System and method of determining short range distance between RF equipped devices

• US 20030036378A1
• Filed: 08/17/2001
• Published: 02/20/2003
• Est. Priority Date: 08/17/2001
• Status: Active Grant

• Current Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Original Assignee: Ericsson, Inc. (Telefonaktiebolaget LM Ericsson)
• Inventors: Dent, Paul W.
• Granted Patent: US 7,010,290 B2
• Time in Patent Office: Days
• US Class Current: 455/414.1
• CPC Class Codes: G01S 11/16 using difference in transit time between electrical and acoustic signals
• CPC Class Codes: G06Q 20/327 Short range or proximity payments by means of M-devices

Abstract

A first, transmitting, device transmits a digitized data message using a short range radio link followed by digital data representing a digitized acoustic signal, such as a tone. Simultaneously, or with a predetermined time delay, the transmitting device emits an acoustic version of the same signal using an acoustic transducer such as a loudspeaker. A second, receiving, device receives the data message and the digitized acoustic signal via the short range radio link and receives the acoustic version of the signal via a microphone, which converts the acoustic signal to a second digitized version of the acoustic signal. Digital signal processing circuits then correlate the second digitized signal received acoustically with the digitized acoustic signal received over the short range radio link to determine a time difference of arrival. The time difference is corrected for any predetermined delay between the radio and the acoustic signal emissions at the transmitter and predetermined processing delays in the receiver. Once the time delay is determined, the receiving device can determine its distance from the transmitting device using the difference between the speed of sound and the speed of radio propagation.

Claims

1. A method of automatically determining the distance between a first RF equipped device and a second RF equipped device comprising:

establishing a radio link between said first RF equipped device and said second RF equipped device;

in said first RF equipped device;

creating an acoustic waveform in the form of first digital audio samples;

transmitting said first digital audio samples via said radio link;

converting said first digital audio samples to an analog audio waveform;

emitting said analog audio waveform as an acoustic signal via a loudspeaker;

in said second RF equipped device;

receiving said first digital audio samples via said radio link;

receiving said acoustic signal via a microphone;

converting said received acoustic signal to second digital audio samples; and

determining the time difference between the arrival of said first digital audio samples and said acoustic signal; and

determining the distance between said first RF equipped device and said second RF equipped device based on the known speed of propagation of radio waves, the known speed of sound, and the time difference between the arrival of said first digital audio samples and said acoustic signal.

2. The method of claim 1 further comprising comparing said first digital audio samples against said second digital audio samples to determine if they match, and if said first digital audio samples match said second digital audio samples, then performing said determining the time difference between the arrival of said first digital audio samples and said acoustic signal.

3. The method of claim 1 wherein said radio link is Bluetooth™

.

4. The method of claim 1 further comprising terminating an exchange of further radio messages between said first and second RF equipped devices if the distance determined is greater than a threshold value.

5. The method of claim 1 further comprising terminating the performance of a financial transaction if the distance determined is greater than a threshold value.

6. In an RF equipped device, a method of automatically determining the distance between said RF equipped device and a second RF equipped device, said second RF equipped device capable of emitting an acoustic signal and transmitting a radio signal, said method comprising:

receiving first digital audio samples via a radio link;

receiving an acoustic signal via a microphone;

converting said received acoustic signal to second digital audio samples; and

determining the time difference between the arrival of said first digital audio samples and said acoustic signal; and

determining the distance from said second RF equipped device based on the known speed of propagation of radio waves, the known speed of sound, and the time difference between the arrival of said first digital audio samples and said acoustic signal.

7. The method of claim 6 further comprising comparing said first digital audio samples against said second digital audio samples to determine if they match, and if said first digital audio samples match said second digital audio samples, then performing said determining the time difference between the arrival of said first digital audio samples and said acoustic signal.

8. The method of claim 6 wherein said radio link is Bluetooth™

.

9. An RF equipped device capable of automatically determining the distance between itself and a second RF equipped device wherein said second RF equipped device emits an acoustic signal and transmits a corresponding radio signal, said RF equipped device comprising:

an RF module that receives first digital audio samples via a radio link;

a microphone that receives an acoustic signal;

a CODEC that converts said received acoustic signal to second digital audio samples; and

a processor that;

determines the time difference between the arrival of said first digital audio samples and said acoustic signal; and

determines the distance from said second RF equipped device based on the known speed of propagation of radio waves, the known speed of sound, and the time difference between the arrival of said first digital audio samples and said acoustic signal.

10. The RF equipped device of claim 9 wherein said processor further compares said first digital audio samples against said second digital audio samples to determine if they match.

11. The RF equipped device of claim 9 wherein said radio link is Bluetooth™

.

12. In an RF equipped device, a computer program product that automatically determines the distance between itself and a second RF equipped device, said second RF equipped device capable of emitting an acoustic signal and transmitting a radio signal, the computer program product having a medium with a computer program embodied thereon, the computer program product comprising:

computer program code for receiving first digital audio samples via a radio link;

computer program code for receiving an acoustic signal via a microphone;

computer program code for converting said received acoustic signal to second digital audio samples; and

computer program code for determining the time difference between the arrival of said first digital audio samples and said acoustic signal; and

computer program code for determining the distance from said second RF equipped device based on the known speed of propagation of radio waves, the known speed of sound, and the time difference between the arrival of said first digital audio samples and said acoustic signal.

13. The computer program product of claim 12 further comprising computer program code for comparing said first digital audio samples against said second digital audio samples to determine if they match, and if said first digital audio samples match said second digital audio samples, then determining the time difference between the arrival of said first digital audio samples and said acoustic signal.

14. The computer program product of claim 12 wherein said radio link is Bluetooth™

.