Automatic adaptive filtering according to frequency modulation rate

• US 5,793,820 A
• Filed: 07/10/1996
• Issued: 08/11/1998
• Est. Priority Date: 07/10/1996
• Status: Expired due to Fees

• Current Assignee: Atheros Communications Incorporated (Qualcomm, Inc.)
• Original Assignee: Intellon Corporation (Qualcomm, Inc.)
• Inventors: Vander Mey, Timothy J.
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): Gluck, Jeffrey W.
• Application Number:
  US08/677,987
• Time in Patent Office: 762 Days
• Field of Search: 375/200, 375/204, 375/350, 455/307, 364/724.19
• US Class Current: 375/350
• CPC Class Codes: H04L 25/03038 with a non-recursive structure H04L25/03031 takes precedence

Abstract

A transversal adaptive finite impulse response (FIR) filter is modified for automatically filtering modulated signal components from a received signal based on frequency modulation rate. Coefficients of the filter are adapted to provide for filtering of signals having undesired modulation rates. The adapting operation includes selectively updating the coefficients using an error signal and iteratively decaying all the coefficients towards zero. The adaptation of the filter coefficients ensures symmetrical coefficient growth and introduces a constant group delay to the received signal to provide for filtering of complex signal components from a received signal according to frequency modulation rate without the use of a reference source.

Claims

1. A method for filtering a modulated signal in which the rate of frequency modulation is variable, the method comprising:

(a) receiving a group of data samples of the modulated signal;

(b) supplying the data samples as input to an adaptive filter;

(c) adapting coefficients of the adaptive filter so that the filter discriminates on the basis of the rate of frequency modulation of the modulated signal.

2. A method for filtering signals according to frequency modulation rate comprising the steps of:

sampling a received signal;

storing data samples of the received signal in a data register;

adapting tap coefficients of a coefficient register for filtering the received signal according to frequency modulation rate such that an undesired modulated signal is substantially attenuated and a desired modulated signal is substantially unattenuated; and

,

supplying a filtered version of the received signal as a filtered output signal.

3. The method of claim 2, wherein said adapting step provides for filtering of the received signal without utilizing data signals supplied from a reference source.

4. The method of claim 2, wherein said desired modulated signal comprises a high-frequency-modulation-rate modulated spread spectrum communication signal and said undesired modulated signal comprises a slowly modulated noise signal.

5. An adaptive filter for filtering out noise signals in a spread spectrum communication network, the filter comprising:

an input for sampling a received signal;

a data register for storing the data samples;

a coefficient register including a plurality of tap coefficients, wherein said tap coefficients are updated and decayed for filtering from the received signal any slowly modulated noise signals and for generating a filtered output signal, wherein said filtered signal includes spread spectrum communication signals having a frequency modulation rate greater than the frequency modulation rate of the modulated signals filtered out.

6. A method for filtering signal components from a received signal according to frequency modulation rate, the method comprising the steps of:

(a) receiving a group of data samples of the received signal;

(b) multiplying each data sample of symmetrical data sample pairs of the group by a coefficient of an adaptive finite impulse response filter, said symmetrical data sample pairs being symmetrical about a center datum of the group;

(c) summing the products of step (b) with the center datum to obtain an error signal;

(d) determining adaptation directions of each data sample of the symmetrical data sample pairs; and

,

(e) adapting the coefficients to cause the error signal to become a filtered version of the received signal, in which signal components are filtered according to frequency modulation rate.

7. The method of claim 6, wherein step (e) further comprises the steps of:

updating a coefficient of the filter using the error signal when each of the data samples of the symmetrical sample pair corresponding to the coefficient has the same adaptation direction; and

,

decaying the coefficients towards zero.

8. The method of claim 7, further comprising the step of:

(f) performing steps (a) through (e) for sequential groups of data samples of the received signal.

9. The method of claim 8, wherein the steps of decaying and updating the coefficients are such that the error signal becomes a filtered version of the received signal containing signal components having frequency modulation rates greater than 2.9×

10⁹ Hz/second.

10. The method of claim 8, wherein the received signal includes structured spread spectrum chirp communication signal components and wherein the steps of decaying and updating the coefficients are such that the error signal becomes a filtered version of the received signal containing the structured chirp signals in substantially unattenuated form.

11. The method of claim 8, wherein said received signal comprises structured signal components having frequency modulation rates less than 2.9×

10⁹ Hz/second and non-structured information signal components having frequency modulation rates greater than 2.9×

10⁹ Hz/second, and wherein the steps of decaying and updating the coefficients are such that the error signal becomes a filtered version of the received signal comprising said non-structured information signals in substantially unattenuated form and said structured signals in substantially attenuated form.

12. The method of claim 11, further comprising the step:

(g) correlating the error signal for extracting the information from the non-structured information signals.

13. The method of claim 8, wherein said received signal comprises structured signal components having frequency modulation rates less than 2.9×

10⁹ Hz/second and structured information signal components having frequency modulation rates greater than 2.9×

10⁹ Hz/second, and wherein the steps of decaying and updating the coefficients are such that the error signal becomes a filtered version of the received signal comprising said structured information signals in substantially unattenuated form and said structured signal components having frequency modulation rates less than 2.9×

10⁹ Hz/second in substantially attenuated form.

14. The method of claim 13, further comprising the step:

(g) correlating the error signal for extracting the information from the structured information signals.

15. The method of claim 8, further comprising the steps of generating a rejected signal, said rejected signal being derived from the sum of the products of step (b) and containing substantially unattenuated signal components having frequency modulation rates less than 2.9×

10⁹ Hz/second and substantially attenuated signal components having frequency modulation rates greater than 2.9×

10⁹ Hz/second.

16. The method of claim 7, wherein steps (d) and (e) further comprise the step of performing a Sign-Sign least means squared algorithm for updating the coefficients of the filter.

