Lifetime maximization for Wireless Sensor Networks using video cameras Andr´e Rossi⋆ , Alok Singh† , Marc Sevaux⋆ ⋆
Universit´ e de Bretagne-Sud, Lab-STICC, Lorient, France {andre.rossi,marc.sevaux}@univ-ubs.fr
†
University of Hyderabad, School of Computer and Information Sciences, India
[email protected]
July 3, 2013 A. Rossi, A. Singh, M. Sevaux (UBS)
Lifetime maximization for camera sensors
July 3 2013
1 / 22
Plan 1
Omni-directional wireless sensor networks
2
Overview
3
Directional wireless sensor networks
4
Column generation approach
5
Comparing the two problem versions
6
Results
7
Camera sensor networks
8
Conclusions
A. Rossi, A. Singh, M. Sevaux (UBS)
Lifetime maximization for camera sensors
July 3 2013
2 / 22
Omni-directional wireless sensor networks
A. Rossi, A. Singh, M. Sevaux (UBS)
Lifetime maximization for camera sensors
July 3 2013
3 / 22
Omni-directional wireless sensor networks
A. Rossi, A. Singh, M. Sevaux (UBS)
Lifetime maximization for camera sensors
July 3 2013
3 / 22
Omni-directional wireless sensor networks
A. Rossi, A. Singh, M. Sevaux (UBS)
Lifetime maximization for camera sensors
July 3 2013
3 / 22
Omni-directional wireless sensor networks c X
Maximize
(1)
tj
j=1
c X
ai,j tj ≤ bi
∀i ∈ {1, . . . , n}
tj ≥ 0
∀j ∈ {1, . . . , c}
[πi ]
(2)
j=1
Maximize 1 −
n X
(3)
(4)
ai,c+1 πi
i=1
1≤
X
ai,c+1
(5)
∀k ∈ {1, . . . , m}
i∈Ck n X
(6)
ai,c+1 ≤ m
i=1
ai,c+1 ∈ {0, 1}
A. Rossi, A. Singh, M. Sevaux (UBS)
∀i ∈ {1, . . . , n}
Lifetime maximization for camera sensors
(7)
July 3 2013
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Overview 3
3
4
2 4
1 si
3
s
2 si
6 5
Omni-directional sensor
2 θ
1
4 0
6 5
Directional sensor
θ
1 si
0
6 5
Camera sensor
Decide when to set the sensor to active state θ Set working direction θ Set focal distance s A. Rossi, A. Singh, M. Sevaux, A column generation algorithm for sensor coverage scheduling under bandwidth constraints, Networks, 60 (3), pp. 141-154, 2012. A. Rossi, A. Singh, M. Sevaux (UBS)
Lifetime maximization for camera sensors
July 3 2013
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Directional wireless sensor networks Each sensor has a given sensing angle ϕ Each active sensor has a working direction θ in [0, 2π) 5π 8
5π 8
π 4
3 7π 8
4
1 si
1 si
6
First problem
π 9
2 4
0 5
A. Rossi, A. Singh, M. Sevaux (UBS)
7π 8
π 9
2
π 4
3
15π 8 16π 9
0 6 5
15π 8 16π 9
Second problem
Lifetime maximization for camera sensors
July 3 2013
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Directional wireless sensor networks Each sensor has a given sensing angle ϕ Each active sensor has a working direction θ in [0, 2π) 5π 8
5π 8
π 4
3 7π 8
4
1 si
1 si
6
First problem
π 9
2 4
0 5
A. Rossi, A. Singh, M. Sevaux (UBS)
7π 8
π 9
2
π 4
3
15π 8 16π 9
0 6 5
15π 8 16π 9
Second problem
Lifetime maximization for camera sensors
July 3 2013
6 / 22
Directional wireless sensor networks Each sensor has a given sensing angle ϕ Each active sensor has a working direction θ in [0, 2π) 5π 8
5π 8
π 4
3 7π 8
4
1 si
1 si
6
First problem
π 9
2 4
0 5
A. Rossi, A. Singh, M. Sevaux (UBS)
7π 8
π 9
2
π 4
3
15π 8 16π 9
0 6 5
15π 8 16π 9
Second problem
Lifetime maximization for camera sensors
July 3 2013
6 / 22
Directional wireless sensor networks Each sensor has a given sensing angle ϕ Each active sensor has a working direction θ in [0, 2π) 5π 8
5π 8
π 4
3 7π 8
4
1 si
1 si
6
First problem
π 9
