(12) United States Patent
`(12) United States Patent
`Marash
`Marash
`
`111111111111111111111111111111111111111111111111111111111111111111111111111
`US006483923Bl
`US006483923B1
`US 6,483,923 BI
`US 6,483,923 B1
`*Nov. 19,2002
`*Nov. 19, 2002
`
`(10) Patent No.:
`(10) Patent No.:
`(45) Date of Patent:
`(45) Date of Patent:
`
`(54) SYSTEM AND METHOD FOR ADAPTIVE
`(54) SYSTEM AND METHOD FOR ADAPTIVE
`INTERFERENCE CANCELLING
`INTERFERENCE CANCELLING
`
`(75) Inventor: Joseph Marash, Haifa (IL)
`(75)
`Inventor:
`Joseph Marash, Haifa (IL)
`
`(73) Assignee: Andrea Electronics Corporation,
`Assignee: Andrea Electronics Corporation,
`(73)
`Melville, NY (US)
`Melville, NY (US)
`
`( * )
`( * ) Notice:
`Notice:
`
`Subject to any disclaimer, the term of this
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`U.S.c. 154(b) by 0 days.
`
`This patent is subject to a terminal dis(cid:173)
`This patent is subject to a terminal dis
`claimer.
`claimer.
`
`(21) Appl. No.: 09/130,923
`(21) Appl. No.: 09/130,923
`(22) Filed:
`Aug. 6, 1998
`(22) Filed:
`Aug. 6, 1998
`
`Related US. Application Data
`Related U.S. Application Data
`
`(63) Continuation of application No. 08/672,899, filed on Jun.
`(63) Continuation of application No. 08/672,899, ?led on Jun.
`27, 1996, now Pat. No. 5,825,898.
`27, 1996, now Pat. No. 5,825,898.
`7
`(51)
`Int. CI? .................................................. H04R 3/00
`CC]i ................................................ .. H0423?)
`(52) U.S. CI. ......................................................... 381/92
`(58) Field of Search ............................................ 381/92
`F'ld fS
`5
`h
`1e
`8
`0
`earc .......................................... .. 381/92
`
`(56)
`(56)
`
`References Cited
`References Cited
`U.S. PATENT DOCUMENTS
`U.S. PATENT DOCUMENTS
`5,825,898 A * 10/1998 Marash ........................ 381/92
`5,825,898 A * 10/1998 Marash ...................... .. 381/92
`* cited by examiner
`* cited by examiner
`Primary Examiner—Forester W. Isen
`Primary Examiner~orester W. Isen
`Assistant Examiner—EliZabeth McChesney
`Assistant Examiner-Elizabeth McChesney
`(74) Attorney, Agent, or Firm—Frommer LaWrence &
`(74) Attorney, Agent, or Firm~rommer Lawrence &
`Haug; Thomas J. KoWalski
`Haug; Thomas 1. Kowalski
`(57)
`ABSTRACT
`ABSTRACT
`(57)
`
`An adaptive system and method for reducing interference in
`An adaptive system and method for reducing interference in
`a signal received from an array of sensors. Adaptive filters
`a signal received from an array of sensors. Adaptive ?lters
`are used to generate cancelling signals that closely approxi
`are used to generate cancelling signals that closely approxi(cid:173)
`mate the interference present in the received signal. The
`mate the interference present in the received signal. The
`adaptive ?lter Weights are converted into the frequency
`adaptive filter weights are converted into the frequency
`domain Where the frequency representation values in a
`domain where the frequency representation values in a
`selected frequency range are truncated to avoid signal leak(cid:173)
`selected frequency range are truncated to avoid signal leak
`age involving narroW band signals. Deodorizing ?lters are
`age involving narrow band signals. Deodorizing filters are
`used to produce the cancelling signals having a ?at fre
`used to produce the cancelling signals having a fiat fre(cid:173)
`quency spectrum. Normalized power difference is used limit
`quency spectrum. Normalized poWer difference is used limit
`the operation of the adaptive ?lters to the case Where there
`the operation of the adaptive filters to the case where there
`IS some dIreCIIOnaI InIerferenCe IO be eliminmd
`is some directional interference to be eliminated.
