Overview of Vanets

Overview of VehicularNetworking

藍崑展成功大學資工系

Overview Vehicular Network

•Scope•Projects•MANET (Mobile Ad-hoc NETwork)•Protocols•Mobility•Security•Transport•Information Dissemination

Scenario

What are in a vehicular network

•Vehicles (on-board unit)•Road side unit/equipment•Communication protocols

–Vehicle to vehicle–Vehicle to road side–Vehicle to handheld device

•Network infrastructure•GPS (optional?)•Back-end system

Connected car scenario

Difference of communications

Applications of a vehicle network

•Safety–Intersection warning

•Vehicle-based•Infrastructure-based

•Vehicle probe–Travel time estimation–Environmental data collection–Road surface data collection

•Emergency vehicle– preemptive traffic control

•Navigation

Intelligent Traffic control withtelematics

Telematics vs. ITS

•Telematics–The integrated use of telecommunications

and informatics within road vehicles

•ITS (intelligent transportation system)–add information and communications

technology to transport infrastructure andvehicles

Approach

Approach

Approach

Approach

Vehicle

Intersection

TrafficLight

Too long….

Too short….

Traffic control

IntersectionPre-timed Traffic light

50sec

70sec

50sec

70sec

Unfair…..

SCOOT (Split, Cycle and OffsetOptimization Technique)

SCATS (Sydney CoordinatedAdaptive Traffic System)

50sec

70sec

50sec

70sec

: Detector

60sec

30sec

60sec

30sec

Limited!!

Case1: Queue istoo long

Case2: Someproblems in the

intersection

TrafficView

: Controller

: Controller

Green time may beextended

Case1: pedestrianCase2: Vehicles inthe Intersection

Too many vehicles.I must wait

Is this for real?



National initiatives

•US–VII (Vehicle Infrastructure Integration)

•Europe–i2010–ERTICO

VII goal

•Safety–E.g. reduce number of car accidents

•Driving quality–E.g. shorter driving time

•New Market–E.g. applications that run on vehicle OBU

VII business model

•Government–builds network infrastructure (DSRC)–Subsidize auto-maker for OBU & application

development

•Auto-maker–All new cars sold in US are VII-compliant–Allow government to run safety-related

application on OBU

VII vision

VII consortium

•Auto-makers: OBE and applications–Ford–GM–DCX (DaimlerChrysler)–BMW–VW–Nissan–Toyota–Honda

•State DOT (Department of Transportation): networkinfrastructure and RSE–Subcontract to Booz Allen Hamilton (a global consulting firm)

Schedule

$54M $3B

Planned deployment

System architecture

(our focus in this course)

On-board equipment (OBE)

Road-Side equipment (RSE)

End-to-End Communication

Putting all together

Multiple applications on top ofDSRC

Current deployment

Future traffic estimate

•WiMax --- 60%•DSRC --- 10%•WiFi --- 10%•Satellite --- 10%•Cellular (e.g. UMTS) --- 10%

Dual Mode OBE

•OBE can be dual mode–Public application (safety, information)

•DSRC–Mandatory by VII–27Mbps, 1km range–802.11p (PHY, MAC), 1609 (upper layer extension)

–Private application (voice, infotainment,navigation)•WiMax, WiFi, Cellular

–Value differentiator of auto-maker OBE

What are in a vehicular network?

What are in a vehicular network?

Communication protocols

i2010

•A European Information Society for growth andemployment

•the European Commission's strategic policyframework laying out broad policy guidelines forthe information society and the media in theyears up to 2010

•3 flagship initiatives–Intelligent Car–Digital Libraries–Ageing Well in the Information Society

