Vehicular networking has significant potential to enable diverse applications associated with traffic safety, traffic efficiency and infotainment. In this survey and tutorial paper we introduce the basic characteristics of vehicular networks, provide an overview of applications and associated requirements, along with challenges and their proposed solutions. In addition, we provide an overview of the current and past major ITS programs and projects in the USA, Japan and Europe. Moreover, vehicular networking architectures and protocol suites employed in such programs and projects in USA, Japan and Europe are discussed.

Vehicular Networking: A Survey and Tutorial on Requirements, Architectures, Challenges, Standards and Solutions

Vehicular ad hoc network (VANET) is an emerging new technology integrating ad hoc network, wireless LAN (WLAN) and cellular technology to achieve intelligent inter-vehicle communications and improve road traffic safety and efficiency. VANETs are distinguished from other kinds of ad hoc networks by their hybrid network architectures, node movement characteristics, and new application scenarios. Therefore, VANETs pose many unique networking research challenges, and the design of an efficient routing protocol for VANETs is very crucial. In this article, we discuss the research challenge of routing in VANETs and survey recent routing protocols and related mobility models for VANETs.

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Routing in vehicular ad hoc networks: A survey

Position-based routing, as it is used by protocols like Greedy Perimeter Stateless Routing (GPSR) [5], is very well suited for highly dynamic environments such as inter-vehicle communication on highways. However, it has been discussed that radio obstacles [4], as they are found in urban areas, have a significant negative impact on the performance of position-based routing. In prior work [6] we presented a position-based approach which alleviates this problem and is able to find robust routes within city environments. It is related to the idea of position-based source routing as proposed in [1] for terminode routing. The algorithm needs global knowledge of the city topology as it is provided by a static street map. Given this information the sender determines the junctions that have to be traversed by the packet using the Dijkstra shortest path algorithm. Forwarding between junctions is then done in a position-based fashion. In this short paper we show how position-based routing can be aplied to a city scenario without assuming that nodes have access to a static street map and without using source routing.

Geographic routing in city scenarios

Vehicular Ad Hoc Networks: A New Challenge for Localization-Based Systems

Direct radio-based vehicle-to-vehicle communication can help prevent accidents by providing accurate and up-to-date local status and hazard information to the driver. In this paper, we assume that two types of messages are used for traffic safety-related communication: 1) Periodic messages (ldquobeaconsrdquo) that are sent by all vehicles to inform their neighbors about their current status (i.e., position) and 2) event-driven messages that are sent whenever a hazard has been detected. In IEEE 802.11 distributed-coordination-function-based vehicular networks, interferences and packet collisions can lead to the failure of the reception of safety-critical information, in particular when the beaconing load leads to an almost-saturated channel, as it could easily happen in many critical vehicular traffic conditions. In this paper, we demonstrate the importance of transmit power control to avoid saturated channel conditions and ensure the best use of the channel for safety-related purposes. We propose a distributed transmit power control method based on a strict fairness criterion, i.e., distributed fair power adjustment for vehicular environments (D-FPAV), to control the load of periodic messages on the channel. The benefits are twofold: 1) The bandwidth is made available for higher priority data like dissemination of warnings, and 2) beacons from different vehicles are treated with ldquoequal rights,rdquo and therefore, the best possible reception under the available bandwidth constraints is ensured. We formally prove the fairness of the proposed approach. Then, we make use of the ns-2 simulator that was significantly enhanced by realistic highway mobility patterns, improved radio propagation, receiver models, and the IEEE 802.11p specifications to show the beneficial impact of D-FPAV for safety-related communications. We finally put forward a method, i.e., emergency message dissemination for vehicular environments (EMDV), for fast and effective multihop information dissemination of event-driven messages and show that EMDV benefits of the beaconing load control provided by D-FPAV with respect to both probability of reception and latency.

