What Are Vehicular Ad Hoc Networks

Published Date: 02 Nov 2017

CHAPTER 1

INTRODUCTION

1.1 overview

Today the wireless communication technologies are finding their role not only in mobile communication but also in Vehicular communications. Presently wireless communication turns out to be the new paradigm used for establishing communication between the mobile users. The wireless communication is becoming more in style than ever before because of its easy deployment. Wireless service is mobile and can be deployed almost everywhere faster than the fixed service. Scalability and flexibility are the two well known characteristic of wireless networking. Wireless networking provides users with network resources and connectivity irrespective of their locations.

There are two broad categories of wireless networks: infrastructure wireless network and infrastructure less wireless network also known as ad-hoc network [1].The infrastructure network contains Base Stations (BSs) or Access Points (APs). Data sent between a wireless client and other wireless clients and nodes on the wired network segment is first sent to the wireless AP or BS. The wireless AP then forwards the data to the appropriate destination. On the other hand, Ad-hoc is used to connect wireless clients directly together, without the need for a wireless AP or BS or a connection to an existing wired network. An ad-hoc network consists of different wireless clients, which send their data directly to each other. In these network no communication infrastructure, no wires and no central controller is required.

If the carriers in wireless network are mobile [2] like cell phone, laptops or personal digital assistant (PDA) then this type of network is called as mobile ad-hoc network (MANET). So a MANET is a type of wireless ad-hoc network consisting of autonomous mobile nodes and supporting no fixed infrastructure and no central controller. The nodes in such networks can organize themselves in an arbitrary fashion. If the carriers are moving vehicles then this type of network is said to be Vehicular Ad-Hoc Network i.e. (VANET). A VANET is an emerging and exciting application of an ad-hoc network that uses moving vehicles as nodes in a network to create a mobile network. It’s a promising paradigm in wireless communication that is aiming to enable road safety by providing driving support services and convenience by providing users interest oriented information services. It’s a special type of MANETs where vehicles are participating in the wireless ad-hoc network for establishing communications among vehicles or vehicles to roadside units or base stations. To accomplish this type of communication each vehicle in a VANET must be equipped with radar systems, Geographic Positioning Systems (GPS), sensors, computer system, cellular technologies, bluetooth etc. that allow them to act as network node.

Both MANETs and VANETs share some characteristics like movements of nodes, low bandwidth as well as self organizing feature of nodes with no controlling authority. But few factors are there which clearly distinguish both concepts like nodes in VANETs have higher mobility, restricted mobility pattern along the predefined highway infrastructure, extremely dynamic topology, frequent network partitioning, good availability of resources (especially energy) compared to small mobile devices and finally the totally new application state of affairs. VANETs will likely be an essential part of future Intelligent Transportation Systems (ITS) [3], [4].

1.2 Vehicular Network DEFINITION AND ARCHITECTURE

1.2.1 What are Vehicular Ad hoc Networks?

With the advancement in wireless technologies and the automotive industry a new class of wireless networks called as Vehicular Networks have emerged. Vehicular networks are formed on roads among moving vehicles equipped with wireless devices that support either homogeneous or heterogeneous technologies. VANETs are considered as one of the ad hoc network’s real-life applications. They enable communications among nearby vehicles as well as between vehicles and nearby fixed equipment, usually known as roadside equipment. Private vehicles, belonging to individuals or private companies and public transportation vehicles (e.g., police cars, ambulances buses and public service vehicles) both can take benefit from VANETs. Roadside equipments can be installed by private or government network operators or service providers. Vehicular networks are helpful in providing various communication services to drivers and passengers. Research community as well as the automotive industry is paying considerable attention to Vehicular Networks. Several governmental authorities and standardization organizations are also showing high interest for these networks. In this context, in North America, a dedicated short-range communications[5] (DSRC) system has emerged, where 75 MHz of spectrum was approved by the U.S. FCC (Federal Communication Commission) in 2003 for vehicular networks communication. Along with it, the Car-to- Car Communication Consortium (C2C-CC) [6] has been initiated in Europe by car manufacturers and automotive OEMs (original equipment manufacturers), with the main objective of increasing road traffic safety and efficiency by means of inter vehicle communication [7].

