USOO7710925B2
`
`US 7,710,925 BZ
`(10) Patent N0.:
`(12) UIllted States Patent
`Poon
`(45) Date of Patent:
`May 4, 2010
`
`
`(54)
`
`SPATIAL PUNCTURING APPARATUS,
`METHOD, AND SYSTEM
`
`............... 375/267
`3/2004 Hwang et a1.
`2004/0042558 A1*
`.............. 375/299
`7/2005 Maltsev et a1.
`2005/0152473 A1 *
`2005/0219999 A1* 10/2005 Kim et a1.
`................... 370/334
`
`(75)
`
`Inventor: Ada S. Y. Poon, Emeryville, CA (US)
`
`FOREIGN PATENT DOCUMENTS
`
`(73) Assignee:
`
`Intel Corporation, Santa Clara, CA
`(US)
`
`WO
`
`WO-2006007138 A1
`
`1/2006
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`{)ng 115Sixl‘gelidecllzogi’} 223113th under 35
`-
`-
`-
`( ) Y
`VS
`
`_
`(21) Appl. No" 1018759111
`.
`Flledi
`
`(22)
`
`(65)
`
`Jun. 23, 2004
`_
`_
`_
`Prlor Publlcatlon Data
`
`(51)
`
`US 2005/0286404 A1
`I t Cl
`(2006 01)
`£110.4Q '7/00
`(52) US. Cl.
`..................... 370/334; 375/267; 455/562.1
`
`Dec. 29’ 2005
`
`OTHER PUBLiCATiONS
`International Search Report and Written Opinion: Dated Aug. 31,
`2005, PCT/U82005/017653; 17 pages.
`Gore, D. A., et al., “Selecting an Optimal Set of Transmit Antennas
`for a Low Rank Matrix Channel”, Acoustics. Speech, and Signal
`Processing,
`Ieee International Conference, vol.
`05,
`(Jun.
`5,
`2000),2785-2788.
`Sandhu, S. , eta1., “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/US2005/
`017653, mailed on Jan. 11, 2007”, 2 pages.
`(Continued)
`
`(58) Field of Classification Search ................. 370/477,
`370/478, 480, 498, 343, 345, 203, 208, 252—254,
`370/310’ 328’ 334334745726377'5/425959/502713 25660T
`See application file for complete search history.
`
`.
`. 7 .
`1:33:31”fiffig’rjggflifigmmakom
`(74) Attorney, Agent, or FirmiDana B. Lemoine; Lemoine
`Patent Serv1ces, PLLC
`
`(56)
`
`References Cited
`
`(57)
`
`ABSTRACT
`
`U'S' PATENT DOCUMENTS
`6,134,231 A
`10/2000 Wright
`6,774,864 B2
`8/2004 Evans et 31.
`............. 455/450
`6,801,775 B1* 10/2004 Gibbons et a1.
`6,917,820 B2 *
`7/2005 Gore et a1.
`............... 455/5621
`2002/0003842 A1 *
`1/2002 Suzuki et al.
`............... 375/259
`2002/0102950 A1
`8/2002 Gore et a1.
`2003/0083016 A1
`5/2003 Evans et a1.
`2003/0185309 A1
`10/2003 Pautler et a1.
`
`Stations in an NxN multiple-input-multiple-output (MIMO)
`wireless network always puncture the weakest spatial chan-
`nel. A receiving station determines channel state information
`for N Spatial Channels and foods book to the transmitting
`Station Channel State information for only N-i Spatial Chon-
`nels- The Channel state information may inoindo a beamform-
`ing matrix to cause the transmitting station to utilize N—I
`Spatial channels-
`
`2003/0186698 A1"< 10/2003 Holma et a1.
`
`............... 455/436
`
`13 Claims, 6 Drawing Sheets
`
`RECEIVE A TRAINING SEQUENCE FROM A
`TRANSMITTER
`
`ESTIMATE N SPATIAL CHANNELS, WHERE
`N IS EQUAL TO A NUMBER OF RECEIVING
`ANTENNAS
`
`DETERMINE THE WEAKEST OF THE N
`SPATIAL CHANNELS
`
`210
`
`220
`
`230
`
`DESCRIBING N—I SPATIAL CHANNELS
`
`TRANS/VII T CHANNEL 8 TA TE INFORMATION
`
`240
`
`200
`
`1
`
`HUAWEI 1009
`
`1
`
`HUAWEI 1009
`
`

