Safety message of communication between vehicles and how to reduce delay times.

1. Adaptive dissemination of safety
data among vehicles
Chisalita, I. 、Shahmehri, N.
Personal, Indoor and Mobile Radio Communications, 2006 IEEE 17th International Symposium on
11-14 Sept. 2006
KUAN-YU, CHEN
stu9458@gmail.com

2. Outline
• Introduction
– Challenge
• Related work
• Protocol overview
• Basic safety messages dissemination
• Evaluation
• Concluding remarks
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3. Introduction(1/3)
• An adaptive approach to dissemination of
safety data among vehicles.
• Support the driver in dangerous traffic
situations.
• Avoid the occurrence of such
situations(collision warning and collision
avoidance).
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4. Introduction(2/3)
• Challenge
– Specific properties of the traffic environment.
– The strict requirements of safety applications.
• Vehicles that are not in each other
communication range may need to exchange
data.
– Forwarding information.
• Vehicles that send their data may not be aware
of the receivers that will make use of it
– Filtering of information.
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5. Introducton(3/3)
• The protocol makes use of contextual information
for sustaining inter-vehicle communication
adaptable to the current traffic situation.
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6. Related work(1/4)
• Three main area about communication
– Group membership in vehicular networks
– Medium access control(MAC) schemes
– Traffic data dissemination.
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7. Related work(2/4)
• Various routing protocols have been
proposed for data dissemination in ad-hoc
networks
• Protocols are less applicable to safety
vehicular communication.
• Require the establishment of routes to a
given destinations.
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8. Related work(3/4)
• Protocols followed a reactive approach,
where notifications are sent when vehicles
detect hazards in traffic.
• Takes a proactive approach where vehicles
are regularly informed about the traffic
situation.
• Used for predicting the occurrence of
dangerous situations.
• e.g. Vehicle suddenly breaks down.
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9. Related work(4/4)
• DSRC (Dedicated Short Range Communication)
– Specifies the MAC layer, the link layer and the radio
layer for vehicular communication systems.
– Vehicle-to-road 、Vehicle-to-vehicle
– Augment DSRC functionality when providing safety
services.
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10. Outline
• Introduction
– Challenge
• Related work
• Protocol overview
• Basic safety messages dissemination
• Evaluation
• Concluding remarks
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11. Protocol overview(1/7)
Problem
• A large number of communicating hosts may
tend to exchange data.
• Produce a heavy load on the communication
channel.
• Difficulties in accessing the transmission medium
and packet collisions.
• Apply two techniques for controlling the
dissemination of safety information.
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12. First(1/2)
• Define an organization of the vehicles in virtual
clusters
– limited in space and in composition.
• Research in traffic safety has indicated that a
vehicle can not extensively benefit by having data
about a large number of vehicles.
• imposed a 300 meters as the cluster size.
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13. First(2/2)
• Impact of the cluster size on the communication
performance.
– maximum number of members is 20.
• The data is importance.(remain)
– The sender be registered in cluster.
• If this does not happen, the data describing the
respective vehicle is removed.
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14. Second
• An anonymous context-based broadcast.
• Receivers need to determine the data if they are
the intended destination of this data.
• Context-based filtering.
– Based on a set of rules defined using research results
in crash analyses.
– Guidelines for developing active safety systems
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15. Protocol overview(2/7)
• Basic Safety Messages (BSM)
Host identity Message sequence number
Message type Vehicle velocity
Vehicle positions(Two consecutive
Vehicle heading
indications)
Vehicle status and size Road identity*
Road type* Road slipperiness*
Speed limit* Number of members
Cluster members identities Other information
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16. Protocol overview(3/7)
• send error
– BSMs are issued at regular time intervals.
– BSM can not be transmitted and a new one is
generated, the older BSM is removed and the new one
is inserted into the buffer.
• Forwarded
– Same cluster may not directly receive data about each
other.
– Packet collision, shadowing or medium access
– Filtering
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17. Protocol overview(4/7)
• VA runs a matching algorithm to determine if
these hosts may have interest in VB’s data.
