High performance echo canceller for high speed modem

• US 5,790,658 A
• Filed: 10/28/1996
• Issued: 08/04/1998
• Est. Priority Date: 10/28/1996
• Status: Expired due to Term

• Current Assignee: Microsemi Semiconductor (U.S.) Inc. (Microchip Technology Incorporated)
• Original Assignee: Advanced Micro Devices, Inc.
• Inventors: Cole, Terry, Yip, Phillip C.
• Primary Examiner(s): Zele, Krista
• Assistant Examiner(s): SAINT SURIN, JACQUES M
• Application Number:
  US08/739,009
• Time in Patent Office: 645 Days
• Field of Search: 379/406, 379/410, 379/399, 379/411, 379/402, 379/407, 370/290, 370/276, 370/282, 370/286, 370/289, 364/724.19, 364/724.01
• US Class Current: 379/406.09
• CPC Class Codes: H04B 3/237 using two adaptive filters, e.g. for near end and for end echo cancelling

Abstract

An architecture for echo cancellation in communication networks is provided that uses a multi-stage adaptation algorithm which operates on echo cancellation filters of different configurations. When each of the configurations exhibit increased sensitivity to a different adaptation parameters, the resulting architecture gains an increased estimation accuracy. The increased accuracy readily translates into improved echo cancellation performances. In one embodiment, the architecture includes a baseband filter configuration and a passband filter configuration for echo cancellation. The increased adaptation sensitivity of the baseband filter configuration allows a more accurate estimate of the frequency offset. This estimate may then used by the passband filter configuration to attain a better echo cancellation performance.

Claims

1. A system for performing echo cancellation in a communications network, comprising:

a local bi-directional two-wire communication line;

a remote bi-directional two-wire communication line;

a four-wire communication line interposed between said local line and said remote line, said four-wire communication line having a transmit path and a receive path, wherein said transmit path is adapted to transfer a transmit signal from said local line to said remote line, and said receive path is adapted to transfer a receive signal from said remote line to said local line;

a local hybrid transformer coupled between said local line and said four-wire line and configured to perform two-wire to four-wire circuit conversion to transfer the transmit signal from said local line to said four-wire line and transfer the receive signal from said four-wire line to said local line, wherein the local hybrid transformer imputes a near echo of the transmit signal upon the receive signal;

a remote hybrid transformer coupled between said four-wire line and said remote line and configured to perform four-wire to two-wire circuit conversion to transfer the transmit signal from said four-wire line to said remote line and transfer the receive signal from said remote line to said four-wire line, wherein the remote hybrid transformer imputes a far echo of the transmit signal upon the receive signal;

a modem which comprises;

a transmitter configured to accept a sequence of input data and thereafter provide said transmit signal;

an echo canceler comprising;

a symbol buffer coupled to receive said sequence of input data;

a first filter operatively coupled to receive a modulated output from said symbol buffer for providing a replica of said far echo in a real domain;

a second filter coupled to said symbol buffer and configured to provide a replica of an analytic representation of said far echo in a complex domain;

a third filter operatively coupled to receive a second modulated output from said symbol buffer for providing a replica of said near echo;

a first summer configured to accept said receive signal and the replica of said near echo for providing a near-echo canceled signal; and

a summer configuration coupled to said first filter to accept the replica of said far echo, coupled to said third filter to accept the replica of said near echo, configured to accept said receive signal, and configured to provide an error signal which is coupled to update coefficients of said first and third filters in accordance with an adaptation algorithm.

2. The system for performing echo cancellation as recited in claim 1, wherein said modem further comprises:

a Hilbert transform filter coupled to said first summer to accept said near-echo canceled signal, and configured to provide an analytic receive signal;

a second summer coupled to said Hilbert transform filter and said second filter for combining said analytic receive signal and said analytic representation of said far echo, the result of the combination being an analytic echo-canceled signal; and

a receiver coupled to said second summer to accept said analytic echo-canceled signal and thereafter provide a sequence of output data.

3. The system for performing echo cancellation as recited in claim 2, wherein said analytic echo-canceled signal is coupled to update coefficients of said second filter.

4. An echo cancellation apparatus comprising:

a symbol buffer configured to receive a sequence of input data;

a first filter in operable communication with the output of said symbol buffer for providing a replica of a far echo in a real domain;

a second filter coupled to said symbol buffer and configured to provide a replica of an analytic representation of said far echo in a complex domains;

a third filter in operable communication with the output of said symbol buffer for providing a replica of a near echo;

a first summer configured to accept a receive signal and coupled to said third filter to accept the replica of said near echo and configured to provide a near-echo canceled signal; and

a summer configuration coupled to said first filter to accept the replica of said far echo, coupled to said third filter to accept the replica of said near echo, configured to accept said receive signal and configured to provide an error signal which is coupled to update coefficients of said first and third filters in accordance with an adaptation algorithm.

5. The echo cancellation apparatus as recited in claim 4, said apparatus further comprising:

a Hilbert transform filter coupled to said first summer to accept said near-echo canceled signal, and configured to provide an analytic receive signal; and

a second summer coupled to said Hilbert transform filter to accept said analytic receive signal, coupled to said second filter to accept said analytic representation of said far echo, and configured to provide an analytic echo-canceled signal.

6. The echo cancellation apparatus as recited in claim 5, wherein said analytic echo-canceled signal is coupled to update coefficients of said second filter.

7. A method for echo cancellation in a communications network comprising the steps of:

buffering a sequence of input data;

applying a first filter to said sequence of input data to construct an estimate of a far echo in a real domain;

applying a second filter to said sequence of input data to construct an analytic representation of said far echo in a complex domain;

applying a third filter to said sequence of input data to construct an estimate of a near echo in a real domain;

subtracting the estimate of said far echo and the estimate of said near echo from a receive signal to determine an error signal for providing filter coefficient updates to said first and third filters;

subtracting the estimate of said near echo from said received signal to determine a near-echo canceled signal;

applying a Hilbert transform to said near-echo canceled signal to determine an analytic receive signal; and

subtracting the analytic representation of said far echo from said analytic receive signal to produce an echo-canceled signal.

8. The method for echo cancellation as recited in claim 7 further comprising the steps of:

applying a first adaptation algorithm to coefficients of the first filter based on said error signal; and

applying a second adaptation algorithm to coefficients of the second filter based on said error-canceled signal.