Vehicle ad-hoc Network (VANETS) Technology

Chapter 1

Introduction

Now a day, everything is moving away from wired technology and leading towards wireless. The fascination of mobility, accessibility and flexibility makes wireless technologies the dominant method of transferring all sorts of information. Satellite televisions, cellular phones and wireless Internet are well-known applications of wireless technologies. This work presents a promising wireless application and introduces a tiny contribution to its research community.

Research in wireless communication field is growing faster, day by day, then any other field. It serves a very broad range or series of different kind of applications using different topologies. Every one of these comes with some new and specialized protocols. In this research, we will present an introduction to a wireless technology. This wireless technology directly affects car accidents and the sales of one of the largest markets. It is the technology of building a strong network between mobile vehicles; i.e. let vehicles communicate to each other. This promising technology is literally called Vehicular Ad-Hoc Networks (VANETs).

1.1 Background

Since the first invention of mobile vehicles, governments and manufacturers have researched accidents to reduce the number of vehicle crashes in order to reduce costs, injuries and fatalities. First of all, VANET technology is going to reduce crashes by doing research in this field. Accordingly, related governmental authorities initiated new projects to the learning institute for study, research, development in the field of wireless technology and VANETs also paying attention in its standards. The ‘Dedicated Short Range Communications (DSRC)’ [1] is a pioneer ITS (Intelligent Transportation Systems which is a branch of the U.S. Department of Transportation [2]) project dedicated to VANET standardization. Then, the acronym or short form ‘DSRC’ becomes a global or familiar name of kind of standards that aim to put VANET technology into life. The DSRC mainly concerns with the communication that is how to make different communication links between vehicle-to-vehicle and vehicle-to/from-roadside units.

1.2 Motivation

In the last few years, vehicular network has gained great attention in industry. Federal communication commission (FCC) has assigned 5.850-5.925GHZ frequency band to promote safe and efficient road trips, which is planned for vehicle-to-vehicle and vehicle-to-infrastructure communication. Car manufacturers, e.g., Audi, BMW and DaimlerChrysler, also formed a Car2Car communication consortium [3], in which the prototype development for inter-vehicle communications is underway.

In near past, IEEE 802.11-based solutions for VANETs are also studied by IEEE 802.11p. IEEE 802.11p Wireless Access in the Vehicular Environment (WAVE) that defines changes to IEEE 802.11 to help Intelligent Transportation Systems (ITS) applications. IEEE 802.11p helps data exchanges between fast moving vehicles with each other and also exchanges data from vehicles to road side unit or from road side unit to vehicles in the licensed ITS band of 5.9 GHz. The Dedicated Short-Range Communications (DSRC) at 5.9 GHz is here today to provide safety that is increasing safety in case of road accidents, reducing highway or road maintenance cost and also improving mobility. Intersection and road departure collisions report for round about 50 percent of all crashes and victims on our roads. On an average day in the United States, vehicular collisions kill 116 and injure 7900[8]. More health care dollars are consumed in the United States treating crash victims than any other cause of illness or injury [8], [10]; the situation in the European Union is similar, with over 100 deaths and 4600 injuries daily, and the annual cost of €160 billion [11]. By getting rid from road victims and crashes, DSRC can provide or play important role in reducing road accidents, deaths, injuries, heavy traffic and increasing road safety by improving communication between vehicles and between vehicles and road side infrastructure. DSRC emerged from a partnership among automobile manufacturers, state and federal transportation officials, toll transponder equipment suppliers and the Federal Communications Commission. There is a recognized need for on-the-go communication with motor vehicles and reliable communication between vehicles to increase highway safety by providing warnings and alerts that enable drivers to take corrective and/or evasive actions. At the same time, it can be able to provide information i.e. real time information to drivers so that to improve mobility and motorist convenience, such as information on congestion or traffic incidents. The car manufacturing industry’s determination to roll out vehicle-to-vehicle communication in the near future and, on the other hand, to the increasing disillusionment concerning the need for the vast number of protocols developed for general Mobile Ad-Hoc Networks (MANETs) in the past few years while on the other side that is for VANETs, industry pressure has created a situation in which an overwhelming interest in solutions to problems leads to a preference for real-world research as opposed to fancy theory. As the concept came from MANETs which totally depend on the subscribers motion as the motion is random it is difficult to cater it but this problem was very negligible when researchers observed it in VANETS. At highways vehicle move in an organized pattern with different speeds so initially it seemed that VANET will easily be implemented. Another major reason for VANET can be Traffic deaths and injuries which is a major health and social issue. While industrialized nations (e.g., the United States) have continuously reduced annual traffic deaths since 1970, annual traffic-related fatalities and injuries remain high (in the United States alone there were over 41,000 deaths and 5 million injuries in 2000, according to the NHTSA) [7]. The economic impact of vehicle crashes in the United States exceeded US$230 billion or 2.3 percent of the U.S. GDP in 2000 [7]. We want to remain connected with the world through net whether at home, airport, at work or even on the roads.

