Adaptive filter

Claim 2

A filter for blocking signal components within a frequency band having independently variable band width and center frequency comprising: first and second notch filters, each having a center frequency which is variable in response to a frequency control signal; means for connecting said first and second notch filters in series; means for supplying an incoming signal having frequency components between lower and upper frequency limits to said first notch filter; computing means for accepting an input signal and determining first and second frequencies such that the powers represented by portions of the input signal in frequency bands lying between pairs of the lower frequency limit, the first frequency, the second frequency and the upper frequency limit are related in accordance with predetermined criteria; means for supplying the output signal of said second notch filter to said computing means as the input signal; and means for supplying signals indicative of the first and second frequencies respectively as the frequency control signals of the said first and second notch filters.

Claim 3

The filter of claim 1 wherein said computing means determines the first and second frequencies such that equal powers are represented by portions of the input signal in frequency bands bounded by the lower frequency limit and the first frequency, the first and second frequencies, and the second frequency and the upper frequency limit.

Claim 4

In a system for dynamically controlling the position of a water craft which is subject to long term displacement forces caused by water flow and wind and shorter term alternating displacement forces caused by wave action, and wherein the shorter term displacement forces have frequencies between lower and upper frequency limits, the system including sensing means for producing a signal indicative of deviation of the craft from a specified position, propulsion means, signal processing means for producing a control signal indicative of substantially only that portion of the deviation signal which results from the long term displacement forces, and means for supplying the control signal to the propulsion means so that the propulsion means tends to reduce deviation of the craft from the specified position, an improved wave filter which comprises: first and second notch filters, each having a variable center frequency between the lower and upper frequency limits; means for connecting said first and second notch filters in series; means for supplying a signal indicative of the deviation signal to the input of said first notch filter; computing means for accepting an input signal having frequency components between the lower and upper frequency limits and determining first and second frequencies suCh that the powers resulting in portions of the input signal in first, second and third frequency bands respectively bounded by the lower frequency limit and the first frequency, the first and second frequencies, and the second frequency and the upper frequency limit are related in accordance with predetermined criteria; means for connecting said second notch filter to said computing means so as to supply the input signal thereto; and means for setting the center frequencies of said first and second notch filters at the first and second frequencies respectively.

Claim 5

In a system for dynamically controlling the position of a water craft which is subject to long term displacement forces caused by water flow and wind and shorter term alternating displacement forces caused by wave action, and wherein the shorter term displacement forces have frequencies between lower and upper frequency limits, the system including sensing means for producing a signal indicative of deviation of the craft from a specified position, propulsion means, signal processing means for producing a control signal indicative of substantially only that portion of the deviation signal which results from the long term displacement forces, and means for supplying the control signal to the propulsion means so that the propulsion means tends to reduce deviation of the craft from the specified position, an improved wave filter which comprises: first and second notch filters, each having a variable center frequency between the lower and upper frequency limits; means for connecting said first and second notch filters in series; means for supplying a signal indicative of the deviation signal to the input of said first notch filter; computing means for accepting an input signal having frequency components between the lower and upper frequency limits and determining first and second frequencies suCh that the powers resulting in portions of the input signal in first, second and third frequency bands respectively bounded by the lower frequency limit and the first frequency, the first and second frequencies, and the second frequency and the upper frequency limit are related in accordance with predetermined criteria; means for connecting said second notch filter to said computing means so as to supply the input signal thereto; and means for setting the center frequencies of said first and second notch filters at the first and second frequencies respectively.

Claim 6

The invention of claim 3 wherein said computing means determines the first and second frequencies such that equal powers result in portions of the input signal in the first, second and third frequency bands.

Claim 7

The invention of claim 3 wherein said computing means comprises: a power computer for determining the total power in the input signal; means for computing a first power in the portion of the input signal in the first frequency band; means for dividing the first power by the total power to obtain a first quotient; means for computing a second power in the portion of the input signal in the third frequency band; means for dividing the second power by the total power to obtain a second quotient; means for subtracting the first quotient from a first predetermined fraction to obtain a first error signal; means for subtracting the second quotient from a second predetermined fraction to obtain a second error signal; means for adding the first error signal to a signal indicative of the first frequency to provide an updated frequency control signal for setting the center frequency of said first notch filter; and means for subtracting the second error signal from a signal indicative of the second frequency to provide an updated frequency control signal for setting the center frequency of said second notch filter.

