United States Patent
`US 7,236,748 B2
`(10) Patent No.:
`(12)
`Li et al.
`(45) Date of Patent:
`Jun. 26, 2007
`
`
`US007236748B2
`
`(54) CLOSED LOOP FEEDBACK IN MIMO
`SYSTEMS
`
`(75)
`
`Inventors: Qinghua Li, Sunnyvale, CA (US),
`eae
`*
`Xintian E, Lin, Palo Alto, CA (US)
`.
`Intel Corporation, Santa Clara, CA
`(US)
`
`.
`:
`(73) Assignee:
`
`7/2003 Walton et al. 0... 455/454
`2003/0125040 Al*
`2003/0210750 Al* 11/2003 Onggosanusi etal. ...... 375/295
`2004/0235433 AL*
`11/2004 Hugl et al. oe. 455/101
`Ootoences ‘I Doves pe et al.
`oon
`2006/0056335 Al
`3/2006 Linetal.
`2006/0056531 Al
`3/2006 Li et al.
`2006/0068718 AL*
`3/2006 Li et al. wessseeccsseeceosees 455/69
`2006/0092054 Al
`5/2006. Liet al.
`
`(*) Notice:
`
`Subject to any disclaimer, the term of this
`OTHER PUBLICATIONS
`patent is extended or adjusted under 35
`Int
`the
`International Search Report
`and Written
`Ovini
`intema-
`ea¥e.
`eport
`an
`ritten
`pinion oO
`ntermationa.
`¢
`U.S.C, 154(b) by 363 days.
`tional Seraching Authority; Dated Jan. 31, 2006; PCT/US2005/
`.
`031585, 1-13.
`(21) Appl. No.: 10/955,826
`International Search Report and Written Opinion of the Interna-
`(22)
`Filed:
`Sep. 30, 2004
`ronalearching Authority; Dated Sep. 16, 2005; PCT/US2005/
`:
`-
`30,
`;
`ages.
`oo.
`.
`.
`“PCT Search Report”, PCT/US2005/031979, (Jan. 23, 2006), 12
`(65)
`Prior Publication Data
`pages.
`Jihoon, C. , “Interpolation based transmit beamforming for MIMO-
`US 2006/0068738 Al
`Mar. 30, 2006
`OFDMwith Limited Feedback”, IEEE International Conference on
`1) ee parame,cay,NaUtraoaarcTeSe
`
`US2005/031585,(Jun. 20, 2004),249-253.
`
`(56)
`
`.
`(2006.01)
`HO4M 1/00
`(52) US. Ch.
`eeceeeecccccceseceseseecesseeeeees 455/69; 455/562.1
`(58) Field of Classification Search 0.0.0.0... 455/69,
`455/562.1, 561, 101, 103, 272-273, 276.1,
`455/277.1, 277.2; 375/299, 347, 370/208
`See application file for complete search history.
`References Cited
`U.S. PATENT DOCUMENTS
`5.999.896 A * 12/1999 Whinnett
`
`_—* cited by examiner
`Primary Examiner—Nguyen T. Vo
`(74) Attorney, Agent, or Firm—LeMoinePatent Services,
`PLLC; Dana B. LeMoine
`
`ABSTRACT
`(67)
`Feedback bandwidth may be reduced in a closed loop
`MIMO system by represemming a beamforming matrix using
`
`
`
`23 Claims, 4 Drawing Sheets
`
`455/561
`
`
`PATEIODIKFIOANGVeet orthogonal generator matrices.
`.......... 370/342
`6,597,678 B1L*
`7/2003 Kuwaharaet al.
`
`1/2005 Liu wees eeeeeeeeeee 455/69
`6,847,805 B2*
`6,927,728 B2
`8/2005 Vooketal.