`
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`RTL923_1001-0011
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`

`
`U.S. Patent
`U.S. Patent
`
`Nov. 19, 2002
`Nov. 19,2002
`
`Sheet 11 0f 15
`Sheet 11 of 15
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`US 6,483,923 BI
`US 6,483,923 B1
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`_
`(
`START PROGRAM )/\/
`. START PROGRAM
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`100
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`110
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`1 10
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`REGISTERS, POTNTERS, N
`REGISTERS, POINTERS,
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`& BUFFERS
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`I WAIT FOR INTERRUPT r---J 20
`120
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`131
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`SAMPLES
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`STORE INPUT @140
`
`152
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`
`1 30
`130
`
`1412
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`INPUTS T.D.L i
`
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`150
`150
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`RESULTS N 172 2
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`A
`
`FIG. 11 A
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`RTL923_1001-0012
`
`

`
`u.s. Patent
`U.S. Patent
`
`Nov. 19, 2002
`Nov. 19,2002
`
`Sheet 12 of 15
`Sheet 12 0f 15
`
`US 6,483,923 BI
`US 6,483,923 B1
`
`r---J---l
`,F REPEAEEAi-EE“,
`I REPEAT 170-180 I
`190
`190
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`MULTIPLY VECTORS
`MULHPLY VECTORS
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`DECOLORIZATION
`DECOLORIZAUON
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`_ FILTER COEFF.
`
`202?
`
`201
`
`201 2
`
`REF .CH.
`
`0 20
`200
`
`STORE DECOLORIZED
`STORE DECOLORIZED
`RESULT
`RESULT
`
`210
`21 O
`N
`
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`REPEAT 250315
`I REPEAT 200-210 I
`220
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`MULHPLY VECTORS
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`
`232
`
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`FILTER COEFF.
`
`231
`
`231 2
`
`FLAT FREQ.
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`CANCEWNG SIGNAL
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`______l______]
`FIG.11B
`
`RTL923_1001-0013
`
`

`
`u.s. Patent
`U.S. Patent
`
`Nov. 19, 2002
`Nov. 19,2002
`
`Sheet 13 0f 15
`Sheet 13 of 15
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`US 6,483,923 BI
`US 6,483,923 B1
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`260
`260
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`264
`264
`
`SUMMATION
`SUMMAHON
`
`OUTPUT TO 0/ A
`OUTPUT TO D/A
`
`' 261
`MAIN CH r
`MAIN CH.
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`262
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`POWER
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`270
`STORE OUTPUT
`270
`sTORE OUTPUT
`RESULT N 282
`RESULT
`282
`T
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`+ POWER AVG. X (1- ex )
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`290
`290
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`REF. CH. POWER AVG. N
`REF. CH. POWER AVG.
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`REPEAT 280-290
`1
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`l
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`F\G.11C
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`RTL923_1001-0014
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`

`
`u.s. Patent
`U.S. Patent
`
`Nov. 19, 2002
`Nov. 19,2002
`
`Sheet 14 0f 15
`Sheet 14 of 15
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`US 6,483,923 BI
`US 6,483,923 B1
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`321
`321
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`320
`
`MAIN CH.
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`POWER
`POWER
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`322
`322
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`BINS
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`390
`3-90
`
`FIG.11D
`FIGMD
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`RTL923_1001-0015
`
`

`
`u.s. Patent
`U.S. Patent
`
`Nov. 19, 2002
`Nov. 19,2002
`
`Sheet 15 0f 15
`Sheet 15 of 15
`
`US 6,483,923 BI
`US 6,483,923 B1
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`NO
`
`YES
`
`TRUNCATE m VALUE
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`REPEAT 360-430
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`I
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`440
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`
`FIG.11 E
`
`RTL923_1001-0016
`
`

`
`US 6,483,923 Bl
`US 6,483,923 B1
`
`1
`1
`SYSTEM AND METHOD FOR ADAPTIVE
`SYSTEM AND METHOD FOR ADAPTIVE
`INTERFERENCE CANCELLING
`INTERFERENCE CANCELLING
`
`This application is a continuation of Ser. No. 08/672,889
`This application is a continuation of Ser. No. 08/672,889
`filed Jun. 27,1996, now U.S. Pat. No. 5,825,898, issued Oct.
`?led Jun. 27, 1996, now US. Pat. No. 5,825,898, issued Oct.
`20, 1998.
`20,1998.
