Wireless Sensor Networks for Emergency Navigation

1. Wireless Sensor Networks for Emergency Navigation Yu-Chee Tseng Deptment of Computer Science National Chiao Tung University

2. Outline • Introduction • System Overview • Environment setting • Regular report • Emergency navigation service • Simulation results • Demonstration • Conclusion

3. Outline • Introduction • System Overview • Environment setting • Regular report • Emergency navigation service • Simulation results • Demonstration • Conclusion

4. Introduction • Wireless Sensor Network • Each sensor has • Limited Memory、Limited CPU、Wireless Transceiver、Sensing Unit • Each sensor can • Sense environments • Communicate with others • Do simple computations

5. Introduction • Traditional Navigation Devices • Advantage • Cheap • Easy deployment • Disadvantage • Fixed direction. • Can not adapt to actual emergency situations.

6. Introduction • Motivation • According to the statistic report of the NFA of Taiwan(內政部消防署）, 228 people died in fire accidents in 2003. • The main reason is that people can not find “right” escaping paths to exits. • Our Goal • to develop an emergency navigation system • for indoor 2D and 3D environments

7. Outline • Introduction • System overview • Environment setting • Regular report • Emergency navigation service • Simulation results • Demonstration • Conclusion

8. System Overview • Our system is composed of 3 parts • Environment setting • Regular reporting • Emergency Navigation

9. navigating reporting Environment Setting • Deploy sensors • Construct reporting tree • Setup initial navigation paths

10. Outline • Introduction • System overview • Environment setting • Regular report • Emergency navigation service • Simulation results • Demonstration • Conclusion

11. Deployment of Sensors • Plan locations of sensors • Define the roles of sensors • Sink • Exit sensors • Normal sensors • Decide navigation links navigation links (for human)

12. Construct a Reporting Tree • Step 1. Discover symmetric links • Each sensor periodically broadcasts HELLOs • When receiving a HELLO, sensors reply ACKs • After receiving an ACK, sensors record the sender ID in its link table HELLO 2 ACK ACK 0 1 3 ACK Link table 2 3

13. Construct a reporting tree (cont.) • Step 2. Construct a spanning tree • Sink floods a BEACON. • For a sensor receives a BEACON, it checks if the sender is in its link table • If yes, it sends a REG(ister) to sink and rebroadcasts BEACON. • Else, drops it BEACON REG BEACON

14. communication links (for packets)

15. Outline • Introduction • System overview • Environment setting • Regular report • Emergency navigation service • Simulation results • Demonstration • Conclusion

16. Reporting Issues • How often a report should be sent? • Will each sensor report individually? • Is there any inaccuracy? • False alarm? • How to save energy of sensors?

17. Outline • Introduction • System overview • Environment setting • Regular report • Emergency navigation in 2D environment • Simulation results • Demonstration • Conclusion

18. Design Principle • When a sensor detects an emergency event, it forms a hazardous region • The navigation algorithm will try to guide people as farther away from hazardous regions as possible

19. Problem Formulation • Each sensor has an altitude. • Sensors in hazardous regions will raise their altitudes. • Each sensor guides people to the neighbor with the lowest altitude • After forming hazardous regions, some sensors may become local minimum ones • A partial link reversal operation is performed to solve this problem

20. Phases of Navigation • Initialization phase • Initial phase is started by Exit sensor • After this phase, every sensor has a default guiding direction. • Navigation phase • This phase starts by the sensor which detects an emergency event.