Example

Description

Obstacle warning

Stopped/Skidding/Slowing down vehicle warning, road obstacle/object-on-road warning

Lane Merge/Lane Change Assistance

Merging/Lane changing vehicles communicates with vehicles in lane to safely and smoothly merge.

Adaptive Cruise/Cooperative Driving

Automatically stop and go smoothly, when vehicles are in heavy roadway traffic; cooperates driving by exchanging cruising data among vehicles.

Intersection/Hidden Driveway Collision Warning

vehicles communicates to avoid collisions at intersections without traffic lights or hidden driveway.

Roadway Condition Awareness

Vehicles communicates to extend vision beyond line of sight (e.g. beyond a big turn or over a hill)

Table-1.1: Example of Vehicle Safety Communication [10]

1.3 Scope of Project

Some of the industries and universities working on VANETs are as follow

• DaimlerChrysler AG
• Fraunhofer FOKUS
• NEC Europe Ltd.
• Robert Bosch GmbH
• Siemens AG
• TEMIC Telefunken
• Microelectronic GmbH
• Universities of Mannheim, Hamburg-Harburg, Karlsruhe, and Hannover.

1.4 Organization of Project

Thisthesisis mainly divided into four chapters. In the first two chapters (1-2) introduction and an overview over the topic and used technologies is given. In the following chapter (3), we have discussed the standards of IEEE and also discussed the MAC Layer and PHY Layer of IEEE 802.11 in detail. In chapter 4, simulation analysis of our work is shown along with the results. In the last chapter, we have summarized this whole thesis, what we have concluded from this project and future work needs to be done are discussed. Finally, in appendix some additional information can be found. In chapter two, VANET’s characteristics, some of its applications and the research challenges faced by governments and car manufactures are discussed, continued by MAC Layer and PHY in chapter three. We have also discussed the WAVE architecture in chapter 2. From chapter three on, we have a look at some protocol improvements and extensions. Some thoughts, tests and their results on VANETs, those are related to our work, can be found in chapter 4.

Chapter 2

VANETs

VANETs (Vehicle ad-hoc Networks) is a form of Mobile Ad-hoc Networks (MANETs), which provide a communication between the vehicles and also fixed equipments, usually defined as road side equipments.

2.1 What is VANET

Vehicle ad hoc network comprises of three words.

i. Vehicle

ii. Ad-hoc

iii. Networks

i. Vehicle

“A machine such as a bus or car for transporting people or goods”. [4]

A lot of progress is happening in the field of vehicles since the invention of wheel. Development is due to provide services to the people and make their task easier.

ii. Ad-hoc

It refers to dealing with special situations as they occur rather than functions that are repeated on a regular basis. For example you just meet someone outside your office and you exchange some words. On the other hand infrastructure system is a system which is fully installed and deployed than it works according to some predefined rules and regulations.

iii. Network

“A system, as in a business or university, consisting of a computer or computers and connected terminals, printers etc. specific, a local area network”.[3]

The concept of networking is introduced because resources are limited and we have to utilize them efficiently. As it is not possible for firms to provide printer, faxes and other machines to everyone so they just inter linked all the devices so that each one can utilize it keeping the cost at minimum.

