II
`
`USOO5627799A
`[11] Patent Number:
`[45] Date of Patent:
`
`I
`
`II
`
`5,627,799
`May 6, 1997
`
`United States Patent [19]
`Hosbuyama
`
`[54] BEAMFORMER USING COEFFICmNT
`RESTRAINED ADAPTIVE FILTERS FOR
`DETECTING INTERFERENCE SIGNAlS
`
`[75]
`
`Inventor: Osamu Hosbuyama. Tokyo. Japan
`
`[73] Assignee: NEe Corporation. Tokyo. Japan
`
`[21] App!. No.: 523,059
`
`[22] Filed:
`
`Sep. 1, 1995
`
`[30]
`
`FOf'Cign Application Priority Data.
`
`Sep. 1, 1994
`(JPI
`Japan .................................... 6-208635
`JnL CI.6 ...................................................... GOIS 15/00
`[51}
`[52] U.S. Cl. .......................... 367/121; 3671901 ; 367/119;
`367/905; 381/94
`[58J Field or Seal"Ch .............................. 367112. 119, 121.
`367/123, 129.901. 905. 103; 128/661.01;
`381194
`
`[56)
`
`Re£erences Cited
`U.S. PATENT DOOJMENTS
`3,763,490 1011973 Hadley et aI ........................... 3421375
`9/1990 Zurek et aI ............................ 381194.1
`4,956,867
`
`UfHER PUBUCATIONS
`
`L Griffiths et al .• "An Alternative Approach to Linearly
`Constrained Adaptive Beamforrning", IEEE Transactions
`on Antennas and Propagation, vol. AP-30, No.1, Jan. 1982.
`pp.27-34.
`S. NordhoIm et aI., 'The Board-Band Wiener Solution for
`Griffiths-Jim Beamfonne.rs", IEEE Transactio"" on Signal
`Processing, vol. 40. No.2. Feb. 1992, pp. 474-479.
`
`I. Qaesson el aI., "A Spatial Filtering Approacb to Robust
`Adaptive Beaming", IEEE Transactions on Antennas and
`Propagation, vol. 40, No.9, Sep. 1992, pp. 1093-10%.
`"Processing Signals Carried By Propagating Waves". Mul(cid:173)
`tidimensional Digital Signal Processing. Prentice-Hall
`Inc., pp. 289-315.
`M.M. Goodwin r:tal., "Con~tantBeamwidth Reamfonning",
`Proceedings of Intemational Conference on Acoustics,
`Speech and Signal Processing 93, pp.I-169-1-172.
`
`Primary Examiner-Ian ). Lobo
`Attomc); A.gen~ or Firm-Sughrue. Mian, Zinn. Macpeak: &
`Seas
`
`[57]
`
`ABsrRACT
`
`In an adaptive array beamfonner. a spatial beamfocming
`filter is connected to a sensor array for respectively filtering
`and swnrning array signals to produce a titst filter output
`conlaining a target signal that arrives in a specified direction.
`First adaptive filters provide transversal-filleting the first
`filler output to produce a second filler output not containing
`the target signal. using a firsl error signal by restraining their
`tap weight coefficients. The array signals are further coupled
`to subtractors. Each subtractor detects a difference between
`the second filter output of the corresponding titst adaptive
`filler and the corresponding sensor signal to derive the first
`error signal. Second adaptive filters provide transversal(cid:173)
`filtering the first error signals of the sublractors to produce
`third filter outputs, using a second error signal, by restrain(cid:173)
`ing their tap weight coefficients. The third filter outputs are
`summed and sublracted from the first filter output to proquce
`an output of the beamfonner. which is supplied as the serond
`error signal to the second adaptive filters
`
`10 Claims, 11 Drawing Sheets
`
`1
`
`,",\'b-----r-r--"-i
`17
`._ C ____ _
`!PAiIAl
`lO\'lPAil Lr-Q'~E"~Y']--+' ;;'.~+
`film r
`,
`! 12
`i ,
`i
`i
`
`iPATIAl
`HIGHPASi
`film
`16
`, ___ . ___ . ___ .1 _____ 1. ___ ,
`! ,
`i
`
`7Q
`OHAY
`
`,
`i
`!
`7101·1
`
`._---,
`
`"
`
`• • • E •
`
`~UAY
`
`i
`~.
`i
`101.1_1
`SIol_I
`!
`. _ __ ._._. ___ ._._._._. _J ---.----------'
`
`RTL898_1023-0001
`
`Realtek 898 Ex. 1023
`
`

`
`U.S. Patent
`
`May 6, 1997
`
`Sheet 1 of 11
`
`5,627,799
`
`FIG. 1
`PRIOR ART
`
`6
`
`A
`o
`o
`~r-~------~~~}--------1 l
`FILTER
`,
`,
`,
`,
`,
`,
`,
`,
`,
`,
`20;
`,
`,
`,
`,
`,
`,
`,
`,
`,
`,
`,
`,
`,
`,
`,
`,
`,
`20M_I
`,
`,
`,
`,
`filTER
`________________ ____________ ________ _ ~-J
`
`4
`
`32
`
`L-{~DIi:EL:~3 YJ--t-!:-- --;-;-3+ ~r--:"""1- r--- - -- -;' __ -o~5
`-
`'---+--, I Jf
`3~o I.----t ~
`LAF (fig.3)
`
`I
`
`i l
`
`
`,
`,
`I
`
`LAF
`
`:
`
`[
`
`I
`
`:
`
`:
`
`'
`
`'
`
`I
`
`~J.f~I--~, -{~~I :J_+_1
`SPATIAL
`A
`I
`HIGHPASS
`0
`I
`: 0
`30)1 :
`FILTER
`:
`,
`' I I
`BANK ! , :
`: E
`I
`'
`' I :
`: R
`I
`{Fig. 2) : , I
`I
`,
`I
`'
`I
`I
`LAF
`'
`I
`~ !