17. The method of claim 6, wherein step (e) further comprises the step of symmetrically adapting the coefficients to provide for a constant group delay.

18. The method of claim 6, wherein there is a center coefficient and step (e) further comprises the step of setting the center coefficient equal to zero for avoiding complete cancellation of the received signal.

19. A communication system for filtering signal components from a received signal according to frequency modulation rate, the system comprising:

a receiver for receiving and generating data samples of a spread spectrum signal;

an adaptive finite impulse response filter including a processor and memory, said processor performing the operations of;

multiplying each data sample of symmetrical data sample pairs of a group of data samples of the received signal by respective coefficients, said symmetrical data pairs being symmetrical about a center datum of the group;

computing a sum of products term representative of the sum of the products of the data samples multiplied with the coefficients;

computing an error signal representative of the sum of the sum of products term with the center datum;

determining adaptation directions of each data sample of the symmetrical sample pairs;

updating a coefficient of the filter using the error signal when each of the data samples of the symmetrical sample pair multiplied with the respective coefficient has the same adaptation direction; and

,

decaying the values of the coefficients towards zero, wherein the processor stores and retrieves from the memory values representative of the data samples, the coefficients, the sum of products term and the error signal, and wherein the processor updates and decays the coefficients for filtering the received signal such that a high-frequency-modulation rate modulated spread spectrum communication signal is substantially unattenuated and any slowly frequency modulated signal is substantially attenuated; and

,

a correlator for receiving the filtered version of the received signal and extracting information from the communication signal included in the filtered signal.

20. A system for filtering signal components from a received signal according to frequency modulation rate, the system comprising:

a receiver for receiving and generating data samples of a signal;

an adaptive finite impulse response filter including a processor and memory, said processor performing the operations of;

multiplying each data sample of symmetrical data sample pairs of a group of data samples of the received signal by a coefficient, said symmetrical data pairs being symmetrical about a center datum of the group;

computing a sum of products term representative of the sum of the products of the data samples multiplied with the coefficients;

computing an error signal representative of the sum of the sum of products term with the center datum;

determining adaptation directions of each data sample of the symmetrical sample pairs;

updating a coefficient of the filter using the error signal when each of the data samples of the symmetrical sample pair multiplied with the respective coefficient has the same adaptation direction; and

,

decaying the values of the coefficients towards zero, wherein the processor stores and retrieves from the memory values representative of the data samples, the coefficients, the sum of products term and the error signal, and wherein the processor updates and decays the coefficients for filtering a modulated signal component from the received signal according to frequency modulation rate and for causing the error signal to become a filtered version of the received signal.

21. The system of claim 20, wherein the processor computes error signals and updates and decays the coefficients for sequential groups of data samples of the received signal.

22. The system of claim 21, wherein the system is a spread spectrum power line system.

23. The system of claim 22, wherein the received signal includes spread spectrum chirp communication signals, and wherein the processor updates and decays the coefficients for generating an error signal containing the chirp signals in substantially unattenuated form.

24. The system of claim 21, wherein the processor updates and decays the coefficients for generating an error signal containing signal components having frequency modulation rates greater than 2.9×

10⁹ Hz/second.

25. The system of claim 21, wherein said received signal comprises structured signal components having frequency modulation rates less than 2.9×

10⁹ Hz/second and non-structured information signal components having frequency modulation rates greater than 2.9×

10⁹ Hz/second, and wherein the processor updates and decays the coefficients for generating an error signal comprising said non-structured information signal components in substantially unattenuated form and said structured signal components in substantially attenuated form.

26. The system of claim 21, wherein said received signal comprises structured signal components having frequency modulation rates less than 2.9×

10⁹ Hz/second and structured information signal components having frequency modulation rates greater than 2.9×

10⁹ Hz/second, and wherein the processor updates and decays the coefficients for generating an error signal comprising said structured information signal components in substantially unattenuated form and said structured signal components in substantially attenuated form.

27. The system of claim 20, wherein the processor performs a Sign-Sign least means square algorithm for determining the adaptation directions based on the signs of the data samples of a data sample pair and for updating the coefficients.

28. An adaptive finite impulse response filter for filtering a received signal according to frequency modulation rate, said filter comprising:

means for grouping data samples of the received signal;

multiplication means for multiplying each data sample of symmetrical data sample pairs of a current group of data samples of the received signal by respective coefficients, said symmetrical data pairs being symmetrical about a center datum of the current group;

sum of products term means for computing the sum of the products of the data samples multiplied by the coefficients;

error signal generating means for computing the sum of the value computed by the sum of products means and the center datum;

adaptation direction means for determining the adaptation directions of each data sample of the symmetrical sample pairs;

updating means for updating a coefficient of the filter using the error signal generated by the error signal when each of the data samples of the symmetrical sample pair multiplied with the respective coefficient has the same adaptation direction; and

,

decaying means for decaying the values of the coefficients towards zero, wherein the updating means and decaying means adapt the values of the coefficients for filtering a modulated signal component from the received signal according to frequency modulation rate and for causing the error signal to become a filtered version of the received signal.

29. The filter of claim 28, wherein said received signal comprises structured signal components having frequency modulation rates less than 2.9×

10⁹ Hz/second and structured information signal components having frequency modulation rates greater than 2.9×

10⁹ Hz/second, and wherein the error signal becomes a filtered version of the received signal comprising said structured information signal in substantially unattenuated form and said signal components having frequency modulation rates less than 2.9×

10⁹ Hz/second in substantially attenuated form.

30. The filter of claim 28, wherein the adaptation direction means and the updating means perform a Sign-Sign least means square algorithm for determining adaptation directions based on the signs of the data samples of a data sample pair and updating the coefficients, respectively.