Hannes Hartenstein

A tutorial survey on vehicular ad hoc networks

There has been significant interest and progress in the field of vehicular ad hoc networks over the last several years. VANETs comprise vehicle-to-vehicle and vehicle-to-infrastructure communications based on wireless local area network technologies. The distinctive set of candidate applications (e.g., collision warning and local traffic information for drivers), resources (licensed spectrum, rechargeable power source), and the environment (e.g., vehicular traffic flow patterns, privacy concerns) make the VANET a unique area of wireless communication. This article gives an overview of the field, providing motivations, challenges, and a snapshot of proposed solutions.

A routing strategy for vehicular ad hoc networks in city environments

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-Chryslers Videlio traffic simulator. While DSRs 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.

Geographic routing in city scenarios

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.

Contention-Based Forwarding for Mobile 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. In this paper, we propose a mechanism to perform position-based unicast forwarding without the help of beacons. In our contention-based forwarding scheme (CBF) 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. We propose three suppression strategies which vary with respect to forwarding efficiency and suppression characteristics. We analyze the behavior of CBF with all three suppression strategies and compare it to an existing greedy position-based routing approach by means of simulation with ns-2. Our results show that CBF significantly reduces the load on the wireless channel required to achieve a specific delivery rate compared to the load a beacon-based greedy forwarding strategy generates.

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

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.

Broadcast reception rates and effects of priority access in 802.11-based vehicular ad-hoc networks

One key usage of VANET is to support vehicle safety applications. This use case is characterized by the prominence of broadcasts in scaled settings. In this context, we try to answer the following questions: i) what is the probability of reception of a broadcast message by another car depending on its distance to the sender, ii) how to give priority access and an improved reception rate for important warnings, e.g., sent out in an emergency situation, and iii) how are the above two results affected by signal strength fluctuations caused by radio channel fading? We quantify via simulation the probability of reception for the two-ray-ground propagation model as well as for the Nakagami distribution in saturated environments. By making use of some IEEE 802.11e EDCA mechanisms for priority access, we do not only quantify how channel access times can be reduced but also demonstrate how improved reception rates can be achieved. Our results show that the mechanisms for priority access are successful under the two-way-ground model. However, with a non-deterministic radio propagation model like Nakagamis distribution the benefit is still obvious but the general level of probability of reception is much smaller compared to two-ray-ground model. The results indicate that -- particularly for safety-critical and sensor network type of applications -- the proper design of repetition or multi-hop retransmission strategies represents an important aspect of future work for robustness and network stability of vehicular ad hoc networks.

Overhaul of ieee 802.11 modeling and simulation in ns-2

NS-2, with its IEEE 802.11 support, is a widely utilized simulation tool for wireless communications researchers. However, the current NS-2 distribution code has some significant shortcomings both in the overall architecture and the modeling details of the IEEE 802.11 MAC and PHY modules. This paper presents a completely revised architecture and design for these two modules. The resulting PHY is a full featured generic module able to support any single channel frame-based communications (i.e. it is also able to support non-IEEE 802.11 based MAC). The key features include cumulative SINR computation, preamble and PLCP header processing and capture, and frame body capture. The MAC accurately models the basic IEEE 802.11 CSMA/CA mechanism, as required for credible simulation studies. The newly designed MAC models transmission and reception coordination, backoff management and channel state monitoring in a structured and modular manner. In turn, the contributions of this paper make extending the MAC for protocol researches much easier and provide for a significantly higher level of simulation accuracy.

