The document discusses a proposed technique for sharing traffic jam information through inter-vehicle communication, utilizing message ferrying to address limitations in previous methods. It identifies issues with low car density leading to lost information and suggests using buses as ferries to retain and propagate traffic information. Experimental results indicate that this method improves the efficiency of information sharing compared to earlier approaches.

1. 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

2. 05/09/2006 FMUIT'06 2
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

3. 05/09/2006 FMUIT'06 3
Outline
⇒Background
- Our previous work
- Problem of our previous work
 Proposed method
 Experimental Result
 Conclusion and Future work

4. 05/09/2006 FMUIT'06 4
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 history
in addition to VICS
 There is a room for improvement in the service range,
operational cost, time lag of the information, etc

5. 05/09/2006 FMUIT'06 5
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

6. 05/09/2006 FMUIT'06 6
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
A
H
I
B
D
C
F
E

7. 05/09/2006 FMUIT'06 7
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
G
E
A
H
I
B
α
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.

8. 05/09/2006 FMUIT'06 8
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

9. 05/09/2006 FMUIT'06 9
Statistics information
area ID （incoming link，outgoing link）
A5 （α，β）
Area passing time
30 sec
60 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

10. 05/09/2006 FMUIT'06 10
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

11. 05/09/2006 FMUIT'06 11
 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

12. 05/09/2006 FMUIT'06 12
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

13. 05/09/2006 FMUIT'06 13
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

14. 05/09/2006 FMUIT'06 14
Outline
 Background
⇒Proposed method
- Introduction of message ferrying
- Improvement idea of problem
 Experimental result
 Conclusion and future work

15. 05/09/2006 FMUIT'06 15
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

16. 05/09/2006 FMUIT'06 16
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
Ferry
Normal node
Known route
Receive

17. 05/09/2006 FMUIT'06 17
Known route
Ferry
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

18. 05/09/2006 FMUIT'06 18
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

19. 05/09/2006 FMUIT'06 19
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

20. 05/09/2006 FMUIT'06 20
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

21. 05/09/2006 FMUIT'06 21
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

22. 05/09/2006 FMUIT'06 22
Outline
 Background
 Proposed method
⇒Performance evaluation
 Conclusion and future work

23. 05/09/2006 FMUIT'06 23
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

24. 05/09/2006 FMUIT'06 24
Experimental environment
Size of each area 300m×300m
Radio range 100m
Size of communication area 200m
Legal speed limit of each link 16.6m/s (60km/h)
Maximum amount of broadcast packet 1500byte
Interval of broadcast 5 seconds
Simulation time 60 minutes
Bus route 2 routes
Run interval of the bus 5 minutes, 7 minutes
The car density is somewhat low by regulating the
number of cars in the simulation

25. 05/09/2006 FMUIT'06 25
Simulator ： NETSTREAM
Field size ： 1.2km×1.2km
Node ： 21
Link ： 78

26. 05/09/2006 FMUIT'06 26
The route a of the bus
The route b of the bus
B
C
D
E
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

27. 05/09/2006 FMUIT'06 27
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 buses
with buses
10 20 30 40 50 60 (min)
information propagation ratio = cars retaining information / all cars passing the linkpair

28. 05/09/2006 FMUIT'06 28
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 buses
with buses
10 20 30 40 50 60 (min)

29. 05/09/2006 FMUIT'06 29
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 buses
with buses
10 20 30 40 50 60 (min)

30. 05/09/2006 FMUIT'06 30
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

31. 05/09/2006 FMUIT'06 31
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 ]