【作者】 王欣；

【导师】 舒炎泰；

【作者基本信息】 天津大学 ， 计算机应用技术， 2010， 博士

【摘要】 容迟/容断移动自组织网络是一种支持节点间歇性连接的新型无线网络。这种网络由于缺乏稳定的端到端路径,数据传输延时普遍较高,无法直接使用现有的无线网络路由协议。因此,设计和改进具有“存储—携带—转发”数据转发模式的异步路由算法是容迟/容断移动自组织网络研究领域的关键问题。流行性算法是容迟/容断移动自组织网络中最早提出的路由算法之一。尽管该算法能有效保证较高的消息投递率和较低的投递延时,但巨大的网络开销严重制约了该算法在网络资源受限时的性能。本文基于流行性算法提出了自适应转发的异步路由算法ARER,该算法根据网络中消息副本的局部密度动态调节节点复制转发的频率。仿真结果证明ARER能合理控制网络中消息副本的数量,有效利用节点缓存空间,显著提高流行性算法的性能。为了利用节点地理位置信息进一步降低网络开销,本文将方向转发的思想引入异步路由算法中,提出了基于方向转发的异步路由算法ADFR。该算法使用年龄指数实现节点间位置信息的异步交换。利用节点位置信息,ADFR通过估计节点运动趋势和计算邻居向量(本节点至邻居节点)与目的向量(本节点至目的节点)之间的夹角来选择合适的转发节点。同时,ADFR还通过估计节点间链路的生存时间来限制转发消息的数量。大量仿真表明,ADFR使得消息能沿着目的节点的运动方向复制转发,在减少网络开销的同时,进一步降低了消息投递延时。现有的异步路由算法大多采用逐跳(hop-by-hop)转发模式,忽视了容迟/容断网络中存在的部分连续路径(partial multi-hop path),错失了许多更好的转发机会。本文在研究ADFR的基础上,针对节点分布不均的容迟/容断网络,提出了混合式路由算法HDFR。HDFR结合同步路由协议DSR和异步路由算法ADFR,通过利用部分连续路径,提高了消息投递率。容迟/容断网络中路由算法的性能受链路生存时间和缓存容量影响,节点通常需要对消息转发或丢弃的顺序进行调度。针对这一问题,我们采用多指标决策理论,提出了基于权重的消息传输和丢弃调度算法。该算法综合考虑了容迟/容断网络中影响消息投递的多种因素,能合理分配消息传输或丢弃的优先级。更多还原

【Abstract】 Delay and Disruption Tolerant Mobile Ad Hoc Network (DTN) is a new approach to wireless networks that may lack continuous network connectivity. The key distinguishing feature of a DTN from a Mobile Ad Hoc Network (MANET) is that there may never be a complete end-to-end path, or such a path is highly unstable and may change or break soon after it has been discovered. Since no end-to-end routing pathes exists most of the time in DTN, conventional MANET routing protocols (synchronous routing) would fail in this context. Therefore, it is necessary to study and improve the performance of asynchronous routing protocols that forward messages by the store-carry-and-forward pattern.As an original asynchronous routing protocol, the Epidemic routing protocol can effectively guarantee the delivery ratio at the cost of high overhead in terms of message replications. This would results in poor performance of Epidemic routing especially in buffer size constraint networks. In this dissertation, we proposed a new routing protocol, called Adaptive Randomized Epidemic Routing (ARER). ARER dynamically adjusts the forwarding probability for each message according to the replication density. The theoretical analysis and simulation results show that our proposed protocol can effectively improve the performance of Epidemic routing.To reduce the overhead of routing protocols in DTN, we introduced the Directional Forward scheme into asynchronous routing and proposed Asynchronous Directional Forward Routing (ADFR) protocol. Using ADFR, a node caches the position information that it ever meets, and selects the appropriate relays according to the directional angles formed by the Neighbor Vector and Destination Vector. Furthermore, ADFR limits the numbers of forwarding messages in one contact by estimating the contact duration. The simulation results show that ADFR outperforms Epidemic, Spray-and-Wai and ARER in all scenarios in terms of delivery ratio and delivery delay.Most of asynchronous routing protocols ignore the existence of partial multi-hop paths in DNT. Thus, they adopt hop-by-hop forwarding pattern and usually miss some appropriate delivery opportunities. Based on the study of ADFR, we proposed a new hybrid routing protocol, called Hybrid Directional Forward Routing (HDFR). HDFR combines the positive aspects of DSR and ADFR. The simulation results show that HDFR can improve the message delivery ratio by discovering and utilizing the partial multi-hop paths in networks.Since the performance of asynchronous routing protocols is affected by contact duration and buffer size of nodes, the priority of message forwarding and dropping should be arranged. In this dissertation, we proposed a Weighted Schedule Mechanism (WSM) based on the Multiple Attribute Decision Making theory. With this new method, the delivery ratio of asynchronous routing protocols can be improved.更多还原