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Sensor Data. 한국기술교육대학교 민준기. Sensor Data Management. Wireless Sensor Network Limited Energy Power Limited Computing Power Sensor Data Management Navie Approach Each Sensor sends data to the base station Do data processing at the base station Problem - PowerPoint PPT Presentation
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Sensor Data
한국기술교육대학교 민준기
Wireless Sensor Network◦ Limited Energy Power◦ Limited Computing Power
Sensor Data Management◦ Navie Approach
Each Sensor sends data to the base station Do data processing at the base station
◦ Problem Each sensor waste its energy quickly in order to send its read-
ing continuously◦ Minimize Energy Consumption◦ In-Network Processing
Sensor Data Management
Data Aggregation
Data Gathering Query Processing
Major Research Topics
TAG (Tiny Aggregation)◦ In-Network Aggregation◦ Tree Routing Based
◦ Simple Approach◦ Cost for Median is very high
Aggregation(1/5)
2
4 3
5 3 2 2
Sum(2,12, 7)
Sum(4,5,3) Sum(3,2,2)
Q-Digest[2]◦ Capture the distribution of sensor data approximately◦ Digest property
count(v) <= floor(n/k) (except leaf node) count(v)+count(vp)+count(vs) >= floor(n/k) (except root node), where v is a node, vp is the parent of v, vs is the sibling of v.n is the number of data, k is compression parameterσ is the range of data
◦ Size of q-Digest <= 3k Each Sensor build q-Digest Parent node
◦ Merges q-Digests of Children◦ Compression
Aggregation(2/5 )
compression
Quantile Query◦ Find value whose rank in n values is qn, where q (0,1)
If q = 0.5, find median<[1,8],1> <[5,6], 2> <[7,8], 2> <[3,3],4> <[4,4], 6>Sorting in increasing right end point <[3,3],4> <[4,4], 6> <[5,6], 2> <[7,8], 2> <[1,8],1> <[4,4],6> exceed 0.5*15= 7.5Thus, 4 is an estimated median
Aggregation(3/5 )
Multiple Aggregation◦ Equivalence Class Reduction[3]
Q = {q1 = {1+2+3}, q2 ={1+2}, q3 = {3}} Equivalent class = set of sensors supports same
query set EC1 = {1,2} , EC2 = {3} Bit Vector EC1 = [1,1,0]T, EC2 = [1,0,1]T
EC1 EC2Q1 1 1 basisQ2 1 0 x v1 = {1+2} 1 0 x v1Q3 0 1 v2 = {3} 0 1 v2
Aggregation(4/5 )
Multiple Aggregation◦ Segmentation Based Method[4]
Dynamic routing, Not tree routing Segment == equivalent class A sensor sends data to a node including same segment as possible STG vs STS
Node 6 can send data to node 5 and 7, in case, node 6 sends data to node 7 STG : node 4 sends data for q2 (=4, 7, 8) and q1+q2 (=4,5)
node 1 receives 3 messages ( from node 2 - 1 message, node 4- 2 messages) STS: multiple routing
node 4 sends data for q2 (=4,5,6,7) to node 1 and q1(=4,5) to node 2 node 1 receives 2 messages
Aggregation(5/5)
In-network aggregation provides a great opportunity for reducing the communication overhead
Since a single aggregated value represents the overall sensing field, it may be insuffi-cient to analysis the correlation among sub-regions of the sensor field
Sensor Data Gathering◦ Exact Data Gathering waste Energy◦ Solution reduce the number of transmission
Gathering(1/8 )
Basic Approach◦ Temporal Suppression
A node does not transmit a value if it has not change since last reported
◦ Spatial Suppression A node suppresses it value if it is identical to those of
its neighboring Approximate Gathering
◦ Sensor readings have errors intrinsically◦ Sensor readings have strong correlations
Gathering(2/8 )
Approximate Data Gathering◦ Each Sensor has a tool to estimate future value◦ The base Station also keep tools
If a sensor does not send data estimation correct If a sensor sends data estimation incorrect
Update tools of the sensor and the basestation
◦ Model Based BBQ[5] KEN[6] PAQ[7]
◦ Filter Based Dual Kalman[9]
◦ Compression Based Wavelet, DFT, SBR[8]etc. A collection of readings of a sensor is transmitted periodically
Gathering(3/8)
Model Based Approach◦ Linear Regression
Xt+1 = aXt+b◦ BBQ, KEN
Multivariate Gaussian model Probability density function: P(X1, X2, X3, …, Xn)
Xi: random variable for sensor readings
Gathering (4/8 )
Approximate Gathering◦ PAQ
Linear Regression and Gaussian model require much time to construct correct model, and much data
AutoRegression(3) model A data Vt = mt+X(t) Vt - mt= X(t) X(t) = aX(t-1)+bX(t-2)+cX(t-3)+b(w)N(0,1) mt is a mean of V to time t, a,b,c is real constants,
b(w) is white noise Predictor P(t) = mt+ a(vt-1 – mt-1)+ b(vt-2 – mt-2) + c(vt-3
– mt-3)
Gathering(5/8)
PAQ◦ Lemma)Let e = v b(w), where v > 1. Then the actual
value at time t is contained in [P(t)-e , P(t)+e)] with probability at most 1/v2.
