Universidade de Aveiro Departamento deElectr´onica, Telecomunicac¸˜oes e Inform´atica 2013
Paulo Jorge
Henriques de Sousa
Comunica¸
c˜
oes veiculares multiprotocolo n˜
ao IP
Universidade de Aveiro Departamento deElectr´onica, Telecomunicac¸˜oes e Inform´atica 2013
Paulo Jorge
Henriques de Sousa
Comunica¸
c˜
oes veiculares multiprotocolo n˜
ao IP
Non-IP multiprotocol for vehicular communications
Dissertac¸˜ao apresentada `a Universidade de Aveiro para cumprimento dos requisitos necess´arios `a obtenc¸˜ao do grau de Mestre em Engenharia Electr´onica e Telecomunicac¸˜oes, realizada sob a orientac¸˜ao cient´ıfca do Pro-fessor Doutor Jo˜ao Paulo Barraca, Professor convidado do Departamento de Electr´onica, Telecomunicac¸˜oes e Inform´atica da Universidade de Aveiro, e do Professor Doutor Joaquim Castro Ferreira, Professor Adjunto na Escola Superior de Tecnologia e Gest˜ao de ´Agueda da Universidade de Aveiro.
o j´uri / the jury
presidente / president Professor Doutor Paulo Bacelar Reis Pedreiras
Professor Auxiliar, Universidade de Aveiro
vogais / examiners committee Professor Doutor Jo˜ao Paulo Barraca
Assistente Convidado, Universidade de Aveiro
Professor Doutor Joaquim Jos´e de Castro Ferreira
Professor Adjunto, Universidade de Aveiro
Professor Doutor Pedro Alexandre de Sousa Gon¸calves
agradecimentos / acknowledgements
I would like to thank my parents for all efforts made during these five years. One of the big reasons that i had to be successful in this important stage of my life, was to recognize that they push all the way to make my grad-uation possible. Regarding my friends during this time, they provided me unforgettable moments and at the same time helped me a lot to overcome difficult and different hurdles in a good mood. I can not forget my girlfriend and address to her a big gratitude by all support in difficult days, her entire understanding, caring, affection, motivation, patience and follow the along the course. I thank all collaborators of Institute of Telecommunications, specially to those who were part of ICSI/HEADWAY Team and showed spirit of mutual aid. I would like to thank my supervisors for guidance, motivation, dedication and availability provided during this year. They were always available to help and without them, my work would be much more difficult.
Palavras-chave VANET, Ad hoc, IEEE 802.11p, IEEE 1609.3, IEEE 1609.2, ISO CALM FAST, ETSI, n˜ao-IP, CAM, DENM, Socket, API, Comunicac¸˜ao inter-veicular
Resumo Ao longo dos ´ultimos anos, todo o ambiente relacionado com o transporte tem sido alvo de grande avanc¸o tecnol´ogico. Por consequˆencia, os ve´ıculos est˜ao a ser equipados com melhor e mais avanc¸ada tecnologia do mercado. Para al´em disso, o crescimento e ambic¸˜ao em aspectos relacionados com a seguranc¸a na estrada e por servic¸os que melhorem o conforto, bem como a qualidade de conduc¸˜ao, est˜ao a levar ao interesse dos grandes construtores em criar um ambiente de cooperac¸˜ao e conectividade entre ve´ıculos. Nesta dissertac¸˜ao, ´e explorado o trabalho relevante que tem sido feito nesta ´
area de redes veiculares, em particular nas indicac¸˜oes dadas pelas normas WAVE (IEEE 1609.x) e ISO CALM. ´E feito um levantamento das suas van-tagens e desvanvan-tagens, e analisadas algumas implementac¸˜oes e conclus˜oes apresentadas em projectos relacionados.
De modo a alcanc¸ar o objectivo de implementar e integrar uma alterna-tiva, escal´avel e modular para a camada de rede e transporte, uma soluc¸˜ao baseada em multiprotocolo n˜ao-IP foi desenvolvida. Esta ideia surge no ˆ
ambito da tentativa de convergˆencia entre normas e o objectivo de desen-volver e implementar uma estrat´egia global para este tipo de situac¸˜oes. Todo o trabalho feito neste ˆambito ´e integrado com outros projectos de dissertac¸˜ao (desenvolvidos tamb´em sob o projecto HEADWAY/ICSI) na ´area da seguranc¸a e verificac¸˜ao de mensagens, e suporte para aplicac¸˜ao (facili-ties layer). Os diferentes m´odulos foram posteriormente migrados para um single board computer (Linux-based e de baixo consumo, Raspeberry PI) que ´e respons´avel pela configurac¸˜ao e trocas de dados entre a aplicac¸˜ao gr´afica (smartphone) e a plataforma DSRC desenvolvida especificamente para comunicac¸˜oes veiculares a 5.9 GHz.
De modo a testar e avaliar o desempenho do sistema, foram realizados al-guns testes, dentre os quais destacam-se: gerac¸˜ao e envio de mensagens CAM ao longo da pilha protocolar e verificac¸˜ao da integridade dos da-dos e restric¸˜oes temporais, e teste da metodologia multiprotocolo (troca em simultˆaneo de mensagens de dois tipos de estrutura de dados). Foram tamb´em realizados testes, tendo em conta o overhead e latˆencia introduzida por cada modulo que comp˜oe o sitema, variando o tamanho das mensagens.
Keywords VANET, Ad hoc, IEEE 802.11p, IEEE 1609.3, IEEE 1609.2, ISO CALM FAST, ETSI, Non-IP, CAM, DENM, Socket, API, Inter-vehicle communi-cation
Abstract Over the last few years, transport systems experienced a great technological advancement. As a consequence, vehicles are increasingly equipped with more electronic features as on board computing devices. Moreover, the growth of related aspects such the provision of road safety or infotainment and increase driver comfort led to growing interest by the manufacturers and consumers for connectivity between vehicles.
This dissertation explores the relevant work done in the area of networking for vehicular environments, in particular projects that followed IEEE 1609.x standards namely WAVE Short Message Protocol (WSMP) or FAST pro-tocol from ISO CALM. A survey was made to understand the strengths and weakness of each one, and also it was analysed some implementation descriptions by other related projects.
Towards the objective to implement an uniform, modular and scalable so-lution that satisfy the critical requirements characteristic of this kind of environments, an alternative based on a multi protocol network stack com-munication was designed. This idea emerges in parallel with the efforts made by standardization entities, in direction to a global standard and uni-form deployment.
All work done in network and transport layer was integrated with other projects (also developed under HEADWAY/ICSI project) such as security verification, encryption and application support functions. It was also in-tegrated all modules in a Linux based machine (in this case it was used Raspberry PI) that support all the configuration and data flow between HMI/smartphone and the DSRC platform responsible for 5.9 GHz commu-nication.
In order to evaluate the performance of the system, it was tested in some scenarios such as CAM dispatch and subsequent verification of data in-tegrity and time constraints, multiprotocol methodology test (exchange at same time of two different type of message structure), overhead and latency introduced by each module for different size of payloads.
