Dhwani

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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.

NFC faces two key challenges today,

• Low adoption due to low levels of hardware penetration – 3-5% penetration in phones worldwide today. Only 5% Point of Sale terminals are NFC enabled.
• Lack of security – No security in Phy-Mac layers. NFC is perceived as difficult to intercept due to close range.  However, eavesdropping has been demonstrated using off-the-shelf  devices from 1 m away.

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.