# US 2008/0187129 A1 · Method and System for Echo Cancellation In A Network Switch > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2008/0187129 A1 - Document ID: US20080187129A1 - Status: Published application - Kind: A1 - Application number: 11/670,316 - Filed: 2007-02-01 - Published: 2008-08-07 - Earliest claimed: 2007-02-01 - Assignees: 3Com Corporation - Inventors: Youhong Lu; Glenn Kosteva; Jenny Jianqiu Jin; Nick Georgacopoulos - Web page: https://patentgrep.com/patent/US20080187129A1 ## CPC - H04B 3/237: {using two adaptive filters, e.g. for near end and for end echo cancelling} - H04B: TRANSMISSION ## Abstract A method and system in network switch for cancelling multiple sources of network echo, including echo that is combined with a persistent, non-echo signal. A first echo canceller cancels a first echo signal that arises from an echo path in the network switch, and second echo canceller cancels a second echo signal that arises from an echo path in an external network device. The first echo canceller operates by first removing any persistent, non-echo signal that may be combined with the first echo signal, then training on the remaining, pure echo signal. The second echo canceller includes two sub-component echo cancellers that are coordinated so as to provide a minimum error signal for cancellation applied to the second echo signal. ## Claims ### Claim 1 A method of cancelling echo in a network switch using two echo cancellers, the method comprising: adjusting a first echo canceller according to a test echo signal, the test echo signal being generated by a first echo path, the first echo path being located in the network switch; receiving a signal comprising a first echo signal and a second echo signal, the first echo signal being generated by the first echo path, and the second echo signal being generated by a second echo path, the second echo path being located externally to the network switch; cancelling the first echo signal with the first echo canceller; adjusting the second echo canceller according to the second echo signal; and cancelling the second echo signal with the second echo canceller. ### Claim 2 (depends on 1) The method of claim 1, wherein adjusting the first echo canceller comprises: activating a communication link between the network switch and an external device; removing from the communication link a connection-status signal, the connection-status signal being received at the network switch via the communication link; transmitting a test signal from the network switch on the communication link; receiving the test echo signal generated by the first echo path, the test echo signal corresponding to an echo of the transmitted test signal; and adjusting the first echo canceller according to the test echo signal. ### Claim 3 (depends on 2) The method of claim 2, wherein the test signal is a noise signal, and wherein removing from the communication link the connection-status signal comprises transmitting from the network switch a cessation signal on the communication link. ### Claim 4 (depends on 2) The method of claim 2, wherein the test signal is a noise signal, and wherein removing from the communication link the connection-status signal comprises adjusting a removal filter according to the connection-status signal, the removal filter thereafter being operational to maximize the suppression in any input signal of any frequency components corresponding to frequency components of the connection-status signal. ### Claim 5 (depends on 4) The method of claim 4, further comprising: applying the removal filter to the noise signal prior to transmitting the noise signal from the network switch on the communication link; and applying the removal filter to the first echo signal prior to adjusting the first echo canceller according to the first echo signal. ### Claim 6 (depends on 2) The method of claim 2, cancelling the first echo signal with the first echo canceller comprises cancelling a first echo of data transmissions, the data transmissions being sent from the network switch to an external device, and the first echo of the data transmissions being generated by the first echo path. ### Claim 7 (depends on 6) The method of claim 6, wherein cancelling the second echo signal with the second echo canceller comprises cancelling a second echo of the data transmissions, the second echo of the data transmissions being generated by the second echo path. ### Claim 8 (depends on 1) The method of claim 1, wherein the first echo path is associated with a two-wire-to-four-wire hybrid circuit in the network switch. ### Claim 9 (depends on 3) The method of claim 3, wherein the connection-status signal is dial tone and the cessation signal comprises at least one dual-tone multi-frequency tone, and wherein activating the communication link between the network switch and the external device comprises completing an analog-loop circuit between the network switch and the external device. ### Claim 10 (depends on 5) The method of claim 5, wherein the connection-status signal is dial tone, and wherein activating the communication link between the network switch and the external device comprises completing an analog-loop circuit between the network switch and the external device. ### Claim 11 (depends on 5) The method of claim 5, wherein the first echo canceller, the second echo canceller, and the removal filter all comprise components of a digital signal processing system, and wherein: adjusting the first echo canceller according to the test echo signal further comprises determining a first set of coefficients for the first echo canceller according to a digital form of the test echo signal; cancelling the first echo signal with the first echo canceller comprises cancelling a digital form of the first echo signal with the first echo canceller using the first set of coefficients; adjusting the second echo canceller according to the second echo signal comprises determining a second set of coefficients for the second echo canceller according to a digital form of the second echo signal; cancelling the second echo signal with the second echo canceller comprises cancelling a digital form of the first echo signal with the second echo canceller using the second set of coefficients; adjusting the removal filter according to the connection-status signal comprises determining a third set of coefficients for the removal filter according to a digital form of the connection-status signal; applying the removal filter to the test signal comprises applying the removal filter to a digital form of the test signal using the third set of coefficients; and applying the removal filter to the first echo signal comprises applying the removal filter to a digital form of the first echo signal using the third set of coefficients. ### Claim 12 (depends on 1) The method of claim 1, wherein adjusting the second echo canceller comprises: applying to the second echo signal a first sub-component echo canceller, thereby yielding a first error signal, the first sub-component echo canceller corresponding to a previous adjustment of the second echo canceller; concurrently applying to the second echo signal a