adaptive cleaning for rfid data streams. rfid: radio frequency identification
DESCRIPTION
RFID data is dirty A simple experiment: 2 RFID-enabled shelves 10 static tags 5 mobile tagsTRANSCRIPT
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Adaptive Cleaning for Adaptive Cleaning for RFID Data StreamsRFID Data Streams
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RFID: Radio Frequency RFID: Radio Frequency IDentificationIDentification
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RFID data is dirtyRFID data is dirtyShelf 0 Shelf 1
RFIDReaders
StaticTags
Mobile Tags
15ft1.5ft
3ft9ft
3ft
3ft
3ft
A simple experiment:•2 RFID-enabled shelves•10 static tags•5 mobile tags
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RFID Data CleaningRFID Data Cleaning
Time
Raw readings
Smoothed output
• RFID data has many dropped readings• Typically, use a smoothing filter to
interpolateSELECT distinct tag_idFROM RFID_stream [RANGE ‘5 sec’]GROUP BY tag_id
Smoothing Filter
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Smoothing filter Smoothing filter
Middleware
Clean RFID
Completeness
Tag dynamics
Read all tags in range
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RFID Data CleaningRFID Data Cleaning
Time
Raw readings
Smoothed output
• RFID data has many dropped readings• Typically, use a smoothing filter to
interpolateSELECT distinct tag_idFROM RFID_stream [RANGE ‘5 sec’]GROUP BY tag_idBut, how to set the size
of the window?
Smoothing Filter
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Window Size for RFID Window Size for RFID SmoothingSmoothing
Fido moving Fido resting
Small windowRealityRaw readings
Large window
Need to balance completeness vs. capturing tag movement
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Truly Declarative Truly Declarative SmoothingSmoothing
• Problem: window size non-declarative Application wants a clean stream
of data Window size is how to get it
• Solution: adapt the window size in response to data
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RFIDRFID
Epoch TagID ReadRate0 1 .90 2 .60 3 .3
Tag 1
Tag 2
Tag 3
Tag 4
Antenna & readerTags
E1 E2 E3 E4 E5 E6 E7 E8 E9E0
Read Cycle (Epoch)
(For Alien readers)
Tag List
1. Interrogation cycle2. Epoch
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Controlled condition real condition
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SMURFSMURF• Statistical Smoothing for Unreliable RFID
Data• Adapts window based on statistical
properties• Mechanisms for:
• Per-tag and multi-tag cleaning
Multi-tagCleaning
SMURFPer-tag
Cleaning
raw RFID streams
cleanedcount readings
cleanedper-tag readings
Application(s) Application(s)
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Per-Tag Smoothing: Model and Per-Tag Smoothing: Model and BackgroundBackground
• Epoch t, Tag population Nt
• pi,t: Per epoch sampling prob.Response count of tag i per epoch
(total interrogation cycle)
Epoch TagID ReadRate0 1 .90 2 .60 3 .3
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• Smoothing window size wi epoch • Per epoch sampling prob: pi
• Number of successful observations of tag i Binominal distribution B(wi,pi)
Per-Tag Smoothing: Model and Per-Tag Smoothing: Model and BackgroundBackground
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Per-Tag Smoothing: Model and Per-Tag Smoothing: Model and BackgroundBackground
• Use a binomial sampling model
Time (epochs)
pi
1
0
Smoothing Window
wi Bernoulli trials
piavg
Si
(Read rate of tag i)
E1 E2 E3 E4 E5 E6 E7 E8 E9E0
Set of epochs where tag i can be seen
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• We want to ensure that there are enough epochs in Wi such that tag i is observed (if it exists within the reader’s range) Completeness
Per-Tag Smoothing: CompletenessPer-Tag Smoothing: Completeness
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Per-Tag Smoothing: Per-Tag Smoothing: CompletenessCompleteness
• If the tag is there, read it with high probability
Want a large window
pi
1
0
Reading with a low pi
Expand the window
Time (epochs)E1 E2 E3 E4 E5 E6 E7 E8 E9E0
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Per-Tag Smoothing: CompletenessPer-Tag Smoothing: Completeness
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Per-Tag Smoothing: Per-Tag Smoothing: CompletenessCompleteness
Expected epochs needed to read
With probability 1-
Desired window size for tag i
1ln*1
avgi
ip
w
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Per-Tag Smoothing: Per-Tag Smoothing: TransitionsTransitions• Detect transitions as statistically
significant changes in the data
pi
1
0
Statistically significant difference Flag a transition and
shrink the window
The tag has likely left by this point
Time (epochs)E1 E2 E3 E4 E5 E6 E7 E8 E9E0
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• Significant difference between mean observed sample size Si and expected size
• Find outlier (2)
Number of successful epochs in a window
Si
Mean
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Per-Tag Smoothing: Per-Tag Smoothing: TransitionsTransitions
# expected readings Is the difference
“statistically significant”?# observed
readings
)1(**2|*||| avgi
avgii
avgiii ppwpwS
•Statistically significantStatistically significant
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Algorithm Algorithm
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SMURF in ActionSMURF in ActionFido moving Fido resting
SMURF
Experiments with real and simulated data show similar results
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Normal sliding window Completeness Transition