Department of Electrical and Computer Engineering

The Ohio State University 1

Evaluation of Intersection Collision WarningSystem Using an Inter-vehicle CommunicationSimulator

Atakan Doğan, Gökhan Korkmaz, Yiting Liu,

Füsun Özgüner, Ümit Özgüner, Keith Redmill, Oscar Takeshita, K. Tokuda

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Outline of Contents

Introduction Vehicle Traffic Simulator Shadowing Effect The Wireless Simulator Simulations Conclusions

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Outline of Contents

Introduction• Background Information• Problems• Inter-vehicle Communication (IVC) Simulator

Vehicle Traffic Simulator Shadowing Effect The Wireless Simulator Simulations Conclusions

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Background Information

Develop a simulator • Study and solve the intersection collision

problems Based on OSU and OKI project Incorporate

• Intelligent Transportation System• Physical Layer• MAC Layer

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ProblemsAnimation of Intersection

warning system

Intersection Collision Scenario

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Problems (Other Scenarios)

SV

SV

SV

SV

POV

POV

POVPOV

POV: Principle other Vehicle

SV: Subject Vehicle

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IVC Simulator

Components of Intersection Collision Warning System

• Local Map DatabaseIntersection position, lanes, speed limit etc.

• Differential GPSVehicle position

• Inter-vehicle Communication System

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IVC Simulator

Vehicle Traffic Simulator

Trace files:• Vehicle information

• Vehicle position•Vehicle velocity

•Shadowing

WirelessSimulator

WSVTS

VTS and WS runs independently of each other

VTS is interfaced to WS through trace files

Input Parameters:•Vehicle density

• Vehicle throughput• Road Information

Shadowing

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Outline of Contents Introduction Vehicle Traffic Simulator

• Vehicle Characteristic Input• Scenario Input• Intersection Collision Simulator

1. Vehicle Management2. Traffic-Light Management

• Message Generator The Wireless Simulator Shadowing Effect Simulations Conclusions

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VTS Block Diagram

VehicleManagement

Road

Traffic LightManagement

Vehicle Characteristic

Input

Scenario Input

Intersection Collision Simulator

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Input Block

Vehicle Characteristic Input• Vehicle Classification• Vehicle Length, Width• Vehicle Speed• Vehicle Origin and Destination• Vehicle Flow Rate

Scenario Input• Collision Scenario• Traffic Light Availability

Intersection

Collision

Simulator

Vehicle Characteristic

Input

Scenario Input

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Simulation Setup Screen

Scenario Input

Traffic Flow Characteristic Input

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Vehicle Management

Turning

NormalDriving

Vehicle Following

Vehicle Management

Driver information:

• Its own speed• Its own position data from DGPS• Turning direction• Other vehicles in Line-of-sight and the estimated distance and speed• Status of traffic lights

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Traffic Light Management

Scenario Input

Cycling Time

Direction

Status

Cycling Time( Two Phase):

G=25sec;Y=5sec

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Message Generator

Initialdataupdate

Transmissionintervals

Retransmissionattempts

Send messages when vehicle crosses initial data update border

Distance-based Transmissions

50 meters

Vehicle Characteristics

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Outline of Contents

Introduction Vehicle Traffic Simulator Shadowing Effect The Wireless Simulator Simulations Conclusions

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Shadowing

TX RX

Block

TX

RX

Block

Blocking area

h

d1 d2

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Shadowing Fresnel-Kirchoff diffraction parameter:

21

21

dd

)d2(dh

Using the Fresnel integral,

4.2),5/20log(0.22

4.21,)1.038.0(1184.020log(0.4

10),20log(0.5e

01),0.6220log(0.5

1,0

ψ(dBm)2

0.95

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Shadowing (Adjacency Matrix)

ε = 0 ε12 ε13 … …

ε21 0 … … …

ε31 … 0 … …

… … … … …

… … … … 0Note:• ε ij diffraction gain (in dB) for receiver j from transmitter i. •This is a symmetric matrix.•Both negative and positive gains are possible.