`
`2
`2
`cancelling signal, and by adjusting its ?lter Weights to
`cancelling signal, and by adjusting its filter weights to
`minimiZe the mean-square value of the output signal. When
`minimize the mean-square value of the output signal. When
`the ?lter Weights settle, the output signal effectively repli
`the filter weights settle, the output signal effectively repli(cid:173)
`cates the source signal substantially free of the noise com(cid:173)
`cates the source signal substantially free of the noise com
`ponent because the cancelling signal closely tracks the noise
`ponent because the cancelling signal closely tracks the noise
`component.
`component.
`Adaptive noise cancelling can be combined With
`Adaptive noise cancelling can be combined with
`beamforming, a known technique of using an array of
`beamforming, a knoWn technique of using an array of
`sensors to improve reception of signals coming from a
`sensors to improve reception of signals coming from a
`10 specific direction. A beamformer is a spatial filter that
`speci?c direction. A beamformer is a spatial ?lter that
`10
`generates a single channel from multiple channels received
`generates a single channel from multiple channels received
`through multiple sensors by ?ltering the individual multiple
`through multiple sensors by filtering the individual multiple
`channels and combining them in such a way as to extract
`channels and combining them in such a Way as to eXtract
`signals coming from a speci?c direction. Thus, a beam
`signals coming from a specific direction. Thus, a beam-
`former can change the direction of receiving sensitivity
`15 former can change the direction of receiving sensitivity
`15
`without physically moving the array of sensors. For details
`Without physically moving the array of sensors. For details
`on beamforming, see B. D. Van Veen and K. M. Buckley,
`on beamforming, see B. D. Van Veen and K. M. Buckley,
`Beamforming: Versatile Approach to Spatial Filtering, IEEE
`Beamforming: Versatile Approach to Spatial Filtering, IEEE
`ASSP Mag. 5(2), 4—24.
`ASSP Mag. 5(2), 4-24.
`Since the beamformer can effectively be pointed in many
`Since the beamformer can effectively be pointed in many
`directions Without physically moving its sensors, the beam
`directions without physically moving its sensors, the beam-
`former can be combined with adaptive noise cancelling to
`former can be combined With adaptive noise cancelling to
`form an adaptive beamformer that can suppress specific
`form an adaptive beamformer that can suppress speci?c
`directional interference rather than general background
`directional interference rather than general background
`noise. The beamformer can provide the primary input by
`noise. The beamformer can provide the primary input by
`spatially filtering input signals from an array of sensors so
`spatially ?ltering input signals from an array of sensors so
`that its output represents a signal received in the direction of
`that its output represents a signal received in the direction of
`a signal source. Similarly, the beamformer can provide the
`a signal source. Similarly, the beamformer can provide the
`reference input by spatially ?ltering the sensor signals so
`reference input by spatially filtering the sensor signals so
`that the output represents a signal received in the direction
`that the output represents a signal received in the direction
`of interference sources. For a seminal article on adaptive
`of interference sources. For a seminal article on adaptive
`beamformers, see L. J. Griffiths & C. W. Jim, An Alternative
`beamformers, see L. J. Grif?ths & C. W. Jim, AnAlternative
`Approach to Linearly Constrained Adaptive Beamforming,
`Approach to Linearly Constrained Adaptive Beamforming,
`IEEE Trans. Ant. Prop. AP-30:27-34, 1982.
`IEEE Trans. Ant. Prop. AP-30:27—34, 1982.
`One problem with a conventional adaptive beamformer is
`One problem With a conventional adaptive beamformer is
`that its output characteristics change depending on input
`that its output characteristics change depending on input
`frequencies and sensor directions with respect to interfer(cid:173)
`frequencies and sensor directions With respect to interfer
`ence sources. This is due to the sensitivity of a beamformer
`ence sources. This is due to the sensitivity of a beamformer
`to different input frequencies and sensor directions. A uni(cid:173)
`to different input frequencies and sensor directions. A uni
`form output behavior of a system over all input frequencies
`form output behavior of a system over all input frequencies
`of interest and over all sensor directions is clearly desirable
`of interest and over all sensor directions is clearly desirable
`in a directional microphone system where faithful reproduc(cid:173)
`in a directional microphone system Where faithful reproduc
`tion of a sound signal is required regardless of where the
`tion of a sound signal is required regardless of Where the
`microphones are located.
`microphones are located.
