Research On Node Relation Aware Cooperative Caching Mechanism In Opportunistic Networks

Different from traditional single-hop and multi-hop wireless networks, Opportunistic Networks can achieve the hop-by-hop “storing-carrying-forwarding” data communication between nodes in scenarios of interrupted wireless links and partitioned networks. Due to the network deployment cost requirements, the buffer resources of nodes in Opportunistic Networks are generally restrained. To enhance the data delivery rate, nodes generate multiple copies for a given message and the storing of redundant copies can severely affect the node buffer utilization. Therefore, designing a reasonable buffer management mechanism is crucial for the performance improvement of Opportunistic Networks. Due to the limited communication range and frequently disconnected links between nodes, the message delivery process is collaboratively achieved by multiple nodes. Therefore, to precisely perceive the collaborative relationship between nodes and accordingly enhance the buffer utilization, a more reasonable buffer management mechanism should be carefully designed.Firstly, this thesis introduces research backgrounds, network architecture, application scenarios and key technologies of Opportunistic Networks. Furthermore, existing buffer management mechanisms for Opportunistic Networks are introduced, analyzed and compared. Eventually, the design objectives of buffer management mechanisms for Opportunistic Networks are proposed.Secondly, by dynamically estimating the message importance degrees according to the message diffusion degrees, a node status aware distributed cooperative cache management mechanism is proposed in this thesis. Based on social network theory, the node activity degree and relative viscosity can be exploited to evaluate the encounter probability between nodes. By collaboratively replacing messages in the buffer, nodes can carry messages with relatively high encounter probabilities with target nodes. Meanwhile, the set of collaborative nodes can be accurately determined for the data forwarding process, according to the encounter probability and encounter duration between nodes. Simulation results show the proposed collaborative buffer mechanism can sufficiently utilize the node buffer resources to substantially improve the network performance.Thirdly, on the basis of the cooperation willingness, a cooperative caching mechanism with cooperation willingness perception is proposed in this thesis. By comprehensively considering the node buffer capabilities and service relationship between nodes, the difference between node collaboration willingness can be evaluated to design the efficient buffer mechanism. Simulation results show the proposed collaborative buffer mechanism can effectively reduce the network load and average delivery delay whiling improving the message delivery rate.Finally, the conclusion and research prospects are given.