Intelligent Transportation Systems

From Good Practices to Standards

Paolo Pagano

• Publisher: CRC Press
• Year: 2016
• ISBN:
  9781315353722
• Edition: 1
• Topic: Biological Sciences
• Subtopic: Biology
• Index: Biological Sciences

Intelligent Transport Systems (ITS) are the way forward for sustainable growth of mobility at all levels (local, regional, national, transnational). The book reviews the current status of Research & Development. It includes connected (and autonomous) cars and buses, real-world large-scale field trials, data analysis and assessment of technological solutions. Standards and normative aspects in the domain of Electronic Fee Collection and Cooperative Systems oriented to probe data collection, safety and non-safety critical applications in vehicular networks, are studied. The book provides the rational, perspectives, and technical issues for the implementation of ITS solutions in a genuine inter-modal scenario, taking the example of a Mediterranean seaport, actively involved in testing and validation of ITS standards.

The novelty of this book is that it covers R&D, standards, and pilots, all under one cover. Rather than stressing the novelty in ICT, the authors have presented the need for system-level integration, assessment of existing (standard) solutions, and piloting experiments in real-world industrial scenarios.

CHAPTER
1

Development of an ITS-G5 Station, from the Physical to the MAC Layer

João Almeida^1,2*, Joaquim Ferreira^1,3 and Arnaldo S.R. Oliveira^1,2

¹Instituto de Telecomunicações, Campus Universitário de Santiago 3810-193 Aveiro, Portugal

²DETI – University of Aveiro, Campus Universitário de Santiago 3810-193 Aveiro, Portugal

³ESTGA – University of Aveiro, 3754-909 Águeda, Portugal

*Corresponding author: [email protected]

Abstract

Wireless vehicular networks for cooperative Intelligent Transportation Systems (ITS) have raised widespread interest in the last few years, due to their potential applications and services. Cooperative applications with data sensing, processing and communication provide an unprecedented potential to improve vehicle and road safety, passenger’s comfort and efficiency of traffic management and road monitoring. Safety, efficiency and comfort applications envisaged for ITS exhibit tight latency and throughput requirements. For example safety critical services require guaranteed maximum latencies lower than 100 ms, while most infotainment applications require QoS support and data rates higher than 1 Mbit/s. In this context, BRISA, a motorway operator, challenged a team from Institute of Telecommunications (IT) to contribute with research in this area, to work specifically on the then emergent IEEE 802.11p amendment. Back then, standards in this field were (and still are) evolving and only a very limited number of Commercially Off The Shelf (COTS) components were available. Available COTS chip sets implemented an incomplete stack and, more importantly, have closed implementations (black box) of the standard, with a limited access to the API and programming model. This was an impairment to BRISA track record on open access to technology and independence from manufacturers. On the other hand, from the point of view of a research institution as IT, having the chance of developing from scratch, new technology and draft protocol implementations was considered quite relevant, as it potentiates the inclusion of innovative solutions beyond standards. Examples of such innovative solutions include support for real-time operation and fault-tolerance mechanisms. That was the rationale behind the development of a new ITS-G5 station, which will be described in a tutorial way in this chapter. The chapter presents the architecture of the PHY and MAC layers developed, including the RF front-end, the baseband PHY processing chains, the time sensitive lower MAC implementation and the software upper MAC. The most important design decisions, the validation methodologies and the interoperability tests are also discussed. The chapter ends with the presentation of the real-time extensions and primitives of the platform enabling the implementation of real-time protocols.

1. Motivation

Road traffic accidents are a serious problem worldwide, being one of the major causes of death. During 2014, there were about 26,000 fatalities, only inside the European Union borders [1]. Vehicular communication systems are being developed with the intention of improving traffic safety, by extending the sensing range of the vehicles via wireless transmission of information. Vehicular communications are an important field of research in the area of Intelligent Transportation Systems (ITS). Future ITS will require dependable wireless communications among vehicles and between vehicles and the roadside infrastructure. Vehicular communication systems can be more effective in preventing road accidents than the case where vehicles act individually to achieve the same goal. This is due to the cooperative techniques that can be exploited when vehicles and the roadside stations are aware of the situation of other parties (e.g. location, speed and heading). As an example of this class of safety applications, chain collisions could be avoided if the information about the first crash is disseminated by all the other nodes in the vicinity of the accident. Dedicated Short-Range Communications (DSRC) is a wireless technology that has been designed to support such visionary applications based on vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications. Vehicular communications supported by DSRC systems operate in the 5.9 GHz reserved spectrum band and exhibit an approximate maximum range of 1000 m.