2 4
0 5
A. Rossi, A. Singh, M. Sevaux (UBS)
7π 8
π 9
2
π 4
3
15π 8 16π 9
0 6 5
15π 8 16π 9
Second problem
Lifetime maximization for camera sensors
July 3 2013
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Directional wireless sensor networks Each sensor has a given sensing angle ϕ Each active sensor has a working direction θ in [0, 2π) 5π 8
5π 8
π 4
3 7π 8
4
1 si
1 si
6
First problem
π 9
2 4
0 5
A. Rossi, A. Singh, M. Sevaux (UBS)
7π 8
π 9
2
π 4
3
15π 8 16π 9
0 6 5
15π 8 16π 9
Second problem
Lifetime maximization for camera sensors
July 3 2013
6 / 22
Directional wireless sensor networks Each sensor has a given sensing angle ϕ Each active sensor has a working direction θ in [0, 2π) 5π 8
5π 8
π 4
3 7π 8
4
1 si
1 si
6
First problem
π 9
2 4
0 5
A. Rossi, A. Singh, M. Sevaux (UBS)
7π 8
π 9
2
π 4
3
15π 8 16π 9
0 6 5
15π 8 16π 9
Second problem
Lifetime maximization for camera sensors
July 3 2013
6 / 22
Directional wireless sensor networks Each sensor has a given sensing angle ϕ Each active sensor has a working direction θ in [0, 2π) 5π 8
5π 8
π 4
3 7π 8
4
1 si
1 si
6
First problem
π 9
2 4
0 5
A. Rossi, A. Singh, M. Sevaux (UBS)
7π 8
π 9
2
π 4
3
15π 8 16π 9
0 6 5
15π 8 16π 9
Second problem
Lifetime maximization for camera sensors
July 3 2013
6 / 22
Directional wireless sensor networks Each sensor has a given sensing angle ϕ Each active sensor has a working direction θ in [0, 2π) 5π 8
5π 8
π 4
3 7π 8
4
1 si
1 si
6
First problem
π 9
2 4
0 5
A. Rossi, A. Singh, M. Sevaux (UBS)
7π 8
π 9
2
π 4
3
15π 8 16π 9
0 6 5
15π 8 16π 9
Second problem
Lifetime maximization for camera sensors
July 3 2013
6 / 22
Directional wireless sensor networks Each sensor has a given sensing angle ϕ Each active sensor has a working direction θ in [0, 2π) 5π 8
5π 8
π 4
3 7π 8
4
1 si
1 si
6
First problem
π 9
2 4
0 5
A. Rossi, A. Singh, M. Sevaux (UBS)
7π 8
π 9
2
π 4
3
15π 8 16π 9
0 6 5
15π 8 16π 9
Second problem
Lifetime maximization for camera sensors
July 3 2013
6 / 22
Directional wireless sensor networks Each sensor has a given sensing angle ϕ Each active sensor has a working direction θ in [0, 2π) 5π 8
5π 8
π 4
3 7π 8
4
1 si
1 si
6
First problem
π 9
2 4
0 5
A. Rossi, A. Singh, M. Sevaux (UBS)
7π 8
π 9
2
π 4
3
15π 8 16π 9
0 6 5
15π 8 16π 9
Second problem
Lifetime maximization for camera sensors
July 3 2013
6 / 22
Directional wireless sensor networks Each sensor has a given sensing angle ϕ Each active sensor has a working direction θ in [0, 2π) 5π 8
5π 8
π 4
3 7π 8
4
1 si
1 si
6
First problem
π 9
2 4
0 5
A. Rossi, A. Singh, M. Sevaux (UBS)
7π 8
π 9
2
π 4
3
15π 8 16π 9
0 6 5
15π 8 16π 9
Second problem
Lifetime maximization for camera sensors
July 3 2013
6 / 22
Directional wireless sensor networks A normalized direction is associated with each target 3 2 4
1 si
6 5
Non-normalized direction A (normalized) direction is dominated if the targets it covers are a strict subset of the targets covered by another direction
A. Rossi, A. Singh, M. Sevaux (UBS)
Lifetime maximization for camera sensors
July 3 2013
7 / 22
Directional wireless sensor networks A normalized direction is associated with each target 3 2 4
1 si
6 5
Non-normalized direction A (normalized) direction is dominated if the targets it covers are a strict subset of the targets covered by another direction
A. Rossi, A. Singh, M. Sevaux (UBS)
Lifetime maximization for camera sensors
July 3 2013
