SYSTEM AND METHOD FOR IMPLEMENTATION OF AN ECHO CANCELLER

• US 20030072439A1
• Filed: 01/27/2000
• Published: 04/17/2003
• Est. Priority Date: 01/27/2000
• Status: Active Grant

• Current Assignee: Qualcomm, Inc.
• Original Assignee: Qualcomm, Inc.
• Inventors: Gupta, Samir K.
• Granted Patent: US 6,606,382 B2
• Time in Patent Office: Days
• US Class Current: 379/406.05
• CPC Class Codes: H04M 9/082 using echo cancellers echo cancellers per se H04B3/23

Abstract

A system and method for canceling an echo signal. An input waveform is provided to an acoustic processor, and a determination is made whether the input waveform includes information representative of an echo signal. If the input waveform includes information representative of an echo signal, an output waveform is formed by attenuating a residual waveform with the acoustic processor. The residual waveform is attenuated by an attenuation factor that gradually changes from an initial attenuation value to a final attenuation value during the attenuation step.

A system and method for adjusting an acoustic signal from a muted state to an unmuted state by varying an attenuation factor applied to an acoustic signal by an acoustic processor. The acoustic signal is provided to an acoustic processor. An output waveform is formed from the acoustic processor by adjusting the attenuation factor from a muted state to a first attenuation value associated with the non-muted state. After the attenuation factor is adjusted to the first attenuation value, the output waveform is formed by gradually changing the attenuation factor from the first attenuation value to a second attenuation value. The input waveform is attenuated by a smaller amount when the second attenuation value is applied to the acoustic signal than when the first attenuation value is applied to the acoustic signal.

Claims

1. A method of canceling an echo signal, comprising the steps of:

(A) providing an input waveform to an acoustic processor;

(B) determining whether said input waveform includes information representative of said echo signal; and

(C) forming an output waveform by attenuating a residual waveform with said acoustic processor if said input waveform includes information representative of said echo signal;

wherein said residual waveform is attenuated by an attenuation factor that gradually changes from an initial attenuation value to a final attenuation value during said attenuation step.

2. The method of claim 1, wherein said attenuation factor decreases linearly from said initial attenuation value to said final attenuation value during said attenuation step.

3. The method of claim 2, further comprising the step of:

(D) after said residual waveform is attenuated by said final attenuation amount during said attenuation step, muting said output waveform.

4. The method of claim 3, wherein said initial attenuation value is equal to 0 db.

5. The method of claim 3, wherein said attenuation factor is decreased from said initial attenuation value to said final attenuation value in equal stepwise increments during said attenuation step.

6. The method of claim 5, wherein said attenuation factor is decreased from said initial attenuation value to said final attenuation value at a rate of 1 db every 5 ms during said attenuation step.

7. The method of claim 5, wherein step (C) further comprises the steps of calculating an attenuation threshold and comparing said attenuation threshold to said attenuation factor, and wherein said attenuation factor is decreased by said stepwise increments until said attenuation factor is less than said attenuation threshold.

8. The method of claim 7, wherein said input waveform is representative of a signal that has been modulated in accordance with code-division-multiple-access (CDMA) modulation.

9. The method of claim 8, wherein said attenuation threshold (K_up) is calculated in accordance with the following equation:

K_up=α

((M*2³²*bnS*G_pred)/(12*E))^0.5

wherein E represents an energy estimate of said input waveform over M samples, bnS is a background noise scale value for a uniformly distributed random noise generator, and G_pred is the prediction gain of a LPC shaping filter associated with said CDMA modulation.

10. The method of claim 1, wherein said echo signal is representative of an acoustic echo resulting from coupling of a microphone and a speaker located at a position associated with a far-end talker.

11. The method of claim 1, wherein said echo signal corresponds to bursty noise supplied into a transmission channel at a position associated with a far-end talker.

12. A method for adjusting an acoustic signal from a muted state to an unmuted state by varying an attenuation factor applied to an acoustic signal by an acoustic processor, comprising the steps of:

(A) providing said acoustic signal to an acoustic processor;

(B) forming an output waveform from said acoustic processor by adjusting said attenuation factor from the muted state to a first attenuation value associated with said non-muted state;

(C) after said attenuation factor is adjusted to said first attenuation value in step (B), forming said output waveform by gradually changing said attenuation factor from said first attenuation value to a second attenuation value;

wherein said input waveform is attenuated by a smaller amount when said second attenuation value is applied to said acoustic signal than when said first attenuation value is applied to said acoustic signal.

13. The method of claim 12, wherein said attenuation factor is increased from said first attenuation value to said second attenuation value in equal stepwise increments during step (C).

14. The method of claim 13, wherein said attenuation factor is increased from said first attenuation value to said second attenuation value at a rate of 1 db every 5 ms during said step (C).

15. The method of claim 13, wherein step (C) further comprises the steps of comparing said attenuation factor to an attenuation threshold, and wherein said attenuation factor is increased by said stepwise increments in step (C) until said attenuation factor is greater than or equal to said attenuation threshold.

16. The method of claim 15, wherein said attenuation threshold is equal to 0 db.

17. The method of claim 12, wherein said input waveform is representative of a signal that has been modulated in accordance with code-division-multiple-access (CDMA) modulation.

18. The method of claim 17, wherein said second attenuation value (K_down) is calculated in accordance with the following equation:

K_down=B((M*2³²*bnS*G_pred)/(12*E))^0.5

wherein E represents an energy estimate of said input waveform over M samples, bnS is a background noise scale value for a uniformly distributed random noise generator, and G_pred is the prediction gain of a LPC shaping filter associated with said CDMA modulation.

19. The method of claim 12, wherein said echo signal is representative of an acoustic blip occurring at a position associated with a near-end talker.

20. A system for canceling an echo signal, comprising:

(A) an acoustic processor that receives an input waveform;

(B) an adaptive filter that determines whether said input waveform includes information representative of said echo signal; and

(C) said acoustic processor including a variable attentuator that forms an output waveform by attentuating a residual waveform if said input waveform includes information representative of said echo signal;

wherein said variable attenuator said residual waveform by an attentuation factor that gradually changes from an initial attentuation value to a final attenuation value if said input waveform includes information representative of said echo signal.

21. A system for adjusting an acoustic signal from a muted state to an unmuted state by varying an attenuation factor applied to an acoustic signal by an acoustic processor, comprising:

(A) an acoustic processor that receives an acoustic signal;

(B) said acoustic processor including a variable attenuator that forms an output waveform by first adjusting said attenuation factor from the muted state to a first attenuation value associated with said non-muted state and, after said attenuation factor is adjusted to said first attenuation value, forming said output waveform by gradually changing said attenuation factor from said first attenuation value to a second attenuation value;

wherein said input waveform is attenuated by a smaller amount when said second attenuation value is applied to said acoustic signal than when said first attenuation value is applied to said acoustic signal.