Method and apparatus for cancelling echo originating from a mobile terminal

• US 6,256,384 B1
• Filed: 12/02/1997
• Issued: 07/03/2001
• Est. Priority Date: 12/02/1997
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Trump, Tõnu
• Primary Examiner(s): Chan, Wing F.
• Application Number:
  US08/982,989
• Time in Patent Office: 1,309 Days
• Field of Search: 379/406, 379/407, 379/408, 379/410, 379/411, 379/345, 379/409, 455/422, 455/575, 455/570, 208/322
• US Class Current: 379/406.08
• CPC Class Codes: H04M 9/082 using echo cancellers echo cancellers per se H04B3/23

Abstract

A novel method and apparatus are disclosed for cancelling echoes originating from a digital mobile handset using an echo canceller located in the network. The method and apparatus thus solve a practical echo problem that many mobile telephone operators have long been faced with. The method includes an algorithm that differs significantly from a conventional network echo canceller algorithm, because of the following basic considerations that influenced a solution to the echo problem: (1) the algorithm should not worsen speech quality for digital mobiles that do not generate echoes; and (2) the echo path is non-linear due to two speech coder/decoder pairs in the echo path and a low echo level.

Claims

1. A method for use in an echo canceler, comprising a plurality of adaptive filters, for controlling an echo signal originating from a digital mobile terminal, comprising the steps of:

determining if an adaptive filter sample histogram maximum value associated with said echo signal is greater than a first predetermined value;

determining if said adaptive filter sample histogram maximum value associated with said echo signal is greater than a second value;

and inserting a non-linearity in an output signal from a network echo canceller in communication with said digital mobile terminal if the following inequalities hold;

3. The echo canceller of claim 1, further comprising a short fixed filter coupled to said histogram logic unit for reducing sensitivity to double talk conditions.

4. The echo canceller of claim 1, wherein said echo canceller resides in a network side of a mobile telephone network.

5. The echo canceller of claim 1, wherein said echo canceller resides in a network side of a fixed telephone network.

6. The echo canceller of claim 1, wherein said means for controlling includes a double talk detector.

7. The echo canceller of claim 1, further comprising a delay line for delaying input signals to said plurality of adaptive filters so that a time span of 512 samples is covered by said plurality of adaptive filters, and a lowpass filter coupled between a network signal input and said plurality of adaptive filters.

8. The echo canceller of claim 1, wherein said plurality of adaptive filters comprises a full-length FIR filter.

9. The echo canceller of claim 1, wherein said mobile terminal comprises a digital mobile phone.

2. An echo canceller found in a mobile services switching center for canceling echo originating from a mobile station, comprising:

a plurality of adaptive filters, each of said adaptive filters for modeling an impulse response of an echo path so that said plurality of adaptive filters span an entire sample;

means for controlling an independent adaptation of each of said plurality of adaptive filters;

a histogram logic unit coupled to an output of each of said plurality of adaptive filters, for determining whether a mobile terminal in communication with said echo canceller is generating echo; and

a non-linear processor responsive to said histogram logic unit, for introducing non-linearity to an output signal from said echo canceller if said mobile terminal is generating echo.

10. A method for use in an echo canceler, comprising a plurality of adaptive filters, for controlling a high frequency echo signal originating from a mobile terminal, comprising the steps of

estimating, in a network echo canceller in communication with said mobile terminal, a power level of said echo signal;

and

inserting a non-linearity in an output signal from said network echo canceller if an adaptive filter sample histogram maximum value associated with said echo signal is greater than a predetermined value.

11. The method of claim 10, wherein said mobile terminal comprises a digital mobile phone.

12. The method of claim 10, wherein said estimating step comprises lowpass filtering of:

13. The method of claim 12, wherein said estimating step comprises estimating said power level as:

$\begin{array}{cc}\hat{P}<br><br>\hat{s}<br><br>\left(t\right)=\frac{127}{128}<br><br>\hat{P}<br><br>\hat{s}<br><br>\left(t\right)-\frac{1}{128}<br><br>{<br><br>{\hat{h}}_{\max }<br><br>\left(t\right)<br><br>}^2<br><br>{<br><br>x_{\max }<br><br>\left(t\right)<br><br>}^2,& \left(12\right)\end{array}$

wherein ĥ

_max(t) is said vector of sub-filter coefficients selected by said histogram, and x_max(t) is said vector of input signal samples in said sub-filter.

14. The method of claim 10, wherein said predetermined value is 4096.