`
`
`ESTIMATE CHANNEL STATE INFORMATION|210
`FROM RECEIVED SIGNALS
`
`DETERMINE A BEAMFORMING MATRIX
`FROM THE CHANNEL STATE INFORMATION
`
`REPRESENT A BEAMFORMING MATRIX
`USING A SUM OF WEIGHTED GENERATOR
`MATRICES
`
`220
`
`230
`
`MATRICES
`
`FEED BACK PARAMETERS THAT DESCRIBE|240
`THE WEIGHTING OF THE GENERATOR
`
`\ 200
`
`1
`
`OnePlus Ex. 1004.0001
`IPR2022-00048
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`1
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`IPR2022-00048
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`

`

`U.S. Patent
`
`Jun. 26, 2007
`
`Sheet 1 of 4
`
`US 7,236,748 B2
`
`
`
`STATION2
`
`
`
`STATION1
`
`104
`
`102
`
`FIG.1
`
`2
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`U.S. Patent
`
`Jun. 26, 2007
`
`Sheet 2 of 4
`
`US 7,236,748 B2
`
`ESTIMATE CHANNEL STATE INFORMATION
`FROM RECEIVED SIGNALS
`
`DETERMINE A BEAMFORMING MATRIX
`FROM THE CHANNEL STATE INFORMATION
`
`MATRICES
`
`REPRESENT A BEAMFORMING MATRIX
`USING A SUM OF WEIGHTED GENERATOR
`
`210
`
`220
`
`230
`
`
`
`FEED BACK PARAMETERS THAT DESCRIBE|240
`
`THE WEIGHTING OF THE GENERATOR
`MATRICES
`
`FIG, 2
`
`3
`
`N 200
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`U.S. Patent
`
`Jun. 26, 2007
`
`Sheet 3 of 4
`
`US 7,236,748 B2
`
`310
`
`
`RECEIVE AT LEAST ONE PARAMETER
`
`320
`
`
`WEIGHT AT LEAST ONE GENERATOR
`
`MATRIX USING INFORMATION DERIVED
`FROM THE AT LEAST ONE PARAMETER
`
`
` 330
` COMBINE THE AT LEAST ONE GENERATOR
`MATRIX TO ARRIVE AT A BEAMFORMING
`
`
`MATRIX
`
`\ 300
`
`FIG. 3
`
`4
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`U.S. Patent
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`Jun. 26, 2007
`
`Sheet 4 of 4
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`US 7,236,748 B2
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`450
`
`OX
`S
`”
`s
`SZ
`oo”
`
`h Ly
`ly O
`= os
`a &
`WWre
`Wy =
`
`FIG.4 400a“
`
`5
`
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`

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`US 7,236,748 B2
`
`1
`CLOSED LOOP FEEDBACK IN MIMO
`SYSTEMS
`
`FIELD
`
`The present invention relates generally to wireless net-
`works, and more specifically to wireless networks that
`utilize multiple spatial channels.
`
`BACKGROUND
`
`Closed loop multiple-input-multiple-output (MIMO)sys-
`tems typically transmit channel state information from a
`receiver to a transmitter. The transmitter may then utilize the
`information to do beam forming. Transmitting the channel
`state information consumes bandwidth that might otherwise
`be available for data traflic.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 shows a diagram of two wireless stations;
`FIGS. 2 and 3 show flowcharts in accordance with various
`embodiments of the present invention; and
`FIG. 4 shows an electronic system in accordance with
`various embodiments of the present invention.
`
`DESCRIPTION OF EMBODIMENTS
`
`In the following detailed description, reference is made to
`the accompanying drawings that show, by wayofillustra-
`tion, specific embodiments in which the invention may be
`practiced. These embodiments are described in sufficient
`detail
`to enable those skilled in the art
`to practice the
`invention. It is to be understood that the various embodi-
`ments of the invention, although different, are not necessar-
`ily mutually exclusive. For example, a particular feature,
`structure, or characteristic described herein in connection
`with one embodiment may be implemented within other
`embodiments without departing from the spirit and scope of
`the invention. In addition,
`it is to be understood that the
`location or arrangement of individual elements within each
`disclosed embodiment may be modified without departing
`from the spirit and scope of the invention. The following
`detailed descriptionis, therefore, notto be taken in a limiting
`sense, and the scope of the present invention is defined only
`by the appended claims, appropriately interpreted, along
`with the full range of equivalents to which the claims are
`entitled. In the drawings, like numerals refer to the same or
`similar functionality throughout the several views.
`FIG. 1 shows a diagram of two wireless stations: station
`102, and station 104. In some embodiments, stations 102 and
`104 are part of a wireless local area network (WLAN). For
`example, one or more of stations 102 and 104 may be an
`access point in a WLAN.Also for example, one or more of
`stations 102 and 104 may be a mobile station such as a
`laptop computer, personal digital assistant (PDA), or the
`like. Further, in some embodiments, stations 102 and 104 are
`part of a wireless wide area network (WWAN), andstill
`further embodiments, stations 102 and 104 are part of a
`wireless personal area network (WPAN).