`Another problem With adaptive beamforming is “signal
`Another problem with adaptive beamforming is "signal
`leakage". Adaptive noise cancelling is based on an assump(cid:173)
`leakage”. Adaptive noise cancelling is based on an assump
`tion that the reference input representing noise sources is
`tion that the reference input representing noise sources is
`uncorrelated with the source signal component in the pri-
`uncorrelated With the source signal component in the pri
`mary input, meaning that the reference input should not
`50 mary input, meaning that the reference input should not
`contain the source signal. But this "signal free" reference
`contain the source signal. But this “signal free” reference
`input assumption is violated in any real environment. Any
`input assumption is violated in any real environment. Any
`mismatch in the microphones (amplitude or phase) or their
`mismatch in the microphones (amplitude or phase) or their
`related analog front end, any reverberation caused by the
`related analog front end, any reverberation caused by the
`55 surroundings or a mechanical structure, and even any
`surroundings or a mechanical structure, and even any
`55
`mechanical coupling in the physical microphone structure
`mechanical coupling in the physical microphone structure
`will likely cause "signal leakage" from the signal source into
`Will likely cause “signal leakage” from the signal source into
`the reference input. If there is any correlation between the
`the reference input. If there is any correlation betWeen the
`reference input and the source signal component in the
`reference input and the source signal component in the
`primary input, the adaptation process by the adaptive ?lter
`60 primary input, the adaptation process by the adaptive filter
`causes cancellation of the source signal component, result(cid:173)
`causes cancellation of the source signal component, result
`ing in distortion and degradation in performance.
`ing in distortion and degradation in performance.
`It is also important to confine the adaptation process to the
`It is also important to con?ne the adaptation process to the
`case where there is at least some directional interference to
`case Where there is at least some directional interference to
`65 be eliminated. Since nondirectional noise, such as wind
`be eliminated. Since nondirectional noise, such as Wind
`65
`noise or vibration noise induced by the mechanical structure
`noise or vibration noise induced by the mechanical structure
`of the system, is typically uncorrelated with the noise
`of the system, is typically uncorrelated With the noise
`
`20
`
`BACKGROUND OF THE INVENTION
`BACKGROUND OF THE INVENTION
`The present invention relates generally to signal
`The present invention relates generally to signal
`processing, and more speci?cally to an adaptive signal
`processing, and more specifically to an adaptive signal
`processing system and method for reducing interference in
`processing system and method for reducing interference in
`a received signal.
`a received signal.
`There are many instances where it is desirable to have a
`There are many instances Where it is desirable to have a
`sensor capable of receiving an information signal from a
`sensor capable of receiving an information signal from a
`particular signal source Where the environment includes
`particular signal source where the environment includes
`sources of interference signals at locations different from
`sources of interference signals at locations different from
`that of the signal source. One such instance is the use of
`that of the signal source. One such instance is the use of
`microphones to record a particular party's speech in a room
`microphones to record a particular party’s speech in a room
`Where there are other parties speaking simultaneously, caus
`where there are other parties speaking simultaneously, caus-
`ing interference in the received signals.
`ing interference in the received signals.
`If one knows the exact characteristics of the interference,
`If one knoWs the eXact characteristics of the interference,
`one can use a fixed-weight filter to suppress it. But it is often
`one can use a ?xed-Weight ?lter to suppress it. But it is often
`difficult to predict the exact characteristics of the interfer(cid:173)
`dif?cult to predict the eXact characteristics of the interfer
`ence because they may vary according to changes in the
`ence because they may vary according to changes in the 25
`25
`interference sources, the background noise, acoustic
`interference sources, the background noise, acoustic
`environment, orientation of the sensor with respect to the
`environment, orientation of the sensor With respect to the
`signal source, the transmission paths from the signal source
`signal source, the transmission paths from the signal source
`to the sensor, and many other factors. Therefore, in order to
`to the sensor, and many other factors. Therefore, in order to
`suppress such interference, an adaptive system that can 30
`suppress such interference, an adaptive system that can
`change its own parameters in response to a changing envi(cid:173)
`change its oWn parameters in response to a changing envi
`ronment is needed.
`ronment is needed.
`An adaptive ?lter is an adaptive system that can change its
`An adaptive filter is an adaptive system that can change its
`own filtering characteristics in order to produce a desired
`oWn ?ltering characteristics in order to produce a desired
`response. Typically, the ?lter Weights de?ning the. charac
`response. Typically, the filter weights defining the. charac- 35
`teristics of an adaptive filter are continuously updated so that
`teristics of an adaptive ?lter are continuously updated so that
`the difference between a signal representing a desired
`the difference betWeen a signal representing a desired
`response and an output signal of the adaptive filter is
`response and an output signal of the adaptive ?lter is
`minimized.