Contents
Contents i
List of Figures iii
List of Tables v Acronyms vii 1 Introduction 1 1.1 Motivation . . . 1 1.2 Objectives . . . 3 1.3 Contributions . . . 3 1.4 Dissertation Outline . . . 3 2 Vehicular Communications 5 2.1 Market Vision and Challenges of ITS deployment . . . 6
2.2 Standardization Process . . . 8
2.3 ITS programmes and ongoing efforts . . . 10
2.3.1 USA . . . 10
2.3.2 Japan . . . 10
2.3.3 Europe . . . 11
2.4 Usage Scenarios . . . 13
2.5 Requirements and time characterization . . . 15
3 Vehicular Communication Standards 17 3.1 Introduction. . . 17
3.2 IEEE 1609 family - WAVE . . . 17
3.3 ISO CALM . . . 19
3.4 Geo-networking . . . 21
3.5 Protocols Evaluation and Deployment strategies . . . 23
3.6 Protocols summary and combined solutions . . . 24
3.7 Facilities in Upper Layers - Application Support . . . 25
3.7.1 CAM Messages . . . 25
4 Network and Transport Layer Specification 29
4.1 Introduction. . . 29
4.2 Existing Solutions . . . 29
4.3 Architecture. . . 31
4.4 Interface and Messages . . . 33
4.4.1 Communication between API’s . . . 33
4.4.2 Service Router - Daemon . . . 35
4.4.3 RecvServer and callback functions . . . 38
5 Integration in the ITS stack and implementation on DSRC platform 41 5.1 Scope . . . 41
5.2 Deployment Scenario . . . 41
5.3 Integration of the modules . . . 44
5.3.1 Application support interface . . . 44
5.3.2 Verification and Crypto Tasks. . . 45
5.4 Integration with DSRC platform . . . 47
5.4.1 Board Overview . . . 48
5.4.2 Integration with board upper MAC driver . . . 49
6 Experimental Results 51 6.1 Testing Scenarios . . . 52
6.1.1 Personal Laptop . . . 52
Different payload size . . . 53
NIP performance evaluation . . . 55
Time elapsed between two machines . . . 57
Time Performance of other modules . . . 59
6.1.2 Raspberry PI . . . 61
Send CAMs at different frequencies. . . 62
NIP performance . . . 64
CAM & FAST Advertisement . . . 66
Conclusions and Future Work 69
List of Figures
1.1 Example of cooperative system in a vehicular communication environment [3] 2
2.1 Challenges associated to ITS and vehicular communication . . . 7
2.2 Communication systems in ITS system architecture, from [13] . . . 8
2.3 DSRC frequency bands especifications, base on [16] . . . 9
2.4 ITS-Safety 2010 frequency bands in Japan, from [4] . . . 11
2.5 Relations between standardization bodies, from [4] . . . 12
2.6 Some of the possible applications and use cases, from [31][32] . . . 14
2.7 Platooning example in traffic light scenario . . . 15
3.1 WAVE Arquitecture, from [15] . . . 18
3.2 WAVE Short Message format . . . 19
3.3 CALM architecture, from [44] . . . 20
3.4 CALM FAST packet structure . . . 21
3.5 Forwarding Types, from [31][32]. . . 21
3.6 General scope o GeoNet, from [47] . . . 22
3.7 ITS Architecture, from [54] . . . 26
3.8 Application flow diagram (CAM message), from [55] . . . 27
3.9 Structure of a DENM, from [57]. . . 28
4.1 CALM FAST - CVIS implementation, according to ISO/DIS 29281 . . . 29
4.2 CALM FAST according to FEILOTS/SPITS . . . 30
4.3 Architecture of the system . . . 31
4.4 Multi protocol Handling . . . 32
4.5 API use case . . . 34
4.6 Internal process flow of the daemon . . . 37
4.7 Client requests handler . . . 39
5.1 Inter vehicular communication test scenario . . . 42
5.2 Layers organization and comparison . . . 43
5.3 Integration Architecture . . . 45
5.4 Time window in modules relantionship . . . 46
5.5 Complete ITS system architecture, from [68] . . . 47
5.6 IT2S board with FPGA and RF frontend modules, from [68] . . . 49
5.7 Device Driver Model - Bind to Device . . . 50
6.2 Jitter associated to packet transmission at 10Hz. . . 53
6.3 Jitter associated to packet transmission at 5Hz . . . 54
6.4 Serialization and Deserialization . . . 55
6.5 Send and Receive . . . 56
6.6 Time elapsed to establish/close connecion . . . 57
6.7 Trip time between two stations . . . 58
6.8 Trip Time between stations . . . 59
6.9 Signature and Verification times . . . 59
6.10 CAM generation Time . . . 60
6.11 Core sytem running at Raspberry PI . . . 61
6.12 Sending 10 messages . . . 62
6.13 Sending 100 messages . . . 62
6.14 Sending 1000 messages . . . 63
6.15 Elapsed time in APIs connection . . . 64
6.16 Serialization and Deserialization Processes . . . 65
6.17 Time necessary to cross NIP. . . 65
6.18 Frequency of transmission for both types of data . . . 66
6.19 Packets captured between two machines . . . 67
List of Tables
2.1 Summary of use cases and technical requirements [4][15] . . . 16
3.1 Overview about standards . . . 24
6.1 Hardware systems comparision . . . 52
6.2 Jitter in trasmission process . . . 54
6.3 Connection Time Analysis . . . 57
6.4 NTP Configuration . . . 58
6.5 Trip Time Analysis . . . 58
6.6 System usage comparision . . . 61
6.7 Jitter Analysis . . . 63
6.8 Connection Time Analysis . . . 64
6.9 Serialization Time Analysis . . . 65
6.10 Time elapsed in the sending and receiving processes . . . 66
Acronyms
API Application Programming Interface ASV Advanced Safety Vehicle
C2C Car to Car
C2C-CC Car-2-Car Communication Consortium CALM Communications Access for Land Mobiles CAM Cooperative Awareness Messages
CEN European Committee for Standardization
CENELEC European Committee for Electro-technical Standardization COOPERS COOPerative SystEMS for Intelligent Road Safety
CVIS Cooperative Vehicle-Infrastructure Systems
DENM Decentralized Environmental Notification Messages DSRC Dedicated Short Range Communications
ETSI European Telecommunications Standards Institute FIFO First In First Out
FPGA Field-Programmable Gate Array GCDC Grand Cooperative Drive Challenge GPU Graphics Processing Unit
GUI Graphical User Interface HD High Definition
HEADWAY Highway Environment ADvanced WArning sYstem HMI Human Machine Interface
IEEE Institute of Electrical and Electronic Engineering ISO International Organization for Standardization IT Instituto de Telecomunicac˜oes
ITS Intelligence Transports Systems IVC Inter-vehicle communication LAN Local Area Network
MAC Medium Access Control
MIMO Multiple Input/Multiple Output NIP Non-IP Protocol
NTP Network Time Protocol OBU On Board Unit
PHY Physical Layer
PSID Provider Service Identifier RSU Road Side Unit
SBC Single Board Computer
SEVECOM Secure Vehicular Communication SMA SubMiniature version A
SPITS Strategic Platform for Intelligent Traffic Systems SSH Secure Shell
TDMA Time Division Multiple Access V2I Vehicle-to-Infrastructure
V2V Vehicle to Vehicle
VANET Vehicular Ad-Hoc Network VM Virtual Machine
VSC Vehicle Safety Communications
WAVE Wireless Access in Vehicular Environment WBSS WAVE Basic Service Set
Chapter 1
Introduction
1.1
Motivation
Over the last decade, the concept of vehicular communications had an exponential growth and many technical developments were achieved due to several Intelligence Transports Sys-tems (ITS) projects developed, specially in USA, Europe or Japan. Vehicular networking is seen as a world of opportunities in the near future. This topic covers areas that span from the provision of basic Internet access, to enabling communication for autonomous control of the entire transportation infrastructure. It is seen as a big step towards the future of transport and vehicular environment, and also a change of paradigm of mobility. Some of the oppor-tunities that can be found, are related to real improvements on system efficiency, congestion, and driver safety, but some also deal with improving the driving experience. As one of the hottest topics in vehicular communications is to improve road safety, developing driver assis-tance systems able to collect data concerning the status of the surrounding environment, to quickly detect potentially dangerous situations and notify the driver whenever required [1]. Annually, about 1.2 million fatal accidents occur around the world and more that 50 million persons are injured. It is expected that in 2020, road traffic fatalities are likely to become one of the leading cause of death [2].
