Transcript ParkNet: Drive-by Sensing of Road

FILA:
FINE-GRAINED INDOOR
LOCALIZATION
Kaishun Wu, Jiang Xiao, Youwen Yi, Min Gao, and Lionel M. Ni
INFOCOM 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

OBJECTIVE
An alternative metric to RSSI
Capable to eliminate
multipath effect
Stabl
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 layer
1. Describe how a signal propagate from TX to RX
2. 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
Processing
Calibration
CSI PROCESSING
TIME-DOMAIN MULTIPATH MITIGATION

1.
2.
3.
Location
Determinatio
n
802.11n bandwidth ~40MHz > coherence bandwidth
 resolvable reflections
IFFT – channel response in frequency  time
domain
Filter –
keep 1st cluster
truncation threshold = 50% of 1st peak value
FFT – channel response in time  frequency
domain
CSI PROCESSING
FREQUENCY-DOMAIN FADING
COMPENSATION
CSI
Processing


Calibration
Location
Determinatio
n
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
CALIBRATION

Relationship between CSIeff and distance



σ : environment factor
@TX, gain of baseband to RF band
@RX, gain of RF band to baseband
antenna gain
n : path loss fading exponent
Fast training algorithm
1.
2.
2 anchors for training
Another anchor for testing
Location
Determinatio
n
CSI
Processing
Calibration
LOCATION DETERMINATION
1.
2.
APs’ coordinate info. from network layer
Distance between AP/object
Effective CSI
 Refined radio propagation model


Trilateration!
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 NICs
 Modified driver to collecting CSI values from
NICs
 Placed on a plastic cart
EXPERIMENTAL SCENARIOS
1.
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 SCENARIOS
3.
Lecture theatre

4.
20m x 20m
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 laboratory
Lecture 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 training
Fix the position of the object at reference nodes
 collect APs’coordinates and CSI
 Moving @ 1m/s
 Collect 20 CSIs and RSSIs at each position


Robust, median = 1.2m
LATENCY
Latency = calibration + determination phase
 Calibration

Data collection
AP transmit message every 0.8ms
Collect 20 CSIs
20 * 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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