WO1991020149A1 - Echo canceller with adaptive voice switch attenuation - Google Patents
Echo canceller with adaptive voice switch attenuation Download PDFInfo
- Publication number
- WO1991020149A1 WO1991020149A1 PCT/EP1991/001130 EP9101130W WO9120149A1 WO 1991020149 A1 WO1991020149 A1 WO 1991020149A1 EP 9101130 W EP9101130 W EP 9101130W WO 9120149 A1 WO9120149 A1 WO 9120149A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- attenuation
- path
- energy
- echocanceller
- attenuator
- Prior art date
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M9/00—Arrangements for interconnection not involving centralised switching
- H04M9/08—Two-way loud-speaking telephone systems with means for conditioning the signal, e.g. for suppressing echoes for one or both directions of traffic
- H04M9/082—Two-way loud-speaking telephone systems with means for conditioning the signal, e.g. for suppressing echoes for one or both directions of traffic using echo cancellers
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B3/00—Line transmission systems
- H04B3/02—Details
- H04B3/20—Reducing echo effects or singing; Opening or closing transmitting path; Conditioning for transmission in one direction or the other
- H04B3/23—Reducing echo effects or singing; Opening or closing transmitting path; Conditioning for transmission in one direction or the other using a replica of transmitted signal in the time domain, e.g. echo cancellers
- H04B3/234—Reducing echo effects or singing; Opening or closing transmitting path; Conditioning for transmission in one direction or the other using a replica of transmitted signal in the time domain, e.g. echo cancellers using double talk detection
Definitions
- the ERLE monitor routine is run in real time, measuring the desired attenuation for each sample of digital speech - i.e. every 125 ⁇ s.
- the energy measurement used for calculating ERLE is down-converted 20 times, effectivly providing a calculation every 20 samples.
Landscapes
- Engineering & Computer Science (AREA)
- Signal Processing (AREA)
- Computer Networks & Wireless Communication (AREA)
- Cable Transmission Systems, Equalization Of Radio And Reduction Of Echo (AREA)
Abstract
This invention relates to an echo canceller (EC) such as for use in a full duplex radio. The echo canceller comprises: an output path (10) for outputting desired signals; an input path (12) for receiving desired signals together with undesired echos from the output path; an adaptive filter (14) for filtering signals on the input path; measuring means (18) for measuring echo attenuation by the adaptive filter; a variable attenuator (15) for attenuating signals on the input path; control means (16) for controlling the variable attenuator to provide a degree of attenuation dependent on the difference between attenuation measured by the measuring means and a predetermined desired attenuation. The echo canceller is particularly useful in any system having large transmission delays like GSM cellular radio telephone system.
Description
ECHO CANCELLER WITH ADAPTIVE VOICE SWITCH ATTENUATION
Background of the Invention
5 This invention relates to an echo canceller (EC) such as for use in a full duplex radio. The echo canceller is particularly useful in any system having large transmission delays like the GSM system.
10 Summary of the Prior Art
A conventional echo canceller calculates a pseudo-echo by convolution (filter operation) with the received signal and the tap coefficients of the adaptive filter (ADF) . The 15 ADF will converge to an estimate of the echopath. This pseudo-echo is subtracted from the actual echo, thereby cancelling the echo. The ADF is usually a N tap FIR filter, where N*T equals the duration of the echo and T denotes the time between samples. In order to eliminate the echo quickly,
20 the ADF must converge to the actual impulse response.
The GSM cellular radio system calls for standards in cancellation of echos not reached in previous systems. The echopath can either be of acoustic nature caused by the coupling between a microphone and loudspeaker in handsfree
25 operation or if can be of electrical nature due to imperfections in the 4 to 2 wire hybrids in the fixed network. Due to the inherent transmission delay in GSM (total loop delay around 200 msec) the typical Echo Return Loss (ERL) required will be 56 dB compared to a typical ERL
30 of 20 dB in conventional cellular systems. As the echo tends to become more annoying as the transmission delay increases, the performance of the EC unit is very important to obtain high conversation quality. * An echo canceller designed to the meet the requirements
35 of the GSM cellular radio system is described in UK Patent Application No. 9000525.7, filed on 10th January 1990.
