FILA: FINE-GRAINED INDOOR LOCALIZATION
Kaishun Wu, Jiang Xiao, Youwen Yi, Min Gao, and Lionel M. NiINFOCOM 2012
- Sowhat 2012.5.21
OUTLINE Introduction
System Design
Evaluation
Discussion
Conclusion
OUTLINE Introduction
System Design
Evaluation
Discussion
Conclusion
MOTIVATION WiFi-based indoor localization RSSI range-based localization
Multipath Variance of RSSIs – 5dB in 1 min at immobile receiver
Capable to eliminate multipath effect
OBJECTIVE
An alternative metric to RSSIStabl
e
OUTLINE Introduction
System Design
Evaluation
Discussion
Conclusion
FOUNDATION OF FILA
OFDM
CSI
Orthogonal Frequency Division Multiplexing
Channel State Information
OFDM Multicarrier modulation scheme
for wideband wireless communication Modulate data on multiple subcarriers in different
frequencies Transmit simultaneously
CSI Channel state/status information Fine-grained value from the PHY layer1. Describe how a signal propagate from TX to RX2. Represent combined effect of
scattering, fading and power decay with distance
Channel properties of each subcarrier
Amplitude Phase
SYSTEM ARCHITECTURE
CSI Processing Calibration
Location Determinatio
n
CSI PROCESSINGTIME-DOMAIN MULTIPATH MITIGATION 802.11n bandwidth ~40MHz > coherence
bandwidth resolvable reflections
1. IFFT – channel response in frequency time domain
2. Filter –keep 1st clustertruncation threshold = 50% of 1st peak
value3. FFT – channel response in time frequency
domain
CSI Processing Calibration
Location Determinatio
n
CSI PROCESSINGFREQUENCY-DOMAIN FADING COMPENSATION Prob. of
simultaneous deep fading occurring on multiple uncorrelated fading envelopes> deep fading occurring on a single freq. system
∵ channel bandwidth of 802.11n > coherence bandwidth∴ freq.-selective fading across all subcarriers uncorrelated
Reduce the variance in CSIs owing to small scale factors
Weighted average
CSI Processing Calibration
Location Determinatio
n
CALIBRATION Relationship between CSIeff and distance
σ : environment factor@TX, gain of baseband to RF band@RX, gain of RF band to basebandantenna gain
n : path loss fading exponent Fast training algorithm
1. 2 anchors for training2. Another anchor for testing
CSI Processing Calibration
Location Determinatio
n
LOCATION DETERMINATION1. APs’ coordinate info. from network layer2. Distance between AP/object
Effective CSI Refined radio propagation model
Trilateration!
CSI Processing Calibration
Location Determinatio
n
OUTLINE Introduction
System Design
Evaluation
Discussion
Conclusion
HARDWARE CONFIGURATION AP :
TP-LINK TL-WR941ND router @ 2.4~2.4835GHz
Receiver: HP laptop with 2.4GHz dual-core CPU
Intel WiFi Link 5300 802.11n NICsModified driver to collecting CSI values from
NICsPlaced on a plastic cart
EXPERIMENTAL SCENARIOS1. Chamber
3m x 4m Ideal free space indoor environment
(only LOS signal exist without multipath reflections)
2. Research laboratory 5m x 8m 3 APs Weekday afternoon
(students seating or walking around)
EXPERIMENTAL SCENARIOS3. Lecture theatre
20m x 20m
4. Corridor 32.5m x 10m Cover corridors, rooms and cubicles Impact of the absence of LOS APs
ROBUSTNESS OF THE REFINED MODAL
TEMPORAL STABILITY OF CSI
DISTANCE DETERMINATION ACCURACY Chamber
Research laboratoryLecture theatre
10 different locations
Positions with serious multipath effect –Accuracy: FILA > RSSI-based by 10 times
Mean distance error
LOCALIZATION ACCURACY IN SINGLE ROOM Research laboratory
Lecture theatre
90% - 1m/1.8m ; median - 0.45m/1.2m
LOCALIZATION ACCURACY IN MULTIPLE ROOMS Corridor 6 APs in multiple rooms Experiment procedure
Offline trainingFix the position of the object at reference nodes collect APs’coordinates and CSI
Moving @ 1m/sCollect 20 CSIs and RSSIs at each position
Robust, median = 1.2m
LATENCY Latency = calibration + determination phase Calibration
Data collectionAP transmit message every 0.8msCollect 20 CSIs20 * 0.8 = 16ms
Calibration processing = 2ms Determination
IFFT, FFT with wireless NICs= ignorable Signal processing + trilateration = 2ms
Total: 16ms + 2ms + 2ms = 20ms
OUTLINE Introduction
System Design
Evaluation
Discussion
Conclusion
DISCUSSION CSI + fingerprint-based method
more accurate localization
Leverage available multiple APs to improve accuracy
Implement FILA on smart phone
OUTLINE Introduction
System Design
Evaluation
Discussion
Conclusion
CONCLUSION Design and implement FILA
CSI with OFDM system
Compared to RSSI-Based in different scenarios Capable to deal with multipath effect
(time domain processing) Stable (freq. domain processing)
Disadvantage Unclear descriptions Comparison of single room/multiple room
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