`i
`JOM_Q)
`__ __ __ __ __________ J
`
`, ,
`
`\ , , , , , , , , , , , , , , , , ,
`
`LAF" Leaky Adaptive Filter
`
`RTL898_1023-0002
`
`

`
`U.S. Patent
`
`May 6, 1997
`
`Sheet 2 of 11
`
`5,627,799
`
`12
`
`FIG. 2 PRIOR ART
`SPATIALHIGHPASSFIlTERBANK6
`------------_._------1-----
`r·-------------·----) 400 i
`,
`11::t~~~==iO=E~FIILTIERE~4~10~ ~2 i
`411
`'
`I
`41) D
`A
`fo
`D H--\-...l...o-i
`,
`: E
`41 Q_I
`: R
`'
`fIlTER
`~-------------------j
`r-------------- -----, 40
`410
`~ 1
`fiLm
`1
`142
`
`fiLTER
`
`f IL TER
`
`filTER
`
`filTER
`
`o
`
`0
`
`411
`
`A
`41 ) D
`, D
`,
`, , ,
`E
`,
`R
`41 Q_I
`
`f iLTER
`~._. _____________ __ J
`r -------------- ----- ) 40
`oJ )
`142
`
`TO
`LEAKY
`ADPTV
`fiLms
`30
`
`410
`
`411
`
`A
`D
`D f-+---r--'--
`: E
`1
`: R
`41Q_l f
`
`0
`
`o
`
`o
`
`1
`o
`
`o
`
`fiLm
`
`FIlTER
`
`filTER
`
`o
`
`!
`FIlTER
`l ______________ . _ __ . .J
`, ,
`: , , :
`
`40M Q
`-·-·-·- ·-·-·------v
`i 42
`41
`!
`411
`fiLm
`0
`
`41)
`
`,
`
`A
`D
`D H---I-~-J
`, E
`'
`1 R !
`41 Q_I !
`1
`i
`!
`F I lTER !
`L _________ .-:.-:-=:=-:::-...:...-:::=:=:.-:-..:.:::-_----' __ J
`
`filTER
`
`fIlTER
`
`RTL898_1023-0003
`
`

`
`U.S. Patent
`
`May 6, 1997
`
`Sheet 3 of 11
`
`5,627,799
`
`FIG. 3
`PRIOR ART
`31
`FROM DELAY 1 ++.~---------------------,
`
`300
`r · ----~---- ·-· --- - -------------- --- ----------
`i
`i
`,
`1
`
`i
`,
`1
`i
`i
`,.
`I
`"
`I
`
`510
`:-----
`-J - ______ :
`:
`. ,55
`,
`!
`XV
`,
`,
`'
`: ,--- --------: :
`, ,
`: 1
`::
`56
`,
`+
`l :
`58
`l : , , , ,
`
`I
`
`I
`
`z-t
`
`J
`
`x
`
`~4,
`x
`~
`
`ill
`v
`
`5lL_l
`'
`
`,
`
`Upd,le
`
`VV"Uit\
`r-
`----------
`
`5/lL_I
`
`Upd, te
`1-.., ,;;Circuit
`
`~57!
`: : , ,
`Leaky )l~ ~~~~~-L~_- ++---01-+ ___ +~+-+_~_ •
`
`Integrator
`
`!
`!
`- I
`i 31
`A
`1l1t~t====t==~==, ~ O
`'I
`:
`0
`E f-t-I -i
`:
`R I
`i
`'
`!
`501
`500
`FO
`:
`[2}-
`A
`/ i
`-------
`Z-I
`Z- I
`o
`l ________ ________ " _ ____ " _ __ ____________ ______ "
`o
`~ ________ ~~~~}_------~i
`
`x
`
`510
`
`III
`
`x
`
`I--
`
`___________ ~ --4
`
`51l_1/
`
`51
`
`51 l7T'
`-
`
`50l_1
`
`~-------------_[JL~EA~KY~A~O~AP~TI~VEJF~ll T~E~R }-------------~
`
`'--
`
`-
`
`RTL898_1023-0004
`
`

`
`U.S. Patent
`
`May 6, 1997
`
`Sheet 4 of 11
`
`5,627,799
`
`FIG. 4
`
`o
`
`5
`
`y ,/'
`
`...
`
`SPATIAL
`, ! lOWPASS
`, , ,
`,
`FILTER
`.. ,//
`!