`

`US 7,710,925 132
`Page 2
`
`OTHER PUBLICATIONS
`_
`_
`_
`_
`_
`94117248, “Office Actlon recelved for Taiwanese patent Application
`No. 94117248, mailed on Aug. 16, 2006”, 2 pages of Office Action
`and 2 pages of English Translation.
`
`2005800205284, “Office Action received for Chinese Patent Appli-
`cation N0, 2005800205284, mailed on Jul. 3, 2009”, 6 pages of
`Office Action and 5 pages of English Translation.
`
`* Cited by examiner
`
`2
`
`

`

`US. Patent
`
`May 4, 2010
`
`Sheet 1 of6
`
`US 7,710,925 B2
`
`
`
`STATIONZ
`
`
`104
`
`
`
`STATION1
`
`102
`
`FIG.1
`
`3
`
`

`

`US. Patent
`
`May 4, 2010
`
`Sheet 2 of6
`
`US 7,710,925 B2
`
`RECEIVE A TRAINING SEQUENCE FROM A
`TRANSMITTER
`
`ESTIMATE N SPATIAL CHANNELS, WHERE
`N IS EQUAL TO A NUMBER OF RECEIVING
`
`ANTENNAS
`
`210
`
`220
`
`DETERMINE THE WEAKEST OF THEN
`
`230
`
`SPATIAL CHANNELS
`
`TRANSMI T CHANNEL STA TE INFORMATION
`
`240
`
`DESCRIBING N-I SPATIAL CHANNELS
`
`FIG. 2
`
`200
`
`4
`
`

`

`US. Patent
`
`May 4, 2010
`
`Sheet 3 0f6
`
`US 7,710,925 B2
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`4x4 OFDM system at 4x36 Mbps (hard decision
`
`demodulation)
`
`
`
`eigenvectors
`
`EbINU (dB)
`
`FIG. 3
`
`1+ SVD feedback 4
`
`eIgenvecto rs
`
`+ SVD feedback 3
`
`
`
`5
`
`

`

`US. Patent
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`May 4, 2010
`
`Sheet 4 of6
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`US 7,710,925 B2
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`402
`
`410
`
`422
`
`DA TA
`
`SOURCES
`
`DIGITAL
`
`BEAMFORMING.
`
`/
`
`400
`
`412
`
`CS!
`
`FIG. 4
`
` N-1
`
`N
`
`500
`
`FIG. 5
`
`6
`
`

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`US. Patent
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`May 4, 2010
`
`Sheet 5 0f6
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`US 7,710,925 B2
`
`DA TA
`
`SOURCES
`
`ANALOG
`
`BEAMFORMING
`
`/
`
`600
`
`CS!
`
`FIG. 6
`
`7
`
`

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`US. Patent
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`May 4, 2010
`
`Sheet 6 0f 6
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`US 7,710,925 B2
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`8k
`
`Ezmmim
`
`moEmmE‘
`
`98108.80%
`
`QtE05:
`
`QE8“
`
`HE
`
`n65%
`
`c:
`
`My.
`
`.\
`
`as
`
`8
`
`
`

`

`US 7,710,925 B2
`
`1
`
`2
`
`SPATIAL PUNC TURING APPARATUS,
`METHOD, AND SYSTEM
`
`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. Transmitting the channel state infor-
`mation consumes bandwidth that would otherwise be avail-
`able for data traffic.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 shows a diagram of two wireless stations;
`FIG. 2 shows a flowchart in accordance with various
`
`embodiments of the present invention;
`FIG. 3 shows simulation 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 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 way of illustration,
`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 understood that 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 modified
`without departing from the spirit and scope of the 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 fill] 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.
`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/IEEE Std. 802.11, 1999 Edition, although this
`
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`is not a limitation of the 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 may be any number. Further, N and
`M may or may not be equal. The remainder ofthis 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
`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 communi-
`cate using Multiple-Input-Multiple-Output (MIMO) tech-
`niques. In general, MIMO systems offer 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.
`
`MIMO systems may operate either “open loop” or “closed
`loop.” In open loop MIMO systems, a station estimates the
`state of the channel without receiving channel state informa-
`tion directly from another station. 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 MIMO systems, 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 much better perfor-
`mance than linear and iterative receivers. For example, at 1%
`packet error rate and 4x36 Mbps, ML receivers are 12 dB
`more power efficient than linear and iterative receivers, or
`equivalently, have four times better propagation range. How-
`ever, ML receivers need 2><105 times more multiplication
`operations than linear and iterative receivers. To approach the
`performance of ML receivers with the complexity of linear
`receivers, and to reduce the feedback bandwidth, the various
`embodiments of the present invention utilize deterministic
`spatial channel puncturing with closed-loop operation.
`As used herein, “puncturing” refers to the non-use of a
`particular spatial channel. For example, in a NxN MIMO
`system, various embodiments of the present invention use
`N—l channels instead of N channels regardless of the instan-
`taneous channel state information. The spatial puncturing is
`
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`

