Near-Field Communication (NFC) enables low data rate, bidirectional communication between devices within close proximity, usually within a few centimeters, in a peer-to-peer manner. The key advantage of NFC is that it eliminates the need for cumbersome network configuration efforts required to set up a communication channel using alternatives such as Bluetooth or WiFi. This is due to its inherent property of association by physical proximity – if two devices can communicate using NFC, then it implies that they must be co-located. As an example, using an NFC enabled mobile phone, a user can make payments by simply bringing the phone close to a reader at the checkout counter, without having to first identify the reader or connect to it. Several NFC-based applications have been proposed or demonstrated, e.g., contact-less payment, access control, social networking, ticketing, museum services, etc. In many cases, NFC is used to automatically initiate and set up a high data rate communication channel such as WiFi or Bluetooth.
Almost all mobile phones have a speaker and a microphone. Dhwani implements an OFDM based acoustic Software Defined Radio (SDR) to transmit data. Acoustic NFC has to overcome several challenges inherent in the Acoustic domain,
- Frequency selective speaker/microphone characteristics due to electromechanical conversion
- Large multipath or echos
- Ambient noise sources
Dhwani solves these problems in order to make acoustic NFC communication practical.
The basic idea of SecureJam is that the transmitter jams the incoming signal by transmitting a Psuedo Noise sequence in such a way that information theoretically, an eavesdropper cannot extract any information from the jammed signal. However, knowing the jamming signal, the receiver can perform self-interference cancelation and subtract the effects of its own jamming signal. Self-interference cancelation is especially difficult in the acoustic domain due to multipath and frequency selectivity. SecureJam leverages a property unique to acoustic communication — the fact that most of the transformation between the transmitted signal and the received signal is in fact due to the static speaker and microphone characteristics.