7 / 22
Directional wireless sensor networks A normalized direction is associated with each target 3
3 2
4
2 4
1 si
1 si
6 5
6 5
Non-normalized direction Normalized direction A (normalized) direction is dominated if the targets it covers are a strict subset of the targets covered by another direction
A. Rossi, A. Singh, M. Sevaux (UBS)
Lifetime maximization for camera sensors
July 3 2013
7 / 22
Directional wireless sensor networks A normalized direction is associated with each target 3
3 2
4
2 4
1 si
1 si
6 5
6 5
Non-normalized direction Normalized direction A (normalized) direction is dominated if the targets it covers are a strict subset of the targets covered by another direction 3 2 4
1 si
6 5
Dominated direction A. Rossi, A. Singh, M. Sevaux (UBS)
Lifetime maximization for camera sensors
July 3 2013
7 / 22
Directional wireless sensor networks A normalized direction is associated with each target 3
3 2
4
2 4
1 si
1 si
6
6
5
5
Non-normalized direction Normalized direction A (normalized) direction is dominated if the targets it covers are a strict subset of the targets covered by another direction 3
3 2
4
2 4
1 si
6 5
Dominated direction A. Rossi, A. Singh, M. Sevaux (UBS)
1 si
6 5
Non-dominated direction
Lifetime maximization for camera sensors
July 3 2013
7 / 22
Directional wireless sensor networks
A. Rossi, A. Singh, M. Sevaux (UBS)
Lifetime maximization for camera sensors
July 3 2013
8 / 22
Column generation approach
1
Group encoding
2
Subproblem
3
Global strategy of the column generation algorithm
4
Benefits of the genetic algorithm for addressing the subproblem
A. Rossi, A. Singh, M. Sevaux (UBS)
Lifetime maximization for camera sensors
July 3 2013
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Group encoding Sensor si has σi directions, for all i in {1, . . . , n}. i−1 X σℓ , and ∀q ∈ {1, . . . , σi }, Agi +q,j = 1 iff sensor si is active gi = ℓ=1
and is working in its q th direction. 5π 8
π 4
3 7π 8
π 9
2 4
1 si
0
Aj =
6 5
A. Rossi, A. Singh, M. Sevaux (UBS)
.. .
15π 8 16π 9
Lifetime maximization for camera sensors
0 0 0 .. .
1 gi + 1 gi + σi
gn + σn
July 3 2013
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Group encoding Sensor si has σi directions, for all i in {1, . . . , n}. i−1 X σℓ , and ∀q ∈ {1, . . . , σi }, Agi +q,j = 1 iff sensor si is active gi = ℓ=1
and is working in its q th direction. 5π 8
π 4
3 7π 8
π 9
2 4
1 si
0
Aj =
6 5
A. Rossi, A. Singh, M. Sevaux (UBS)
.. .
15π 8 16π 9
Lifetime maximization for camera sensors
1 0 0 .. .
1 gi + 1 gi + σi
gn + σn
July 3 2013
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Group encoding Sensor si has σi directions, for all i in {1, . . . , n}. i−1 X σℓ , and ∀q ∈ {1, . . . , σi }, Agi +q,j = 1 iff sensor si is active gi = ℓ=1
and is working in its q th direction. 5π 8
π 4
3 7π 8
π 9
2 4
1 si
0
Aj =
6 5
A. Rossi, A. Singh, M. Sevaux (UBS)
.. .
15π 8 16π 9
Lifetime maximization for camera sensors
0 1 0 .. .
1 gi + 1 gi + σi
gn + σn
July 3 2013
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Group encoding Sensor si has σi directions, for all i in {1, . . . , n}. i−1 X σℓ , and ∀q ∈ {1, . . . , σi }, Agi +q,j = 1 iff sensor si is active gi = ℓ=1
and is working in its q th direction. 5π 8
π 4
3 7π 8
π 9
2 4
1 si
0
Aj =
6 5
A. Rossi, A. Singh, M. Sevaux (UBS)
.. .
15π 8 16π 9
Lifetime maximization for camera sensors
0 0 1 .. .