– The process ends if such a host if found.
VB
VA
Host
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18. Protocol overview(5/7)
• Produces a peak-load on the channel and can
reduce communication performance
• Before forwarding a BSM, a host waits an amount
of time randomly selected between 0 and the
transmission rate of BSMs.
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19. Protocol overview(6/7)
• Filtering and forwarding.
– Using a context-based technique.
• Traffic Postulates
– P1: The vehicles in close proximity have important
data. Their number is limited
– P2: Vehicles in front and behind traveling on the same
road and in the same direction have data of interest.
– P3: Vehicles coming from an opposite direction can
constitute a danger on undivided roads.
– P4: Vehicles can collide if they arrive at an intersection
at the same time.
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20. Protocol overview(7/7)
• Inclusion rule
– (I1) The Euclidean distance between sender and
receiver is less than SAT ± ΔD. (ΔD is a hysterezis
threshold)
• Regular rules
– (R1)The sender and the receiver are traveling on the
same road AND have similar heading.
– (R2) The sender and the receiver are on the same
undivided road AND have different headings AND the
sender is ahead of the receiver.
– (R3) The sender and the receiver are traveling on
different roads AND a route contention is detected.
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21. Outline
• Introduction
– Challenge
• Related work
• Protocol overview
• Basic safety messages dissemination
• Evaluation
• Concluding remarks
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22. Basic safety messages
dissemination(1/3)
• Providing vehicles with up-to-date traffic
information in a regular manner can be
performed using two approaches.
• First
– The constant rate approach, where BSMs are sent
at fixed regular intervals.
– The analysis indicated a rate of 10 BSMs/second
as appropriate
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23. Basic safety messages
dissemination(2/3)
• Second
– Adaptive approach
– General enough as to accommodate a large
diversity of situations.
– Velocities of the vehicles and the traffic density.
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24. Basic safety messages
dissemination(3/3)
• vehicles velocity
– Residential areas, 30 to 50 km/h
– On country roads, 70 to 100 km/h
– Highway, 100 to 150 km/h
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25. Evaluation(1/10)
• GloMoSim v2.3
• Evaluation
– BSMs delivery delay
– packet collisions
– send errors
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26. Evaluation(2/9)
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27. Evaluation(3/10)
• BSMs delivery delay
– The efficiency of information filtering was
measured by the information filtering rate.
– the ratio between accepted BSMs and received
BSMs.
• packet collisions
– The collisions were normalized with the number
of BSMs correctly received.
• send errors
– Number of BSMs issued by a host.
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28. Evaluation(4/10)
• System bandwidth,10 - 2000 kbps.
• Communication service area or cluster size, 50
- 600 m.
• Network load, 6 – 20 vehicles/km/lane.
• Vehicles mobility, 10 - 40 m/s.
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29. Evaluation(5/10)
Propagation model Two-ray
Channel AWGN and Rician fading
Radio model Based on IEEE 802.11
Frequency 2.4GHz and 5.9 GHz
MAC scheme Non-persistent CSMA
Transmission Power 12 dBm (i.e. ～317m range)
BSM size 112 bytes
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30. Evaluation(6/10)
• BSMs delay as a function of load density
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31. Evaluation(7/10)
• Packet collisions as a function of mobility
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32. Evaluation(8/10)
• Information filtering rate under mobility
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33. Evaluation(9/10)
• Send errors as a function of load density
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34. Evaluation(10/10)
• The extended version of the protocol
considerably outperformed the basic version
in most of the tests.
• Areas of improvements
– Efficient information filtering.
– Forwarding techniques.
– Better MAC schemes.
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35. Concluding remarks(1/2)
• Propose a protocol that makes use of
contextual information for controlling the
vehicular communication.
• Future work will focus on improvements of
the protocol.
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36. Concluding remarks(2/2)
• The development of a prototype system using
on-market devices (e.g. 802.11 WLAN cards or
DSRC transceivers when these will be available)
is intended.
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