The convergence speed of the ADF is often too low to meet the required performance.
Summary of the Invention
According to the present invention, an echo canceller is provided comprising: an adaptive filter, measuring means for measuring echo attenuation by the adaptive filter, a variable attenuator and control means for controlling the variable attenuator to provide a degree of attenuation dependent on the difference between attenuation measured by the measuring means and a predetermined desired attenuation.
Preferably the attenuator provides up to half of the total desired attenuation. Preferably the attenuator provides no more than 10 to 15dB of maximum total attenuation.
It is preferred that the variable attenuator provides low or negligible attenuation when there is at less than 3 dB of signal on the output path (A energy) above noise level on that path. Preferably the attenuator responds to a signal on the input path, (B energy) to provide a relatively low level of attenuation at a high level of such a signal and higher attenuation at a lower level of such a signal. Preferably, on opening in response to a signal on the input path (b energy) the attenuator opens at a controlled rate. Such a rate may be one millisecond for full opening.
At a low level of input signal (B energy) and a low level of output signal (A energy) the attenuator may be arranged to open slowly - eg taking 200 milliseconds to open when there is no B energy and when A energy is less than 3 dB over noise.
The invention has the effect of compensating the slow convergence of the ADF by introducing a voice switch mode whenever the performance of the ADF is insufficient. A specific embodiment will be described in which the voice switch does not suffer from problems of speech clipping and background noise switching.
Brief Description of the Drawings
Fig. 1 shows an echocanceller with adaptive voice switch attenuation in accordance with the invention. Fig. 2 shows a flow diagram of the ERLE computation routine.
Fig. 3 shows a flow diagram of the voice attenuation routine.
Description of the Preferred Embodiment
Referring to Fig. 1, there is shown an output power 10 having a loudspeaker 11 and an input path 12 having a microphone 13. The loudspeaker and microphone are typically mounted on the interior of a vehicle. The echocanceller comprises a fullband adaptive filter 14, the details of which are known in the art (reference is made, for example, to Y.Itoh et al, "An acoustic echo canceller for teleconference" proceedings of ICC-85,1985 ppl498-1502) or a sub-band adaptive filter. The echocanceller further comprises a variable attenuator 15 and a control unit 16 having computation means 17. and 18. Measurements of energy on the input path are taken at points B and C before and after adaptive filtering and these are entered into computation means 18.
The computation means 18 in effect measures the attenuation achieved by the ADF 14. The control unit 16 controls the attenuator 15 to augment the measured attenuation by the necessary amount to bring the total attenuation to 30 dB. The measured attenuation is only augmented when there is energy on the output path 10. This is measured by computation means 17.
The computation of the ADF attenuation is described in Fig. 2. Computation means 18 computes the ERLE factor (which is an estimate of the current echocanceller performance and is computed by the formula:
ERLE = (C energy - C noise) / (B energy - C noise)
The flow diagram of Fig. 2 shows an example of an ERLE factor computation, although this can be computed in various ways. Referring to that figure, step 21 determines whether the ADF has, in fact, provided any attenuation, and if so, step 22 computes the factor ERLE'. In step 23, no further action is taken if ERLE' is greater than 50 dB. Otherwise, ERLE' is filtered in a two-order IIR filter, with fc = 0.1 hz (step
24) . The output of this filter is ERLE. In steps 25, 26 and 27, ERLE is decremented or incremented by a predetermined amount, according to whether it is greater or less than ERLE' respectively. Provided ERLE is greater than 0 this provides the ERLE factor. If ERLE is less than 0, it is set to 0 in step 29. After the ERLE computation routine of Fig. 2, the control unit 16 performs a set voice attenuation routine, described in Fig. 3. If ERLE is greater than 30 dB, as determined by step 31, no additional attenuation is required and step 32 sets the attenuation of the attenuator 15 at a minimum limit, which is 3 dB. Otherwise, if ERLE is not greater than 30 dB, step 33 sets the attenuation at 30 dB minus ERLE. If the maximum attenuation as set in step 33 is greater than 15 dB (step 34), that maximum attenuation is capped at 15 dB in step 35. Steps 34 and 35 ensure that the attenuator 15 does not in fact provide more than 15 dB.
