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`US 7,570,696 B2
`(10) Patent No.:
`a2) United States Patent
`
`
`
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`
`
`Aug. 4, 2009
`(45) Date of Patent:
`Maltsevet al.
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`US007570696B2
`
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`
`
`11/2001 Luzetal.
`6,321,073 BL
`
`
`
`
`
`10/2002 Wallace etal.
`6,473,467 B1
`
`
`
`
`12/2002 Tsurumi et al.
`6,498,929 B1
`
`
`
`
`4/2004 Mohindra
`6,717,981 B1
`4/2005 Andersonet al.
`6,876,859 B2
`
`
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`8/2005 Vooketal. wwe 342/377
`6,927,728 B2*
`Inventors: Alexander A. Maltsev, Nizhny
`
`
`
`
`
`
`
`
`
`8/2006 Oonoetal.
`7,085,587 B2
`Novgorod (RU); Ali S Sadri, San Diego,
`
`
`
`
`
`
`
`
`3/2007 Ozawa
`7,196,579 B2
`CA (US); Sergey A. Tiraspolsky,
`
`
`
`
`
`
`
`
`8/2008 Song
`7,409,189 B2
`Nizhny Novgorod (RU); Alexander
`
`
`
`
`
`
`
`
`
`10/2001 Jongrenctal.
`2001/0033622 Al
`Flaksman, Nizhny Novgorod (RU);
`
`
`
`
`
`
`
`
`
`
`
`Alexei V Davydov, Nizhny Novgorod 2002/0094792 Al=7/2002: Oono etal.
`
`
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`
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`2003/0064696 Al
`4/2003 Akamineetal.
`(RU)
`2003/0181170 Al
`9/2003 Sim
`
`
`
`
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`
`
`
`
`
`
`(54) MULTIPLE INPUT MULTIPLE OUTPUT
`
`
`MULTICARRIER COMMUNICATION
`
`
`
`SYSTEM AND METHODSWITH QUANTIZED
`
`
`BEAMFORMING FEEDBACK
`
`
`
`
`
`(75)
`
`
`
`
`
`
`(73) Assignee:
`
`
`
`
`
`
`
`Intel Corporation, Santa Clara, CA
`
`(US)
`
`
`
`
`
`(Continued)
`
`
`FOREIGN PATENT DOCUMENTS
`
`
`
`
`1416688 Al
`5/2004
`
`
`
`
`
`EP
`
`(Continued)
`
`OTHER PUBLICATIONS
`
`
`
`
`
`
`
`
`
`
`
`
`Stephens, A. P., “IEEE 802.11 TGn Comparison Criteria”, IEEE
`
`
`
`
`
`
`
`802.11-02/814r2, (IEEE P802.1—Wireless LANs),(Nov. 2003),5
`pgs.
`
`
`
`
`
`;
`(Continued)
`
`
`
`Primary Examiner—Khai Tran
`
`
`
`
`
`
`(74) Atiorney, Agent, or Firm—Schwegman, Lundberg &
`
`
`
`
`Woessner, P.A.; Gregory J. Gorrie
`
`
`(57)
`
`ABSTRACT
`
`
`
`
`
`
`
`
`
`
`A multicarrier receiver generates a quantized transmit beam-
`
`
`
`
`
`
`
`
`former matrix (V) for each subcarrier of a multicarrier com-
`
`
`
`
`
`
`munication channel for use by a multicarrier transmitting
`
`
`
`
`
`
`
`station. lhe multicarrier receiver applies a corrected receiver
`
`
`
`
`
`
`
`
`beamformer matrix (U”) to received subcarriers signals gen-
`
`
`
`
`
`
`
`erated by signals received fromthe transmitting station.
`
`
`
`
`34 Claims, 11 Drawing Sheets
`
`
`
`po
`
`
`
`
`(*) Notice:
`
`
`
`
`
`(65)
`
`
`
`(51)
`
`(56)
`
`
`
`
`
`
`
`
`
`Subject to any disclaimer, the termof this
`
`
`
`
`patent is extended or adjusted under 35
`
`
`
`
`U.S.C. 154(b) by 1240 days.
