Method and System for Filtering a Signal and for Providing Echo Cancellation

Abstract

The present invention provides for adaptive filters that have improved computational and memory bandwidth proprieties. When applied to telecommunication applications, the present invention additionally provides for improved methods and systems of canceling echoes. In one embodiment of the adaptive filter of the present invention, a filter, preferably an adaptive finite impulse response (FIR) filter, of an appropriate length, N, is chosen. Once the filter is chosen, convergence is achieved and the filter is converted to an infinite impulse response (IIR) filter. In the course of operation, data is received from an input source and used to adapt the zeroes of the IIR filter using the least means square (LMS) approach, keeping the poles fixed. The adaptation process generates a set of converged filter coefficients that are then applied to the input signal to create a modified signal used to filter the data. The novel adaptive filter method and system presented herein can be used to improve the calculation of the echo impulse response by, among other things, reducing the computational complexity and memory requirements of the coefficient calculation conducted within the adaptive filter.

1 - 18 . (canceled) 
     
     
         19 . An adaptive filter, comprising: a filter input for receiving a first signal; a filter output for outputting a second signal based upon said first signal to a summation device; an error input for receiving an error input signal generated by a comparison of the second signal against a third signal; a plurality of finite impulse response (FIR) coefficients wherein said FIR coefficients are determined by deriving a FIR filter having a predetermined number of coefficients and obtaining convergence of said coefficients; and a plurality of infinite impulse response (IIR) coefficients wherein said IIR coefficients have a plurality of poles and a plurality of zeroes and wherein said IIR coefficients are derived from at least some of said FIR coefficients, wherein said adaptive filter monitors the error input signal and, if the error input signal exceeds a predetermined threshold, re-deriving the IIR coefficients by re-deriving at least some of said FIR coefficients and obtaining convergence of said at least some of said FIR coefficients. 
     
     
         20 . The adaptive filter of  claim 19  wherein convergence of said FIR coefficients is achieved using a Least-Mean-Square approach. 
     
     
         21 . The adaptive filter of  claim 19  wherein updating the zeroes of said IIR coefficients is achieved using a Least Means Square approach. 
     
     
         22 . A method for adaptively filtering a signal, wherein said method is performed by and within a processor, comprising the steps of: deriving a plurality of finite impulse response (FIR) coefficients wherein said FIR coefficients are determined by deriving a FIR filter having a predetermined number of coefficients and obtaining convergence of said coefficients; deriving a plurality of infinite impulse response (IIR) coefficients wherein said IIR coefficients have a plurality of poles and a plurality of zeroes and wherein said IIR coefficients are derived from at least some of said FIR coefficients; receiving a first signal; outputting a second signal wherein the second signal is a function of the IIR coefficients and the first signal; receiving an error input signal generated by a comparison of the second signal against a third signal; updating the zeroes of said IIR coefficients based upon said error input signal and not updating the poles of said IIR coefficients; monitoring the error input signal; and if the error input signal exceeds a predetermined threshold, re-deriving the IIR coefficients by re-deriving at least some of said FIR coefficients, and obtaining convergence of said at least some of said FIR coefficients. 
     
     
         23 . The adaptive filter of  claim 22  wherein convergence of said at least some of said FIR coefficients is achieved using a Least-Mean-Square approach. 
     
     
         24 . A system for canceling an undesirable signal within a second signal generated by the transmittal of a first signal through a cross-coupling pathway, comprising: a summation device for summing a third signal and the second signal to produce an error signal; and an adaptive filter comprising a filter input for receiving the first signal, a filter output for outputting the third signal based upon said first signal to the summation device, an error input for receiving the error signal, a plurality of finite impulse response (FIR) coefficients; and a plurality of infinite impulse response (IIR) coefficients wherein said IIR coefficients have a plurality of poles and a plurality of zeroes and wherein said IIR coefficients are derived from at least some of said FIR coefficients, wherein said adaptive filter monitors the error input signal and, if the error input signal exceeds a predetermined threshold, re-deriving the IIR coefficients by re-deriving at least some of said FIR coefficients and obtaining convergence of said at least some of said FIR coefficients.