Method and System for Ultrasonic Signaling, Ranging and Location Tracking

• US 20140192622A1
• Filed: 01/10/2014
• Published: 07/10/2014
• Est. Priority Date: 01/10/2013
• Status: Active Grant

• Current Assignee: Carnegie Mellon University
• Original Assignee: Carnegie Mellon University
• Inventors: Rowe, Anthony, Lazik, Patrick
• Granted Patent: US 9,927,512 B2
• Time in Patent Office: Days
• US Class Current: 367/117
• CPC Class Codes: G01S 1/725 Marker, boundary, call-sign or like beacons transmitting signals not carrying directional information
• CPC Class Codes: G01S 1/753 Signal details
• CPC Class Codes: G01S 5/0036 of measured values, i.e. measurement on mobile and position calculation on base station
• CPC Class Codes: G01S 5/18 using ultrasonic, sonic, or infrasonic waves
• CPC Class Codes: G01S 5/28 by co-ordinating position lines of different shape, e.g. hyperbolic, circular, elliptical or radial

Abstract

An indoor ultrasonic location tracking system that can utilize standard audio speakers to provide indoor ranging information to modern mobile devices like smartphones and tablets. The method uses a communication scheme based on linearly increasing frequency modulated chirps in the audio bandwidth just above the human hearing frequency range where mobile devices are still sensitive. The method uses gradual frequency and amplitude changes that minimize human perceivable (psychoacoustic) artifacts derived from the non-ideal impulse response of audio speakers. Chirps also benefit from Pulse Compression, which improves ranging resolution and resilience to both Doppler shifts and multi-path propagation that plague indoor environments. The method supports the decoding of multiple unique identifier packets simultaneously. A Time-Difference-of-Arrival pseudo-ranging technique allows for localization without explicit synchronization with the broadcasting infrastructure. An alternate received signal strength indicator based localization technique allows less accurate localization at the benefit of sparser transmission infrastructure.

Claims

1. A method for locating a mobile device comprising the method steps of:

modulating an ultrasound signal with i. a transmitter identifier, ii. one or more symbols capable of Pulse Compression, and iii. a fade-in preceding each symbol of the one or more symbols and a fade-out following the each symbol of the one or more symbols or a fading function applied to the each symbol of the one or more symbols;

transmitting the modulated ultrasound signal;

receiving the modulated ultrasound signal;

demodulating the modulated ultrasound signal to form a demodulated ultrasound signal;

extracting the transmitter identifier from the demodulated ultrasound signal; and

determining the location of the mobile device based on the transmitter identifier.

2. The method according to claim 1, wherein the determining step comprises the step of looking up the transmitter identifier in a transmitter map to determine the location of the mobile device.

3. The method according to claim 1, wherein:

the step of modulating the ultrasonic signal further comprises modulating the ultrasound signal with i. a preamble capable of Pulse Compression, and ii either a fade-in preceding the preamble and a fade-out following the preamble or a fading function applied to the preamble;

the demodulating step comprises the step of matched filtering only the preamble to cross correlate the preamble with a preamble template to form the demodulated ultrasound signal;

extracting the preamble to characterize a transmission channel having characteristics; and

estimating a distance between the device and the transmitter based on the characteristics of the transmission channel.

4. The method according to claim 1, wherein the demodulating step comprises the step of matched filtering only the one or more symbols to cross correlate the one or more symbols with a symbols template to form the demodulated ultrasound signal.

5. The method according to claim 3, wherein the demodulating step comprises the step of matched filtering the preamble and the one or more symbols to cross correlate the preamble with a preamble template and the one or more symbols with a symbols template to form the demodulated ultrasound signal.

6. The method according to claim 1, wherein the demodulating step comprises the step of Fractional Fourier Analysis to form the demodulated ultrasound signal.

7. The method according to claim 1, wherein the demodulating step further comprises the step of Successive Interference Cancellation to form the demodulated ultrasound signal.

8. The method according to claim 1, wherein:

the step of extracting further comprises extracting a signal strength of the modulated ultrasound signal; and

the step of determining the location of the mobile device based on the signal strength.

9. The method according to claim 1, wherein the step of receiving the modulated ultrasound signal is performed by a plurality of mobile devices.

10. The method according to claim 1, wherein the step of receiving the modulated ultrasound signal is performed by a mobile device.

11. The method according to claim 1, wherein the step of transmitting the modulated ultrasound signal is performed by a plurality of mobile devices.

12. The method according to claim 11, further comprising:

a step of transferring the modulated ultrasonic signal and a receiver identifier to a processor for demodulation; and

the step of determining the location of the mobile device based on the transmitter identifier and the receiver identifier.

13. The method according to claim 1, wherein the step of transmitting the modulated ultrasound signal is performed by a mobile device.

14. The method according to claim 13, further comprising:

a step of transferring the modulated ultrasonic signal and a receiver identifier to a processor for demodulation; and

the step of determining the location of the mobile device based on the transmitter identifier and the receiver identifier.

