05/09/2006 FMUIT'06 1

A Technique for Information Sharing using Inter-Vehicle Communication with Message Ferrying

Takashi Shinkawa, Takashi Terauchi, Tomoya Kitani, Naoki Shibata†, Keiichi Yasumoto,

Minoru Ito, and Teruo Higashino† †

Nara Institute of Science and Technology† Shiga University

† †Osaka University

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Overview of our proposal Problem of a technique for traffic jam information sharing

using inter-vehicle communication （ our previous work ）

- It is a technique to propagate the message through the node (ferry) that regularly moves on the known route

• When car density of an area becomes 　 low temporarily, collected information is lost.• When there is no car in a region, traffic jam

information must be collected from scratch.

• Message Ferrying

Introduction of message ferrying

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Outline

⇒Background- Our previous work- Problem of our previous work

Proposed method Experimental Result Conclusion and Future work

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Background

The traffic jam in urban areas is becoming a big problem in many countries

• As services to provision traffic information to avoid traffic jam

　　 VICS (Vehicle Information and Communication System)

It provides traffic information collected in management center

　　　 CYBER NAVI (Pioneer)It uses statistical traffic information generated from historyin addition to VICS

There is a room for improvement in the service range, operational cost, time lag of the information, etc

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Our previous work

Purpose- To realize a mechanism for cars to autonomously

collect and exchange traffic information Approach

- To reduce the initial infrastructure cost and the operational cost of the system

- To cover a large service area We adopt inter-vehicle communication We do not use infrastructure or a management

center

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Collecting traffic information Divide the road map into rectangles called areas Let cars measure the time (called area passing

time) to pass each area Let cars exchange area passing time with

neighboring cars and make statistics of area passing time (called traffic information)

A6

A9

A2

A5

A1 A3

A4

A7 A8

G

AH

IB

D

C

FE

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Area passing time

（ incoming link ， outgoing link ）　 area passing time（ α ， β ）　　 150 sec（ α ， γ ） 220 sec．．．（ ε ， α ） 40 sec．．．（ ε ， δ ） 30 sec

Area Passing Time＝ (area ID ， incoming link ID ， outgoing link ID ， area passing time ，car ID)

linkpair

GE

AH

IBα

βδ

ε

D

C

F

Area border γ

Area passing time is collected for each pair of incoming link and outgoing link of area (we call the pair of links linkpair)

Each car passes an area through multiple intersections.

⇒By averaging area passing time for each linkpair, we can make traffic jam information taking into account the influence of traffic lights/turns.

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Propagation of area passing time Area passing time is broadcasted when a car passes the

area border When a car receives area passing time, it accumulates

the time for the same linkpair

Area border

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Statistics information

area ID 　（ incoming link ， outgoing link ）A5 　　　　　 （ α ， β ）Area passing time 　

　 30 sec60 sec．．．40 sec

average area passing time 　　 41 sec

The available bandwidth is limited⇒

The number of received data items of area passing times increases- Cars may not be able to exchange all the data items with other cars

When the number of data items exceeds C, statistics information is generated by averaging over C area passing times

C : a predefined threshold

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Propagation of statistics information

Each car regularly broadcasts both area passing time and statistics information which it holds

Area passing time and statistics information is updated and kept by cars on each area

Area border

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When each car crosses the area border, the data outside its responsible areas are discarded

Neighboring areas

The area where the car is running (A1)

Traffic information of A1 is retained

Traffic information of A1 is retained

How to retain and discard information

⇒ Each car retains and broadcasts the data generated for a set of areas called responsible areas

The available network bandwidth is limited

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Traffic information of A1 is discarded

Neighboring areas

How to retain and discard information

The area where the car is running (A1)

When each car crosses the area border, the data outside its responsible areas are discarded

⇒ Each car retains and broadcasts the data generated for a set of areas called responsible areas

The available network bandwidth is limited

Traffic information of A1 is retained

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Problem of previous work

Problem1 ： When car density of an area becomes low temporarily - The information may be lost

Problem2 ： When there is no other car with the latest traffic information on the area- The traffic information must be collected from

the scratch.

Introduction of message ferrying

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Outline

Background

⇒Proposed method- Introduction of message ferrying- Improvement idea of problem

Experimental result Conclusion and future work

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Message ferrying[1]

It is a technique to propagate the message through special nodes (called ferries) that regularly move along the known routes- The purpose of message ferrying is to achieve

efficient data propagation in disconnected ad hoc networks

[1]Wenrui Zhao and Mostafa H. Ammar, “Message Ferrying: Proactive Routing in Highly-partitioned Wireless Ad Hoc Networks”, FTDCS 2003

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Send

Overview of message ferrying

n1

n2

Ferry : Ferries regularly move along the known routes- Ferries can collect messages from normal nodes and send the

collected messages destination Normal node : Normal nodes freely move

- Normal nodes send messages to ferries or receive messages from ferries

Normal nodes can use ferries to efficiently send messages to other normal nodes outside of its radio range

