Vehicular Networks

  Vehicular networks have attracted a lot of attention in recent years. Many projects have been initiated by government, industry, and academia to improve driving safety, provide travel assistance, improve traffic flow, and decrease fuel consumption. These projects exploit vehicular communications and networking technologies, generally referred to as vehicular ad⁃hoc networks (VANETs) or more generally, vehicular networks. VANET includes vehicle⁃to⁃infrastructure and vehicle⁃to⁃vehicle communications and can be based on short⁃range and medium⁃range communication as well as cellular systems. The development and deployment of vehicular networks is also considered one of the critical foundations of the intelligent transportation system industry.

  The purpose of this special issue is to explore recent developments in VANETs and stimulate discussion on future research on large⁃scaled VANET applications. This special issue comprises six papers covering the most active areas of research in VANETs. Three papers are dedicated to network communication protocols. Respectively, these papers describe network coding, QoS in V2I communications, and data routing schemes. Another two papers focus on novel VANET applications and services. One of these papers proposes real⁃time routing and the other proposes network⁃enhanced GPS techniques. The last paper describes a practical prototype vehicle system comprising connected vehicles.

  The first paper by Yuanguo Bi et al. describes the problem of satisfying the diverse QoS requirements of various vehicular applications and efficiently utilizing limited wireless channel resources. The authors propose a cross⁃layer rate⁃control scheme to solve this problem. By tracking throughput, aggregate arrival rate, and buffer size at the bottleneck RSU in a timely manner, source sending rates can be adjusted in order to avoid buffer overflow or underflow at the RSU. In addition, bandwidth can be efficiently allocated to different types of multimedia services by taking the bandwidth requirements of each service into account. Simulation results show that this solution improves system throughput and ensures wireless channel resources are efficiently used. This solution also satisfies the different QoS requirements of multimedia services in V2I networks.

  The second paper “Advanced Leader Election for Virtual Traffic Lights” describes a novel vehicular networking application called Virtual Traffic Light (VTL). This solution replaces current infrastructure⁃based traffic lights. The authors present the results of an evaluation of an improved VTL system designed to manage arbitrary intersection geometries. The effect of VTL on traffic flow and overall network performance is determined for two scenarios: a realistic urban road network and a synthetic single intersection. The results show that VTL positively affects the driving experience of simulated vehicles.

  The third paper “Trajectory⁃Based Data Forwarding Schemes for Vehicular Networks” describes two data⁃forwarding schemes based on vehicle trajectory in VANETs. Vehicle trajectory is a good asset when designing data⁃forwarding schemes for multihop V2I or I2V data delivery because it allows for either a better forwarding metric computation or better estimation of the location of the packet destination vehicle.

  The paper “Unveiling the Challenges for Improving Data Availability in Vehicular Networks with Network Coding” describes a network⁃coding⁃based approach for improving data availability in VANETs. An empirical study with trace⁃driven simulations shows that performance can be significantly improved, but codes received by a retrieving node tend to be linearly correlated. This is a serious issue because linear correlation of codes degrades data retrieval. The authors show this by designing synthetic networks that have community structures with dramatically different features and conducting experiments on these networks. The authors also discuss opportunities for improving network⁃coding⁃based approach for data availability in vehicular network by developing community⁃aware techniques for codes distribution.

  The paper “Networking⁃GPS: Cooperative Vehicle Localization Using Commodity GPS in Urban Area” describes a new cooperative vehicle localization algorithm called Networking⁃GPS. The objective of this algorithm is to mitigate the multipath effect, which can severely degrade the localization performance of GPS receivers. The correlation between the similarity of SNR values from different GPS satellites and relative distance among different GPS receivers is identified. An evaluation based on real GPS traces shows that Networking⁃GPS can improve accuracy in the face of the multipath effect.

  Finally, the paper “Anatomy of Connected Cars” describes the Internet of Vehicles, which is poised to become a reality as connected vehicles are mandated by the US Department of Transportation. This paper identifies the main characteristics of IoV information flow and two roadblocks to IoV deployment. The authors argue exploitation of community WiFi connectivity and shifting from a node⁃centric paradigm to a content⁃centric paradigm can accelerate IoV deployment and reduce costs.

  The papers in this special issue are a snapshot of current issues in the field of VANETs. Large⁃scale VANET application is still in its infancy, and much current work focuses on the development of applications. There is a gap between the deployment of VANET applications and the existing vehicular communication protocols. The papers in this special issue show how that gap is closing.

  We are grateful to all authors who submitted their papers for publication in this special issue. We thank Zongjian He, a PhD student at Hong Kong Polytechnic University for his great effort and enthusiastic support for this special issue.