Intelligent Transportation Systems

Transportation systems are very important in modern life; therefore, massive research efforts has been devoted to this field of study in the recent past. Effective vehicular connectivity techniques can significantly enhance efficiency of travel, reduce traffic incidents and improve safety, alleviate the impact of congestion; devising the so-called Intelligent Transportation Systems (ITS) experience. This chapter aims to provide basic concepts and background that is useful for the understanding of this book. An overview of intelligent transportation systems and their applications is presented, followed by a brief discussion of vehicular communications. The chapter also overviews the concepts related to dependability on distributed real-time systems in the scope if ITS.

Visible Light Communication (VLC) is the technique adopting electromagnetic frequencies in the visible spectrum for free space optical communications. Although its practical use is still at early stages, in the last few years research activities have been exploring different solutions to achieve high data rates and reliable links using common LEDs and light sensors. VLC can be used in a variety of applications or end user segments, exploiting already existing lighting infrastructures and thus making VLC a cheap communication system. Among these applications, a prominent case study is that of ITS (Intelligent Transportation Systems), where car headlamps and traffic lights can be used to communicate and fulfil the requirements of road safety applications. This option turns to be particularly effective in short range direct communications to exploit its line-of-sight feature and overcome the issues related to the isotropic nature of radio waves. Recently IEEE undertook standardization activities on VLC, resulting in the IEEE 802.15.7 standard, which disciplines PHY and MAC layer services for Visible-light Personal Area Networks (VPANs). This chapter shows the recent achievements of the experimental research in the scope of VLC prototyping for ITS. Special attention is devoted to the development of a VLC prototype based on IEEE 802.15.7 standard, using low cost embedded systems as the target platforms. The aim is to provide useful considerations for achieving devices suitable to be integrated in existing PANs, or to cooperate with other wireless networks to provide communication services in complex architectures like ITS.

The development of wireless vehicular networks for cooperative Intelligent Transport Systems (ITS) opened the possibility of launching cooperative applications that can improve vehicle and road safety, passenger’s comfort and efficiency of traffic management. These applications exhibit tight latency and throughput requirements, for example safety critical services such as the Emergency Electronic Brake Light require guaranteed maximum latencies lower than 100 ms, while most infotainment applications require QoS support and data rates higher than 1 Mbit/s. Current wireless communication standards such as IEEE 802.11-2012 amendment 6 and ETSI-G5 have some drawbacks in what concerns their medium access control technique, which is based in CSMA/CA, particularly for high speed and high density environments. To deal with such environments, an infrastructured based TDMA protocol, the Vehicular Flexible Time Triggered protocol was proposed. In this chapter several protocol parameters are quantified, taking in account realistic scenarios and current wireless communication standards, that are applicable in these environments. To deploy such an infrastructured based network in an entire motorway might be expensive, therefore a concept of safety zone is used whenever there is a part of the motorway that is covered by road side units that implement the protocol. A worst case approach is used in order to prove that the V-FTT protocol has a bounded delay in what concerns the time occurred between a safety event detection and the instant of time of its reception by all vehicles travelling in the safety zone. With the exception of the lowest bit rate (3 Mbps), the V-FTT protocol has a guaranteed bounded delay under the maximum allowed latency of the most common safety vehicle applications.