FerryNormal node

Known route

Receive

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Known routeFerry

Basic ideas of our proposal Our previous work

- Traffic information is exchanged only among normal cars

Our proposed Method- Buses (that regularly move along the known routes)

are used as ferries - Traffic information is exchanged among normal cars

through buses

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How to cope with Problem1

Traffic information of A1 is lost

Problem1- When car density of an area becomes low temporarily,

the collected traffic information may be lost completely

No information of A1

Traffic information of A1 is retained

Area(A1)

When there are less than two cars in each radio range

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The revival of traffic information becomes possible

Our solution for Problem1

Area(A1)

Keep holding information of A1

Let buses hold traffic information of each area even when they are out of the responsible areas- Buses can have large capacity hard disk drives

When traffic information on an area is completely lost　⇒ the bus can regularly revive the traffic information which the

bus obtained when passing the area last time

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How to cope with Problem2

Problem2- When there is no car with the latest traffic

information on the area Cars cannot obtain traffic information of the area at all

Necessary information is not provided

No latest traffic information

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Our solution for Problem2

Buses use area passing time which they measured by themselves and traffic information collected in the past

Propagate traffic information that buses measured

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Outline

Background Proposed method

⇒Performance evaluation Conclusion and future work

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Overview of Experiment

To what extent, the proposed method (with buses) can improve our previous method (w/o buses) with respect to information propagation ratio.

We have implemented our method and conducted simulation with traffic flow simulator NETSTREAM developed by Toyota Central R&D Labs

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Experimental environment

Size of each area 300m×300mRadio range 100mSize of communication area 200mLegal speed limit of each link 16.6m/s (60km/h)Maximum amount of broadcast packet 1500byteInterval of broadcast 5 secondsSimulation time 60 minutesBus route 2 routesRun interval of the bus 5 minutes, 7 minutes

The car density is somewhat low by regulating the number of cars in the simulation

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Simulator ： NETSTREAMField size ： 1.2km×1.2kmNode ： 21Link ： 78

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The route a of the bus

The route b of the bus

B

C

DE

F

G

H

I

J

K

L

M

N

O

P

R

S

Q

A A11

A13

A4

A12

A9 A10A8

A6

A3

A7A5

A2A1

A14

As information propagation ratio, we measured the number of cars retaining traffic information on the following linkpairs of areas A5, A13 and A6

Experiment

Linkpair on bus route a⇒C-D-E in area A5

Linkpair on bus route b ⇒A-G-J in area A13

Linkpair which is not on bus route

⇒M-N-R in area A6

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Linkpair C-D-E on bus route a At time 40 and 50, more cars retain traffic information At time 20 and 30, there is no improvement by buses

- There were no cars in the radio ranges of the bus during this time interval- There is a little information which normal cars measured

0

0.2

0.4

0.6

0.8

1

1 2 3 4 5 6

without buseswith buses

10 20 30 40 50 60 (min)

information propagation ratio = cars retaining information / all cars passing the linkpair

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Linkpair A-G-J on bus route b Much more cars retaining traffic information

- There is much more information which normal cars measured Linkpair A-G-J than Linkpair C-D-E- At time 60, there is no improvement by buses

There were no cars in the radio ranges of the bus during this time interval There is little information which normal cars measured

0

0.2

0.4

0.6

0.8

1

1 2 3 4 5 6

without buseswith buses

10 20 30 40 50 60 (min)

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Linkpair M-N-R which is not on bus route

There is almost no effect by buses- The cars following this route can hardly communicate

with buses

0

0.2

0.4

0.6

0.8

1

1 2 3 4 5 6

wothout buseswith buses

10 20 30 40 50 60 (min)

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Conclusion and future work

Conclusion- We proposed an extension of our previous work to

improve efficiency of traffic information sharing using inter-vehicle communication

- Our method based on the message ferrying technique improve the efficiency to a certain extent

Future work- Enhance our method to utilize ferries more aggressively

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Shinkawa, T., Terauchi, T., Kitani, T., Shibata, N., Yasumoto, K., Ito, M. and Higashino, T.: A Technique for Information Sharing using Inter-Vehicle Communication with Message Ferrying, International Workshop on Future Mobile and Ubiquitous Information Technologies (FMUIT'06).DOI:10.1109/MDM.2006.23 [ PDF ]

Kitani, T., Shinkawa, T., Shibata, N., Yasumoto, K., Ito, M., and Higashino, T.: Efficient VANET-based Traffic Information Sharing using Buses on Regular Routes, Proc. of 2008 IEEE 67th Vehicular Technology Conference (VTC2008-Spring), pp. 3031-3036.DOI:10.1109/VETECS.2008.326 [PDF ]