Intelligent Car

•Night vision

•Advanced cruisecontrol–Use radar to maintain

safe distance

Intelligent car

•CyberCars–Driver-less–Run at low speed (30km/hr)–Can avoid obstacles–Park automatically–With a fee, users would have

access right•CyberCars2

–Follow-up project–Focus on V-to-V and V-to-

infrastructure communication

Intelligent Car

•CarTalk project–Focus on vehicle-to-

vehicle communication–Information is

transmitted from onecar to another car

–Vehicles nearby forman ad-hoc network

ERTICO

•Europe-based•ERTICO represents the interests and expertise

of around 100 Partners•provides a platform for its Partners to define

common research & development needs•acquires and manages publicly funded ITS

development & deployment projects on behalf ofits Partners

•Plan the deployment of ITS•Influence decision makers and opinion leaders

Organization• Board members

– Industry• Renault• Volkswagen AG• Siemens• FIAT/IVECO• Navteq• Robert Bosch

– Public Authorities• UK Department for Transport• Slovenian Ministry of Transport• Swedish Road Administration

– Infrastructure Operators• ASFA• Thales• Vodafone

– Users• ADAC• RACC

– Others• TNO

projects• Safety

– ADASIS Forum — advancing map-enhanced driver assistance systems– AIDE — enhancing safety with adaptive driver assistance systems– ERTRAC — contributing to European road transport research priorities– eSafety Forum — making Europe's roads safer for everyone– FeedMAP — enabling quick and inexpensive map updates– GST — creating easy access to dynamic safety services– HeavyRoute — supporting quicker and safer freight transport– IP PReVENT— supporting the driver, preventing accidents– •MAPS&ADAS — using digital maps to improve road safety– •RESPONSE3 — bringing ADAS to market quickly and safely– SAFESPOT — supporting smart vehicles on safe roads– SpeedAlert Forum — keeping drivers informed of speed limits at all times

• Security– EOS — building a European security partnership for the 21st century– EURAM — generating a European risk assessment methodology for critical infrastructures

• Efficiency & Environment– AGILE — making the most of satellite navigation services– CVIS — facilitating vehicle and infrastructure cooperation– •DEPN — dismantling non-technical barriers to CVIS deployment– •FOAM — building a framework for open application management– ETNITE — improving ITS training and education– FRAME Forum — providing continuity and compatibility for European ITS architecture– RCI — contributing to free-flow road charging– SISTER — promoting the integration of satellite and terrestrial communication with Galileo for road transport

E-call•A mandate for all vehicles in EU after 2010/9•Under eSafety Forum

E-call requirement



Mobile Ad Hoc Networks

•Formed by wireless hosts which may bemobile

•Without (necessarily) using a pre-existinginfrastructure

•Routes between nodes may potentiallycontain multiple hops

Mobile Ad Hoc Networks

•May need to traverse multiple links toreach a destination

A

B

Mobile Ad Hoc Networks(MANET)

•Mobility causes route changes

A

B

Why Ad Hoc Networks ?

•Ease of deployment

•Speed of deployment

•Decreased dependence on infrastructure

To summarize

Many Applications

•Personal area networking–cell phone, laptop, ear phone, wrist watch

•Military environments–soldiers, tanks, planes

•Civilian environments–Mesh networks– taxi cab network–meeting rooms–sports stadiums–boats, small aircraft

•Emergency operations–search-and-rescue–policing and fire fighting

Applications: Vehicular Ad-hocnetwork

Applications: Wireless SensorNetwork

Applications: Mesh Network

Many Variations

•Fully Symmetric Environment–all nodes have identical capabilities and responsibilities

•Asymmetric Capabilities– transmission ranges and radios may differ–battery life at different nodes may differ–processing capacity may be different at different nodes–speed of movement

•Asymmetric Responsibilities–only some nodes may route packets–some nodes may act as leaders of nearby nodes (e.g., cluster

head)

Many Variations

•Traffic characteristics may differ in different adhoc networks–bit rate–timeliness constraints–reliability requirements–unicast / multicast / geocast–host-based addressing / content-based addressing /

capability-based addressing

•May co-exist (and co-operate) with aninfrastructure-based network

Many Variations•Mobility patterns may be different

–people sitting at an airport lounge–New York taxi cabs–kids playing–military movements–personal area network

•Mobility characteristics–speed–predictability

•direction of movement•pattern of movement

–uniformity (or lack thereof) of mobility characteristics amongdifferent nodes

Challenges

•Limited wireless transmission range•Broadcast nature of the wireless medium

–Hidden terminal problem (see next slide)•Packet losses due to transmission errors•Mobility-induced route changes•Mobility-induced packet losses•Battery constraints•Potentially frequent network partitions•Ease of snooping on wireless transmissions (security

hazard)

