Vehicles on the road with some common interests can cooperatively form a platoon-based driving pattern, in which a vehicle follows another vehicle and maintains a small and nearly constant distance to the preceding vehicle. It has been proved that, compared with driving individually, such a platoon-based driving pattern can significantly improve road capacity and energy efficiency. Moreover, with the emerging vehicular ad hoc network (VANET), the performance of a platoon in terms of road capacity, safety, energy efficiency, etc., can be further improved. On the other hand, the physical dynamics of vehicles inside the platoon can also affect the performance of a VANET. Such a complex system can be considered a platoon-based vehicular cyber-physical system (VCPS), which has attracted significant attention recently. In this paper, we present a comprehensive survey on a platoon-based VCPS. We first review the related work of a platoon-based VCPS. We then introduce two elementary techniques involved in a platoon-based VCPS, i.e., the vehicular networking architecture and standards, and traffic dynamics, respectively. We further discuss the fundamental issues in a platoon-based VCPS, including vehicle platooning/clustering, cooperative adaptive cruise control, platoon-based vehicular communications, etc., all of which are characterized by the tightly coupled relationship between traffic dynamics and VANET behaviors. Since system verification is critical to VCPS development, we also give an overview of VCPS simulation tools. Finally, we share our view on some open issues that may lead to new research directions.

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A Survey on Platoon-Based Vehicular Cyber-Physical Systems

With the rapid development of the Intelligent Transportation System (ITS), vehicular communication networks have been widely studied in recent years. Dedicated Short Range Communication (DSRC) can provide efficient real-time information exchange among vehicles without the need of pervasive roadside communication infrastructure. Although mobile cellular networks are capable of providing wide coverage for vehicular users, the requirements of services that require stringent real-time safety cannot always be guaranteed by cellular networks. Therefore, the Heterogeneous Vehicular NETwork (HetVNET), which integrates cellular networks with DSRC, is a potential solution for meeting the communication requirements of the ITS. Although there are a plethora of reported studies on either DSRC or cellular networks, joint research of these two areas is still at its infancy. This paper provides a comprehensive survey on recent wireless networks techniques applied to HetVNETs. Firstly, the requirements and use cases of safety and non-safety services are summarized and compared. Consequently, a HetVNET framework that utilizes a variety of wireless networking techniques is presented, followed by the descriptions of various applications for some typical scenarios. Building such HetVNETs requires a deep understanding of heterogeneity and its associated challenges. Thus, major challenges and solutions that are related to both the Medium Access Control (MAC) and network layers in HetVNETs are studied and discussed in detail. Finally, we outline open issues that help to identify new research directions in HetVNETs.

Heterogeneous Vehicular Networking: A Survey on Architecture, Challenges, and Solutions

Modern society faces serious problems with transportation systems, including but not limited to traffic congestion, safety, and pollution. Information communication technologies have gained increasing attention and importance in modern transportation systems. Automotive manufacturers are developing in-vehicle sensors and their applications in different areas including safety, traffic management, and infotainment. Government institutions are implementing roadside infrastructures such as cameras and sensors to collect data about environmental and traffic conditions. By seamlessly integrating vehicles and sensing devices, their sensing and communication capabilities can be leveraged to achieve smart and intelligent transportation systems. We discuss how sensor technology can be integrated with the transportation infrastructure to achieve a sustainable Intelligent Transportation System (ITS) and how safety, traffic control and infotainment applications can benefit from multiple sensors deployed in different elements of an ITS. Finally, we discuss some of the challenges that need to be addressed to enable a fully operational and cooperative ITS environment.

Sensor Technologies for Intelligent Transportation Systems.

Intelligent transportation systems (ITS) are becoming a crucial component of our society, whereas reliable and efficient vehicular communications consist of a key enabler of a well-functioning ITS. To meet a wide variety of ITS application needs, vehicular-to-vehicular and vehicular-to-infrastructure communications have to be jointly considered, configured, and optimized. The effective and efficient coexistence and cooperation of the two give rise to a dynamic spectrum management problem. One recently emerged and rapidly adopted solution of a similar problem in cellular networks is the so-termed device-to-device (D2D) communications. Its potential in the vehicular scenarios with unique challenges, however, has not been thoroughly investigated to date. In this paper, we for the first time carry out a feasibility study of D2D for ITS based on both the features of D2D and the nature of vehicular networks. In addition to demonstrating the promising potential of this technology, we will also propose novel remedies necessary to make D2D technology practical as well as beneficial for ITS.

D2D for Intelligent Transportation Systems: A Feasibility Study

5G is ongoing, and it is an emerging platform that not only aims to augment existing but also introduce a plethora of novel applications that require ultra-reliable low-latency communication. It is a new radio access technology that provides building blocks to retrofit existing platforms (e.g., 2G, 3G, 4G, and WiFi) for greater coverage, accessibility, and higher network density with respect to cells and devices. It implies that 5G aims to satisfy a diverse set of communication requirements of the various stakeholders. Among the stakeholders, vehicles, in particular, will benefit from 5G at both the system and application levels. The authors present a tutorial perspective on vehicular communications using the building blocks provided by 5G. First, we identify and describe key requirements of emerging vehicular communications and assess existing standards to determine their limitations. Then we provide a glimpse of the adopted 5G architecture and identify some of its promising salient features for vehicular communications. Finally, key 5G building blocks (i.e., proximity services, mobile edge computing and network slicing) are explored in the context of vehicular communications, and associated design challenges are highlighted.

