Omid Abari Deepak Vasisht, Dina Katabi, Anantha Chandrakasan An E-Toll Transponder Network for Smart Cities

Electronic Toll Transponders 80% of the cars in US have them Some states are making it mandatory

Opportunities Localization

Opportunities Adjust traffic-light timing Smart street-parking Detect red-light runner One infrastructure for many smart services

Challenge: No MAC to Prevent Collision Physical Isolation Interference Wireless query One car responds Wireless query All cars respond at the same time What can we do?

I don't care 'Cause I've never been so high Follow me to the dark Let me take you past our satellites

Caraoke A system that delivers smart services using existing e-toll transponders despite interference Software-Hardware solution: – Count cars – Localize cars – Decode transponders Built and evaluated on our campus streets with existing e-toll transponders

Count cars: How to count despite interference? Localize cars Decode transponders

Counting Despite Interference Time-Domain Freq-Domain Carrier Data Spike

Counting Despite Interference Time-Domain Freq-Domain Carrier Data Spike Caraoke can count transponders despite interference Toll transponders have difference in their carrier frequency

Count cars Localize cars: How to localize despite interference? Decode transponders

Localizing Transponders Localization requires knowing the channel How to extract channels in the presence of interference?

Localizing Transponder Time-Domain Freq-Domain Spike Use the channel to find the Angle-of-Arrival

Localizing Transponder

Cars are always on the road plane Intersect spatial angle with road plane Hyperbola Intersects hyperbolas across multiple readers to find the exact location of the car

Count cars Localize cars Decode transponders: How to decode despite interference?

Solution: Coherent Combining Real Imag

Solution: Coherent Combining Real Imag

Solution: Coherent Combining Real Imag ++= Caraoke uses channel information to combine responses coherently and decode the ID

Custom Hardware Design Self-Sustaining – Harvest Solar Energy

Custom Hardware Design Self-Sustaining – Harvest Solar Energy Low-Cost – Replace TX chain with simple PLL Power: 9mW; Cost: $40

Experimental Results

Evaluation MIT campus- four streets Caraoke readers were placed on 12.5-feet poles Standard E-ZPass transponders on the cars

Accuracy of Counting Transponders Higher accuracy and significantly lower cost than camera-based systems [R.L., JEI’13; J.M. Urbana‘08 ]

Accuracy of Localizing Transponders Caraoke enables enough accuracy to detect occupied versus available parking spots

Speed Detection Accuracy Caraoke detects the speed to within 8%

Required Time for Decoding Caraoke enables real-time smart city services

Related Work Wireless Interference – They require changing transmitter or leverage intrinsic asynchrony in protocols (S. G. Sigcomm’12, J. W. Sigcomm’08, etc.) Automated Payment – They require a gate and physical isolation (McDonald’s drive-through) Smart Parking – They require sensors on parking spots or Wi-Fi devices in cars (Street Line, S. M. MobiSys’10, S. N. Mobicom’13, etc.)

Conclusion A system for delivering smart services using existing e-toll transponders Can count, localize and decode transponders in the presence of interference We built it into a small PCB

Omid Abari Deepak Vasisht, Dina Katabi, Anantha Chandrakasan An E-Toll Transponder Network for Smart Cities