`1
`M-I I
`''-I~::r,--H--I
`'--------'
`
`(3
`DELAY
`
`SPATIAL
`HIGH PASS
`fiLTER
`
`16
`
`'
`
`11
`
`17
`.-~----- r -----)
`r-r---{~~=r---tl~+
`+
`1
`! 12
`-
`'
`1
`1
`,
`1
`i
`,--------- _ _ 1. ___ _ _ .1...-__ ) I
`'
`!
`8
`I'
`,
`.~ I
`1
`i '
`!
`i ! 100 ,r----t
`!
`(70 H LAf
`~ DELAY
`. 1
`LAF
`i !
`1
`I'
`, 1
`1 '
`7
`I'
`' 1 101
`I' (
`I
`(' I
`!
`A
`,I
`DELAY
`LAf
`o
`,
`!
`I
`i !
`I 0
`:
`I
`'
`E
`' :
`I
`I
`:
`'
`R
`. ,
`1
`I i '
`,
`1
`,7M-1
`'
`1
`I-LH! ~~I~
`i
`LAF
`DELAY
`i
`!
`'--
`10M_I
`9M-l
`1. __ _ . ___ ._ . _ __________ ) ___________ ___ .1
`
`; , , ,
`i
`I ,
`I , , ,
`I , , ,
`
`RTL898_1023-0005
`
`

`
`U.S. Patent
`
`May 6,1997
`
`Sheet 5 of 11
`
`5,627,799
`
`FIG. 5
`
`17
`r---"----- ------.
`\3
`~r_~~OE~~~Y]---_t'~++r-~·
`I
`12
`-
`
`-~
`
`SPATIAL
`! LOWPASS
`!
`f iLTER
`, ,
`
`SPA TlAL
`HIGHPASS
`fi LTER
`16
`r---.i----- f---- ---'-------.
`,
`I
`,
`I
`,
`I
`·
`.
`I
`I
`,
`I
`I
`W-r
`,
`i !
`I
`,
`' I
`I
`I ,
`,
`,
`I 131
`I
`I ,
`( I
`i
`I
`•
`,
`NCAF
`· !
`I
`,
`,
`I
`,
`,
`,
`,
`I
`,
`,
`,
`I
`,
`,
`I
`,
`,
`,
`I
`,
`,
`,
`I
`,
`I
`,
`I
`I
`i
`,
`+
`•
`,
`I
`,
`9M_I
`I
`,
`I
`________________ ______ J
`
`13\0 I
`NCAf
`
`11
`
`90
`
`+
`91
`•
`
`A
`,
`D
`, D
`,
`,
`,
`,
`E
`, R
`,
`,
`,
`•
`,
`,
`, ,
`,
`,
`
`I
`NCAF
`,
`-
`13M-I
`--------------)
`
`.
`
`i , , , , , .
`
`, , , , , , , , , , , , , ,
`
`/0
`DElAY
`
`( 71
`DELAY
`
`M-I
`
`DELAY
`
`8,0 I
`H LAf
`
`+
`
`+
`
`~I I
`H LAf
`-
`, +
`,
`,
`,
`,
`,
`,
`,
`,
`
`8M;1
`
`LAF
`
`-
`
`+
`
`NCAf ~ Norm-Constrained Adaptive Filter
`
`RTL898_1023-0006
`
`

`
`U.S. Patent
`
`May 6, 1997
`
`Sheet 6 of 11
`
`5,627,799
`
`~
`
`FIG. 6
`II
`fROM DELAY J + +v-
`130
`r .
`---~--- ---- - -------- --------------------- --~ ·
`~ CONSTRAINT I
`x
`•
`COEFFICENT
`I
`•
`GENERfTOR
`I ,
`I ,
`I
`,
`I
`·
`I
`,
`I
`,
`I
`,
`I
`,
`
`630
`,------ ------V
`6 0-
`66
`+
`63 Update
`I 68 , ~ Circuit \..-...
`-
`67
`
`- - - ______ 0
`
`x
`L-
`L _____ --- -,
`
`--~
`
`z-
`
`,
`,
`, ,
`, ,
`,
`J )h-I
`-
`-
`
`L.1 6Jt-l
`
`-
`-
`
`(fig. 7)
`
`,
`
`69 )
`r-
`A
`0
`0
`E
`R
`
`62
`
`A
`0
`0
`E
`R
`
`' -
`
`I
`,
`I
`;
`,
`I
`,
`---------~;t~ 61t~
`I
`,
`I ,
`I ,
`l-
`601
`I
`------- ~ i
`Z-I
`___ . _ __ ._. _____ . _ ____ __ . ___ .J
`I~
`
`,
`,
`, ,
`,
`
`60t_l
`
`~ ~
`611,)
`
`x
`610,)
`f-
`
`600
`Z-I
`------------
`
`fROM
`SUBTR·
`ACTORS
`90-9M-1
`
`- , , , , , , , , , , , , ,
`
`'-
`
`NORM·CONSTRAINED ADAPTIVE FILTER
`
`13{
`
`, ,
`NORM·CONSTRAINED ADAPTIVE FILm
`
`,IlM_1
`
`, , , , , , , , , , ,
`
`RTL898_1023-0007
`
`

`
`U.S. Patent
`
`May 6, 1997
`
`Sheet 7 of 11
`
`5,627,799
`
`FIG. 7
`70
`r------------------I-----
`'I
`72
`710
`,
`I
`,
`!