1 gi + 1 gi + σi
gn + σn
July 3 2013
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Group encoding One column of the master problem may represent different groups p X Maximize tj j=1 p σi X X Agi +q,j tj ≤ bi ∀i ∈ {1, . . . , n} q=1 j=1 tj ≥ 0 ∀j ∈ {1, . . . , p} 1
Aj = s1
s2 2
A. Rossi, A. Singh, M. Sevaux (UBS)
}s }s
1
2
Lifetime maximization for camera sensors
July 3 2013
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Group encoding One column of the master problem may represent different groups p X Maximize tj j=1 p σi X X Agi +q,j tj ≤ bi ∀i ∈ {1, . . . , n} q=1 j=1 tj ≥ 0 ∀j ∈ {1, . . . , p} 1
Aj = s1
s2 2
A. Rossi, A. Singh, M. Sevaux (UBS)
1 0 0 1
}s }s
1
2
Lifetime maximization for camera sensors
July 3 2013
11 / 22
Group encoding One column of the master problem may represent different groups p X Maximize tj j=1 p σi X X Agi +q,j tj ≤ bi ∀i ∈ {1, . . . , n} q=1 j=1 tj ≥ 0 ∀j ∈ {1, . . . , p} 1
Aj = s1
s2 2
A. Rossi, A. Singh, M. Sevaux (UBS)
1 0 0 1
}s }s
1
1
Aj = 2
s1
s2 2
Lifetime maximization for camera sensors
0 1 1 0
}s }s
July 3 2013
1
2
11 / 22
Subproblem Subproblem: σi n X X Maximize 1 − Agi +q,j πi q=1 i=1 σi X Agi +q,j ≤ 1 q=1 X Ah,j ≥ 1 h∈C k σi n X X Agi +q,j ≤ m i=1 q=1 Agi +q,j ∈ {0, 1}
∀i ∈ {1, . . . , n} ∀k ∈ {1, . . . , m}
∀i ∈ {1, . . . , n}, ∀q ∈ {1, . . . , σi }
A genetic algorithm is used for returning many attractive groups The ILP formulation is solved only upon failure of the genetic algorithm
A. Rossi, A. Singh, M. Sevaux (UBS)
Lifetime maximization for camera sensors
July 3 2013
12 / 22
Global strategy of the column generation algorithm Start
Master problem
Subproblem with GA Yes
Yes
Attractive group found?
No Yes Fourth attempt?
No Subproblem with ILP
Attractive group found?
No End
A. Rossi, A. Singh, M. Sevaux (UBS)
Lifetime maximization for camera sensors
July 3 2013
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Benefits of GA for addressing the subproblem
n 50
100
ϕ
ILP alone
GA + ILP
2π 3 π 2 π 3 2π 3 π 2 π 3
0.250 0.312 0.234
0.046 0.062 0.063
Speedup factor 5.435 5.032 3.714
1.840 3.713 5.273
0.281 0.265 0.281
6.548 14.011 18.765
CPU time in seconds Problem is more difficult when sensing angle ϕ is small The benefit of GA is more visible with hard problem instances
A. Rossi, A. Singh, M. Sevaux (UBS)
Lifetime maximization for camera sensors
July 3 2013
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Comparing the two problem versions LM-PDS: predefined directions, LM-CDS: contextual directions LM-PDS may be infeasible while LM-CDS is feasible π 4
π 4
1 si
1 0
2
si
0 2
15π 8
LM-PDS
15π 8
LM-CDS
Lifetime with LM-CDS is larger than with LM-PDS. A. Rossi, A. Singh, M. Sevaux (UBS)
Lifetime maximization for camera sensors
July 3 2013
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Comparing the two problem versions LM-PDS: predefined directions, LM-CDS: contextual directions LM-PDS may be infeasible while LM-CDS is feasible π 4
π 4
1 si
1 0
2
si
0 2
15π 8
LM-PDS
15π 8
LM-CDS
Lifetime with LM-CDS is larger than with LM-PDS. A. Rossi, A. Singh, M. Sevaux (UBS)
Lifetime maximization for camera sensors
July 3 2013
15 / 22
Comparing the two problem versions LM-PDS: predefined directions, LM-CDS: contextual directions LM-PDS may be infeasible while LM-CDS is feasible π 4
π 4
1 si
1 0
2
si
0 2
15π 8
LM-PDS
15π 8
LM-CDS
Lifetime with LM-CDS is larger than with LM-PDS. A. Rossi, A. Singh, M. Sevaux (UBS)
Lifetime maximization for camera sensors
July 3 2013
15 / 22
Comparing the two problem versions LM-PDS: predefined directions, LM-CDS: contextual directions LM-PDS may be infeasible while LM-CDS is feasible π 4