Safety improvement is not the only target of vehicular communications, it can also con-tribute to avoid congestion by finding better routes in real time. This could have significant economic impact by saving fuel and time. Major drive for the deployment of vehicular com-munications are related to road safety applications. In parallel, there has been an increasing interest in providing Internet services. The Internet connectivity capability is seen by con-sumers as a very valuable feature and could foster a widespread adoption of wireless vehicular communications, by providing safety, comfort and infotainment services sharing the same access technology.
The future of road traffic is imagined as cooperative world, in which vehicles are aware of their environment as depicted in figure 1.1. In this visionary scenario, cooperation between vehicles is mandatory to achieve optimized traffic efficiency, safety and security, as opposed
to non-cooperative solutions.
Figure 1.1: Example of cooperative system in a vehicular communication environment [3]
Inter-vehicle communication (IVC)is attracting considerable attention from the research community and automotive industry, since the number of projects and research programmes, as well as investment in this area, has been growing every year. Researchers have shown im-portant results, wherein cooperative intelligent systems can be used for low maintenance cost decision support applications, that allow decision-makers to take more complex decisions [4]. However, several challenges arise among technical aspects and important requirements related to high mobility of vehicles, ranging from relative speeds between nodes and real-time nature of applications, to trade-off between different ways to notify other stations (advantages and drawbacks of ad-hoc broadcast) [5]. Due to the particularities of vehicular environment, e.g., high-speed mobility causing unpredictable time-varying changes in connectivity, IP protocols are not suitable for safety communications as they require channel scanning, authentication and association. Safety vehicular communications rely instead on non-IP protocols, either WAVE Short Message Protocol or Fast Network and Transport Protocol. In this context, the motivation of this dissertation is to explore some of these challenges, notably on the non-IP communications support for safety wireless vehicular communications.
1.2
Objectives
Regarding all aspects referred above, the purpose of this dissertation is to develop a solution for non-IP wireless vehicular communication. That solution aims to move toward the convergence of the ideas that have emerged in recent years. To do so, one of the objectives is to study and revisit the most relevant work that has been done along the past years in vehicular networks and present an implementation for network and transport layer. The analysis and discussion of related deployments, alongside of the study ofWAVE Short Message Protocol (WSMP)from WAVE IEEE 1609.3, ISO CALM FAST and IEEE 802.11p protocols, will be the starting point of this project. The main goal of this dissertation, is to develop a system that satisfy requirements of vehicular communications such as time constraints, scalability for further upgrades and above all, ensure reliability and feasibility. That system will be based on multiprotocol features, since the aim is to handle both protocols at same time (WSMP and CALM FAST) and integrate it with the IT2S platform, a 5.9 GHz communication DSRC board developed at IT/Aveiro. Other objective is the integration of the multiprotocol non-IP communications with upper layers of the ITS protocol stack, namely with facilities layer, such as CAM/DENM data exchange and the addiction of security strategies specified in IEEE 1609.2.
Finally, it is intended to test the performance of system through simulations in different scenarios and, if possible, move to real case with measurements in the road. With results obtained, the appropriate conclusions will be drawn related to the system behaviour as well as its feasibility and reliability.
1.3
Contributions
The research area of vehicular communications is constantly changing and, sometimes what is now given as standard, tomorrow it could be something that is out of date and no longer makes sense. Looking from the perspective of contribution to the research area, some-thing new and innovative was done. It will be presented in the next sections a multiprotocol system based on two worldwide recognized standards (WSMP and CALM FAST). Despite the desire and some efforts already made towards the unification of these two standards, the work done in the scope of this dissertation can be considered somehow innovative. The methodol-ogy followed by this dissertation can contribute, in some way to enable the communication between two systems that follow different communication protocols. At least during a phase in which there is still no prevalent standard.
1.4
Dissertation Outline
This dissertation is organized in seven main chapters. Apart from the introduction, a review of the state of the art in vehicular communications is done. Here, some background aspects and overview about vehicular communications are studied, as well as exploration of
associated projects in particular the relevant ITS projects carried worldwide. In the chapter 3, the main standards for ITS networking purposes are studied. A close look at the most important standards such ISO CALM and WAVE 1609 of IEEE, as well as the major focus of the moment of ETSI in higher layers of ITS protocol stack (CAM and DENM) are discussed. The description of Network and Transport Layer proposed in this project, is made in chapter 4. The architecture of whole system and some assumptions that are taken from other projects, as well as the data flow and data structures are explained. Important software details and specifications are addressed. In chapter 5, integration with other modules developed also in the scope of HEADWAY/ICSI project is explained. It is presented the target for a full ITS testbed/platform. Finally, the validation of the system performance in different scenarios and at different circumstances is characterized. Performance evaluation of each module and consequent impacts for the global system is discussed (chapter 6). The conclusions drawn (what is the outcome of this dissertation) and possible future work and improvements are summarized in chapter 7.
Chapter 2
Vehicular Communications
Over the recent years, several initiatives to create safer and more efficient driving condi-tions, emerged and begun to draw strong attention and support. Vehicular communications play a central role in this effort, enabling a variety of applications for safety, traffic efficiency, driver assistance, and infotainment. Inter-vehicle communication (IVC) area is attracting considerable attention from the research community and automotive industry [6]. Communi-cation in this type of environments received significant attention especially from the ad-hoc networking community as one prime application area for mobile ad-hoc networks. In this con-text routing protocols have been modified and tested to cope with vehicular mobility patterns, roadside gateways were investigated as a means of Internet access, and medium access mech-anisms have been developed to support multi-hop car-to-car communication. These efforts led to the establishment of the termVehicular Ad-Hoc Network (VANET). Thereby,VANET
concept is emerging as a new class of wireless network, spontaneously formed between moving vehicles equipped with wireless interfaces that could have similar or different radio interface technologies, employing short-range to medium-range communications systems [7]. In the
VANET, the nodes are vehicles and the network is established through communications that are made among nearby vehicles and optional fixed equipment on the roadside (On Board Unit (OBU)and Road Side Unit (RSU)) [8].
