Multi-hop Vehicular Communication for ITS 

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Transport Systems

Wouldn’t it be great to drive our cars smoothly to our destinations without having to stop at traffic lights? To have our car detect the traffic signal state and the speed of the vehicles ahead of us and, as if by magic, adjust the speed of our vehicle appropriately within zone speed limits, clear respective intersections without having to stop waiting for the light to change and get us to our destinations rapidly and safely?
Vehicles stopped at intersections are considered the worst polluters on the roads [5], and thus by coordinating the vehicle speed such that such stops are avoided or reduced, contributes significantly to decreasing pollution and at the same time decreasing travel time, resulting in both ecological and economical gain.
Drastic steps are already taken by governments and automobile manufacturers in dif-ferent parts of the world to control pollution by promoting the usage of eco-friendly vehicles [6], by giving benefits to consumers, in form of lesser carbon taxes and lower insurance premiums. Besides governments, major parcel-carrier companies implement a « no-left-turn » [7] policy for their carriages in order to avoid left turns at intersections and thus reduce idling – which in turn lowers fuel consumption.
People are slanted towards their personal economic welfare [8, 9], rather than ecological welfare – and it is worthwhile to note that the financial gain received by drivers will be the driving force for a rapid deployment and the betterment of ITS in today’s world.
Vehicles are used as means of carriage to transport passengers and goods, from one place to another. There are three major modes of transportation: land, air and sea. Land-based vehicles have the major share compared to the ships and airplanes [10, 11, 12] among the transport vehicles in the globe. The larger a system is, the more complex it becomes to maintain. People form one of the major components that control the transport system. To maintain such a highly complex system, co-operation from automobile drivers is required – and this is difficult because many drivers (i) are self-centered, (ii) don’t think alike and (iii) may not be able to take all the parameters into consideration when faced with a real-time task: driving their vehicles [13, 14].
Statistics on traffic fatalities show that every year, over 40,000 cases are reported in Western Europe, a similar number in the U.S., over 6,000 in Japan, and over a million worldwide [15]. In addition, traffic congestion incurs further economic loss. For exam-ple, the Texas Transportation Institute estimated that, in 2000, the 75 largest metropoli-tan areas experienced 3.6 billion vehicle-hours of delay, resulting in 21.6 billion litres in wasted fuel and $67.5 billion in lost productivity [16]. Economic loss accompanies human loss as well, eventually posing a threat to the safety and the sustainability of transportation system.
At present, technologies based on standalone systems are relied upon for traffic and fuel efficiency. People use navigation devices to find routes easily to a new destination. In addition to route guidance, these devices [17] provide the most efficient route to a destination by calculating route based on actual or statistical speeds driven on roads, rather than simply speed limits. For the consumer using such a navigation device, it results in a better fuel economy on a day-to-day basis. With constant use of such devices, the money invested in having them, is easily harvested back within a short duration of time [18]. All these technologies project – an individualistic view – to form a reliable, efficient and ecological system.
Another example, of human reliance on the standalone technology, is the use of ve-hicles driven with a hybrid engine, to attain better fuel economy. When the first hy-brid vehicles came out in 1997, they were considered un-necessary due to the low cost of oil at that time. This situation did not last long. Fuel prices started to in-crease rapidly [19] and vehicle manufacturers realized the importance [20] of hybrid technology. Such technology was then promoted under various green car programmes [18, 21, 22] and governments supported such programmes under various energy policy acts [23, 24, 25, 26]. Car makers and governments have realized that people act eco-logically when they see a direct, individual (economic) gain for doing so. In a similar manner, to realize an integrated ITS system with wide support and collective advan-tage, the individual benefits to the driver, in participating to such a system, should be made clear.