π 4
1 si
1 0
2
si
0 2
15π 8
LM-PDS
15π 8
LM-CDS
Lifetime with LM-CDS is larger than with LM-PDS. A. Rossi, A. Singh, M. Sevaux (UBS)
Lifetime maximization for camera sensors
July 3 2013
15 / 22
Comparing the two problem versions LM-PDS: predefined directions, LM-CDS: contextual directions LM-PDS may be infeasible while LM-CDS is feasible π 4
π 4
1 si
1 0
2
si
0 2
15π 8
LM-PDS
15π 8
LM-CDS
Lifetime with LM-CDS is larger than with LM-PDS. A. Rossi, A. Singh, M. Sevaux (UBS)
Lifetime maximization for camera sensors
July 3 2013
15 / 22
Comparing the two problem versions LM-PDS: predefined directions, LM-CDS: contextual directions LM-PDS may be infeasible while LM-CDS is feasible π 4
π 4
1 si
1 0
2
si
0 2
15π 8
LM-PDS
15π 8
LM-CDS
Lifetime with LM-CDS is larger than with LM-PDS. A. Rossi, A. Singh, M. Sevaux (UBS)
Lifetime maximization for camera sensors
July 3 2013
15 / 22
Results n
LM-PDS
ϕ # opt.
50
100
200
400
2π 3 π 2 π 3 2π 3 π 2 π 3 2π 3 π 2 π 3 2π 3 π 2 π 3
LM-CDS
avg. LT
avg. CPU
5 5 5
2.94 2.91 2.65
0.14 0.10 0.17
5 5 4
5.97 5.49 4.82
4 1 0 0 0 0
# opt.
From LM-PDS to LM-CDS
avg. LT
avg. CPU
5 5 5
3.60 3.60 3.21
0.06 0.12 0.11
avg. LT +22.58% +23.75% +20.91%
avg. CPU −56.91% +18.06% −35.91%
248.13 87.46 336.69
5 4 2
6.60 6.35 5.71
1.98 0.72 0.36
+10.63% +15.62% +18.39%
−99.20% −97.63% −31.29%
12.93 11.30 9.42
14.26 6.05 dnf
4 3 1
13.82 13.01 10.95
6.09 15.24 11.03
+6.88% +15.13% +16.22%
−57.31% −55.16% -
25.90 20.68 16.19
dnf dnf dnf
1 0 0
29.58 24.58 18.38
1085.15 dnf dnf
+14.21% +18.87% +13.53%
-
LM-CDS allows for more than 10% longer lifetime than LM-PDS LM-CDS is not more difficult than LM-PDS A. Rossi, A. Singh, M. Sevaux (UBS)
Lifetime maximization for camera sensors
July 3 2013
16 / 22
Camera sensor networks CCD
LENS SHARP ZONE
Optical axis
Dn (s) s: focal distance A. Rossi, A. Singh, M. Sevaux (UBS)
s
Df (s)
f : focal length
H: Hyperfocal distance
Lifetime maximization for camera sensors
July 3 2013
17 / 22
Camera sensor networks CCD
LENS SHARP ZONE
Optical axis
Dn (s) s: focal distance A. Rossi, A. Singh, M. Sevaux (UBS)
s
Df (s)
f : focal length
H: Hyperfocal distance
Lifetime maximization for camera sensors
July 3 2013
17 / 22
Camera sensor networks CCD
LENS SHARP ZONE
Optical axis
Dn (s) f s: focal distance A. Rossi, A. Singh, M. Sevaux (UBS)
f : focal length
s
Df (s)
H: Hyperfocal distance
Lifetime maximization for camera sensors
July 3 2013
17 / 22
Camera sensor networks Camera sensor networks can be modeled by LM-CDS plus a specific constraint due to focal distance. s(H − f ) Dn (s) = is the near distance of acceptable sharpness H + s − 2f s(H − f ) Df (s) = is the far distance of acceptable sharpness H −s 100
Df (s)
SHARP ZONE Dn (s)
30
s
0 1
A. Rossi, A. Singh, M. Sevaux (UBS)
45
Lifetime maximization for camera sensors
July 3 2013
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Camera sensor networks: normalized pairs For all sensors, a pair (θ, s) is a working direction and a focal distance. A normalized pair is such that ◮ ◮ ◮
there exists k such that disti,k ≤ Rs and θ = θk Dn (s) ≤ disti,k ≤ Df (s) there exists k ′ such that disti,k ′ = Df (s)
1
1
3
1
3
4
4 2
si
si
A. Rossi, A. Singh, M. Sevaux (UBS)
3
4 2
Non-normalized
1
3 4 2 si
Normalized
Non-normalized
Lifetime maximization for camera sensors
2 si
Normalized
July 3 2013
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Camera sensor networks: non-dominated pairs A non-dominated pair is such that the set of targets it covers is not a strict subset of targets covered by another pair.