`In some embodiments, stations 102 and 104 may operate
`partially in compliance with, or completely in compliance
`with, a wireless network standard. For example, stations 102
`and 104 may operate partially in compliance with a standard
`such as ANSI/IEEFEStd. 802.11, 1999 Edition, although this
`is not a limitation of the present invention. As used herein,
`the term “802.11”refers to any past, present, or future IEEE
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`the 1999
`including, but not limited to,
`802.11 standard,
`edition. Also for example, stations 102 and 104 may operate
`partially in compliance with any other standard, such as any
`future IEEE personal area network standard or wide area
`network standard.
`
`Stations 102 and 104 each include multiple antennas.
`Eachof stations 102 and 104 includes “‘n” antennas, where
`n may be any number. In some embodiments, stations 102
`and 104 have an unequal numberof antennas. The remainder
`ofthis description discusses the case where stations 102 and
`104 have an equal number of antennas, but the various
`embodiments of the invention are not so limited. The
`
`“channel” through whichstations 102 and 104 communicate
`may include manypossible signal paths. For example, when
`stations 102 and 104 are in an environment with many
`“reflectors” (e.g. walls, doors, or other obstructions), many
`signals may arrive from different paths. This condition is
`known as “multipath.” In some embodiments, stations 102
`and 104 utilize multiple antennas to take advantage of the
`multipath and to increase the communications bandwidth.
`For example, in some embodiments, stations 102 and 104
`may communicate using Multiple-Input-Multiple-Output
`(MIMO)techniques. In general, MIMOsystemsoffer higher
`capacities by utilizing multiple spatial channels made pos-
`sible by multipath.
`In some embodiments, stations 102 and 104 may com-
`municate using orthogonal frequency division multiplexing
`(OFDM)in each spatial channel. Multipath may introduce
`frequency selective fading which may cause impairments
`like inter-symbol interference (IS]). OFDM is effective at
`combating frequency selective fading in part because
`OFDMbreaks each spatial channel into small subchannels
`such that each subchannel exhibits a more flat channel
`
`characteristic. Each channel may be scaled appropriately to
`correct any attenuation caused by the subchannel. Further,
`the data carrying capacity of each subchannel may be
`controlled dynamically depending on the fading character-
`istics of the subchannel.
`
`MIMOsystems may operate either “open loop”or “closed
`loop.” In open loop MIMOsystems, a station estimates the
`state of the channel without receiving channel state infor-
`mation directly from another station. In general, open loop
`systems employ exponential decoding complexity to esti-
`mate the channel. In closed loop systems, communications
`bandwidth is utilized to transmit current channelstate infor-
`
`thereby reducing the necessary
`mation between stations,
`decoding complexity. The communications bandwidth used
`for this purpose is referred to herein as “feedback band-
`width.” When feedback bandwidth is reduced in closed loop
`MIMOsystems, more bandwidth is available for data com-
`munications.
`The current channel state information may be represented
`by an n by n unitary beamforming matrix V determined
`using a singular value decomposition (SVD)algorithm, and
`the transmitter may process an outgoing signal using the
`beamforming matrix V to transmit
`into multiple spatial
`channels. In a straightforward implementation, the receiver
`sends each element of the unitary matrix V back to the
`transmitter. This
`scheme involves
`sending information
`related to the 2n? real numbers for any n by n complex
`unitary matrix, where n is the numberofspatial channels in
`the MIMOsystem.
`In some embodiments of the present invention, the beam-
`forming matrix V is represented by n?-1 real numbers
`instead of 2n? real numbers. By sending n?~1 real numbers
`instead of 2n? real numbers to represent the beamforming
`matrix, the feedback bandwidth may be reduced. Various
`OnePlus Ex. 1004.0006
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`US 7,236,748 B2
`
`V =explécoa,rws
`
`n2-1
`
`Oy Ge
`
`k=
`
`
`
`=e4V
`
`(4)
`
`3
`embodiments of the present invention exploit the structure
`of unitary matrixes and represent the unitary matrices by a
`combination of n?-1 orthogonal generator matrices, where
`the feedback numbers are the projections on the generator
`bases. For example, multiple hermitian generator matrices
`known to both the transmitter and receiver may be utilized
`to represent the beamforming matrix. Further, the numbers
`are also angles from -z to = of an (n?-1)-dimension polar
`coordinate, which facilitate a fine control of quantization
`error.
