1、安徽建筑工业学院毕 业 设 计（翻译）专 业： 网络工程专业 班 级： 07网络工程1班 学生姓名： 学 号： 指导老师： Ad Hoc网络路由技术浅析 未来移动通信网络除了以低成本达到高数据率外，还要求网络组网灵活，具有适应性和生存能力。无线自组织网络(Ad hoc)1-4是一种没有预定的基础设施支撑的自组织可重构的多跳无线网络，可以作为蜂窝移动网络的有效加强。因此，移动自组织网络将因其灵活性而在未来移动通信网络中扮演重要作用。 1 AdHoc网络路由协议 Ad hoc网络中，由于通信半径的限制，网络节点之间是通过多跳数据转发机制进行数据交互的，需要路由协议完成分组转发决策。与传统路由协议相
2、比，Ad hoc路由协议的设计面临着网络拓扑动态变化、带宽受限、信道容量变化、移动终端有限的可用资源等新的问题和挑战。 早在1996年，因特网工程任务组(IETF)就成立了移动Ad hoc网络工作小组(MANET WG)，其核心任务就是研究无线自组织网络环境下基于IP协议的路由协议规范和接口设计。IETF RFC2501详细给出了无线Ad hoc网络的应用场合、特征和性能要求。目前，MANET WG已经公布了一系列的有关Ad hoc路由的草案，如动态源路由算法(DSR)、基于反向路径转发的拓扑分发协议(TBRPF)、优化链路状态路由算法(OLSR)、按需距离矢量路由算法(AODV)、临时按序路
3、由算法(TORA)、区域路由算法(ZRP)；此外，研究还提出了许多Ad hoc路由协议，如目的序列距离矢量路由算法(DSDV)、无线路由协议(WRP)、陆标路由协议(LANMAR)、位置辅助路由(LAR)、鱼眼状态路由算法(FSR)。 这些路由协议根据所采用的基本路由机制的不同，可分为基于链路状态的路由协议、基于距离矢量的路由协议、源路由协议及反向链路协议；按照网络逻辑结构的不同，可分为平面结构的路由协议和分层结构的路由协议；按照路由发现策略的不同，可分为表驱动路由协议、按需路由协议以及混合路由协议。 2 大规模AdHoc网络中的路由技术 Ad hoc网络规模性5的研究可以广义地定义为：研究当
4、网络中有大量节点存在时，网络能否为分组提供可以接受的服务，它与网络大小、节点分布的密度、运行的环境(传播模型、地型环境等)及移动性相关。 对于中小规模(通常为几十个节点)Ad hoc网络路由协议的研究已取得了重要进展，而大规模Ad hoc网络的路由技术是Ad hoc网络研究的一个难点，它是指可以支持数百到数千个网络节点的路由算法。国际上早期的一些初步研究结果6，如Santivanez等人提出的基于链路状态法的模糊链路状态(FSLS)算法，研究了节点数为100400时的部分性能；Woo和Singh提出了一个基于位置修正的SLURP算法，研究了节点数为501 000时的算法性能；Jinying L
5、i等提出了基于区域的网格(Grid)系统，研究了100600个节点时的算法性能；Rahul Jain等人提出了基于地理位置的路由算法，研究101000个节点的算法性能。 现有的路由协议或者利用全网泛洪(Global flooding)或者利用分层的方法完成路由的发现。但是，前者由于开销太大并不适合大规模的网络；后者在分层的过程中需要交互大量信息，而且可能由于节点的移动造成性能的急剧恶化。为了克服这些缺陷Nitin Nahata等人提出了一种基于连接(Contact)点的适用于大规模Ad hoc网络的高效的路由发现策略7。它基于“小世界(Small world)”的概念，采用了一种混合的方式：在
6、节点的R跳(通常是35跳)范围内采用先验式的路由算法，如DSDV，而在R跳以外通过Contact点进行反应式的路由发现。Contact点是一些捷径点，它通过减小分割度来把网络划分成为一些“小世界”。图1所示为这个过程的示例。此外，Taejoon Park等人还提出了一种基于地理位置的适用于Ad hoc网络的路由协议8，它在节点本地区域和分布区域中结合了位置更新机制，同时还根据位置更新门限得到一个最优的配置，以此减小总的路由开销。该协议具有可扩展性，并且路由开销较小，从而延长了节点的寿命。 3 基于新物理层技术的AdHoc路由 为了满足人们日益增长的通信需求，能够提供更大带宽的物理层传输技术层出
7、不穷，如认知无线电技术、协同通信技术以及多输入多输出(MIMO)天线技术等。它们的出现为Ad hoc网络路由技术的进一步发展带来新的契机。 3.1基于认知无线电的路由协议 众所周知，频谱资源十分有限，一些非授权频段占用拥挤，而那些授权频段却经常空闲，因此，可以考虑在授权用户不用自己的频率资源时，让一些非授权用户去暂时性地有效利用该空闲频谱，认知无线电9就是基于这种想法提出来的一种更智能的频谱共享技术，它可以感知无线通信环境，依据一定的学习和决策算法，动态地检测和有效地利用空闲频谱，大大降低了频谱和带宽对无线技术发展的束缚。它要求非授权用户和授权用户在对频谱资源利用时达到一个平衡，使得非授权用户
8、能在不影响授权用户的前提下进行一些自己的通信。 认知无线电技术的特点使得节点间的链路可能经常发生变化，因此，这样的路由协议首先应该是鲁棒的(Robustness)，这种鲁棒性是基于多路径分析的。多一条备选的路由可以大大降低一条路径失效对网络造成的影响，使得网络具备鲁棒性。此外，这样的路由协议还应满足3点要求10： (1)路由协议应该是先验式的 如果采用了反应式的路由协议，更新路由表太浪费时间，分组若要以最小的时延传输就需要采用先验式的路由算法。但是，先验式路由协议会引入更多的控制分组数，而且路由信息的不断更新反而会缩短节点能量的持续时间。 (2)路由协议应该是基于链路状态的 由于物理层的参数经
9、常变化，节点的移动性及传输半径也可能改变，节点的认知能力也有所差异，因此，节点间的链路可以通过计算链路的可靠性来进行选择。 (3)路由协议应该是分级的 分级的路由协议支持不同的移动组。目前认知无线电环境下，以信道的切换次数以及信道的切换频率为衡量标准，已经有基于控制信道的路由算法以及基于空时分组码的路由算法。 3.2基于协同通信的路由协议 协同通信11-13利用节点间的相互协作进行数据通信。它充分利用了无线电波的全向传播特性，使无线网络中的节点相互协作形成了虚拟的天线阵列来获得传统多输入多输出天线技术的空间分集增益，当前协同通信的主要方式有：编码协同，放大中继，解码中继等方式。相对于其他协同方
10、式，编码协同方式将协同通信技术和信道编码技术相结合，在不消耗更多系统资源(带宽等)的前提下获得完全的分集增益。图2所示为协同路由和一般多跳路由的区别。 当有从S节点到D节点的数据要发送时，数据依靠中间节点的中继就会到达目的节点，而对于协同路由来说，数据可以经过S1D完成传输，同时，位于节点S覆盖范围内的节点2、3也可以听到这样的信息，它们可以不用付出额外的能量去传输数据，这样，就可以消耗更小的能量。目前，基于协同技术的路由可大致分为两类，分别是基于能量的路由策略和基于带宽的路由策略。基于能量的路由策略12-13主要针对单个源和目的节点的应用环境，在保证源节点发射信号在接收节点处能达到接收信噪比
