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CILoS: A CDMA Indoor Localization System
Waqas ur Rehman, Eyal de Lara, Stefan Saroiu
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Motivation
People spend most of their time indoors GPS does not work indoors
Emergency response Social-Mobile Navigation Mobile Games Advertising
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Fingerprinting – Building a radio map
AP1: -41 AP2: -54AP3: -92
AP4: -35AP5: -64AP6: -72
AP1: -41 AP2: -54AP3: -92
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Fingerprinting – K Nearest Neighbors
Current Fingerprint
AP1: -40 AP2: -56AP3: -83
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Signal Fingerprinting Approaches 802.11 GSM
CDMA Power adaptation to accommodate network load
High temporal variations in signal strength Use signal delay
Signal strength
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Signal Strength vs. Signal Delay Variations
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CDMA Networks
Base stations share the same spectral bandwidth Base stations are tightly synchronized with GPS Base stations cooperate to transmit pilot signal
32768 symbols64
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CDMA Networks
Base stations share the same spectral bandwidth Base stations are tightly synchronized with GPS Base stations cooperate to transmit pilot signal
PN offset
Key idea: Fingerprint PN offsets
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Data Collection
Condor CDMA scanner Recorded signal delay
and strength over all channels in Downtown Suburb
6 channels in downtown 4 channels in suburb
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Average Visible PNs
Interference limits # of visible base stations Wide fingerprints require scanning multiple
frequency bands
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Localization Algorithms
Simple Algorithms 1 Channel All Channel
Feature Selection Algorithms
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Localization Error
Downtown Suburb0
2
4
6
8
10
12
14
16
18
20 1 ChannelAll ChannelsFeature Selection
Err
or
(me
ters
)
Wide fingerprints help Careful PN selection critical
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Localization Error CDF (Downtown)
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Comparison with WiFi and GSM
All Sources Feature Selection0
1
2
3
4
5
6
7
8
9
10WiFi GSM
CDMA
Err
or
(me
ters
)
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Floor Level Localization
WiFi GSM CDMA0
20
40
60
80
100S
uc
ce
ss
ful
Pre
dic
tio
ns
(%
)
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Conclusions
Signal delay is a reliable metric for fingerprinting
Temporal stability
Spatial variability
CILoS achieves median accuracy of 5 meters
Wide signal fingerprints critical to accuracy
Feature selection really helps
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Future Works
Get it to work on commodity cell phone Requires
Access to PN offsets Scan multiple frequency bands
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Question?
www.cs.toronto.edu/~delara