`
`A mathematical background of the SVD operation is
`provided below, and then examples are provided to describe
`various embodiments of the present invention that utilize
`hermitian generator matrices to represent beamforming
`matrices of any size. Further examples are also provided
`illustrating compact feedback formats for 2x2 MIMO sys-
`tems.
`
`A transmit beamforming matrix may be found using SVD
`as follows:
`
`H=-UDV'
`
`x=Vd
`
`qd)
`
`(2)
`
`20
`
`25
`
`where det(V)=1 and w is a global phase. In some embodi-
`ments, ip is not fed back to the transmitter. The term e”” can
`be factored out from V in equation (4) and absorbed by the
`data vector d in equation (2). The term e”” rotates the QAM
`constellation of d’s elements and the rotation may be com-
`pensated by the training. Accordingly,
`in some embodi-
`ments, 1) may be droppedto reduce feedback bandwidth and
`only n?-1 angles (i.e. a, .
`.
`. a,,2_,) are fed back. Further, in
`some embodiments, adaptive bit loading is utilized to reduce
`the feedback bandwidth further. For example, various
`parameters may be quantized with different numbersofbits
`prior to feeding back the parameters.
`In embodiments in which n?-1 angles(i.e.a, ...a,2_,) are
`fed back, the feedback angles are computed by the receiver
`that received channel training symbols. After the angles are
`computed, the receiver feeds back the angles to the trans-
`mitter of training symbols.
`Although various embodiments of the present invention
`where d is the n-vector of code bits for n data streams; x is
`feed back n?31 1 angles, it can be shown that n-1 of those
`the transmitted signal vector on the antennas; H is the
`angles are not neededat the transmitter since the training can
`channel matrix; H’s
`singular value decomposition is
`compensate the effect. When the n-1 angles referred to
`H=UDV’; U andVare unitary; D is a diagonal matrix with
`aboveare not included in the feedback, the numberof angles
`H’s eigenvalues; V is n by n, andnis the numberofspatial
`fed back is reduced to n?-n parameters.
`channels. To obtain V at the transmitter, the transmitter may
`Feeding back n?-1 parameters instead of n?—n parameters
`send training symbols to the receiver;
`the receiver may
`provides more information at the transmitter that may be
`evaluate H, compute the matrix V'; and the receiver may
`useful in many ways. For example, in OFDM systems with
`feedback parameters representing V to the transmitter. As
`m subcarriers, the transmitter uses a beamforming matrix for
`described more fully below, the number of feedback param-
`each of the m OFDMsubcarriers. In some embodiments of
`eters used to represent V may be reducedbyrepresenting the
`the present invention, n°-1 parameters are fed back for less
`beamforming matrix using a weighted sum of orthogonal
`than all of the m subcarriers, and the transmitter may then
`generator matrices.
`interpolate to arrive at the beamforming matrices for the
`A generic n by n complex matrix satisfying the following
`remaining subcarriers. Extra information is provided by the
`condition VV'=I, is a unitary matrix. All n by n unitary
`n-1 angles, and the interpolation may make useofthis extra
`matrices may be considered to form a group U(n). Its generic
`information.
`representation may be written as:
`
`40
`
`45
`
`(3)
`
`we
`V =explék=1
`
`a Gy
`
`where G,is the k-th hermitian generator matrix; a, is the
`angle of the k-th rotation and it is between -m and a; and i
`is the square root of -1. Example generator matrices for n=2,
`3, and 4 are providedat the end ofthis description. It should
`be noticed that the set of generator matrices for n=m is a
`subset of the set for n=m+1. Therefore, a 4 by 4 system may
`store only the matrices for n=4, and matrices for n=2 and
`n=3 may be determined from the stored matrices. Although
`example generator matrices are only provided up to n=4, this
`is not a limitation of the present invention. Any numberof
`generator matrices, corresponding to various values of n,
`may be utilized without departing from the scope of the
`present invention.
`It is noted that the last generator G,2 in U(n) is a scaled
`identity matrix and it commutes with all other generator
`matrices. Accordingly, the unitary matrix can be written as
`
`The feedback angles may be computed as follows.
`1) Singular value decomposition of the channel matrix H
`
`H-UDV
`
`50
`
`where' is the conjugate transpose operation.
`2) Eigenvalue decomposition of matrix V
`
`V=M DM"!
`
`6)
`
`(6)
`
`where D is a diagonal matrix with norm 1 diagonal
`elements.