1.2.2 Architecture of Vehicular Ad hoc Networks

Vehicular network’s architecture allows communication among nearby vehicles and between vehicles and nearby fixed roadside equipment. There are three available communication approaches (i) a pure wireless vehicle-to-vehicle ad hoc network (V2V) allowing standalone vehicular communication with no infrastructure support, (ii) a wired backbone with wireless last hops that can be seen as a WLAN-like vehicular network, (iii) and a hybrid vehicle-to-road (V2R) architecture that does not rely on a fixed infrastructure in a constant manner, but can exploit it for improved performance and service access when it is available. In this latter case, vehicles can communicate with the infrastructure either in a single hop or multi hop fashion according to the vehicle’s positions with respect to the point of attachment with the infrastructure. The V2R architecture implicitly includes V2V communication.

The architecture for vehicular networks is proposed within the C2C-CC, distinguishing between three domains: in-vehicle, ad hoc, and infrastructure domain. Fig. 1.1 illustrates this reference architecture. The in-vehicle domain refers to a local network inside each vehicle logically composed of two types of units: (i) an on-board unit (OBU) and (ii) one or more application unit(s) (AUs).

Figure 1.1 Architecture of VANETs.

An OBU is a device in the vehicle having communication capabilities (wireless and/or wired), while an AU is a device executing a single or a set of applications while making use of the OBU’s communication capabilities. An AU can be an integrated part of a vehicle and be permanently connected to an OBU. It can also be a portable device such as a laptop or PDA that can dynamically attach to (and detach from) an OBU. The AU and OBU are usually connected with a wired connection, while wireless connection is also possible (using, e.g., Bluetooth, WUSB, or UWB). This distinction between AU and OBU is logical, and they can also reside in a single physical unit.

The ad hoc domain is a network composed of vehicles equipped with OBUs and roadside units (RSUs) that are stationary along the road. OBUs of different vehicles form a mobile ad hoc network (MANET), where an OBU is equipped with communication devices, including at least a short range wireless communication device dedicated for road safety. OBUs and RSUs can be seen as nodes of an ad hoc network, respectively, mobile and static nodes. An RSU can be attached to an infrastructure network, which in turn can be connected to the Internet. RSUs can also communicate to each other directly or via multi hop, and their primary role is the improvement of road safety, by executing special applications and by sending, receiving, or forwarding data in the ad hoc domain.

In VANETs there are two types of infrastructure domain access : RSU and hot spot. RSUs allow OBUs to access the infrastructure and remains connected to the Internet. OBUs may also communicate with Internet via public, commercial, or private hot spots (Wi-Fi hot spots). In the absence of RSUs and hot spots, OBUs can utilize communication capabilities of cellular radio networks (GSM, GPRS, UMTS, WiMax, and 4G) if they are integrated in the OBU.

Both V2V and V2R use Dedicated Short-Range Communications (DSRC) operating in the 5.9 GHz band as shown in Fig.1.1. The Federal Communications Commission (FCC) allocated a new 75 MHz band DSRC at the 5.9 GHz frequency for ITS applications in North America. The IEEE 802.11p standard [8] and WAVE (Wireless Access for Vehicular Environment) suite were recently released for trial use [9]. Several applications in VANETs require data routing protocols for establishing these two types of communication. The Routing approaches adopted in the network characterize performance of the communication. Routing is the most important and challenging issue to be handle in VANETs because of high mobility of vehicles. Thus routing protocols for VANETs must cope with the partitioning of networks due to connectivity problem [7].

1.3 Characteristics of VANETs.

Vehicular networks have special behavior and characteristics that distinguish them from other types of mobile networks. The unique, attractive and challenging features of VANETs are as follows [10], [11]:

High mobility: The environment in which vehicular networks operate is extremely dynamic and includes extreme configurations: on highways, relative speeds of up to 300 km/h may occur, while density of nodes may be 1–2 vehicles 1 km on low busy roads. On the other hand, in the city, relative speeds can reach up to 60 km/h and node density can be very high, especially during rush hour.

Predictable mobility Pattern: Unlike classic mobile ad hoc networks, where it is hard to predict the node’s mobility, vehicles tend to have very predictable movements that are (usually) limited to roadways. Roadway information is often available from positioning systems and map based technologies such as GPS. Given the average speed, current speed, and road trajectory, the future position of a vehicle can be predicted.