Vehicular connectivity can be fairly considered a future killer application, adding extra value to the car industry and operator’s services. Taking into account the constant growth of automotive market and the increasing demand for the car safety, also driven by regulatory (governmental) domain, the potential of car-to-car connectivity is immense. Such system should be suitable for a wide spectrum of applications, including safety related, traffic and fleet control and entertainment. First, issues concerning architecture, security, routing, performance or QoS need to be investigated. Standardization of interfaces and protocols should be carefully planned to ensure interoperability, as vehicles coming from different vendors must communicate seamlessly. Having different competing systems would result in decreased market penetration and poor overall system efficiency, thus only one common system can be deployed. And finally, wise deployment strategy has to be proposed, as most application would become functional only after certain market penetration is reached. The first milestone of standardization process was the allocation of 75 MHz of DSRC (Dedicated Short Range Communications) spectrum to accommodate Vehicle-to-Vehicle (V2V) and Vehicle-to- Infrastructure (V2I) communication for safety-related applications by US Federal Communications Commission (1999). Commercial applications are also allowed to operate in this spectrum.

2.2 VANETs Applications

According to the DSRC, there are over one hundred recommended applications of VANETs. These applications are of two categories, safety and non-safety related application. Moreover, they can be categorized into OBU-to-OBU or OBU-to-RSU applications. Some of these applications are as followed:

2.2.1 Co-operative Collision Warning

Co-operative collision warning is an OBU-to-OBU safety application, that is, in case of any abrupt change in speed or driving direction, the vehicle is considered abnormal and broadcasts a warning message to warn all of the following vehicles of the probable danger. This application requires an efficient broadcasting algorithm with a very small latency.

2.2.2 Lane Change Warning

Lane-change warning is an OBU-to-OBU safety application, that is, a vehicle driver can warn other vehicles of his intention to change the traveling lane and to book an empty room in the approaching lane. Again, this application depends on broadcasting.

2.2.3 Intersection Collision Warning

Intersection collision warning is an OBU-to-RSU safety application. At intersections, a centralized node warns approaching vehicles of possible accidents and assists them determining the suitable approaching speed. This application uses only broadcast messages. In June 2007, General Motors ‘GM’ addressed the previously mentioned applications and announced for the first wireless automated collision avoidance system using vehicle-to-vehicle communication (Figure-2.1), as quoted from GM, If the driver doesn’t respond to the alerts, the vehicle can bring itself to a safe stop by avoiding a collision.

2.2.4 Approaching Emergency vehicle

Approaching emergency vehicle is an OBU-to-OBU public-safety application, that is, high-speed emergency vehicles (ambulance or police car) can warn other vehicles to clear their lane. Again, this application depends on broadcasting.

2.2.5 Rollover Warning

Rollover warning is an OBU-to-RSU safety application. A RSU localized at critical curves can broadcast information about curve angle and road condition, so that, approaching vehicles can determine the maximum possible approaching speed before rollover.

2.2.6 Work Zone Warning

Work zone warning is an OBU-to-RSU safety application. A RSU is mounted in work zones to warn incoming vehicles of the probable danger and warn them to decrease the speed and change the driving lane.

2.2.7 Near Term [5]

• Traffic Signal Violation Warning
• Curve Speed Warning
• Emergency Electronic Brake Lights

2.2.8 Mid Term [5]

• Pre-Crash Warning
• Cooperative Forward Collision Warning
• Left Turn Assistant
• Lane Change Warning
• Stop Sign Movement Assistance

Application

Comm. type

Freq

Latency

Data Transmitted

Range

Traffic Signal Violation

12V One-way, P2M

10 Hz

100msec

Signal Status, Timing, Surface Heading, Light Position, Weather

250m

Curve Speed Warning

12V One-way, P2M

1 Hz

1000msec

Curve Location, Curvature, Speed Limit, Bank, Surface

200m

Emergency Brake Light

Vehicle to Vehicle Two-way, P2M

10 Hz

100msec

Position, Deceleration Heading, Velocity

200m

Pre-Crash Sensing

Vehicle to Vehicle Two-way, P2P

50 Hz

20msec

Vehicle type, Yaw Rate, Position Heading, Acceleration,

50m

Collision Warning

Vehicle to Vehicle One-way, P2M

10 Hz

100msec

Vehicle type, Position, Heading Velocity, Acceleration, Yaw Rate

150m

Left Turn Assist

12V and V21 One-way, P2M

10 Hz

100msec

Signal Status, Timing, Position, Direction, Road Geom., Vehicle Heading

300m

Lane Change Warning

Vehicle to Vehicle One-way, P2M

10 Hz

100msec

Position, Heading, Velocity, Acceleration, Turn Signal Status

150m

Stop Sign Assist

12V and V21 One-way

10 Hz

100msec

Position, Velocity, Heading, Warning

300m

Table-2.1: Eight high-priority vehicular safety applications as chosen by NHTSA and VSCC. Note that communication freq. ranges from 1-50 Hz and Max. Communication range spam 50-300 meters. P2M represents “Point-to-Multipoint”, 12V represents “infrastructure to vehicle” and V21 represents “Vehicle-to-Infrastructure”. [5]

