Authors: Omid Abari, Deepak Vasisht, Dina Katabi and Anantha Chandrakasan
Link to the public review
What we can do today with the current e-toll transponders is limited.
This is because only one transponder at a time can be read by an RFID reader since the
transponders do not have any MAC protocol. If we can overcome this barrier, a lot of applications
can come out. Cities can deploy readers at traffic lights to spot cars that pass at red light,
estimate the crowdedness of intersections and the speeds of the cars (to detect violations). To achieve this, the authors proposed a networked system of e-toll transponders and readers, where
the RFID readers are enabled to work with collisions, without modifying the design of existing transponders.
The presenter explained that they exploit the carrier frequency offset (CFO) of the transponders. He explained that they looked at the collision in the frequency domain and observed spikes corresponding to the CFOs of the colliding transponders. He also explained that they can get the number of transponders by counting the number of spikes.
They also can localize cars into their parking spots by exploiting the differences in CFOs and apply RF-based localization.
The presenter explained that decoding of IDs is also possible by combining multiple collisions in a way that boosts up the SNR of a target transponder above the others.
The presenter showed that Karaoke counts cars accurately with an average error of 2% and can localize cars into their parking spots with an error of only 4 degrees.
Number of car ids being correctly decoded increases as the number of cars increase.
Q: Do you expect millions of queries to the transponders? How long does the battery last?
A: Power consumption is really low and the number of queries do not matter.
Q: What if people take the transponders out, if they cheat or jam?
A: Vision is that the transponders will be mandatory. And these will be illegal actions.
Q: Is it not easy to spoof the system? Someone builds a system that creates spikes and makes the system think there are a lot of cars in a region?
A: This will be illegal.