Method and circuit for echo-cancellation in two-way communications

• US 6,731,752 B1
• Filed: 11/08/2000
• Issued: 05/04/2004
• Est. Priority Date: 11/08/2000
• Status: Expired due to Term

• Current Assignee: Benhov GmbH, LLC (Intellectual Ventures LLC)
• Original Assignee: Viadux, Inc
• Inventors: Chaplik, Naom, Poonpol, Chanchai, Robinson, Mark T.
• Primary Examiner(s): TIEU, BINH KIEN
• Application Number:
  US09/708,403
• Time in Patent Office: 1,273 Days
• Field of Search: 379/90.01, 379/93.03, 379/93.05, 379/93.06, 379/406.01, 379/345, 379/344, 379/349, 379/386, 379/387.01, 379/388.06, 379/390.04, 379/391, 379/394, 379/399.01, 379/402, 379/403, 379/404, 379/413.02
• US Class Current: 379/402
• CPC Class Codes: H04B 3/23 using a replica of transmitted signal in the time domain, e.g. echo cancellers
• CPC Class Codes: H04M 1/74 with means for reducing interference; with means for reducing effects due to line faults

Abstract

A hybrid circuit models a plurality of attributes of a communication system including a subscriber line coupled to a line interface circuit. The plurality of attributes includes subscriber line impedance, and impedance of a coupling transformer. The attributes are based on other factors, such as whether or not bridge taps exist at or near the line interface circuit on the subscriber line. The plurality of attributes are modeled by a specific arrangement of resistive and capacitive elements to substantially duplicate the collective transformative effects of the attributes on a transmission signal being sent out on the subscriber line. The transmission signal is transformed and provided to an output, where it is subtracted from a composite signal representing a combination of the actual transformed transmission signal and a receive signal. The subtraction yields an isolated receive signal, which is later processed to recover the full receive signal.

Claims

1. In a communication system having a subscriber line carrying outbound transmission and inbound receive signals overlapping in time and frequency domains, a circuit for providing transmission signals for removal from receive signals at a subscriber line interface, comprising:

an input/output section that couples an outbound transmission signal to provide a copy of the transmission signal at an input of the circuit;

a filter section, connected to the input, for filtering aliasing frequencies from the copy of the transmission signal; and

a modeling section, connected to the filter section, and being configured to model a plurality of attributes of the communication system, wherein the model transforms the copy of the transmission signal to substantially duplicate the transformative effects of the plurality of attributes on the outbound transmission signal, and for providing a transformed transmission signal to an output of the circuit at the input/output section.

2. The circuit according to claim 1, wherein the plurality of attributes include an impedance of the subscriber line and an impedance of the line interface.

3. The circuit according to claim 1, wherein the input includes a first line and a second line, and wherein the output includes a first line and a second line.

4. The circuit according to claim 3, wherein the filter section comprises a first resistor connected to the first input line, a second resistor connected to the second input line, and a capacitor connected to the first and second resistors opposite the first and second input lines, respectively.

5. The circuit according to claim 3, wherein the modeling section comprises:

a first combination of a resistor R3, a resistor R6, a resistor R8 and a capacitor C6, connected in series, and wherein the capacitor C6 is connected to the first output line;

a second combination of a resistor R4, a resistor R7, a resistor R9 and a capacitor C7, connected in series, and wherein the capacitor C7 is connected to the second output line;

a capacitor C3 connected in parallel with the resistor R6;

a capacitor C4 connected in parallel with the resistor R7;

a resistor R5 connected between resistors R3 and R6;

a capacitor C2 connected between resistors R4 and R7, and connected to the resistor R5;

a resistor R10 connected to a node between the resistor R8 and the capacitor C6; and

a capacitor C5 connected to a node between the resistor R9 and the capacitor C7, and connected to the resistor R10.

6. The circuit according to claim 3, wherein the input/output section is adapted to remove a DC component from the copy of the transmission signal at an input of the circuit, and to restore the DC component to the copy of the transmission signal at an output of the circuit, and wherein the input/output section further comprises:

a resistor R11 connected to the first output line;

a resistor R12 connected between the resistor R11 and the second output line;

a resistor R13 connected to a node between the resistors R11 and R12, and connected to the first input line; and

a resistor R14 connected to the node between the resistors R11 and R12, and connected to the second input line.

7. The circuit according to claim 3, wherein the modeling section comprises:

a first combination of a resistor R16 and a capacitor C9, connected in parallel;

a second combination of a resistor R17 and a capacitor C10, coupled in parallel;

a third combination of a resistor R18, a capacitor C12, and a resistor R20, connected in series, wherein the resistor R18 is connected to the first combination;

a fourth combination of a resistor R19, a capacitor C13, and a resistor R23, connected in series, wherein the resistor R19 is connected to the second, combination;

a fifth combination of a resistor R24 and a capacitor C11, connected in series, wherein the resistor R24 is connected to a node between the resistor R18 and the capacitor C12, and wherein the capacitor C11 is connected to a node between the resistor R19 and the capacitor C13.

8. The circuit according to claim 3, wherein the input/output section is adapted to remove a DC component from the copy of the transmission signal at an input of the circuit, and to restore the DC component to the copy of the transmission signal at an output of the circuit, and wherein the input/output section further comprises:

a first combination of a resistor R21 and a resistor R22, connected in series; and

a second combination of a resistor R25 and a resistor R26, connected in series, wherein the resistor R25 is connected to the first input line and the resistor R26 is connected to the second input line;

wherein the resistor R21 is connected to the first output line, the resistor R23 is connected to the second output line, and a node between the resistor R21 and the resistor R22 is connected to a node between the resistor R25 and the resistor R26.

9. In a communication system having a subscriber line carrying overlapping transmission and receive signals in time and frequency domains, a method of providing the transmission signal for removal from the receive signal at a line interface, comprising:

coupling an outbound transmission signal to provide a copy of a pure transmission signal;

filtering the copy of the transmission signal to remove aliasing frequencies;

transforming the filtered copy of the transmission signal based on a model of a plurality of attributes of the communication system, wherein the model substantially duplicates the transformative effects of the plurality of attributes on the outbound transmission signal; and

outputting the transformed copy of the transmission signal.

10. The method of claim 9, wherein the plurality of attributes includes an impedance of the subscriber line at a point on the subscriber line where the outbound transmission signal is combined with a inbound receive signal.

11. The method of claim 10, wherein the plurality of attributes further includes impedance characteristics of circuit components of the line interface.

12. The method of claim 9, further comprising removing a DC component of the copy of the transmission signal before the transforming, and restoring the DC portion to the transformed copy of the transmission signal.

13. A circuit for modeling a digital transmission on a two-way communication system, comprising:

an input that couples an outbound transmission signal from a transmission device to provide a copy of the transmission signal prior to being combined with an inbound receive signal on the communication system, wherein a bandwidth of the inbound receive signal is approximately equal to a bandwidth of the outbound transmission signal;

a modeling section connected to the input, comprising a plurality of resistive elements and a plurality of capacitive elements, the resistive and capacitive elements arranged so as to model a plurality of attributes of the communication system carrying the combined transmission and receive signals which overlap in time and frequency domains, the modeling section being further configured to substantially duplicate on the copy of the transmission signal the transformative effects of the plurality of attributes on the outbound transmission signal; and

an output connected to the modeling section that provides transformed copy of the transmission signal.