VANET : vehicular applications and inter-networking technologies

Foreword. About the Editors. Preface. Acknowledgements. List of Contributors. 1 Introduction (Hannes Hartenstein and Kenneth P. Laberteaux). 1.1 Basic Principles and Challenges. 1.2 Past and Ongoing VANET Activities. 1.3 Chapter Outlines. 1.4 References. 2 Cooperative Vehicular Safety Applications (Derek Caveney). 2.1 Introduction. 2.2 Enabling Technologies. 2.3 Cooperative System Architecture. 2.4 Mapping for Safety Applications. 2.5 VANET-enabled Active Safety Applications. 2.6 References. 3 Information Dissemination in VANETs (Christian Lochert, Bjorn Scheuermann and Martin Mauve). 3.1 Introduction. 3.2 Obtaining Local Measurements. 3.3 Information Transport. 3.4 Summarizing Measurements. 3.5 Geographical Data Aggregation. 3.6 Conclusion. 3.7 References. 4 VANET Convenience and Efficiency Applications (Martin Mauve and Bjorn Scheruermann). 4.1 Introduction. 4.2 Limitations. 4.3 Applications. 4.4 Communication Paradigms. 4.5 Probabilistic, Area-based Aggregation. 4.6 Travel Time Aggregation. 4.7 Conclusion. 4.8 References. 5 Vehicular Mobility Modeling for VANETs (Jerome Harri). 5.1 Introduction. 5.2 Notation Description. 5.3 Random Models. 5.4 Flow Models. 5.5 Traffic Models. 5.6 Behavioral Models. 5.7 Trace or Survey-based Models. 5.8 Integration with Network Simulators. 5.9 A Design Framework for Realistic Vehicular Mobility Models. 5.10 Discussion and Outlook. 5.11 Conclusion. 5.12 References. 6 Physical Layer Considerations for Vehicular Communications (Ian Tan and Ahmad Bahai). 6.1 Standards Overview. 6.2 Previous Work. 6.3 Wireless Propagation Theory. 6.4 Channel Metrics. 6.5 Measurement Theory. 6.6 Emperical Channel Characterization at 5.9 GHz. 6.7 Future Directions. 6.8 Conclusion. 6.9 Appendix: Deterministic Multipath Channel Derivations. 6.10 Appendix: LTV Channel Response. 6.11 Appendix: Measurement Theory Details. 6.12 References. 7 MAC Layer and Scalability Aspects of Vehicular Communication Networks (Jens Mittag, Felix Schmidt-Eisenlohr, Moritz Killat, Marc Torrent-Moreno and Hannes Hartenstein). 7.1 Introduction: Challenges and Requirements. 7.2 A Survey on Proposed MAC Approaches for VANETs. 7.3 Communication Based on IEEE 802.11p. 7.4 Performance Evaluation and Modeling. 7.5 Aspects of Congestion Control. 7.6 Open Issues and Outlook. 7.7 References. 8 Efficient Application Level Message Coding and Composition (Craig L Robinson). 8.1 Introduction to the Application Environment. 8.2 Message Dispatcher. 8.3 Example Applications. 8.4 Data Sets. 8.5 Predictive Coding. 8.6 Architecture Analysis. 8.7 Conclusion. 8.8 References. 9 Data Security in Vehicular Communication Networks (AndreWeimerskirch, Jason J Haas, Yih-Chun Hu and Kenneth P Laberteaux). 9.1 Introduction. 9.2 Challenges of Data Security in Vehicular Networks. 9.3 Network, Applications, and Adversarial Model. 9.4 Security Infrastructure. 9.5 Cryptographic Protocols. 9.6 Privacy Protection Mechanisms. 9.7 Implementation Aspects. 9.8 Outlook and Conclusions. 9.9 References. 10 Standards and Regulations (John B Kenney). 10.1 Introduction. 10.2 Layered Architecture for VANETs. 10.3 DSRC Regulations. 10.4 DSRC Physical Layer Standard. 10.5 DSRC Data Link Layer Standard (MAC and LLC). 10.6 DSRC Middle Layers. 10.7 DSRC Message Sublayer. 10.8 Summary. 10.9 Abbreviations and Acronyms. 10.10 References. Index.

Position-aware ad hoc wireless networks for inter-vehicle communications: the Fleetnet project

The Fleetnet project aims at the development of a wireless ad hoc network for inter-vehicle communications. We present the rationale behind the choice of an appropriate radio hardware and the use of a position-based routing approach and outline applications to exploit the Fleetnet platform. In addition, we discuss simulation of vehicle movements as a basis for protocol evaluation as well as aspects of Internet integration of Fleetnet. We state the basic problems together with the intended approach of tackling these challenges, thereby providing an overview of the Fleetnet project

Fair sharing of bandwidth in VANETs

We address the challenge of how to share the limited wireless channel capacity for the exchange of safety-related information in a fully deployed vehicular ad hoc network (VANET). In particular, we study the situation that arises when the number of nodes sending periodic safety messages is too high in a specific area. In order to achieve a good performance of safety-related protocols, we propose to limit the load sent to the channel using a strict fairness criterion among the nodes. A formal definition of this problem is presented in terms of a max-min optimization problem with an extra condition on per-node maximality. Furthermore, we propose FPAV, a power control algorithm which finds the optimum transmission range of every node, and formally prove its validity under idealistic conditions. Simulations are performed to visualize the result of FPAV in a couple of road situations. Finally, we discuss the issues that must be taken into account when implementing FPAV.