Hidden Terminal Problem

B CA

Nodes A and C cannot hear each other

Transmissions by nodes A and C can collide at node B

Nodes A and C are hidden from each other

Research on Mobile Ad HocNetworks

Variations in capabilities & responsibilitiesX

Variations in traffic characteristics, mobility models, etc.X

Performance criteria (e.g., optimize throughput, reduceenergy consumption)

=Significant research activity

The Holy Grail

•A one-size-fits-all solution–Perhaps using an adaptive/hybrid approach

that can adapt to situation at hand

•Difficult problem

•Many solutions proposed trying to addressa sub-space of the problem domain

VANET vs. MANET

•VANET (Vehicular Ad-hoc Network) canbe considered a subset of MANET (MobileAd-hoc Network)–Nodes do not move in any random direction–Nodes are powered (energy is not an issue)–Node contact time is limited

•Intermittent connectivity might occur

–Node speed is bounded•Mostly high speed, but occasionally stop and slow

moving



802.11p•WAVE (Wireless Access in Vehicular Environment)•Based on .11a•5.9GHz•Data rate: 6-27Mbps•Designed for general Internet access, can be used for

ETC as well•7 licensed channels•Use open off-the-shelf chipset and software•Vehicle-to-roadside and vehicle-to-vehicle•Command-response and peer-to-peer

Ch 172 Ch 174 Ch 176 Ch 178 Ch 180 Ch 184Ch 182

Frequency (GHz)

5.85

0

5.86

0

5.87

0

5.88

0

5.89

0

5.90

0

5.91

0

5.92

0

Control Channel

Service Channels Service Channels

Critical Safetyof Life

High PowerPublic Safety

802.11p

•Target for high speed vehicle•Short latency (<50ms) for MAC•Random MAC address for preserving

privacy•IPv6 for network layer (with header

compression allowed)•Multiple stack options above network layer

Some technical terms•DSRC (dedicated short-range communication)

–Apply to many forms of short-range low-latency radio–5.85 to 5.925GHz in North America

•OBU: a device performs the functions of 802.11 stationwith additional WAVE functions

•RSU: a device performs the functions of 802.11 accesspoint with additional WAVE functions

•WBSS (WAVE basic service set): A set of OBUsoperating in a WAVE mode controller by an RSU

•WIBSS (WAVE independent basic service set): A set ofOBUs operating in a WAVE mode that forms a self-contained network–Do not use beacons–Connection is created/tore-down on-dmand

WAVE

•Differences from 802.11–High reliability–Low latency

•From association to end of data exchange <100ms

Channel access

•Control channel–Broadcast (no reply)

•Service channel–Data transmission

•If an OBU does not hear anything within100ms, it switches back to control channel

Power control

•Pubic safety application are allowed higherpower transmission than privateapplication

•The reference point for RF power is thecenter of front bumper of the vehicle

Safety-related message

•Get higher priority during transmission•Normally sent on control channel•Use EDCA (.11e)

802.16

•aka WiMax–Wireless Metro Internet

•Fast last mile access to network•Target Applications

–Data–Voice–Video–Real time videoconferencing

•Fast cable/fiber to end user is expensive

Usage Scenarios

Comparison of wireless standards

Why WiMax?

•Better spectral efficiency than 3G–Consider multiple antennas right from the start–OFDM is more amenable to MIMO implementation

•Higher peak data rate•Higher average throughput•Support more symmetric linnks•Lower cost

–IP architecture from bottom up

•But 3G has a better mobility support

Why WiMax?