`1
`i
`,
`i
`1
`,
`,
`1
`,
`I
`,
`I
`,
`I
`,
`I
`,
`I
`,
`I
`I
`i
`,
`,
`I
`,
`I
`'-----
`,
`I
`L ______________________ J
`'
`I
`
`(}
`
`I--
`
`(, l I--
`,
`,
`,
`,
`,
`,
`,
`,
`7\1 i
`( , )p
`
`I--
`
`7l
`
`A
`D I- ( , ) 1 /p
`D
`E
`R
`
`711
`
`FROM
`UPDATE
`CIRCUITS
`63
`
`L/
`
`7~
`
`DIVISION
`CIRCUIT
`
`l - 8
`
`8
`L P '-
`
`~5
`
`MINIMUM
`SELECTOR
`
`~ 11
`
`-
`
`FIG. 10
`OUTPUT
`
`In -------------.,.---
`
`'n ---!'----~----'--- INPUT
`o
`
`---'<------------- 'n
`
`RTL898_1023-0008
`
`

`
`U.S. Patent
`
`May 6, 1997
`
`Sheet 8 of 11
`
`5,627,799
`
`FIG. 8
`
`S
`
`SPATIAL
`i LOWPASS
`i
`FILTER
`• ,
`
`\3
`DELAY
`
`17
`( __ ;-_'L __ ,----- -1
`. +
`.
`! 12
`-
`I
`I •
`I • I •
`SPATIAL
`16
`HIGHPASS
`I
`i
`(. -
`...<,FllTER
`.--_________ L. _ __ __ .
`I I
`..
`140 t,----., I I
`..
`,
`/0 H em
`DELAY
`
`I
`
`II I~o ,r--;
`
`11
`
`o
`\,~
`';
`I ,///
`
`,
`
`i , , , , , , ,
`• , , , , ,
`• ,
`• , ,
`•
`
`_-
`·
`I
`•
`I
`
`•
`
`i
`· I · I
`
`( 71
`DELAY
`,
`, ,
`, , ,
`•
`,
`• , ,
`,
`7M_1
`
`DELAY
`
`•
`I
`r--LH-l~J-t~ ~
`!
`! 0
`I
`,
`•
`: E
`I
`, R
`•
`!
`I
`I
`•
`I
`r---'i •
`•
`r-1-H-cb-1' '-
`I
`!
`!!
`I
`10M_I
`9M_1
`' __ _ __________ _________ ~ ~ ________ ____ _ J
`
`(eAF = (oeflici~ n t·Constrained Adaptive Filter
`
`RTL898_1023-0009
`
`

`
`U.S. Patent
`
`May 6, 1997
`
`Sheet 9 of 11
`
`5,627,799
`
`FIG. 9
`FROM SUBTRACTOR 9k
`
`COEFFICIENT(cid:173)
`CONSTRAINlD
`ADAPTIVE FILTER
`
`--/------- -------- _ ___ ____ _ __ ___ L ________ __ _
`~ ~-
`';)5 V V Circuit '--
`------ ------: 830
`' ,
`,
`t--
`, ,
`,
`86
`, ,
`+
`,
`,
`88 ,
`, ,
`, , ,
`I- I
`, ,
`87 ,
`, ,
`,
`,
`,
`,
`,
`,
`,
`,
`,
`,
`----- - ---- -
`• I
`,
`I ,
`I
`
`X
`
`LM
`
`c-
`
`-
`
`X
`
`83, Update
`
`----- ---_.
`
`~N-I
`
`-
`
`i-
`
`J3N-'
`
`f-
`
`,
`,
`,
`,
`,
`,
`,
`,
`, ,
`
`,
`,
`, ,
`,
`
`MEMORY
`I
`IN
`_, ~N-'
`,
`,
`i
`i
`,
`,
`,
`,
`,
`,
`,
`,
`,
`,
`,
`,
`,
`,
`,
`,
`I,
`~,
`10
`'0
`r- ~9
`A
`D
`D
`E
`R TO SUBTR-
`ACTOR 9k
`
`I
`•
`I •
`800
`80,
`I
`FROM
`Z-1
`-
`Z-1
`Z-1
`-------
`•
`I
`FILTER 2 ,
`J
`'----------------- --- ---- ------------------ - -
`
`---------;;N~
`81N~ -r
`~
`
`82
`
`r-
`
`X
`
`810
`
`X)
`
`81,
`
`~
`
`~
`
`RTL898_1023-0010
`
`

`
`u.s. Patent
`
`May 6,1997
`
`Sbeet 10 of 11
`
`5,627,799
`
`o
`
`FIG . 11
`
`5
`
`SPATIAL
`! LOWPASS
`, , ,
`:
`fiLTER
`
`(l
`
`17
`__ __ _ \.:.: __ '-__ _
`
`~-r---{~~~----+I~+
`'+}---f
`! 12
`
`DELAY
`
`,
`I ,
`I
`,
`I .
`,
`,
`I I
`,
`,
`I I
`,
`,
`I I
`,
`,
`. ,
`I I
`I I
`I
`,
`,
`. .