Hereupon, a world of opportunities that covers a lot of technological areas arises. Vehicular communications area span from providing basic Internet access to enabling communication for autonomous control of the entire vehicle in a way analogous to packet switching in computer networks. Vehicular networking protocols will allow nodes, in this case, vehicles or road-side infrastructure units, to communicate with each other over single or multiple hops. In other words, nodes will act both as end points and routers, with vehicular networks emerging as the first commercial instantiation of the mobile ad-hoc networking technology. Nevertheless, since this vehicular communication concept has self-organizing operation and unique features, is unavoidable that there are advantages and disadvantages. A rich set of tools are offered to drivers and authorities, but a formidable set of abuses and attacks becomes possible. Hence, the security of vehicular networks is indispensable, because otherwise these systems could
lead to unwanted behaviour, in ways that would actually jeopardize the benefits of their deployment [9].
Focusing on safety perspective, one key challenge forVehicle to Vehicle (V2V) communi-cation technologies, it will be achieve fully deployment in high-density vehicular scenarios due to the high data load. The high load on the channel is likely to result in an increased amount of packet collisions and, consequently, in decreased safety level, as seen by the active-safety application. Thus, beacon messages will not successfully be decoded, even when sent by a nearby vehicle, and event-driven messages will show a slow unreliable dissemination process. Thereby, strategies to face off the load on the medium, that results from periodic message exchange, should carefully be addressed to prevent deterioration of the quality of reception of safety-related information [10].
Among the distinctive features ofIVC, it can be mentioned the warnings for environmen-tal hazards (warnings about weather conditions as rain or ice on the road) or abrupt vehicle kinetic changes as emergency braking, traffic and road conditions (alternative routes can be available according to congestion or construction sites), automatic toll collect and tourist information. Taking into account the exchange of information between vehicles and/or in-frastructures, two types of messages can be identified: periodic and event driven. Regarding the first one, this kind of messages are typically called beacons and are associated to the exchange of status information that contain the vehicle’s position, speed, heading, etc. They can be used by safety applications to detect potentially dangerous situations for the driver, for instance in case of a highway entrance with poor visibility or when a tight curve is next. Thereunto, a global navigation system, e.g., a GPS is mandatory in vehicles equipment in or-der to determine its absolute position. On the other hand, when an abnormal condition or an imminent risk is detected by a vehicle, an event-driven message is generated and disseminated through parts of the vehicular network with the highest priority. Throughout chapter 3, it will be addressed and studied in more detail these kind of messages in particular the standards defined byEuropean Telecommunications Standards Institute (ETSI) (CAM/DENM).
2.1
Market Vision and Challenges of ITS deployment
As previously mentioned, one of the applications ofIVCis associated to safety applications and cooperative driving systems. One of the major requirement in this type of application is to assure the fast delivery of information to the cars in the affected area, typically in the originator’s neighbourhood. Interest in a message is given by the physical location rather than a node’s identity, as the identities of the receivers are unknown to the sender. However there are some key issues in vehicular systems that are crucial for introduction in the consumer market. The slowly increasing penetration rate as well as the presence of legacy devices yields a number of challenges:
• consumers only buy technology useful for them andIVCneeds to offer working services that can add something more to the users;
• services need to keep working with an increasing number of equipped cars;
• future and legacy applications need to work in parallel, thus they need to be designed for coexistence with respect to both hardware and software.
Thus, vehicular communications must deal with aim of increase of the quality and system efficiency but also with the improvement of driving experience. Features as internet access and infotainment applications are definitely essential [11].
As they come up with new applications and new desires for the future of vehicular mobility, new challenges arise in several ways (figure2.1). Since the communication will flow over de air, questions about reliability and efficiency of data exchange arises. As refereed early, high-density scenarios will cause overload of the systems and errors, interferences and collisions will be unavoidable. Regarding these critical scenarios, they can change rapidly. Dynamic topologies are necessary to deal with different and singular scenarios as urban, highway or rural ones. To establish and deploy these different and dynamic network topologies, important requirements emerge such as capability of forwarding data in a broader area, multi-networks management, etc.
Vehicular communication security is maybe a major challenge, having a great impact on future deployment and applications of vehicular networks. Thereby appropriate and efficient security mechanisms should be added so that authentication, access control, trust and secure communication between vehicles is achieved. Sometimes the safety and security are confused and it is necessary to separate them. Safety rather concerns peoples’ safety on roads including drivers and passengers, while security concerns the secure data transfer. Nevertheless, the non secure data transfer has an impact on peoples’ safety even when intelligent traffic is in place so IVC need to take into account both issues because in fact, they are very close. For providing vehicular communication security, robust and distributed security mechanisms should exist. These mechanisms should adapt to any vehicular environment and any type of application [12].
Figure 2.1: Challenges associated to ITS and vehicular communication
In order to face of and overcome these challenges, car manufacturers and public transport authorities have invested a lot and joined forces to propel Intelligence Transports Systems (ITS) field. One of these examples was the creation of Car-2-Car Communication
Consor-tium (C2C-CC)that was initiated by important European car manufacturer’s as BMW, Audi, FIAT, etc. With the main objective of achieving interoperability in vehicular environments and trying an harmonization of worldwide standards, theC2C-CC work is linked to the cre-ation of an open European industry standard for CAR-2-X communiccre-ation based on wireless LAN technology and develop deployment strategies. Otherwise, ETSI, concerning vehicular communications, founded an ITS committee that works in all ITS deployment (figure2.2).
Figure 2.2: Communication systems in ITS system architecture, from [13]
A lot ofITSprogrammes and projects directed their work to define and develop the essen-tial “components” for create this cooperative mobile world. Frequency spectrum allocation, standards, agreements needed to achieve such requirements of this type of communications were elaborated and contributed to modulate and finalize the concept of VANET and “paving the way to unlimited opportunities for car-to-car applications” [14]. There are many publi-cations of test-beds that arose based on new standards and several International Consortia with the aim of vehicular communications promotion and demonstration of their feasibility and effectiveness.
In the standardization process in vehicular communications, the first barrier was linked to the need of allocate frequencies for this purpose.
2.2
Standardization Process
In the late 90’s, the U.S. Federal Communication allocated 75 MHz of theDedicated Short Range Communications (DSRC) spectrum at 5.9 GHz, to be used exclusively for
vehicle-to-vehicle and infrastructure-to-vehicle-to-vehicle communication in North America whereas in Japan, the allocated frequency bands for DSRCpurpose range from 5.770 to 5.850 GHz. On the other hand, in Europe, the process was more complicated. Compared to the U.S.A or Japan, the process for frequency allocation was considerably more complex and slow since, all European countries and their national authorities are involved. After a few years of work for frequency regulation and study of compatibility aspects, the European Commission made a decision, and the spectrum has been allocated since 2008 (frequency bands 5.875-5.905 GHz for road safety) [15]. In figure 2.3, it is shown also the ISM band reserved internationally for radio frequency energy (for industrial, scientific, and medical purposes).
Figure 2.3: DSRC frequency bands especifications, base on [16]
Dedicated Short Range Communication (DSRC) is a general RF solution aimed at es-tablishing a communication link among vehicles and roadsides infrastructures. One of the important problems for DSRC deployment is maintaining high performance under heavy channel load.