•Better spectral efficiency than 3G–Consider multiple antennas right from the start–OFDM is more amenable to MIMO implementation

•Higher peak data rate•Higher average throughput•Support more symmetric linnks•Lower cost

–IP architecture from bottom up

•But 3G has a better mobility support

802.20

•Target for very high mobility–> 250 kmph–Operate below 3.5GHz–4Mbps downlink and 1.5Mbps uplink–Still under developing

•Lack of consensus•Issues with the standardization process

•802.22–Target for rural and remote area–Define a cognitive radio

•Take advantage of unused TV channels•Operate in VHF and low UHF bands and lead to greater

range

M-Taiwan Project

WiMax Network Usage Model

WiMax Features•Broad bandwidth

–Up to 134.4 Mbit/s in 28 MHz channel (in 2-66 GHz)•32Mb/s -134.4Mb/s•1.25/2.5/5/10/14/20/25/28MHz per channel (3.5/7/8.75/13.5MHz)

•Supports multiple services simultaneously with full QoS–Efficiently transport IPv4, IPv6, ATM, Ethernet, etc.–Wireless transportation system (ferry)

•Bandwidth on demand (frame by frame)–Similar to HIPERLAN Type II (frame-based protocol) and

DOCSIS (Data Over Cable Service Interface Specifications)–Centralized control

•MAC designed for efficient used of spectrum•Comprehensive, modern, and extensible security

•Supports multiple frequency allocations from 2-66 GHzin 802.16 (10-66GHz), 802.16a (2-11GHz)and 802.16e(<6GHz) 700MHz–Single carrier (SC) for line-of-sightsituations–OFDM and OFDMA (MC) for non-line-of-sight situations

•OFDM: orthogonal frequency division multiplexing•OFDMA: orthogonal frequency division multiple access

–OFDMA = 1.25 MHz, 2.5, 5, 10, 14 and 20 MHz channels (and more)

•Access schemes:–TDD (time division duplex) and FDD(frequency division duplex)

•Link adaptation: Adaptive modulation and coding•Point-to-multipoint (star) topology and mesh network

extension•Support for adaptive antennas and space-time coding (in

802.16a)•Extension to mobility

TDM vs. OFDM

802.16 vs. 802.16e

•Downlink data rate: 9.4Mbps vs. 46Mbps•Uplink data rate: 3.3Mbps vs. 7Mbps•Multiplexing: TDM vs. OFDMA•Modulation: both use QPSK, 16QAM, 64QAM•Coverage: 3-5 miles vs. 2 miles•Frequency band: 3.5GHz/5.8GHz vs. 2.3GHz/

2.5GHz/3.5GHz–5.8GHz is license-exempt

802.15.1

• aka Bluetooth

• For the last 10 meters

Target products

•Intelligent devices–PC–Cellular phone–PDA

•Data peripheral–Keyboard–Mouse–Camera–Printers

•Audio peripheral–Headset–Speaker–Stereo receiver

•Embeddedapplications–Cars: power lock

control–Grocery store update–MIDI music instrument

Usage models

•Computer to Computer File Transfer•Synchronization•3 in 1 Phone•Ultimate Headset•Computer Speakerphone•Cordless Computer•Conference Table•…..

characteristics•Unlicensed 2.4GHz radio band

– ISM (industrial, scientific,medical) band -Available worldwide–Also used by Microwave ovens, 802.11, HomeRF…

•Gross data rate of 1 Mbit/s•Basic 10m range extended to 100m with amplifiers•TDMA -TDD -Frequency hopping]

–hopping to a new frequency 1600 times a second•small packet size•Mixed voice / data paths•Encryption•Low power•Low cost•Extremely small

Piconet

•A piconet is characterized by the master–Frequency hopping scheme–Access code–Timing synchronization

• Master determines the bit rate allocated toeach slave

•Slaves do not synchronize to the master–Calculate offsets to master’s Bluetooth clock–Monitor timing drift

•Only one master–Dynamically selected–Roles can be switched •

•Up to 7 active slaves–Active piconet

•Up to 255 parked slaves–Can be reactivated quickly

•No central network structure–“Ad-hoc”network

Scatternet

Scatternet

• Interconnectedpiconets

•One master perpiconet

•Few devices sharedbetween piconets–Master/Slave–Slave/Slave–Need special features

•No central networkstructure–“Ad-hoc”network

Scatternet applications

Data exchange across piconets

802.15.4

•aka ZIGBEE•Also target Personal Area Networks market•Designed for the wide ranging automation

applications•Operates in the

–868MHz band at a data rate of 20Kbps in Europe–914MHz band at 40Kbps in the USA,–2.4GHz ISM bands Worldwide at a maximum data-

rate of 250Kbps.