Steps 36 and 37 set a lower limit on the attenuation of the attenuator 15 at 3 dB.
The B energy and C energy measurements are absolute values of samples at point B and C in Fig. 1, respectively, filtered through a two-order IRR filter, with cutoff frequency 50 Hz. The B energy and C energy values represent the summation of speech and noise at these respective points and will follow the envelope of speech on the input path 12. Values for C noise are absolute values of samples at point c, filtered through a two-order IRR filter with cutoff frequency 0.1 hz. Thus the measurement of C noise is an estimate of the noise floor at point C.
The voice switch attenuation of the attenuator 15 is set to keep the total attenuation/cancellation at the required value, ie 30 dB, and the voice controller attenuator (or voice switch) will in this particular case by limited by 3 and 15 dB, although other limits for this range could be chosen. Thus the attenuation can vary continously between 3 and 15 dB, thereby avoiding any annoying effect of changing from pure ADF attenuation to a voice switched mode. Such annoying effect could be experienced if the circuit switched between pure ADF at ERLE factors greater than 30dB and pure switched mode at ERLE factors below 30dB.
Continuously varying attenuation is achieved because the ERLE monitor routine is run in real time, measuring the desired attenuation for each sample of digital speech - i.e. every 125μs. Preferably, the energy measurement used for calculating ERLE is down-converted 20 times, effectivly providing a calculation every 20 samples.
Claims
1. An echocanceller comprising: an output path (12) for outputting desired signals; an input path (10) for receiving desired signals together with undesired echos from the output path; and an adaptive filter (14) for filtering signals on the input path characterized by: measuring means (18) for measuring echo attenuation by the adaptive filter; a variable attenuator (15) for attenuating signals on the input path; control means (16) for controlling the variable attenuator to provide a degree of attenuation dependent on the difference between attenuation measured by the measuring means and a predetermined desired attenuation.
2. An echocanceller according to claim 1, further comprising: means (17) for measuring energy on the output path; and means for controlling the variable attenuator to provide greater attenuation of signals on the input path at a high level of energy on the output path than at a low level.
3. An echocanceller according to claim 1 or 2, wherein no more than 15 dB of total attenuation is provided by the attenuator.
4. An echocanceller according to claim 1 or 2, wherein the variable attenuator provides low or negligible attenuation when there is at least a predetermined level of signal on the output path above noise level on that path.
,
5. An echocanceller according to any one of the preceding claims, wherein the attenuator responds to signals on the input path (B energy) to provide a relatively low level of attenuation at a high level of such a signal and higher attenuation at a lower level of such a signal.
6. An echocanceller according to any one of the preceding claims, wherein the attenuator is arranged to open at a controlled rate in response to a signal on the input path (B energy) .
7. An echocanceller according to claim 6 wherein said rate is a fast rate and wherein the attenuator is arranged to open at a slow rate at a low level of input signal (B energy) and a low level of output signal (A energy) .