11、门限的基础上，通过为协同节点最优化地分配功率，从而达到降低网络总能量开销的目的。基于带宽11的路由策略主要是通过引入协同通信技术，以最大化源节点到目的节点间路径的带宽为目标完成路由决策。协同技术在该种路由机制中主要有两种应用方式11。一种是在选择好一条源到目的节点路由的基础上，通过在每一跳节点间根据对带宽的改善程度有选择地进行协同，达到提升路由传输能力的目的。这种方式可称为基于协同的路由。另一种方式是在路由选择的同时就考虑到协同技术对每跳传输带宽的影响，从而决定每跳传输是否采用协同通信技术，并选择该情况下带宽最大的路由进行数据传输。该方式称为动态协同路由。 3.3基于MIMO的路由协议 MIM
12、O系统利用空分复用和分集，在不增加额外功率和带宽的前提下提供高的频谱利用率，作为智能天线技术中一个最复杂的技术，MIMO链路现在被普遍应用，并且已经进入了无线局域网(WLAN)、WiMAX及Ad hoc领域，与其相关的路由技术也是现在研究的一个热点问题。 目前基于MIMO的适应于无线自组织网络的路由协议并不多见。K.Sundaresan等人在2005年的IEEE 的国际会议(ICNP)上，发表了论文Routing in Ad-Hoc Networks with MIMO Links14。该文给出了一种适应于MIMO信道条件的自适应路由协议。该协议通过利用MIMO系统两种不同的工作模式：空间复用
13、和空间分集来实现路由的自适应选择。在空间复用模式中，节点通过每个天线发射不同的数据流，能够获得复用增益，提高链路以及整个路由的传输容量。在空间分集模式中，节点在每根天线上发送相同的数据流，以获得分集增益。这种分集技术能够有效地提高通信系统的抗干扰能力，降低系统传输的误比特率，提高链路及路由传输的可靠性，能够满足无线信道条件较差环境的应用要求。 4 结束语 本文综述了无线Ad hoc网络中的主要路由协议，着重介绍了能够适应大规模网络环境的Ad hoc网络路由协议及基于新物理层技术的Ad hoc网络路由协议。这些方法在一定程度上可在不同层面满足Ad hoc网络的路由需求。随着人们需求的不断提高，网
14、络的规模化发展是一个必然趋势。如何在大规模的网络中提出更能符合实际应用的路由协议，并结合新的物理层技术实现网络中多种路由协议的平滑过渡是今后Ad hoc网络路由技术研究的重要方向。Analysis of Ad Hoc Network Routing TechnologyAuthor: ShengMin LiJiandong TianYe Future mobile communication network in addition to the cost to achieve high data rate, also called network networking flexibility,
15、 adaptive and survival. Wireless ad hoc networks (Ad hoc) 1-4 and is not a pre-self-organization of infrastructure support reconfigurable multi-hop wireless networks, cellular mobile network as an effective strengthening. Therefore, mobile ad hoc network because of its flexibility in the future mobi
16、le communication networks play an important role.1 AdHoc network routing protocolsAd hoc networks, due to limited communication radius of the network nodes multi-hop data forwarding through the data exchange mechanism, the need to complete the routing protocol packet forwarding decisions. Compared w
17、ith the traditional routing protocol, Ad hoc routing protocol design facing dynamic network topology, bandwidth limited channel capacity change, mobile terminals such as the limited resources available to new problems and challenges.Back in 1996, the Internet Engineering Task Force (IETF) set up a M
18、obile Ad hoc Networks Working Group (MANET WG), its core mandate is to study the environment of wireless ad hoc network routing protocols based on IP protocol specification and interface design. IETF RFC2501 given in detail in wireless Ad hoc network applications, features and performance requiremen
19、ts. Currently, MANET WG has published a series of draft on Ad hoc routing, such as dynamic source routing algorithm (DSR), based on reverse path forwarding topology distribution protocol (TBRPF), optimized link state routing algorithm (OLSR), by distance vector routing algorithm to be (AODV), the te