features

•Standards-based•Interoperability and worldwide usability•Low data-rates•Ultra low power consumption•Very small protocol stack•Support for small to excessively large networks•Simple design•Security•Reliability

Bluetooth vs. Zigbee

•Bluetooth aims to cover more applications–Introduce complexity–increase cost and power consumption

Data rate

•Bluetooth–Higher data rate–audio, graphics and pictures, file transfer over small

networks–performance of a Bluetooth network drops when more

than 8 devices are present•ZigBee

–better suited for transmitting smaller packets overlarge networks

–mostly static networks with many, infrequently useddevices• like home automation, toys, remote controls, etc.

–can handle 65000+ devices.

power

•Bluetooth–Aim as a cable replacement for items like phones,

laptop computers and headsets•expect regular charging and use a power model like a mobile

phone

•ZigBee–limited power requirement

•better for devices where the battery is rarely replaced•designed to optimize slave power requirements (> 2 years)

latency

•Bluetooth–3 seconds to either join a network or to change to

active from sleeping state•though faster in accessing the channel (around 2ms).

•ZigBee–outstanding choice for timing critical, low power

applications•The join time for a new slave is typically 30ms•slave changing from sleeping to active, or accessing the

channel is typically 15ms



Why VANET simulation?

•Real-world experimentation–Currently no test-bed available–Hard to explore scalability–Classical problem with repeatability

•Emulation–Uses real sw/hw in simulated environment to ensure

accuracy–Higher scalability, but still limited

•Network simulation (e.g. NS-2, GloMoSim, SWANS)–Scalable to large number of nodes–Easy to vary system configuration–Repeatability–…

•Desirable simulation characteristics–Scalability - interesting problem instances–Generalizable - should enable a wide range of scenarios–Feedback loop - enable self-steering (e.g., traffic advisory)–Close correspondence with real world

A realistic mobility model is crucial to the evaluationof VANET protocols and applications

The importance of a mobility model

•Mobility –key component of VANETsimulators–Mobility constraints (e.g., streets, buildings)

•Affects velocities and distances between nodes,which affects radio transmission

–Nodes should physically interact with oneanother•E.g., avoid collisions

–Central to “feedback loop”in many scenarios•Cars can change trajectory in response to data

What we want for VANET mobility

Random waypoint consideredharmful

•Random Waypoint (RWP)–Benefits

•Simple•Low overhead•Common

–Disadvantages•NOT representative of

mobility for worst-case orgeneral-case performance

•Nodes cannot interact wrtmobility

•Encourages use of openfield simulation

RWP effects on wirelesscommunication

•Every position on map is a waypoint withequal probability–Artificially high density near center of map

•Nodes generally cannot leave the field–Data does not leave the field

•Arbitrary stopping points and stoppingtimes–Affects links among nodes

•Arbitrary speeds and speed distributions

Mobility traces

•Advantages–Represents real motion–Little overhead in simulation

•Disadvantages–Difficult to obtain–Rarely distributed (legal issues)–Difficult to generalize–Does not allow feedback loop

Vehicular motionCongestion leads to hot

spots at intersections

Vehicles spend more timenear intersections even

when uncongested

Car mobility & wirelesscommunication

•Nodes tend to spend more time at intersections– Increases interference in this region–Can reduce connectivity

•Buildings further reduce connectivity betweennodes on different streets

•Nodes often travel in opposite or orthogonaldirections–Short interaction time window

•Vehicular congestion slows nodes–Can stabilize topology, but can reduce overall connectivity

•A new mobility model for VANETs is needed…

Network Mobility

•IETF NEMO WG–RFC 3963 : Network Mobility (NEMO) Basic

Support Protocol (Jan. 2005)

•Extension of Mobile IPv6

•Mobile Router (MR)–Operates Mobile IPv6–Establishes a bi-directional tunnel to its

corresponding Home Agent (HA)

Network Mobility

114

InternetInternet

HA_MR

CN_MN 2::

4::

BU

4::2->7::2

5::/prefixlen,6::/prefixlenforward to MR

7::

MR

LFRLFN

6::

5::

