OKI Project - Phase 2

Simulator Development Overview

Department of Electrical and Computer Engineering

The Ohio State University

August 2004

August 2004 2

Topics

• Overview• Wireless simulator• Physical layer modeling• Traffic and driver behavior simulator• Next steps• Demonstration

August 2004 3

Overview• Advance the simulators developed for OKI phase 1• Incorporate new features/considerations

– Wireless simulator [Alberto Avila]• Multiple transmissions, retransmission interval, repeater• Real-time interface with vehicle traffic simulator

– Physical model [Heelim Teh]• Incorporate modulation, reflection, blockages, and shadowing

– Intelligent transportation system (ITS) [Yiting Liu]• Real-time interface vehicle traffic simulator with wireless simulator• Collision warning system implementation• Driver behavior model implementation

August 2004 4

Offline Wireless SimulatorObjective:

• Accurate representation of broadcast medium performance • Based on protocol and physical specifications• Incorporate physical layer to determine path loss and frame error rate• Flexibility on scenario parameters:

• MAC protocol [Dolphin; 802.11 a;b;a R/A]• Building location• Repeater presence• Initial data transmission distance• Transmission interval• Maximum number of retransmissions• Retransmission interval

August 2004 5

Offline Wireless Simulator

• Dolphin protocol (CSMA) [Phase 1]

• Multiple transmissions within area

• Retransmissions within interval [5]

• Physical specification [Phase 1]

• Transmit power [10 dBm]

• Receiver sensitivity [-82 dB]

• Repeater

• Single retransmission

Initialdataupdate

Data update interval

Repeater[single retransmission]

Transmissionintervals

Retransmissionattempts

August 2004 6

Statistical information:- Packet collision probability- Vehicle density- Frame error rate - Latency

Statistical information:- Packet collision probability- Vehicle density- Frame error rate - Latency

Trace files:

- Vehicle information

- Vehicle position

- Vehicle velocity

OfflineWirelessSimulator

Vehicle Traffic Simulator

Input Parameters:

- Vehicle density

- Vehicle throughput

- Transmission interval

Physical layermodel

Statistical information:- Packet collision probability- Vehicle density- Frame error rate - Latency

Multiple scenarios with different input parameters

Offline Wireless Simulator

August 2004 7

Offline Wireless Simulator

Simulation data available:• Vehicle packet collision rate• Base station packet collision rate• Vehicle density• Out of range average• Frame error rate• Coverage rate• Delivery rate

August 2004 8

Online Wireless Simulator

Objective:• Provide packet transmission success determination• Low latency• Incorporate physical layer to determine path loss and frame error rate

Why?• Offline simulator is computation, memory intensive• CSIM is event driven, virtual time scale

August 2004 9

Online Wireless Simulator

Functionality:• Estimate collision rate probability for specific scenario parameters and vehicle conditions • Low latency response (< 200 msec)• Encapsulate data from offline wireless simulator• Handle a variety of simulation scenarios:

• Intersection type (signal/no signal)• Repeater• Building• Transmission interval; retransmissions

August 2004 10

Vehicle Traffic

Simulator

Packet Generator

Collision Warning System

• Allows real-time feedback to the vehicle traffic simulator. This, in turn, enables driver behavior to be affected by information received from other vehicles through the online wireless simulator.

Communication protocolProtocol parametersScenario parameters

Vehicle densityVehicle positionsVehicle sources

Receiver vehicleSource vehicleReception time

Online Wireless Simulator

Driver Behavior

Online Wireless Simulator

Offlinesimulator

data

- Density- Distance- Interval- ....

