Vehicular ad hoc network

A vehicle ad- hoc network (English Vehicular Ad Hoc Network, VANET ) is a mobile ad hoc network ( MANet ), whose nodes are vehicles. When nodes in a VANET vehicles are usually considered. As with a MANet is a self-organizing and decentralized network. Vehicle Ad -hoc networks are, in contrast to MANETs, only the subject of research in computer science. Established a national or international vehicle ad-hoc network for the vehicle-to -vehicle communication does not exist.

Network architecture and characteristics

A vehicle ad -hoc network consists of mobile nodes or vehicles ( engl. Car) and base stations along the road and transport network (English Road -Side Units, RSU). A compound is referred to in VANET communication partners according as vehicle-to -vehicle communication (English car to car, C2C) and vehicle-to- base station communication (English Car to Infrastructure, C2I ). A vehicle ad -hoc network is therefore usually regarded as a hybrid of pure infrastructure -based, cellular communication and ad hoc communication.

A VANET must meet special requirements, which arise from its application and determine the network characteristics.

Thus, the nodes of a VANET moving at different, but compared to typical MANETs usually very high speeds. Through this highly dynamic topology arising correspondingly short connection times (slow fading). With an average vehicle speed of 100 kilometers per hour and a maximum transmission and reception range of 200 meters, for example, can be used for oncoming vehicles to be a close connection only for about 4 seconds. Concepts for VANET - based security applications see vehicle speeds before up to 250 km / h.
Changing environmental conditions lead to a continuously changing signal propagation and fast fading or complete shading. This leads to frequent disconnections.
Nodes (vehicles ) move normally after corresponding patterns, for example, the local conditions (eg road network, highway, one-way street ) subject to the usual movement patterns (eg accelerating, cornering ) and collective patterns (eg jam). This provides information for motion prediction can take, for example, can be used in a corresponding VANET routing algorithm.

Routing

Just as a MANet a VANET requires flexible routing algorithms that differ from those established in wired or cell-based systems methods. Plays a special role in a VANET, the convergence of the algorithm, such as dealing with a highly dynamic network topology and asymmetric connections. The otherwise typical for routing in MANETs problem of energy supply plays no essential role in VANET. In addition to the topology - based routing go geo -based routing protocols based on the regular availability of position information for all network nodes.

Topology - based routing

In topology - based routing in VANETs, a distinction flat routing and hierarchical routing. If one of the routing algorithm, a flat network structure underlying the network from any network node is considered as a single region. That each node forwards data to all nodes in range (his ready to receive neighbor). The main advantage of such flat routing protocols is that they require no specialized network nodes and involve known and organizational mechanisms. Lack of coordination leads to highly dynamic topologies such as in VANETs, however at a high cost for the maintenance of the routing table. A strictly the idea of the flat routing is the following, complete storage of all participants in the local routing table, due to the high number of participants in a VANET not efficiently realized. Therefore, flat routing protocols in VANET deployments and simulations are often considered only in limited scenarios. Hierarchical routing combats this problem by organizing nodes into groups and the allocation of functions by means of selected nodes within and outside the group opposed. The grouping is done by geographical area or on the reception quality in explicit clusters, which can also be organized hierarchically. Each cluster we by a cluster across communicating nodes (Cluster Head ) represents.

In addition, hybrid method of proactive and reactive routing exist.

Many proactive routing protocols come from the Link State (LS ) protocol. The proactive routing protocols in MANETs include eg Dynamic Destination - Sequenced Distance Vector ( DSDV ), Wireless Routing Protocol ( WRP ), Global State Routing ( GSR), Fisheye State Routing ( FSR), Topology Broadcast Based on Reverse Path Forwarding ( TBRPF ) or Optimized Link State Routing ( OLSR ). The cost of proactive routing in VANETs are characterized by the constant change of routing table entries, only some of which are actually used, very high. Caused by the frequent sending of packets with updated routing information for a VANET, typically with limited bandwidth, high communication overhead. Of the proactive protocols, only the hierarchical FSR is considered in VANET deployments usually.

Among the reactive routing protocols such as Ad- hoc On-demand Distance Vector ( AODV ), Dynamic Source Routing ( DSR), Associativity Based Routing (ABR ), Lightweight Mobile Routing ( LMR ) and the pace Rally Ordered Routing Algorithm ( TORA ). In particular, AODV and DSR can be found in many VANET deployments again. Reactive routing protocols determine only when needed ( on demand) route, whereby the communication overhead and administrative expenses for the care of the routing tables is reduced. These are significant advantages for use in VANETs, however, arises from the determination of reactive routing at each affected node delay. This can be compensated in MANETs through an intermediate memory for recently established routes, but can be in VANETs, due to the highly dynamic network topology does not implement as efficient.

Geo -assisted routing

Due to the wide distribution and availability of GPS receivers in vehicles Geo - supported were focused from the start routing protocols in the development of VANET concepts.

Known VANET research projects

In the research project FleetNet of the German Federal Ministry of Education and Research (BMBF ) were developed between September 2000 and December 2003 solutions to exchange data via multi-hop routes between nearby vehicles.

Network on Wheels (NOW ) is a also supported by the BMBF research project, which was founded by Daimler AG, BMW AG, Volkswagen AG, the Fraunhofer Institute for Open Communication Systems and the NEC Germany GmbH and Siemens AG in 2004. Objectives of this project are to develop technical solutions to key issues in the area of communication protocols and data security.

Secure Vehicular Communication ( SEVECOM ) is an EU-funded project, which aims to investigate the safety and anonymity in vehicle networks and to guarantee. The project includes, among other things, the Daimler AG, Robert Bosch GmbH, Ulm University, as well as Trialogue as project coordinator.

VANET deployments

NEC Car2X Communication Stack is a Linux implementation of a commercial VANET stacks. The NEC Car2X stack supports IPv4, IPv6 and geographical routing.
U2VAS, the University of Ulm VANET stack (written: U2VAS ) is a Java implementation of a VANET stacks. U2VAS is completely modular and currently implemented position-based routing ( multi-hop CGGC ), visualization, as well as authenticity and authentication using a public key infrastructure (PKI).
The ACuP Communication Framework is a C implementation of a performance VANET stacks for research purposes, especially in the field of driver assistance and active safety. The modularly expandable Car2X framework allows high data rates and has a client API for Windows and Linux.

Motor vehicle Vehicular communication systems Skip zone Ad hoc On-Demand Distance Vector Routing Cache (computing)

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