`NCAf
`I
`I I
`9M_1
`13M_1
`-
`l _______________________ ) ~ _____________ ....J
`
`11
`
`, , ,
`
`1 l~ I
`NCAf
`
`1 (1 I
`NCAf
`,
`, ,
`, ,
`,
`, , ,
`,
`,
`
`CCAf 0 Coefficient-ConSirai ned Adap1ive filter
`NCAf 0 Norm-Constrained Adaptive filter
`
`RTL898_1023-0011
`
`

`
`U.S. Patent
`
`May 6, 1997
`
`Sheet 11 of 11
`
`5,627,799
`
`1 ~ ,
`I" :--
`';""
`,
`,
`~ :
`
`I
`
`I
`I
`
`I
`
`~
`
`I
`
`, ,
`I , ,
`
`I
`I
`
`I
`
`,
`, ,
`I ,
`
`I
`I
`
`FIG. 12
`
`2
`\
`
`SPATIAL
`LOWPASS
`fiLTER
`
`,15
`
`SPATIAL
`LOWPASS
`FILTER
`
`/0
`DELAY
`
`( 71
`DELAY I
`, ,
`I ,
`I ,
`I , ,
`I ,
`1M- I
`
`I
`
`DELAY
`
`T o DElAY J
`
`REFEREN CE
`SI~ AL
`
`TO ADAPTIVE FILTERS
`80 -8M_I OR 140-14M_I
`
`,
`
`>-
`
`TO SU BTRACTORS 90 - 9M_I
`
`~
`
`, ,
`,
`,
`,
`, ,
`,
`, ,
`, ,
`
`, , , , ,
`
`/ , , , , ,
`
`• , , , , , , , , , , , , , , , , , , , ,.
`
`RTL898_1023-0012
`
`

`
`5,627,799
`
`1
`BEAMFORMER USING COEFfiCIENT
`RESTRAINED ADAPfIVE FILTERS FOR
`DETECTING INTERFERENCE SIGNALS
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`The present invention relates generally to interference
`cancelers. and more particularly to a generalized sidelobe
`CLlnceler. or adaptive bcamfocmc:r for an array of SCD$()rlj
`such as microphones and the like.
`2. Description of the Related Art
`It is known that wideband signals propagating across an
`array of sensors in directions that are different than the beam
`steering direction of the array suffer a distortion that is
`similar to lowpass filtering.
`According to a prior art microphone array. signals
`detected by an array of microphones are lowpass filtered and
`summed together to detect a target signal thaI arrives in a
`particular direction. The adaptive microphone array beam(cid:173)
`fonner is one form of the generalized sidelobe canceler as
`described in an article "An alternative Approach to Linearly
`COD strained Adaptive Beamfonning". Uoyd 1. Griffiths and
`Charles W. Jim, the IEEE Transactions on Antenna and
`Propagation, Vol. AP-30. No. L January 1982. pages 27-34.
`As described in an article 'The Broad-Band Wiener Solution
`for Griffiths-Jim Beamformers", S. Nordholm. 1 Claesson
`and P. Eriksson, the IEEETransactions on signal Processing,
`VoL 40, No.2, February 1992, pages 474-478 (hereinafter
`referred to as Document 1), the generalized sidelobe can(cid:173)
`celer compf"ises, a spatial lowpass filter connected to an
`array of microphones for filtering signals from the array and
`summing the filtered signals so that only the desired signal
`is contained in the summed signal. A plurality of spatial
`highpass filters are provided to fmn a spatial bighpass filter
`bank. Each spatial highpass filer is connected to a selected
`pair of microphones for filtering and summing the sensor
`signals to detect the interlcrencc signals. A plurality of
`adaptive filters are provided for using the interference sig(cid:173)
`nals as reference signals to detect those components having
`high correlation with the interference signals contained in
`the detected target signal.
`Since the spatial bighpass filters of Document 1 are of
`nonadaptive type and each uses two microphone outputs. the
`range of signals which must be rejected is very narrow, As
`a result, a slight departure from the intended direction causes
`a leakage of the desired signal into the interference path of
`the beamfonner.
`To overcome the prior art shortcoming, a proposal has
`been made to implement a spatial bighpass filter for receiv(cid:173)
`ing more than two microphone outputs as described in an
`article "A Spatial Fllterlng Approach to Robust Adapdve
`Beaming". 1. Qaesson et al, the 1EEE Transactions on
`Antennas and Propagation. Vol. 40, No.9, September 1992, S5
`pages 1093 to 1096 (hereinafter referred to as Document 2).
`According to Document 2, each of the bighpass filters that
`comprise the spatial highpass filter broadens the range of
`arrival angles by receiving multiple spatial samples from a
`selected set of microphone outputs using a plurality of leaky 60
`adaptive filters.
