problem of rate control for multimedia over heterogeneous networks. In this part, we develop and evaluate a framework for optimal rate allocation over multiple heterogeneous networks based on cross-layer design framework. At first, we develop and evaluate a distortion model according to the observed available bit rate and the round trip time in each access network, as well as each application's rate-distortion characteristic. Then, the rate allocation is formulated as a convex optimization problem that minimizes the sum of expected distortion of all application streams. In order to get a satisfying and simple resolution for this problem, we propose a piecewise-approximate theorem to simplify the convex optimal problem and prove its validity in theory. Furthermore, the realization of the fast heuristic rate allocation algorithm for achieving an optimal or close-to-optimal end-to-end QoS under the overall limited resource budget is the highlight of this paper.In the end, a brief summary of all discussed topics in this dissertation is given. The main contributions of this dissertation and several further studies or worth studies are pointed out at this part.