摘要：
Ad hoc网络是一种工作在无固定结构环境下的自组织的无线移动网络。它适用于军事或是一些战略应用场合，例如，战场上部队快速展开和推进、发生地震或水灾后的营救等。在没有网络基础设施的情况下，Ad hoc网络可以快速组网，其节点可以移动，网络中的每个节点既充当主机又充当路由器。由于Ad hoc网络具有组网快捷、灵活，且不受有线网络约束等优点而具有广泛的应用前景。 由于Ad hoc网络的拓扑动态性，使得常规路由协议在该环境下无法正常运行。因此，对该环境下路由协议的研究成为了Ad hoc网络中研究的主要课题。
本文首先研究了现有的Ad hoc路由协议，分别介绍了两类路由协议，主动路由协议和按需路由协议。然后使用网络仿真软件NS-2对代表了Ad hoc的两类协议的四种典型路由协议进行了仿真，包括AODV，DSR，DSDV和TORA。给出了在不同的移动和流量场景下，这四种Ad hoc典型路由协议的仿真结果。结果表明按需路由DSR的性能较优越，特别是在路由开销方面。但是在高负载的情况下，其路由发现机制中的查询泛洪会使这种优势大大降低。
针对这种情况，本文提出了一种新的控制按需路由查询泛洪的多径路由技术。它使用备选路由来减少泛洪发生的频率。文中研究了两种不同的多径技术，一种只在源路由有备选路由，另一种是初始路由中的所有节点都有备选路由。仿真结果表明这两种多径技术都能显著减少协议的路由开销，而且当初始路由中的所有节点都有备选路由时，协议的路由开销更小。
目前，关于Ad hoc网络路由协议的研究才刚刚起步，而路由协议是关系到Ad hoc网络能否运行的关键因素，因此本文对Ad hoc网络中路由协议的研究和优化不仅在理论方面具有重要意义，而且为其应用提供了科学依据。
关键词：Ad hoc网络、NS-2、路由开销、DSR、多径路由
Abstract：
A mobile Ad hoc network is an autonomous system of mobile hosts connected by wireless links. Such networks are useful in military and other tactical applications, e.g., emergency rescue or exploration missions, where cellular infrastructure is unavailable or unusable. In such a network, each mobile node operates not only as a host but also as a router. This network has a series of the strengths, for example:MANET can be built rapidly and easy, and it is not set measures to by wired network, and so on.无忧论文 【http://www.uklunwen.com】>Because of constantly changing topology, Ad hoc networks can't adopt traditional protocols. Research of routing protocols becomes the most important part of the research of Ad hoc. This dissertation presents a comparative simulation study of on-demand protocols with the more traditional proactive protocols on a common platform across a range of traffic and mobility scenarios. This simulation cover a range of design choices: AODV, DSR, DSDV, TORA. The simulation results show that on-demand protocols indeed demonstrate low routing overheads, but over-reliance on query flooding can actually cause on-demand protocols to lose most of this overhead advantage at high loads.
As a countermeasure, we develop and evaluate a technique called multipath routing that reduces the routing overhead for on-demand protocols. Multipath routing, focuses on reducing the frequency of query flooding by exploring multiple, disjoint routes per flood operation. This provides the routing protocol with alternate routes when the primary route breaks. Two variations were explored. In the first, only the source gets multiple alternate routes. In the second, each intermediate node on the primary route gets an alternate route (aside from the source). Simulation results show that either of these techniques can reduce routing overheads significantly. When each intermediate node on the primary route gets an alternate route, the routing overheads are smaller.
At present, the research about Ad hoc network ro
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