Automatic adaptive filtering according to frequency modulation rate
First Claim
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.
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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.
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Citations
30 Claims
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1. A method for filtering a modulated signal in which the rate of frequency modulation is variable, the method comprising:
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(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.
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2. A method for filtering signals according to frequency modulation rate comprising the steps of:
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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. - View Dependent Claims (3, 4)
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5. An adaptive filter for filtering out noise signals in a spread spectrum communication network, the filter comprising:
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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.
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6. A method for filtering signal components from a received signal according to frequency modulation rate, the method comprising the steps of:
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(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. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. A communication system for filtering signal components from a received signal according to frequency modulation rate, the system comprising:
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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.
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20. A system for filtering signal components from a received signal according to frequency modulation rate, the system comprising:
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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. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27)
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28. An adaptive finite impulse response filter for filtering a received signal according to frequency modulation rate, said filter comprising:
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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. - View Dependent Claims (29, 30)
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Specification