1 compression and storage schemes in a sensor network with spatial and temporal coding techniques...
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Compression and Storage Schemes in a Sensor Network with Spatial and Temporal Coding TechniquesYou-Chiun Wang, Yao-Yu Hsieh, and Y
u-Chee Tseng
IEEE Vehicular Technology Conference, 2008
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Outline
Introduction Multi-resolution compression and storage
(MCS) framework Compression and storage schemes Implementation and experimental results Conclusions
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Introduction
The communication overhead will dominate sensor node’s energy consumption
Sensing data reported from sensor nodes often exhibit a certain degree of data correlation Spatial correlation Temporal correlation
People may query different resolutions of sensing data from a wireless sensor network
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Multi-resolution compression and storage (MCS) framework
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Compression and storage schemes Spatial compression scheme Temporal compression scheme Storage scheme
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Spatial compression scheme
Layer-1 compression Layer-i (i > 1) compression Decompression
Compression ratio: ( 0 ≦ γ < 1 )
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Layer-1 compression
A layer-1 processing node collects the sensing data from the sensor nodes in its block
M = (si,j)k×k
M =
28 27 28 29
29 28 28 29
30 29 28 29
29 29 28 28
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Layer-1 compression (2D-DCT) Two-dimensional discrete cosine transform (2
D-DCT) method 2D-DCT will compact those significant values
in the upper-left part of the transformed matrix
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Layer-1 compression (RZS)
A reduced zigzag scan (RZS) method is applied to translate M’ into an one dimensional array
k2×λ
λ = 1 −γ
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Layer-i (i > 1) compression
Reduce the length of array D (passed from the layer i−1) to λi × k2 elements
Layer-1
Layer-2
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Decompression
The sink recovers the corresponding array D to a two-dimensional matrix M’ = (ti,j)k×k
Adopt the inverse 2D-DCT method to transform M to a new matrix M’’ = (si,j)k×k
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Temporal compression scheme
The temporal compression scheme is performed by each sensor node
Users can specify a small update threshold δ to determine whether a node should transmit its data or not
δ= 2°C
S1,1= 28°C
Range: 28°C ± 2°C
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Storage scheme(1/2)
For a node i, we will store frames ft, ft−1, ft−3, ft−
7, · · · , and ft−2ni−1
+1
1 2 3
ft ft−1 ft−3
4 3 1
5 4 2
→
→
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Storage scheme(2/2)
fj has been stored in node i’s local memory, node I directly replies fj to the sink
j < t−2ni−1 +1, node i replies a fail message to the sink because fj is too old to be stored in node i
5 4 2
f3 = ?
(f4+f2)/2
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Implementation and experimental results We use the MICAz Motes as sensor nodes a
nd processing nodes Set the system parameters α = 4 and k = 2 We use this prototype to collect indoor tempe
ratures during 25 hours The compression ratio γ is set to 0.25 The update threshold δ is set to 0.2°C
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The total amount of message transmissions
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Average temperatures reported by the 16 nodes
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Conclusions
MCS provides multi-resolution data compression and storage in a wireless sensor network
MCS can effectively reduce message transmissions of sensor nodes
MCS framework not only significantly reduces the message transmissions but also preserves important characteristics of sensing reports
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Thank you!
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M
26 28 30
26 28 29
26 27 28
M’
77.9 118.5 126.7
110 167.4 172.9
109.8 161 166.5