`
`3) Natural logarithm of V
`
`log(P)=M log(D)M
`
`)
`
`where log(D) essentially computes the phase of diagonal
`elements of D.
`
`4) Project log(V) to the n?-1 generator matrixes
`
`ay =—FtraceflogV)GE],
`
`for k= 1.0, WI
`
`®)
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`OnePlus Ex. 1004.0007
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`OnePlus Ex. 1004.0007
`IPR2022-00048
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`

`5
`. a,2_,) to the transmitter,
`.
`The receiver may transmit(a, .
`which may then reconstruct the beamforming matrix V as
`follows.
`
`6
`We can expand V in series as
`
`US 7,236,748 B2
`
`10
`
`15
`
`20
`
`30
`
`35
`
`40
`
`45
`
`n2-1
`A= i>) ayGy
`k=l
`
`A= PAP!
`
`V = Pdiaglexp(,)--- exp(a,)|P+
`
`(9)
`
`(10)
`
`dl)
`
`and the transmitter may perform transmit beamforming
`
`as:
`
`x=Vd
`
`(12)
`
`Various embodiments of the present invention also reduce
`the range of the quantized feedback numbers from (-—%, 9%)
`to (-1, 1]. For example, real numbers included in a beam-
`forming matrix generally take on values of (-9, 0), while
`the angles a, may take on values of (-a, a]. In some
`embodiments, the range of (-z, 1] can be represented with
`fewer bits, and in other embodiments, greater precision is
`provided because of the smaller range.
`
`Compact Feedback Formats for 2x2 MIMO Systems
`Asdescribed above, various embodiments of the present
`invention provide compact feedback formats for n by n
`MIMO systems, where n may be of any size. In some
`embodiments, compact feedback formats are further devel-
`oped for the case of MIMO systems with two spatial
`channels. These compact formats may be utilized in 2 by 2
`MIMOsystems, or in higher order systemsthat use less than
`all available spatial channels.
`Two compact feedback schemesare described below. The
`first scheme feeds back one sign bit and three real numbers
`between -1 and 1. The computation of the numbers utilizes
`basic trigonometric functions which may be implemented by
`the FFT table for 802.11 OFDM modulation. The recon-
`
`struction of the unitary matrix utilizes a square root opera-
`tion. The second scheme feeds back three angles with ranges
`(0,70), [0,20), and (-2,71]. Two of the three ranges are smaller
`than the more general case described above and leads to a
`smaller quantization error under the same numberof quan-
`tization bits.
`
`Asdescribed above, any unitary matrix V can be written
`
`as
`
`1
`
`V = exp(écoa,2 exp| é
`
`k=
`
`aG. =e 4V
`
`
`
`(13)
`
`where G,is the k-th hermitian generator matrix; a, is the
`angle of the k-th rotation andit is between —z and 7; i is the
`square root of -1; V is unitary and det(V)=1; wp is a global
`phase. V can be computed as
`
`
`
`(15)
`
`”
`
`
`
`For 2x2 matrix V, (15) can be simplified by using
`
`3
`
`> mG,|
`
`k=1
`
`2
`
`
`
`=1,
`
`to yield:
`
`V=cos(®)G,ti sin(®)(7,G,+12G>+n3G3)
`
`(16)
`
`In this representation, we can limit ® in [0, x) and n, are
`real between [-1,1]. Using the orthogonal and unitary prop-
`erty, we have:
`
`_,
`1
`cos(y) = 3 trace (VG4)
`
`Ny = —— trace (VG) for k= 1,2,3
`2sin(y)
`
`Since (n,, nj, n,) is a real, unit 3-vector,
`described by two angles 8,® as follows.
`n =sin(0)cos(o)
`
`ny=sin(0)sin(@)
`
`n3=cos(@)
`
`ay)
`
`(18)
`
`it can be
`
`(19)
`
`(20)
`
`(21)
`
`is between [-a, 2).
`where @ is between [0, 2) and
`From above, we derive two schemes to feed back infor-
`mation representing the beamforming matrix V. Scheme 1
`sends back cos(®), n,, n;, and the sign of n,. The feedback
`numbers are between [-1,1] except for the sign bit. This
`scheme limits the quantization range and doesn’t require
`sine and cosine functions during reconstruction. Scheme 2
`sends back ®, 6 and 9, which are between[0, 2), [0, 1), and
`(0,27), respectively. This scheme utilizes sine and cosine
`functions during reconstruction. In some embodiments, the
`angles may be quantized at low resolution to reduce over-
`head, and existing 64 or 128 FFT tables in 802.11 OFDM
`baseband systems may be used to approximate the sine and
`cosine functions. The schemesare illustrated next.