Physical layermodel

August 2004 11

Packet Collision Rate vs Vehicle Density 100 Vehicles

0.0000

0.0050

0.0100

0.0150

0.0200

0.0250

0.0300

0.0350

0.00 10.00 20.00 30.00 40.00 50.00 60.00Vehicle Density

Pa

ck

et

Co

llis

ion

Ra

te

Wireless Simulation ResultsPacket Collision Rate vs Throughput - Mean

No Signal - No Buildings - No Repeater 100 m - 100 Vehicles

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0 20 40 60 80 100Packet Transmission Interval

Pa

ck

et

Co

llis

ion

Ra

te

Vehicle rate - High throughput

Vehicle rate - Medium throughput

Vehicle rate - Low throughput

Packet Collision Rate vs Throughput - MeanSignal - Buildings - Repeater

100 m - 100 Vehicles

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

0.016

0.018

0 20 40 60 80 100Packet Transmission Interval

Pa

ck

et C

olli

sio

n R

ate

Vehicle rate - High throughput

Vehicle rate - Medium throughput

Vehicle rate - Low throughput

No signal,low throughput

Signal,med/high throughput

August 2004 12

Physical Layer

OfflineWirelessSimulator

Physical layermodel

• Leveraged by both offline and online wireless simulators

Online Wireless Simulator

Offlinesimulator

data

- Density- Distance- Interval- ....

Physical layermodel

August 2004 13

Objective:• Provide a simple and accurate channel model for the Dedicated Short Range Communications (DSRC) in an urban environment• Determine path loss, frame error rate

Functionality:• Flexibility for different physical environments and conditions:

• Buildings• Repeater• Vehicle types

Physical Layer

August 2004 14

Scenario Setup

TX

RX1

Building Building

BuildingBuildingRX4

RX3

RX2

SidewalkSidewalk

Sidewalk Sidewalk

August 2004 15

•Line-of-sight communication:- TX↔RX2, TX↔RX3

•No-line-of-sight communication:•Shadowing caused by other vehicles on the street:

- TX↔RX4•Blockage caused by building at the corners:

- TX↔RX1

Possibilities

August 2004 16

• When the source and the destination vehicle have a clear, unobstructed communication.• For example, between TX and RX2, RX3.

I can see you, too!

I can see you!

Line-of-Sight

Line-of-sight Communication

August 2004 17

• When there is line-of-sight, the received power is mainly contributed by the direct path and the reflection.

Two-ray Model

Direct path rt

h0

Distance: r

Reflection path rrht hr

Virtual reflection surface

August 2004 18

22

4)(

r

jkr

t

jkr

r

eR

r

erLd

rt

• Path Loss[1]

rt: distance between TX ant. and RX ant. =rr: reflection path length from TX ant. to RX ant. = R: reflection coefficient.k: wave number.ht: TX antenna height.

hr: RX antenna height.

h0: virtual reflection surface height.

[1]: Y. Oda, K. Tsunekawa and H. Hata, “Advanced LOS path loss model in microcellular mobile communications”, IEEE Trans. Vehicular Technology, vol. 49, (6) pp.2121-2125, Nov. 2000

22 )( rt hhr

200

2 hhhhr rt

Two-ray Model

August 2004 19

Virtual Reflection Surface [h0]

• Due to different traffic densities and street characteristics, reflected ray does not necessarily come from the ground.

• Each h0 corresponds to a specific traffic density and street characteristic.

• To get h0:– Collect field test results.– Compute the free space propagation path loss.– Use the difference between the above two and the two-

ray path loss equation to computer h0.

August 2004 20

When there are large obstacles between the source and the destination vehicles, the line-of-sight communication is obstructed.

• Communications between TX and RX1, RX4.

???Where

are you? Obstacle

No-line-of-sight Communication

August 2004 21

TX

RX4

d

1

d2h

α

RX2

dtej

Ldtj

210

2

2

1log20)(

• For modeling shadowing effect. Ex., TX ↔ RX4

• Fresnel integral: [2]

where the Fresnel-Kirchoff parameter

ν =

21

21

21

21 22

dd

dd

dd

ddh

Knife Edge Model

[2] T. S. Rappaport, Wireless Communications. New Jersey: Prentice Hall, 2002

August 2004 22

Knife Edge Model

2

410

2

210

42log10

42log10

s

s

s

s

rr

xw

rr

xw

1 ≤ ν ≤ 2.4

0 ν ≤ -1

0.62-(0.520log10-1 ≤ ν ≤

0

.95(0.5exp(-020log10

0 ≤ ν ≤ 1

))0.1-(0.38-0.1184-(0.420log 210

.2250

(20log10ν > 2.4

Ld(ν) =

August 2004 23

•Finding a virtual source located in the line-of-sight with both the transmitter and receiver.

