Sensor Network for Traffic Accident Detection and Notification

8/3/2019 Sensor Network for Traffic Accident Detection and Notification

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Sensor Network for Traffic AccidentDetection and Notification

Gezhi Zhong

Vineet Tripathi

Bidisa Rai


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Motivation

Statistical reports show Accidents ahead account for alarge percentage of fatal accidents on highways.

Such accidents occur because vehicles behind have nomeans of knowing about the accidents/congestion thathave occurred ahead in the road.

We are designing a sensor network that will informincoming vehicles of these accidents/congestions well inadvance so that the drivers of the vehicles may takeappropriate actions.


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Motivation contd. (Previous Work)

Present traffic monitoring systems use expensive devices such as videocameras, magnetic loop detectors that are expensive, difficult to deployand not very scalable.

- Our solution will use inexpensive sensor motes that are small,cheap, easy to deploy and scalable.

Previous work using infrastructure sensor networks in the area havefocused mainly on the capture of periodic data to generate statisticalreports and analyses.

- Our solution will save lives in real time!!

The use of vehicular networks for traffic monitoring requires advancedsensors in the vehicles themselves. Many individuals are not willing tobear the extra cost of fitting these special devices to their vehicles.

- Our solution will require minimal (if at all) additions to the vehicle.


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Motivation contd. (Previous Work)

Vehicular network solutions differ greatly in their

design, protocol and implementation. As such avehicle that uses one vehicular solution will notbe able to communicate with other vehiclesalong the road unless they all implement the

same solution. This can be a very grave problem.- Our solution is generic and does not face

the above problem.


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Motivation contd. (Challenges)

Sensors are very resource-constrained: power, memory, computation.- Our solution minimizes resource consumption.

Vehicles on highways usually travel at high speeds between 65 to 70 mph. Theyneed to be informed of the accident/congestion up ahead as quickly as possiblebefore it is too late.

- Our solution is designed to sense accidents as soon as they occur andcommunicate this information to the rest of the relevant network very quickly.

Users are often unwilling to learn (or just plain lazy) how to use new systems.- Our solution requires minimal interaction with the user and will be

perceived as very uncomplicated by the user


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Motivation contd. (Unique Solution)

Our solution introduces two very unique ideas:

1. It integrates an ad-hoc sensor network with a vehicular network tocreate an effective, energy-efficient traffic accident detection andnotification system without all of the problems mentioned above. As farwe know this has never been done before.

2. We also introduce the new concept of Virtual Group and WatchdogGroup of sensors that will track the motion of a car and will greatlyincrease the reliability of the network while decreasing the energy-consumption of the sensors.


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Intuition behind solution

Sensors placed along-side highway roads will

detect a traffic accident and will communicate thismessage to sensors further down the road, whichwill in turn notify incoming vehicles of the accidentup-ahead.


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Detailed Design

Assumptions:

1. Highways

2. Unidirectional traffic

3. Vehicles are equipped with bi-directional radios thatcan do two things:

i. Transmit alarm message when accident occurs.ii. Receive notification of accident broadcast by

sensor.


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Detailed Design: Two Concepts

1. Watchdog Groups: Sensors are divided into groups of n

each, say three sensors S1, S2 and S3. When there is notraffic on the highway, in each group one sensor (S1) willbe on for a certain fixed period of time while the other two(S2 and S3) remain off. After this fixed period S2 will wakeup and S1 and S3 will sleep and so on. Synchronized timerswill be used to control the sleep/wake cycle of sensors ineach group.


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Watchdog Group

n = 3

Watchdoggroup 1

Watchdoggroup 2

awake asleep awakeasleep asleep asleepawakeasleep awakeasleepawake awake


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Watchdog Group contd.

REASONS:

a. To average power consumption (batteries will lastlonger on average).

c. To increase reliability: do not depend on only onesensor (as was our previous case with only a specialsensor). If a sensor fails there will be other workingsensors in close vicinity. Also backup case.


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Detailed Design contd.

2. Virtual Groups: Sensors are again divided intogroups of n each. But in this case, the group is notfixed but rather moves along the highwayfollowing the motion of the vehicle being sensed.


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Virtual Group

n = 3

Virtual Group


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Virtual Group contd.

REASON: Save power consumption - Virtual

Grouptracks

motion of vehicle, thereforenot all sensors along road will have to wakeup simultaneously.


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Detailed Design contd.

Normal Operation:

- Car approaches junction.- Special sensor (always on) at junction detects car,

alerts closest neighboring sensor, S1.

- S1 will alert S2, S2 will alert S3. Now S1, S2 and S3will be awake (Virtual Group 1).


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Detailed Design (Normal Operation

contd.)

As car moves out of sensing range of S1 and into sensing range ofS2, S1 goes to sleep while S2 notifies S3 to wake up S4. Sonow S1 will be asleep while S2, S3 and S4 will be awake(Virtual Group 2). And so on.

- As we can see the Virtual sensor Groups will track the motionof the car and will inform the sensors ahead to wake up and beready before the car reaches them.

- This way we conserve power as not all of the sensors will have toturn on simultaneously and wait for the car to reach them.


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Normal Operation

Special SensorVirtual group


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Detailed Design contd.: Accident Occurs:

- Detection of accident: Air-bag trigger in cars that detects the accident willtrigger the car radio to broadcast accident alarm message.

- We use air-bag triggers because:i. It provides greater accuracy in detecting actual accidents and not

just false alarms.ii. It simplifies the work of the sensors (lesser sensing, lesser

computation).ii. Air-bag triggers are already present in vehicles; does not require

additional add-ons.

- The sensor closest to the car that receives the alarm message will wakeup the sensors behind it (if they are already not awake).

- The sensor will then broadcast an Event Notification message with the

TTL field set to a fixed value so that the message does not propagatefurther than is required.


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Case Accident


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Special Cases

1. Very long stretch of highway with no exits:

- Accident occurs.

- Vehicle must be informed before it leaves all exits behind.

- To relay message from one sensor to next until it reachescar will be too slow.

- Use access point to convey message directly to sensorclosest to next-to-last exit (as far in advance as feasible).

- Sensor will inform vehicle before it reaches last exit andlooses all chances to re-route.


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Very long stretch of road w/no exit

Long stretch of road with no exit


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Special Cases contd.

2. Backup Case - In case of sensor failure:

- Normally sensors communicate with each otheron a per-hop basis.

- If a sensor goes down, its immediatelyneighboring sensors on both sides will increase

their sensing and communication range.

- The increase in power consumption is a smallprice to pay for greater reliability.


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Backup Casen = 3


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Issues

Concept of Watchdog Group does introduce a certainamount of redundancy. But:

Provides Reliability: Even if Special Sensor (SS) goes downthe entire link will not go out of service: sensors in watchdoggroup will continue to wake on/off periodically and can detectany accident if it occurs.

Greater network Sensitivity: If all sensors along link areasleep until woken up by SS, an event missed by SS will bemissed by all sensors. Watchdog group can protect againstsuch a mishap.


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Further Work

Calculate feasible duty cycle.

Calculate time synchronization. Messages between sensors for

synchronization.

Resolve MAC layer issues.


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Q&A


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Thank you

Documents

Sensor Network for Traffic Accident Detection and Notification