`Scheme 1 is illustrated as follows.
`1) Singular value decomposition of the channel matrix H
`H=UDV'
`(22)
`
`where' is the conjugate transpose operation.
`2) Remove the global phase of the unitary matrix V
`
`V=
`
`
`Vv
`V deV)
`
`(14)
`
`65
`
`| Ul
`v
`VderV)
`
`(23)
`
`OnePlus Ex. 1004.0008
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`US 7,236,748 B2
`
`7
`3) Compute feedback numbers
`
`1 a
`cos(y) = girace(V G4)
`-i
`
`Ny =
`
`2¥ 1 —cos?(g)
`
`trace(VGi)
`
`(24)
`
`(25)
`
`4) Receiver quantizes cos(®), n,, n,, and sends back with
`sign(n,)
`The transmitter may then reconstruct V using cos(®), n,,
`n, and sign(n,)
`
`8
`may be performed in a different order. Further, in some
`embodiments, someactions listed in FIG. 2 are omitted from
`method 200.
`
`Method 200 is shown beginning at block 210 in which
`channel state information is estimated from received signals.
`The channel state information may include the channel state
`matrix H described above. At 220, a beamforming matrix is
`determined from the channel state information. In some
`embodiments, this corresponds to performing singular value
`decomposition (SVD) as described above with reference to
`equation (1). The beamforming matrix V is also described
`above.
`
`10
`
`ny=sign(n ,)v1-n77—n3-
`
`P=cos(®)G,-ivI-cos?(®) (0 ,G,+n>Go+n3G3)
`Scheme2 is illustrated as follows.
`
`(26)
`
`15
`
`(27)
`
`1) Singular value decomposition of the channel matrix H
`H=UDV'
`(28)
`
`20
`
`where ' is the conjugate transpose operation.
`2) Remove the global phase of the unitary matrix V
`
`V=
`
`
`V
`Vdei(V)
`
`3) Compute feedback numbers
`
`Lo
`cos(y) = qimace(V G4)
`-i
`——— trace(VG;,)
`2v 1 - cos?(y)
`‘
`
`y=
`
`4) Calculate angle @ and
`
`@ = arccos(n3), 6c [0, 2)
`
`arctan(~*), ny =O
`Ay
`arctan(~*) +2,n, <0
`Ay
`
`(29)
`
`(30)
`
`1)
`
`(32)
`
`5) Receiver quantizes and feeds back ®, 6 and
`The transmitter may then reconstruct V using ®, 6 and o>
`n =sin(0)cos()
`(33)
`
`n=sin(O)sin(p)z3=cos(@)
`
`(34)
`
`(35)
`V=cos(@)G,+isin(®) (2, G,+G>+n3G3)
`FIG. 2 shows a flowchart in accordance with various
`
`embodiments of the present invention. In some embodi-
`ments, method 200 maybe usedin, or for, a wireless system
`that utilizes MIMO technology.
`In some embodiments,
`method 200, or portions thereof, is performed by a wireless
`communications device, embodiments of which are shown
`in the various figures. In other embodiments, method 200 is
`performed bya processoror electronic system. Method 200
`is not limited by the particular type of apparatus or software
`element performing the method. The various actions in
`method 200 may be performed in the order presented, or
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`At 230, a beamforming matrix is represented using a sum
`of weighted generator matrices. For example, as shown
`above in equation (3), in some embodiments, the beamform-
`ing matrix may be represented using a sum of weighted
`hermitian generator matrices. In other embodiments,
`the
`beamforming matrix may be represented using equation
`(16). The parameters may be generated by projecting the
`beamforming matrix onto the generator matrices
`as
`described above with reference to the various embodiments
`
`of the present invention.
`At 240, parameters that describe the weighting of the
`generator matrices are fed back to a transmitter. For
`example,
`in embodiments that utilize equation (3),
`the
`parameters may include coefficients such as (a,
`.
`.
`. a,2_,),
`and in embodiments that utilize equation (16), the param-
`eters may include coefiicients such as cos(®), n,, n,, and the
`sign of n,. Further, in some embodiments that utilize equa-
`tions (16)-(21), the parameters may include ®, 6 and 9.