Present Developments Towards ITS

The term Intelligent Transport System [27] (ITS) captures an advanced information and telecommunications network for users, roads and vehicles, in order to improve safety and reduce vehicle wear, transportation times, and fuel consumption. Thus, ITS aims to improve the efficiency and safety of transport systems, while making road networks less congested and less polluting. Vehicles form one of the major components of ITS [28], a betterment of the transport system, in terms of safety and efficiency can be achieved [15]. In order to understand the scope of vehicular communication within ITS, it is necessary to understand the historical contribution from the major players of 1ITS,.1.1ITSandtheinJapanrevolution towards building an intelligent transport system.
In Japan, in the late 1980’s the Public Works Research Institute of the Ministry of Con-struction initiated development of a Road Automobile Communication System (RACS) [29] under a joint research program with 25 private companies. The subject of the devel-opment project was to establish the following systems using roadside transmitting bea-cons: a navigation system, an information system, and an individual communication system. Followed by RACS, steps were taken to integrate traffic information and route guidance into the navigation systems, under a project named AMTICS – Advanced Mo-bile Traffic Information and Communication System [30]. The project demonstrated a system, which displayed on a screen in each vehicle, traffic information such as con-gestion, regulations in force, road work, and parking in real time, and also the vehicle’s present position and its route. At the Exhibition of Flowers and Greenery in April, 1990 in Osaka, taxis, shuttle buses – and trucks as well as passenger cars, were equipped with AMTICS to demonstrate its applicability. In the spring of 1996, VICS (Vehicle In-formation and Communication System) [31] demonstrated driver information services including dynamic route guidance and ASV (Advanced Safety Vehicle), aiming to pro-vide active safety for passenger cars.
Experiments related to Automated Highway Systems have been conducted since 1995 on a test track and an expressway – and cooperative driving, with inter-vehicle com-munication, was tested in the spring of 1997 [32]. Besides government projects, navi-gation systems have become widespread, and inter-vehicle distance warning systems for trucks and an intelligent cruise control system for passenger cars have become com-mercially available [33, 34]. At present, co-operative communication between vehicles [32] is considered an important step towards building an integrated ITS efficiently, and to1.1secure.2ITSexpandabilityinUSA of the system [27].
The Intermodal Surface Transportation Efficiency Act of 1991 (ISTEA) [35] established a Federal program to research, develop, and operationally test, Intelligent Transport Systems and to promote their implementation. The program was designed to facili-tate deployment of technology to enhance efficiency, safety, and convenience of surface transportation, resulting in improved traffic flow, saved lives and time, and increased productivity. Before that, the Mobility 2000 team laid the groundwork for the formation of Intelligent Vehicular Highway Systems (IVHS) [28]. To further demonstrate fully au-tomated test vehicles, a key project called the Automated Highway System (AHS) was carried out in the early 90’s by the National Automated Highway System Consortium (NAHCS) [36].
The strategic research plan [37] of ITS-USA in the next five years includes to:
1. Reduce highway crashes and their tragic consequences
2. Enable vehicles of all types to predict state of the traffic signals, to eliminate un-necessary stops and help people drive in the most fuel efficient manner.
3. Enable travelers to get accurate travel time information about all modes and route options and the potential environmental impacts of their choices.
4. Provide data to transportation managers, to accurately assess multi-modal trans-portation system performance.
The plan explores the transformative capabilities of wireless technology to make sur-face transportation safer, smarter and greener. The core of the research plan is a pro-gram called I telliDriveSM[38], a multimodal initiative that aims to enable safe, interoperable wireless connectivity between vehicles, infrastructure and passengers’ devices to sup-1port.1.3safety,ITSinmobilityEuropeand environmental enhancements.
The PROMETHEUS (Program for European Traffic with Efficiency and Unprecedented Safety), initiated by the European car manufacturing industry, was the key starting step towards ITS in Europe [39]. As an initiative to make autonomous driving possible, in 1986 the Robot Car « VaMoRs » [40] demonstrated to drive all by itself on a street cleared of traffic for safety reasons.
To bring intelligence into transportation system, for people and goods across Europe, ERTICO [41], the network of Intelligent Transport Systems and Services stakeholders in Europe, is active in the following sectors as defined in [42]:
• Safe Mobility oriented towards zero accidents
• Co-operative Mobility oriented towards fully connected vehicles and infrastruc-ture
• Info Mobility oriented towards fully informed people
• Eco Mobility oriented towards a reduced impact on the environment
Field Operational Tests (FOTs) have been introduced by ERTICO as an evaluation method for driver support systems and other functions to demonstrate that such systems can deliver real world benefits. The FESTA (Field opErational teSt supporT Action) con-sortium issued a handbook [43] to provide guidelines for the conduction of FOTs. This handbook provides an overview of the whole process of planning, preparing, executing, analyzing and report ng an FO , and also iv related information regarding administrative, logistic, leg l nd thical issues. The results of this project are monitored and consider d by FOT re ted proj ts in Europ , eg., DriveC2X [44] develops a detailed system specification nd fun tio ally verified prototype to be used in future field1.2Currentlyoperatioaltests. Technologies to assistITS
Intelligent Transport Systems (ITS) includes types of communications in vehicles, be-tween vehicles (e.g. car-to-car), and between vehicles and fixed locations (e.g. car-to-infrastructure). Communication lies at the core of an ITS system [45], and the sys-tem architecture must meet a set of contrasting functional requirements, as imposed by the ITS system. The communication technology used should ensure adequacy with respect to critical services such as icy-road warning, fog warning, traffic-jam pile-up prevention, et cetera. In this section, currently available technologies to assist ITS are discussed.