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB9013751A GB2245459A (en) | 1990-06-20 | 1990-06-20 | Echo canceller with adaptive voice switch attenuation |
GB9013751.4 | 1990-06-20 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1991020149A1 true WO1991020149A1 (en) | 1991-12-26 |
Family
ID=10677919
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/EP1991/001130 WO1991020149A1 (en) | 1990-06-20 | 1991-06-19 | Echo canceller with adaptive voice switch attenuation |
Country Status (4)
Country | Link |
---|---|
AU (1) | AU7968191A (en) |
GB (1) | GB2245459A (en) |
IE (1) | IE912102A1 (en) |
WO (1) | WO1991020149A1 (en) |
Cited By (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO1993009609A1 (en) * | 1991-11-04 | 1993-05-13 | Nokia Telecommunications Oy | A method for non-linear signal processing in an echo canceller |
EP0542882A1 (en) * | 1990-08-03 | 1993-05-26 | Coherent Communications Systems Corp. | Residual echo elimination |
EP0627139A1 (en) * | 1992-02-19 | 1994-12-07 | Picturetel Corporation | Feedback level estimator between loudspeaker and microphone |
EP0692903A1 (en) * | 1994-07-13 | 1996-01-17 | Mitsubishi Denki Kabushiki Kaisha | Hands-free communication apparatus with echo canceler |
WO1996022651A1 (en) * | 1995-01-19 | 1996-07-25 | Ericsson Inc. | Method of and apparatus for echo reduction in a hands-free cellular radio communication system |
FR2748174A1 (en) * | 1996-04-30 | 1997-10-31 | Sagem | HANDS-FREE TELEPHONE SET |
DE19639580A1 (en) * | 1996-09-26 | 1998-04-09 | Deutsche Telekom Ag | Acoustic echo reduction method for hands-free telephone set |
EP0878949A2 (en) * | 1997-05-16 | 1998-11-18 | Mitsubishi Denki Kabushiki Kaisha | Hands-free telephone |
Families Citing this family (12)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
ES2101633B1 (en) * | 1994-05-31 | 1998-03-01 | Alcatel Standard Electrica | FIXED CELL PHONE TERMINAL FOR TWO-WIRE TELECOMMUNICATION SERVICES. |
ES2101638B1 (en) * | 1994-09-30 | 1998-03-01 | Alcatel Standard Electrica | FIXED CELL PHONE TERMINAL FOR TWO-WIRE TELECOMMUNICATION SERVICES. |
JP2928130B2 (en) * | 1995-04-19 | 1999-08-03 | 埼玉日本電気株式会社 | Hands-free communication device |
JP4261622B2 (en) * | 1997-01-23 | 2009-04-30 | モトローラ・インコーポレイテッド | Non-linear processing apparatus and method in communication system |
US6580793B1 (en) | 1999-08-31 | 2003-06-17 | Lucent Technologies Inc. | Method and apparatus for echo cancellation with self-deactivation |
JP3576430B2 (en) * | 1999-09-01 | 2004-10-13 | 沖電気工業株式会社 | Automatic gain controller |
US6507653B1 (en) | 2000-04-14 | 2003-01-14 | Ericsson Inc. | Desired voice detection in echo suppression |
DE10030926A1 (en) * | 2000-06-24 | 2002-01-03 | Alcatel Sa | Interference-dependent adaptive echo cancellation |
US6622030B1 (en) * | 2000-06-29 | 2003-09-16 | Ericsson Inc. | Echo suppression using adaptive gain based on residual echo energy |
FR2816791A1 (en) * | 2000-11-15 | 2002-05-17 | Atlinks | Telephone loudspeaker unit echo limiting system having signal intensity set during receiver output transmission following set level base noise/parasitics determined. |
JP4282260B2 (en) * | 2001-11-20 | 2009-06-17 | 株式会社リコー | Echo canceller |
US9973633B2 (en) | 2014-11-17 | 2018-05-15 | At&T Intellectual Property I, L.P. | Pre-distortion system for cancellation of nonlinear distortion in mobile devices |
Citations (3)
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---|---|---|---|---|
GB2125657A (en) * | 1980-03-17 | 1984-03-07 | United Networks Inc | Loudspeaker telephone system |
JPS6041849A (en) * | 1983-08-18 | 1985-03-05 | Toshiba Corp | Loudspeaker telephone set |
EP0282393A1 (en) * | 1987-03-03 | 1988-09-14 | France Telecom | Device for the realization of the hands free function in a telephone set associated with the functions of gain switching and echo cancelling |
-
1990
- 1990-06-20 GB GB9013751A patent/GB2245459A/en not_active Withdrawn
