Dual mode LMS nonlinear data echo canceller

• US 4,977,591 A
• Filed: 11/17/1989
• Issued: 12/11/1990
• Est. Priority Date: 11/17/1989
• Status: Expired due to Term

• Current Assignee: Verizon Patent and Licensing Incorporated (Verizon Communications Inc.)
• Original Assignee: NYNEX Corp. (Verizon Communications Inc.)
• Inventors: Chen, Walter Y., Haddad, Richard A.
• Primary Examiner(s): Ng, Jin F.
• Assistant Examiner(s): Augustus, Jhancy
• Application Number:
  US07/438,598
• Time in Patent Office: 389 Days
• Field of Search: 379/406, 379/410, 379/411, 370/32, 370/32.1
• US Class Current: 379/406.1
• CPC Class Codes: H04B 3/231 Echo cancellers using readout of a memory to provide the echo replica
• CPC Class Codes: H04B 3/238 using initial training sequence

Abstract

An adaptive nonlinear data driven echo canceller is disclosed. Unlike other approaches to nonlinear echo cancellation, the inventive echo canceller treats the nonlinearity of the echo path as nonlinear noise associated with transmitting data symbols through a linear echo path. In comparison to a conventional LMS data driven linear echo canceller, the inventive echo canceller utilizes only an additional small random access memory for storing a nonlinear function for estimating the effect of the nonlinear echo path on transmitted data symbols. The same LMS algorithm is used to estimate the linear echo path and the nonlinear function. The signal processing power of a conventional linear data driven LMS echo canceller is sufficient to implement the inventive nonlinear echo canceller and the convergence speed of the nonlinear echo canceller can be less than three times that of the conventional linear LMS echo canceller.

Claims

1. An echo canceller for cancelling an echo signal comprising

means operative during a training period and using a least mean square algorithm to estimate a finite impulse response of a linear component of an echo path, and

means operative during a subsequent dual mode phase and using a least mean square algorithm for estimating both a nonlinear function representative of a nonlinear component of said echo path and said finite impulse response of said linear component of said echo path,

wherein said means operative during said dual mode phase alternately estimates said nonlinear function and said finite impulse response.

2. The echo canceller of claim 1 wherein said means operative during said dual mode phase includes a random access memory for storing values of said nonlinear function.

3. An echo canceller for generating an estimated echo signal e(k) to cancel an echo signal e(k) generated by a transmission channel from a data signal X(k), where k is a time index, said echo canceller comprising

memory means for storing a vector f(X_k)_k where f(.) is a nonlinear function representative of a nonlinear component of an echo transmission path of said echo signal and X_k is a vector formed from the values of the signal X(k) for the last n values of the time index k where n is an integer,

means for obtaining a vector H_k corresponding to an estimated finite impulse response of a linear component of said echo transmission path, and

means for obtaining the product of (X_k +f(X_k)_k) and H_k to form said estimated echo signal e(k).

4. The echo canceller of claim 3 wherein said echo canceller includes means for iteratively estimating said vector f(X_k)_k and for iteratively estimating said finite impulse response.

5. The echo canceller of claim 4 wherein said estimating means utilize a least means square algorithm to estimate both said vector f(X_k)_k and said finite impulse response.

6. A method for cancelling an echo in a telecommunications channel used to transmit a digital data signal, said method comprising the steps of

during a training period, using a least mean square algorithm to estimate the finite impulse response of a linear component of an echo path, and

during a subsequent dual mode phase, using a least mean square algorithm to both estimate a nonlinear function representative of a nonlinear component of said echo path and said finite impulse response of said linear component of said echo path,

wherein during said dual mode phase, alternately, said nonlinear function is estimated and said finite impulse response is held constant and said finite impulse response is estimated and said nonlinear function is held constant.

7. The method of claim 6 wherein during said dual mode phase, said finite impulse response is estimated during every m^th iteration of said least mean square algorithm, where M is a number between 2 and 5.

8. A method for cancelling an echo in a telecommunications channel used to transmit a digital data signal, said method comprising the steps of

during a training period, using a least mean square algorithm to estimate the finite impulse response of a linear component of an echo path, and

during a subsequent dual mode phase, using a least mean square algorithm to both estimate a nonlinear function representative of a nonlinear component of said echo path and said finite impulse response of said linear component of said echo path,

wherein said method further comprises the step of storing values of said nonlinear function in a random access memory.

10. A method for generating an estimated echo signal e(k) for use in an echo canceller to cancel an echo signal e(k) where k is a time index comprising the steps of storing a nonlinear data vector Y_k =ψ

(X_k), where X_k is a data vector formed from the values of said signal X(k) being transmitted for the last n values of the index k where n is an integer and where ψ

is a nonlinear function representing the effect of a nonlinear component of a transmission path of said echo signal e(k), and forming the product of Y_k H_k where H_k is an estimate of a finite impulse response of a linear component of said echo path to obtain said estimated echo signal e(k).

9. The method of claim 10 wherein said nonlinear function representative of said nonlinear component of said echo path includes no delay.

11. The method of claim 10 wherein said nonlinear data vector Y_k and said finite impulse response H_k are estimated iteratively using a least mean square algorithm.

12. The method of claim 11 wherein alternatively, said finite impulse response is held constant and said nonlinear vector Y_k is estimated and said nonlinear vector Y_k is held constant and said finite impulse response H_k is estimated.

13. An echo canceller comprising

means for storing values of a nonlinear function representative of a nonlinear component of an echo path,

means for storing values representative of a finite impulse response of a linear component of said echo path, and

means for executing a least mean square algorithm for alternately estimating said values of said nonlinear function and said values representative of said finite impulse response.

14. A method for cancelling an echo in a communications channel comprising

storing values of a nonlinear function representative of a nonlinear component of an echo path,

storing values representative of a finite impulse response of a linear component of an echo path, and

executing a least mean square algorithm for alternately estimating said values of said nonlinear function and said values representative of said finite impulse response.