US007710925B2
`
`a2) United States Patent
`US 7,710,925 B2
`(10) Patent No.:
`
` Poon (45) Date of Patent: May4, 2010
`
`
`(54)
`
`SPATIAL PUNCTURING APPARATUS,
`$
`METHOD, AND SYSTEM
`
`(75)
`
`Inventor: Ada S. Y. Poon, Emeryville, CA (US)
`
`3/2004 Hwang etal. ............ 375/267
`2004/0042558 Al*
`7/2005 Maltsev etal. ............ 375/299
`2005/0152473 Al*
`2005/0219999 AI* 10/2005 Kimetal.
`....00. 370/334
`
`(73) Assignee:
`
`Intel Corporation, Santa Clara, CA
`(US)
`
`Wo
`
`WO-2006007138 Al
`
`1/2006
`
`FOREIGN PATENT DOCUMENTS
`
`(*) Notice:
`
`Subject to any disclaimer, the term ofthis
`ee enattiusted under 3°
`S.C.
`154(b)
`by
`ys.
`;
`(21) Appl. No.: 10/875,111
`;
`Filed:
`
`(22)
`
`Jun. 23, 2004
`to.
`:
`Prior Publication Data
`US 2005/0286404 Al
`Dec, 29, 2005
`Int. Cl
`HOLO oy
`(2006.01)
`(52) US.CL we 370/334; 375/267; 455/562.1
`(58) Field of Classification Search ................. 370/477,
`370/478, 480, 498, 343, 345, 203, 208, 252-254,
`370/310, 328, aaOeaseisen| on
`See application file for complete search history.
`References Cited
`
`(65)
`
`(51)
`
`(56)
`
`U.S. PATENT DOCUMENTS
`6,134,231 A
`10/2000 Wright
`6,774,864 B2
`8/2004 Evansetal.
`6,801,775 B1* 10/2004 Gibbonsetal. .......... 455/450
`6,917,820 B2*
`7/2005 Goreetal. wees 455/562.1
`2002/0003842 AL*
`1/2002 Suzuki etal. occ 375/259
`2002/0102950 Al
`8/2002 Gore et al.
`2003/0083016 Al
`$/2003 Evans et al.
`2003/0185309 Al
`10/2003 Pautleretal.
`2003/0186698 Al* 10/2003 Holmaetal.
`
`......0000.. 455/436
`
`OTHER PUBLICATIONS
`International Search Report and Written Opinion: DatedAug. 31,
`2005; PCT/US2005/017653; 17 pages.
`Gore, D. A., et al., “Selecting an Optimal Set of Transmit Antennas
`for a Low Rank Matrix Channel”, Acoustics. Speech, and signal
`8
`afe
`(
`Processing,
`leee International Conference, vol.
`035,
`(Jun.
`5,
`2000),2785-2788.
`Sandhu,S. , et al., “Near-Optimal Selection of Transmit Antennas for
`a MIMO Channel based on Shannon Capacity”, Signals, Systems and
`Computers, (Oct. 29, 2000),567-571.
`PCT/US2005/017653, “International Preliminary Report on Patent-
`ability received for PCT Patent Application No. PCT/U82005/
`017653, mailed on Jan. 11, 2007”, 2 pages.
`(Continued)
`.
`oe DG
`irimaryExaminerRickyNgoakorn
`(74) Attorney, Agent, or Firm—Dana B. Lemoine; Lemoine
`Patent Services, PLLC
`(57)
`
`ABSTRACT
`
`Stations in an NxN multiple-input-multiple-output (MIMO)
`wireless network always puncture the weakest spatial chan-
`nel. A receiving station determines channelstate information
`‘for N spatial channels and feeds back to the transmitting
`Station channel state information for only N-1 spatial chan-
`nels. The channelstate information mayinclude a beamform-
`ing matrix to cause the transmitting station to utilize N-1
`spatial channels.
`
`13 Claims, 6 Drawing Sheets
`
`
`RECEIVE A TRAINING SEQUENCE FROMA|279
`TRANSMITTER
`
`ESTIMATE N SPATIAL CHANNELS, WHERE
`NIS EQUAL TO A NUMBER OF RECEIVING
`
`990
`
`DESCRIBING N-1 SPATIAL CHANNELS
`
`1
`
`HUAWEI 1009
`
`

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`US 7,710,925 B2
`Page 2
`
`OTHER PUBLICATIONS
`
`94117248, “Office Action received for Tatwanese patent Application
`No. 94117248, mailed on Aug. 16, 2006”, 2 pages of Office Action
`and 2 pages of English Translation.
