IEEE Transactions on Vehicular Technology 
      Special Section on Vehicular Communications Networks

Traffic congestion, delays, and accidents in transportation systems
have caused significant loss of life, wasted energy, and loss of
productivity. To improve the safety, security, and efficiency of
transportation systems and to enable new mobile services and
applications for the traveling public, intelligent transportation
systems (ITS) have been developed, which apply rapidly emerging
information technologies in vehicles and transportation
infrastructures. The development of inter/intra-vehicle and
infrastructure-to-vehicle mobile, mesh, and ad hoc networks is one of
the most challenging and critical issues for the ITS industry and is
of considerable interest to the communication and networking research
community. This special section consists of 18 papers, selected from
78 submissions, that represent the state of the art in this
fast-moving research area. The objectives of this section are to
facilitate the deployment of vehicular communication networks and to
promote further research and activities that enable new transportation
products and services, such as advanced traffic management, vehicle
control, safety control, networking and information services on the
road, etc.

Wireless intervehicular communication is expected to enable a broad
range of information applications in the future. Safety applications,
including incident detection, are the top priority. In the first
paper, "Efficient Coordination and Transmission of Data for
Cooperative Vehicular Safety Applications," Robinson, Caveney,
Caminiti, Baliga, Laberteaux, and Kumar present a Message Dispatcher
architecture for efficiently communicating vehicle data among
neighboring vehicles. This paper provides important insights for
wireless-channel-usage optimization and describes an experimental
deployment in several vehicles at the Toyota Technical Center, Ann
Arbor, MI. In the second paper, "Extending Driver's Horizon Through
Comprehensive Incident Detection in Vehicular Networks," a
comprehensive and efficient incident-detection approach is proposed by
Chatzigiannakis, Grammatikou, and Papavassiliou. The approach
provides an effective way to process and organize information taken at
different times from different locations and to integrate it into a
consistent model. In the third paper, "Data Pouring and Buffering on
the Road: A New Data Dissemination Paradigm for Vehicular Ad Hoc
Networks," Zhao, Zhang, and Cao propose a data pouring and buffering
paradigm to address the data-dissemination problem in vehicle ad hoc
networks (VANETs), considering the unique characteristics of VANETs.

In high-mobility, high-density, random-topology vehicular networks,
sharing limited wireless resources and reliably communicating between
vehicles are very challenging. In the fourth paper, "Reliable
Neighborcast," Maxemchuk and Tientrakool introduce a new
communication paradigm -- reliable neighborcast -- and present a
reliable-neighborcast protocol that operates as an overlay on existing
reliable broadcast protocols. In the fifth paper, "Distributed
Mobility Transparent Broadcasting in Vehicle to Vehicle Networks,"
Yang, Ye, and Sikdar propose a broadcast protocol to achieve efficient
broadcasting in vehicle-to-vehicle networks. In the sixth paper, "A
Distributed MAC Scheme for Emergency Message Dissemination in
Vehicular Ad Hoc Networks," the objective is to ensure that emergency
messages in VANETs can be disseminated in a timely manner; Peng and
Cheng present a fully distributed medium-access-control (MAC) scheme,
based on a pulse-control mechanism, which realizes strict packet-level
priority scheduling for emergency packets.

In addition to safety, VANETs will support a wide range of multimedia
(e.g., video/audio) and data (e.g., e-maps, road/vehicle-traffic/
weather information) applications. In the seventh paper,
"Clustering-Based Multi-Channel MAC Protocols for QoS-Provisionings
Over Vehicular Ad Hoc Networks," Su and Zhang propose a cluster-based
multichannel communication scheme. The communication scheme integrates
clustering with contention-free and contention-based MAC protocols.
An analytical model is developed to determine the delay for safety
messages transmitted by cluster-head vehicles and the MAC parameters
that result in acceptable delays. Directional antennas reduce radio
interference and improve channel utilization; however, they constrain
the MAC-protocol design because of deafness and other problems. To
address this issue, in the eighth paper, "LMA: Location and Mobility
Aware Medium Access Control Protocols for Vehicular Ad Hoc Networks
Using Directional Antennas," Feng develops a location- and
mobility-aware MAC protocol for vehicle networks deploying directional
antennas.