1 3 4 2 si
{1, 3}
A. Rossi, A. Singh, M. Sevaux (UBS)
Lifetime maximization for camera sensors
July 3 2013
20 / 22
Camera sensor networks: non-dominated pairs A non-dominated pair is such that the set of targets it covers is not a strict subset of targets covered by another pair.
1
1
3
3
4
4 2
si
2 si
{1, 3}
A. Rossi, A. Singh, M. Sevaux (UBS)
{2, 3}
Lifetime maximization for camera sensors
July 3 2013
20 / 22
Camera sensor networks: non-dominated pairs A non-dominated pair is such that the set of targets it covers is not a strict subset of targets covered by another pair.
1
1
3
1
3
4
3
4 2
si
4 2
si
{1, 3}
A. Rossi, A. Singh, M. Sevaux (UBS)
2 si
{2, 3}
Lifetime maximization for camera sensors
{1, 2, 3}
July 3 2013
20 / 22
Camera sensor networks: non-dominated pairs A non-dominated pair is such that the set of targets it covers is not a strict subset of targets covered by another pair.
1
1
3
1
3
4
3
4 2
4 2
si
si
{1, 3}
2 si
{2, 3}
{1, 2, 3}
1 3 4 2 si
{3, 4} A. Rossi, A. Singh, M. Sevaux (UBS)
Lifetime maximization for camera sensors
July 3 2013
20 / 22
Camera sensor networks: non-dominated pairs A non-dominated pair is such that the set of targets it covers is not a strict subset of targets covered by another pair.
1
1
3
1
3
4
3
4
4
2
2
si
si
{1, 3}
2 si
{2, 3}
1
{1, 2, 3}
1
3
3
4
4 2
si
2 si
{3, 4} A. Rossi, A. Singh, M. Sevaux (UBS)
{4} Lifetime maximization for camera sensors
{3, 4} July 3 2013
20 / 22
Camera sensor networks: non-dominated pairs A non-dominated pair is such that the set of targets it covers is not a strict subset of targets covered by another pair.
1
1
3
1
3
4
3
4
4
2
2
si
2
si
{1, 3}
si
{2, 3}
1
{1, 2, 3}
1
3
1
3
4
3
4 2
si
4 2
si
{3, 4} A. Rossi, A. Singh, M. Sevaux (UBS)
2 si
{4} Lifetime maximization for camera sensors
{3, 4} July 3 2013
20 / 22
Camera sensor networks: occlusion and obstacles Target k is occluded if there exists a target k ′ such that disti,k ′ < disti,k that prevents form fully seeing target k from si .
1
1
3
3
4
4 2
2
si
si
Target 3 is occluded by target 4
An obstacle hides target 1
Occlusions and obstacles make the problem easier as less targets can be covered by si .
A. Rossi, A. Singh, M. Sevaux (UBS)
Lifetime maximization for camera sensors
July 3 2013
21 / 22
Conclusions Lifetime maximization for directional sensors ◮ ◮
with predefined directions with contextual directions
Contextual directions makes much more sense than predefined directions Column generation algorithm enhanced with genetic algorithm Extension to focal distance for camera wireless sensors Efficient and flexible Matheuristic based on open source code Exact approach that can be used as a heuristic Camera wireless sensors with zoom (angle ϕ is variable) Toward more realistic consumption models
A. Rossi, A. Singh, M. Sevaux (UBS)
Lifetime maximization for camera sensors
July 3 2013
22 / 22