The DSRC is a key enabling technology for the next generation of cooperation systems since, it has the general purpose of provide RF communications link among vehicles and roadsides. It can be defined as a radio technology and medium-range wireless communication capability that permits very high data transmission in critical communication situations. Is essentially based on IEEE 802.11a [17] with an adjustment for low overhead operations in the
DSRCspectrum. Therefore with the objective of adopting a single standard for the physical and medium access protocol layers, emerged the standard known as 802.11p [18][19].
2.3
ITS programmes and ongoing efforts
As already stated, the opportunities and areas covered by the applications of the coopera-tive systems rapidly captured important support and increasingly are emerging R&D projects directed to ITS field. Many of the results and recommendations already achieved, derived from ITS programmes and projects that currently are completed or are in ongoing process around the world.
2.3.1 USA
In United States, among the ones that are taking more impact are the SafeTrip21 - Safe and Efficient Travel through Innovation and Partnership for the 21st century. A project that begun in 2008 and continues today with the main purpose of accomplishing operational tests and demonstration, in order to accelerate the deployment of near-market-ready ITS
technologies that have the ability and the potential to deliver safety and mobility benefits. The main goal is to explore/validate the benefits of real-time traveller information gathered from traffic probes [20]. Another one is Vehicle2Vehicle (V2V) communication for safety, a key research program that aims to develop V2V active safety applications that address the most critical crash scenarios, estimate accurately the safety benefits and work alongside with industry to enable market factors. It sub serve and help the deployment of the V2V
communication based safety systems that should enhance safety across the vehicle fleet within the USA [21].
Also associated to safety applications, Vehicle Safety Communications (VSC-A) was a project that, between 2006 and 2009 had focused on development and testing communication-based vehicle safety systems to determine whether vehicle positioning in combination with
DSRC at 5.9 GHz can improve the autonomous vehicle based safety systems and/or enable new communication-based safety applications. From Vehicle Safety Communications (VSC), some important requirements were specified related to the traffic safety applications. Some of them are: safety messages should have a maximum latency of 100 ms, a generation frequency of 10 messages per second and they should be able to travel for a minimum range of 150 meters. VSC-A had a significant participation in the development of important standards such as IEEE 802.11p and IEEE 1609 [22].
2.3.2 Japan
Currently, the main public and private organizations that are responsible for research, deployment, and standardization (figure 2.4) of ITS in Japan are the DSRC Forum Japan,
ITS Info-communications Forum and Public and Private sectors Joint Research. Among the relevant projects done in ITSscope are: Smartway Cooperative Systems, a concept that was developed based on Japan’s experiences in the deployment ofITSand consists of road/vehicle communication and processing systems. Smartway has progressed to become a cooperative vehicle-highway system that collects data using on board sensors and provides information
directly to a driver through the networking of road and vehicle. Smartway system supports vehicle to infrastructure communication at 5.8 GHz, combining a variety of services including warning in a singleOBU. The SmartwayOBUsystem was successfully demonstrated in field and became operational in Summer of 2006. It was a great boost on reversing the negative legacy of motorization.
Figure 2.4: ITS-Safety 2010 frequency bands in Japan, from [4]
One of the pioneers in ITS area (begun in the early 2000s) was theAdvanced Safety Vehicle (ASV). It marked the development of new methods and devices to improve the safety of the transportation system, such as emergency braking, parking aid, blind curve accidents, right turn assistance and pedestrian accidents, blind intersection and image of cognitive assistance. Throughout the different phases of the program, some important car manufactures developed important technologies that propelled V2V communication. On the other hand, ITS-Safety program was created. Known as a Public/Private Co-operations program with main focus on ITS safety and security. It was a large-scale test of future automotive ITS and had the contribution of Nissan, Honda and Mazda companies in which they were presented advanced safety prototype vehicles. It was used a millimetre wave radar system to sense the distance between vehicles or vehicle and obstacles.
2.3.3 Europe
In the same way, the scope of European programs are mainly focused on the improvement of road safety. This can be realized by providing standardized and common communica-tion approaches. Among the main entities that are responsible for planning/developing such standards (figure 2.5) are the European Committee for Standardization (CEN), European Committee for Electro-technical Standardization (CENELEC) and ETSI [4]. Some of the projects that stood out were: Communications for eSafety (COMeSafety), focused on the consolidation of the research results obtained in others European projects and organizations
and their implementation.
Figure 2.5: Relations between standardization bodies, from [4]
It Provides an open integrating platform for both the exchange of information and the presentation of relevant results achieved. Some of the work done is associated to worldwide harmonization, with activities and initiatives elsewhere as well as frequency allocation for ITS applications. An effort was made in the disclosure and dissemination of the system properties towards all stakeholders [23]. SAFESPOT project developed a Safety Margin Assistant to increase the road safety, capable of detecting in advance dangerous situations on the road and able to extend the driver awareness of the surrounding environment in time and space. Through dynamic cooperative networks, the information gathered on board and at the roadside is shared. SAFESPOT system is based on safety related information provided by the communication network and the in-vehicle sensors [24].
One of the most recognized worldwide is Cooperative Vehicle-Infrastructure Systems (CVIS), a major European R&D project that works in design, development and test technolo-gies needed to support vehicles communication. It has developed several vehicular applications namely the guidance of the fastest possible path towards the destination and emergency vehi-cle warning [25]. Secure Vehicular Communication (SEVECOM)also added relevant work and conclusions in security and privacy requirements associated to vehicular communications. It was designed a security architecture that is used as input for security related ETSI ITS WG5 and ISO CALM standards. A few of work topics were: threats, such as bogus information
and identity cheating as well as authentication and privacy.
Between 2006 and 2010, COOPerative SystEMS for Intelligent Road Safety (COOPERS)
and their partners collaborated in the enhancement the road safety by using a cooperative traffic management. The main purpose was to define, develop and test new safety related services and equipment and applications using two-way communication between road infras-tructure and vehicles from a traffic management perspective [26][27]. More recently, GeoNET project, that although finalized in 2012, contributed to the development of geographic ad-dressing and routing (geonetworking) solutions that still in ongoing process. The proposed idea consists in the use of reliable and scalable communication capabilities, which enable the exchange of information in a particular geographic area (usually located far away from the source of information) [28][29].
2.4
Usage Scenarios
All ideas and concepts introduced early in this document can be used for several scenarios. In this section it will be presented some particular applications of vehicular networks and their use cases. When talking about vehicular networks, a broad range of situations can be met. Frequently these situations can be divided in Road Safety, Traffic Efficiency and Infotainment Applications [4].
In the first one, information and assistance to the drivers is provided in order to achieve more safety, and to avoid collisions. Here, vehicles present in the affected area, calculate the concrete risk for a collision with other vehicles at an intersection that can be controlled or not. In both situations, there are questions about if one vehicle enters in an intersection without all due driver consideration of the traffic conditions and, accordingly increases the risk of collision. In order to correct disseminate this information correctly it is necessary that vehicles have the capability to broadcast cooperative awareness messages and accordingly to receive and process them. A roadside unit need to be installed if line-of-sight between vehicles is obstructed [30].