5G for Vehicular Communications

Recent advances in various wireless communication technologies and the emergence of computationally rich vehicles are pushing vehicular ad hoc network (VANET) research to the forefront in academia and industry. A lot of research results have been published in various areas (such as routing, broadcasting, security and others) of VANET in the last decade covering both vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) scenarios. One specific area of VANET that still faces significant challenges is the design of reliable and robust media access control (MAC) protocols for V2V communications. The authors present a survey of V2V MAC methods (including various VANET standards) that have been proposed for VANETs over the last few years. The authors also focus on the benefits and limitations of the proposed MAC techniques as well as their ease of implementation in practice and future deployment. In addition some of the challenges that still need to be addressed to enable the implementation of highly efficient and high performance MAC protocols for V2V communications are discussed. Finally, some innovative solutions that can be developed to address these challenges are proposed.

Survey of media access control protocols for vehicular ad hoc networks

To address the need for autonomous control of remote and distributed mobile systems, Machine-to-Machine (M2M) communications are rapidly gaining attention from both academia and industry. M2M communications have recently been deployed in smart grid, home networking, health care, and vehicular networking environments. This paper focuses on M2M communications in the vehicular networking context and investigates areas where M2M principles can improve vehicular networking. Since connected vehicles are essentially a network of machines that are communicating, preferably autonomously, vehicular networks can benefit a lot from M2M communications support. The M2M paradigm enhances vehicular networking by supporting large-scale deployment of devices, cross-platform networking, autonomous monitoring and control, visualization of the system and measurements, and security. We also present some of the challenges that still need to be addressed to fully enable M2M support in the vehicular networking environment. Of these, component standardization and data security management are considered to be the most significant challenges.

Machine-to-Machine (M2M) Communications in Vehicular Networks

The emergence of computationally rich vehicles and recent advances in wireless communication technologies are fuelling vehicular network research in industry and academia. A key challenge to the successful deployment of vehicular communication is the implementation and efficiency of the medium access control (MAC) layer. There are mainly two types of MAC approaches, namely contention based and contention free. The current standard, IEEE 802.11p, is a contention-based approach, which has the severe limitation of unbounded transmission delays. An alternative contention-free approach called dedicated multi-channel MAC (DMMAC) has been proposed in the literature. In this work the authors analyse these two approaches, discuss their limitations and introduce an improved approach called medium access with memory bifurcation and administration (MAMBA). The authors evaluate the performance of the three approaches in highway and urban scenarios, for both low- and high-density traffic. The authors' performance evaluation results show that MAMBA improves throughput and message delivery ratio by up to 150 and 205' over IEEE 802.11p and DMMAC approaches, respectively. MAMBA also improves on the latency achieved by the other methods by up to 72 and 99' respectively, compared to IEEE 802.11p and DMMAC.

Performance comparison of media access control protocols for vehicular ad hoc networks

Although the quadrature mixing radio front-end offers an attractive way to perform frequency translation, its image-rejection capability is severely affected by the gain and phase imbalances (I/Q imbalances) between its two analog signal paths. Digital signal processing techniques have widely been proposed to compensate for these mixer imperfections. Of these techniques, the class of blind compensation techniques seems very attractive since no test signals are required. This paper presents a novel I/Q imbalance extraction technique that uses a Cholesky decomposition of the received signal's covariance matrix to extract the exact imbalances of the front-end. An analysis is also presented on extracting and separating the imbalances of a cascaded imbalanced modulator and demodulator. Both a block-based and an adaptive variant of the technique are proposed, and a performance evaluation over multipath channels is presented.

A Blind $I/Q$ Imbalance Compensation Technique for Direct-Conversion Digital Radio Transceivers

The ubiquitous presence of smartphones provides a new platform on which to implement sensor networks for Intelligent Transport Systems (ITS) applications. Smartphone-based driving behavior monitoring has applications in the insurance industry, fleet management, driver training, and for law enforcement. In this paper we propose a Maximum Likelihood (ML) classifier to identify and classify the recklessness of driving maneuvers using the embedded sensors and GPS receiver of a smartphone. We compare the developed approach to the commonly used Dynamic Time Warping (DTW) based method. The solutions are both suitable for real-time applications, such as driver assistance and safety systems. An endpoint detection algorithm is used on filtered accelerometer and gyroscope data to find the start- and endpoints of driving events. The events are isolated with the endpoint detection algorithm are then classified using the DTW algorithm and an ML classifier. Results show that the ML classifier outperforms the DTW approach.

G.-J. van Rooyen

Papers

Survey of media access control protocols for vehicular ad hoc networks

Machine-to-Machine (M2M) Communications in Vehicular Networks

Performance comparison of media access control protocols for vehicular ad hoc networks

A Blind $I/Q$ Imbalance Compensation Technique for Direct-Conversion Digital Radio Transceivers

Performance Comparison of Dynamic Time Warping (DTW) and a Maximum Likelihood (ML) Classifier in Measuring Driver Behavior with Smartphones