Reduced complexity recursive least square lattice structure adaptive filter by means of limited recursion of the backward and forward error prediction squares

1. A method for an m-stage recursive least squares lattice structure adaptive filter, the method comprising:

receiving an input signal at an interface of the adaptive filter;

recursively updating filter coefficients for each stage of the adaptive filter with a processor operative in conjunction with stored data and instructions for each stage of the adaptive filter, including

reducing a number of updates of a forward error prediction squares and backward error prediction squares of the filter coefficients by performing the updates up to a predefined number of stages of the adaptive filter, and

holding the forward error prediction squares and the backward error prediction squares constant during the remainder of the stages of the adaptive filter; and

producing a filtered signal as an output signal of the adaptive filter at an interface of the adaptive filter.

2. The method of claim 1 wherein updating filter coefficients comprises limiting updating of the forward error prediction squares and the backward error prediction squares to a predefined portion of filter length.

3. The method of claim 2 wherein limiting updating of the forward error prediction squares and the backward error prediction squares to a predefined portion of the filter length comprises updating the forward error prediction squares and the backward error prediction squares of approximately one-half of all filter stages.

4. The method of claim 1 wherein receiving an input signal comprises receiving digital data representative of a time-varying signal.

5. A method for reducing computational complexity of an in-stage adaptive filter, the method comprising:

receiving an input signal at an input interface of the adaptive filter;

filtering the input signal by a processor operative in conjunction with stored data and instructions for each stage of the adaptive filter, to produce a filtered signal, including

updating recursively a forward error prediction square term for a first portion of a length of the adaptive filter;

updating recursively a backward error prediction square term for the first portion of the length of the adaptive filter; and

keeping the updated forward and backward error prediction square terms constant for a second portion of the length of the adaptive filter; and

providing the filtered signal at an output interface of the adaptive filter.

6. The method of claim 5 wherein updating the forward error prediction square term comprises updating the forward error prediction square term for approximately one-half of the length of the adaptive filter and updating the backward error prediction square term comprises updating the backward error prediction square term for approximately one-half of the length of the adaptive filter.

7. The method of claim 5 wherein further comprising: updating all filter coefficients up to a predefined number of taps of the adaptive filter for a first set of filter updates; and holding constant the forward error prediction square term and the backward error prediction square term while updating the rest of the filter coefficients during a second set of filter updates.

8. The method of claim 7 further comprising: during the second set of filter updates, using the constant forward error prediction square term to update a backward reflection coefficient; and using the constant backward error prediction square term to update a forward reflection coefficient.

9. An m-stage adaptive filter comprising:

an interface to receive an input signal;

a processor operative in conjunction with stored data and instructions to recursively update filter coefficients for each stage of the adaptive filter while producing a filtered signal, the processor configured to

reduce a number of updates of the forward error prediction squares and backward error prediction squares of the filter coefficients by performing the updates up to a predefined number of stages of the adaptive filter, and

hold the forward error prediction squares and the backward error prediction squares constant during the remainder of the stages of the adaptive filter; and

an interface to provide the filtered signal as an output signal.

10. The adaptive filter of claim 9 wherein the processor is operative to

update recursively the forward error prediction squares for a first portion of a length of the adaptive filter; update recursively the backward error prediction squares for the first portion of the length of the adaptive filter; and

keep the updated forward error prediction squares and backward error prediction squares constant for a second portion of the length of the adaptive filter.

11. The adaptive filter of claim 10 wherein the processor is operative to

update all filter coefficients up to a predefined number of taps of the adaptive filter for a first set of filter updates; and

hold constant the forward error prediction squares and the backward error prediction squares while updating the rest of the filter coefficients during a second set of filter updates.