In some scenarios, the collision could be considered unavoidable and the data periodically exchanged can be used to optimize vehicle equipment such as air-bag, motorized seat belt pre-tensioners or extensible bumpers (figure2.6(a)). By sharing information between vehicles and road side units, critical events such as emergency/hard braking (figure2.6(b)) detected by a sudden deceleration of the vehicle (the vehicle that brakes hard sends a broadcast message to other vehicles to warn them - DENM), wrong way driving, emergency vehicle arriving, are detected to contribute to active road safety.
Another big step further is made in the optimization of traffic flow. These improvements can be based on speed control in such way that unnecessary stopping is avoided (e.g., traffic lights), co-operative and adaptive cruise control and platooning. The risk of accident can be also reduce through speed limit warnings (figure2.6(d)), in case of bad weather conditions or on bad road segments that are difficult to observe. Provide traffic information and alternative
itinerary provisioning and recommendation could help driver, directing him to alternative route and get around the congested area (figure2.6(c)).
(a) Crash Advise (b) Hard braking
(c) Optimized navigation system (d) Speed Warning
Figure 2.6: Some of the possible applications and use cases, from [31][32]
In figure2.7, an example of traffic lights with the use of platooning way is presented. Two vehicles are passing in group (platoon) in a traffic light and a third one arrive, it communicates withRSUand, if there is time to pass the green light, the vehicle will ask to join the platoon. Regarding to Infotainment Applications, a lot of requirements not only related to the vehicular network must be met in order to provide these kind of services. Facilities as parking zone management, universal and interoperable toll collection device and technology or more global Internet Services are among such possible applications. The automotive industry is looking for creative solutions and ways to innovate the driving experience (in part due to market crisis and economic downturn). One of the strategies already decided, is to avail on the demand for the same dynamic multimedia experience in the car that people now expect in their everyday lives. Some statistics predict that over 35 million in vehicle infotainment systems will be deployed by 2015 [33].
The most of infotainment services are related to the provision of classic IP applications, like browsing, reading e-mail or using social networks but, in order to enable these kind of features, a standardized method of data access is required [34][35]. Bringing infotainment services to the vehicular environment requires to comply with standard protocols and mechanisms that allow heterogeneous networks to be interconnected in the Internet. However, this area is out
of this document scope and it will be not considered in depth.
Figure 2.7: Platooning example in traffic light scenario
2.5
Requirements and time characterization
The application scenarios and all of the safety services associated have specific character-istics and requirements in terms of latency, range and type of communication. In table 2.1, a summary is made about the most important use cases and their time restrictions that was based on work stated in [4][31]. The examples presented are part of the three main fields mentioned before (Road Safety, Traffic Efficiency and Infotainment Applications). One of the conclusions that can be drawn from this information is that the minimum transmission frequency is similar for all cases (ranging from 1 to 10 Hz). Looking at the communication mode, awareness periodic messages as well as event-triggered messages can satisfy the most of situations described. Hereupon the importance of Cooperative Awareness Messages (CAM)
andDecentralized Environmental Notification Messages (DENM)makes sense since, all data exchange in this situations can be organized in this two standards.
The allowable latency is the maximum duration of time permitted between the beginning of information transmission and its reception and in most cases this value can not surpass 100 ms. When one of the challenges is to bring more efficiency and safety to the roads, to
minimize latency is crucial, specially when hard real-time requirements arrive (for instance due to the high travelling speed of vehicles).
In table 2.1 is presented a resume of technical requirements that must be met and their associated use cases.
Table 2.1: Summary of use cases and technical requirements [4][15]
Use Cases Communication
Mode Transmission Frequency Critical Latency Co-operative collision warning Co-operation
aware-ness between vehicles > 10Hz < 100ms Hard/Emergency
braking
Co-operation
aware-ness between vehicles > 10Hz < 100ms Lane Change Warning Co-operation
aware-ness between vehicles > 10Hz < 100ms Collision risk warning Time limited periodic
messages on event > 10Hz < 100ms Emergency vehicle
warning
Periodic message
broadcasting > 10Hz < 100ms Traffic light optimal
speed advisory Periodic or permanent broadcasting of mes-sages 1 - 10 Hz < 100ms Co-operative adaptive cruise control Cooperation aware-ness 1 - 2 Hz < 100ms
Electronic toll collec-tion
Unicast full duplex
Chapter 3
Vehicular Communication
Standards
3.1
Introduction
Given the particularities of Vehicular Ad-Hoc Network (VANET), the network layer can support either IP and non-IP. Focusing only on networking protocols that do not rely on IP, there are two perspectives on how to disseminate data over the network. One of them rely on broadcast topologies in which packets travel from a source node to all nodes located at a specific distance. In this field, researchers are working on efficiency optimization for repetitive local broadcasting of vehicle status info (e.g. position, heading, speed, etc). On the other hand, geographic data dissemination concepts such as Georouting or Geocasting are in study and development.
In the next section, it will be discussed the most important standards for network and transport layers.
3.2
IEEE 1609 family - WAVE
Wireless Access in Vehicular Environment (WAVE)was introduced by IEEE as a complete protocol stack proposal. It is the combination of IEEE 802.11p and IEEE 1609 protocol [36]. Basically,WAVEis a mode of operation used by IEEE 802.11 devices to operate in the DSRC band.
The IEEE 1609 family is composed by six sub-standards and each one is associated to different issues at different layers. In Figure 3.1, it is depicted the two major blocks that represent the Management and Data Plane of the protocol stack. The first one (in the left side) is responsible by performing system configuration and maintenance functions. This group also encompasses WAVE security services that provide features such as authentication of control information specified in 1609.2 [37] and channel coordination between multiple channels of the spectrum - 1609.4 [38].
Figure 3.1: WAVE Arquitecture, from [15]
The Data Plane, contains the communication protocols and hardware used for delivering data, from or to applications. It also carries traffic between management plane entities on different machines, or between management plane entities and applications (e.g., for notifica-tions) [39].
The WAVE architecture supports both IP and non-IP applications. For the IP applica-tions, it supports IPv6 traffic whereas for non-IP applicaapplica-tions, a protocol defined in IEEE 1609.3 [39], WAVE Short Message Protocol (WSMP) is used. Designed in order to optimize operation in vehicular environments, it supports a high data rate, with a low latency, com-munication between devices. In case of IP based comcom-munications, latency has a big impact on network performance, as high latency causes packet loss (due to handshake and synchro-nization processes). TheWSMPensures proper addressing and routing service systems while enhancing high priority and time sensitive communication to vehicles.
WithWSMP, it is possible to the applications directly control physical layer characteris-tics, such as channel number and transmitter power, used in transmission of messages. WSMP
packets require special services such, being transmitted using a particular power or data-rate. Such requirements impose challenges in the lower layers. The MAC and PHY layers need to process each packet to adjust radio power and data-rate according to packet information. Although the use ofWAVE Basic Service Set (WBSS)(building block of a network, e.g, an ac-cess point and all associated stations) is relevant inDedicated Short Range Communications (DSRC) networks, since WSMP can exchange data in both CCH and SCH, WAVE devices can communicateWSMP messages over WAVE networks withoutWBSS. In a such scenario, the application is registered in the management entity (WME) and deliverWSMP data for transmission. The data is addressed to a broadcast MAC address and then, the MAC layer extracts the required channel information so that transmission is prepared. The receiver
de-vice accepts the packet and passes it up the communication stack. The WSMP stack delivers data to the locally registered application, based on the Provider Service Identifier (PSID)
contained in theWSMPpacket [40]. ThePSIDis a 4 octets value that identifies the type of information and, based on that value, the data is forwarded to the corresponding path.