20、mporary sequential routing algorithm (TORA), the regional routing algorithm (ZRP); In addition, the study also raised a number of Ad hoc routing protocols, such as the target sequence distance vector routing algorithm (DSDV), Wireless Routing Protocol (WRP), Landmark Routing Protocol (LANMAR), Locat
21、ion Aided Routing (LAR), fish-eye state routing algorithm (FSR).The routing protocol used in accordance with the basic routing mechanism can be divided into link state routing protocol, based on distance vector routing protocols, source routing protocol and the reverse link protocol; according to th
22、e different logical structure of the network can be divided into planar structure for the hierarchical structure of the routing protocols and routing protocols; according to the different route discovery strategies can be divided into table-driven routing protocols, on-demand routing protocol and hy
23、brid routing protocols.2 large-scale routing in AdHoc NetworksAd hoc network size of 5 can be broadly defined as the study: To study a large number of nodes when the network exists, whether the packet network to provide acceptable service, which the network size, node distribution density, operating
24、 environment (propagation model, ground-based environment) and mobility related.For small and medium scale (usually dozens of nodes) Ad hoc routing protocol research has made important progress, and large-scale Ad hoc network Ad hoc network routing technology is a difficult study, it is one that can
25、 support hundreds to thousands of network nodes, the routing algorithm. Early international results of some preliminary studies 6, and others such as Santivanez proposed link-state method based on fuzzy link state (FSLS) algorithm to study the number of nodes 100 and 400, part of the performance; Wo
26、o and Singh proposed a location-based correction SLURP algorithm to study the number of nodes is 50 to 1 000, the algorithm performance; Jinying Li and other proposed based on the regional grid (Grid) system to study the 100 to 600 nodes when the algorithm performance; Rahul Jain et al proposed loca
27、tion-based routing algorithm to study the 10 to 1000 nodes the algorithm performance.Or use the existing routing protocols flood the whole network (Global flooding) or use a layered approach to complete the route discovery. However, the former as too costly is not suitable for large-scale networks;
28、the latter is required in the stratification process large amounts of information interaction, and may be due to node mobility caused a sharp deterioration in performance. To overcome these shortcomings Nitin Nahata, who proposed a connection-based (Contact) point for large-scale Ad hoc network rout
29、ing discovery and efficient strategy 7. It is based on Small World (Small world) concept, using a hybrid approach: the nodes of the R hop (usually 3 to 5 hops) within the a priori type of routing algorithm used, such as DSDV, and in R Contact point jump outside the reaction through route discovery.