Virtual Source Model

TX

r

rs

wsVS

RX1

xBuilding Building

BuildingBuilding

August 2004 24

• Path loss (dB):

2

410

2

210

42log10

42log10

s

s

s

s

rr

xw

rr

xw

, r ≤ rb

, r > rb

rtb

hhr

4)(rLd , where

Virtual Source Model

August 2004 25

Vehicle Traffic

Simulator

Message Generator

Collision Warning System

Driver Behavior

ITS Components

•Vehicle traffic simulator (VTS):Simulates traffic network and intersection behavior

•Message generatorSends messages when vehicles cross specific borders

•Collision warning systemGenerates warning message based on received information

•Driver behavior moduleSimulates individual vehicle’s response to various warning messages

August 2004 26

Vehicle Traffic SimulatorTraffic Flow Characteristic

Input

Scenario Input

VehicleManagement

Road

Traffic LightManagement

August 2004 27

Simulation Setup Screen

Scenario Input

Traffic Flow Characteristic Input

August 2004 28

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

August 2004 29

Traffic Light Management

Scenario Input

Cycling Time

Direction

Status

Cycling Time( Two Phase):

G=25sec;Y=5sec

August 2004 30

Message Generator

Initialdataupdate

Data update interval

Predefined Transmission Set:

• Initial data update

• Data update interval

• Retransmission times

Send messages when vehicle crosses data update interval borders

RetransmissionsRetransmissions

August 2004 31

Collision Warning System

• Three level warning system: Warning level 1-- ELEVATED

Danger ahead; Need to decelerate

Warning level 2-- HIGHModerate danger ahead; Decelerate immediately

Warning level 3--SEVERECritical situation; Severe danger ahead

Stop immediately

Collision probability

August 2004 32

Collision Warning System• Time-to-collision (TTC):

– The time required for two vehicles to collide if they continue at their present speed and on the same path

– The lower the TTC, the higher the collision risk

• Time-to-avoidance (TTA):– The required stopping distance time

R

llRTTC

21

RR: relative distance : : relative velocityli : Vehicle i’s length along the route contention

g

vTTA

: Speed reduction parameter If 1, then full stop

μ: Friction coefficient

August 2004 33

Collision Warning System• Get communication data• Compute route contention• If no route contention

– No warning• Else

– Compute TTC and TTA – If TTC >= TTA+ driver’s response

time (1.93 s -2.53 s) • If deceleration>=TTA deceleration

– No warning• Else if deceleration < TTA

deceleration– Warning level 1

• Else if no acceleration – Warning level 2

• Else (acceleration) – Warning level 3

• Else – No warning

August 2004 34

Effects of Collision Warning SystemAnimation of Intersection

warning system

Intersection Collision Scenario

August 2004 35

Driver Response Module

• Aggressive driver: – Only response to warning level 3– Initial accelerator release only

• Normal driver: – Response to both warning level 3 and level 2– Braking to warning level 3– Decelerate slowly to warning level 2

• Conservative driver: – Response to all the warnings– Braking to warning level 3 and warning level 2– Decelerate quickly to warning level 1

August 2004 36

Next Steps• General

– Evaluate QoS for collision avoidance application• Wireless simulator

– Improve correlation of scenario and traffic conditions to collision rate probability

– Incorporate different types of traffic for multiple intersection applications

• Physical layer– Incorporate configurable modulation type– Handle various obstacle types

• Traffic simulator– Improve collision warning system– Provide a more detailed driver model