【作者】 周欢；

【导师】 King Yeung Yau； 孙优贤； 陈积明；

【作者基本信息】 浙江大学 ， 控制科学与工程， 2014， 博士

【摘要】 随着无线便携设备(如：ipad、PDAs、智能手机等)的大量普及,机会移动网络应运而生。这类网络突破了传统网络对实时连通性的要求限制,更适合实际的自组网需求。机会移动网络在传感器网络、野生动物追踪、车载网络和不发达地区的网络服务等领域具有广阔的应用前景,极大地改善了人们的生产和生活方式,因而近年来引起了学术界的密切关注。在机会移动网络中,由于时变的网络拓扑,网络中节点到节点之间很难保证有一条稳定的连通的路径。因此,节点如果有数据需要去传输的话只能先存储需要发送的数据,然后转发给和它机会性接触的其它节点。这个数据交换过程被称为“存储-携带-转发”机制,是机会移动网络中传输数据的一种基本策略。目前已经有很多的学者对机会移动网络中的数据传输问题进行了研究,但是现有的数据传输研究存在两个方面的不足：1)没有考虑节点的能量限制；2)缺乏合适的激励机制。本文结合该方向的最新研究成果,首先对邻居发现过程中的能量节省问题进行了研究,然后考虑占空比模式下的数据转发和自私环境下的数据分发问题,并提出了相应的数据转发机制和数据分发激励机制。本文主要工作和贡献包括以下几个方面：1.简要回顾了机会移动网络的产生背景、概述、主要特性、应用领域及其研究现状。2.研究了机会移动网络在随机路点模型(Random Way-Point model)下能量效率和接触机会之间的折衷。首先提出了一种理论模型去研究基于随机路点模型的接触探测过程,分别得到了单点探测概率和双点探测概率的表达式。然后,基于提出的理论模型,分析了在不同情况下能量效率和有效接触总数之间的折衷。实验结果表明,“好的折衷点”会随着节点移动速度的变化而显著变化。3.研究了机会移动网络中占空比模式下的邻居发现过程,并且为占空比机会移动网络中的邻居发现过程设计了一种能量有效的自适应工作机制。提出的自适应工作机制使用节点间过去的接触历史记录去预测节点间未来的接触信息,从而在每个周期内自适应地配置网络中每个节点的工作机制。实验结果表明,自适应工作机制在有效的接触数、递送率和递送延时方面的表现,都要优于随机工作机制和周期性工作机制。4.研究了占空比机会移动网络中占空比操作对数据转发的影响,并且为占空比机会移动网络设计了一种能量有效的数据转发策略。该策略考虑了节点间的接触频率和接触时长,并且设法将数据包沿着可以最大化占空比模式下数据传递概率的路径转发。实验结果表明,提出的数据转发策略的递送率和传染路由(Epidemic Routing)的递送率相比比较接近,但是相应的递送开销却要比传染路由的递送开销减少很多。同时,提出的数据转发策略的递送率比Bubble Rap协议和Prophet协议的递送率都要高,但是相应的递送开销却只是稍微大于Bubble Rap的递送开销。5.研究了机会移动网络中自私环境下的数据分发问题,并且提出了一种适用于自私机会移动网络的基于激励驱动的发布/订阅数据分发机制。该机制采用“针锋相对”(Tit-For-Tat,简称为TFT)机制来激励网络中的节点互相合作。同时,该机制也提出了一种新颖的数据交换协议来实现两节点接触过程中的数据交换,目的是最大化节点缓存中储存的数据的效用值。在大量基于真实数据集的性能评估中,提出的机制在总新鲜值、总传递数据和总传输开销方面都优于已有机制。最后对全文进行了总结,并对未来的研究方向进行了展望。更多还原

【Abstract】 Recently, with the rapid proliferation of wireless portable devices (e.g., ipad, PDAs, smartphones and so on), Opportunistic Mobile Networks (OppNets) begin to emerge. With-out the constraint of real-time connectivity, OppNets are more suitable for the actual ad hoc network requirements. OppNets can be widely applied in wireless sensor networks, wildlife monitoring, vehicular networks, and providing network services in underdeveloped areas, etc. Being able to greatly improve people’s production and life style, OppNets have gained high attention from global researchers.In OppNets, it is hard to guarantee end-to-end path due to the time-varying network topology, and thus nodes with data to transmit have to exchange data with relay nodes within their communication range. This data exchange process is referred to as the store-carry-forward mechanism, which works as a basic strategy of data transmission in Opp-Nets. Many researchers have studied data transmission in OppNets, but the existing studies have two aspects of deficiencies:1) without consider the energy constraint of nodes in OppNets;2) lack of proper incentive schemes for data transmission in OppNets. Based on the latest results, this dissertation first investigates energy saving in neighbor discovery, then studies data forwarding in the duty-cycle mode and data dissemination in the selfish environment, and proposes the corresponding data forwarding strategy as well as incentive scheme for OppNets. The novelty and contributions are summarized as follows:1. A brief review on the background, overview, main characteristics, application field and related work of OppNets is provided.2. Exploring the trade-off between energy efficiency and the contact opportunities based on the Random Way-Point model in OppNets. In order to investigate this trade-off, this dissertation first proposes a model to quantify the detecting probability in Opp-Nets. Then, based on the proposed model, this dissertation analyzes the trade-off between energy efficiency and the total number of effective contacts under differ-ent situations. Simulation results show that the good trade-off points are obviously different when the speed of nodes is different.3. Exploring neighbor discovery in duty-cycle OppNets, and designing an energy-efficient adaptive working schedule for duty-cycle OppNets. The proposed adaptive work-ing schedule uses the past recorded contact histories to predict the future contact information, so as to adaptively configure the working schedule of each node in the network. Extensive simulations results demonstrate that the proposed adaptive work-ing schedule is superior to the random working schedule and the periodical working schedule algorithms in terms of the number of effect contacts, delivery ratio and delivery delay.4. Exploring the impact of duty-cycle operation on data forwarding in duty-cycle Opp-Nets, and designing an efficient data forwarding strategy for duty-cycle OppNets. The proposed forwarding strategy takes into account both the contact frequency and the contact duration, and manages to forward data copies along the opportunistic for-warding paths which maximize the data delivery probability in duty-cycle OppNets. Simulation results show that the proposed data forwarding strategy is close to Epi-demic Routing in terms of delivery ratio but with significantly reduced delivery cost. Additionally, the proposed strategy outperforms Bubble Rap and Prophet in terms of delivery ratio with reasonable delivery cost.5. Exploring data dissemination in selfish OppNets, and proposing an incentive-driven publish/subscribe (pub/sub) content dissemination scheme, called ConDis (Content Dissemination), for selfish OppNets. In ConDis, the Tit-For-Tat (TFT) scheme is em-ployed to deal with selfish behaviors of nodes in OppNets. ConDis also implements a novel content exchange protocol when nodes are in contact, and the objective is to maximize the utility of the content inventory stored in nodes’buffer. Extensive realistic trace-driven simulation results show that ConDis is superior to other ex- isting schemes in terms of total freshness value, total delivered contents, and total transmission cost.The conclusions and future work are depicted in the end of the dissertation.更多还原