Claim 8

The filter of claim 5 wherein said first and second predetermined fractions are each one third.

Claim 9

The filter of claim 5 wherein said power computer comprises: a comb filter for producing a plurality of signals respectively indicative of the amplitudes of portions of the input signal in a plurality of frequency bands; means for squaring each of said plurality of signals; means for integrating each of a plurality of squared signals with respect to time to obtain a plurality of power signals indicative of the powers represented in each of said plurality of frequency bands; and means for summing the plurality of power signals to determine the total power.

Claim 10

The filter of claim 7 wherein: said means for computing the first power comprises means for summing the power signals in bands of said plurality of frequency bands bounded by frequencies lower than the first freqeucny and a portion of the power signal in the band containing the first frequency, the portion being proportional to the portion of the band below the first frequency; and said means for computing the second power comprises means for summing the power signals in bands of said plurality of frequency bands bounded by frequencies higher than the second frequency and a portion of the power signal in the band containing the second frequency, the portion being proportional to the portion of the band above the second frequency.

Claim 11

An adaptive filter for attenuating components of a signal in accordance with at least one signal parameter comprising: a plurality of signal filters, each having a signal transfer characteristic which is variable in response to a control signal, the variable transfer characteristic being suitable for optimizing a predetermined signal parameter; means for connecting said plurality of signal filters in series; means for supplying an incoming signal to the input of the first filter in said series; computing means for analyzing a signal and producing control signals for causing said plurality of filters to opTimize the predetermined signal parameter; means for supplying the output signal of the last filter in said series to the input of said computing means; and means for supplying the control signals produced by said computing means to said plurality of signal filters so as to independently vary the transfer characteristics of at least two filters.

Claim 12

An adaptive filter for attenuating components of a signal in accordance with at least one signal parameter comprising: a plurality of signal filters, each having a signal transfer characteristic which is variable in response to a control signal, the variable transfer characteristic being suitable for optimizing a predetermined signal parameter; means for connecting said plurality of signal filters in series; means for supplying an incoming signal to the input of the first filter in said series; computing means for analyzing a signal and producing control signals for causing said plurality of filters to opTimize the predetermined signal parameter; means for supplying the output signal of the last filter in said series to the input of said computing means; and means for supplying the control signals produced by said computing means to said plurality of signal filters so as to independently vary the transfer characteristics of at least two filters.

Claim 13

The adaptive filter of claim 9 wherein: said plurality of signal filters comprises first and second notch filters, each capable of attenuating signal components in a frequency band whose center frequency is variable in response to a control signal; and said computing means produces control signals suitable for varying the center frequencies of said first and second notch filters so that equal powers are represented by portions of the output signal from second notch filter in frequency bands below the center frequency of said first filter, between the center frequencies of said first and second filters, and above the center frequency of said second filter respectively.

Claim 14

The filter of claim 10 wherein said computing means comprises: a spectral analyzer for producing a plurality of sample power signals each indicative of the power represented by signal components in a frequency band of the output signal from said second notch filter; means for summing all sample power signals to produce a total power signal; means for summing complete and fractional sample power signals at frequencies less than the center frequency of said first notch filter to produce a first partial power signal; means for summing complete and fractional sample power signals at frequencies greater than the center frequency of said second notch filter to produce a second partial power signal; and summing means for combining the total and first and second partial power signals to produce error signals for updating the control signals for said first and second notch filters.

Claim 17

The method of claim 12 wherein: the steps of attenuating variable portions of the input and first intermediate signals comprise attenuating frequency bands centered on first and second variable center frequencies respectively; and the step of generating first and second control signals comprises generating signals suitable for controlling the first and second center frequencies so that equal powers are represented by portions of the second intermediate signal in frequency bands below the first center frequency, between the first and second center frequencies, and above the second center frequency.