ISA Lab., CICS, CU 1

2. Survey of VANETs

A Tutorial Survey on Vehicular Ad Hoc Networks

State of the art and research challenges for VANETs

ISA Lab., CICS, CU 2

2.1 Introduction

VANETs comprise vehicle-to-vehicle and vehicle-to-infrastructure communications based on wireless local area network technologies.

Vehicular connectivity can be fairly considered a future killer application, adding extra value to the car industry and operator’s services.

Such system should be suitable for a wide spectrum of applications, including safety-related, traffic and fleet control, and entertainment.

The major goals of these activities are to increase road safety and transportation efficiency, as well as to reduce the impact of transportation on the environment.

ISA Lab., CICS, CU 3

2.2 Wireless SpectrumThe allocation of 74 MHz of DSRC (Dedicated Short Range Communication) spectrum to accommodate Vehicle-to-Vehicle (V2V) and Vehicle-to-Infrastructure (V2I) communication for safety-related applications by US Federal Communications Commission (1999).The wide adoption of IEEE 802.11 technologies.

IEEE 802.11 is a set of standards carrying out wireless local area network (WLAN) computer communication in the 2.4, 3.6 and 5 GHz frequency bands.

ISA Lab., CICS, CU 4

2.3 VANET ApplicationsIntegrating a network interface, GPS receiver, different sensors and on-board computer given an opportunity to build a powerful car-safety systems, capable of gathering, processing and distributing information.

Four main groups from the connectivity point of viewcar-to-car traffic

car-to-infrastructure

car-to-home

routing-based

Theses applications are either safety-related or comfort-related.

ISA Lab., CICS, CU 5

Safety-related applications 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 notification, e.g. emergency braking alarms.

Another, more advanced example is cooperative driver assistance systems, which exploits the exchange of sensor data or other status information among cars.

Comfort applications The general aim of these applications is to improve passenger comfort and

traffic efficiency.

That could include POI (Points Of Interest) localization, current traffic or weather information and interactive communication.

ISA Lab., CICS, CU 6

All kinds of applications, which may run on top of TCP/IP stack might be applied here, e.g. online games or instant messaging.

Another application is reception of data from commercial vehicles and roadside infrastructure about their business.

2.4 Research Challenges in VANETs

The unique characteristics of VANETs

rapid topology changes and frequent 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

ISA Lab., CICS, CU 7

Wireless Access technology

Cellular technology (2/2.5/3G)

IEEE 802.11p based technology

Combined wireless access: CALM M5 (Continuous Air Interface for Long and Medium range)

Spectrum issues

The FCC has already allocated 75 MHz of spectrum at 5.9 GHz (from 5.850 to 5.925 GHz) for C2C and C2I communication (US).

Europe allocates 210 MHz for primary use of safety critical applications at 5.9 GHz range (5.875 – 5.925 GHz).

The same technology would then allow using additional spectrum at either in the 5 GHz RLAN band or in the 5.8 GHz IRM (industrial, scientific and medical) band for non-safety critical and commercial applications.

ISA Lab., CICS, CU 8

Broadcasting and message dissemination

Narrow bandwidth solutions: FM radio

Wider bandwidth digital services: DAB, DVB, DVB-H, S-DMB, T-DMB and DDB

Satellite broadcasting

Location-aware broadcasting would limit the broadcast range only to the site of interest, thus reducing overhead.

Routing issues

Frequent network partitioning in VANETs requires a different approach, e.g. the ‘carry and forward’ idea, where, if no direct route exists, a packet is carried by a node until it could be forwarded to a node being closer to the destination.

ISA Lab., CICS, CU 9

Power managementPower management in VANET is not concerned about energy efficiency, but rather about the transmission power – when too high, the ongoing transmission could disrupt another transmission at a distant node due to interferences.

Security and PrivacySeveral threats potentially exist, including fake messages causing disruption of traffic or even danger, compromising drivers’ private information, etc.

Anonymity must be preserved – the communications should not make the vehicle tracking or identification possible for non-trusted parties.

VANET modeling and simulationVehicles do not move randomly but rather follow the road infrastructure; road signs, traffic lights and other cars influence nodes’ behavior.

ISA Lab., CICS, CU 10

Nodes move at high relative speed, network density changes very dynamically, depending on location, recent events (e.g. accidents) or time of day.

2.5 Current Projects and StandardizationEurope

Cooperative driving: carTALK 2000

Driver information and warning issues: PReVent WILLWARN, SAFESPOT, FleetNet

USA

VSC (Vehicle Safety Communication Consortium): working on the development of DSRC standards, protocols and applications, applying inter-vehicle and road-to-vehicle communications.

ISA Lab., CICS, CU 11

Japan

Vehicle cooperative systems

ASV stands for an Advanced Safety Vehicle and builds on C2CC.

AHS stands for Advanced Highway System, and is promoted by Advanced Cruise-Assist Highway System Research Association (ASHRA).