`minimized.
`The use of adaptive filters for reducing interference in a 40
`The use of adaptive ?lters for reducing interference in a
`received signal has been known in the art as adaptive noise
`received signal has been knoWn in the art as adaptive noise
`cancelling. It is based on the idea of cancelling a noise
`cancelling. It is based on the idea of cancelling a noise
`component of a received signal from the direction of a signal
`component of a received signal from the direction of a signal
`source by sampling the noise independently of the source
`source by sampling the noise independently of the source
`signal and modifying the sampled noise to approXimate the
`signal and modifying the sampled noise to approximate the 45
`45
`noise component in the received signal using an adaptive
`noise component in the received signal using an adaptive
`filter. For a seminal article on adaptive noise cancelling, see
`?lter. For a seminal article on adaptive noise cancelling, see
`B. WidroW et al., Adaptive Noise Cancelling: Principles and
`B. Widrow et aI., Adaptive Noise Cancelling: Principles and
`Applications, Proc. IEEE 63:1692-1716,1975.
`Applications, Proc. IEEE 63:1692—1716, 1975.
`Abasic con?guration for adaptive noise cancelling has a
`A basic configuration for adaptive noise cancelling has a
`primary input received by a microphone directed to a desired
`primary input received by a microphone directed to a desired
`signal source and a reference input received independently
`signal source and a reference input received independently
`by another microphone directed to a noise source. The
`by another microphone directed to a noise source. The
`primary input contains both a source signal component
`primary input contains both a source signal component
`originating from the signal source and a noise component
`originating from the signal source and a noise component
`originating from the noise source. The noise component is
`originating from the noise source. The noise component is
`different from the reference input representing the noise
`different from the reference input representing the noise
`source itself because the noise signal must travel from the
`source itself because the noise signal must travel from the
`noise source to the signal source in order to be included as
`noise source to the signal source in order to be included as
`the noise component.
`the noise component.
`The noise component, however, is likely to have some
`The noise component, hoWever, is likely to have some
`correlation with the reference input because both of them
`correlation With the reference input because both of them
`originate from the same noise source. Thus, a filter can be
`originate from the same noise source. Thus, a ?lter can be
`used to filter the reference input to generate a cancelling
`used to ?lter the reference input to generate a cancelling
`signal approximating the noise component. The adaptive
`signal approximating the noise component. The adaptive
`?lter does this dynamically by generating an output signal
`filter does this dynamically by generating an output signal
`Which is the difference betWeen the primary input and the
`which is the difference between the primary input and the
`
`RTL923_1001-0017
`
`

`
`US 6,483,923 Bl
`US 6,483,923 B1
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`10
`10
`
`3
`3
`component of the received signal, the adaptive ?lter cannot
`component of the received signal, the adaptive filter cannot
`generate a cancelling signal approximating the noise com
`generate a cancelling signal approximating the noise com(cid:173)
`ponent.
`ponent.
`Prior art suggests inhibiting the adaptation process of an
`Prior art suggests inhibiting the adaptation process of an
`adaptive ?lter When the signal-to-noise ratio (SNR) is high
`adaptive filter when the signal-to-noise ratio (SNR) is high
`based on the observation that a strong source signal tends to
`based on the observation that a strong source signal tends to
`leak into the reference input. For example, US. Pat. No.
`leak into the reference input. For example, U.S. Pat. No.
`4,956,867 describes the use of cross-correlation between
`4,956,867 describes the use of cross-correlation betWeen
`two sensors to inhibit the adaptation process when the SNR
`tWo sensors to inhibit the adaptation process When the SNR
`is high.
`is high.
`But the prior art approach fails to consider the effect of
`But the prior art approach fails to consider the effect of
`directional interference because the SNR-based approach
`directional interference because the SNR-based approach
`considers only nondirectional noise. Since nondirectional.
`considers only nondirectional noise. Since nondirectional.
`noise is not correlated to the noise component of the
`noise is not correlated to the noise component of the
`15
`received signal, the adaptation process searches in vain for
`received signal, the adaptation process searches in vain for 15
`neW ?lter Weights, Which often results in cancelling the
`new filter weights, which often results in cancelling the
`source signal component of the received signal.
`source signal component of the rec