Potentially large scale: Unlike most ad hoc networks studied in the literature that usually assume a limited network size, vehicular networks can in principle extend over the entire road network and so include many participants.

Unlimited transmission power: Mobile device power issues are usually not a significant constraint in vehicular networks as in the case of classical ad hoc or sensor networks, since the node (vehicle) itself can provide continuous power to computing and communication devices.

Higher computational capability: Indeed, operating vehicles can afford significant computing, communication, and sensing capabilities.

Partitioned network: Vehicular networks will be frequently partitioned. The dynamic nature of traffic may result in large inter vehicle gaps in sparsely populated scenarios and hence in several isolated clusters of nodes.

Network topology and connectivity: Vehicular network scenarios are very different from classic ad hoc networks. Since vehicles are moving and changing their position constantly, scenarios are very dynamic. Therefore the network topology changes frequently as the links between nodes connect and disconnect very often. Indeed, the degree to which the network is connected is highly dependent on two factors: the range of wireless links and the fraction of participant vehicles, where only a fraction of vehicles on the road could be equipped with wireless interfaces [7].

1.4 Potential Applications OF VEHICULAR Networks

The applications of VANETs can be classified into following categories [12]:

Safety oriented,

Commercial oriented,

Convenience oriented and

Productive Applications.

1.4.1 Safety Applications

Safety applications include monitoring of surrounding roads, approaching vehicles, surface of the road, road curves etc. The Road safety applications can be classified as:

Real-time traffic: The real time traffic data can be stored at the RSU and can be available to the vehicles whenever and wherever needed. This can play an important role in solving the problems such as traffic jams, avoid congestions and in emergency alerts such as accidents etc.

Co-operative Message Transfer: Slow/Stopped Vehicle will exchange messages and co-operate to help other vehicles. Though reliability and latency would be of major concern, it may automate things like emergency braking to avoid potential accidents. Similarly, emergency electronic brake light may be another application.

Post Crash Notification: A vehicle involved in an accident would broadcast warning messages about its position to trailing vehicles so that it can take decision with time in hand as well as to the highway patrol for tow away support.

Road Hazard Control Notification: Cars notifying other cars about road having landslide or information regarding road feature notification due to road curve, sudden downhill etc.

Cooperative Collision Warning: Alerts two drivers potentially under crash route so that they can mend their ways [13].

Traffic Vigilance: The cameras can be installed at the RSU that can work as input and act as the latest tool in low or zero tolerance campaign against driving offenses [14].

1.4.2 Commercial Applications

Commercial applications will provide the driver with the entertainment and services as web access, streaming audio and video. The Commercial applications can be classified as:

Remote Vehicle Personalization/ Diagnostics: It helps in downloading of personalized vehicle settings or uploading of vehicle diagnostics from/to infrastructure.

Internet Access: Vehicles can access internet through RSU if RSU is working as a router.

Digital map downloading: Map of regions can be downloaded by the drivers as per the requirement before traveling to a new area for travel guidance. Also, Content Map Database Download acts as a portal for getting valuable information from mobile hot spots or home stations.

Real Time Video Relay: On-demand movie experience will not be confined to the constraints of the home and the driver can ask for real time video relay of his favorite movies.

Value-added advertisement: This is especially for the service providers, who want to attract customers to their stores. Announcements like petrol pumps, highways restaurants to announce their services to the drivers within communication range. This application can be available even in the absence of the Internet.

1.4.3 Convenience Applications

Convenience application mainly deals in traffic management with a goal to enhance traffic efficiency by boosting the degree of convenience for drivers. The Convenience applications can be classified as:

Route Diversions: Route and trip planning can be made in case of road congestions.

Electronic Toll Collection: Payment of the toll can be done electronically through a Toll Collection Point. A Toll collection Point shall be able to read the OBU of the vehicle. OBUs work via GPS [15] and the on-board odometer or tachograph as a back-up to determine how far the Lorries have travelled by reference to a digital map and GSM to authorize the payment of the toll via a wireless link. TOLL application is beneficial not only to drivers but also to toll operators.

Parking Availability: Notifications regarding the availability of parking in the metropolitan cities helps to find the availability of slots in parking lots in a certain geographical area.