`
`200580020528 .4, “Office Action received for Chinese Patent Appli-
`cation No. 200580020528.4, mailed on Jul. 3, 2009”, 6 pages of
`Office Action and 5 pages of English Translation.
`
`* cited by examiner
`
`2
`
`

`

`U.S. Patent
`
`May4, 2010
`
`Sheet 1 of 6
`
`US 7,710,925 B2
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`
`
`STATION2
`
`
`
`STATION4
`
`104
`
`102
`
`FIG.1
`
`3
`
`

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`U.S. Patent
`
`May4, 2010
`
`Sheet 2 of 6
`
`US 7,710,925 B2
`
`RECEIVE A TRAINING SEQUENCE FROMA|712
`TRANSMITTER
`
`
`
`ESTIMATE N SPATIAL CHANNELS, WHERE
`N IS EQUAL TO A NUMBER OF RECEIVING
`ANTENNAS
`
`DETERMINE THE WEAKEST OF THE N
`SPATIAL CHANNELS
`
`220
`
`230
`
`TRANSMIT CHANNEL STATE INFORMATION|240
`DESCRIBING N-1 SPATIAL CHANNELS
`
`4
`
`

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`U.S. Patent
`
`May4, 2010
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`Sheet 3 of 6
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`US 7,710,925 B2
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`4x4 OFDM system at 4x36 Mbps (hard decision
`demodulation)
`
`
`
`(“-B-SVD- feedback4
`
`eigenvectors
`
`eigenvectors
`
`-#— SVD - feedback 3
`
`Eb/NO (dB)
`
`FIG. 3
`
`5
`
`

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`U.S. Patent
`
`May4, 2010
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`Sheet 4 of 6
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`US 7,710,925 B2
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`DATA
`SOURCES
`
`DIGITAL
`BEAMFORMING
`
` 402
`
`400
`
`CSI
`
`FIG. 4
`
`N-1
`
`6
`
`

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`U.S. Patent
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`May4, 2010
`
`Sheet 5 of 6
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`US 7,710,925 B2
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`ANALOG
`
`DATA
`SOURCES
`
`BEAMFORMING
`
`FIG. 6
`
`7
`
`

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`U.S. Patent
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`May4, 2010
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`Sheet 6 of 6
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`US 7,710,925 B2
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`02
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`L4NYFH14
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`FOVIYFLNI
`
`09|YOSSI00UdOVAAHd
`
`022AYOWIN
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`LOld
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`OP!02
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`7
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`a
`f_'\
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`8
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`US 7,710,925 B2
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`1
`
`SPATIAL PUNCTURING APPARATUS,
`METHOD, AND SYSTEM
`
`FIELD
`
`The present invention relates generally to wireless net-
`works, and more specifically to wireless networksthatutilize
`multiple spatial channels.
`
`BACKGROUND
`
`Closed loop multiple-input-multiple-output (MIMO)sys-
`tems typically transmit channel state information from a
`receiver to a transmitter. Transmitting the channelstate infor-
`mation consumes bandwidth that would otherwise be avail-
`able for data traffic.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 showsa diagram of two wireless stations;
`FIG. 2 shows a flowchart in accordance with various
`embodiments of the present invention;
`FIG. 3 showssimulation results;
`FIG. 4 shows a diagram of a wireless communications
`device;
`FIG. 5 shows dimensions of a channel state information
`matrix;
`FIG. 6 shows a diagram of a wireless communications
`device; and
`FIG. 7 shows a system diagram in accordancewith various
`embodiments of the present invention.
`
`20
`
`25
`
`DESCRIPTION OF EMBODIMENTS
`
`In the following detailed description, reference is made to
`the accompanying drawings that show, by way ofillustration,
`specific embodiments in which the invention may be prac-
`ticed. These embodiments are described in sufficient detail to
`enable those skilled in the art to practice the invention. It is to
`be understoodthat the various embodiments of the invention,
`although different, are not necessarily 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 moditied
`without departing from the spirit and scope ofthe invention.
`The following detailed description is, therefore, not to be
`taken in a limiting sense, and the scope of the present inven-
`tion is defined only by the appended claims, appropriately
`interpreted, along with the full range of equivalents to which
`the claimsare entitled. In the drawings, like numerals refer to
`the same or similar functionality throughout the several
`views.