`
`
`
`
`(21) Appl. No.: 10/877,943
`(22) Filed:
`Jum. 25, 2004
`
`
`
`
`
`
`
`
`Prior Publication Data
`
`
`
`
`US 2005/0287978 Al
`Dec. 29, 2005
`
`
`Int. Cl.
`
`
`
`(2006.01)
`HOAL 27/28
`
`
`
`
`(52) US. cl. ssersnennnernannnntinnietnernenicnien 375/260
`
`
`
`
`
`(58) Field of Classification Search veers 375/260,
`
`
`
`
`
`375/347, 267, 147, 150, 149; 455/403, 562.1,
`
`
`
`
`
`
`455/101, 102, 103, 69, 73; 342/372, 368,
`342/377, 383
`
`
`
`
`
`
`
`See application file for complete search history.
`
`
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`
` safy|& HULTPLEXERTT 8
`
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`
`
`
`
`Y
`FFT & cycuc
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`:
`
`
`
`
`
`
`
`
`tLe
`=f
`ca
`
`
`
`
`
`
`
`—l DEWAPPER
`ANG & RF
`
`
`TT] RX SUBCARRIER
`OROCESSING
`
`
`
`
`
`
`BEAMFORWER = EWAPPER
`LJ
`a]
`
`
`
`lg - ne
`M4
`at
`
`
`
`
`
`
`
`
`
`
`acAnroRKER|Vi), OMe
`
`
`
`
`cine |_MM|area catcucaon [ve 8
`
`
`ESTIMATOR
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`
`2a
`Ree
`
`
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`
`
`
`
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`
`Aug.4, 2009
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`Sheet 1 of 11
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`US 7,570,696 B2
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`TINNVHOST
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`U.S. Patent
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`U.S. Patent
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`Aug. 4, 2009
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`Sheet 2 of 11
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`US 7,570,696 B2
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`Sheet 3 of 11
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`US 7,570,696 B2
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`US 7,570,696 B2
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`CHANNEL USED FOR TX WEIGHT VECTORS CALCULATION
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`US 7,570,696 B2
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`BITS
`PER IX
`
`WEIGHT COEFFICIENT
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`US 7,570,696 B2
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`TRANSMITTING STATION PROCEDURE
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`{QQ
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`RECEIVE QUANTIZED TRANSMIT BEAMFORMING
`
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`MATRICES (V) FROM RECEIVING STATION
`
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`APPLY 10 EACH SUBCARRIER
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`US 7,570,696 B2
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`RON
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`ESTIMATE CHANNEL FROM PREAMBLE TO GENERATE
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`CHANNEL MATRIX FOR EACH SUBCARRIER
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`QUANTIZE CHANNEL MATRICES
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`SEND QUANTIZED IX BEAMFORMING MATRICES 10
`
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`TRANSMITTING STATION
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`Aug. 4, 2009
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`Sheet 10 of 11
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`US 7,570,696 B2
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`U.S. Patent
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`Aug. 4, 2009
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`Sheet 11 of 11
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`US 7,570,696 B2
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`US 7,570,696 B2
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`
`1
`MULTIPLE INPUT MULTIPLE OUTPUT
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`MULTICARRIER COMMUNICATION
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`SYSTEM AND METHODS WITH QUANTIZED
`BEAMFORMING FEEDBACK
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`quencydivision multiplexed (OFDM)receiverin accordance
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`with some embodiments of the present invention.
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`DETAILED DESCRIPTION
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`TECHNICALFIELD
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`Embodiments of the present invention pertain to wireless
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`communications, and in some embodiments, to multicarrier
`communications.