Unlike the IP data packet delivery, the transmission parameters are directly specified for every single Wave Short Message (WSM) (figure 3.2), which leads to higher efficiency in transmission process as well as minimal channel consumption.
Figure 3.2: WAVE Short Message format
3.3
ISO CALM
CALM is the ITS communication architecture for Vehicle-to-Vehicle (V2V) and Vehicle-to-Infrastructure (V2I) continuous communication specified by ISO. Has been applied and enhanced by ITS European projects, such as COMeSafety, COOPERS, SAFESPOT or CVIS [23][24][25][26]. In the last one, was presented one of the first approaches to the deployment of the CALM architecture. It was validated and tested in the field with the purpose of “create a unified and open solution” [41].
One of the challenges in ITS field remains to provide multiple services, available in multiple different platforms, while maintaining an user-friendly interface that requires minimum inter-vention from the driver. CALM proposes the use of multiple available technologies, instead of single use of 802.11p proposed by WAVE, and can support multiple types of application and multiple types of media simultaneously (e.g. Infra-red, GSM, DSRC, Satellite, Bluetooth, RFID). The CALM architecture provides an abstraction layer for vehicle applications where all methods of transmission and communication are managed. This depends of what is sup-posed to provide and what is available, there is no requirement for implemented equipment to support all the possible media.
The main characteristics of CALM consist in the capability to allow continuous (or quasi-continuous) communications, inter-operability and seamless handover between networks and applications. Despite CALM being based on IPv6 (fully compatible with internet services and functionalities) [15][41], in order to meet the requirement for very fast short communications in time critical situations, a non-IP solution with lower processing overhead and lower latency was added and called CALM FAST [42]. CALM FAST networking and transport stack works in parallel with IP side and is defined for support user applications with restrict latency requirements such safety related ones.
A major set of emerging ITS services is the information provision to the vehicles, by a ser-vice provider that acts as a serser-vice user. These serser-vice providers could be a roadside (RSU) or a mobile station (OBU). The distinctive characteristics of CALM non-IP networking method are: pre-defined mapping of services on communication media, fast service advertisement and groupcasting management rather than IP based service discovery, supporting geo-networking, fast session establishment of short sessions, mainly broadcast messages and single-hop com-munications, short message length, low latency and high reliability.
In figure3.3, it is depicted the CALM FAST network layer as part of CALM architecture. CALM FAST is a complete network layer protocol that provides a connectionless datagram service but where reliability and in-order arrival are not guaranteed. CALM FAST has its own forwarding tables, which are updated dynamically by the CALM manager based on incom-ing and outgoincom-ing service advertisements, which contain the NWrefs (source and destination network addresses that works like port numbers) used by the application side to stablish com-munication pipes with network layer. The address and routing management is done by the CALM manager, and no manual configuration of FAST addresses or routing is needed. The protocol was primarily designed for single-hop communications, although it supports n-hop broadcasts in the extended CALM FAST protocol variant [43].
Figure 3.4: CALM FAST packet structure
In figure 3.4, its is presented the CALM FAST network packet structure (NPDU). The packet is formed by network header and the payload, the segment usually called TPDU. The first field is composed by NWrefs, that contains the source and destination addresses as mentioned above. The payload is divided in two parts: the header in which control information lies (information about type of message and ID of source station) and the body that incorporate the type of data (service ID) and the data itself (service data). FAST NPDU can carry different payloads simultaneously, so service ID and service Data fields can be replicated for each service available.
3.4
Geo-networking
The main concepts of geo-networking are based on beaconing, location-service, and for-warding of data. A geo-networking beaconing carry periodic data. It is a special case of periodic groupcasting, applying the MAC broadcast address as destination address. The lo-cation service provides the geographical lolo-cation of a certain peer station identified by its ID (station ID). Depending on the destination type, different geo-routing schemes may be used (figure3.5).
(a) Broadcast
(b) Unicast
Geographical networking consists in the delivery of network packets to nodes within a limited geographical area. The nodes can be addressed using geographic concepts such as locations and areas, and routing decisions can be based on inter-node distance or relative movement. When geo-unicast strategies are used, data is routed from a source node to a single destination node for which the exact geographical location is known (through node/station ID). Since this location will change over time, a position service is required to maintaining a mapping in real-time between vehicle identity and exact location. Geo-broadcast is frequently used for dissemination of information to a geographical target area. Data transmission to the target area depends on the location of source node, if it is inside or not of the target area. In the first case, it can be used MAC broadcast frame. Otherwise, the broadcast packet is forwarded towards the targeted area until reaching a node belonging to it [45][46].
The most important geographic networking standard, which is currently under develop-ment, is the protocol defined by the C2C-CC together with ETSI. So far, working groups and standardization bodies are advancing towards to reliable connectivity between vehicles, and making road safety their highest priority. However, there is an increasing interest in also enabling Internet access from the vehicles (the Internet connectivity capability is seen by consumers as a very valuable feature in any electronic device). Providing Internet access for vehicles, it’s seen as a great step in the growth of comfort and would attract users towards the installation of a communication system in their cars and this would facilitate market penetration of VANETs. The GeoNet project has been developed in the past three years and rely on the IPv6 standard and geonetworking concepts presented (figure3.6).
Figure 3.6: General scope o GeoNet, from [47]
The most important and relevant work done on the geographic networking area was defined by the C2C-CC together with ETSI [48].
GeoNet (Geographic addressing and routing for vehicular communications) intend to take into account the work already done but also create a baseline software implementation inter-facing with IPv6. The goal of GeoNet is thus to implement and, formally test a networking mechanism as a standalone software module which can be incorporated into cooperative sys-tems. With this purpose, it must be possible to achieve transparent IP connectivity between vehicles and the infrastructure side, even in cases when delivery must be hopped over several vehicles or cached along the way [47]. Although Geo-routing has been extensively investi-gated, the purpose of this document is present a solution for vehicular communications based on non-IP protocols, so this subject will not be addressed in detail.
3.5
Protocols Evaluation and Deployment strategies
With the aim of substantiating and validating these protocols, some ideas and solutions regarding their deployment and evaluation were presented. Among the ways about how to validate new protocols and methodologies, we can mention the proof of concept in which is proved that such protocol admits some of announced properties, simulation of the behaviour in a non-real scenario, experimentation in the “field” (real scenario) or emulation. Thus, some related works are discussed next. In [49], an implementation of a system composed by 802.11p/WAVE integrated solution is presented. It was used a Linux-based platform due to its free, portable, scalable and secure characteristics. The performance of such system was evaluated on road. The road test scenarios consisted of transmission experimentations betweenRoad Side Unit (RSU)and On Board Unit (OBU), under different distances and in both unicast and broadcast ways. In [31], a prototype implementation for the WAVE based next generationDSRC systems is proposed. That system was focused to safety critical and infotainment applications. It is based on integration of WSMP from WAVE with a Field-Programmable Gate Array (FPGA) that carries all MAC layer and digital PHY. It was a effort toward a further goal of design a full WAVE compliant and embeddable communication. Related to ISO CALM standards, CVIS implementation brings a complete communication platform that offersVehicle to Vehicle (V2V),V2I and Internet based communication (IPv6 network mobility - NEMO). Alongside CALM FAST, network protocol used for effective groupcasting, theCooperative Awareness Messages (CAM) service was integrated (it will be presented next). Highlighting the powerful feature of ISO CALM architecture, in terms of multi media platform support, three wireless access technologies were used: the medium-range 5.9 GHz 802.11p / CALM M5 (ISO 21215), short-medium-range CALM IR (ISO 21214) and long-range CALM 2G/3G (ISO 21212- 21213) [50].
