# US 8,787,561 B2 · Techniques for implementing adaptation control of an echo canceller to facilitate detection of in-band signals > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,787,561 B2 - Document ID: US8787561B2 - Status: Granted - Kind: B2 - Application number: 12/768,366 - Filed: 2010-04-27 - Published: 2011-10-27 - Granted: 2014-07-22 - Earliest claimed: 2010-04-27 - Assignees: Freescale Semiconductor, Inc. - Applicants: Roman A. Dyba; Wen Wu Su; Hongyang Deng - Inventors: Roman A. Dyba; Wen Wu Su; Hongyang Deng - Web page: https://patentgrep.com/patent/US8787561B2 ## CPC - H04B 3/23: using a replica of transmitted signal in the time domain, e.g. echo cancellers - H04B: TRANSMISSION ## Abstract A technique for detecting in-band signaling tones in a communication system includes performing a first adaptation of an adaptive filter of an echo canceller in response to detection of a far-end harmonic signal. In this case, the adaptive filter provides an echo estimation signal. The technique also includes subtracting the echo estimation signal from a near-end signal that includes one or more in-band signaling tones to provide an error signal. The technique further includes detecting, using a tone detector, the one or more in-band signaling tones in the error signal. ## Claims ### Claim 1 A method of detecting in-band signaling tones in a communication system, comprising: performing a first adaptation of an adaptive filter of an echo canceller in response to detection of a far-end harmonic signal, wherein the adaptive filter provides an echo estimation signal; subtracting the echo estimation signal from a near-end signal that includes one or more in-band signaling tones to provide an error signal; detecting, using a tone detector, the one or more in-band signaling tones in the error signal; and performing a second adaptation of the adaptive filter in response to detection of a far-end non-harmonic signal. ### Claim 2 (depends on 1) The method of claim 1, wherein the one or more in-band signaling tones include one or more dual-tone multi-frequency (DTMF) signals. ### Claim 3 (depends on 1) The method of claim 1, wherein the harmonic signal is a ring tone and the non-harmonic signal is voice. ### Claim 4 (depends on 1) The method of claim 1, wherein the error signal does not include a substantial echo signal component and the tone detector shares the adaptive filter of the echo canceller. ### Claim 5 (depends on 1) The method of claim 1, wherein the error signal is not distorted by non-linear processing of the echo canceller and the tone detector does not include a separate adaptive filter. ### Claim 6 (depends on 1) The method of claim 1, wherein the adaptive filter implements an affine projection (AP) algorithm, a normalized least mean squares (NLMS) algorithm, a least mean squares (LMS) algorithm, or a recursive least squares (RLS) algorithm. ### Claim 7 A communication device, comprising: a control circuit; an adaptive filter in communication with the control circuit, wherein the adaptive filter is configured to perform a first adaptation in response to detection of a far-end harmonic signal, and wherein the adaptive filter provides an echo estimation signal and the adaptive filter is further configured to perform a second adaptation in response to detection of a far-end non-harmonic signal; an adder in communication with the control circuit, wherein the adder is configured to subtract the echo estimation signal from a near-end signal that includes one or more in-band signaling tones to provide an error signal; and a tone detector in communication with the control circuit, wherein the tone detector is configured to detect the one or more in-band signaling tones in the error signal, and wherein the first adaptation modifies filter coefficients of the adaptive filter and the filter coefficients are finite impulse response (FIR) time-domain filter coefficients. ### Claim 8 (depends on 7) The communication device of claim 7, wherein the one or more in-band signaling tones include one or more dual-tone multi-frequency (DTMF) signals. ### Claim 9 (depends on 7) The communication device of claim 7, wherein the harmonic signal is a ring tone and the non-harmonic signal is voice. ### Claim 10 (depends on 7) The communication device of claim 7, wherein the error signal does not include a substantial echo signal component and the tone detector shares the adaptive filter of the echo canceller. ### Claim 11 (depends on 7) The communication device of claim 7, wherein the error signal is not distorted by non-linear processing of the echo canceller and the tone detector does not include a separate adaptive filter. ### Claim 12 (depends on 8) The communication device of claim 8, wherein the adaptive filter implements an affine projection (AP) algorithm, a normalized least mean squares (NLMS) algorithm, a least mean squares (LMS) algorithm, or a recursive least squares (RLS) algorithm. ### Claim 13 An echo canceller, comprising: a processor circuit configured to: implement an adaptive filter that is configured to perform a first adaptation in response to detection of a far-end harmonic signal, wherein the adaptive filter provides an echo estimation signal; subtract the echo estimation signal from a near-end signal that includes one or more in-band signaling tones to provide an error signal; provide the error signal to a tone detector that is configured to detect the one or more in-band signaling tones in the error signal; and perform a second adaptation in response to detection of a far-end non-harmonic signal. ### Claim 14 (depends on 13) The echo canceller of claim 13, wherein the first adaptation modifies filter coefficients of the adaptive filter to first values and the second adaptation modifies the filter coefficients to second values, and wherein at least some of the first and second values are different and the filter coefficients are finite impulse response (FIR) time-domain filter coefficients. ### Claim 15 (depends on 13) The echo canceller of claim 13, wherein the one or more in-band signaling tones include one or more dual-tone multi-frequency (DTMF) signals and the harmonic signal is a ring tone. ### Claim 16 (depends on 13) The echo canceller of claim 13, wherein the error signal does not include a substantial echo signal component and is not distorted by non-linear processing of the echo canceller, and wherein the tone detector does not include a separate adaptive filter. ### Claim 17 (depends on 13) The echo canceller of claim 13, wherein the adaptive filter implements an affine projection (AP) algorithm, a normalized least mean squares (NLMS) algorithm, a least mean squares (LMS) algorithm, or a recursive least squares (RLS) algorithm.