V-Scope: An Opportunistic Wardriving Approach to Augmenting TV Whitespace Databases Tan Zhang, Suman Banerjee University of Wisconsin Madison 1Tan Zhang / V-Scope / Mobicom 2013 SRC

2 Spectrum Database Good Propagation Range Vacant TV Channels Up to 180MHz Spectrum About 2km Single Location Measurement Motivation Primary Users TV Whitespaces Channel Database Measurement Use wide-area measurements to quantify database performance

3Tan Zhang / V-Scope / Mobicom 2013 SRC Motivation Spectrum Sensors Measure 1,000,000 different locations over 150 square km at Madison, WI Measure 1,000,000 different locations over 150 square km at Madison, WI

Accuracy of Commercial Databases 4Tan Zhang / V-Scope / Mobicom 2013 SRC Device Under Protection TV0.1% Microphone0.02% Databases are efficient in protecting primary users

Accuracy of Commercial Databases 5Tan Zhang / V-Scope / Mobicom 2013 SRC Spectrum Waste in Protecting TV 42% Wasted Area Large Waste of Whitespace Spectrum

Accuracy of Commercial Databases 6Tan Zhang / V-Scope / Mobicom 2013 SRC Reservation duration is too coarse-grained Protection radius is too large Reservation duration is too coarse-grained Protection radius is too large Spectrum Waste in Protecting Microphone Spectrum Waste Reserved Locations for Microphones How to accurately determine whitespace channels? How to improve databases with measurements? How to accurately determine whitespace channels? How to improve databases with measurements?

V-Scope Architecture 7Tan Zhang / V-Scope / Mobicom 2013 SRC 2 TV -70dBm Occupied Wireless Gateway Loc2, TV, -70dBm Loc2, Occupied V-Scope Server Database

Challenge in Detecting Primary Signals Strong Signals (-60dBm) Weak Signals (-114dBm) Tan Zhang / V-Scope / Mobicom 2013 SRC 8 Where are the features? FCC requires to detect primary signal up to -114dBm TV MIC Pilot Tone

Key technique: narrowing capture bandwidth to reduce noise floor Zoom-in Detection Algorithm 9Tan Zhang / V-Scope / Mobicom 2013 SRC 20MHz 5MHz FFT bins Reduce noise floor by 4x

Zoom-in around potential features Zoom-in Detection Algorithm 10Tan Zhang / V-Scope / Mobicom 2013 SRC TV MIC Pilot Pilot Frequency Peak Frequency Zoom-in 12dB lower Achieve > 95% accuracy in detecting primary signals from -40dBm to -114dBm

Region Specific Model 11Tan Zhang / V-Scope / Mobicom 2013 SRC Improve any propagation model by fitting its parameters with measurements Global V-Scope TV Tower

Weighted Regression Fitting 12Tan Zhang / V-Scope / Mobicom 2013 SRC Large Prediction Error Measurement Use weighted regression to compensate density variation

Improvement in Predicting Whitespaces Use 80% measurements to fit a free-space model Use this model to predict whitespaces at other locations Use -114dBm threshold to determine TV whitespaces 13Tan Zhang / V-Scope / Mobicom 2013 SRC 4x Reduction Prediction Under Protection Commercial Database 0.1% V-Scope0.037%

Web Front-end 14Tan Zhang / V-Scope / Mobicom 2013 SRC

Conclusion Developed a system leveraging public vehicles to collect wide-area whitespace measurements. Commercial databases waste large amount of whitespaces. Developed a model refinement procedure that can effectively enhance databases. 15Tan Zhang / V-Scope / Mobicom 2013 SRC

Thanks a lot for your attention! Questions? Rock Star in winter, 2012

Back-up Slides 17Tan Zhang / V-Scope / Mobicom 2013 SRC

Weighted Regression Fitting 18Tan Zhang / V-Scope / Mobicom 2013 SRC Measurement Validation Error Capture measurement density

Power Estimation of Primary Signals 19Tan Zhang / V-Scope / Mobicom 2013 SRC Frequency Power fcfc bw

Issues with Amplification Strong TV signals saturates RF front-end of spectrum analyzers Amplification makes saturation worse 20Tan Zhang / V-Scope / Mobicom 2013 SRC “Ghost” spectrum pattern Saturation Area