Bearing in mind reliable and efficient multi-hop networking protocols to achieve their foreseen benefits, some geo-routing protocols have been proposed. In [51], a contribution regarding a novel infrastructure-assisted routing approach is added. The performance of the proposed infrastructure-assisted routing approach was evaluated using the NS-2 simulator and Simulation of Urban Mobility (SUMO). The solution presented introduces a simple and
new graphical representation of the road-topology map that takes into account the relaying capabilities of RSU for multi-hop vehicular communications and, that can be applied to existing topology-aware routing protocols. The benefits announced depend on infrastructure deployment strategy.
3.6
Protocols summary and combined solutions
In order to make a better insight over all protocols presented early, an overview of the main features and objectives of the same is shown in table3.1. It is fundamental to make a trade off and take care about some important aspects. One of the common factors associated with these standards and standardization activities around the world is that, although many other existing technologies can be used, the IEEE 802.11p technology gathers consensus and is targeted to be the globalV2Vtechnology regarding the lower layers ofIntelligence Transports Systems (ITS)protocol stack [52].
Table 3.1: Overview about standards
Protocol Standards Summary
WAVE WSMP IEEE 1609.3
Alternative for IPv6 in routing and transport services. A thin protocol that allows physi-cal layer parameters control by application side. Designed to consume minimal channel capac-ity and bring performance that IP based strate-gies don’t achieve. Overload is reduce drasti-cally compared to UDP/IPv6 packet (overhead 11 bytes instead of 52 bytes).
CALM FAST ISO/FDIS 29281
Integrated in architecture that brings multi-ple possibilities of communication/transmission (make use of a wide range of technologies). Sim-ple but effective protocol. Supports broadcast and unicast communication modes. Does not have specific handover strategies (relies on IPv6 and medium-specific solutions). As theWSMP, CALM FAST is designed as alternative of IPv6 for fast and low latency data exchange (vehicu-lar communications).
GeoNet ETSI TS 102 636-3
Based on geonetworking methodologies (use-ful when forwarding tables have invalid en-tries). Complex protocol specially when multi-hop is considered. Still in progress the discus-sion of many open fields. Several underlying link layer technologies (media-independent and media-dependent functionality is separated).
In contrast to what happens with IEEE 802.11p, concerning to the higher layers, such consensus is not achieved. As mentioned before, CALM was designed in order to support multiple types of transmission and communication including various evolutions of the IEEE 802.11p standard. In fact, some ideas have emerged in which the main goal is to harmonize the standards already developed (ETSI, ISO, IEEE and many others are working together) with the aim of elaborating a global standard. Some important steps are being taken such as: CEN, the European Committee for Standardization jointly with ETSI is currently developing a harmonized scheme for application identifier, ISO and IEEE are working together to har-monize FAST and WAVE and recently was signed a Memorandum of Understanding between European vehicle manufacturers on Cooperative ITS [53]. In the last one, it was approved a joint guideline to develop vehicular communications environments making use of ISO/IEEE protocols which are complemented by protocols from ETSI.
At the same time, VANETs will have to support the different functionalities provided by both the IPv6 as the non-IP solutions for the deployment of cooperative applications. This vision is shared by the different standardization bodies active in this domain and in the GeoNet project it was researched how IPv6 connectivity can be provided on top of the non-IP based networking protocols such CALM FAST or WSMP.
3.7
Facilities in Upper Layers - Application Support
The facilities layer covers the three upper layer of the OSI reference model. However, ITS exhibits some particularities, which lead to an evolution of the OSI model. Following that model, there are three types of facilities such as: application support facilities, information support and communication support (figure 3.7). Examples of the application support fa-cilities are related to the management the periodic time-triggered position messages called Cooperative Awareness Messages (CAM) and event-driven hazard warnings, Decentralized Environmental Notification Messages (DENM).
3.7.1 CAM Messages
Cooperative vehicular systems regularly broadcast their identity and location information, and this is made through the exchange of messages. CAM messages are periodic and time-triggered position messages transmitted by vehicles and infrastructure units (OBUandRSU) and with this it is possible to acquire positioning and status information about what is happening in the surroundings. This information is emitted by neighbouring nodes that are located within a single hop distance.
The main aim ofCAMis to assist vehicle drivers in their driving activities to be aware of the presence of other vehicles or situations in its vicinity such as emergency vehicle approach-ing. CAM messages are composed by a set of fields that span from position, movement to basic attributes and basic sensor information.
Figure 3.7: ITS Architecture, from [54]
In figure 3.8 is presented the flow of CAM between two stations, since generation to reception and dissemination of the data. Firstly, CAM is constructed in the facilities layer (1) where all data resides in specific databases, and then is injected in transport and network layers (2). The messages are inserted in the payload of the network protocol available and passed down the stack. In lower layers, the packet is processed and prepared for broadcasting through ad-hoc network (3)(4). In the other side (second ITS station), the packets are received and processed in same way. The information about source and destination of the data is extracted (5) and, according to this information the CAM message is delivered to facilities layer (6). Here, the information is decoded and forwarded to the relevant facilities (7). Then, information is delivered to the application layer and used to display information in the smartphone orHuman Machine Interface (HMI)(10).
Figure 3.8: Application flow diagram (CAM message), from [55]
3.7.2 DENM messages
The DENM transmission is triggered by specific safety related events, such as a hard breaking vehicle, or when a vehicle is trying to park and the other vehicles need to stop and wait for the conclusion of “event”. DENM messages are disseminated upon detection of these types of events and the transmission will continue until the event disappears. In contrast to a CAM message, the DENM is not only designed to be broadcast in the single-hop neighbourhood but also to be forwarded to other nodes in order to cover a larger area [56][57]. A DENMcan be updated if the evolution of the event is detected. Communication systems of the ITS stations should be capable of keeping a DENM alive inside the relevance area, as long as the theDENMstill valid, even though the originator ITS station of theDENM
has stopped sending DENMs or has moved away from the event position. The termination of the DENMbroadcasting could be achieved by a predefined expiry time, by the originator station sending a specific version of DENM(cancellation DENM) or by an authorized third ITS station, by sending a negation DENM [57]. Upon the reception of a DENM, an ITS station analyses if it is concerned by the event and provides corresponding information or warning (for instance through HMI).
The simplified DENM structure is presented in figure 3.9. There are three main parts in the DENM data structure: the management container, the situation container and the location container. Each container is composed by a sequence of data elements and data frames.
The management container, as the own name implies, holds management information of a DENM. The specific data elements which constitute this container, indicate aspects as the reliability level, the event evolution and the event termination. Regarding the situation and location containers, they describe respectively the detected event as well as its potential impact to the road safety or traffic flow and, the event position and the relevance area.