on connectivity-aware and reliable data dissemination in vanets

车载自组织网络可以通过多跳无线广播实现远距离的数据传输,但网络拓扑的快速变化和无线通信质量的不稳定会导致数据传输性能的不稳定.为了应对这些挑战,文中提出了一种适用于城市场景的可靠的、连通度感知的数据分发机制.该机制利用实时收集的交通流量数据,建立路口车辆排队长度变化的马尔可夫模型,并基于此模型估算路段间无线网络连通度的实时变化,以便数据沿最小延迟路径进行转发.该机制还考虑到城市环境对无线信号的干扰,用覆盖消除规则改进了贪心广播算法,通过多候选转发策略增强了路段间数据传输的可靠性.模拟实验结果表明,与基于传染病的数据分发协议、基于静态节点的自适应数据分发协议相比,文中提出的机制能实现高可靠、低延迟的数据分发.国家自然科学基金(60970027,91124001)资助In VANETs (Vehicular Ad-hoc Networks), data can be transmitted to long-distance targets through multi-hop wireless broadcast, but the rapid changes in network topology and unstable wireless communication quality will cause performance unsteady for data transmission over VANETs. To meet the challenges, a reliable and connectivity-aware data dissemination mechanism which is applicable to urban scenarios is proposed. The proposed mechanism uses the traffic-flow data collected at intersections in realtime to build a Markov model of queue length change of vehicles, and then estimate the real-time varying of connectivity of wireless networks on the roads of two adjacent intersections so as to choose the minimum delay path to forward the data. For reliable data transmission, an improved greedy broadcast algorithm which merges into coverage elimination rule and multi-candidate strategy is also designed to ease the interference of urban environments. The simulation experimental results show that our mechanism can achieve high reliable and low-delay data dissemination in comparison with the epidemic-based protocol and the static-node-assisted adaptive data dissemination protocol

spatio-temporal event detection using pub/sub middleware

摘要:许多物联网应用根据带有时空关系约束的事件决定其下一步的动作.为了支持物联网应用检测这些时空事件,构建了发布/订阅中间件OPS4ST.OPS4ST允许用户在订阅中表达事件之间的多种时序、空间和逻辑关系；同时实现了时空事件的分布式检测,其能高效地检测到用户在订阅中所关心的时空事件是否发生.通过模拟实验评估了系统的性能和开销,实验结果表明,OPS4ST具有令人满意的性能和可接受的开销.国家自然科学基金(60970027)资助Many applications in the internet of things(IoT) decide their next actions according to the occurrences of events with temporal and spatial constraints.In order to help IoT applications to detect spatio-temporal events,the paper built a Pub/Sub middleware OPS4ST.OPS4ST permits users to express in their subscriptions diverse temporal,spatial and logical relationships of events,implements the detection of spatio-temporal events in a distributed way,and can efficiently detect whether the spatio-temporal events to which the users pay attention in their subscriptions occur.The paper also evaluated OPS4STs matching performance and costs by simulation experiments.The experimental results show that OPS4ST can achieve satisfying performance and acceptable overheads