2.2.9 Comfort related applications

• Traffic efficiency
• Better navigation
• Internet access

The whole theme of these applications is improving passenger’s comfort and traffic efficiency. That includes nearest POI (Points of Interest) localization, current traffic or weather information and interactive communication. All kinds of applications might be applied here. Another application is reception of data from commercial vehicles and roadside infrastructure about their businesses (‘wireless advertising’). Enterprises (shopping malls, fast foods, gas stations, hotels) can set up stationary gateways to transmit marketing data to potential customers passing by.

The important feature of comfort/commercial applications is that they should not interfere with safety applications. In this context traffic prioritizing and use of separate physical channels is a viable solution.

2.2.10 Safety related applications

• Accidence avoiding
• Danger warnings
• Intersection coordination
• Cooperative driving

Safety-related applications may be grouped in three main classes: assistance (navigation, cooperative collision avoidance, and lane-changing), information (speed limit or work zone info) and warning (post crash, obstacle or road condition warnings). They usually demand direct communication due to their delay-critical nature. One such application would be emergency notifications, e.g. emergency braking alarms. In case of an accident or sudden hard breaking, a warning is sent to the subsequent cars. That information could also be propagated by cars driving in the opposite direction and, thereby, conveyed to the vehicles that might run into the accident. Another, more advanced example is cooperative driver assistance system, which exploits the exchange of sensor data or other status information among cars. The basic idea is to broaden the range of perception of the driver beyond his field of vision and further on to assist the driver with assistance applications. Transmitting this data to cars following on the same road, drivers get information about hazards, obstacles or traffic flow ahead; hence driving is more efficient and safer. Some applications of this kind are operating only when certain penetration of VANET enabled cars is reached. [6]

2.3 VANETs Characteristics

Although VANETs, Wireless Sensor Networks and Wireless Mesh Networks are special cases of the general MANETs, VANETs possess some noticeable characteristics that make its nature a unique one. These properties present considerable challenges and require a set of new especially designed protocols.

• Due to the high mobility of vehicles, that can be up to one hundred fifty kilometers per hour, the topology of several VANET changes frequently and unexpectedly. Hence, the time that a communication link exists between two vehicles is very short especially when the vehicles are traveling in opposite directions. A one solution to increase the lifetime of links is to increase the transmission power, but increasing a vehicle’s transmission range will increase the collision probability and mortify the overall throughput of the system. The other solution having a set of new protocols is employing a very low latency.
• Another effect of these high speed nodes is that the usefulness of the broadcasted messages is very critical to latency. For example, if we assume that a vehicle is unexpectedly stopping or suddenly stops, it should broadcast a message to warn other vehicles of the probable danger. Considering that the driver needs at least 0.70 to 0.75 sec to initiate his response [7], the warning message should be delivered at virtually zero sec latency.
• In VANETs, location of nodes changes very quickly and unpredictably, so that, building an efficient routing table or a list of neighbor nodes will tire out the wireless channel and reduce the network efficiency. Protocols that rely on prior information about location of nodes are likely to have a poor performance.
• However, the topologies of a VANET can be a benefit because vehicles are not expected to leave the covered road; therefore, the running direction of vehicles is predictable to some extent.
• Although, the design challenge of protocols in wireless sensor networks is to minimize the power consumption, this is not a problem in VANETs. Nodes in VANETs depend on a good power supply (e.g. vehicle battery and the dynamo) and the required transmission power is small compared with power consumption of on-board facilities (e.g. air-condition).
• It is predicted that, as VANET is deployed in the beginning, only a small percentage of vehicles will be outfitted with transceivers. Thus, the benefits of the new technology, especially OBU-to-OBU applications, will not go up until many years. Furthermore, the limited number of vehicles with transceivers will lead to a numerous fragmentation of the network. Even when VANET is fully deployed, fragmentation may still exist in rural areas, thereupon, any VANET protocol should expect a fragmented network.
• Privacy, safety and security are of fundamental effect on the public receiving of this technology. In VANETs, every node represents a specific person and its location tells about his location.