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Vehicle-to-Vehicle Communication: Fair Transmit Power Control for Safety-Critical Information

Routing of data in a vehicular ad hoc network is a challenging task due to the high dynamics of such a network. Recently, it was shown for the case of highway traffic that position-based routing approaches can very well deal with the high mobility of network nodes. However, baseline position-based routing has difficulties to handle two-dimensional scenarios with obstacles (buildings) and voids as it is the case for city scenarios. In this paper we analyze a position-based routing approach that makes use of the navigational systems of vehicles. By means of simulation we compare this approach with non-position-based ad hoc routing strategies (dynamic source routing and ad-hoc on-demand distance vector routing). The simulation makes use of highly realistic vehicle movement patterns derived from Daimler-Chrysler's Videlio traffic simulator. While DSR's performance is limited due to problems with scalability and handling mobility, both AODV and the position-based approach show good performances with the position-based approach outperforming AODV.

A routing strategy for vehicular ad hoc networks in city environments

The discrepancy between real-world radio channel behavior and its standard modeling in simulations (unit disk graph) is a major reason for protocols to perform differently - often worse - than predicted when deployed in a real-world setup. As researchers having to deal with real ad hoc networks are aware of, assuming a fixed border for a node's communication range might not only lead to inaccurate results but also to a wrong judgment on the comparison between different protocols. We have set up a simulation study to investigate the effects of realistic channel characteristics on packet forwarding strategies for vehicular ad hoc networks. The contributions of this paper are threefold: i) we provide a performance evaluation of various routing/forwarding strategies under the realistic non-deterministic Nakagami radio propagation model and compare the results with the ones obtained using the standard two-ray-ground model. Validated German highway movement patterns are used to model node mobility. ii) We demonstrate that realistic channel conditions present an opportunity and not only a drawback for some forwarding strategies. More specifically, we show that for contention-based forwarding (CBF) techniques, realistic channel characteristics provide a positive impact in terms of an increased average hop distance. iii) We provide an analytical derivation of the expected hop distance for CBF that provides a basis to optimally adjust CBF parameters

Effects of a realistic channel model on packet forwarding in vehicular ad hoc networks

Existing position-based unicast routing algorithms, which forward packets in the geographic direction of the destination, require that the forwarding node knows the positions of all neighbors in its transmission range. This information on direct neighbors is gained by observing beacon messages each node sends out periodically. Due to mobility, the information that a node receives about its neighbors becomes outdated, leading either to a significant decrease in the packet delivery rate or to a steep increase in load on the wireless channel as node mobility increases. We describe a mechanism to perform position-based unicast forwarding without the help of beacons. In our contention-based forwarding (CBF) scheme, the next hop is selected through a distributed contention process based on the actual positions of all current neighbors. For the contention process, CBF makes use of biased timers. To avoid packet duplication, the first node that is selected suppresses the selection of further nodes. Since the basic scheme can lead to packet duplication, we describe alternative ways of suppressing those. In addition to that, we compare the CBF schemes and standard greedy forwarding by means of simulation with ns-2.

/pdf/a-novel-forwarding-paradigm-for-position-based-routing-with-96r2htmru2.pdf

A novel forwarding paradigm for position-based routing (with implicit addressing)

Within the framework of the FLEETNET project, a real-world ad hoc network testbed was built using cars as mobile nodes. These cars were equipped with computing and communication devices. As ad hoc routing algorithm, position-based forwarding implemented on Linux-based laptops was used, exploiting position information gathered by on-board navigation systems. We report on measurements and experiences with this testbed for static 1-hop and 3-hop scenarios as well as for mobile 3-hop scenarios. Beside the power, loss-rate, throughput and delivery ratio measurements, we present our methodology for conducting experiments with 'real-world' mobile ad hoc networks and discuss problems of beacon-based position-based routing due to radio fluctuations.

H. Fussler

Papers

A routing strategy for vehicular ad hoc networks in city environments

Effects of a realistic channel model on packet forwarding in vehicular ad hoc networks

A novel forwarding paradigm for position-based routing (with implicit addressing)

Performance measurements of a vehicular ad hoc network