second sub-component echo canceller, thereby yielding a second error signal, the second sub-component echo canceller corresponding to an initialized adjustment of the second echo canceller; determining the smaller of the first error signal and the second error signal; outputting from the second echo canceller the smaller of the first error signal and the second error signal; adjusting the second sub-component echo canceller according to the second echo signal to minimize the second error signal; outputting from the second echo canceller the second error signal; and setting the first sub-component echo canceller to be the same as the second sub-component echo canceller. ### Claim 13 (depends on 12) The method of claim 12, wherein determining the smaller of the first error signal and the second error signal comprises determining the smaller of a first time average of the first error signal and a second time average of the second error signal, the first time average and the second time average each being determined in the same time interval. ### Claim 14 (depends on 13) The method of claim 13, wherein each of the first sub-component echo canceller and the second sub-component echo canceller comprise components of a digital signal processing system, and wherein: applying to the second echo signal the first sub-component echo canceller comprises applying the first sub-component echo canceller to a digital form of the second echo signal using a previous set of coefficients; concurrently applying to the second echo signal the second sub-component echo canceller comprises concurrently applying the second sub-component echo canceller to a digital form of the second echo signal using an initialized set of coefficients; determining the smaller of the first time average of the first error signal and the second time average of the second error signal further comprises determining the smaller of a first digital time average of a digital form the first error signal and a second digital time average of a digital form of the second error signal, the first digital time average and the second digital time average each being determined over the same digital time window; adjusting the second sub-component echo canceller according to the second echo signal comprises determining a new set of coefficients for the second sub-component echo canceller according to a digital form of the second echo signal; and setting the first sub-component echo canceller to be the same as the second sub-component echo canceller comprises setting the coefficients of the first sub-component echo canceller to be the same as the new set of coefficients. ### Claim 15 A network switch comprising: an internal network interface operable to communicatively couple the network switch with at least one communication device; an external network interface operable to communicatively couple the network switch with an external device; at least one digital signal processor (DSP); DSP data storage; a first DSP-based echo canceller operable to cancel echo from a first echo path, the first echo path being located in the network switch; a second DSP-based echo canceller operable to cancel echo from a second echo path, the second echo path being located externally to the external interface of the network switch; and DSP-language instructions stored in DSP data storage executable by the at least one DSP to cancel echo from the first echo path using the first DSP-based echo canceller and to cancel echo from the second echo path using the second DSP-based echo canceller. ### Claim 16 (depends on 15) The system of claim 15, wherein the DSP-language instructions stored in DSP data storage are further executable by the at least one DSP to: determine a first set of coefficients for the first DSP-based echo canceller according to a test echo signal received from the first echo path; store the first set of coefficients in DSP data storage; cancel a first echo signal received from the first echo path with the first DSP-based echo canceller using the first set of coefficients; determine a second set of coefficients for the second DSP-based echo canceller according to a second echo signal received by way of the external interface from the second echo path; store the second set of coefficients in DSP data storage; and cancel the second echo signal with the second DSP-based echo canceller using the second set of coefficients. ### Claim 17 (depends on 16) The system of claim 16, wherein the DSP-language instructions stored in DSP data storage are further executable by the at least one DSP to: activate a communication link between the network switch and an external device via the external interface; remove from the communication link a connection-status signal, the connection-status signal being received at the external interface via the communication link; transmit a test signal on the communication link via the external interface; receive the test echo signal from the first echo path, the test echo signal corresponding to an echo of the transmitted test signal; determine the first set of coefficients for the first DSP-based echo canceller according to the received test echo signal; and store the first set of coefficients in DSP data storage. ### Claim 18 (depends on 17) The system of claim 17, wherein the first echo signal corresponds to a first echo of data transmissions, the data transmissions being sent from the network switch via the external interface, and the first echo of the data transmissions being generated by the first echo path. ### Claim 19 (depends on 16) The system of claim 16, wherein the DSP-language instructions stored in DSP data storage are further executable by the at least one DSP to: apply to the second echo signal the second DSP-based echo canceller using a previous set of coefficients retrievable from DSP data storage, the result being a first error signal; concurrently apply to the second echo signal the second DSP-based echo canceller using an initialized set of coefficients retrievable from DSP data storage, the result being a second error signal; determine the smaller of the first error signal and the second error signal; output from the second DSP-based echo canceller the smaller of the first error signal and the second error signal; determine the second set of coefficients for the second DSP-based echo canceller according to the second echo signal; store the second set of coefficients in DSP data storage; output from the second DSP-based echo canceller the second error signal using the second set of coefficients; replace the previous set of coefficients with the second set of coefficients; and store the replaced previous set of coefficients in DSP data storage. ### Claim 20 (depends on 18) The system of claim 18, wherein the second echo signal corresponds to a second echo of the data transmissions, the second echo of the data transmissions being generated by the second echo path. ### Claim 21 (depends on 15) The system of claim 15, wherein: the network switch comprises a first two-wire-to-four-wire hybrid circuit, and the first echo path is associated with the first two-wire-to-four-wire hybrid circuit in the network switch.