High-speed modem with uplink remote-echo canceller

• US 6,597,732 B1
• Filed: 01/14/1999
• Issued: 07/22/2003
• Est. Priority Date: 01/14/1999
• Status: Expired due to Term

• Current Assignee: RPX Corporation
• Original Assignee: Eric M. Dowling
• Inventors: Dowling, Eric Morgan
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Kim, Kevin
• Application Number:
  US09/231,471
• Time in Patent Office: 1,650 Days
• Field of Search: 375/222, 375/224, 379/3, 379/22.02, 379/27.03, 379/406.01, 379/406.1
• US Class Current: 375/222
• CPC Class Codes: H04B 3/23 using a replica of transmitted signal in the time domain, e.g. echo cancellers
• CPC Class Codes: H04L 25/4927 using levels matched to the quantisation levels of the channel

Abstract

A high-speed modem operates at speeds as high as 64 kbps in both the downlink direction from a digital modem to an analog subscriber and at an increased speed in the uplink direction from the analog subscriber back to the digital modem. Known systems provide a 56 kbps connection in the downlink direction but only provide for as high as a 33.6 kbps connection in the uplink direction. The present invention centers on the development of apparatus, systems, and methods for remote-echo cancellation whereby signal processing in the modem endpoints is used to remotely cancel an echo component at the input to a network-interface'"'"'s ADC. Heretofore, this echo component has limited the achievable uplink data rate. Hence the present invention enables symmetric 56 kbps modem connections using POTS lines or the POTS channel within a DSL when line conditions warrant.

Claims

1. A cooperative modem apparatus coupled to a digital network and operative to cooperate with an analog subscriber modem located across said digital network, said cooperative modem apparatus assisting said analog subscriber modem in developing one or more adaptive parameters for use in a remote-echo canceller, said remote-echo canceller operative to produce a remote-echo cancellation signal which combines with an echo at the input to a network-interface ADC coupled via a subscriber line to said analog subscriber modem, said cooperative modem apparatus comprising:

a training signal generator which generates a training signal, the training signal being used at least partially to cause said parameter to be adjusted in said remote-echo-canceller; and

a receiver coupled to said digital network and operative to receive a signal that at least partially comprises a composite-remote-echo-error signal, wherein said composite-remote-echo-error signal is produced substantially at said network-interface ADC at least partially in response to said subscriber modem transmitting the remote-echo-cancellation signal via said subscriber line, the remote-echo-cancellation signal being produced by said remote-echo-canceller using said one or more adaptive parameters.

2. The cooperative modem apparatus according to claim 1, further comprising:

an adaptive parameter computation module operative to derive from said training signal and said composite-remote-echo-error signal said adaptive parameter; and

a transmitter coupled to said digital network and operative to transmit a digitally encoded representation of said adaptive parameter.

3. The cooperative modem apparatus according to claim 1, further comprising:

a transmitter coupled to said digital network and operative to transmit a digitally encoded representation of said training signal and a digitally encoded representation of said error signal.

4. The cooperative modem apparatus according to claim 1, further comprising:

a digital interface coupleable to said digital network, whereby said cooperating modem apparatus is a digital modem.

5. The cooperative modem apparatus according to claim 2, further comprising:

an analog interface coupleable to said digital network via a second subscriber line, whereby said cooperating modem apparatus is an analog modem and said digitally encoded representations are modulated onto an uplink modem signal.

6. The cooperative modem apparatus according to claim 1, wherein said training signal is a digital representation of an analog version of said training signal which is generated by a network-interface DAC and coupled via said subscriber line to said subscriber modem.

7. The cooperative modem apparatus according to claim 6, wherein said composite-remote-echo-error signal received by said receiver is a digital representation of an analog version of said composite-remote-echo-error signal sampled at the input to said network-interface ADC, and said analog version of said composite-remote-echo-error signal is produced in response to said analog version of said training signal and an analog version of said remote-echo cancellation signal after it has propagated through said subscriber line and passed through a line filter.

8. A method of cooperative training carried out in a subscriber modem comprising the steps of:

receiving via a subscriber line a training signal sent from a cooperating modem;

deriving at least partially in response to said training signal an adaptive parameter;

processing a downlink signal using said adaptive parameter in order to generate a remote-echo cancellation signal; and

coupling said remote-echo cancellation signal onto said subscriber line, whereby said remote-echo cancellation signal combines with a network echo signal in order to produce a composite-remote-echo-error signal;

wherein the composite-remote-echo-error signal has substantially lower power than the network echo signal, and the network echo signal and the remote echo cancellation signal combine at a point that is remote from the subscriber modem.

9. The method of claim 8, further comprising the step of:

updating a parameter variable used to derive said remote-echo cancellation signal by receiving a modulated and digitally encoded representation of a parameter from said subscriber line, demodulating said parameter, and writing said parameter variable with said parameter.

10. The method of claim 9, further comprising the step of:

transmitting a second training signal onto said subscriber line.

11. The method of claim 8, further comprising the steps of:

receiving via said subscriber line a modulated and digitally encoded representation of an error signal sent from said cooperating modem;

demodulating said modulated and digitally encoded representation of said error signal to produce said error signal;

applying an adaptation algorithm to derive from said training signal and said error signal a parameter-correction value, and applying said parameter-correction value to update a parameter used in said step of deriving.