15. A method for locating a mobile device comprising the method steps of:

providing a plurality transmitters, wherein each transmitter of the plurality transmitters has a transmitter identifier;

modulating an ultrasound signal with i. a transmitter identifier, ii. one or more symbols capable of Pulse Compression, and iii. a fade-in preceding each symbol of the one or more symbols and a fade-out following the each symbol of the one or more symbols or a fading function applied to the each symbol of the one or more symbols;

transmitting the modulated ultrasound signal from each transmitter of the plurality transmitters to form a plurality of modulated ultrasonic signals;

receiving the plurality of modulated ultrasound signals;

demodulating the plurality of modulated ultrasound signals to form a plurality of demodulated ultrasound signals;

extracting the transmitter identifiers from the plurality of demodulated ultrasound signals; and

determining the location of the mobile device based on the transmitter identifiers.

16. The method according to claim 15, wherein the determining step comprises the step of looking up the transmitter identifiers in a transmitter map to determine the location of the mobile device.

17. The method according to claim 15, wherein:

the step of modulating the ultrasonic signal further comprises modulating the ultrasound signal with i. a preamble capable of Pulse Compression, and ii either a fade-in preceding the preamble and a fade-out following the preamble or a fading function applied to the preamble;

the demodulating step comprises the step of matched filtering only the preamble to cross correlate the preamble with a preamble template to form the demodulated ultrasound signal;

extracting the preamble to characterize a transmission channel;

estimating a distance between the device and the transmitter based on the transmission channel; and

determining the location of the mobile device based on the transmission channel.

18. The method according to claim 15, wherein the demodulating step comprises the step of matched filtering only the one or more symbols to cross correlate the one or more symbols with a symbols template to form the demodulated ultrasound signal.

19. The method according to claim 18, wherein the demodulating step comprises the step of matched filtering the preamble and the one or more symbols to cross correlate the preamble with a preamble template and the one or more symbols with a symbols template to form the demodulated ultrasound signal.

20. The method according to claim 15, wherein the demodulating step comprises the step of Fractional Fourier Analysis to form the demodulated ultrasound signal.

21. The method according to claim 15, wherein the demodulating step further comprises the step of Successive Interference Cancellation to form the demodulated ultrasound signal.

22. The method according to claim 15, wherein:

the step of extracting further comprises extracting a signal strength of the modulated ultrasound signal; and

the step of determining the location of the mobile device based on the signal strength.

23. The method according to claim 15, wherein the step of receiving the modulated ultrasound signal is performed by a plurality of mobile devices.

24. The method according to claim 15, wherein the step of receiving the modulated ultrasound signal is performed by a mobile device.

25. The method according to claim 15, wherein the step of transmitting the modulated ultrasound signal is performed by a plurality of mobile devices.

26. The method according to claim 25, further comprising:

a step of transferring the modulated ultrasonic signal and a receiver identifier to a processor for demodulation; and

the step of determining the location of the mobile device based on the transmitter identifier and the receiver identifier.

27. The method according to claim 15, wherein the step of transmitting the modulated ultrasound signal is performed by a mobile device.

28. The method according to claim 27, further comprising:

a step of transferring the modulated ultrasonic signal and a receiver identifier to a processor for demodulation; and

the step of determining the location of the mobile device based on the transmitter identifier and the receiver identifier.

29. A method for locating a mobile device comprising the method steps of:

providing a plurality of transmitters, wherein each transmitter of the plurality transmitters has a transmitter identifier;

providing a mobile device;

triggering the mobile device to begin a recording at a constant rate;

modulating an ultrasound signal with i. a transmitter identifier, ii. one or more symbols capable of Pulse Compression, and iii. a fade-in preceding each symbol of the one or more symbols and a fade-out following the each symbol of the one or more symbols or a fading function applied to the each symbol of the one or more symbols;

simultaneously transmitting the modulated ultrasound signal from each transmitter of the plurality transmitters to form a plurality of modulated signals;

receiving the plurality of modulated ultrasound signals by the mobile device;

demodulating the plurality of modulated ultrasound signals to form a plurality of demodulated ultrasound signals, wherein the preamble of each demodulated ultrasound signal denotes time of arrival within the recording to determine relative times of arrival between each transmitter of the plurality of transmitters;

extracting the transmitter identifiers and the relative times of arrival;

pairing the transmitter identifiers with each of the relative times of arrival;

looking up the transmitter identifiers in a transmitter map to determine location of each transmitter of the plurality of transmitters;

determining time differences of arrival between the plurality of demodulated ultrasonic signals; and

determining location of the mobile device based on the time differences of arrival and the location each transmitter of the plurality of transmitters.

30. The method according to claim 29, wherein:

the step of modulating the ultrasonic signal further comprises modulating the ultrasound signal with i. a preamble capable of Pulse Compression, and ii either a fade-in preceding the preamble and a fade-out following the preamble or a fading function applied to the preamble; and

the demodulating step comprises the step of matched filtering only the preamble to cross correlate the preamble with a preamble template to form the demodulated ultrasound signal.

31. The method according to claim 29, wherein the demodulating step comprises the step of matched filtering only the one or more symbols to cross correlate the one or more symbols with a symbols template to form the demodulated ultrasound signal.

32. The method according to claim 30, wherein the demodulating step comprises the step of matched filtering the preamble and the one or more symbols to cross correlate the preamble with a preamble template and the one or more symbols with a symbols template to form the demodulated ultrasound signal.

33. The method according to claim 29, wherein the demodulating step comprises the step of Fractional Fourier Analysis to form the demodulated ultrasound signal.

34. The method according to claim 29, wherein the demodulating step further comprises the step of Successive Interference Cancellation to form the demodulated ultrasound signal.

35. The method according to claim 29, further comprising the step of providing a plurality of mobile devices.