Research On Dynamic Coding Control Mechanism In Opportunistic Networks

With the development and popularization of personal handheld devices, such asintelligent devices and Personal Digital Assistant, the architecture of Mobile Ad-hocNetworks is proposed, where there are no infrastructure and central control node, and theend-to-end path is established by the nodes to achieve communication. However, in somepractical applications scene, the nodes sparse distribution, intermittent connectivity and soon, these problems lead to the communication path fracture, meanwhile a large number ofresources are consumed to reconstruct and recover path. To solve this problem,researchers have proposed opportunistic networks, which utilize the “store-carry-forward”and cooperation method to transmit packets. Consequently, it is of great significance todesign an efficient packets forwarding mechanism.In recent years, network coding method has a variety of advantages: improvingtransmission efficiency, solving the problem of the bottleneck link and reducing thenetwork overhead, etc, seveal packets forwarding mechanisms in opportunistic networks,which are based on network coding, were proposed by researchers. However, it needs tosacrifice the node processing capabilities to improve packets forwarding efficiency.Therefore, it is very important to choose coding node and process coded packets fordesigning the mechanism with network coding in opportunistic networks.Firstly, the research background and studying status of the opportunistic networksare introduced. Then the basic principle of network coding is provided minutely, and fivetypical network coding mechanisms are described emphatically, and finally the content ofthis chapter is summarized.Secondly, on the basis of combined network coding method, a coding capabilityaware packets forwarding mechanism for opportunistic networks is proposed throughmeasuring node properties. To model the connection between the nodes, temporal graphis established to model opportunistic networks topology. Considering about the parameterof average encounter time interval, shortest length of path, reachability, the utility value ofthe node forwarding can be obtained; furthermore, the coding node can be selectedreasonably. Results show that the proposed scheme can improve the data delivery ratioand reduce the network overhead ratio. Next, in order to manage redundancy copies effectivly, a dynamic control codingredundancy mechanism with buffer management is proposed. According to the number ofreceived original packets, the relay nodes adaptively determine the number of receivingcoded packets to limit the packets coding opportunities indirectly. Meanwhile, based onoriginal packets diffusion degree and coded packets correlation, the generationredundancies can be determined, moreover, high redundancy copies are replaced timely.Simulation results show that the proposed mechanism can improve the utilization rate ofnode buffer and control the redundancy copies.