USOO7415074B2
`
`(12) United States Patent
`Seto et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7415,074 B2
`Aug. 19, 2008
`
`(54) MIMO TRANSMISSION AND RECEPTION
`METHODS AND DEVICES
`
`(75) Inventors: Ichiro Seto, Fuchu (JP): Tsuguhide
`Aoki, Kawasaki (JP); Hiroshi Yoshida,
`Yokohama (JP)
`(73) Assignee: Kabushiki Kaisha Toshiba, Tokyo (JP)
`(*) Notice:
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 647 days.
`(21) Appl. No.: 11/016,808
`
`(22) Filed:
`
`Dec. 21, 2004
`
`(65)
`
`Prior Publication Data
`US 2005/O163244A1
`Jul. 28, 2005
`
`(30)
`Jan. 9, 2004
`
`Foreign Application Priority Data
`(JP)
`............................. 2004-004848
`
`(51) Int. Cl.
`(2006.01)
`H04K L/It
`(2006.01)
`H04L 27/28
`(2006.01)
`H04L I/02
`(2006.01)
`H04B 7/02
`(52) U.S. Cl. ....................................... 375/260; 375/267
`(58) Field of Classification Search ....................... None
`See application file for complete search history.
`References Cited
`
`(56)
`
`U.S. PATENT DOCUMENTS
`
`5,497.398 A * 3/1996 Tzannes et al. ............. 375,260
`6,917,311 B2 * 7/2005 Hosur et al. .................. 341/SO
`6,985.434 B2 *
`1/2006 Wu et al. .................... 370,208
`2004.0005018 A1*
`1/2004 Zhu et al. ................... 375/340
`2005, 0163244 A1
`7/2005 Seto et al.
`
`2005/0180313 A1* 8, 2005 Kim et al. ................... 370,208
`2005, 0180515 A1* 8, 2005 Orihashi et al. ...
`... 375,260
`2007/0153928 A1* 7/2007 Liu et al. .................... 375,260
`
`
`
`FOREIGN PATENT DOCUMENTS
`
`JP
`JP
`WO
`
`2000-2363.13
`2001-148676
`WOO1,71928 A2
`
`8, 2000
`5, 2001
`9, 2001
`
`OTHER PUBLICATIONS
`U.S. Appl. No. 1 1/201,385, filed Aug. 8, 2005, Aoki.
`U.S. Appl. No. 1 1/087,601, filed Mar. 24, 2005, Aoki.
`U.S. Appl. No. 1 1/076,051, filed Mar. 10, 2005, Aoki et al.
`U.S. Appl. No. 1 1/018,251, filed Dec. 22, 2004, Aoki et al.
`U.S. Appl. No. 1 1/016,808, filed Dec. 21, 2004, Seto et al.
`U.S. Appl. No. 1 1/132,279, filed May 19, 2005, Aoki.
`U.S. Appl. No. 1 1/132,376, filed May 19, 2005, Aoki et al.
`Jan Boer, et al., “Backwards compatibility”, ftp://ieee: wireless(aftp.
`802wirelessworld.com, IEEE 802.11-0714rO, Sep. 2003, 7 Pages.
`Yasutaka Ogawa, et al., “A MIMO-OFDM System for High-Speed
`Transmission'. Vehicular Technology Conference on, USA. vol. 1,
`Oct. 9, 2003, pp. 493-497.
`* cited by examiner
`Primary Examiner Shuwang Liu
`Assistant Examiner Gina McKie
`(74) Attorney, Agent, or Firm Oblon, Spivak, McClelland,
`Maier & Neustadt, P.C.
`
`(57)
`
`ABSTRACT
`
`In a wireless transmitting device which performs transmis
`sion by an OFDM using a plurality of subcarriers orthogonal
`to each other, a plurality of preambles to which a plurality of
`different subcarrier groups selected from a plurality of sub
`carriers within an OFDM signal band are allocated are trans
`mitted by using a plurality of transmit antennas, and data is
`transmitted by using the antennas after the preambles are
`transmitted.
`
`4 Claims, 11 Drawing Sheets
`
`200
`
`Transmission
`data
`
`Digital
`modulator
`
`Fading
`information
`
`Subcarrier
`division
`Controller
`
`205A
`
`205B
`
`e Transmitter
`
`Y-205C
`
`Y-205D
`
`Transmitter
`
`Exhibit 1036
`Panasonic v. UNM
`IPR2024-00364
`Page 1 of 20
`
`

`

`U.S. Patent
`
`Aug. 19, 2008
`
`Sheet 1 of 11
`
`US 7,415,074 B2
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`Exhibit 1036
`Panasonic v. UNM
`IPR2024-00364
`Page 2 of 20
`
`