A huge research effort has been devoted to the transportation sector in order to make it safer and more efficient, leading to the development of the so-called Intelligent Transportation Systems (ITS). In ITS there is a closed loop interaction between vehicles, drivers and the transportation infrastructure, supported by dedicated networks, usually referred to as vehicular networks. While some of the enabling technologies are entering their mature phase, the communication protocols proposed so far aren’t able to fulfill the timeliness contraints of many ITS services, specially in road congestion scenarios. In order to tackle this issue, several medium access protocols (MAC), either relying on infrastructure or based on direct ad-hoc communication, have been designed. A great number of these protocols employ Time Division Multiple Access (TDMA) techniques to manage communications and attain some degree of determinism. Although the use of spatial reuse algorithms for TDMA protocols (STDMA) has been extensively studied as to increase the efficiency of standard ad-hoc and mesh networks, ITS networks exhibit a combination of features and requirements that are unique and aren’t addressed by these algorithms. This chapter (This chapter is an extended work of [21]) discusses some of the most relevant challenges in providing deterministic real-time communications in ITS vehicular networks as well as the efforts that are being taken to tackle them. Focus on TDMA infrastructure-based protocols and on the challenges of employing spatial reuse methods in vehicular environments is placed. A novel wireless vehicular communication architecture called V-FTT, which aims at providing deterministic communications in vehicular networks, is also presented. The chapter concludes with the design of a traffic scheduling analysis, a STDMA slot assignment algorithm and a Matlab simulator for V-FTT.

Vehicular networks are now an emergent field of research and applications. Using wireless communications in these networks offers a wide range of possibilities, but at the same time poses demands in terms of bounded delay, particularly in safe-ty-related applications. This chapter elaborates on the efficiency of MAC protocols based on IEEE 802.11p/WAVE standard to timely deliver safety messages. It covers several aspects of an infrastructure-based MAC protocol, and also details the characteristics needed for a safety-critical and bounded delay MAC protocol within a specific scenario. On the other side of the spectrum, an alternative solution is relying solely in V2V-based communications to disseminate safety messages. In this sense, it is also presented an approach for cases where the infrastructure may not be accessible (e.g., tunnels), or even not feasible to have total RSU coverage.

This chapter proposes a direction aware cluster-based multichannel MAC (DA-CMAC) protocol for Vehicular Ad-Hoc Networks (VANETs) in which vehicles travelling in the opposite direction may result in a short communication period. Clustering based on the direction of travel can reduce the cost of reconfiguration due to the short communication period. Each cluster consists of Cluster Head (CH), Cluster Members (CMs) and Gateway Vehicles (GV). CH calculates priorities of CMs based on the value of eligibility function that is received from the CM and assign each CM a unique priority based on the future position of CM, CM ID, and eligibility function. The eligibility function is calculated using the number of connected neighbors, average speed deviation, and the average distance between neighbors and itself. Clusters are independently managed and locally reconfigured as vehicles travel. Moreover, the proposed DA-CMAC protocol manages the channel access and allocates time slots to its CMs, reducing access and merging collisions in the channel, by grouping the time slots into two sets based on the direction of movement. Each CMs are allocated with one time slot in both control service channel to achieve fairness in channel access. Simulation results of DA-CMAC are compared with HCA protocol. Simulation results show that the DA-CMAC protocol have higher reliability of packets, fewer CH changes and fewer number of access collisions compared with HCA protocol.

Communication primitives consider information delivery with different guarantees regarding their reliability. The provision of reliability and predictability needs to overcome a number of challenges with respect to failures and a number of known impossibility results. This chapter covers a number of these challenges in the context of vehicular systems and networks. We start by showing the medium access control (MAC) protocol for wireless mobile ad hoc networks can recover from timing failures and message collision and yet provide a predictable schedule in a time-division fashion without the need for external reference, such as commonly synchronized clock. We then consider the case of transport layer protocols and show how to deal with settings in which messages can be omitted, reordered and duplicated. We also consider how mobile ad hoc networks and vehicular networks can organize themselves for emulating virtual nodes as well as emulating replicated state-machines using group communication. In this context, we discuss the different alternatives for overcoming well-known impossibilities when considering cooperative vehicular applications. Finally, we exemplify applications and discuss their validation.

