Adaptive digital filter having non-recursive and recursive filter elements

• US 5,014,232 A
• Filed: 04/07/1989
• Issued: 05/07/1991
• Est. Priority Date: 06/03/1988
• Status: Expired due to Term

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Andre, Tore M.
• Primary Examiner(s): Malzahn, David H.
• Application Number:
  US07/334,712
• Time in Patent Office: 760 Days
• Field of Search: 364/724.17, 364/724.16, 364/724.19, 364/724.2, 375/14, 333/166
• US Class Current: 708/322
• CPC Class Codes: H03H 21/0012 Digital adaptive filters
• CPC Class Codes: H04B 3/237 using two adaptive filters, e.g. for near end and for end echo cancelling

Abstract

An adaptive digital filter including a non-recursive part and a recursive part, and which can be updated in a simple and reliable manner. The recursive part of the filter has a plurality of separate, permanently set recursive filters (13-16) with different impulse responses, and a linear combination is formed with adaptive weighting factors (W0-W3) from the output signals of the recursive filters (13-16). The filter is updated by a single (e(n)) being utilized for updating the non-recursive part (11) of the filter and the adaptive weighting factors (W0-W3) in the recursive part of the filter.

Claims

1. An adaptive digital filter for filtering digital input signals, comprising:

non-recursive filtering means for non-recursively filtering said input signals;

recursive filtering means for recursively filtering said input signals, said recursive filtering means including;

a plurality of preset recursive filters each recursive filter having a different impulse response characteristic;

a plurality of multiplication means, associated with said plurality of recursive filters, for multiplying an output signal of each recursive filter by a corresponding adaptive multiplication factor; and

summing means for forming a linear combination of output signals from said multiplication means;

means for generating an update signal on the basis of an output signal from said summing means and an output from said non-recursive filtering means; and

updating means for updating both said non-recursive filtering means and said adaptive multiplication factors in accordance with said update signal.

2. The adaptive filter according to claim 1, wherein said recursive filters are of the first degree.

3. The adaptive filter according to claim 2, further comprising:

delay means connected to said input signal, for delaying said input signal to said recursive filtering means for a predetermined delay period.

4. The adaptive filter according to claim 1, further comprising:

combining means for linearly combining output signals from said recursive filters and transmitting linear combinations of said recursive filter output signals to said plurality of multiplication means.

5. An adaptive digital filter for filtering a digital input signal, comprising:

non-recursive filtering means for non-recursively filtering said input signal;

recursive filtering means for recursively filtering said input signal;

summing means for summing output signals from said non-recursive filtering means and said recursive filtering means;

error generating means for calculating a difference between an output signal from said summing means and a reference signal;

adjusting means for adjusting said non-recursive filtering means and said recursive filtering means based on said difference.

6. The adaptive filter according to claim 5, wherein said non-recursive filtering means includes:

a plurality of first delay means for generating a series of first delayed input signals;

a plurality of weighting means for weighting said first delay inputs, wherein said adjusting means adjusts the value of each weighting means.

7. The adaptive digital filter according to claim 5, wherein said recursive filtering means includes plural recursive filters, each recursive filter having a preset impulse response characteristic.

8. The adaptive filter according to claim 7, wherein each recursive filter includes:

summing means for summing said input signal and a feedback signal;

second delay means for delaying an output signal of said summing means;

multiplication means for multiplying an output signal of said second delay means by a preset constant and generating said feedback signal; and

weighting means for weighting an output signal of said second delay means, said adjusting means adjusting the value of said weighting means in accordance with said difference.

9. The adaptive digital filter according to claim 8, further comprising:

combining means for linearly combining the output signals of each of said weighting means to generate a linear combination of the infinite impulse responses of said recursive filters.

10. The adaptive digital filter according to claim 8, further comprising:

combining means for linearly combining recursive output signals of said second delay means and transmitting linear combinations of said recursive output signal to said plurality of weighting means.

11. An adaptive digital filter for filtering a digital input signal, comprising:

non-recursive filtering means having a finite impulse response for filtering said input signal;

recursive filtering means having an infinite impulse response for filtering said input signal;

summing means for summing output signals from said non-recursive filtering means and said recursive filtering means;

differencing means for calculating a difference between an output signal from said summing means and a desired signal;

adjusting means for adjusting said non-recursive filtering means and said recursive filtering means relative to said difference.

12. The adaptive digital filter according to claim 11, wherein said recursive filtering means includes a plurality of recursive filters of the first degree.