K. DANIEL WONG
he field of inter-vehicular communications (IVC, also known as vehicle-to-vehicle communications, V2V, or vehicular ad hoc networks, VANETs) has been gaining momentum in recent years. Numerous emerging communications applications are unique to the vehicular setting. These applications include safety applications that will make driving safer, mobile commerce, and roadside information services that can intelligently inform drivers about congestion, businesses, and services in the vicinity of the vehicle, as well as other types of locally relevant news. Existing forms of entertainment may penetrate the vehicular domain, and new forms of entertainment may emerge, all supported by IVC capabilities. These emerging services are not well supported by the limited communication options available on cars today. Appropriately, the growing importance of IVC has been recognized by governments, corporations, and the academic community. IVC is recognized as an important component of intelligent transport systems (ITS) in various national ITS plans. As such, governments have allocated spectrum for IVC and similar applications (e.g., various concepts of dedicated short-range communications, DSRC, such as wireless access in vehicle environment, WAVE). Government and industry cooperation has funded large IVC partnerships or projects such as Crash Avoidance Metrics Partnership (CAMP), Advanced Driver Assistance Systems in Europe (ADASE2), Networkon-Wheels, Fleetnet, and Cartalk2000. Academic conferences and workshops on IVC are beginning to grow in popularity (e.g., VANET, Autonet, and V2VCOM). However, in order to prepare for future deployment, much research remains to be conducted. The unique requirements of inter-vehicular applications and the unique features of the vehicular network mean that new networking solutions are required for IVC. Because of rapidly changing topology due to vehicle motion, the vehicular network closely resembles an ad hoc network. However, the constraints and optimizations are remarkably different. Vehicles in general are constrained to move within roads. Power efficiency is not as important for IVC as it is for traditional ad hoc networking, since vehicles have a powerful and rechargeable source of energy.
Nevertheless, many research challenges remain. From the network perspective, security and scalability are two significant challenges, whereas in a more local context, important questions arise regarding good medium access control (MAC) protocols for IVC, and how to design systems within a DSRC framework. Meanwhile, even as researchers are working on enabling the applications for IVC that have been identified so far, new applications continue to be proposed for IVC. Although power efficiency is less of a concern, scalability may still be critical for IVC as it is for traditional ad hoc networks. One reason is that because of the nature of the vehicular applications, there might be more flooding/broadcasting in IVC than in traditional ad hoc networking. This could easily overwhelm the limited bandwidth of the radio links if the communication protocols are not well designed. In many areas of telecommunications, network security is becoming increasingly important for specific applications. For example, e-commerce and financial transactions are among the main drivers for increased Internet security. In the case of IVC, vehicle safety applications are among its major drivers. Where people’s lives are at stake, it is of course essential to secure IVC against abuse. Another aspect of IVC networks that requires security is the routing protocol. Geographic position-based routing protocols have been identified as promising for use in IVC. However, false position data on users, whether from malfunctioning equipment or from users with malicious intent, could create insurmountable problems in geographic position-based routing. MAC protocols are important for efficient utilization of wireless link resources. Because vehicles move along roads, directional antenna-based MAC mechanisms might be especially useful for IVC. Meanwhile, the allocation of spectrum for DSRC and its breakdown into seven channels affords opportunities for IVC system designs based on the use of these channels, and on the soon-to-come IEEE 802.11p. In this feature topic we are pleased to present seven articles addressing important topics within the field of IVC such as those discussed above. They give a good sampling of the state of the art in some of the many important research chal-
IEEE Wireless Communications • October 2006
GUEST EDITORIAL lenges being worked on in this growing field. The contributions provide perspectives from both industry and academia. These seven articles were selected from the 55 received submissions (a very strong response to our Call for Papers). This is another indicator that IVC research is healthy and thriving! The motivations, challenges, and previously proposed solutions and architectures for IVC security are surveyed in “Securing Vehicular Communications” by Raya et al. The article also introduces new ideas on certificate revocation customized for IVC security. Various position verification approaches have been proposed to protect IVC systems from false position data, as discussed in the second article, “Position Verification Approaches for Vehicular Ad Hoc Networks” by Leinmüller et al. They also propose a new approach