`US 7,710,925 B2
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`3
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`4
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`deterministic in the sense that one spatial channel is always
`punctured, and an N><N system will always use N—l spatial
`channels. By always only utilizing N—l spatial channels in a
`N><N MIMO system, the amount of channel state information
`to be transmitted is reduced, and the feedback bandwidth is
`reduced.
`
`FIG. 2 shows a flowchart in accordance with various
`
`embodiments of the present invention. In some embodiments,
`method 200 may be used in a wireless system that utilizes
`MIMO technology. 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 correspond to 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 channel state information describ-
`
`the
`ing the N—l spatial channels. In some embodiments,
`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 is reduced in size, thereby reducing the
`feedback bandwidth. Mathematical descriptions of various
`acts shown in FIG. 2 are provided below.
`
`Let the input/output (I/O) model be
`
`y:Hx+z
`
`where x,- is the signal on the ith transmit antenna, y,- is the
`signal received at the ith receive antenna, Hi]. is the channel
`gain from the jth transmit antenna to 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
`
`y:HPx+Z
`
`Upon singular value decomposition (SVD), we have
`H: U2 W
`
`where U and V are N><N unitary matrices, and Z is a
`diagonal matrix with positive entries. Matrix V is the transmit
`beamforming matrix. When V represents N spatial channels,
`V includes 2N2 real numbers, and when V represents N—l
`channels, V includes 2NG\I— 1) real numbers.
`
`Assume elements of H are independent complex Gaussian
`distributed with zero mean and unit variance. Denote the gain
`of the ith spatial channel as 7HOV1§7V1§ .
`.
`. i N), where 7t,
`denotes the entries in diagonal matrix 2. The distribution of
`RN can be shown as
`
`fiM=Ne—"N,
`
`from which its expected value may be derived as
`
`l
`
`Em] = fi'
`
`Also, the overall expected value for k,- may be derived as
`
`10
`
`l
`
`E N(Al +A2+... +AN) ZN.
`
`Accordingly, the ratio of the expected gain of the weakest
`spatial channel to the overall expected gain is
`
`15
`
`Em]
`
`l
`E—R A
`N(i+ 2+
`
`A
`+N)
`
`1
`
`2'
`
`As shown above, the gain of the weakest spatial channel is
`l/N2 ofthe overall expected gain. For example, the gain ofthe
`weakest spatial channel is 9.5 dB below the overall expected
`gain in a 3x3 system and is 12 dB below the overall expected
`gain in a 4><4 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—l) instead of N2. This reduces not only the
`feedback bandwidth but also the computational complexity
`because the receiver now needs to compute N—l 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 embodiment ofthe 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 packet error rate vs. Eb/NO of a 4><4 48-tone
`OFDM system using a 64-state convolutional code, space-
`time interleaver, and 64-QAM with hard-decision demodula-
`tion. As can be seen in FIG. 3, in a 4><4 system, when the
`receiver drops the weakest spatial channel and only sends
`three beam-forming vectors,
`the
`system performance
`approaches the ML openloop receiver 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
`data signals from data sources 402 and forms signals to drive
`four antennas. In operation, digital beamforming block 410
`receives channel state information (CSI) on node 412. In
`some embodiments, the channel state information is in the
`form of beamforming vectors received from another station.
`In embodiments represented by FIG. 4, digital beamforming
`block 410 receives three beamforming vectors, each of length
`four. This corresponds to a NxN—l feedback matrix with
`N:4.
`
`Transmitter 400 always punctures one spatial channel. In
`the example embodiments represented by FIG. 4, N:4, one
`spatial channel is always punctured, and three spatial chan-
`nels are always used. Because three spatial channels are
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`always used, data sources 402 only includes three baseband
`data circuits to source three separate data streams. This is
`contrast to a transmitter that includes four baseband data
`
`circuits to source four separate data streams, even though one
`may be punctured.
`Radio frequency blocks 422, 424, 426, and 428 may
`include circuitry to modulate signals, frequency convert sig-
`nals, amplify signals, or the like. For example, RF blocks 422,
`424, 426, and 428 may include circuits such as mixers, ampli-
`fiers, filters, or the like. The present invention is not limited by
`the contents or function of RF blocks 422, 424, 426, and 428.
`Transmitter 400 may include many functional blocks that
