CS 851 Presentation: Differentiated Surveillance for Sensor Network

1
CS 851 PresentationDifferentiated 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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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?

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Problem statement Sensing Coverage
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Problem statement Sensing Coverage
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Problem statement Sensing Coverage
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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.

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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

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Differentiated surveillance solution
Introduction

• Degree of coverage (DOC)
• Differentiated surveillance
• Providing different degrees of sensing coverage
  for a sensor network according to different
  requirements

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Differentiated surveillance solution
Introduction
DOC 1
DOC 2
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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

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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

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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

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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

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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

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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?

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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 nodes sensing range at
  ANY time

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Basic design without differentiation 100
sensing coverage

• 100 Grid point sensing coverage 100 sensing
  coverage guarantee? No.

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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 nodes conservative
  sensing range at ANY time.

d
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Basic design without differentiation - decide
working schedule

• A schedule example

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
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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

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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.

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Basic design without differentiation decide
working schedule

• Concepts
• A nodes 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 nodes working period is
  determined as follows
• Tj Ref Tfront , Tj Ref Tend)
• And all the other time the node is sleeping.

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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
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Basic design without differentiation decide
working schedule

• 3) Assuming RefN is the (i)th Ref, Ns four
  parameter tuple is computed as follows
• TfronN (Ref(i)- Ref(i-1))/2, 1ltiltM
• TendN (Ref(i1)-Ref(i))/2, 1ltiltM
• 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) Ns working period for point P (TwN(P)) is
  decided by
• Tj RefN TfrontN , Tj RefN TendN), j
  0, 1, 2,
• TwA(P1) 100j4010, 100j4025) 100j30,
  100j65)

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Basic design without differentiation decide
working schedule

• 5) Calculate the union of TwN(Px) for all grid
  points within Ns sensing area, choose this union
  as the final working period of N (TwN).

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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

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Enhanced design with differentiation

• Provide different DOC according to different
  requirements

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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 nodes working period as follows
• Tj Ref Tfronta , Tj Ref Tenda)

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Enhanced design with differentiation An example
Schedule for Grid Point P1 (a1)
(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
Tj Ref Tfront , Tj Ref Tend)
100j 30, 100j 65) TwB 100j 65, 100j
105) TwC 100j 5, 100j 30)
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Enhanced design with differentiation An example
Question - Can the algorithm guarantee 100
DOCgt2 sensing coverage by setting a2? Answer -
Yes
Schedule for Grid Point P1 (a2)
(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 Tj Ref Tfront2,Tj Ref
Tend2) 100j 20, 100j 90) TwB
100j 40, 100j 120) TwC 100j -10,
100j 40)
0
A
B
C
30
65
5
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Enhanced design with differentiation An example
Question - Can the algorithm guarantee 100
DOCgt3 sensing coverage by setting a3? Answer -
No
Schedule for Grid Point P1 (a3)
(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 Tj Ref Tfront3,Tj Ref
Tend3) 100j 10, 100j 115)
T TwB 100j 15, 100j 135) T TwC
100j -25, 100j 50)
0
A
B
C
30
65
5
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Enhanced design with differentiation An
extension to guarantee 100 DOCgta

• My Extension to guarantee 100 DOCgta 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
30
65
5
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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

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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
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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
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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

refC
refB
refA
TwA
TwB
TwC
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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
TwA1
TwA2
TwA3
TwA2
TwA3
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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

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Related Work Communication Coverage

• SPAN, ASCENT providing a communication coverage
  within an energy conservation context

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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 neighbors contribution, so no
  guarantee on sensing coverage

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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.

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Related Work Sensing Coverage 2

• Drawbacks
• Require broadcasting at the beginning of each
  round
• Underestimate the area that the neighbor nodes
  can cover

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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

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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

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Evaluation 1 Energy Conservation
Total Energy Consumption per Unit of
Time Sponsored Coverage Basic Design 2nd
Pass Optimization
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Evaluation 1 Energy Conservation
?
Single Node Energy Consumption Standard
Deviation Sponsored Coverage Basic
Design Multiple Round Extension
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Evaluation 1 Energy Conservation
Half-life of the network Sponsored
Coverage Basic Design 2nd Pass Optimization
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Evaluation 2 Sensing Coverage
Actual Degree of Coverage for Differentiated
Surveillance
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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

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Conclusion and Discussion

• Conclusion
• Novelty - guarantee not only full sensing
  coverage to a certain geographic area, but also
  sensing coverage with specific degree of
  coverage.
• Scalability - localized distributed algorithm
• Power management - Good job in energy
  conservation and balancing
• Robustness - fixed schedule throughout the life
  time, expensive fault tolerant extension, can not
  work without clock synchronization, can not
  support mobility

?
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Conclusion and Discussion

• Discussion 1
• This solution can not guarantee certain degree of
  coverage more than 2.
• Discussion 2
• Each node chooses its Ref randomly. What if
  multiple neighbors have the same Refs?
• A simple solution is to order the same Refs by
  node ID.

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Conclusion and Discussion

• Discussion 3
• In initialization phase, each node should send
  out Ref broadcast and should receive all Refs
  from 2r neighbors. It is very hard in high
  density sensor network. So there must be some
  nodes which are ignored and have not attended the
  scheduling algorithm in initialization phase.
• An extension, which allows these nodes to attend
  the scheduling later, is necessary.

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Conclusion and Discussion

• Discussion 4
• Each node decides its working schedule only based
  on sensing coverage. Some other layer protocols
  or applications may need a different working
  schedule. How to integrate with other working
  schedule will be a big problem.

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Conclusion and Discussion

• Discussion 5
• The baseline - Sponsored coverage scheme can
  provide fault-tolerance and support certain
  mobility since it updates neighbor hood
  information every round
• DS without the expensive fault tolerance scheme
  can not provide fault-tolerance at all
• So it is unfair to compare the power consumption
  between DS without fault-tolerance and the
  baseline with fault-tolerance.

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Thanks!