21. Terminology • D：The radius of the hazardous region • Aemg： A large constant which represents the maximum altitude • Ai：The altitude of sensor i • Ii：The altitude obtained in the initialization phase • ej,i：The hop count from emergency sensor j to sensor i

22. Initialization phase • Every exit sensor sets its altitude to 0 and broadcasts an initialization packet. • When receiving an initialization packet, a sensor adds its hop count by 1. • Then, it compares the hop count with its current altitude ∞ 0 ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞

23. Initialization phase (cont.) • If the hop count is smaller than its altitude, it resets its altitude and setups its initial guiding direction to that sender. • Then, it rebroadcasts this packet. 0 ∞ 1 ∞ 2 ∞ 1 ∞ 2 ∞ 3 ∞ 2 ∞ 3 ∞ 4

24. Navigation phase • When a sensor x detects an emergency, it will set its altitude to the maximum altitude Aemg (let it be 200). • Then it broadcasts an emergency packet EMG(seq, x, x, Aemg, 0) • seq：sequence number • x：emergency ID • w： sender ID • Aw：altitude of sender • h：hop count to emg. location 10 11 12 11 12 200 13 12 13 14

25. Navigation phase (cont.) • When a sensor node y receives a EMG packet originated from node x, it will do the following steps. • Step1: • Decide that the emergency is a new one or not • If it’s a new emergency, record this event and set the hop count ex,y to h+1. • Else, compare the h and ex,y. If h is smaller than ex,y , set ex,y to h+1. • Record the altitude (Aw) in the navigation link table. 10 11 12 11 200 13 12 13 14

26. Navigation phase (cont.) • Step 2: • If eX,Y was changed in step1 and eX,Y ≦D, y considers itself within hazardous region. Then it re-calculates its altitude as follows： 10 11 61 12 11 61 200 13 63 12 13 63 14

27. Navigation phase (cont.) • Step 3: • If y has a local minimum altitude and it’s not an exit, it must adjust its altitude as follows： • = altitudes of y’s neighbors • STA = standard deviation • A bigger value means closer to the hazardous region. So we need to adjust the altitude faster. • |Ny| = number of neighbors of y. • A smaller | Ny | means less escape ways. So we need to adjust the altitude faster. • δis a small constant. Static adjustment 10 61 12 Five iterations 61 200 63 Our scheme Three iterations 12 63 14 63.1

28. Navigation phase (cont.) • Step 4: • y has to broadcast an EMG(seq, x, y, Ay, ex,y) packet if any of the following conditions matches. • It’s a new emergency • y has changes its altitude or ex,y in the previous steps. • Step 5: • If y is in hazardous regions and it sees an exit sensor which is in Ny and which is also in hazardous regions, then y chooses this exit sensor • In all other cases, y directs users to a safer sensor first, and then gradually to a safe exit.

29. Example—Altitude after initial phase Exit 10x10 Grid Network

30. One emergency event –after step 1, 2 & 4 Local minimum

31. One emergency event–final result

32. Two emergency events–after step 1, 2 & 4 Local minimum

33. Two emergency events–final result

34. Outline • Introduction • System overview • Environment setting • Regular report • Emergency navigation service • Simulation results • Demonstration • Conclusion

35. Simulation results • We compare our navigation algorithm with “Distributed algorithm for guiding navigation across a sensor network”(MobiCom 03) • This algorithm guides people to the nearest exits • However, nearest exits may not be good choices

36. Case1. Our algorithm will choose to pass hazardous region areas as farther away from emergency locations as possible. Case2. Our algorithm will not guide people passing through the hazardous region. Case3. Only the sensors near the exit in the hazardous region will guide people to that exit. Simulation results

37. Outline • Introduction • System overview • Environment setting • Regular report • Emergency navigation service • Simulation results • Demonstration • Conclusion

38. Demonstration • System Components • MICAz sensors • Environment monitoring • Navigation • Sink • MIB510 serial Gateway • Gateway between wireless sensor network and PC • PC • Control Host

39. Demonstration second event (emergency time) first event (emergency time) exit (normal time)

40. A Short Summary • Novel indoor monitoring and navigation services based on wireless sensor network technolgoies • emergency will raise sensors’ altitudes • navigation similar to TORA protocol, but different in that emergencies will disturb altitudes • altitude adjustment is designed for quicker convergence • navigation in emergency applications requires safer paths, but not necessarily longer paths