`However, a large number of microphones (the Q value)
`are required to implement a beamformer having a wide
`range of rejection angles. for each group of spatial highpass
`filters in the filter bank. H a sufficient nwnber of miaa- 6~
`phones is not provided. the degree of design freedom must
`be sacrificed. resulting in a beamfonner having a low noise
`
`2
`canceling capability. The difference between the assumed
`direction and the actual arrival direction of the target signal,
`or a look-direction error. is of another concern because it
`degrades the target signal, or a look-direction error. is of
`5 another concern because it degrades the target signal In
`order to compensate for this shortcoming. the spatial high(cid:173)
`pass filter bank of the prior art needs as many spatial
`highpass filters as is necessary (0 provide a wide range of
`angles to reject the target signal to prevent its leakage into
`10 the Interference palh of the beamfonner.
`
`SUMMARY OF THE INVENTION
`It is therefore an object of the present invention to provide
`an adaptive array bearnfonner with a reduced number of
`15 sensors while allowing a look-direction error.
`According to the present invention. there is provided an
`adaptive array beamformer comprising an array of spatially
`distributed sensors. and a spatial beamfonning filter con(cid:173)
`nected to the sensors for respectively filtering output signals
`20 of the sensors and summing the filtered output signals to
`produce a first filter output containing a target signal arriving
`at the array in a specified direction. A plurality of first
`adaptive filters are provided. each having a tapped-delay line
`connected to receive the first filter output. a coefficient
`25 update circuit for producing tap weight coefficients indicat(cid:173)
`ing correlations between tap signals from the tapped-delay
`line and a first error signal applied thereto. a plurality of
`multipliers for weighting the tap signals with the
`coefficients. respectively, and means for summing the
`30 weighted tap signals to produce a second filter output not
`containing the target signal The coefficient update means
`includes restraining means for preventing the coefficients
`from increasing indefinitely. A plurality of first subtractors
`are provided, each detecting a difference between a COITe-
`35 sponding sensor signal and the second filter output of the
`corresponding first adaptive filter and supplying the di1fer(cid:173)
`ence to the coefficient update circuit of the corresponding
`first adaptive filter as the first error signal. A plurality of
`second adaptive filters are provided, each having a tapped-
`40 delay line connected to receive the error signal from a
`coaespooding one of the first subtractors. a coefficient
`update circuit for producing tap weight coefficients indicat(cid:173)
`ing correlations between tap signals from the tapped-delay
`line and a second error signal applied thereto, a multiply-
`4S and-sum circuit for weighting the tap signals with the
`coefficients respectively and summing the weighted tap
`signals to produce a third filter output. The coefficient update
`circuit includes restraining means for preventing the coef(cid:173)
`ficients from increasing indefinitely. An adder is provided
`SO for summing the third filter outputs from the second adaptive
`filters, A second subtractor detects a difference between the
`first filter output and the output of the adder and supplying
`the difference to the coefficient update circuit of the second
`adaptive filters as the second error signal.
`In a preferred embodiment. a second spatial bcamforming
`filter is connected to the sensors for respectively filtering
`output signals of the sensors and summing the filtered output
`signals to produce a second filter output containing the target
`signal, the second spatial beamfonning filter having a
`greater beam width than a beam width of the first spatial
`beamfonning filter. The first adaptive filters are connected to
`the output of the second spatial beamfonniog filter. instead
`of to the output of the first-named spatial beamforming filter.
`BRlEF DESCRIPTION OF THE DRAWINGS
`The present invention will be described in further detail
`with reference to the accompanying drawings, in which:
`
`RTL898_1023-0013
`
`

`
`5,627,799
`
`3
`FIG. 1 is a block diagram of a prior art adaptive array
`beamfonner;
`FlG. 2 is a block diagram of the spatial highpass filter of
`the FIG. 1 prior art;
`PIG. 3 is a block diagram of the leaky adaptive filters of
`the FIG. 1 prior art;
`FIG. 4 is a block diagram of an adaptive array beam(cid:173)
`former according to a first embodiment of the present
`invention:
`FIG. 5 is a block diagram of an adaptive array beam(cid:173)
`former according to a second embodiment of the present
`invention;
`FIG. 6 is a block diagram of the nonn constraint adaptive
`filters of lhe second embodiment;
`FIG. 7 is a block diagram of the constraint coefficient
`generator used io FIG. 6;
`FIG. 8 is a block diagram of an adaptive array beam(cid:173)
`former according to a third embodiment of the present
`invention;
`FIG. 9 is a block diagram of the coefficient-oonslrained
`adaptive filters of the third embodiment;
`FlG. 10 is a graphic representation of the input/output
`characteristic of the limiters of FIG. 9;
`FlG. 11 is a block diagram of an adaptive array beam(cid:173)
`fonner according to a fourth embodiment of the present
`invention; and
`FlG. 12is a block diagram ofa modification of the present
`invention.
`
`DEI'AllED DESCRIPTION
`Before proceeding with the detailed description of the
`present invention. it may provide helpful to provide an
`explanation of the prior art with reference to FlGS. 1 to 3.
`In FIG. 1. a linear array of microphones lo- I M _ L of identical
`operating characteristics are located at sufficient distances
`from signal sources of interest so that the wavefront of each
`signal at the microphones is considered to be linear. The
`microphones are connected to FIR transversa! filters
`ZOo-20M_1 of a spatiallowpass filter 2. the outputs of the
`filters 20 being summed by an adder 26 to produce an output
`containing the target signal from a particular (assumed)
`direction and signals from other directions which are uncor(cid:173)
`related with the target signal. The outputs of filters 20 are
`applied through a timing adjustment delay circuit 3 to a
`subtractor 32 of a canceler 4.