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`10
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`BACKGROUND
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`Wireless communication systems conventionally use feed-
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`backto allow a transmitting station to adaptit’s transmissions
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`to changing channel conditions. One problem with multicar-
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`rier communication systems that use manysubcarriers, such
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`as systems employing orthogonal frequency division multi-
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`plexed (OFDM)signals, is that the channel conditions may be
`different for each ofthe subcarriers. The amount of feedback
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`to adapt to changing channel conditions maybe significant
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`and consumes bandwidth as well as uses additional energy.
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`This is especially a concern when multiple antennasare used
`to communication additional data streams over the same sub-
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`carriers, as in the case of multiple input multiple output
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`(MIMO)systems. Thus, there are general needs for systems
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`and methods that may adapt to changing channel conditions
`with less feedback.
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`BRILI DESCRIPTION OF THE DRAWINGS
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`The following description and the drawingsillustrate spe-
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`cific embodiments of the invention sufficiently to enable
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`those skilled in the art to practice them. Other embodiments
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`may incorporate structural, logical, electrical, process, and
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`other changes. Examples merely typify possible variations.
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`Individual components and functions are optional unless
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`explicitly required, and the sequence of operations may vary.
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`Portions and features of some embodiments may be included
`in or substituted for those of others. Embodiments of the
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`invention may be referred to, individually or collectively,
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`herein by the term “invention” merely for convenience and
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`without intending to voluntarily limit the scope of this appli-
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`cation to any single invention or inventive concept if more
`than oneis in fact disclosed.
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`FIG. 1 is a block diagram of a multicarrier transmitter in
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`accordance with some embodimentsof the present invention.
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`Multicarrier transmitter 100 may be part of a wireless com-
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`munication device and maytransmit multicarrier communi-
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`cation signals comprising a plurality of subcarriers, such as
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`orthogonalfrequency division multiplexed (OFDM) commu-
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`nication signals, although the scope of the invention is not
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`limited in this respect.
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`In accordance with same embodiments, multicarrier trans-
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`mitter 100 may apply quantized transmit beamforming coef-
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`ficients to symbol-modulated subcarriers of a multicarrier
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`communication signal ina signal path before an inverse Fou-
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`rier transform (IFFT) is performed on the subcarriers. The
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`quantized transmit beamforming coefficients may comprise
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`predetermined numbersofbits for each subcarrier indicating
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`amounts to weight an amplitude and shift a phase of an
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`associated symbol-modulated subcarrier. In some embodi-
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`ments, multicarrier transmitter 100 may comprise a plurality
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`of transmit subcarrier beamformers 108 to apply the quan-
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`tized transmit beamforming coefficients to symbol-modu-
`lated subcarriers 107.
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`In some embodiments, the transmit subcarrier beamform-
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`ers 108 mayapplythe quantized transmit beamforming coef-
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`ficients in the frequency domain to frequency-domain sym-
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`bol-modulated subcarriers 107 before an IFFT is performed
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`on the symbol-modulated subcarriers. In some embodiments,
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`a quantized transmit beamformer matrix (V) generated by a
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`receiving station includes the transmit beamforming coetti-
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`cients. In some embodiments, the transmit beamforming
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`coefficients may be complex values.
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`The use of quantized transmit beamforming coefficients
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`may significantly reduce the amount of feedback provided by
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`a receiving station. In some embodiments, closed loop adap-
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`tive beamforming may performed by transmitter 100. The
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`adaptive beamforming maygenerate signals for different spa-
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`tial channels by taking into account multipath differences in
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`the communication channel. Another purposeofthe adaptive
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`beamforming is to take into account the channel conditions
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`(i.e., adapt to changing channel conditions of a fading chan-
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`nel) as well as take into account channel conditions between
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`the transmitting and receiving stations.
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`In some embodiments, multicarrier transmitter 100 may be
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`part ofa closed loop multiple-input multiple-output (MIMO)
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`system that performs adaptive beamforming based on singu-
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`lar value decomposition (SVD). In these embodiments, the
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`MIMOsystem may be viewed as a plurality of decoupled
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`(independent or orthogonal)
`single-input
`single-output
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`(SISO) systems referred to as orthogonal spatial channels.