Any requirement of privacy can ease a third party monitoring person’s daily activities. However, from the other point of view, higher authorities should gain access to identity information to ensure punishment of illegal actions, where, there is a fear of a possible misuse of this feature. The tampering with messages could increase false alarms and accidents in some situations defeating the whole purpose of this technology.

Finally, the key difference between VANET protocols and any other form of Ad-Hoc networks is the design requirement. In VANETs, the key design requirement is to minimize latency with no prior topology information. However, the key design requirement of Wireless Sensor Network is to maintain network connectivity with the minimum power consumption and the key proposed design requirement of Wireless Mesh Network is reliability.

WE can summarize the main characteristics of VANETs as follows;

• High mobility of nodes
• No prior information about the exact location of neighbor nodes
• Predictable topology (to some extent)
• Significant latency requirement especially in cases of safety related applications
• No problem with power
• Slow migration rate
• High possibility to be fragmented
• Crucial effect of security and privacy

2.4 Research Challenges in VANETs

When deploying of a vehicular networking system, a number of issues have to be determined, often from distant fields of expertise, ranging from applications improvement up to efficient issues. VANET could be considered as an instantiation of MANETs (Mobile Ad hoc Networks); however their behavior is fundamentally different. These unique characteristics of these networks are as follows:

• Rapid topology changes and fragmentation, resulting in small effective network diameter
• Virtually no power constrains
• Variable, highly dynamic scale and network density
• Driver might adjust his behavior reacting to the data received from the network, inflicting a topology change

Here we briefly mention some of the core research challenges that need to be discussed.

2.5 Wireless Access technology

There are several wireless access standards that could be used as a foundation for VANET technology. In general the major seek is to provide a set of air interface protocols and parameters for high-speed vehicular communication by mean of one or more different media.

2.5.1 Cellular technology (2/2.5/3G)

The key role of 2/2.5G i.e. cellular technology are coverage and security, and 3G, slowly but steadily coming over 2/2,5G, provides enhanced and better capacity and bandwidth. Several telematic and fleet management projects already uses cellular technology (e.g. SMS reports), on the other hand it is comparatively more expensive, together with limited bandwidth and latency make it impossible to use as a main communication means.

2.5.2 IEEE 802.11p based technology

IEEE is working on a variation of 802.11 standards that would be applied to support communication between vehicles and the roadside, or, alternatively, among vehicles themselves, operating at speeds up to 200 km/h, handling communication ranges as high as 1,000 meters. PHY and MAC layers are based on IEEE 802.11a, shifted to the 5.9 GHz band (5.850-5.925 GHz within US). The technology is promoted by the car industry both in Europe and US. Estimated deployment cost is foreseen to be relatively low due to large production volumes. C. Combined wireless access one of the most significant and important efforts in combining those wireless access technologies is done by ISO TC 204 WG16. It builds on the top of IEEE 802.11p, using additional set of interface protocols. Currently supported standards include: Cellular Systems: GSM/GPRS (2/2.5G) and UMTS (3G), Infrared Communication and wireless systems in 60 GHz band. Using all those interfaces in a single, uniform system would result in increased flexibility and redundancy, thus improving applications’ performance. Apart from interoperability issues, CALM is also engaged in the standardization of the protocols, network layer and the management services.

2.6 WAVE Architecture

WAVE system architecture is totally a set of WAVE standards that describes the communication stack of vehicular nodes and the physical air link between them. Any RSU may have two interfaces, one for the WAVE stack or architecture or wireless networks and the other for external interfaces like wired line Ethernet that may be used to get access to internet and for connection to internet it is mainly used. Similarly, each OBU may have two interfaces, one for the wireless WAVE stack and the other for sensor-connections and human interaction.