`The outputs of the M microphones are further cODnected
`to a spatial highpass filter bank 6 to produce (M-Q-l)
`output signals. The filter bank 6 operates so that the signals
`including the target signal as well as signals in the neigh(cid:173)
`borhood of the assumed direction are rejected.. The outputs
`of the filler bank 6 thus contain the undcsircd signab as
`dominant components. The outputs of filter bank 4) are fed
`through leads Fo-FM-Q to leaky adaptive filters 3Oo-30M -Q
`of the canceler 4. Leaky adaptive filters 30 of the canceler
`delect undesired signals contained in the output signal of the
`beamformer at terminalS having a high correlation with the
`undesired signals detected by the spatial highpass filter 6 by
`adaptively updating their tap weight values using the output
`of the beamformer as a signal indicating the amount of
`correction oror. The high correlation signals detected by the
`leaky adaptive filters 30 are combined by an adder 31 and
`fed to the subtractor 32 where it is subtracted from the
`time-coincident signal from spatial lowpass filter 2. whereby
`the undesired signals are canceled at the output terminalS of
`the beamformer.
`
`20
`
`4
`Each of the filters 20 has a tapped delay line formed by
`delay elements 220- 220-2 fonning (G-l) delay-line taps
`which are connected to corresponding tap weight multipliers
`23 for respectively weighting the tap signals with particular
`~ tap weight coefficients supplied from a tap weight memory
`24 (where G is equal to or greater than 2). the weighted tap
`signals being summed by an adder 25 and fed to the adder
`26. The tap weight memory 24 of each filter 20 stores a set
`of tap weight coefficients whose values are determined so
`10 that filters ZO exhibit particular characteristics which result
`in an output containing the target signal. If the assumed
`direction is Dormatlo the length of the microphone array. the
`integer G=2 is used and the tap weight coefficient of the
`multiplier 230 is set equal to "I". Other design approaches
`15 are described in "Multidime nsional Digital Signal
`Processing". Prentice-Hall. Inc. pages 289-315. 1984 and
`IEEE. Proceedings of International Conference on
`Acoustics. Speech and Signal Processing 93. pages
`169-172.
`Spatial highpass filter bank 6 of the type described in
`Document 2 is shown in FIG. 2. Filter bank ., is made up
`of(M-Q-l) groups 40 ofQ highpass filters 41 each. and an
`adder 42. which each group forming a spatial higlipass filter.
`where Q is equal to or greater than "3". Each spatial filter 40
`25 receives a selected set of the microphone outputs such that
`the signals from the microphones positioned closer to the
`center of the array are coupled to an increasing number of
`filters 41 . Thus. the signals incident on the center area of the
`microphone array fare filtered through a greater number of
`30 filters 41 than the signals incident on the edges of the array
`are. Highpass filters 41 are basically of the same transversal
`filter configuration as the filterl; 20. but with different delay
`line lengths (G) and different filter characteristics.
`The characteristics of the highpass fillers 41 of filler bank
`35 6 are those of a rejection filter whrxcin a group of signals
`propagating in the assumed direction are rejected at the
`output of adder 42 of each spatial highpass filter 40. A basic
`design method for this type of spatial filter is described in
`Document 2. One important consideration is the degree of
`40 design freedom which is detennined by the number of
`microphones used. For an M-microphone array, it is repre(cid:173)
`sented by M--Q+L With the use of a large Dumber of
`microphones a beamformer having a wide rejection angle
`with high attenuation can be implemented. Advantageously,
`45 the target signal can be rejected in the interference path of
`such beamfonners even though the asswned direction differs
`from its actual arrival direction.
`In each of the leaky adaptive filters 30 (FlG. 3). a
`corresponding output signal from the filter bank 5 is suc-
`50 cessively shifted through delay-line taps formed by delay
`elements 500 -50£.-.2 and the tap signals are weighted respec(cid:173)
`tively by (1.-1) multipliers 51 with tap weight coefficients
`supplicd from update circuits 530-53£.--1 and then summed
`by adder 52 for coupling to the adder 31. Each update circuit
`.5.5 53 operates in accordance with the least mean square (LMS)
`algorithm. The output of beamfonner from subtractor 32.
`rcpresenting a correction error. is weighted by a stepsize J.I
`in a multiplier 54 and applied. to a multiplier 55 of each
`update circuit 53 for detecting a correlation between the
`60 weighted error and a corresponding tap signal. Each update
`circuit 53 includes a leaky integrator fonned'by an adder 56.
`a multiplier 57 and a delay element 58. The correlation
`output of multiplier 55 is summed with a feedback signal
`from multiplier 57 and delayed by a symbol interval by
`65 delay element 58. The delayed symbol is applied to the
`corresponding tap weight mUltiplier 51 as an updated tap
`weight coefficient as well as to the multiplier 57 where it is
`
`RTL898_1023-0014
`
`

`
`5,627,799
`
`5
`scaled down by a factor a (equal to less than unity) and fed
`back to the adder 56. Because of this scale-down feedback.