`
`55
`
`2
`is nota limitation ofthe present invention. As used herein, the
`term “802.11” refers to any past, present, or future IEEE
`802.11 standard, including, but not limited to, the 1999 edi-
`tion.
`Stations 102 and 104 each include multiple antennas. Sta-
`tion 102 includes “N”antennas, and station 104 includes “M”
`antennas, where N and M maybe any number. Further, N and
`M mayor maynot be equal. The remainderofthis description
`discusses the case where N and M are equal, but the various
`embodiments of the invention are not so limited. The “‘chan-
`nel” through which stations 102 and 104 communicate may
`include many possible signal paths. For example, when sta-
`tions 102 and 104 are in an environment with many “reflec-
`tors” (e.g. walls, doors, or other obstructions), many signals
`mayarrive 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 communi-
`cate using Multiple-Input-Multiple-Output (MIMO) tech-
`niques. In general, MIMOsystemsoffer higher capacities by
`utilizing multiple spatial channels made possible by multi-
`path.
`In some embodiments, stations 102 and 104 may commu-
`nicate using orthogonal frequency division multiplexing
`(OFDM) in each spatial channel. Multipath may introduce
`frequency selective fading which may cause impairments like
`inter-symbol interference (ISI). OFDM is effective at com-
`bating frequency selective fading in part because OFDM
`breaks each spatial channel into small subchannels such that
`each subchannel exhibits a more flat channel characteristic.
`Scaling appropriate for each subchannel may be implemented
`to correct any attenuation caused by the subchannel. Further,
`the data carrying capacity of each subchannel may be con-
`trolled dynamically depending on the fading characteristics
`of the subchannel.
`MIMOsystems mayoperate either “open loop”or “closed
`loop.” In open loop MIMOsystems, a station estimates the
`state of the channel without receiving channelstate informa-
`tion directly from anotherstation. In general, open loop sys-
`tems employ exponential decoding complexity to estimate
`the channel. In closed loop systems, communications band-
`width is utilized to transmit current channel state information
`between stations, thereby reducing the necessary decoding
`complexity, and also reducing overall throughput. The com-
`munications bandwidth used for this purpose is referred to
`herein as “feedback bandwidth.” When feedback bandwidth
`is reduced in closed loop MIMOsystems, more bandwidth is
`available for data communications.
`Three types of receiver architectures for MIMO systems
`include: linear, iterative, and maximum-likelihood (ML). In
`open-loop operation, ML receivers have muchbetter perfor-
`mancethan linear and iterative receivers. For example, at 1%
`packet error rate and 4x36 Mbps, ML receivers are 12 dB
`
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`US 7,710,925 B2
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`3
`deterministic in the sense that one spatial channelis always
`punctured, and an NxN system will always use N-1 spatial
`channels. By always only utilizing N-1 spatial channels in a
`NxN MIMOsystem, the amountof channelstate information
`to be transmitted is reduced, and the feedback bandwidth is
`reduced.
`
`FIG. 2 shows a flowchart in accordance with various
`embodiments ofthe present invention. In some embodiments,
`method 200 may be used in a wireless system that utilizes
`MIMOtechnology. In some embodiments, method 200, or
`portions thereof, is performed by a processor or electronic
`system, embodiments of which are shown in the various
`figures. In other embodiments, method 200 is performed by a
`wireless communications device. Method 200 is not limited
`by the particular type of apparatus or software element per-
`forming the method. The various actions in method 200 may
`be performed in the order presented, or may be performed in
`a different order. Further, in some embodiments, some actions
`listed in FIG. 2 are omitted from method 200.
`
`Method 200 is shown beginning at block 210 in which a
`receiving station receives a training pattern from a transmit-
`ting station. For example, station 102 may transmit a training
`pattern, and station 104 may receive the training pattern. At
`220, the receiving station estimates N spatial channels, where
`N is equal to a number of receiving antennas. In some
`embodiments, this may correspondto station 104 computing
`a current channel matrix describing the current state of the N
`spatial channels. At 230, the receiving station determines the
`weakest of the N spatial channels, and at 240, the receiving
`stations transmits back the channelstate information describ-
`ing the N-1 spatial channels. In some embodiments,
`the
`channel state information is in the form of a transmit beam-
`forming matrix. In these embodiments, the receiver computes
`a transmit beamforming matrix from the current channel
`matrix and then sends the beamforming matrix back to the
`transmitter. In various embodiments of the present invention,
`one spatial channel is always punctured, and the transmit
`beamforming matrix 1s reduced in size, thereby reducing the
`feedback bandwidth. Mathematical descriptions of various
`acts shown in FIG,2 are provided below.
