System for dynamically adapting the length of a filter

• US 5,909,384 A
• Filed: 10/04/1996
• Issued: 06/01/1999
• Est. Priority Date: 10/04/1996
• Status: Expired due to Term

• Current Assignee: Conexant Systems Incorporated (Synaptics Incorporated)
• Original Assignee: Conexant Systems Incorporated (Synaptics Incorporated)
• Inventors: Cohen, Ron, Tal, Nir, Shapira, Nir
• Primary Examiner(s): MOISE, EMMANUEL LIONEL
• Application Number:
  US08/726,187
• Time in Patent Office: 970 Days
• Field of Search: 364/724.19, 364/724.2, 364/724.011, 370/289, 370/290, 379/410, 379/411, 379/416, 382/261
• US Class Current: 708/322
• CPC Class Codes: G06F 17/10 Complex mathematical operations function generation by table look-up G06F1/03; evaluation of elementary functions by calculation G06F7/544
• CPC Class Codes: H03H 17/0229 reducing the number of taps
• CPC Class Codes: H03H 2017/0245 Measures to reduce power consumption H03H17/0223 takes precedence
• CPC Class Codes: H04B 3/23 using a replica of transmitted signal in the time domain, e.g. echo cancellers
• CPC Class Codes: H04L 2025/03585 Modifying the length
• CPC Class Codes: H04M 9/082 using echo cancellers echo cancellers per se H04B3/23

Abstract

A novel system by which the utilization of a central processing unit (CPU) in performing filtering operations can be reduced by shortening the filter'"'"'s length thus degrading the performance of the system down to a predetermined level or threshold. The present invention is applicable to such systems that incorporate filters whereby shortening their length decreases the performance of the system and to such systems where a reliable quality criteria exists that can be measured during run time. A method iteratively minimizes the filter'"'"'s length so that the quality criteria does not fall below a predetemined threshold level. In addition, a signal to noise ratio (SN) criteria is suggested for estimating the quality of the reception of communication signals. An implementation is suggested for the method in the particular case of an echo cancellation adaptive filter. In addition, a method for determining an immediate approximation of the echo canceler filter'"'"'s length as opposed to finding it iteratively.

Claims

1. A method of dynamically adjusting the length of a digital filter having a plurality of taps, said digital filter utilized in a system wherein said system has at least one measurable quality criteria Q. said method comprising the steps of:

measuring said at least one measurable quality criteria in said system, wherein said measurable quality criteria is derived from any point within said system other than from said dipital filter or from said plurality of taps therein;

comparing said measured at least one quality criteria against a predetermined threshold;

removing M taps from said digital filter and repeating said steps of measuring and comparing if said measured at least one quality criteria is above said predetermined threshold; and

adding M taps to said digital filter if said measured at least one quality criteria is below said predetermined threshold.

2. The method according to claim 1, wherein said at least one quality criteria is a measurable signal to noise ratio at a point within said system.

3. A method of dynamically adjusting the length of an adaptive digital filter (ADF) having an adaptation procedure and a plurality of taps, said ADF utilized in a system wherein said system has at least one measurable quality criteria Q, said method comprising the steps of:

waiting for said adaptation procedure of said ADF to converge;

measuring said at least one measurable quality criteria in said system, wherein said measurable quality criteria is derived fom any point within said system other than from said adaptive digital filter or from said plurality of taps therein;

comparing said measured at least one quality criteria against a predetermed threshold;

removing M taps from said ADF and repeating said steps of measuring and comparing if said measured at least one quality criteria is above said predetermined threshold; and

adding M taps to said ADF if said measured at least one quality criteria is below said predetermined threshold.

4. A method of dynamically adjusting of an adaptive digital filter (ADF) having a plurality of taps, said plurality of taps having an associated set of filter coefficients, said ADF utilized in a system wherein said system has a measurable signal to noise ratio (SNR), said method comprising the steps of:

waiting for said ADF to converge;

measuring said SNR at a suitable point in said system other than within said adaptive digital filter from said plurality of tops therein;

storing said filter coeffcients;

comparing said measured SNR against a predtermined threshold;

removing M taps from said ADF and repeating said steps of measuring and comparing if said measured SNR is above said predetermined theshold; and

restoring said filter coefficients previously stored if said measured SNR is below said predetermined threshold.