`the integrator operates as a leaky integrator which differs
`from normal integratOl"s where the scale factor is unity. The
`leaky integration prevents the tap weight coefficient from s
`growing indefinitely when the target signal. when there is a
`leakage of the target signal to the interference path (i.e .• the
`outputs of filter bank ()) of the beamformer due to the
`inherent variability of microphone characteristics and posi(cid:173)
`tional CITorS of the microphones. Otherwise. the intecference 10
`signals produced by the adaptive filters would become
`identica110 the components of the signal in the main path of
`the beamfonner. and the resulting cancellation would sub(cid:173)
`stantially remove the target signal.
`However, in order to implement a beamformer having a
`wide range of rejection angiCli. a large number of micro(cid:173)
`phones (the Q value) are required for each group of spatial
`highpass filters in the filter bank. If a sufficient number of
`microphones is not provided. the degree of design freedom
`must be sacrificed, resulting in a beamformer having a 10",\
`noise cancelling capability.
`Referring now to flO. 4. there is shown an adaptive array
`beamfonner according to a first embodiment of the present
`invention in which parts corresponding to those of FIG. 1 are
`marked by the same numerals as those used in flG. 1. the
`description thereof being omitted for simplicity. The adap(cid:173)
`tive array beamfonner of this emOOdi.ment comprises a
`spatial highpass filter 16 and a canceler 17. Spatial highpass
`filters 16 includes M delay circuits 7o-7M~1 connected
`respectively to the microphones ~-IM~I' M leaky adaptive
`filters 8o-8M _ 1 and M subtractors '0-9M _ 1 connected
`respectively to the outputs of the M delay circuits 7.
`The spatiallowpass filter 2. connected to the microphone
`array, provides spatial lowpass filtering of the individual
`microphone signals and summing the lowpass-filtered sig(cid:173)
`nals in the same manner as in the prior art beamformer to
`detect the target signal. The output of the spatial lowpass
`filter 2 is applied to all the leaky adaptive filters 8 as a
`reference signal as well as to the delay 3. The outputs the
`microphone array are passed. through corresponding delay 40
`circuits 7 to subtractors , to which the outputs of leaky
`adaptive filters 8 are also supplied to be subtracted from the
`corresponding microphone outputs. The output of each
`subtractor 9 is coupled to the corresponding leaky adaptive
`filter 8 as an error signal to update their tap weight values. 45
`The M delay circuits 7 provide a delay to the microphone
`outputs so that they are time coincident at the inputs of
`corresponding subtractors 9 with the output signals of leaky
`adaptive filters 8.
`Each of the leaky adaptive filters 8 is identical in structure SO
`to that shown in flG. 3. Correlations between the reference
`signal and each of the error signals are detected by the leaky
`adaptive filters 8. As described previously in connection
`with the prior art, the strength of a leaky adaptive filter foc
`restraining the growth of tap weight is proportional to the ss
`magnitude of the tap weight value itself. As a result, if the
`optimum value for the tap weight coefficient (which mini(cid:173)
`mizes the error input of the leaky adaptive filter) is relatively
`large, the tap weight value cannot converge to the optimum
`value, resulting in a substantial amount of error from the 60
`q>timum value. This implies that depending on the tap
`weight value the correlation capability of the leaky adaptive
`filters 8 differs significantly. Therefore, those signal
`components, which require a greater tap weight value for
`enabling their correlation to be detected, cannot sufficiently 6S
`be removed, while those signals requiring a lower tap weight
`value can be removed sufficiently.
`
`6
`With respect to the signal arriving in the assumed direc(cid:173)
`tion as well as to those arriving in near-assumed directions,
`the output of spatial lowpass tilter 2 contains the same
`amount of such signal components as those detected by the
`microphone array, and the maximum tap weight value
`necessary for removing them from the interference path of
`the beamformer is as small as "I". The leaky adaptive filters
`8 are therefore deSigned with a low maximum tap weighl
`value so that the target signal components are completely
`remuved at tht: outputs of subtractor.; 9.
`With respect to the interference signals. on the other hand.
`the output of the spatiallowpass filter 2 contains a smaller
`amount of interference signals than those detected by the
`microphone array. Therefore. the tap weight value necessary
`is for the leaky adaptive filters 8 to remove the interference
`signals is much higher than "1". Thus. the amount of
`removal at the outputs of subtractors 9 is much less in the
`case of the interference signals than in the case of the target
`signal components. If normal adaptive filters are used
`20 instead of the leaky adaptive filters 9. their tap weight values
`would be allowed to grow indefinitely. and as a result, not
`only the interference signals but the target signal compo(cid:173)
`nents are removed.
`Canceler 17 includes M leaky adaptive filters 10o- 10M _ 1
`2S connected respectively to the outputs of corresponding sub(cid:173)
`tractors 9 to receive the interference signals detected in a
`manner just described. Each of the leaky adaptive filters 10
`is identical in characteristic to the prior art leaky adaptive
`filters. Although most of the target signal components are
`removed. there is still a small amount of their leakage at the
`outputs of subtractors 9. Due to the adaptive leaky integra(cid:173)
`tion of filters 10, the growth of their tap weight values due
`to the presence of such smaIl amount of leakage of the target
`signal are re