`Let the input/output (1/O) model be
`
`prAx+z
`
`wherex, is the signal on the ith transmit antenna,y, is the
`signal received at the ith receive antenna, H,, is the channel
`gain from the jth transmit antennato the ith receive antenna,
`and z, is the noise on the ith receive antenna. In closed-loop
`MIMO,the receiver may send a pre-coding matrix P back to
`the transmitter and the I/O model becomes
`
`prAPx+z
`
`Upon singular value decomposition (SVD), we have
`H=-UZzY
`
`4
`from whichits expected value may be derived as
`
`1
`Blaw] = 5
`
`Also, the overall expected value for A, may be derived as
`
`a 0
`
`1
`E wh tant... Ay} HN.
`
`Accordingly, the ratio of the expected gain of the weakest
`spatial channel to the overall expected gain is
`
`a 5
`
`FIAy]
`
`1
`+Ao.+...
`FE) —(A;
`via + 2+...
`
`+A
`+Ay)
`
`1
`
`As shown above, the gain of the weakest spatial channelis
`1/N? ofthe overall expected gain. For example,the gain ofthe
`weakest spatial channel 1s 9.5 dB below the overall expected
`gain in a 3x3 system and is 12 dB below the overall expected
`gain in a 4x4 system. In the various embodiments of the
`present invention, this weakest spatial channel is always
`punctured for N>2, and the size of the feedback matrix
`becomes N(N-1) instead of N?. This reduces not only the
`feedback bandwidth but also the computational complexity
`because the receiver now needs to compute N-1 beamform-
`ing vectors instead of N beamforming vectors and utilizes N
`spatial channels. In addition to reducing the feedback band-
`width, the performance of the communications link as mea-
`sured by various parameters may increase as a result of
`always puncturing one spatial channel.
`FIG. 3 shows simulation results comparing the perfor-
`mance of one embodimentofthe present invention, as well as
`the performance of a ML system and a system that feeds back
`all N beamforming vectors. The performance measure shown
`in FIG,3 plots the packeterrorrate vs. E,/N, of a 4x4 48-tone
`OFDMsystem using a 64-state convolutional code, space-
`timeinterleaver, and 64-QAM with hard-decision demodula-
`tion. As can be seen in FIG. 3, in a 4x4 system, when the
`receiver drops the weakest spatial channel and only sends
`three beam-forming vectors,
`the
`system performance
`approaches the ML openloopreceiver and is much better than
`that of sending all beamforming vectors.
`FIG. 4 shows a transmitter with digital beamforming.
`Transmitter 400 may be included in a station such as station
`102 or station 104 (FIG. 1). Transmitter 400 includes data
`sources 402, digital beamforming block 410, radio frequency
`(RF) blocks 422, 424, 426, and 428, and antennas 432, 434,
`436, and 438. Digital beamforming block 410 receives three
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`US 7,710,925 B2
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`6
`5
`transmitter 600 may include a scrambler, a forward error
`always used, data sources 402 only includes three baseband
`correction (FEC) encoder, interleaver, an M-ary quadrature
`data circuits to source three separate data streams. This is
`contrast to a transmitter that includes four baseband data
`amplitude modulation (QAM) mapperand other functional
`blocks.
`circuits to source four separate data streams, even though one
`FIG. 7 shows a system diagram in accordancewith various
`may be punctured.
`embodimentsof the present invention. Electronic system 700
`Radio frequency blocks 422, 424, 426, and 428 may
`includes antennas 710, physical
`layer (PHY) 730, media
`include circuitry to modulate signals, frequency convert sig-
`access control (MAC) layer 740, Ethernet interface 750, pro-
`nals, amplify signals, or the like. For example, RF blocks 422,
`cessor 760, and memory 770. In some embodiments, elec-
`424, 426, and 428 may include circuits such as mixers, ampli-
`
`fiers, filters, or the like. The present inventionis not limited by tronic system 700 may beastation capable of puncturing one
`spatial channel. For example, electronic system 700 may be
`the contents or function of RF blocks 422, 424, 426, and 428.