`are omitted from FIG. 4 for ease of illustration. For example,
`transmitter 400 may include a scrambler, a forward error
`correction (FEC) encoder, interleaver, an M-ary quadrature
`amplitude modulation (QAM) mapper and other functional
`blocks.
`
`The various items shown in FIG. 4 may be implemented in
`many different ways. For example, in some embodiments,
`portions of transmitter 400 are implemented in dedicated
`hardware, and portions are implemented in software. In other
`embodiments, all of transmitter 400 is implemented in hard-
`ware. The present invention is not limited in this respect.
`FIG. 5 shows dimensions of a channel state information
`
`matrix. Matrix 500 represents a channel state information
`matrix that may be transmitted back to a transmitter from a
`receiver. In some embodiments, matrix 500 corresponds to a
`beamforming matrix V, described above, having dimensions
`NxN—l. This corresponds to an N><N MIMO system that
`always punctures one spatial channel. In embodiments in
`which N:4, a beamforming matrix having the same dimen-
`sions as matrix 500 may be input to digital beamforming
`block 410 at node 412 (FIG. 4).
`FIG. 6 shows a transmitter with analog beamforming.
`Transmitter 600 may be included in a station such as station
`102 or station 104 (FIG. 1). Transmitter 600 includes data
`sources 610, RF blocks 612, 622, and 624, analog beamform-
`ing block 630, and antennas 642, 644, 646, and 648. Analog
`beamforming block 630 receives three RF signals from RF
`blocks 612, 622, and 624 and forms signals to drive four
`antennas.
`In operation, analog beamforming block 630
`receives channel state information (CSI) on node 632. In
`some embodiments, the channel state information is in the
`form of beamforming vectors received from another station.
`In embodiments represented by FIG. 6, analog beamforming
`block 630 receives three beamforming vectors, each of length
`four. This corresponds to a NxN—l feedback matrix such as
`matrix 500 (FIG. 5) with N24.
`Transmitter 600 always punctures one spatial channel. In
`the example embodiments represented by FIG. 6, N:4, one
`spatial channel is always punctured, and three spatial chan-
`nels are always used. Because three spatial channels are
`always used, data sources 610 only includes three baseband
`data circuits to source three separate data streams. Further,
`because three spatial channels are always used, transmitter
`600 only has three RF blocks 612, 622, and 624. This is
`contrast to a transmitter that includes four baseband data
`
`circuits and four RF blocks to source four separate data
`streams, even though one may be punctured.
`Radio frequency blocks 612, 622, and 624 may include
`circuitry to modulate signals, frequency convert signals,
`amplify signals, or the like. For example, RF blocks 612, 622,
`and 624 may include circuits such as mixers, amplifiers,
`filters, or the like. The present invention is not limited by the
`contents or function of RF blocks 612, 622, and 624.
`Transmitter 600 may include many functional blocks that
`are omitted from FIG. 6 for ease of illustration. For example,
`
`transmitter 600 may include a scrambler, a forward error
`correction (FEC) encoder, interleaver, an M-ary quadrature
`amplitude modulation (QAM) mapper and other functional
`blocks.
`
`FIG. 7 shows a system diagram in accordance with various
`embodiments of the present invention. Electronic system 700
`includes antennas 710, physical
`layer (PHY) 730, media
`access control (MAC) layer 740, Ethernet interface 750, pro-
`cessor 760, and memory 770. In some embodiments, elec-
`tronic system 700 may be a station capable of puncturing one
`spatial channel. For example, electronic system 700 may be
`utilized in a wireless network as station 102 or station 104
`
`(FIG. 1). Also for example, electronic system 700 may be a
`transmitter such as transmitter such as transmitter 400 (FIG.
`4) or 600 (FIG. 6) capable of beamforming, or may be a
`receiver capable of performing channel estimation and deter-
`mining a weakest spatial channel to be punctured.
`In some embodiments, electronic system 700 may repre-
`sent a system that includes an access point or mobile station as
`well as other circuits. For example, in some embodiments,
`electronic system 700 may be a computer, such as a personal
`computer, a workstation, or the like, that includes an access
`point or mobile station as a peripheral or as an integrated unit.
`Further, electronic system 700 may include a series of access
`points that are coupled together in a network.
`In operation, system 700 sends and receives signals using
`antennas 710, and the signals are processed by the various
`elements shown in FIG. 7. Antennas 710 may be an antenna
`array or any type of antenna structure that supports MIMO