Scalable and reliable routing is a critical issue for multihop,
mobile, and highly dynamic VANET. In the ninth paper, "A Stable
Routing Protocol to Support ITS Services in VANET Networks," Taleb,
Sakhaee, Jamalipour, Hashimoto, Kato, and Nemoto propose a routing
protocol that groups vehicles according to their velocity vectors,
which decreases the rate at which links between vehicles change. In
the tenth paper, "Conditional Transmissions: A Communication Strategy
for Highly Dynamic Vehicular Ad Hoc Networks," Ducourthial, Khaled,
and Shawky propose a novel approach for routing in highly dynamic
networks, relying on condition-based communication. Instead of using
addresses or positions, a message is sent with some conditions used
for retransmission or reception. Simulations and experiments on a
road show the effectiveness of the solution. In the 11th paper, "A
Multihop Peer Communication Protocol with Fairness Guarantee for IEEE
802.16 Based Vehicular Networks," Yang, Ou, Chen, and He propose a
multihop communication protocol for relaying and peer collaboration
when vehicles can reach IEEE 802.16 base stations.

The following five papers consider localization, mobility management,
and network-topology control. In the 12th paper, "Vehicular Node
Localization Using Received Signal Strength Indicator," Parker and
Valaee present a cooperative vehicle-position-estimation algorithm,
which achieves higher accuracy and greater reliability than GPS-based
positioning solutions, by using intervehicle distance measurements
taken by a radio ranging technique. In the 13th paper, "Performance
Evaluation of SUVnet with Real-Time Traffic Data," Huang, Luo, Li, Li,
Li, Shu, and Wu construct a mobility model using the GPS data from
more than 4000 taxis collected in Shanghai, China. Based on this
model, the network topology, connectivity, and performance are
studied. In the 14th paper, "Optimized FMIPv6 Using IEEE802.21 MIH
Services in Vehicular Networks," Mussabbir, Yao, Niu, and Fu propose a
cross-layer mechanism to make intelligent handover decisions and to
optimize handover procedures in vehicular networks. In the 15th paper,
"Design and Implementation of a SIP-Based Mobile and Vehicular
Wireless Network with Push Mechanism," to maintain Internet
connectivity anytime and anywhere, Tseng, Chen, and Cheng propose a
SIP-based mobile-network gateway, which is equipped with both internal
and external wireless interfaces. In the 16th paper, "The Optimal
Placement of Gateways in Vehicular Networks," Li, Huang, and Fang
propose 1-D and 2-D placements of gateways that minimize the average
number of hops from access points to gateways so that the
communication delay is decreased.

In addition to intervehicle communications, intravehicle communication
networks are also an important component of future ITS systems. In the
17th paper, "Systematic Message Schedule Construction for
Time-Triggered CAN," Schmidt and Schmidt propose a framework to
construct message schedules in time-triggered controller area
networks, considering several performance metrics, such as bandwidth
utilization and jitter, and taking hardware constraints into account.

Future proliferation of ITS will also depend on its ability to enforce
security measures. In the last paper, "GSIS: A Secure and Privacy
Preserving Protocol for Vehicular Communications," Lin, Sun, Ho, and
Shen identify some of the unique design requirements in the aspects of
security and privacy preservation for VANETs and propose a novel
secure and privacy-preserving protocol based on group signatures and
identity-based signature techniques. Extensive simulations are
conducted to verify the effectiveness of the proposed protocol under
various road-system scenarios.

In closing, the guest editors would like to acknowledge the
contributions of the many experts who submitted their work,
participated in the review process, and provided constructive and
helpful comments to the authors to improve the technical content and
presentation quality of the papers. They would also like to extend
their sincere thanks to Dr. T. Wong, the former Editor-in-Chief, and
Dr.W. Zhuang, the Editor-in-Chief of the IEEE TRANSACTIONS ON
VEHICULAR TECHNOLOGY, for their support and help in bringing this
special section to press. We hope you will enjoy the papers in this
collection.

Guest Editors:
Xuemin (Sherman) Shen, University of Waterloo, Canada
(e-mail: xshen@bbcr.uwaterloo.ca)
Nicholas F Maxemchuk, Columbia University, USA
(e-mail: nick@ee.columbia.edu)
Lin Cai, University of Victoria, Canada
(e-mail: cai@uvic.ca)