`utilized in a wireless network as station 102 or station 104
`Transmitter 400 may include many functional blocks that
`are omitted from FIG.4 for ease of illustration. For example,
`(FIG. 1). Also for example, electronic system 700 may be a
`transmitter 400 may include a scrambler, a forward error
`transmitter such as transmitter such as transmitter 400 (FIG.
`correction (FEC) encoder, interleaver, an M-ary quadrature
`4) or 600 (FIG. 6) capable of beamforming, or may be a
`amplitude modulation (QAM) mapperand other functional
`receiver capable of performing channel estimation and deter-
`blocks.
`mining a weakest spatial channel to be punctured.
`Thevarious items shown in FIG.4 may be implemented in
`In some embodiments, electronic system 700 may repre-
`many different ways. For example, in some embodiments,
`sent a system that includes an access point or mobile station as
`portions of transmitter 400 are implemented in dedicated
`well as other circuits. For example, in some embodiments,
`hardware, and portions are implemented in software. In other
`electronic system 700 may be a computer, such as a personal
`embodiments, all of transmitter 400 is implemented in hard-
`computer, a workstation, or the like, that includes an access
`ware. The present invention is not limited in this respect.
`point or mobile station as a peripheral or as an integrated unit.
`FIG. 5 shows dimensions of a channel state information
`Further, electronic system 700 may include a series of access
`matrix. Matrix 500 represents a channel state information
`points that are coupled together in a network.
`matrix that may be transmitted back to a transmitter from a
`In operation, system 700 sends and receives signals using
`receiver. In some embodiments, matrix 500 corresponds to a
`antennas 710, and the signals are processed by the various
`beamforming matrix V, described above, having dimensions
`elements shown in FIG. 7. Antennas 710 may be an antenna
`NxN-1. This corresponds to an NxN MIMO system that
`array or any type of antenna structure that supports MIMO
`always punctures one spatial channel. In embodiments in
`processing. System 700 may operate in partial compliance
`which N=4, a beamforming matrix having the same dimen-
`with, or in complete compliance with, a wireless network
`standard such as an 802.11 standard.
`sions as matrix 500 may be input to digital beamforming
`block 410 at node 412 (FIG.4).
`Physical layer (PHY) 730 is coupled to antennas 710 to
`FIG. 6 shows a transmitter with analog beamforming.
`interact with a wireless network. PHY 730 may includecir-
`Transmitter 600 may be included in a station such as station
`cuitry to support the transmission and reception of radio
`102 or station 104 (FIG. 1). Transmitter 600 includes data
`frequency (RF) signals. For example, in some embodiments,
`sources 610, RF blocks 612, 622, and 624, analog beamform-
`PHY 730 includes an RF receiver to receive signals and
`ing block 630, and antennas 642, 644, 646, and 648. Analog
`perform “front end” processing such as low noise amplifica-
`beamforming block 630 receives three RF signals from RF
`tion (LNA), filtering, frequency conversion or the like. Fur-
`blocks 612, 622, and 624 and forms signals to drive four
`ther, in some embodiments, PHY 730 includes transform
`antennas.
`In operation, analog beamforming block 630
`mechanisms and beamforming circuitry to support MIMO
`receives channel state information (CSI) on node 632. In
`signal processing. Also for example, in some embodiments,
`PHY 730 includes circuits to support frequency up-conver-
`some embodiments, the channel state information is in the
`form of beamforming vectors recetved from anotherstation.
`sion, and an RF transmitter.
`In embodiments represented by FIG. 6, analog beamforming
`Media access control (MAC) layer 740 may be any suitable
`block 630 recetves three beamforming vectors, each of length
`media access control layer implementation. For example,
`four. This corresponds to a NxN-1 feedback matrix such as
`MAC740 may be implemented in software, or hardware or
`matrix 500 (FIG. 5) with N=4.
`any combination thereof. In some embodiments, a portion of
`‘Transmitter 600 always punctures one spatial channel. In
`MAC 740 may be implemented in hardware, and a portion
`the example embodiments represented by FIG. 6, N=4, one
`may be implemented in software thatis executed by processor
`spatial channel is always punctured, and three spatial chan-
`760. Further, MAC 740 may include a processor separate
`nels are always used. Because three spatial channels are
`from processor 760.
`always used, data sources 610 only includes three baseband
`In operation, processor 760 reads instructions and data
`data circuits to source three separate data streams. Further,
`from memory 770 and performs actions in response thereto.
