1. 1 Virtual Patrol : A New Power Conservation Design for Surveillance Using Sensor Networks Prasant Mohapatra, Chao Gui Computer Science Dept. Univ. California, Davis

2. 2 Outline Introduction Working model – On-demand Temporary Patrol – Coverage-oriented Continuous Patrol Senstrol (SENSor network paTROL operations) – Patrol setup phase Patrol setup dissemination Sleep schedule setup Patroller host handover – Patrolling phase Performance evaluation Conclusion

3. 3 Introduction Surveillance is a typical application among a wide range of sensor network applications A surveillance sensor network detects any event in the monitored field – toxic gas leak, forest fire, battle field surveillance, intruding personnels or vehicles

4. 4 Introduction Real life solutions of field surveillance – Stationary watchtowers – Patrolling sentinels – Hybrid solutions combining the two are also possible Given a curve in the field as the desired patrol path – "virtual patrol“ can be achieved by sequentially waking up and turning off sensor nodes that are located on the patrol path

5. 5 Introduction ~Example Senstrol Scenario~ Battle field surveillance Soldiers hide at A Plan arbitrary patrol path Inject the path info. to nearest sensor Path info. disseminated to all sensors along path Virtual patrol carried out A B On-demand Temporary Patrol

6. 6 Working model Two working model – On-demand Temporary Patrol (OT-Patrol) Can be applied to specific locations or paths – Coverage-oriented Continuous Patrol (CC-Patrol) can also be used for covering entire field Coverage-oriented Continuous Patrol (CC-Patrol) – sensing range of the virtual patroller can sweep through every position in the network field

7. 7 Working model ~ Coverage-oriented Continuous Patrol (CC-Patrol) ~ the network’s power consumption rate is much lower than the conventional surveillance operations

8. 8 Senstrol ~key concepts~ There is an imaginary "patroller" moving along patrol path, with constant speed v p – sensor nodes near patrol path should be active when and only when the "patroller" is within node’s duty range – duty range would be the same as sensing range

9. 9 Senstrol ~key concepts~ only nodes within the duty range of the current VP location need to be active

10. 10 Senstrol A patrol is initiated by a user at the starting location – Portable computer is used to disseminate the patrol setup information The patrol setup information is forwarded to the node closest to the starting point – serves as the first node of the new patrol

11. 11 Senstrol (SENSor network paTROL operations) Patrol setup phase – Patrol setup dissemination – Sleep schedule setup – Patroller host handover Patrolling phase

12. 12 Senstrol ~Patrol dissemination~ The first node of new patrol (Patrol Host) has the patrol setup information (PATROL_INFO) that will be disseminated to the other involved nodes – Path trajectory Contains the parameters for defining the specific Bezier curve – Patrol speed v p The constant speed that the imaginary patroller uses while moving along the path – Iteration period T i The time that the patroller takes to traverse the path from start to end – Patrol duration P D The time that the user desires the path to be patrolled – Patroller time

13. 13 Senstrol ~Patrol dissemination~ Imaginary reference clock: “Patroller time” At the beginning, the first node PH (Patroller host), records zero on patroller time-stamp, maps it to its local clock As the patroller time advances, PH will broadcast PATROL_INFO to the nearby sensors – Time-stamps of patroller time are attached to each broadcast packet – A receiver N i can set up its own mapping using the packet

14. 14 Senstrol ~Patrol dissemination~ When N i receives packet P (PATROL_INFO) at its local time-stamp t local (P), P carries a patroller time-stamp t(P) – t local (P) = t(P) +T offset (i) Mapping of patroller time to the local time at node N i

15. 15 Senstrol ~Patrol dissemination~ PH broadcast PATROL_INFO at constant interval T diss Each node starts an initial sleep time of uniformly random length in the range [0, T slot ] – Time is discretized into slots,T slot At beginning of T slot, node wakes up for a short time period T up, turns off to sleep for the remaining time of the slot – Default sleep schedule – Intended for the sensor nodes to be able to receive the PATROL_INFO packets

16. 16 Senstrol ~Patrol dissemination~ N0N0 N1N1 N2N2 N3N3 N4N4 N5N5 N6N6 N7N7 N0N0 N4N4 T diss N5N5 N6N6 Dissemination Procedure: 1. PH broadcast PAT_INFO packets, constant interval (T diss ) 2. Near-by nodes conduct default sleep schedule ( T slot, T up ) 3. all near-by nodes receive PAT_INFO packet After receiving PAT_INFO, each node calculate its own sleep schedule T up T slot

17. 17 Senstrol ~ Sleep schedule setup ~ After receiving the PATROL_INFO packet from PH, sensor node calculate its sleep schedule – Set up the mapping from "patroller time" and its local time – Calculate the time period during which the virtual patroller (VP) is within its duty range – Set future sleep schedule, and the iteration period received from PATROL_ INFO packet Time is divided into T i,, for VP to traverse the path from start to end

18. 18 Senstrol ~ Sleep schedule setup ~ Wake up period

19. 19 Senstrol ~ patroller host handover ~ When VP moves close to the boundary of current PH’s transmission range – PH needs to select next PH and handover the host’s duty to its descendant – Current PH identifies the time when its distance to the VP reaches a threshold of (1-δ)R t

20. 20 Senstrol ~ patroller host handover ~ Handover procedure – the PH broadcast PH_ELECT message – PH can wait duration T elect for returning messages – Receiver chooses random delay in [0, T elect ], and reply to the PH – PH sends confirm message to the selected descendant

21. 21 Senstrol ~Patroller Host Handover~ A D C E Patroller Host PH_ELECT message Reply message Confirm message Patroller Host

22. 22 Senstrol ~ Patrolling Phase ~ Patrolling phase

23. 23 Senstrol ~ Patrolling Phase ~ A B

24. 24 Performance evaluation GloMoSim simulator 400m x 400m field 800 nodes, uniform random distribution Transmission power 10dBm (10mW) Receiving sensitivity, the lowest signal power that may be reliably received by the receiver -65 dBm (0.3μW) VP speed 5 m/s

25. 25 Energy Consumption vs. Duty Range

26. 26 Energy Consumption vs. Patrol Speed

27. 27 Energy Consumption vs. Node Density the number of nodes participating in the patrol setup

28. 28 Conclusion Introduce Virtual Patrol operations in Surveillance Sensor Network Two models of Virtual Patrol – On-demand Temporary patrol – Coverage-oriented Continuous patrol Future work – extend the Senstrol to support multiple patrollers