【作者】 郭雅；

【导师】 黄本雄；

【作者基本信息】 华中科技大学 ， 信息与通信工程， 2012， 博士

【摘要】 车载自组网络(VANET)是多跳移动自组网(MANETs)的一个特殊子集。配备无线接口的车辆,能够互相通信,也能与高速公路和城市道路沿线的固定设备通信。为了支持发现和维护路径,以实现在VANETs内高效的数据传输,同时为了在高可靠性、高吞吐量和尽可能低的延迟上进行信息传递,有效路由是本研究主要的问题之一。车辆移动性(包括高速,可预见,受限移动模式)和相关的PHY/MAC层实现具有独特的特征,显著地影响着实际VANETs路由协议的性能,仿真结果就可能会有所不同。因此,不同于先前这方面的工作,本研究的第一部分(包括开发新的高速公路、停车标志以及交通标志的流动性模型)考虑在修改的802.11a以及实际的车辆移动模式下的基于拓扑和基于地理的路由协议。仿真结果表明在VANETs中基于地理的路由协议适用于被动协议,在指定小/大移动性参数下的综合评估,可用来辅助解决与将来结合IEEE802. 11p设备的路由协议的配置问题。以改善吞吐量为首要目标,本研究的第二部分研究了两个新兴的方法,即网络编码(NC)和机会路由,在VANETs中的影响。NC策略通过从信源发送编码数据包到相应的信宿来细化网络中精确的数据流,并将中间节点的工作从简单的存储转发扩展到存储处理转发。另一方面,利用无线媒介的广播特性,OR主要由两部分组成,即转发组选择和转发组节点之间的优先次序,抑制了自组网络中重复数据的传输,并显著提高无线白组网络的传输可靠性和网络吞吐量等性能。根据OR机会包转发范式,NC感知路由范式考虑在中间节点上的编码机会以支持在无线自组网络中高效的数据包传递。在数据传输上,编码感知的路由协议或者处理路由选择问题,或者关注无线网络上的报文转发问题。因此,无线网络中网络编码感知路由的基本问题与确定最高编码机会的路由和找到每个节点精确的编码能力有关。探索在无线自组网络中NC感知路由的同时,这个初步的综合研究还提供了NC感知路由协议的分类。按照不同的标准,NC感知路由分为不同的类别,即主动的、被动的、集中式、分布式、源路由和逐跳路由。此外,找出一类适合高动态VANETs的NC感知路由协议也是本研究的一部分。从现有文献的来看,逐跳路由和主动NC感知路由技术比集中式源路由更适合VANETs.此外,在一个特定的高速公路的移动场景下,本研究仿真得到编码增益和编码传输的百分比,以此进一步说明了在VANETs中可使用逐跳NC感知路由。最后,确定了NC感知路由中的挑战和具体的设计问题后,本研究提出白适应基于拓扑的面向流的逐跳NC感知路由。在该方法中,编码节点需要将多个单播数据流进行编码,同时实时地估计网络的拓扑结构。仿真结果表明该方法比非编码感知路由更有优势。希望这项工作为在VANETs场景下与NC感知路由相关的研究开辟新的研究方向更多还原

【Abstract】 A Vehicular Ad hoc NETwork (VANET) is a special subset of multi-hop Mobile Ad hoc NET works (MANETs) in which vehicles equipped with wireless interfaces are able to communicate with each other as well as with fixed equipments alongside highways and city roads. To support path discovery and path maintenance for efficient data transmission within VANETs, effective routing is one of the main research issues with the primary objective of information transfer in terms of high reliability, throughput, and lowest possible delay. Unique characteristics of vehicular mobility dynamics (including high speed, predictable, restricted mobility patterns) and underlying PHY/MAC layer implementation significantly affect the performance of routing protocols in real VANETs as obtained results may vary to a great extent. Therefore, contrary to earlier work in this area, the first part of this study (with proposed modified Freeway, Stop Sign, and Traffic Sign mobility models) considers realistic vehicular mobility patterns with modified 802.11a for the evaluation of topological and geographical routing protocols. Obtained simulation results demonstrate the suitability of geographical routing protocols over reactive protocols in VANETs and this comprehensive evaluation with specific macro-/micro-mobility parameters will assist to address challenges associated with future deployment of routing protocols integrated upon devices with IEEE 802.11 p.With the primary objective of throughput improvements, the second part of this treatise deals with the study of two emerging approaches i.e., Network Coding (NC) and Opportunistic Routing (OR) as well as their implications within VANETs. NC scheme refines the precise flow of data in a network by transmitting encoded packets from certain source(s) to respective receiver(s) and extends the job of intermediate nodes from simple store-and-forward to store-process-and-forward. On the other hand, mainly composed of two components i.e. forwarder set selection and the prioritization among nodes of forwarder set, OR by taking advantage of the broadcast nature of wireless medium, suppresses duplicate data transmissions in ad hoc networks and significantly improves the performance of wireless ad hoc networks in terms of transmission reliability and network throughput. Following the opportunistic packet forwarding paradigm of OR, the NC-aware routing paradigm considers coding opportunities at intermediate nodes to support efficient packet delivery in wireless ad hoc networks. Concerning data delivery, coding-aware routing protocols either deal with route selection issues or focus on packet forwarding issues within wireless networks. Therefore, the fundamental issues with NC-aware routing in wireless networks are related to identify routes with the highest coding opportunities and the finding of exact coding capabilities at each coding node. While exploring the implications of NC-aware routing in wireless ad hoc networks, this preliminary comprehensive study provides the taxonomy of NC-aware routing protocols. Following different criteria, NC-aware routing protocols have been classified into distinct categories i.e., Active, Passive, Centralized, Distributed, Source, and Hop-by-hop.In addition, finding out a class of NC-aware routing protocols, which is suitable to highly dynamic VANETs is also the part of this study. From the synthesis of available literature, it has been concluded that hop-by-hop and active NC-aware routing techniques are more suitable for VANETs in comparison with centralized and source NC-aware routing techniques. Moreover, in a specific freeway mobility scenario, obtained simulation results in terms of coding gain and percentage of encoded transmissions also strengthen the use of hop-by-hop NC-aware schemes in VANETs. In the last, while identifying challenges and specific design issues with the implementation of the NC-aware routing in VANETs, an adaptive topology-based flow-oriented hop-by-hop NC-aware routing scheme has been proposed. In the proposed approach, a coding node takes into account the composition of multiple unicast data flows and encodes data packets while estimating the topology of the network at any instant of time. Obtained simulation results indicate the significance of proposed scheme over non-coding aware routing in VANETs. It is hoped that this work will open up new research directions with reference to the use of NC-aware routing within the context of VANETs.更多还原