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CILoS: A CDMA Indoor L li ti S tLocalization System
Waqas ur Rehman, Eyal de Lara, Stefan Saroiu
Motivation
People spend most of their time indoorsp pGPS does not work indoors
Emergency responseSocial-Mobile ?
?? ??
NavigationMobile GamesAdvertising ?
????? ?
Fingerprinting – Building a radio mapAP1: -41 AP2: -54
AP4: -35AP5: -64
AP3: -92AP5: 64AP6: -72
AP1: -41 AP2: -54AP3: -92
Fingerprinting – K Nearest Neighbors
AP1: -40
Current Fingerprint
AP1: 40 AP2: -56AP3: -83
Signal Fingerprinting Approaches
802.11802.11GSM Signal strength
CDMAPower adaptation to accommodate network loadPower adaptation to accommodate network load
High temporal variations in signal strength Use signal delayUse signal delay
5
Signal Strength vs. Signal Delay Variations
CDMA Networks
Base stations share the same spectral bandwidthBase stations are tightly synchronized with GPSBase stations cooperate to transmit pilot signal
32768 symbols64
7
CDMA Networks
Base stations share the same spectral bandwidthBase stations are tightly synchronized with GPSBase stations cooperate to transmit pilot signal
PN offset
8
PN offset
Key idea: Fingerprint PN offsets
Data Collection
Condor CDMA scannerCondor CDMA scannerRecorded signal delay and strength over all channels in
DowntownSuburb
6 channels in downtown4 channels in suburb
9
Average Visible PNs
Interference limits # of visible base stationsWid fi i t i i lti lWide fingerprints require scanning multiple frequency bands
Localization Algorithms
Simple AlgorithmsSimple Algorithms1 ChannelAll ChannelAll Channel
Feature Selection Algorithms
11
Localization Error
161820 1 Channel
All ChannelsFeature Selection
121416
met
ers)
Feature Selection
68
10
Erro
r (m
024
0Downtown Suburb
Wide fingerprints helpWide fingerprints helpCareful PN selection critical
Localization Error CDF (Downtown)
Comparison with WiFi and GSM
910 WiFi
GSM
678
ers)
CDMA
456
ror (
met
e
23Er
r
01
All Sources Feature Selection
Floor Level Localization100
%)
60
80
ctio
ns (%
40
60
ful P
redi
20
Succ
essf
0WiFi GSM CDMA
S
Conclusions
Signal delay is a reliable metric for fingerprinting
Temporal stability
Spatial variability
CIL S hi di f 5 tCILoS achieves median accuracy of 5 meters
Wide signal fingerprints critical to accuracyWide signal fingerprints critical to accuracy
Feature selection really helps
16
y p
Future Works
Get it to work on commodity cell phoneGet it to work on commodity cell phoneRequires
Access to PN offsetsAccess to PN offsetsScan multiple frequency bands
17
