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CS 851 Presentation: Differentiated Surveillance for Sensor Network

CS 851 Presentation: Differentiated Surveillance for Sensor Network. Presented by Liqian Luo Reference: 1. T. Yan, T. He, and J. A. Stankovic, “Differentiated Surveillance for Sensor networks”, First ACM Conference on Embedded Networked Sensor Systems (SenSys 2003), Los Angeles, CA 2003.

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CS 851 Presentation: Differentiated Surveillance for Sensor Network

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  1. CS 851 Presentation:Differentiated Surveillance for Sensor Network Presented by Liqian Luo Reference: 1. T. Yan, T. He, and J. A. Stankovic, “Differentiated Surveillance for Sensor networks”, First ACM Conference on Embedded Networked Sensor Systems (SenSys 2003), Los Angeles, CA 2003

  2. Assessment of the Paper • Pros • The first algorithm to guarantee different degrees of coverage for different requirements • Good performance in power conservation and balancing • Cons • Pessimistic degree of coverage estimation • Lack of flexibility • Require clock synchronization; Do not support mobility; work/sleep schedule never changes after decided; Expensive fault tolerance

  3. Outline • Problem Statement • Differentiated Surveillance solution • Introduction • Design goals • Assumptions • Basic design without differentiation • Enhanced design with differentiation • Extensions and Optimizations • Related Work • Evaluation • Conclusion and Discussion

  4. Roadmap • Problem Statement • Differentiated Surveillance solution • Introduction • Design goals • Assumptions • Basic design without differentiation • Enhanced design with differentiation • Extensions and Optimizations • Related Work • Evaluation • Conclusion and Discussion

  5. Problem statement • How to provide sensing coverage for a sensor network in a power-efficient way?

  6. Problem statement – Sensing Coverage

  7. Problem statement – Sensing Coverage

  8. Problem statement – Sensing Coverage

  9. 0 F 2 T 1 T Problem statement – Degree of Sensing Coverage • Current solutions regard the sensing coverage to a certain geographic area as a binary. • This paper argues that higher degree of sensing coverage is desired to obtain high detection confidence since individual nodes are not reliable.

  10. Roadmap • Problem Statement • Differentiated Surveillance solution • Introduction • Design goals • Assumptions • Basic design without differentiation • Enhanced design with differentiation • Extensions and Optimizations • Related Work • Evaluation • Conclusion and Discussion

  11. 0 2 1 Differentiated surveillance solution – Introduction • Degree of coverage (DOC) • Differentiated surveillance • Providing different degrees of sensing coverage for a sensor network according to different requirements

  12. Differentiated surveillance solution – Introduction DOC = 1 DOC = 2

  13. Roadmap • Problem Statement • Differentiated Surveillance solution • Introduction • Design goals • Assumptions • Basic design without differentiation • Enhanced design with differentiation • Extensions and Optimizations • Related Work • Evaluation • Conclusion and Discussion

  14. Differentiated surveillance solution – Design Goals • Provide energy efficient sensing coverage for a geographic area covered by sensor nodes • extend system life • Reduce total energy consumption • Reduce energy consumption variation among nodes • provide differentiated surveillance

  15. Roadmap • Problem Statement • Differentiated Surveillance solution • Introduction • Design goals • Assumptions • Basic design without differentiation • Enhanced design with differentiation • Extensions and Optimizations • Related Work • Evaluation • Conclusion and Discussion

  16. r < 2r Differentiated surveillance solution – Assumptions • Each node knows its own location and nodes are not moving. • Neighboring nodes are roughly time synchronized. • The sensing area of a node is a circle with radius r centered at the location of this node. • Radio radius is larger than 2r

  17. Roadmap • Problem Statement • Differentiated Surveillance solution • Introduction • Design goals • Assumptions • Basic design without differentiation • Enhanced design with differentiation • Extensions and Optimizations • Related Work • Evaluation • Conclusion and Discussion

  18. For EACH POINT p in a certain geographic area, Guarantee that at ANY TIME, p is covered by at least one node’s sensing range. Basic design without differentiation – Goal • Goal: find a work-sleep schedule for each node which achieves 100% Sensing coverage guarantee. • Ideally we should consider each point in the area when do scheduling, but it is impossible because the number of points is infinite. What can we do?

  19. r Basic design without differentiation –100% sensing coverage • Solution – 100% Grid point sensing coverage • Divide whole network into grids • For each grid point x, guarantee that x is covered by at least one node’s sensing range at ANY time

  20. r r r r Basic design without differentiation –100% sensing coverage • 100% Grid point sensing coverage = 100% sensing coverage guarantee? No.