OBU is not full-duplex so, therefore, it cannot transmit messages simultaneously, so DSRC is half-duplex. The RSU and OBU can send messages only when the channel becomes idle and also confirmed that it is idle. If the channel is busy, RSU and OBU need to wait and if the channel is idle then RSU or OBU will send the signal Request to Send (RTS) to control channel. The control channel will allocate the channel on the basis of high priority first followed by low priority. The high priority messages are those messages related to public safety.

The WAVE architecture is defined by the IEEE 1609 family of standards and uses the IEEE 802.11p amendment to extend the use of 802.11 to vehicles. The IEEE 1609 family is composed of four standards describing the resource manager, security services, networking services and multi- channel operations.

WAVE standard consists of five complementary parts

• 802.11p “Wireless Access in Vehicular Environments (WAVE)” [8] which is an amendment to the well known IEEE 802.11 Wireless LAN Standard and covers the physical layer of the system.
• 1609.1 “Resource Manager” [8] that covers optional recommendations for the application layer. [13], [14]
• 1609.2 “Security Services for Applications and Management Messages” [8] that covers security, secure message formatting, processing and exchange. [13], [14]
• 1609.3 “Networking Services” [8] that covers the WAVE communication stack. [13], [14]
• 1609.4 “Multi-Channel Operation” [8] that covers the arrangement of multiple channels and how they should be used. [13], [14]

The most evident part is its dual stack. Whereas there is a well-known stack, called TCP/IP stacks and on the other hand there is a stack, called WAVE Short Message stack. The function of the WAVE Short Message stack is to provide a connectionless transport protocol i.e. without checking the connection that whether connection is made or not, similar to UDP but on a single-hop basis. The safety applications are supposed to use this stack only while non-safety applications can use both. It should be noted that the devise or design of this approach is focused on non-safety applications and considers safety as a black box.

2.6.1 IEEE 1609.1 – Resource Manager

The IEEE 1609.1 standard defines the architecture and data flows of WAVE. It also describes command messages and data formats. [9], [8]. The standard explains how data communication between road side units and vehicle on board units occurs. The discussion of this standard’s operation will be based on the standard defines applications residing on the on board unit as Resource Command Processors and those residing in road side units or elsewhere as Resource Manager Applications. The Resource Manager is the focus of this standard and is also the application that is responsible for managing communication between multiple Resource Manager Applications and Resource Command Processors. [9], [8]

WAVE communication imitates a client-server architecture that is managed by the Resource Manager. For example, in the case where a company wants to provide traffic updates by analyzing vehicle speed statistics in a stretch of highway, the application that analyzes the traffic data (a Resource Manager Application) would reside on the road side unit or a remote server that is connected to a road side unit. When the Resource Manager Application sends a request for the speed of the vehicle the Resource Manager application in the road side unit receives the request then forwards it to the vehicle’s Resource Command Processor application using WAVE. The vehicle then replies to the Resource Manager which forwards the message to the Resource Manager Application. If another passing vehicle asks for traffic updates by sending a request to the road side unit, the roles of client and server from the previous case are switched.

WAVE is designed to provide secure communications and minimize the cost of on board units by minimizing the amount of processing required by them. All only desired information relevant to road safety will be transferred.

2.6.2 IEEE 1609.2 – Security Services

The IEEE 1609.2 standard defines secure message formats and processing and infers circumstances for using secure message exchange. [13], [8]. It deals with security services for applications and management messages. Security is important in WAVE because vehicles transmit sensitive information that could constitute a violation of privacy if accessed by unauthorized parties. The efficacy and reliability of a system where information is gathered and shared among autonomous entities raises concerns about the authenticity of the received data. For example, a bad actor could misrepresent its observations in order to gain advantage (e.g. a vehicle V falsely reports that its desired road R is stopped with traffic, thereby encouraging others to avoid R and providing a less-congested trip for V on R). More malicious actors could impersonate other vehicles or road-side infrastructure in order to trigger safety hazards. Vehicles could reduce this threat by creating networks of trust, and ignoring, or at least distrusting, information from un-trusted senders. [13], [8]

A trusted communication generally requires two properties are met:

• The sender is conclusively identified as a trusted source.
• While in transit, the contents of the sender’s message are not tampered.

WAVE maintains security by ensuring confidentiality and authenticity in message transmissions. The final standard is expected to address privacy issues with the current version. WAVE ensures confidentiality