Active Prediction: It anticipates the upcoming topography of the road, which is expected to optimize fuel usage by adjusting the cruising speed before starting a descent or an ascent. Secondly, the driver is also assisted [16].

1.4.4 Productive Applications

We are intentionally calling it productive as this application is additional with the above mentioned applications. The Productive applications can be classified as:

Environmental Benefits: AERIS research program [17] is to generate and acquire environmentally relevant real-time transportation data, and use these data to create actionable information that support and facilitate "green" transportation choices by transportation system users and operators. Employing a multi-modal approach, the AERIS program will work in partnership with the vehicle to vehicle (V2V) communications research effort to better define how connected vehicle data and applications might contribute to mitigating some of the negative environmental impacts of surface transportation.

Time Utilization: If a traveler downloads his email, he can transform jam traffic into a productive task and read on-board system and read it himself if traffic stuck. One can browse the Internet when someone is waiting in car for a relative or friend.

Fuel Saving: When the TOLL system application for vehicle collects toll at the toll booths without stopping the vehicles, the fuel around 3% is saved, which is consumed when a vehicles as an average waits normally for 2-5 minutes.

1.5 Challenges of Vehicular Networks

The special behavior and characteristics of Vehicular networks creates some challenges for vehicular communication. These challenges can have a great impact on the future deployment of these networks. A number of technical challenges need to be resolved in order to deploy vehicular networks and to provide useful services for drivers and passengers in such networks. Scalability and interoperability are two important issues that should be satisfied, and the employed protocols and mechanisms should be scalable to numerous vehicles and interoperable with different wireless technologies. The Challenges of VANETs can be classified as follows [7]:-

1.5.1 Reliable Communication and MAC Protocols

Vehicular networks experience multihop communication similar to ad hoc networks, which can potentially extend the network operator fixed infrastructure and thus provide virtual infrastructure among the moving vehicles. Multihop wireless communication represents a major challenge on the reliability of communication in VANETs. Efficient MAC (medium access control) protocols need to be in place, while adapting to the highly dynamic environment of vehicular networks, and considering message priority of some applications (e.g., accident warnings). In spite of the dynamic topology and the high mobility, fast association and low communication latency should be satisfied between communicating vehicles in order to guarantee (i) service reliability for safety-related applications while taking into consideration the time sensitivity during message transfer, and (ii) the quality and continuity of service for nonsafety applications. Moreover, MAC protocols should take into consideration the heterogeneous communication that is liable to take place between different wireless technologies (e.g., Wi-Fi and GSM) in vehicular networks.

1.5.2 Routing and Dissemination

Vehicular networks differ from conventional ad hoc wireless networks by not only experiencing rapid changes in wireless link connections, but also having to deal with different types of network densities [18]. For example, vehicular networks on freeways or urban areas are more likely to form highly dense networks during rush hour traffic, while vehicular networks are expected to experience frequent network fragmentation in sparsely populated rural freeways or during late night hours. Moreover, vehicular networks are expected to handle a wide range of applications ranging from safety to leisure. Consequently, routing and dissemination algorithms should be efficient and should adapt to vehicular network characteristics and applications, permitting different transmission priorities according to the application type (safety-related or not). Until now, most of vehicular network research has focused on analyzing routing algorithms to handle the broadcast storm problem in a highly dense network topology [19],[20] under the oversimplified assumption that a typical vehicular network is a well-connected network in nature.

However, in the future, these networks are expected to observe high penetration with lesser infrastructure support, and hence it is important in this case to consider the disconnected network problem, which is a crucial research challenge for developing a reliable and efficient routing protocol that can support highly diverse network topologies. As for message dissemination, the dissemination algorithms should depend on the network density as well as the application type. For example, message dissemination in safety-related applications should be mostly broadcast-like, in a way to assure the message propagation to the required cluster of vehicles without causing a broadcast storm. In non safety-related applications, message transfer through unicast or multicast transmission is more suitable.

