Processing audio signals for presence detection

Patent metadata

Field	Value
Publication number	US-11402499-B1
Application number	US-202017015795-A
Country	US
Kind code	B1
Filing date	Sep 9, 2020
Priority date	Aug 29, 2018
Publication date	Aug 2, 2022
Grant date	Aug 2, 2022

Abstract

This disclosure describes presence-detection devices that detect movement of a person by emitting ultrasonic signals into an environment, and characterizing the change in the frequency, or the Doppler shift, of the reflections of the ultrasonic signals off the person caused by the movement of the person. The techniques include downsampling the audio signals from the carrier frequency range down to a frequency range with a center frequency around 0 Hz. A filter is applied to attenuate signals around 0 Hz and below (or above), such as the emitted signals. In addition to removing the emitted signals, the negative side (or positive side) of the audio signals are removed, but the Doppler shift is still represented in the remaining portion of the audio signals. By removing a portion of the audio signals, the amount of processing required to detect the Doppler shift in the reflections of the ultrasonic signals is reduced.

First claim

What is claimed is:

1. A presence-detection device comprising:
a microphone;
a loudspeaker;
one or more processors; and
one or more computer-readable media storing computer-executable instructions that, when executed by the one or more processors, cause the one or more processors to:
cause the loudspeaker to emit an ultrasonic signal at a carrier frequency into an environment of the presence-detection device, the carrier frequency being in a first frequency range of 20 kilo-hertz (kHz) to about 96 kHz;
generate, at least partly using the microphone, an analog signal representing the ultrasonic signal and a reflection signal corresponding to a reflection of the ultrasonic signal off an object in the environment, the analog signal representing the reflection signal at a first frequency that is different than the carrier frequency;
downmodulate the analog signal to a second frequency range of between 0 kHz and 2 kHz;
attenuate, using a high-pass filter having a cutoff frequency of 0 Hz to about 12 Hz, a portion of the analog signal that represents the ultrasonic signal;
determine, at least partly using a Fourier transform algorithm, a logarithmic transform algorithm, and the analog signal, feature data corresponding to the reflection signal; and
determine, based at least in part on the feature data, that the object is in motion.

2. The presence-detection device of claim 1 , comprising further computer-executable instructions that, when executed, cause the one or more processors to:
cause the loudspeaker to emit, over a period of time, ultrasonic sweep signals into the environment, each ultrasonic sweep signal of the ultrasonic sweep signals having a frequency within a third frequency range of between 20 kHz and 96 kHz;
generate, at least partly using the microphone or another microphone of the presence-detection device, first data representing the ultrasonic sweep signal;
determine a first signal-to-noise (SNR) ratio for a fourth frequency range within the third frequency range;
determine a second SNR ratio for a fifth frequency range within the third frequency range, the fifth frequency range being different than the fourth frequency range;
determine that the first SNR ratio is greater than the second SNR ratio; and
configure the loudspeaker to emit the ultrasonic signal at the carrier frequency that is within the fourth frequency range.

3. The presence-detection device of claim 1 , comprising further computer-executable instructions that, when executed, cause the one or more processors to:
prior to attenuating the portion of the analog signal, downsampling the analog signal at a rate of about 2 kHz.

4. A computing device comprising:
a loudspeaker;
a microphone;
one or more processors; and
one or more computer-readable media storing computer-executable instructions that, when executed by the one or more processors, cause the one or more processors to:
cause the loudspeaker to emit an ultrasonic signal into an environment;
receive a reflected signal, corresponding to the ultrasonic signal, at the microphone, the reflected signal originating at an object in the environment;
generate, at least partly using the microphone, a first signal having a first frequency, the first signal having a first portion representing the reflected signal and a second portion representing the ultrasonic signal;
downmodulate the first signal to a second frequency, the second frequency having a value between 0 kHz and 2 kHz;
subsequent to downmodulating the first signal, attenuate the second portion using a high-pass filter with a cutoff frequency corresponding to a frequency range associated with the second portion to generate a second signal;
determine, based at least in part on the second first signal, feature data representing a frequency characteristic of the reflected signal; and
determine, based at least in part on the feature data, that the object is in motion.

5. The computing device of claim 4 , wherein the cutoff frequency is in a range of substantially 0 Hz to substantially 20 Hz.

6. The computing device of claim 4 , wherein the first frequency has a value between 20 kilo-hertz (kHz) and 96 kHz.

7. The computing device of claim 4 , comprising further computer-executable instructions that, when executed, cause the one or more processors to:
cause the loudspeaker to emit, over a period of time, ultrasonic sweep signals into the environment, each ultrasonic sweep signal of the ultrasonic sweep signals having a frequency within a first frequency range of between 20 kHz and 96 kHz;
generate, at least partly using the microphone or another microphone of the computing device, first data representing the ultrasonic sweep signal;
determine a first signal-to-noise (SNR) ratio for a second frequency range within the first frequency range;
determine a second SNR ratio for a third frequency range within the first frequency range, the third frequency range being different than the second frequency range;
determine that the first SNR ratio is greater than the second SNR ratio; and
configure the loudspeaker to emit the ultrasonic signal at a carrier frequency that is within the second frequency range.

8. The computing device of claim 7 , comprising further computer-executable instructions that, when executed, cause the one or more processors to, prior to the period of time:
cause the loudspeaker to output second audio data including a command for a user to at least one of:
move through the environment;
move the computing device from a first location in the environment to a second location in the environment; or
change an orientation of the computing device.

9. The computing device of claim 4 , wherein the loudspeaker emits the ultrasonic signal into the environment at a first carrier frequency, comprising further computer-executable instructions that, when executed, cause the one or more processors to:
determine that a signal-to-noise ratio (SNR) value for the first signal is less than a threshold SNR value; and
cause the loudspeaker to emit the ultrasonic signal into the environment according to a second carrier frequency.

10. The computing device of claim 4 , wherein the microphone comprises a first microphone, further comprising:
a second microphone; and
further computer-executable instructions that, when executed, cause the one or more processors to:
generate, at least partly using the second microphone, a third signal representing the reflected signal and the ultrasonic signal;
downmodulate the third signal from a third frequency to a fourth frequency that is in the second frequency range;

attenuate a second portion of the third signal that represents the ultrasonic signal;
determine, based at least in part on the third signal, second feature data representing a second frequency characteristic of the reflected signal; and
determine, based at least in part on the feature data and the second feature data, a direction associated with the motion of the object.

11. The computing device of claim 4 , comprising further computer-executable instructions that, when executed, cause the one or more processors to:
apply a Fourier transform algorithm to the second signal; and
determine magnitude data and phase data corresponding to the reflected signal,
wherein to determine that the object is in motion is based at least in part on the magnitude data.

12. A method comprising:
causing a loudspeaker of a computing device to emit, over a period of time, an ultrasonic sweep signal into an environment of the computing device, the ultrasonic sweep signal being emitted at a plurality of different frequencies in a frequency range during the period

Assignees

• Amazon Tech Inc

Inventors

• Kamath Koteshwara Krishna
• Pruthi Tarun
• Li Ke

Classifications

• G01S15/588

  measuring the velocity vector · CPC title

• G01S15/523

  for presence detection (burglar, theft or intruder alarms G08B13/00, e.g. G08B13/16) · CPC title

• G01S7/539

  using analysis of echo signal for target characterisation; Target signature; Target cross-section · CPC title

• G06F3/011

  Arrangements for interaction with the human body, e.g. for user immersion in virtual reality (blind teaching G09B21/00) · CPC title

• H04R1/406

  microphones · CPC title