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`The appended claims are directed to some of the various
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`embodiments of the present invention. However, the detailed
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`description presents a more complete understanding of
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`embodiments of the present invention when considered in
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`connection with the figures, wherein like reference numbers
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`refer to similar items throughout the figures and:
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`FIG.1 is a block diagram of a multicarrier transmitter in
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`accordance with some embodimentsofthe present invention;
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`FIG. 2 is a block diagram of a multicarrier receiver in
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`accordance with some embodimentsofthe present invention;
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`FIGS. 3A and 3B illustrate quantization schemesin accor-
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`dance with some embodimentsofthe present invention;
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`FIGS. 4A and 4Billustrate amplitude and phase subfields
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`of quantized beamforming coefficients in accordance with
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`some embodimentsofthe present invention;
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`FIG.5 illustrates channel measurements for use in gener-
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`ating quantized beamformer coefficients for groups of sub-
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`carriers in accordance with some embodimentsofthe present
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`invention;
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`TIGS. 6A and 6Billustrate quantized transmit beamform-
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`ing coefficients in accordance with some embodiments of the
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`present invention;
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`FIG.7 is a flow chart of a multicarrier signal transmission
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`procedure in accordance with some embodiments of the
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`present invention;
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`FIG. 8 is a flow chart of a multicarrier signal reception
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`procedure in accordance with some embodiments of the
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`present invention;
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`FIG. 9 is a functional diagram illustrating the operation of
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`a 4x2 multiple-input multiple-output (MIMO) orthogonal
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`frequency division multiplexed (OFDM)transmitter in accor-
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`dance with some embodiments of the present invention; and
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`FIG.10 is a functional diagram illustrating the operation of
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`a multiple-input multiple-output (MIMO) orthogonal fre-
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`Page 14 of 26
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`3
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`The numberof orthogonal spatial channels is generally not
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`greater than a minimum numberoftransmit and minimum
`number of receive antennas.
`In accordance with some
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`embodiments ofthis invention, the spatial channels may be
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`substantially orthogonal. The substantial orthogonality is
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`achieved by applying appropriate transmit and receive beam-
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`forming coefficients.
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`In some embodiments, encoded bit stream 103 may be
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`separated by bit demultiplexer of circuitry 104 into several
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`flows (data streams) in accordance with the numberof spatial
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`channels. These flows maybereferred to as spatial bit streams
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`and may comprise the same numberof bits when identical
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`modulation and/or coding schemes are used for each of the
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`spatial channels. The spatial bit streams may contain different
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`numbers of bits when different modulation and/or coding
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`schemesare used for each of the spatial channels, although
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`the scope ofthe invention is not limited in this respect.
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`In some embodiments, each spatial channel may be used
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`communicate separate and/or independent data streams on
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`the samesubcarriers as the otherspatial channels allowing the
`transmission of additional data without an increase in fre-
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`quency bandwidth. The use of spatial channels takes advan-
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`tage of the multipath characteristics of the channel.
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`In accordance with closed loop MIMO embodimentsofthe
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`present invention, when spatial channels are substantially
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`orthogonal, each spatial channel may be associated with a
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`beamformingpattern, rather than an antenna. Signals in each
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`spatial channel may be transmitted from the available anten-
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`nas simultaneously. In other words, each antenna maytrans-
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`mit signals with different weights which are specific to the
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`individual antenna. Examples of these embodiments are
`described in moredetail below.
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`In some embodiments, multicarrier transmitter 100 may
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`comprise encoder 102, which may be a forward errorcorrect-
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`ing (FEC) encoder,
`to apply error-correcting codes to bit
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`stream 101 and generate encoded bit stream 103. In some
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`embodiments, multicarrier transmitter 100 may also com-
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`prise bit demultiplexer and interleaver circuitry 104 to per-
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`mute bits of encodedbit stream 103 and demultiplex thebits
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`into a plurality of spatial/frequency channels.
