Research On QoS Of Network-Coding-Based Wireless Networks

On the basis of information theory, Ahlswede and some researchers put forward the conception of network coding in Early2000s, which could highly improve the transmission capacity of the network so as to transmit more information with the limited network resource. Much work is targeted at finding a feasible route from a source to a destination without considering application requirements or current network traffic. Therefore, with too much traffic, the network may easily become overloaded, and the application can not improve its performance under a given network traffic condition. While this may be acceptable for data transfer, it is not acceptable for the real-time applications which require quality of service (QoS) support from the network. With the appearance of the business which requires strict QoS, QoS routing protocol for wireless networks is of great importance.Firstly, this thesis describes basic concepts, primary characteristics and typical applications of network coding, and summarizes the progress on routing protocols. Then, we comprehensively summarize and analyze the researches of recent years on the QoS issues, and discuss the problems which must be solved to support QoS in the future. Finally, we combine network coding and QoS to propose the new solution.We combine network coding and QoS to propose two new encoding schemes. The first encoding scheme is Preferred Retransmit Algorithm, which focuses on network coding based broadcast scheduling in wireless networks with the packet delay constraint and aims at minimizing the number of retransmissions. We firstly propose Cache-based Multicast Retransmission Coding and then compare it with the other coding scheme named Weighted Clique Coding. Secondly we analyze their respective advantages and disadvantages. Finally we dynamically select the scheme to enhance the transmission efficiency. The other encoding scheme is Package Length Select Retransmit Algorithm, which will dynamically select the package length and encode the packages to enhance the QoS of the real-time applications. Firstly we analyze the impact to the delay by changing the length of the package. Secondly we define a parameter for describing the gain of coding. Finally we design a algorithm, which will select the package length and encode the packages for each transmission, so as to reduce the number of the packages missing deadline. To show the efficiency of our algorithms, we present simulations using MATLAB. Results of our experiments show that Preferred Retransmit Algorithm can reduce the number of retransmissions and Package Length Select Retransmit Algorithm can decrease the deadline miss ratio of packages.