Caraoke: An E-Toll Transponder Network for Smart Cities

Electronic toll collection transponders, e.g., E-ZPass, are a widely-used wireless technology. About 70 % to 89 % of the cars in US have these devices, and some states plan to make them mandatory. As wireless devices however, they lack a basic function: a MAC protocol that prevents colli-sions. Hence, today, they can be queried only with direc-tional antennas in isolated spots. However, if one could in-teract with e-toll transponders anywhere in the city despite collisions, it would enable many smart applications. For ex-ample, the city can query the transponders to estimate the ve-hicle flow at every intersection. It can also localize the cars using their wireless signals, and detect those that run a red-light. The same infrastructure can also deliver smart street-parking, where a user parks anywhere on the street, the city localizes his car, and automatically charges his account. This paper presents Caraoke, a networked system for de-livering smart services using e-toll transponders. Our design operates with existing unmodified transponders, allowing for applications that communicate with, localize, and count transponders, despite wireless collisions. To do so, Caraoke exploits the structure of the transponders ’ signal and its prop-erties in the frequency domain. We built Caraoke reader into a small PCB that harvests solar energy and can be easily de-ployed on street lamps. We also evaluated Caraoke on four streets on our campus and demonstrated its capabilities