`In some
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`embodiments, permuted bits may be separated by bit demul-
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`tiplexer of circuitry 104 into one or morespatial streams
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`associated with each spatial channel. Each of the spatial
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`streams may be permuted byaninterleaver of circuitry 104 in
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`accordance with aninterleaving pattern. Then, bit demulti-
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`plexer of circuitry 104 may separate each of the permuted
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`spatial streams into groups for modulation on the data sub-
`carriers of the multicarrier communication channel. The
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`grouping of bits may depend on the modulationlevels for the
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`subcarrier and may be provided by processing circuitry 116,
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`although the scope of the invention is not limited in this
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`respect.
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`Tn some embodiments, multicarrier transmitter 100 may
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`also comprise symbol] mappingcircuitry 106 for each spatial
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`stream and/orspatial channel to gencrate symbol-modulated
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`subcarriers 107 fromspatial channel multiplexed bit streams
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`105. Transmit subcarrier beamformers 108 may be associated
`with each subcarrierofthe multicarrier communication chan-
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`nel and may apply quantized transmit beamforming coeffi-
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`cients 118 to each subcarrier signal to generate frequency-
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`domain symbol-modulated subcarriers 109 for each transmit
`antenna 114.
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`In some embodiments, multicarrier transmitter 100 may
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`also comprise inverse fast Fourier transform circuitry (IFFT)
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`circuitry 110 for each transmit antenna 114 to perform an
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`JFFT on symbol-modulated subcarriers 109 after application
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`of quantized transmit beamforming coefficients 118 by trans-
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`Page 15 of 26
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`mit subcarrier beamformers 108 to generate time-domain
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`samples 111 for each transmit antenna 114. In some embodi-
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`ments, a cyclic extension may be added to time-domain
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`samples 111 to help reduce the effects of intersymbolinter-
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`ference, although the scope ofthe invention is not limited in
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`this respect.
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`In some embodiments, multicarrier transmitter 100 may
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`also comprise digital to analog conversion (DAC)circuitry
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`and radio-frequency (RE) circuitry 112 which maybe asso-
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`ciated with one of transmit antennas 114. Circuitry 112 may
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`generate RF signals for transmission from time-domain
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`samples 111 generated by the IFFT circuitry 10.
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`In some embodiments, multicarrier transmitter 100 may
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`also comprise processing circuitry 116 to provide transmit
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`parameters to various elements of transmitter 100. For
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`example, processing circuitry 116 may provide interleaving
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`parameters 120 for the interleaver ofcircuitry 104, subcarrier
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`modulation levels 122 to each of symbol mappingcircuitry
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`106, IFFT size information 124 to IFFT circuitry 110, and
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`code type and/or coding rate information 126 to encoder 102,
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`although the scope of the invention is not limited in this
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`respect. In some embodiments, circuitry 116 may assign the
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`transmit parameters based on channel feedback information
`115 received from another communication station for fast
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`link adaptation.
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`In some embodiments, transmit antennas 114 may be used
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`for transmitting a plurality of spatial streams on a plurality of
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`spatial channels over the multicarrier communication chan-
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`nel. In these embodiments, the numberofthe spatial streams
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`and/or spatial channels may be less than or equal to the
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`numberofthe transmit antennas. In some embodiments, four
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`antennas 114 may be used to transmit up to four spatial
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`streams over corresponding spatial channels, although the
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`scopeofthe present inventionis not limited in this respect.
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`Tn some embodiments, the quantized transmit beamform-
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`ing coefficients for each subcarrier may represent a quantized
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`transmit beamforming matrix (V) for each subcarrier. In some
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`embodiments, each quantized transmit beamforming matrix(
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`V) may be a unitary matrix having a numberofrows equaling
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`the number of the transmit antennas, and a numberofcol-
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`umns equaling the numberof the spatial streams (or spatial
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`channels). As used herein, the use of the terms “rows” and
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`Tn some embodiments, elements of each quantized trans-
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`mit beamforming matrix (V) may comprise an amplitude
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`subfield and a phase subfield with eachfield having predeter-
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`mined numbersofbits. In some embodiments, the amplitude
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`subfield represents the square of the amount to weight the
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`amplitude of an associated symbol-modulated subcarrier.