1.5.3 Security

Vehicular communication security is a major challenge, having a great impact on the future deployment and application of vehicular networks. Indeed, security and privacy are major concerns in the development and acceptance of services and should not be compromised by ease-of-use of service discovery protocols. As the demand for service discovery is growing, passengers may use services in foreign networks and create immense security problems for themselves and for other network users. Consequently, it is important to propose innovative solutions for secure communication between participants as well as authorized and secure service access. To enhance the vehicular network access ubiquity, these solutions should take advantage of (i) the ad hoc multi hop authentication and communication concepts, which on one hand allow secure communication and on the other hand extend the infrastructure coverage with the minimum deployment cost for the network operator, and (ii) the distributed-based authentication.

Appropriate security architectures should be in place providing communication between vehicles and allowing different service access. A set of security mechanisms suitable for any vehicular network environment should be developed, providing trust, authentication, access control, and authorized and secure service access. In this context, authentication optimization is important to be studied for both infrastructure-based and infrastructure-less communications, aiming to facilitate the reauthentication process that may need to take place during the vehicle mobility. Due to the open and dynamic environment of vehicular networks, nodes cooperation is an important aspect that should be satisfied for allowing successful communication between vehicles. Nodes may behave selfishly by not forwarding messages for others in order to save power and bandwidth or just because of security and privacy concerns. Consequently, appropriate mechanisms should be developed to detect selfishness and enforce node cooperation in vehicular network environment.

1.5.4 IP Configuration and Mobility Management

The potential vehicle-to-infrastructure architecture is promising in allowing vehicular Internet access as well as provision of Internet-related services to drivers and passengers. However, two technical challenges exist under this issue: IP address configuration and mobility management. These challenges can threaten the service quality and the service continuity. Regarding the vehicular network characteristics, IP address configuration should be carried out in an automatic and distributed manner. So far, there is no standard for IP auto configuration in ad hoc networks, and hence the problem becomes complex for vehicular networks. As for mobility management, this is a crucial problem for non safety applications, where message dissemination is not broadcast-based. The absence of mobility management mechanism threatens service commercialization in vehicular networks and loses the benefit of the vehicle to- infrastructure architecture since all Internet-related services would guarantee neither service quality nor their continuity.

1.6 Motivation for thesis

Vehicular Ad Hoc Networks (VANETs), an extension of mobile ad hoc networks (MANETs) were developed with a view to enable real-time communication between mobile nodes (either vehicles or road side infrastructure) over wireless links, primarily with a view to enable traffic safety and efficiency.

The communication between nodes in a VANET faces many unique challenges. This is especially true for safety-critical applications like collision avoidance, pre-crash sensing, lane change etc. Factors like high vehicle speeds, low signal latencies, varying topology, total message size, traffic density etc induce challenges that makes conventional wireless technologies and protocols unsuitable for VANETs. Thus there is a need to simulate the routing protocols in a real world traffic model. This model should be capable of intelligent driver model with Intersection management (IDM-IM) and changing lane (IDM-LC). The simulation done under IDM-IM and IDM-LC on a real city map with real world traffic scenario will truly determine the characteristics of various routing protocols. From such simulations we will be able to select the best protocol suited for VANETs.

1.7 Problem Statement

Due to the node mobility feature of VANETs, several simulation based studies have been done using the traditional ad hoc routing protocols. Their simulation work did not represented the real world traffic situations. Also simple road topologies and constant speed of vehicle was used to study the behavior of routing protocols. The effect of mobility and density of vehicles on the performance of routing protocols in VANETs is not yet studied in real world traffic scenarios that support Intelligent Driver Model with Intersection management (IDM-IM) and changing lane (IDM-LC). This thesis analyzes the impact of mobility and density of vehicles on Proactive and Reactive routing protocols namely DSDV, AODV, DSR and AOMDV in a realistic vehicular network. It evaluates the performance parameters like average end to end delay, Normalized Routing overload, Packet Delivery Ratio and Average throughput of these protocols by varying the vehicle speed and density. A comparison among these protocols is carried out based on above metric parameters to see how well they perform in a real world traffic scenario. The simulation is carried out on a City Model and the real city map of Afton Oaks, Houston, USA based on TIGER[21] database from U.S. Census Bureau. Based on the simulation results, under the given simulated environment, one of the selected protocols is proposed for VANETs.

1.8 Outline of Thesis

Chapter 2 describes the background of VANETs and the literature survey. In Chapter3 we have described the various routing protocols and the mobility models. Chapter 4 describes the Methodology and Simulation results. Finally we provide the conclusion and future works in chapter 5.