30、Contact points are some shortcuts point division by reducing the degree to which the network is divided into a number of small world. Figure 1 shows an example of this process.In addition, Taejoon Park, who also proposed for a location-based routing protocol for Ad hoc networks 8, its regional node
31、in the local area and the distribution of a combination of location update mechanism, and also under the threshold to get a location update optimal configuration, thereby reducing the total routing overhead. The protocol is extensible, and less routing overhead, thus extending the life of the node.3
32、 physical layer technology based on new AdHoc RoutingIn order to meet the growing communications needs, providing greater bandwidth to the physical layer transmission technology after another, such as cognitive radio, cooperative communications and multiple-input multiple-output (MIMO) antenna techn
33、ology. They appear as Ad hoc network routing technology, further development has brought new opportunities.3.1 Routing Protocol based on cognitive radioAs we all know, very limited spectrum resources, a number of non-authorized frequency band occupied by crowded, and those bands are often free licen
34、se, so you can consider the frequency of authorized users without their own resources, so that some non-authorized users to temporarily effective use of the free spectrum cognitive radio 9 is based on the idea put forward a more intelligent spectrum sharing technology that can sense wireless communi
35、cation environment, according to some learning and decision-making algorithm, dynamic detection and effective use of idle spectrum, greatly reduce the frequency and bandwidth constraints of wireless technology development. It requires non-authorized users and authorized users of the spectrum reached
36、 a balanced use of resources, so unauthorized users can not affect the authorized user under the premise of some of their communications.Cognitive radio technology features make the link between nodes may change frequently, so this should first routing protocol is robust (Robustness), this robustnes
37、s is based on the multi-path analysis. More than one alternative path routing can significantly reduce the impact of failure on the network, making network has robustness. In addition, such a routing protocol should meet the requirements of 3 10:(1) routing protocol should be a priori-likeIf using a
38、 reactive routing protocol, routing table updates a waste of time, packet transmission delay to a minimum on the need to adopt a priori type of routing algorithm. However, a priori routing protocol will be the introduction of more number of control packets and routing information constantly updated
39、but will shorten the duration of the node energy.(2) routing protocol should be based on link-stateSince the physical layer parameters often change, node mobility and transmission range may also change the nodes cognitive abilities also vary, so the link between nodes link reliability can be calcula
40、ted to be selected.(3) routing protocol should be gradedHierarchical routing protocols to support different mobile groups. Current cognitive radio environment, the number of channel switching and channel switching frequency measurements have been based on the control channel routing algorithm and ST
41、BC-based routing algorithm.3.2 Routing Protocol Based on Cooperative CommunicationCooperative communication 11-13 The mutual cooperation between the nodes for data communication. It takes full advantage of radio waves all the propagation characteristics of the wireless network nodes collaborate to f
42、orm a virtual antenna array to get the traditional multiple-input multiple-output antenna technology, spatial diversity gain, the current cooperative communication of the main methods are: Code Collaborative , zoom relay, decoding relay, etc. Compared to other collaborative, coding collaboration col
43、laborative communication technology way and channel coding technology, not consume more system resources (bandwidth, etc.) under the premise of diversity gain access to the full. Figure 2 shows the route and general coordination of the difference between multi-hop routing.When a node from S to D nod
44、e to send data, the data will rely on intermediate nodes to reach the relay destination node, and for collaborative route, the data can be subjected to S 1 D completes the transfer, while at the node S 2,3 nodes within the coverage area can also be heard this information, they can not pay the extra
45、energy to transmit data, so that can consume less energy.Currently, collaborative technology-based routing can be broadly divided into two categories, namely, the energy-based routing strategy and routing policy based on bandwidth. Energy-based routing strategy 12-13 the main source and destination
46、nodes for a single application environment, in ensuring the source node transmit signals at the receiving node can achieve the received SNR threshold, based on the node through the optimal allocation of cooperative power, which can reduce the total energy cost for the purpose of the network. Based o
47、n the bandwidth 11 routing strategy is through the introduction of collaborative communications technology, to maximize the source node to destination node bandwidth of the path between the target to complete the routing decisions. Cooperative routing in this kind of application, there are two main
48、ways 11. A good choice is a source route to the destination node, based on the hop by each node based on the bandwidth between the degree of selective improvement of coordination, to enhance the transmission capacity of the purpose of routing. This can be called a route based on collaboration. Another way is in the r
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