-
1991
- 1991-06-19 IE IE210291A patent/IE912102A1/en unknown
- 1991-06-19 WO PCT/EP1991/001130 patent/WO1991020149A1/en unknown
- 1991-06-19 AU AU79681/91A patent/AU7968191A/en not_active Abandoned
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB2125657A (en) * | 1980-03-17 | 1984-03-07 | United Networks Inc | Loudspeaker telephone system |
JPS6041849A (en) * | 1983-08-18 | 1985-03-05 | Toshiba Corp | Loudspeaker telephone set |
EP0282393A1 (en) * | 1987-03-03 | 1988-09-14 | France Telecom | Device for the realization of the hands free function in a telephone set associated with the functions of gain switching and echo cancelling |
Non-Patent Citations (2)
Title |
---|
PATENT ABSTRACTS OF JAPAN vol. 9, no. 169 (E-328)(1892) July 13, 1985 & JP-A-60 41 849 (TOSHIBA ) March 5, 1985 see the whole document * |
PROCEEDINGS OF EUSIPCO-88 - FOURTH EUROPEAN SIGNAL PROCESSING CONFERENCE vol. 2, September 5, 1988, GRENOBLE (FR) pages 495 - 498; W.ARMBRUSTER: 'High Quality Hands-free Telephony using Voice Switching optimised with Ech o Cancellation ' see page 496, right column, line 1 - page 498, left column, line 4 * |
Cited By (19)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0542882A1 (en) * | 1990-08-03 | 1993-05-26 | Coherent Communications Systems Corp. | Residual echo elimination |
EP0542882A4 (en) * | 1990-08-03 | 1993-08-11 | Coherent Communications Systems Corp. | Residual echo elimination with proportionate noise injection |
US5283784A (en) * | 1990-08-03 | 1994-02-01 | Coherent Communications Systems | Echo canceller processing techniques and processing |
WO1993009609A1 (en) * | 1991-11-04 | 1993-05-13 | Nokia Telecommunications Oy | A method for non-linear signal processing in an echo canceller |
AU653655B2 (en) * | 1991-11-04 | 1994-10-06 | Nokia Telecommunications Oy | A method for non-linear signal processing in an echo canceller |
US5396488A (en) * | 1991-11-04 | 1995-03-07 | Nokia Telecommunications Oy | Method for non-linear signal processing in an echo canceller |
EP0627139A1 (en) * | 1992-02-19 | 1994-12-07 | Picturetel Corporation | Feedback level estimator between loudspeaker and microphone |
EP0627139A4 (en) * | 1992-02-19 | 1995-08-30 | Picturetel Corp | Feedback level estimator between loudspeaker and microphone. |
EP0692903A1 (en) * | 1994-07-13 | 1996-01-17 | Mitsubishi Denki Kabushiki Kaisha | Hands-free communication apparatus with echo canceler |
US5721771A (en) * | 1994-07-13 | 1998-02-24 | Mitsubishi Denki Kabushiki Kaisha | Hands-free speaking device with echo canceler |
WO1996022651A1 (en) * | 1995-01-19 | 1996-07-25 | Ericsson Inc. | Method of and apparatus for echo reduction in a hands-free cellular radio communication system |
GB2312817A (en) * | 1995-01-19 | 1997-11-05 | Ericsson Ge Mobile Inc | Method of and apparatus for echo reduction in a hands-free cellular radio communication system |
GB2312817B (en) * | 1995-01-19 | 1999-08-04 | Ericsson Ge Mobile Inc | Method of and apparatus for echo reduction in a hands-free cellular radio communication system |
FR2748174A1 (en) * | 1996-04-30 | 1997-10-31 | Sagem | HANDS-FREE TELEPHONE SET |
EP0805583A1 (en) * | 1996-04-30 | 1997-11-05 | Sagem Sa | Hand-free telephone set |
DE19639580A1 (en) * | 1996-09-26 | 1998-04-09 | Deutsche Telekom Ag | Acoustic echo reduction method for hands-free telephone set |
DE19639580C2 (en) * | 1996-09-26 | 1998-09-17 | Deutsche Telekom Ag | Device for reducing acoustic echoes |
EP0878949A2 (en) * | 1997-05-16 | 1998-11-18 | Mitsubishi Denki Kabushiki Kaisha | Hands-free telephone |
EP0878949A3 (en) * | 1997-05-16 | 2003-06-04 | Mitsubishi Denki Kabushiki Kaisha | Hands-free telephone |
Also Published As
Publication number | Publication date |
---|---|
IE912102A1 (en) | 1992-01-01 |
AU7968191A (en) | 1992-01-07 |
GB9013751D0 (en) | 1990-08-08 |
GB2245459A (en) | 1992-01-02 |
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