Wireless vehicular communications have been a trending topic in the last few years, leading to the development of a complete set of new standards and the emergence of innovative vehicular applications. Despite the obvious benefits of vehicular networks, it has been a challenging issue to design dependable vehicular communication systems. This is mainly due to the high speed mobility scenarios that are involved and the open nature of these networks. As a consequence, there are scalability problems with the proposed medium access control (MAC) methods under highly dense traffic environments. This results in large values for the end-to-end delay and for the probability of packet drops, compromising the reliability of vehicular communications. Besides that, there are few strategies to enhance fault-tolerance in vehicular systems, whose operation strongly depends on the dynamic topology of the network and on the real-time guarantees provided by the communications protocol. Based on these arguments, this chapter presents a fault-tolerant architecture to improve the dependability of infrastructure-based vehicular networks. The presence of road-side units (RSUs) and a backhauling network adds a degree of determinism that is useful to enforce real-time and dependability, both by providing global knowledge and supporting the operation of collision-free deterministic MAC protocols. One of such protocols is V-FTT, for which the proposed architecture was designed as a case study. Notice, however that this architecture is protocol independent and can be adapted to any wireless communications system. The chapter’s final sections specially focus on the design of fail silent RSUs, by presenting the proposed implementation and the obtained experimental results.

In order to provide Dependable Vehicular Communications for Improved Road Safety, it is necessary to have reliable Vehicular-to-Infrastructure (V2I) and Vehicle-to-Vehicle (V2V) communication. Such requirements demand that the handover process as vehicles move between adjacent Roadside Units (RSUs) be examined in detail to understand how seamless communication can be achieved. Since the use of beacons is a key part of VANETs, it is necessary to investigate how the beaconing process affects the opportunities to effect handovers. A framework is needed to be able to calculate the regions of overlap in adjacent RSU coverage ranges to guarantee ubiquitous connectivity. A highly mobile environment, therefore, makes this a serious challenge and points to the need to look at proactive handover techniques. This chapter, therefore, explores the development of the proactive handover mechanisms required to provide seamless connectivity and dependable communication in VANET environments.

The availability of more realistic road conditions and dynamics provides sound ground to study the issues of Vehicular ad-hoc Network (VANET). In this chapter a new heterogeneous traffic flow based mathematical model is presented, to gain the time and space dynamics of vehicles. To achieve more accurate and realistic data about road conditions, microscopic parameters of varying safety distance between the vehicles and vehicular length are considered in the model. The density dynamics under different road scenarios are calculated under the influence of these constraints with the use of a defined mathematical model. The model is able to capture the impact of road constraints such as traffic lights and road incidents, on the traffic flow. The concept of Vehicular Ad-hoc Networks (VANET) has given mankind opportunities for secure and safe journeys on the roads. VANET is defined as a subclass of Mobile Ad-hoc Networks which holds the characteristics of ad-hoc networks. However due to the dynamic road conditions, traffic flow theory concepts, mobility constraints, human behaviours and vehicular characteristics VANET exhibits different dynamics. These factors have strong influences on the VANET architecture from physical to application layers. This highlights different areas of interest in VANET for researchers to investigate. This study aims to capture the impact of traffic flow theory constraints on the vehicular density under the heterogeneous traffic flow on the road. The microscopic and macroscopic characteristics of vehicles moving on the roads are utilized for the improvement of VANET connectivity dynamics.

The rapid technological growth is now providing global opportunities to enable intelligent transportation system (ITS) to tackle road traffic accidents which is considered one of the world’s largest public injury prevention problem. For this purpose, eCall is an initiative by EU with the purpose to bring rapid assistance to an accident location presents HDy Copilot, an application for accident detection integrated with multimodal alert dissemination, both via eCall and IEEE 802.11p (ITS-G5). The proposed accident detection algorithm receives inputs from the vehicle, via ODB-II, and from the smartphone sensors, namely the accelerometer, the magnetometer and the gyroscope. Android smartphone is used as human machine interface, so that the driver can configure the application, receive road hazard warnings issued by other vehicles in the vicinity and cancel countdown procedures upon false accident detection. The HDy Copilot is developed for Android OS as it provides open source APIs that allow access to its hardware resources. The application is implemented and tested on IEEE 802.11p based prototype and the generated results show that it successfully detects collisions, rollovers and performs the eCall along with sending Minimum Set of Data (MSD).