Proof) Chebychev inequality P(|vt- P(t)| > e) <= b(w)2/e2 = b(w)2/v2b(w)2 = 1/v2
◦ Generally v is 6 or 7◦ Using above Lemma, PAQ decide when it updates its
model.
Gathering(6/8)
-e -d d -e
Well fit Parital fit Outlier
Filter Based◦ Mode Based Approach requires much data to con-
struct models◦ Each node has the filter according to the last re-
ported sensor reading |Vnew – Vold| > e, the reading is sent to the base sta-
tion
Gathering(7/8)
Dual Kalman Filter◦ Base station has as many filters as the number of
sensors◦ Discrete Kalman Filter◦ Ex) moving object
State model : xt = vt-1*dt+xt-1
vt = vt-1 Measure model: z (real position)
z = [1 0]T x +vt
, where vt is measurement white Guassion noise
Gathering(8/8 )
project current state
Estimatenext state
Prediction stepComputeKalman gain
Updatesystem state
Correction step
Updateerror covariance
Initial state
Join Operation◦ An important operator◦ It allows to relate measurements taken at differ-
ent nodes.
Query Processing(1/6)
L R
General Join Plans[12,13]
Query Processing(2/6)
L R
Naive
L RSequential
L RCentroid
Optimal Join Location[14]◦ Weighted Fermat Problem
One wants to find the point with the property that the weighted sum of the distances from the point to the vertexes of a triangle is minimized.
Query Processing(3/6)
Synopsis Join[13]◦ Prunes non-candidate tuples and only joins candi-
date tuples◦ Preliminary Join
Eliminate non-candidate tuples
◦ Final Join
Query Processing(4/6)
TPSJ [10]◦ Preprocessing: Query Decomposition
Query Q
Decomposed Queries Q1 Q2
Page 21
Query Processing(5/6)
TPSJ◦ Fist phase
Query Q1 execute◦ Second phase
Query Q2 is executed with the injecting of R1 into the network
Page 22
Query Processing(6/6)
Sensor◦ Light weight◦ Wireless
Sensor Data Management◦ Reduce Energy consumption
In-network Processing Aggregation Gathering Query Processing
Conclusion
[1] S. Madden et.al., “TAG: Aggregation Service for Ad-Hoc Sensor Networks”, OSDI, 2002 [2] N. Shrivastava et.al., “Medians and Beyond: New Aggregation Techniques for Sensor Networks,”
ACM Sensys 2004 [3] N. Trigoni et.al., “Multi-Query Optimization for Sensor Networks” DCOSS 2005 [4]N. Trigoni, et.al., "Routing and Processing Multiple Aggregate Queries in Sensor Networks,“ ACM
SenSys, 2006. [5] A. Deshpande et.al., "Model-Driven Data Acquisition in Sensor Networks,“ VLDB, 2004. [6] D. Chu et.al., "Approximate Data Collection in Sensor Networks using Probabilistic Models,“
ICDE, 2006 [7] D. Tulone et. al., “PAQ: Time Series Forecasting For Approximate Query Answering In Sensor
Networks,” European Conf. Wireless Sensor Networks, 2006 [8] A. Deligiannakis et.al., “Compressing Historical Information in Sensor Networks,” ACM SIGMOD
2004 [9] A. Jain et.al., “Adaptive Stream Resource Management Using Kalman Filters,” ACM SIGMOD 2004 [10] X. Yang et.al., “In-Network Execution of Monitoring Queries in Sensor Networks,” ACM SIGMOD
2007. [11]M. Stern et.al., “Towards Efficient Processing of Gneral-Purpose Joins in Sensor Networks,” ICDE
2009. [12]A. Pandit et.al, “ Communication-Efficient Implementation of Range-Joins in Sensor Networks,”
International Conference on Database Systems for Advanced Applications (DASFAA), 2006 [13] H. Yu et.al, “In-Network Join Processing for Sensor Networks,” APWeb 2006. [14] A. Coman et.al, “On Join Location in Sensor Networks,” MDM 2007.
Reference