5. The method according to claim 4, wherein M is equal to one.

6. A method of dynamically adjusting the length of a least mean squares (LMS) echo canceler initially having L_max number of taps, said echo canceler utilized in a system wherein said system as at least one measurable quality criteria Q, said method comprising the steps of:

waiting for said echo canceler to converge, said echo canceler utilizing said L_max ;

number of taps;

measuring said at least one measurable quality criteria in said system, wherein said measurable quality criteria is derived from any point within said system other than from said echo canceler or from said taps therein;

comparing said measured at least one quality criteria against a predetermined threshold;

removing M taps from said echo canceler and repeating said steps of waiting, measuring and comparing if said measured at least one quality criteria is above said predeterined threshold; and

adding M taps to said echo canceler if said measured at least one quality criteria is below said predetermined threshold.

7. The method according to claim 6, wherein said at least one quality criteria comprises the signal to noise ratio (SNR) at the output of a slicer within said system.

8. A method of dynamically adjusting the length of an adaptive echo canceler initially having L_max number of taps, said taps having an associated set of filter coefficlents, said echo canceler utilized in a system wherein said system comprises a measurable signal to noise ratio (SNR) and echo to signal ratio (ESR), said method comprising the steps of:

waiting for said echo canceler to converge, said echo canceler utilizing said L_max number of taps;

measuring an initial SNR, called SNR_old, at a suitable point within said system;

measuring the ESR at a second suitable point within said system;

calculating a percentage of energy that can be removed from said echo canceler utilizing said SNR_old and said ESR; and

removing M taps from said echo canceler in accordance with said calculated percentage of energy.

9. In a digital filter having a length fir_-- len representing both the number of taps and associated coefficients, a pointer to the first coefficient represented by fir_-- coefs_-- ptr, said filter having a head and a tail, said filter processing a set of data samples wherein a pointer data_-- ptr points to the next sample to be processed, said digital filter utilized in a system wherein said system has at least one measurable quality criteria Q, a method of removing M taps from said head of said filter, said method comprising the steps of:

measuring said at least one measurable quality criteria in said system, wherein said measurable quality criteria is derived from any point within said system other than from said digital filter or from said plurality of taps therein;

comparing said measured at least one quality criteria against a predetermined threshold;

decrementing said filter length fir_-- len by M;

incrementing said pointer to the first coefficient fir_-- coefs_-- ptr by M;

incrementing said data pointer data_-- ptr by M; and

repeating said steps of measuring and comparing if said measured at least one quality criteria is above said predetermined threshold.

10. In a digital filter having a length fir_-- len representing both the number of taps and associated coefficients, a pointer to the first coefficient represented by fir_-- coefs_-- ptr, said filter having a head and a tail, said filter processing a set of data samples wherein a pointer data_-- ptr points to the next sample to be processed, said digital filter utilized in a system wherein said system has at least one measurable quality criteria Q, a method of adding M taps to said head of said filter, said method comprising the steps of:

measuring said at least one measurable quality criteria in said system, wherein said measurable quality criteria is derived from any point within said system other than from said digital filter or from said plurality of taps therein;

comparing said measured at least one quality criteria against a predetermined threshold;

incrementing said filter length fir_-- len by M;

decrementing said pointer to the first coefficient fir_-- coefs_-- ptr by M; and

decrementing said data pointer data_-- ptr by M.

repeating said steps of measuring and comparing if said measured at least one quality criteria is below said predetermined threshold.

11. In a digital filter having a length fir_-- len representing both the number of taps and associated coefficients, said filter having a head associated with a first coefficient and a tail associated with the last coefficient, a pointer to said first coefficient represented by fir_-- coefs_-- ptr, a pointer to the next sample to be processed represented by data_-- ptr, a method of realizing a digital filter with M taps removed from said head of said filter, said method comprising the steps of:

decrementing said filter length fir_-- len by M;

incrementing said pointer to the first coefficient fir_-- coefs_-- ptr by M;

incrementing said data pointer data_-- ptr by M thereby reducing the number of data samples to be filtered by M; and

executing the digital filter utilizing the remaining number of taps and coefficients represented by the value (fir_-- len-M) and the set of data samples reduced in number by M.

12. In a digital filter having a length fir_-- len representing both the number of taps and associated coefficients, said filter having a head associated with a first coefficient and a tail associated with the last coefficient, a pointer to said first coefficient represented by fir_-- coefs_-- ptr, a pointer to the next sample to be processed represented by data_-- ptr, a method of realizing a digital filter with M taps added to said head of said filter, said method comprising the steps of:

incrementing said filter length fir_-- len by M;

decrementing said pointer to the first coefficient fir_-- coefs_-- ptr by M;

decrementing said data pointer data_-- ptr by M thereby increasing the number of samples to be filtered by M; and

executing the digital filter utilizing the increased number of taps and coefficients represented by the value (fir_-- len+M) and the set of data samples increased in number by M.