  21. r Rc Rc Rc Rc Basic design without differentiation –100% sensing coverage • Solution – Conservative sensing radius (Rc) • Rc = r – d/ • For each grid point x, guarantee that x is covered by at least one node’s conservative sensing range at ANY time. d

  22. A schedule example Point x B A C Basic design without differentiation - decide working schedule If we want to provide sensing coverage for point x, we can have either A or B or C awaken. A scheduling example of A, B and C 100 0 30 70 Node A 10 60 Node B 5 45 Node C time Waking Sleeping

  23. Basic design without differentiation –decide working schedule • Challenge: For each node, how to coordinate with other nodes and decide its own schedule? • Solution - Random Reference Point Scheduling Algorithm

  24. Decide working schedule for sensing round T Basic design without differentiation –decide working schedule • Concepts • Initialization Phase • In this phase, nodes find their own positions, synchronize time with neighboring nodes and decide their own working schedule. • Sensing Phase • Nodes enter this phase after initialization phase and choose to sense or sleep according to their schedules. • Sensing Round - T • Sensing phase is divided into sensing rounds with equal duration T. A node has the same schedule for each round.

  25. Basic design without differentiation –decide working schedule • Concepts • A node’s working schedule is determined by Four parameter tuple – (T, Ref, Tfront, Tend) • Ref: a random time reference point chosen by a node within [0, T) • Tfront: the duration of time prior to Ref • Tend: the duration of time after Ref. • By this tuple, A node’s working period is determined as follows: • [T*j + Ref – Tfront , T*j + Ref + Tend) And all the other time the node is sleeping.

  26. Point P1 B refC refA refB 100 A 20 40 90 C Basic design without differentiation –decide working schedule • Solution – Random Reference Point Scheduling Algorithm 1) Each node N chooses a “Reference Point (Ref)” randomly from [0, T) and broadcasts its Ref and position. e.g. T = 100, RefA = 40, RefB= 90, RefC = 20 2) For each grid point P in its own sensing area, N sorts all the Refs from nodes (including N) which can also sense P in ascending order. For A according to point P1, we have: Ref(1) = RefC = 20, Ref(2) = RefA = 40, Ref(3) = RefB = 90 0

  27. t refC refA refB refC 20 40 90 t 0 30 65 Basic design without differentiation –decide working schedule 3) Assuming RefN is the (i)th Ref, N’s four parameter tuple is computed as follows: • TfronN = (Ref(i)- Ref(i-1))/2, 1<i<M • TendN = (Ref(i+1)-Ref(i))/2, 1<i<M TfrontA = (Ref(2)-Ref(1))/2 = (40-20)/2 = 10 TendA = (Ref(3)-Ref(2))/2 = (90-40)/2 = 25 (T, RefA, TfrontA, TendA) = (100, 40, 10, 25) 4) N’s working period for point P (TwN(P)) is decided by: [T*j + RefN – TfrontN , T*j + RefN + TendN), j = 0, 1, 2, … TwA(P1) = [100*j+40–10, 100*j+40+25) = [100*j+30, 100*j+65)

  28. TwA(P1) TwA(P2) TwA(P3) 5 … . . . 50 TwA(Pn) 45 65 TwA 5 65 100 0 Basic design without differentiation –decide working schedule 5) Calculate the union of TwN(Px) for all grid points within N’s sensing area, choose this union as the final working period of N (TwN).

  29. Roadmap • Problem Statement • Differentiated Surveillance solution • Introduction • Design goals • Assumptions • Basic design without differentiation • Enhanced design with differentiation • Extensions and Optimizations • Related Work • Evaluation • Conclusion and Discussion

  30. DoC = 3 DoC = 2 DoC = 1 Enhanced design with differentiation • Provide different DOC according to different requirements

  31. Enhanced design with differentiation • Goal • provide sensing coverage with DOC = a • Solution • Extend 4-parameter tuple to 5-parameter tuple (T, Ref, Tfront, Tend, a) • Determine a node’s working period as follows: • [T*j + Ref – Tfront*a , T*j + Ref + Tend*a)

  32. Point P1 B 0 A A C B refC refA refB 20 40 90 C 5 30 65 Enhanced design with differentiation – An example Schedule for Grid Point P1 (a=1) (T, RefA, TfrontA, TendA) = (100, 40, 10, 25) (T, RefB, TfrontB, TendB) = (100, 90, 25, 15) (T, RefC, TfrontC, TendC) = (100, 20, 15, 10) TwA = [T*j + Ref – Tfront , T*j + Ref + Tend) = [100*j + 30, 100*j + 65) TwB = [100*j + 65, 100*j + 105) TwC = [100*j + 5, 100*j + 30)

  33. refC refA refB 20 40 90 Enhanced design with differentiation – An example Question - Can the algorithm guarantee 100% DOC>=2 sensing coverage by setting a=2? Answer - Yes Schedule for Grid Point P1 (a=2) (T, RefA, TfrontA, TendA, a) = (100, 40, 10, 25, 2) (T, RefB, TfrontB, TendB, a) = (100, 90, 25, 15, 2) (T, RefC, TfrontC, TendC, a) = (100, 20, 15, 10, 2) TwA = [T*j + Ref – Tfront*2,T*j + Ref + Tend*2) = [100*j + 20, 100*j + 90) TwB = [100*j + 40, 100*j + 120) TwC = [100*j -10, 100*j + 40) 0 A B C 5 30 65

