AirTrack: L ocating N on-WiFi Interferers using Commodity WiFi Hardware
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Transcript of AirTrack: L ocating N on-WiFi Interferers using Commodity WiFi Hardware
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AirTrack: Locating Non-WiFi Interferers using Commodity WiFi Hardware
Ashish Patro, Shravan Rayanchu, Suman Banerjee University of Wisconsin-Madison
Sep 20, 2011 / Mobicom 2011 SRC
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Talk Outline• How non-WiFi devices affect WiFi traffic?
• How to detect non-WiFi transmissions using “commodity” WiFi cards?
• How to physically locate these non-WiFi devices?
• Evaluation
Sep 20, 2011 / Mobicom 2011 SRC
Some Non-WiFi devices
Analog Cordless Phone
Video Camera Microwave OvenZigBee
FHSS Cordless Phone
Bluetooth SCO/ACL Game Controllers Audio
Transmitter
Narrowband/High-duty devices Broadband devices
Frequency-hopping devices
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Problem
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Non-WiFi devices exist in 2.4GHz/5.8GHz spectrum and impact WiFi performance
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Scenario Access Point
GOALS• How do we detect and locate these non-WiFi devices?• How to do this in real time using commodity WiFi cards?
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Why use commodity WiFi cards?• Software-only solution that works on top of the cards
• Can easily deploy this software solution in current WLANs
• No additional expensive hardware needed• e.g. spectrum analyzers
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What do commodity WiFi cards provide?
Wireless Card
WiFi Packets
Packet Capture
FFT Samples
Non-WiFi devices
Sub-carrier energy
samples
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-73, -65, -72, …
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Talk Outline• How non-WiFi devices affect WiFi traffic?
• How to detect non-WiFi transmissions using “commodity” WiFi cards?
• How to physically locate these non-WiFi devices?
• Evaluation
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How to detect non-WiFi devices?
Capture energy
samplesPo
we
r
Frequency TimingProperties
Duration
Bandwidth
“Tagged Pulses”
e.g., Bluetooth
“Classify”Pulses
Extract ``Feature
s’’ Identify
``Pulses”
Sniffer
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Talk Outline• How non-WiFi devices affect WiFi traffic?
• How to detect non-WiFi transmissions using “commodity” WiFi cards?
• How to physically locate these non-WiFi devices?
• Evaluation
Sep 20, 2011 / Mobicom 2011 SRC
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AirTrack Overview Access Point(with Sniffer)
Culprit Device Locations:
1. Analogphone @ Room 1042. Analogphone @ Room 1103. FHSS Phone @ Room 1054. ZigBee @ Room 108
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Device Localization
S1 S2
S3
S1: -40dbS2: -70dbS3: -75db
Use RSSI vector to localize each device
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How to create RSSI vectors?
Same pulse caught by multiple sniffers
FHSS Pulse
S1
S2
S3
S1: -70dbS2: -60dbS3: -45db
S1: -70db
S2: -60db
S1: -45db
“Merge”
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Merge pulses using matching start/end times and center frequency + bandwidth
Synchronize the APs
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A problem…
FHSS Device 1
FHSS Device 2
We can’t decode non-WiFi pulses
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How many devices?Which pulse belongs to what device?
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How to segregate pulses?
FHSS phoneMerged Pulses
FHSS Pulse Cluster 2
FHSS Pulse Cluster 1• Cluster using• RSSI vector• Timing properties
• Algorithms• DBSCAN• EM + k-Means
Clustering process segregates pulses belonging to different device instances
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Each “Pulse Cluster” is a device
FHSS Pulse Cluster 2
FHSS Pulse Cluster 1
S1: -40dbS2: -70dbS3: -75db
S1: -70dbS2: -60dbS3: -45db
FHSS Device 1
FHSS Device 2
Each cluster is represented by an RSSI Vector
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Putting it together…
Synchronize access points
“Tagged Pulses”
Access Point (with Sniffer)
AirTrack
Locate non-WiFi devices using multiple Sniffers
Localize each device
(Pulse Cluster)
Merge + Cluster pulses
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Putting it together…
Synchronize access points
“Tagged Pulses”
Access Point (with Sniffer)
AirTrack
Locate non-WiFi devices using multiple sniffers
Localize each device
(Pulse Cluster)
Merge + Cluster pulses
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Localization algorithms• AP locations are known
• Tested various algorithms with different requirements
Algorithm Input Parameters
Fingerprint Known Fingerprints
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Localization algorithms• AP locations are known
• Tested various algorithms with different requirements
Algorithm Input Parameters
Fingerprint Known Fingerprints
RSS Triangulation Device Transmit Power + Propagation Model
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Localization algorithms• AP locations are known
• Tested various algorithms with different requirements
Algorithm Input Parameters
Fingerprint Known Fingerprints
RSS Triangulation Device Transmit Power + Propagation Model
Pairwise AP Propagation Model
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Pairwise AP algorithm
Pairwise AP: S0,S2 Pairwise AP: S3,S5
We can localize without knowing device transmit power
FHSS Cordless Phone
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Talk Outline• How non-WiFi devices affect WiFi traffic?
• How to detect non-WiFi transmissions using “commodity” WiFi cards?
• How to physically locate these non-WiFi devices?
• Evaluation
Sep 20, 2011 / Mobicom 2011 SRC
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Clustering results
FHSS Phones Microwave Oven FHSS Phones
Time domain clustering RSS domain clustering
• Each cluster is a unique active device• AirTrack can differentiate between multiple devices
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Localization Accuracy
Localization error < 6 metres for 80% of the locations
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Summary
• Presented a system for real-time localization of non-WiFi devices using commodity WiFi cards.
• Localization works in the presence of multiple device instances.
• Don’t require to know the device transmit power for localization.
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Demo
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Thank You!!
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