Patent ID: 7010290

Claim:
A method of determining the distance between a portable wireless communication device and an RF equipped Point-of-Sale device based on propagation delay between a pulse code modulation (PCM) RF signal and an acoustic signal that are emitted from the portable wireless communication device and received by the RF equipped Point-of-Sale device, the method comprising: establishing an RF link between the portable wireless communication device and the RF equipped Point-of-Sale device; in the portable wireless communication device: creating a multi-tone acoustic signal in the form of PCM modulated first digital audio samples; transmitting the PCM modulated first digital audio samples via the RF link; converting the PCM modulated first digital audio samples to an analog audio waveform such that the analog audio waveform is the acoustic equivalent of the PCM modulated first digital audio samples; acoustically emitting the analog audio waveform via a loudspeaker; in the RF equipped Point-of-Sale device: receiving the PCM modulated first digital audio samples via the RF link; receiving the analog audio waveform via a microphone; converting the analog audio waveform to PCM modulated second digital audio samples; comparing the PCM modulated first digital audio samples against the PCM modulated second digital audio samples to determine if they match, and if the PCM modulated first digital audio samples match the PCM modulated second digital audio samples, then determining the distance between the portable wireless communication device and the RF equipped Point-of-Sale device based on the known speed of propagation of radio waves, the known speed of sound, and the time difference between the arrival of the PCM modulated first digital audio samples and the acoustic signal.