`In some embodiments, n?-1 parameters are chosen to
`represent the weighting of generators matrices. For example,
`in a 2 by 2 MIMOsystem, three parameters may be used to
`represent the sum of the weighted generator matrices. In
`other embodiments, a sign bit is used in conjunction with
`n?-1 parameters to reduce the quantization range of one or
`more parameters.
`Prior to feeding back to the transmitter, the parameters
`may be quantized in the ranges appropriate for the range of
`the parameters selected. For example, in embodiments that
`feed back (a, .. . a,2_,), the angles a, can be quantized in the
`range [-7, 7). Further,
`in embodiments that feed back
`cos(®), nj, n;, and the sign of n,, the parameters may be
`quantized in the range of [-1, 1). In still further embodi-
`ments, the parameters ®, 0 and may be quantized between
`(0, «),
`[0, 2), and [0,2 2), respectively. The quantized
`parameters maybe transmitted using any type of protocol or
`any type of communicationslink, including a wireless link
`such as a wireless link between stations like those described
`with reference to FIG. 1.
`
`In some embodiments, parameters are fed back for less
`than all OFDM subcarriers. For example, parameters may be
`fed back for every other OFDM subcarrier, or parameters
`maybe fed back for fewer than every other OFDM subcar-
`rier.
`In these embodiments, a system that receives the
`parameters may interpolate to arrive at beamforming matri-
`ces for each OFDM subcarrier.
`FIG. 3 shows a flowchart in accordance with various
`embodiments of the present invention. In some embodi-
`ments, method 300 maybe usedin, or for, a wireless system
`that utilizes MIMO technology.
`In some embodiments,
`method 300, or portions thereof, is performed by a wireless
`communications device, embodiments of which are shown
`in the various figures. In other embodiments, method 300 is
`performed bya processoror electronic system. Method 300
`is not limited by the particular type of apparatus or software
`element performing the method. The various actions in
`OnePlus Ex. 1004.0009
`IPR2022-00048
`
`9
`
`OnePlus Ex. 1004.0009
`IPR2022-00048
`
`

`

`US 7,236,748 B2
`
`10
`9
`cation (LNA), filtering, frequency conversion or the like.
`method 300 may be performed in the order presented, or
`Further, in some embodiments, PHY 430 includes transform
`may be performed in a different order. Further,
`in some
`embodiments, someactions listed in FIG. 3 are omitted from
`mechanisms and beamforming circuitry to support MIMO
`method 300.
`signal processing. Also for example, in some embodiments,
`Method 300 is shown beginning at block 310 in which at
`PHY 430 includes circuits to support frequency up-conver-
`least one parameter is received. In some embodiments, this
`sion, and an RFtransmitter.
`may correspond to a transmitter receiving one or more
`Media access control
`(MAC) layer 440 may be any
`parameters that represent a sum ofrotated generator matri-
`suitable media access control
`layer implementation. For
`ces. In some embodiments,
`the parameters may include
`example, MAC 440 may be implemented in software, or
`coefficients with which the generator matrices are to be
`hardware or any combination thereof. In some embodi-
`weighted, and in other embodiments, the parameters may
`ments, a portion of MAC 440 may be implemented in
`include other angle parameters such as ®, 0 and , or
`hardware, and a portion may be implemented in software
`coefficients such as cos(®), n,, n;, all of which are described
`that is executed by processor 460. Further, MAC 440 may
`above with reference to the previous figures.
`include a processor separate from processor 460.
`At 320, at least one generator matrix is weighted using
`information derived from the at least one parameter, and at
`In operation, processor 460 reads instructions and data
`330,
`the generator matrices are combined to arrive at a
`from memory 470 and performsactions in responsethereto.
`beamforming matrix. For example, hermitian generator
`For example, processor 460 may access instructions from
`matrices may be weighted and combined as shown in
`memory 470 and perform method embodiments of the
`equations (9)-(11),
`(26)-(27), or
`(33)-(35). Further,
`the
`present invention, such as method 200 (FIG. 2) or method
`beamforming matrix may be used in beamforming as
`300 (FIG. 3) or methods described with reference to other
`described above with reference to the various embodiments
`figures. Processor 460 represents any type of processor,
`of the present invention.
`including but not limited to, a microprocessor, a digital
`In some embodiments, the acts of block 310 mayresult in
`signal processor, a microcontroller, or the like.