Safety critical vehicular applications are inherently hard real-time systems for which the failure of meeting a deadline can lead to severe damage and pose significant threat to human life [2]. The first few steps in attempting to provide the necessary quality of service were given by acknowledging that vehicular communications require specifically designed communication systems in order to cope with high network dynamics and short connection times [3]. Some standards attempting to solve these issues were developed, namely the IEEE WAVE and ETSI ITS-G5 [4], both based on the same IEEE 802.11 physical layer [5] but containing specific features tailored for vehicular environment use, such as: reduced bandwidth channels, increased maximum power and segregated frequency bands. The main differences between these two standards are the medium access mechanisms, with WAVE using only the already existing Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) and Enhanced Distributed Channel Access (EDCA) mechanisms, while ITS-G5 adding Decentralized Congestion Control (DCC) on top of them, as an upper layer function that strive to limit the channel load by changing MAC and other transmission parameters. However, these methods have been proved insufficient in dealing with what is regarded as one of the most challenging issues in providing hard real-time characteristics to vehicular communication systems: deterministic channel access under high load conditions [3, 6, 7]. In this context, ITS stations need to be equipped with mechanisms to support deterministic communications at the lowest possible layer of the communications stack, in order to provide bounded transmission delays, reduced jitter and strict traffic isolation between safety and infotainment message streams, i.e., support for deterministic Medium Access Control (MAC) protocols.

Despite the use of dedicated spectrum and specially designed devices, the current standards governing VANET still fall short of providing dependable MAC, as desirable if this technology is to be used in support of safety applications. Moreover, study of novel MAC mechanisms is hampered by the fact that the highly dynamic channel makes it difficult to conduct simulated experiments properly [3], calling for the use of actual devices that implement the relevant standards but at the same time allow experimentation with new mechanisms, beyond current standards. Despite the growing popularity of Software Defined Radio (SDR), open implementations of IEEE 802.11p, capable of supporting the operation of deterministic MAC protocols both at hardware and software level, are not widely available. Furthermore, existing implementations of IEEE 802.11p lack support for deterministic Medium Access Control (MAC) protocols that require a set of requirements, which, to the best of one’s knowledge, are not usually available in COTS transceivers.

The work presented in this chapter describes some contributions made within the scope of two projects: HEADWAY (Highway Environment ADvanced WArning sYstem) and ICSI (Intelligent Cooperative Sensing for Improved traffic efficiency). The former project aims to implement a communications platform compliant with IEEE 802.11p standard and the IEEE 1609.x sub-standards, while the latter is focused on the development of a deterministic MAC protocol, timely security services and fault-tolerance mechanisms for cooperative systems based on IEEE WAVE and ETSI ITS-G5. The main contribution of this chapter is a detailed description of the design of a ITS-G5 station, which was built from scratch, with the development of all the OSI layers, from the Physical (PHY) up to the Application. For this purpose, a SDR approach was adopted where the time-critical operations are implemented in hardware (Physical and Lower MAC layers) and the other operations are implemented in software (Upper MAC layer and above). The developed platform can operate either as a road-side unit (RSU), when integrated in the road infrastructure, or as an on-board unit (OBU), when it’s used as a vehicle communications device.

Several other projects have decided to adopt a different approach to the development of IEEE WAVE/ETSI ITS-G5 compliant platforms, by extending or tweaking the functionality on top of equipment compliant with the IEEE 802.11a/g family, so that it provides the same services and functionality as the WAVE standards. That approach has obvious advantages in terms of development time, since the bulk of the work is done by a third party implementation, but the core of the device is still a black box to which the develope...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Dedication
• Table of Contents
• Preface
• 1. Development of an ITS-G5 Station, from the Physical to the MAC Layer
• 2. When Buses Become Smart: The OBIT Experience
• 3. Data Management and Data Sharing in Field Operational Tests
• 4. Design, Implementation and Field Trail of DSRC-based Transit Signal Priority System
• 5. Toward Smart Autonomous Cars
• 6. Tolling Systems: Towards a Global Set of Standards
• 7. Cooperative ITS: The SDO Perspective for Early Deployment
• 8. Probe Vehicle Information Systems
• 9. Complex Infrastructures: The Benefit of ITS Services in Seaports
• Index