Research And Implementation On Key Technologies Of Network Reprogramming In Wireless Sensor Networks

Wireless Sensor Networks (WSN), which are self-organizing multihop network systems through wireless communication, are composed of tens of thousands of sensor nodes densely scattered in monitoring areas. After deployed, the network has a strong requirement of function updating and security upgrading. As monitoring nodes may be unreachable and the number is very large, it is unsuitable to do code updating by traditional way through directly connected serial or parallel cables one at a time. The network reprogramming technology is born on this background. It distributes code image to the whole network through wireless channel and then finishes code reloading. The paper makes research on network reprogramming technology and the key point is focused on code dissemination protocol and reloading mechanism.Firstly, on the basis of deep study of current classic code dissemination protocol, we propose a high performance protocol IDEP (an Influence, Distance and residual Energy sensitive code dissemination Protocol), which supports multihop and synthetically considers of many factors such as energy cost, completion time and so on. To get autonomy, IDEP adopts a popular epidemic approach; to promise reliability, it introduces a NACK-based retransmission mechanism; to reduce energy cost, it adopts a sender selection algorithm based on Influence, Distance and residual Energy, restrains redundant messages of sorts effectively, and decreases the frequency of off-chip Flash reading and writing; to save completion time, it supports spatial multiplex; to save and make full use of MCU memory resource, it utilizes a sharing mechanism to share the storage and uses a way of chain to organize the storage space. We use TOSSIM to simulate in this paper and the result reveals that compared to classic dissemination protocol Deluge, IDEP has almost the same completion time as before, but produces less messages and saves more energy.Secondly, to save energy and completion time more, we propose a new permanent reloading mechanism supporting multihop. Energy cost and distributing speed has direct ratio with the image size. The distributing image of traditional reloading mechanism contains all the universal functions to guarantee the capacity of reloading after code updating, and it will lead to big size of image; permanent reloading mechanism keeps some universal functions such as the image distribution fixed in the nodes sending only application module and relative basic function modules, and it will greatly reduce the size of image and considerably save the energy. The image storage structure is given and fixing image and distributing image software structure are framed in the paper. Simulation shows that the mechanism remarkably reduces the energy cost and completion time compared to traditional reloading mechanism. Thirdly, on the WSN experiment platform implemented by project developing team, based on the TinyOS operating system transplanted to sensor nodes, we use nesc language to realize IDEP and permanent reloading mechanism. At the same time, according to the concrete requirement of engineering practice, multi-mode integration oriented mechanism for dissemination and reloading is realized. From the point of practical test demands, we also use java to develop the monitoring software, implementing message parsing, filtering, statistic, process analysis and so on. To test correlative functions, we do experiments on remote reloading system and give the test report.Finally, the conclusion and prospect is given in the last part of the thesis. We conclude the paper, list the future work to be done and discuss the direction of study in times to come.