Sensor Network for Traffic Accident Detection and Notification

1. Sensor Network for Traffic Accident Detection and Notification Gezhi Zhong Vineet Tripathi Bidisa Rai

2. Motivation Statistical reports show �Accidents ahead� account for a large percentage of fatal accidents on highways. Such accidents occur because vehicles behind have no means of knowing about the accidents/congestion that have occurred ahead in the road. We are designing a sensor network that will inform incoming vehicles of these accidents/congestions well in advance so that the drivers of the vehicles may take appropriate actions.

3. Motivation contd. (Previous Work) Present traffic monitoring systems use expensive devices such as video cameras, magnetic loop detectors that are expensive, difficult to deploy and 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 have focused mainly on the capture of periodic data to generate statistical reports and analyses. - Our solution will save lives in real time!! The use of vehicular networks for traffic monitoring requires advanced sensors in the vehicles themselves. Many individuals are not willing to bear the extra cost of fitting these special devices to their vehicles. - Our solution will require minimal (if at all) additions to the vehicle.

4. Motivation contd. (Previous Work) Vehicular network solutions differ greatly in their design, protocol and implementation. As such a vehicle that uses one vehicular solution will not be able to communicate with other vehicles along 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.

5. 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. They need to be informed of the accident/congestion up ahead as quickly as possible before it is too late. - Our solution is designed to sense accidents as soon as they occur and communicate 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

6. Motivation contd. (Unique Solution) Our solution introduces two very unique ideas: 1. It integrates an ad-hoc sensor network with a vehicular network to create an effective, energy-efficient traffic accident detection and notification system without all of the problems mentioned above. As far we know this has never been done before. 2. We also introduce the new concept of Virtual Group and Watchdog Group of sensors that will track the motion of a car and will greatly increase the reliability of the network while decreasing the energy-consumption of the sensors.

7. Intuition behind solution Sensors placed along-side highway roads will detect a traffic accident and will communicate this message to sensors further down the road, which will in turn notify incoming vehicles of the accident up-ahead.

8. Detailed Design Assumptions: 1. Highways 2. Unidirectional traffic 3. Vehicles are equipped with bi-directional radios that can do two things: i. Transmit alarm message when accident occurs. ii. Receive notification of accident broadcast by sensor.

9. 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 no traffic on the highway, in each group one sensor (S1) will be on for a certain fixed period of time while the other two (S2 and S3) remain off. After this fixed period S2 will wake up and S1 and S3 will sleep and so on. Synchronized timers will be used to control the sleep/wake cycle of sensors in each group.

10. Watchdog Group

11. Watchdog Group contd. REASONS: To average power consumption (batteries will last longer on average). c. To increase reliability: do not depend on only one sensor (as was our previous case with only a special sensor). If a sensor fails there will be other working sensors in close vicinity. Also backup case.

12. Detailed Design contd. 2. Virtual Groups: Sensors are again divided into groups of n each. But in this case, the group is not �fixed� but rather �moves� along the highway following the motion of the vehicle being sensed.

13. Virtual Group

14. Virtual Group contd. REASON: Save power consumption - Virtual Group �tracks� motion of vehicle, therefore not all sensors along road will have to wake up simultaneously.

15. 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 S3 will be awake (Virtual Group 1).

16. Detailed Design (Normal Operation contd.) As car moves out of sensing range of S1 and into sensing range of S2, S1 goes to sleep while S2 notifies S3 to wake up S4. So now 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 motion of the car and will inform the sensors ahead to wake up and be ready before the car reaches them. - This way we conserve power as not all of the sensors will have to turn on simultaneously and wait for the car to reach them.

17. Normal Operation

18. Detailed Design contd.: Accident Occurs: Detection of accident: Air-bag trigger in cars that detects the accident will trigger 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 wake up 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 propagate further than is required.

19. Case Accident

20. 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 reaches car will be too slow. Use access point to convey message directly to sensor closest to next-to-last exit (as far in advance as feasible). Sensor will inform vehicle before it reaches last exit and looses all chances to re-route.

21. Very long stretch of road w/no exit

22. Special Cases contd. 2. Backup Case - In case of sensor failure: Normally sensors communicate with each other on a per-hop basis. If a sensor goes down, its immediately neighboring sensors on both sides will increase their sensing and communication range. The increase in power consumption is a small price to pay for greater reliability.

23. Backup Case

24. Issues Concept of Watchdog Group does introduce a certain amount of redundancy. But: Provides Reliability: Even if Special Sensor (SS) goes down the entire link will not go out of service: sensors in watchdog group will continue to wake on/off periodically and can detect any accident if it occurs. Greater network Sensitivity: If all sensors along link are asleep until woken up by SS, an event missed by SS will be missed by all sensors. Watchdog group can protect against such a mishap.

25. Further Work Calculate feasible duty cycle. Calculate time synchronization. Messages between sensors for synchronization. Resolve MAC layer issues.

26. Q&A

27. Thank you ?