`This is discussed more detail below with reference to FIGS.
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`4A and 4B. Some embodiments may use uniform quantiza-
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`tion of the square amplitudes of the transmit beamforming
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`coefficients. This uniform quantization may be near to opti-
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`mal fora typical randomRayleigh indoor channel because the
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`square amplitudes of the transmit beamforming coefficients
`have a distribution that is close to uniform.
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`In some embodiments, multicarrier transmitter 100 may be
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`part of a transmitting station and mayreceive channel feed-
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`back information 115 comprising a quantized transmit beam-
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`forming matrix (V) for each subcarrier [roma receiving sta-
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`tion. In these embodiments, processing circuitry 116 may
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`provide quantized transmit beamforming coefficients 118
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`from the quantized transmit beamforming matrix (V) to a
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`corresponding one of transmit subcarrier beamformers 108.
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`In these embodiments, the receiving station may measure
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`signals received from transmitter 100 to estimate a channel
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`Page 15 of 26
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`

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`US 7,570,696 B2
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`5
`6
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`individual subcarrier modulation assignments. This may be
`transfer matrix (H) for each subcarrier of the multicarrier
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`referred to as adaptive bit loading (ABL). Accordingly, one or
`communication channel, and may generate the quantized
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`beamforming matrix (V) for each subcarrier from the channel
`more bits may be represented by a symbol modulated on a
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`subcarrier. The modulation assignments for the individual
`transfer matrix (H). In these embodiments, the receiving sta-
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`subchannel may be based on the channel characteristics or
`tion maytransmit the quantized beamforming matrix (V)for
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`channel conditions for that subcarrier, although the scope of
`each subcarrier to the transmitting station in a response
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`the invention is not limited in this respect. In some embodi-
`packet, although the scope of the invention is not limited in
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`ments, the subcarrier modulation assignments may range
`this respect. In some ofthese embodiments, the receiving
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`from zero bits per symbol to up to ten or morebits per symbol.
`station may measure a preamble ofapacket received from the
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`In terms of modulation levels, the subcarrier modulation
`transmitting slalion to estimate the channel transfer matrix
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`assignments may comprise binary phase shift keying
`(A) for each subcarrier of the multicarrier communication
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`(BPSK), which communicates onebit per symbol, quadrature
`channel. In some embodiments, the receiving station may
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`phase shitt keying (QPSK), which communicates two bits per
`measure a physical
`layer convergence protocol
`(PLCP)
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`symbol, 8PSK, which communicates three bits per symbol,
`header of a packet received from the transmitting station to
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`16-quadrature amplitude modulation (16-QAM), which com-
`estimate the channel transfer matrix (H) for each subcarrier,
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`municates four bits per symbol, 32-QAM, which communi-
`although the scope of the invention is not limited in this
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`catesfive bits per symbol, 64-QAM, which communicates six
`respect. In some of these embodiments,the receiving station
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`bits per symbol, 128-QAM,which communicates seven bits
`may perform a singular value decomposition (SVD) on the
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`per symbol, and 256-QAM, which communicates eight bits
`channel transfer matrix (H) to generate the quantized beam-
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`per symbol. Modulation orders with higher data communica-
`forming matrix (V) for each subcarrier. These embodiments
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`are discussed in moredetail below.
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`tion rates per subcarrier may also be used.
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`In some embodiments, the frequency spectrums for the
`In some embodiments, the predetermined numbersofbits
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`multicarrier communication channel may comprise subchan-
`comprising the quantized beamforming matrix (V) may be
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`nels in either a 5 GHz frequency spectrum or a 2.4 GHz
`lower during initial portions of a packet exchan