Testable echo cancelling method and device

• US 5,008,923 A
• Filed: 04/17/1990
• Issued: 04/16/1991
• Est. Priority Date: 04/19/1989
• Status: Expired due to Term

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: Tajimi, Michiko, Kitamura, Youichi
• Primary Examiner(s): SCHREYER, STAFFORD
• Application Number:
  US07/509,797
• Time in Patent Office: 364 Days
• Field of Search: 379/3, 379/4, 379/406, 379/410, 379/407, 370/13, 370/13.1, 375/10, 371/20.1
• US Class Current: 379/3
• CPC Class Codes: H04B 3/231 Echo cancellers using readout of a memory to provide the echo replica
• CPC Class Codes: H04B 3/234 using double talk detection

Abstract

A communications system adaptive echo canceller integrally contains a test far-end talker signal generator, an echo signal generator for generating an echo signal with a simulated echo path, a residual echo detector for detecting a residual echo based on the output of a subtracter, and a switching unit for switching an input and output signal of the echo canceller into an echo canceller test mode. Further, it provides a bypassing unit for, in a test mode, separating a call/talk connected to the echo cancellers from the echo cancellers and forming a bypass path between trunk circuits and a transmission circuit. The bypassing unit results in being able to realize a test for the echo canceller while a talk is alive.

Claims

1. A testable echo canceller comprising an input and an output terminals for a far-end talker signal, an input and an output terminals for near-end talker signal a memory for storing said input far-end talker signal, a tap coefficient memory for storing a tap coefficient of an echo estimator, the echo estimating means for generating a pseudo echo signal based on the contents of said far-end talker signal memory and said tap coefficient memory, a subtracter means for subtracting said psuedo echo signal from an echo signal passed through an echo path for producing a residual echo signal, a tap coefficient updating means for serially updating said tap coefficient based on said far-end talker signal and said residual echo signal, a test far-end talker signal generating means for generating a far-end talker signal used for the test, a test echo signal generating means for generating a test echo signal with a simulated echo path, a residual echo detector having an output terminal connected to said subtracter means and for detecting a residual echo signal, and a control means for controlling formation of a path for an input and output signal passed to the echo canceller and formation of a testing circuit for making sure of the function with the echo canceller itself.

2. The testable echo canceller claimed in claim 1, wherein said control means includes a first switching means for switching in input of said far-end talker signal memory between an output of said test far-end talker signal generating means and said input far-end talker signal terminal, a second switching means for switching between an output of said test echo signal generating means and echo path, and a third switching means for switching an output of said subtracter means between the input of said residual echo detecting means and said near-end talker signal output terminal.

3. The testable echo canceller claimed in claim 2, wherein said first switching means establishes a path for supplying the output of said test far-end talker signal generating means to said test echo signal generating means and said far-end talker signal memory.

4. The testable echo canceller claimed in claim 2 further including switching means for forming a path for directly connecting said far-end talker signal input terminal to output terminal in a testing mode of the echo canceller in a manner to enable the test for said echo canceller to be performed while a call/talk is alive.

5. The testable echo canceller claimed in claim 1, wherein said test far-end talker signal generating means, said test echo signal generating means, and said residual echo detecting means are capable of respectively executing their own functions under a stored program.

6. The testable echo canceller claimed in claim 1, wherein said test far-end talker signal generating means is a white noise generator operated under a program.

7. In a communication system including at least one trunk circuit, testable echo cancellers connected to said trunk circuit(s), a signal converting means for receiving or sending a signal from or to said testable echo cancellers and coverting said signal, and a signal sending or receiving interface circuit connected to said signal converting means,

said communications system comprising a test indicating means being connected to said testable echo canceller(s), indicating start of a test for each echo canceller, and collecting a testing result,

said testable echo canceller comprising a far-end talker signal memory for storing a far-end talker signal being input thereto, a tap coefficient memory storing a tap coefficient of an echo estimator, the echo estimating means for generating a pseudo echo signal from said far-end talker signal memory and said tap coefficient memory, a subtracter means for substracting the pseudo echo signal from an echo signal flown through an echo path for producing a residual echo signal, a tap coefficient updating means for sequentially correcting said tap coefficient based on said far-end talker signal and residual echo signal, a far-end talker signal generating means for generating a test far-end talker signal, an echo signal generating means for generating an echo signal with a simulated echo path, a residual echo detecting means for detecting a residual echo signal, end a control means for forming a test signal path in a manner to, in a test mode, supply a signal from said far-end talker signal generating means to said echo canceller, and supply an output of said subtracter means to said residual echo detecting means.

8. The communications system claimed in claim 7, wherein said test indicating means serves to supply the test mode signal to said control means included in said testable echo canceller for starting said control means.

9. The communications system claimed in claim 8, wherein said test indicating means serves to selectively or sequentially test said testable echo cancellers based on a program.

10. The communications system claimed in claim 7 further including a bypassing means for enabling said near-end talker signal to bypass said testable echo cancellers in response to the test-starting indication given to said control means.

11. The communications system claimed in claim 7 further including a testing method for the testable echo cancellers,

said method comprising the steps of issuing a test-starting command from said test indicating means to said testable echo cancellers,

connecting said far-end talker signal memory to said far-end talker signal generating means in response to said test-starting command, supplying a echo signal from said echo signal generating means to said subtracter means, and switching the signal path in a manner to connecting an output terminal of said subtracter means to said residual echo detecting means, and

determining if the echo cancellers function normally or abnormally based on the output sent from said residual echo detecting means in said test indicating means.

12. The testing method for said testable echo cancellers claimed in claim 11 further comprising the step of, in a test mode, forming a path between said trunk circuit and said signal converting means, said path enabling the far-end talker signal to bypass said testable echo cancellers.

13. A testing method for communications equipment adaptive testable cancellers comprising the steps of;

pre-providing a far-end talker signal generator program means for generating a test far-end talker signal, an echo signal generator program means for simulating an echo path and generating an echo signal, and a residual echo detector program means for detecting a residual echo signal based on an output of each echo canceller together with the echo cancellers,

switching far-end talker signal input and output terminals for said echo cancellers in a manner to form a test path where, in a test mode, said far-end talker signal generating program is connected to a far-end talker signal memory contained in said each echo canceller and said echo signal generator program means is connected to an input terminal of a subtracter means contained in said each echo canceller, and said residual echo detecting program is connected to said output terminal of said subtracter, and

testing a function of said echo canceller in the formed test path.