1. 1 ROME: Road Monitoring and Alert System through Geo-Cache Bin Zan, Tingting Sun, Marco Gruteser, Yanyong Zhang WINLAB, Rutgers University

2. Road Monitoring in Mobile Sensor Networks  New road monitoring services are enabled by cars with sensing, communication, computing and storage capabilities.  System Assumption  Location-based interests  Data items are accessed through queries after they are generated. 2 camera GPS rotation sensor accelerometer vibration sensor cell phone DSRC Communication Sensing Positioning Skid Resistance Surface Distress Road Roughness

3. Data Collection Challenges in Mobile Networks  Centralized  Bandwidth (Cellular)  Cost (DSRC)  Storage 3  Query-response  Difficult to locate data source afterwards  Local aggregation  Data are stored around where they are generated by passing cars  Short-ranged radios have larger bandwidth than cellular links

4. Location Aggregation  Three local aggregations.  Aggregation content format 4 LocationTimeEvent IdDetector (−92315:74000)2:00PM1VD 3245 (−92316:73989)2:30PM2SX 1443 (−92316:73989)2:45PM3MK 3098 Duration 2 hours

5. Geo-Cache Concept  Anchor Location: Locations of interest, where sensed results are aggregated.  Geo-Cache  Aggregated information around the Anchor Location.  Geo-Cache Collection Protocol  Protocols to hand over information through inter-vehicle communication as nodes move away. 5

6. Geo-Cache Collection Protocol  Broadcast Geo-Cache (Baseline)  Periodically broadcasting Geo-Cache to those closer to the anchor location, until time-to-live timer expires.  High overhead  Relay Geo-Cache  Acknowledgment  Overhearing  Delayed Geo-Cache 6

7. Relay Geo-Cache  Relay Protocol  Acknowledgement 7 A B C ACK

8. Relay Geo-Cache 8 A B C  Relay Protocol  Acknowledgement

9. Relay Geo-Cache 9 A B C ACK Handoff  Relay Protocol  Acknowledgement

10. Relay Geo-Cache 10 A B C  Relay Protocol  Overhearing

11. Relay Geo-Cache 11 A B C  Relay Protocol  Overhearing

12. Relay Geo-Cache 12 A B C Handoff  Relay Protocol  Overhearing

13. Delayed Geo-Cache (Boomerang)  Relay protocol incurs high overhead when detection probability is low  Delayed protocol: cars keep their Geo-Cache locally, and later hand off to an opposite collector 13 AB Detect C

14. Delayed Geo-Cache (Boomerang) 14 ABC D  Relay protocol incurs high overhead when detection probability is low  Delayed protocol: cars keep their Geo-Cache locally, and later hand off to an opposite collector

15. Delayed Geo-Cache (Boomerang) 15 AB D C  Relay protocol incurs high overhead when detection probability is low  Delayed protocol: cars keep their Geo-Cache locally, and later hand off to an opposite collector

16. Delayed Geo-Cache (Boomerang) 16 B D C Geo-Cache back to Anchor Location A  Relay protocol incurs high overhead when detection probability is low  Delayed protocol: cars keep their Geo-Cache locally, and later hand off to an opposite collector

17. When Nobody is Around …  What if the handoff process cannot find a candidate (the current carrier is the only node in the area)?  Infrastructure: cellular, WiFi, road-side DSRC units, etc. 17

18. Performance Evaluation  Performance metrics  Communication Overhead  Geo-Cache anchoring delay (the time between when the geo-cache is carried away from the anchor and when it returns)  NJTP Trace  Represents relatively sparse off-peak traffic from 6 to 8 AM, south NJ.  Synthetic workload  70km two lane road.  Cars’ arrival rate as Poisson distribution.  Average speed: 30 m/s.  Radio range: 100m for dense traffic and 250m for sparse traffic  NS2  802.11b as PHY and MAC  Two-ray-ground propagation model 18

19. Performance Evaluation  Broadcast Geo-Cache vs. Relay Geo-Cache. 19

20. Performance Evaluation  Delayed (Boomerang) vs. Relay Geo-Cache. 20

21. Conclusion  New mobile sensing applications are being enabled  Local aggregation through the Geo-Cache structure provides a cost-effective method for mobile sensing  Delayed Geo-Cache protocol can significantly reduce the communication overhead while anchoring the Geo-Cache especially with lower detection probabilities. 21

22. Questions & Answers 22