`parameters for
`less than all OFDM subcarriers being
`Memory 470 represents an article that includes a machine
`received. For example, parameters may be received for
`readable medium. For example, memory 470 represents a
`every other OFDM subcarrier, or parameters may be
`random access memory (RAM), dynamic random access
`received for fewer than every other subcarrier. In these
`memory (DRAM), static random access memory (SRAM),
`embodiments, method 300 may interpolate to arrive at
`read only memory (ROM), flash memory, or any other type
`OFDM subcarrier beamforming matrices for which no
`of article that includes a medium readable by processor 460.
`parameters were received.
`FIG. 4 shows a system diagram in accordance with
`Memory 470 may store instructions for performing the
`various embodiments of the present invention. Electronic
`execution of the various method embodimentsofthe present
`system 400 includes antennas 410, physical layer (PHY)
`invention. Memory 470 mayalso store beamforming matri-
`430, media access control (MAC) layer 440, Ethernet inter-
`ces or beamforming vectors.
`face 450, processor 460, and memory 470. In some embodi-
`Although the various elements of system 400 are shown
`ments, electronic system 400 may be a station capable of
`separate in FIG. 4, embodiments exist that combine the
`representing beamforming matrices using generator matri-
`circuitry of processor 460, memory 470, Ethernet interface
`ces as described above with reference to the previous
`450, and MAC 440 in a single integrated circuit. For
`figures. In other embodiments, electronic system 400 may be
`example, memory 470 may be an internal memory within
`a station that receives quantized parameters, and performs
`processor 460 or may be a microprogram control store
`beamforming in a MIMO system. For example, electronic
`within processor 460. In some embodiments, the various
`system 400 may beutilized in a wireless network as station
`elements of system 400 may be separately packaged and
`102 or station 104 (FIG. 1). Also for example, electronic
`45
`mounted on a commoncircuit board. In other embodiments,
`system 400 may beastation capable of performing the
`the various elements are separate integrated circuit dice
`calculations shown in any of the equations (1)-(35), above.
`packaged together, such as in a multi-chip module, and in
`In some embodiments, electronic system 400 may repre-
`still further embodiments, various elements are on the same
`sent a system that includes an access point or mobilestation
`as well as other circuits. For example, in some embodiments,
`integrated circuit die.
`electronic system 400 may be a computer, such as a personal
`Ethernet
`interface 450 may provide communications
`computer, a workstation, or the like, that includes an access
`between electronic system 400 and other systems. For
`point or mobile station as a peripheral or as an integrated
`example, in some embodiments, electronic system 400 may
`unit. Further, electronic system 400 may includea series of
`be an access point that utilizes Ethernet interface 450 to
`access points that are coupled together in a network.
`communicate with a wired network or to communicate with
`In operation, system 400 sends andreceives signals using
`antennas 410, and the signals are processed by the various
`elements shown in FIG. 4. Antennas 410 may be an antenna
`array or any type of antenna structure that supports MIMO
`processing. System 400 may operate in partial compliance
`with, or in complete compliance with, a wireless network
`standard such as an 802.11 standard.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`50
`
`55
`
`60
`
`Physical layer (PHY) 430 is coupled to antennas 410 to
`interact with a wireless network. PHY 430 may include
`circuitry to support the transmission and reception of radio
`frequency (RF) signals. For example, in some embodiments,
`PHY 430 includes an RFreceiver to receive signals and
`perform “front end” processing such as low noise amplifi-
`
`65
`
`10
`
`other access points. Some embodiments of the present
`invention do not
`include Ethernet
`interface 450. For
`
`example, in some embodiments, electronic system 400 may
`be a network interface card (NIC) that communicates with a
`computer or network using a bus or other type ofport.
`Although the present invention has been described in
`conjunction with certain embodiments,it is to be understood
`that modifications and variations may be resorted to without
`departing from the spirit and scope of the invention as those
`skilled in the art readily understand. Such modifications and
`variations are considered to be within the scope of the
`invention and the appended claims.
`OnePlus Ex. 1004.0010
`IPR2022-00048
`
`10
`
`OnePlus Ex. 1004.0010
`IPR2022-00048
`
`

`

`11
`
`Generator Matrices
`For U(2) group, the generator matrices are:
`
`10
`o
`1
`0 -i
`01
`a-(; bel; bel, “i bo=( |
`
`For U(3) group, the generator matrices are:
`
`90
`0
`1
`9 -i 0
`910
`G,=|1 0 O),G,=)% 0 O}G;=)0 -1 0},
`00 0
`9
`0
`0
`9
`0
`0
`
`0