2

All traffic must passthrough the bi-directional tunnelbetween the MRand itscorresponding HA.=>Triangularrouting

2



Security Issues for VANET

•Nodes may be misbehave or try tocompromise security at all layers of theprotocol stack

MAC Layer

•Disobey protocol specifications for selfishgains

•Denial-of-service attacks

MAC Layer Misbehavior

Wirelesschannel

Wirelesschannel

Access Point

A B

Nodes are required to followMedium Access Control(MAC) rules

Misbehaving nodes mayviolate MAC rules

Wirelesschannel

Wirelesschannel

Access Point

C D

Example

•We will illustrate MAC layer misbehaviorwith example misbehaviors that can occurwith IEEE 802.11 DCF protocol

One Possible Misbehaviors

•Causing collisions with other hosts’RTS orCTS

•Those hosts will exponentially backoff onpacket loss, giving free channel to themisbehaving host

Another possible Misbehaviors:“Impatient”Transmitters

•Smaller backoff intervals

•Shorter Interframe Spacings

“Impatient”Transmitters

•Backoff from biased distribution

–Example: Always select a small backoff value

Transmit

wait

B1 = 1

B2 = 20

Transmit

wait

B2 = 19

B1 = 1Misbehavingnode

Well-behavednode

Network Layer

Misbehaving hosts may create many hazards

•May disrupt route discovery and maintenance:Force use of poor routes (e.g., long routes)

•Delay, drop, corrupt, misroute packets

•May degrade performance by making goodroutes look bad

Watchdog Approach

•Verify whether a node has forwarded apacket or not

B DC EA

B sends packet to C

Watchdog Approach•Verify whether a node has forwarded a packet or not•B can learn whether C has forwarded packet or not•B can also know whether packet is tampered with if no

per-link encryption

B DC EA

C forwards packet to D

B overhears CForwarding the packet

Watchdog Approach:Buffering & Failure Detection

•Forwarding by C may not be immediate: B mustbuffer packets for some time, and compare themwith overheard packets

•Buffered packet can be removed on a match

•If packet stays in buffer at B too long, a “failuretally”for node C is incremented

•If the failure rate is above a threshold, C isdetermined as misbehaving, and source nodeinformed

127

Secure communication andanonymity

•Assume that every node has a unique and staticGlobal ID (GID) and a set of pseudonyms (PID)used as network addresses that can changeduring communication

•Nodes exchange their GID and the GID publickey prior to unicast communications betweenthem

•Despite we can have unicast communicationsusing PIDs we cannot know the other personsidentity

•Applying asymmetric cryptography, apseudonym is associated with a public/privatekey pair.

•A certificate signed by a trusted certificateauthority (CA) binds public key and GID

•A node can change its pseudonym andassociated signature and certificate in order toprevent identity and location tracking



Transport Layer(End-to-End Communication)

•How to secure end-to-end communication?

•Need to know keys to be used for securecommunication

•May want to anonymize thecommunication

131

•Two routes: A-B-D-F (BAD), A-C-D-F(GOOD)

Fig. 1. A link rupture event is more likely to occur betweenvehicles A, B, and D.

Source Destination

Geographical routing

Source Node

Destination Node

Choose node A (theclosest node) for the

next hop

Restricted Greedy Routing

Repair strategy based on real street

Detecting junctions

Beacon message

Correlation coefficient

Intermittent connectivity on theroad

Drive-thru Interent

•Wireless LANs are pervasive•Can we use wireless LANs on the road to

provide Internet access?•WLANs => connectivity islands•How to deal with intermittent connectivy

and exploit short connection period?

Connection splitting



Information DisseminationMotivation & Scenario

• Two cars crash while travelingsouthbound on a highway, nearbyvehicles cooperate to:– inform the closest ambulance and

police stations– alert approaching vehicles telling them

to slow down– notify the highway entrances north of

the accident

• Messages should ideally propagate– towards specific target areas– along the routes where the vehicle

density is higher

Information Dissemination

•How to route messages towards specifictarget areas while considering theunderlying vehicle density

•Assuming each vehicle knows itsgeographical location and communicationrange–How to find the preferred paths to reach the

target areas?

Documents

Overview of Vanets