that does not require dedicated devices for position verification, but relies on concepts of computed trust values the members of a VANET can compute for themselves. Kosch et al., in “The Scalability Problem of Vehicular Ad Hoc Networks and How to Solve It,” introduce a new way to address the scalability problem in IVC. It is based on considering the relevance of a message and giving priority accordingly. The scalability problem could be eased if good MAC protocols are used. The fourth article, “A Survey and Qualitative Analysis of MAC Protocols for Vehicular Ad Hoc Networks” by Menouar et al., explores various MAC protocols that have been proposed for IVC. These include ADHOC MAC, directional antenna-based MAC protocols, and IEEE 802.11 and its adapted versions for IVC, such as WAVE. The fifth and sixth articles discuss IVC in the context of the availability of the DSRC spectrum at 5.9 GHz and its channelization. “Design of 5.9 GHz DSRC-Based Vehicular Safety Communication” by Jiang et al. discusses a congestion control scheme for the DSRC control channel, enhanced performance of broadcast messaging, and concurrent usage of the multiple DSRC channels by diverse applications. Meanwhile, Zhang et al. propose a cluster-based ad hoc networking protocol taking advantage of DSRC’s seven channels. This work is reported in “Cluster-Based Multi-Channel Communications Protocols in Vehicle Ad Hoc Networks.” Finally, the seventh article, “MobEyes: Smart Mobs for Urban Monitoring with a Vehicular Sensor Network,” by Lee et al. presents a surveillance application for IVC. Here, the idea is to use the vehicles as sensors that may be used to monitor a variety of urban events, from pollution to traffic congestion and even criminal activities. Collectively, the sensor
IEEE Wireless Communications • October 2006
data stored in cars represents a very rich database that can be “mined” a posteriori for forensic crime investigation. Thus, we conclude by noting that the field of IVC is still wide open: there is room not just for better network protocols, but also for new visionary applications. We thank all contributors who submitted articles for this feature topic. We also thank all the reviewers who helped with thoughtful and timely reviews. Last but not least, we thank Dr. Michele Zorzi, the previous Editor-in-Chief of this magazine, for initial discussions and approving this feature topic, and Dr. Abbas Jamalipour, the current Editor-inChief, for his thoughtful support, involvement, and suggestions throughout the whole process of putting together and shaping this feature topic.
BIOGRAPHIES K. DANIEL WONG [SM’03] ([email protected]
) received his B.S.E. (with highest honors) from Princeton University, and his M.Sc. and Ph.D. from Stanford University, all in electrical engineering. His research interests include mobility management for IP networks, ad hoc networks (including IVC), cellular networks, network security, and other topics in wireless communications (e.g., OFDM). He is currently an assistant professor at Malaysia University of Science and Technology. He is a board member of the Sister Societies Board of IEEE Communications Society, and a member of the editorial board of IEEE Communications Surveys and Tutorials. He is the author of Wireless Internet Telecommunications (Artech House, 2004). K.E. TEPE ([email protected]
) is an assistant professor in the Electrical and Computer Engineering Department of the University of Windsor, Ontario, Canada. He received M.S. and Ph.D. degrees in electrical engineering from Rensselaer Polytechnic Institute, Troy, New York, in 1996 and 2000, respectively. He worked as a research scientist at Telcordia Technologies, and as a post doctorate associate at Wireless Information Networks Laboratory (WINLAB), Rutgers University, New Jersey, before joining the University of Windsor. His research interests are in wireless communication systems, wireless ad hoc networks, sensor networks, and network security. W AI C HEN received a B.Sc. degree from Zhejiang University, and M.Sc., M.Phil., and Ph.D. degrees from Columbia University. He is with Applied Research at Telcordia Technologies (formerly Bellcore), where he is chief scientist and director of Ubiquitous Networking and Services Research. He is a co-chair of the V2VCOM and IEEE Autonet Workshops. His research interests include automotive networking and applications, wireless communications systems, and mobile ad hoc networks. M ARIO G ERLA [F ’02]received a graduate degree in engineering from the Politecnico di Milano in 1966, and M.S. and Ph.D. degrees in engineering from the University of California at Los Angeles (UCLA) in 1970 and 1973. After working for Network Analysis Corporation, New York, from 1973 to 1976, he joined the Faculty of the Computer Science Department at UCLA where he is now a professor. His research interests cover distributed computer communication systems and wireless networks. He has designed and implemented various network protocols (channel access, clustering, routing, and transport) under DARPA and NSF grants. Currently he is leading the ONR MINUTEMAN project at UCLA, with a focus on robust scalable network architectures for unmanned intelligent agents in defense and homeland security scenarios. He is also conducting research on scalable TCP transport for the next-generation Internet (see www.cs.ucla.edu/NRL for recent publications).