`processing. System 700 may operate in partial compliance
`with, or in complete compliance with, a Wireless network
`standard such as an 802.11 standard.
`
`Physical layer (PHY) 730 is coupled to antennas 710 to
`interact with a wireless network. PHY 730 may include cir-
`cuitry to support the transmission and reception of radio
`frequency (RF) signals. For example, in some embodiments,
`PHY 730 includes an RF receiver to receive signals and
`perform “front end” processing such as low noise amplifica-
`tion (LNA), filtering, frequency conversion or the like. Fur-
`ther, in some embodiments, PHY 730 includes transform
`mechanisms and beamforming circuitry to support MIMO
`signal processing. Also for example, in some embodiments,
`PHY 730 includes circuits to support frequency up-conver-
`sion, and an RF transmitter.
`Media access control (MAC) layer 740 may be any suitable
`media access control layer implementation. For example,
`MAC 740 may be implemented in software, or hardware or
`any combination thereof. In some embodiments, a portion of
`MAC 740 may be implemented in hardware, and a portion
`may be implemented in software that is executed by processor
`760. Further, MAC 740 may include a processor separate
`from processor 760.
`In operation, processor 760 reads instructions and data
`from memory 770 and performs actions in response thereto.
`For example, processor 760 may access instructions from
`memory 770 and perform method embodiments of the
`present invention, such as method 200 (FIG. 2) or methods
`described with reference to other figures. Processor 760 rep-
`resents any type of processor, including but not limited to, a
`microprocessor, a digital signal processor, a microcontroller,
`or the like.
`
`Memory 770 represents an article that includes a machine
`readable medium. For example, memory 770 represents a
`random access memory (RAM), dynamic random access
`memory (DRAM), static random access memory (SRAM),
`read only memory (ROM), flash memory, or any other type of
`article that includes a medium readable by processor 760.
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`US 7,710,925 B2
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`Memory 770 may store instructions for performing the execu-
`tion of the various method embodiments of the present inven-
`tion.
`
`Although the various elements of system 700 are shown
`separate in FIG. 7, embodiments exist that combine the 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 of the present inven-
`tion do not include Ethernet interface 750. For example, in
`some embodiments, electronic system 700 may be a network
`interface card m1C) that communicates with a computer or
`network using a bus or other type of port.
`Although the 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 of the inven-
`tion and the appended claims.
`What is claimed is:
`
`1. A method comprising:
`receiving a training sequence from a transmitter;
`estimating N spatial channels in a multiple-input-multiple-
`output (MlMO) system, wherein N is equal to a number
`of receiving antennas;
`performing singular value decomposition to determine an
`N><N transmit beamforming matrix;
`removing one transmit beamforming vector from the N><N
`transmit beamforming matrix to yield N—1 transmit
`beamforming vectors, wherein the one transmit beam-
`forming vector removed corresponds to a weakest of 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
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`(MIMO) wireless system to yield N—l spatial channels,
`where N is equal to a number of receiving antennas and is
`greater than one, by always feeding back only N—l 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 encoded with 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 (MlMO) system, wherein N is equal to a number
`of receiving antennas;
`performing singular value decomposition to determine an
`N><N transmit beamforming matrix;
`removing one transmit beamforming vector from the N><N
`transmit beamforming matrix to yield N—l
`transmit
`beamforming vectors, wherein the one transmit beam-
`forming vector removed corresponds to a weakest ofthe
`N spatial channels; and
`transmitting the N—l transmit beamforming vectors to the
`transmitter.
`
`8. The computer-readable medium of claim 7 wherein the
`channel state information includes a beamforming matrix to
`cause the transmitter to utilize N—l 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 (MlMO) 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—l spatial channels, where N is
`greater than one.
`11. The wireless communications device of claim 10
`wherein the wireless communications device includes N—l
`
`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.
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