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`US 7,710,925 B2
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`7
`Memory 770 maystore instructions for performing the execu-
`tion ofthe various method embodiments ofthe present inven-
`tion.
`Although the various elements of system 700 are shown
`separate in FIG. 7, embodiments exist that combinethe cir-
`cuitry of processor 760, memory 770, Ethernet interface 750,
`and MAC 740 in a single integrated circuit. For example,
`memory 770 may be an internal memory within processor
`760 or may be a microprogram control store within processor
`760. In some embodiments, the various elements of system
`700 may be separately packaged and mounted on a common
`circuit board. In other embodiments, the various elements are
`separate integrated circuit dice packaged together, such as in
`a multi-chip module, and in still further embodiments, vari-
`ous elements are on the same integrated circuit die.
`Ethernet
`interface 750 may provide communications
`between electronic system 700 and other systems. For
`example, in some embodiments, electronic system 700 may
`be an access point that utilizes Ethernet interface 750 to
`communicate with a wired network or to communicate with
`other access points. Some embodiments ofthe present inven-
`tion do not include Ethernet interface 750. For example, in
`some embodiments, electronic system 700 may be a network
`interface card (NIC) that communicates with a computer or
`network using a bus or other type ofport.
`Althoughthe present invention has been described in con-
`junction 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 ofthe inven-
`tion and the appendedclaims.
`Whatis claimedis:
`1. A method comprising:
`receiving a training sequence from a transmitter;
`estimating N spatial channels in a multiple-input-multiple-
`output (MIMO)system, wherein N is equal to a number
`of receiving antennas;
`performing singular value decomposition to determine an
`NxXNtransmit beamforming matrix;
`removing one transmit beamforming vector from the NxN
`transmit beamforming matrix to yield N-1 transmit
`beamforming vectors, wherein the one transmit beam-
`forming vector removed corresponds to a weakestof the
`N spatial channels; and
`transmitting the N-1 transmit beamforming vectors to the
`transmitter.
`2. The method of claim 1 wherein N is equal to four.
`3. The method of claim 1 wherein N is equal to three.
`4. A method comprising always puncturing one spatial
`channel
`in an N.times.N multiple-input-multiple-output
`
`10
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`15
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`20
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`25
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`(MIMO) wireless system to yield N-1 spatial channels,
`where N is equal to a numberof receiving antennas and is
`greater than one, by always feeding back only N-1 transmit
`beamforming vectors from a receiver to a transmitter.
`5. The method of claim 4 wherein N is equal to four.
`6. The method of claim 4 wherein N is equal to three.
`7. A computer-readable medium encodedwith instructions
`that when executed by a computer cause the computer to
`perform:
`receiving a training sequence from a transmitter;
`estimating N spatial channels in a multiple-input-multiple-
`output (MIMO)system, wherein N is equal to a number
`of receiving antennas;
`performing singular value decomposition to determine an
`NxN transmit beamforming matrix;
`removing one transmit beamforming vector from the NxN
`transmit beamforming matrix to yield N-1 transmit
`beamforming vectors, wherein the one transmit beam-
`forming vector removed corresponds to a weakest ofthe
`N spatial channels; and
`transmitting the N-1 transmit beamforming vectors to the
`transmitter.
`8. The computer-readable medium of claim 7 wherein the
`channelstate information includes a beamforming matrix to
`cause the transmitter to utilize N-1 spatial channels.
`9. The computer-readable medium of claim 7 wherein the
`channel state information describes spatial channels in an
`orthogonal frequency division multiplexing (OFDM) mul-
`tiple-input-multiple-output (MIMO) system.
`10. A wireless communications device having N antennas,
`the wireless communications device having a combination of
`hardware and software components to determine and a weak-
`est of N spatial channels and to always puncture the weakest
`of N spatial channels, wherein the wireless communications
`device includes a combination of hardware and software to
`transmit N—1 beamforming vectors to a transmitter for use in
`antenna beamforming into N-1 spatial channels, where N is
`greater than one.
`11. The wireless communications device of claim 10
`wherein the wireless communications device includes N-1
`baseband data circuits to source data to a beamforming net-
`work.
`12. The wireless communications device of claim 10
`wherein N is equal to four, and three spatial channels are
`always used.
`13. The wireless communications device of claim 10
`wherein N is equal to three, and two spatial channels are
`always used.
`
`12
`
`