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The Research and Application on Forwarding Mechanism in the Opportunistic Networks

Author: DengZuoBo
Tutor: LiLian
School: Lanzhou University
Course: Applied Mathematics
Keywords: opportunistic networks forwarding localization path prediction Markov chain middleware contact time coverage
CLC: TN929.5
Type: PhD thesis
Year: 2011
Downloads: 300
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Abstract

Since the ad hoc networking technology emerged from last century, there has been abundant research production which hardly been prevalent to implement in reality. The most important reason is that the ad hoc network could work unless with a complete connectivity condition, and the data can be forwarded via mid-nodes from source to destination. However, because of the network disconnecting frequently caused by movement of nodes, block of some other objects, signal interference, invalidation of nodes or energy limit, the network is often divided into several regions which cannot communicate each other but keeping link within them.Then the opportunistic network (Oppnet) was proposed for this situation. In the Oppnet, all of the nodes are divided into several isolated parts in which nodes can link each other. There might be no a whole existing path from source to destination. The only communication opportunity is created through the encounter among moving nodes, and then data could be transferred between two meeting nodes. Therefore, as a more natural manner of networking, the Oppnet is fit for networking and application of those mobile devices with capability of short-distance communication, for instance, wireless sensors, vehicular intelligent devices and hand devices.The forwarding mechanism is one of the key problems in Oppnet research, which means to choose the most reasonable mid-node for the next hop. The thesis mainly focuses on the aspect of this problem and has achieved the following work.1. A distributed computing environment which is called ON-DEC based on Oppnet was proposed to carry out distributed computing in many hand mobile devices. We described its work flow at first and analyze the dissemination method occurred during the down phase which includes two different way called DWOF and DWF respectively, and then we compared these two ways and proved DWF was more effective. Based on this result, we demonstrated the upper bound of value for k which could be used to control the number of copy of tasks.2. During the up phase, we proposed a forwarding mechanism based on path prediction called TPFA. The core step of the mechanism was to establish Markov probability transition matrix by analyzing the data set of history trace about the nodes in order to predict the next path at crossway afterwards. At the same time, a fault-tolerant mechanism was built to insure the data can be transferred to another right node while there was an error in prediction, which could help the data being sent back to the AP with a higher successful rate.3. Afterward, we discussed the point technology to implement the whole mechanism. Since some kind of different OS and IDE are often used during the corrent mobile developing, we proposed an over platform middleware of communication service, and then discussed its fundamental design principle and structure.4. In the third part of the thesis, we proposed an Oppnet based monitoring system, which aimed at improving on the inadequacy of current near-earth monitoring technology in the desert environment. The system can sensor data about the wind or desert and characterize the wind in the desert condition. We designed the framework of the system firstly and then analyzed how to deploy the base stations and removable wireless sensors. Next we computed the lower bound of nodes’number which ensured enough data acquired by sensors could be uploaded to the base stations.5. After that, a queue localization algorithm DELA based on the location information of nodes movement at different places covered by two or three base stations, displacement and moving state of nodes was proposed to calculate the nodes’location.6. At last, we proposed an adaptive forwarding mechanism CTFM which could decide whether it’s time to upload the data to the base stations according to the contact time between the node and base station. If node moves too fast or the contact time is too short to forward data, it would stop broadcasting to save the finite energy.

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