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Sign-based Communication

A variable message sign (VMS) [46], can be seen as one of the initial steps to bring intelligence to the transport system. It is an electronic traffic sign used on highways to give travelers information about special events. These signs alert drivers about traffic congestion, accidents, incidents, roadwork zones, or speed limits on a specific highway segment. They act as route guidance systems, suggesting drivers to take alternative routes, limit travel speed, warn of duration and location of incidents or just inform of the actual raffic conditions [47]. In some places, signs are set up with permanent, semi-static displays indicating predicted travel times to important traffic destinations such as major cities or interchanges along the route. As a proof of its longevity, these signs were widely introduced in France in the early 90’s under President François Mitterrand, and 1are,.2.essentia2Satellitey,unchangedCommunicationtoday.
Global Navigation Satellite Systems (GNSS) [48, 49, 50, 51] provide autonomous geo-spatial positioning with global coverage. GNSS allows small receivers to determine their location (longitude, latitude, altitude) to within a few meters using time signals transmitt d along a line- f-sight by radio from satellites. With the help of such devices, users can easily navigate to their destinations by matching their location on a map. Examples of GNSS include the NAVSTAR Global Positioning System [52] (GPS) of USA, the Russian GLONASS [53], the European Union’s Galileo positioning system [54] and 1the.2.People’s3TerrestrialRadioBroadcastRepublicofChina’sBeidou navigation system [55]
Radio Data System, or RDS, is a communication protocol standard for embedding small amounts of digital information in conventional FM radio broadcasts, [56, 57] for deliv-ering traffic and travel information to drivers. It is typically digitally coded using the FM-RDS system on conventional FM radio broadcasts. It allows access to accurate, timely and relevant information [58], in the language chosen by the user. Services, both public and commercial, are operational in many countries worldwide. RDS is also used for the digitally coded Traffic Message Channel (TMC), which is widely introduced all over Europe within funded European Union projects [59]. RDS-TMC is nowadays gen-erally used by GPS navigational devices, that use the TMC messages also for dynamic 1re.-2routing.4Dedicated[17]. Short-Range Communications DedicatedCellularShot-Range Communicationunications(DSRC) provide communications between a vehicle and the road-side units in specific locations, for example toll plazas. DSRC operates on dio frequencies in the 5.9 GHz Industrial, Scientific and Medical (ISM) band. This c n be used to support specific Intelligent Transport System applications 1such.2.5as ElectronicMobileFeeCollection [60].

Table of contents :

1 Introduction to Intelligent Transport Systems 
1.1 Present Developments Towards ITS
1.1.1 ITS in Japan
1.1.2 ITS in USA
1.1.3 ITS in Europe
1.2 Currently Available Technologies to assist ITS
1.2.1 Sign-based Communication
1.2.2 Satellite Communication
1.2.3 Terrestrial Radio Broadcast
1.2.4 Dedicated Short-Range Communications
1.2.5 Cellular Mobile Communication
1.2.6 Image Recognition
1.3 Enhancing ITS services using Vehicular Communication
1.4 Socio-Economic Impact of ITS-based Vehicular Communication
1.5 Broadcasting ITS events using Mobility Information of Vehicles
1.6 Summary
2 Multi-hop Vehicular Communication for ITS 
2.1 Radio Characteristics of Vehicular Networks
2.1.1 Radio Range
2.1.2 Causes of Radio Irregularity
2.1.3 Impact of Radio Irregularity
2.1.4 Interference Computation and Signal Reception
2.2 Node Characteristics in a Vehicular Network
2.2.1 Node Speed
2.2.2 Node Mobility Pattern
2.2.3 Node Density
2.2.4 Node Heterogeneity
2.3 Flooding in Vehicular Networks
2.3.1 Probabilistic Methods
2.3.2 Counter-Based Methods
2.3.3 Coverage-Based Methods
2.4 Exploiting Location Information for Flooding in Vehicular Networks
2.5 Functional Requirements for ITS Event Dissemination Algorithms
2.6 Summary
3 Ecient Flooding in Vehicular Networks
3.1 Location Specific Forwarding
3.2 Backfire – Controlling Redundant Receptions
3.3 Dynamic Scheduling – Decreasing Delay
3.4 Controlling Event Dissemination Frequency – Reducing Bandwidth Utilization
3.5 Adaptive Backfire – Increasing Connectivity
3.6 Summary
4 MHVB Protocol Specication for Location-based Flooding 
4.1 Packet Format
4.2 Configuration
4.3 Transmission of MHVB packet
4.3.1 Jitter
4.4 Processing MHVB packet
4.5 Determining Backfire
4.6 Triggering Dynamic Scheduling
4.7 Summary
5 ITS-Specic Quantitative Evaluation of Position-Based Broadcast Protocols 
5.1 Mobility Scenarios
5.2 Chosen Protocols
5.3 Simulation Settings
5.4 Performance evaluation of MHVB protocol under ITS requirements
5.5 Impact of Defer Times on Packet Re-transmission
5.6 Packet Freshness
5.7 Performance of Individual Components of MHVB
5.7.1 Performance of Sectoral Backfire
5.7.2 Performance of Dynamic Scheduling
5.7.3 Impact of Varied Relative Speed between Lanes
5.7.4 Varied Application Requirements
5.8 Summary
6 Securing Position-based Vehicular Communication for Intelligent Transport Systems 
6.1 Attack Possibilities on ITS event dissemination
6.1.1 Identity-based attacks
6.1.2 Attacks on ITS data validity
6.1.3 Mobility Data Manipulation
6.2 Analysis of Position-based Attack
6.3 Counter-measures
6.3.1 Detection and Fusion – Trust Evaluation
6.3.2 Trustworthiness Sensors
6.3.2.1 Basic-trust Sensor – Prior Trust
6.3.2.2 Reception Range Threshold
6.3.3 Trust Decision – Handling False Data
6.4 Summary
7 Conclusion 
Bibliography

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