  34. refC refA refB 20 40 90 Enhanced design with differentiation – An example Question - Can the algorithm guarantee 100% DOC>=3 sensing coverage by setting a=3? Answer - No Schedule for Grid Point P1 (a=3) (T, RefA, TfrontA, TendA, a) = (100, 40, 10, 25, 3) (T, RefB, TfrontB, TendB, a) = (100, 90, 25, 15, 3) (T, RefC, TfrontC, TendC, a) = (100, 20, 15, 10, 3) TwA = [T*j + Ref – Tfront*3,T*j + Ref + Tend*3) = [100*j + 10, 100*j + 115) = T TwB = [100*j + 15, 100*j + 135) = T TwC = [100*j -25, 100*j + 50) 0 A B C 5 30 65

  35. refC refA refB 20 40 90 Enhanced design with differentiation – An extension to guarantee 100% DOC>=a • My Extension to guarantee 100% DOC>=a sensing coverage • Separate the time line into segments by using Refs and the middle points between Refs • Instead of expanding Tw by its own Tfront or Tend, expand one segment on both sides when a is increased by 1. 0 A B C 5 30 65

  36. Roadmap • Problem Statement • Differentiated Surveillance solution • Introduction • Design goals • Assumptions • Basic design without differentiation • Enhanced design with differentiation • Extensions and Optimizations • Related Work • Evaluation • Conclusion and Discussion

  37. Optimizations and Extensions – Second Pass Optimization A • Existing Problem • Taking the union of Tw for all grid points within sensing range as final Tw will be more than efficient to provide coverage guarantee • Solution • make a second pass optimization to reduce the redundancy 1 B 2 TwA(1) TwA TwB(1) TwB(2) TwB

  38. Why not the one with the shortest Tw? Optimizations and Extensions – Second Pass Optimization A • Second Pass Optimization 1)After getting the final Tw, each node sends it to neighbors within the distance of 2r 2)Within 2r neighbors that have not recalculated their Tw, the one with the longest Tw recalculates its Tw and sends it to 2r neighbors 3) Repeat 2) until everyone has recalculated its Tw. 1 B 2 TwA(1) TwA TwB(1) TwB(2) TwB

  39. Optimizations and Extensions – Multi-Round Extension for Energy Balance • Existing Problem • Reference points are selected randomly instead of uniformly, which results in big variation in Tw among nodes and big variation in power consumption. • Solution • Multi-Round Extension refA refB refC TwA TwB TwC

  40. Optimizations and Extensions – Multi-Round Extension for Energy Balance • Multi-Round Extension • Instead of calculating a single schedule, calculate M schedules according to M independently selected random Refs for each node. • At each round T in sensing phase, the nodes choose one schedule consecutively. TwA1 TwA2 TwA3 TwA1 TwA2 TwA3

  41. Roadmap • Problem Statement • Differentiated Surveillance solution • Introduction • Design goals • Assumptions • Basic design without differentiation • Enhanced design with differentiation • Extensions and Optimizations • Related Work • Evaluation • Conclusion and Discussion

  42. Related Work – Communication Coverage • SPAN, ASCENT: providing a communication coverage within an energy conservation context

  43. b a Related Work – Sensing Coverage 1 • Energy Efficient Robust Sensing Coverage: a probing-based mechanism • After a sleeping node wakes up, use a probing message to see whether there is another node working within its sensing area. If no, it takes the responsibility of sensing until it dies. • Drawbacks • Overestimate neighbor’s contribution, so no guarantee on sensing coverage

  44. Related Work – Sensing Coverage 2 • A Node Scheduling Scheme for Energy Conservation: sponsored coverage scheme • At the beginning of each round, each node advertises its position to neighbors • After receiving neighbors’ position advertises, each node calculates its eligibility for going to sleep. Here, a back-off scheme is used to avoid simultaneous actions of multiple nodes.

  45. Related Work – Sensing Coverage 2 • Drawbacks • Require broadcasting at the beginning of each round • Underestimate the area that the neighbor nodes can cover

  46. Roadmap • Problem Statement • Differentiated Surveillance solution • Introduction • Design goals • Assumptions • Basic design without differentiation • Enhanced design with differentiation • Extensions and Optimizations • Related Work • Evaluation • Conclusion and Discussion

  47. 160 140 160 140 Evaluation - Introduction • Nodes are distributed with a uniform random distribution in a 160 X 160 rectangle • Guarantee sensing coverage in the inner 140 X 140 rectangle to eliminate the edge effect • sensing radius = 10, communication radius = 25

  48. Evaluation 1 – Energy Conservation • Total Energy Consumption per Unit of Time • Sponsored Coverage • Basic Design • 2nd Pass Optimization

  49. Evaluation 1 – Energy Conservation ? Single Node Energy Consumption: Standard Deviation Sponsored Coverage Basic Design Multiple Round Extension

  50. Evaluation 1 – Energy Conservation Half-life of the network Sponsored Coverage Basic Design 2nd Pass Optimization

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