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Outline of Contents

Introduction Vehicle Traffic Simulator Shadowing Effect The Wireless Simulator

• MAC Layer• Physical Layer

Simulations Conclusions

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WS Process Structure

Main process: initialization, termination, VTS interface, etc.

Each process (except Main) implements MAC and PHY layers

All processes run in parallel in the simulated time

MainProcess

Process 1

Process 2

Process 3

Process n

n: no of vehicles

MACPHY

MACPHY

MACPHY

MACPHY

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MAC Layers 802.11 CSMA/CA

802.11a, 802.11b, and 802.11a R/A are implemented

RTS, CTS, and ACK packets are not implemented because

Broadcast Application => More than one destination

Short Data Packets

Nodes wait DIFS amount of time before sending their packets

If nodes sense the channel busy, they wait a random amount of time

DOLPHIN Non-persistent CSMA

5 retransmissions

Vehicles transmit one packet in each slot

slot length = 20 msec

5 retransmissions

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PHY Layer

Path loss, shadowing, and fading: Modeled

Carrier sensing and capture: Modeled

Noise: Cumulative Signal reception: SNR threshold based

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Signal PowerA packet will be received when the received signal power is larger than the threshold.The received signal power is computed as:

ψ(dBm)PL(dBm)(dBm)P(dBm)P tr

er transmittat thepower signal :(dBm)t

P

losspath :PL(dBm)

receiver at thepower signal :(dBm)r

P

shadowing :ψ(dBm)

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Fading Gilbert-Elliot model:

Good Bad

Pgb

Pbg

Pge: bit error probability in Good state

Pbe: bit error probability in Bad state

1-Pgb 1-Pbg

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Outline of Contents

Introduction Vehicle Traffic Simulator Shadowing Effect The Wireless Simulator Simulations Conclusions

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Simulation time

Wireless repeater

Building location

Truck

Bus

Motorcycle

Car

Intersection Type •Traffic signal

• North – South•Stop sign

Last message

Critical messages

Last collision

Transmitter

Receiver

ReceiverCollision warning

Motorcycle

Simulation Results

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Simulation Results

Performance metric for Wireless Communication

packetsdtransmitteofnumberTotal

packetsdtransmittelySuccessfulRateSuccessPacket

____

____

For a packet to be treated as successful, it should be received by ALL receivers in the region. Even if one vehicle can not hear the transmission, this packet is treated as unsuccessful.

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Simulation Results

Dolphin at 0.5 Mbps

10.9900.997Right angle

10.9930.996Left turn

light

10.9920.996Right turn

10.9830.995Left turn

MaximumMinimumMeanScenario

Packet Success Rate

10.9900.997Right angle

10.9930.996Left turn

light

10.9920.996Right turn

10.9830.995Left turn

MaximumMinimumMeanScenario

Packet Success Rate

802.11 a R/A, left turn(Similar Results for other Scenarios)

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Outline of Contents

Introduction Vehicle Traffic Simulator Shadowing Effect The Wireless Simulator Simulations Conclusions

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Conclusions Successfully incorporated two time-scales (C++)

• VTS: millisecond• WS: microsecond

Simulator• Simulate different intersection collision scenarios• Simulate various road and traffic conditions

1. Traffic flow etc2. Speed limit etc.

• Evaluate inter-vehicle communication Warning System can be rely on inter-vehicle

communication• High packet success rate (DOLPHIN)• Only short packet is needed for transmission

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Conclusions

Distance-based packet transmission• Improve medium utilization• Reduce unnecessary packets• Lower packet collision probability

Most packet losses due to physical layer To reduce physical layer errors

• Lower data rates can be used Number of Retransmissions have positive

impact on packet successful rate

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Recent Development

A Simulation Study of An Intersection Collision Warning System (ITST 2004)

• Wireless Communication (MAC, PHY) Current Status:

• Drivers’ Model, Three-level Warning System• Repeater, Buildings, Transmission Intervals

Demo for 11th World Congress on ITS (2004)• Vehicle and Traffic Simulator and Intersection

Collision Warning System• Performance of Wireless Intersection Collision

Warning System