Mitel Networks Corporation

Mitel Knowledge Corporation

Mitef Networks Corporation

Jan Radecki

Dieter Schulz

Mirjana Popovic

Renee Johnston

The present invention relates generally to tone detection in echo canceling systems, and more particularly to a method of monitoring oscillations of adaptive filter coefficients for narrow band tone detection in echo cancellation systems. The invention is directed at improving communication in a telephone communication network having one or more hybrid connections. A method for detecting continuous tones in an echo canceling system having an adaptive filter is provided. Continuous tones have a deleterious effect on the performance of adaptive filters. In the present invention, the adaptive filter coefficients are monitored. Oscillation of those coefficients indicates continuous tone presence.

Narrow band tone detection in echo canceling system

A method for detecting echo path changes in an echo canceller using the statistics of the echo canceling behavior (i.e. signal and performance information), to distinguish between new line and double talk conditions. A moving counter is incremented or decremented based on monitored levels of ERL (Echo Return Loss), ERLE (Echo Return Loss Enhancement), noise and signal energies. When the counter reaches a predetermined threshold value indicative of sustained poor echo cancellation performance, a determination is made that there is a probable new line condition (i.e. echo path change). This echo path change information is then passed to the echo canceller to enable re-convergence.

Method for detecting echo path changes in echo cancellers

An echo canceller comprising a digital filter having adaptive coefficients which are updated to simulate an echo response, a temporary register for storing default coefficients, and a controller for monitoring ERLE and in the event the ERLE is greater than a first predetermined threshold then enabling the digital filter and replacing the default coefficients in the temporary register with the adaptive coefficients, and in the event the ERLE is less than a second predetermined threshold then disabling the digital filter and replacing the adaptive coefficients with said the default coefficients from the temporary register.

Echo canceller employing H-register and storage register

An echo cancellation system for detecting and canceling echo from a network speech path, comprising a pool of echo locators for detecting pure echo delay and dispersion of time, a pool of echo cancellers, a pool of line watchdogs for detecting presence or absence of echo in the network speech path, and a control system for (i) locating and applying an echo locator from the pool of echo locators to the network speech path for detecting the pure echo delay and dispersion of time of any echo in the network speech path, and thereafter returning the echo locator to the pool of echo locators; (ii) locating and applying an echo canceller from the pool of echo cancellers to the network speech path for canceling the echo using the pure delay and dispersion time, and thereafter returning the echo canceller to the pool of echo cancellers; and (iii) locating and applying a line watchdog from the pool of line watchdogs to the network speech path for detecting said presence or absence of echo, and in the event the presence of said echo is detected then re-executing (i).

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Ottawa, Canada

Jan Radecki