Low complexity frequency domain echo canceller for DMT transceivers

• US 6,377,683 B1
• Filed: 05/29/1998
• Issued: 04/23/2002
• Est. Priority Date: 05/29/1998
• Status: Expired due to Term

• Current Assignee: Hewlett Packard Enterprise Development LP (Hewlett-Packard Enterprise Company)
• Original Assignee: 3Com Corporation (HP Inc.)
• Inventors: Dobson, William Kurt, Christiansen, Mark W.
• Primary Examiner(s): WOO, STELLA L
• Application Number:
  US09/087,001
• Time in Patent Office: 1,425 Days
• Field of Search: 379/410, 379/406, 379/406.01, 379/406.08, 379/406.09, 379/406.1, 379/406.12, 379/406.13, 370/286, 370/292, 375/148, 375/296, 375/346
• US Class Current: 379/406.12
• CPC Class Codes: H04B 3/23 using a replica of transmitted signal in the time domain, e.g. echo cancellers
• CPC Class Codes: H04L 2025/03414 Multicarrier
• CPC Class Codes: H04L 27/2601 Multicarrier modulation systems
• CPC Class Codes: H04L 5/143 for modulated signals H04L5/1469 takes precedence

Abstract

A low-complexity frequency domain echo canceller for use in a full-duplex DMT transceiver. The transceiver includes a modulator that utilizes DMT modulation methods for communication over the transmission medium, a demodulator for receiving DMT signals, and a frequency domain echo canceller for removing echoes of the transmitter'"'"'s signal from the receive signal. The echo canceller models the echo channel characteristic as an FIR filter that distorts the transmitted signal that is received by the receiver section of the full-duplex transceiver. The echo is removed from the received signal by determining the frequency domain characteristic of the echo channel. A local replica of the echo is generated in the frequency domain using the echo characteristic and is subtracted from the frequency domain representation of the received signal.

Claims

1. An echo canceling method for use in a full-duplex DMT transceiver comprising the steps:

calculating a transmit echo frequency characteristic;

transmitting a data signal;

receiving a composite signal consisting of a data signal from a distant end transmitter and a transmit echo signal;

transforming the received composite signal to a received composite frequency signal;

generating a replica of the transmit echo signal using the transmit echo frequency characteristic; and

subtracting the replica from the received composite frequency signal.

2. The echo canceling method of claim 1, wherein the step of calculating a transmit echo frequency characteristic further comprises the steps of:

transmitting a training signal;

receiving a corresponding echo signal;

converting the received echo signal to the frequency domain; and

forming a ratio of the converted echo signal to the frequency domain representation of the transmitted training signal.

3. The echo canceling method of claim 1, wherein the step of calculating a transmit echo characteristic is performed in the absence of a signal from a distant end transmitter.

4. The echo canceling method of claim 1, wherein the step of transmitting a data signal includes the steps of:

specifying the magnitude and phase of a plurality of carriers; and

generating a corresponding time-domain signal.

5. The echo canceling method of claim 1, wherein the step of transmitting a data signal is performed in timed relation to the received data signal from the distant end transmitter.

6. The echo canceling method of claim 1, wherein the step of generating a replica of the transmit echo signal comprises the step of multiplying a frequency domain representation of the transmit signal by the transmit echo frequency characteristic.

7. The echo canceling method of claim 1, wherein the step of transforming the received composite signal to a received composite frequency signal includes performing a Fourier transform on the received composite signal.

8. The echo canceling method of claim 7, wherein a cyclic prefix is removed prior to performing the Fourier transform.

9. The echo canceling method of claim 1, further comprising the step of updating the transmit echo characteristic in response to the frame sychronization.

10. An echo canceling method for use in a full-duplex DMT transceiver comprising:

calculating a transmit echo frequency characteristics;

transmitting a data signal;

receiving a composite signal comprising a data signal from a distant end transmitter and a transmit echo signal;

synchronizing the received composite signal on a receive frame synchronizer;

selecting a window of samples associated with the received composite signal on the receive frame synchronizer;

determining a time offset associated with the selected window of samples;

updating the echo characteristic based on the time offset associated with the selected window of samples;

generating a replica of the transmit echo signal using the updated echo characteristic; and

subtracting the replica from the received composite frequency signal.

11. The method of claim 10, wherein the step of calculating a transmit echo frequency characteristic comprises:

transmitting a training signal;

receiving a corresponding echo signal;

converting the received echo signal to the frequency domain; and

forming a ratio of the converted echo signal to the frequency domain representation of the transmitted training signal.

12. The method of claim 10, wherein the step of generating a replica of the transmit echo signal comprises multiplying a frequency domain representation of the transmit signal by the updated echo characteristic.

13. The method of claim 10, wherein the step of transforming the received composite signal to a received composite frequency signal includes performing a Fourier transform on the received composite frequency.

14. The method of claim 10, wherein the step of synchronizing the received composite signal comprises synchronizing the received composite signal using a correlator.