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`205A
`
`205B
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`205C
`
`300
`
`Digital
`demodulator
`
`Receive data
`
`305
`
`U.S. Patent
`
`Aug. 19, 2008
`
`Sheet 2 of 11
`
`US 7415,074 B2
`
`200
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`Transmitter
`
`8
`Transmission data
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`301A
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`estimator
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`l
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`estimator
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`Channel
`estimator
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`F. G. 3
`
`Exhibit 1036
`Panasonic v. UNM
`IPR2024-00364
`Page 3 of 20
`
`

`

`U.S. Patent
`
`Aug. 19, 2008
`
`Sheet 3 of 11
`
`US 7415,074 B2
`
`[ne]
`
`30
`
`
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`H
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`F. G. 4A
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`20
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`30
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`Subcarrier number
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`
`30
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`-20
`
`O
`Subcarrier number
`FG, 4C
`
`20
`
`30
`
`Subcarrier number
`F. G. 4D
`
`Exhibit 1036
`Panasonic v. UNM
`IPR2024-00364
`Page 4 of 20
`
`

`

`U.S. Patent
`
`Aug. 19, 2008
`
`Sheet 4 of 11
`
`US 7415,074 B2
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`
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`0
`
`-10
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`O
`Subcarrier number
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`10
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`Subcarrier number
`F. G.5D
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`30
`
`30
`
`Exhibit 1036
`Panasonic v. UNM
`IPR2024-00364
`Page 5 of 20
`
`

`

`U.S. Patent
`
`Aug. 19, 2008
`
`Sheet 5 of 11
`
`US 7415,074 B2
`
`401
`
`402
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`403
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`DOWn
`COnverter
`
`Variable gain
`amplifier
`
`A/D
`COnverter
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`Gain
`
`From digital
`demodulator 304
`
`F. G. 6
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`
`
`
`Wireless
`transmitter
`apparatuS
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`O
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`receiver
`apparatuS
`
`Exhibit 1036
`Panasonic v. UNM
`IPR2024-00364
`Page 6 of 20
`
`

`

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`U.S. Patent
`U.S. Patent
`
`Aug. 19, 2008
`Aug.19, 2008
`
`Sheet 6 of 11
`Sheet 6 of 11
`
`US 7415,074 B2
`US 7,415,074 B2
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`Exhibit 1036
`
`Panasonic v. UNM
`
`IPR2024-00364
`Page 7 of 20
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`Exhibit 1036
`Panasonic v. UNM
`IPR2024-00364
`Page 7 of 20
`
`

`

`U.S. Patent
`U.S. Patent
`
`Aug. 19, 2008
`Aug.19, 2008
`
`Sheet 7 of 11
`Sheet 7 of 11
`
`US 7415,074 B2
`US 7,415,074 B2
`
`||||||||
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`Exhibit 1036
`
`Panasonic v. UNM
`
`IPR2024-00364
`Page 8 of 20
`
`Exhibit 1036
`Panasonic v. UNM
`IPR2024-00364
`Page 8 of 20
`
`

`

`U.S. Patent
`
`Aug. 19, 2008
`
`Sheet 8 of 11
`
`US 7415,074 B2
`
`205A
`
`205B
`
`Transmitter
`
`Transmitter
`
`Transmitter
`
`Transmitter
`
`Transmission
`data
`
`Digital
`modulator
`
`Fading
`information
`
`Subcarrier
`division
`Controller
`
`F. G. 10
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`
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`
`Exhibit 1036
`Panasonic v. UNM
`IPR2024-00364
`Page 9 of 20
`
`

`

`U.S. Patent
`
`Aug. 19, 2008
`
`Sheet 9 of 11
`
`US 7,415,074 B2
`
`
`
`Tx
`
`H--
`
`H
`
`-20
`
`O
`Subcarrier number
`FG, 12A
`
`O
`Subcarrier number
`F. G. 12B
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`Subcarrier number
`F. G. 12C
`
`30
`
`30
`
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`Subcarrier number
`F. G. 12D
`
`20
`
`30
`
`Exhibit 1036
`Panasonic v. UNM
`IPR2024-00364
`Page 10 of 20
`
`

`

`U.S. Patent
`
`Aug. 19, 2008
`
`Sheet 10 of 11
`
`US 7415,074 B2
`
`[ne]
`
`Tx1
`
`
`
`În
`
`20
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`F. G. 13A
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`30
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`
`20
`
`30
`
`Exhibit 1036
`Panasonic v. UNM
`IPR2024-00364
`Page 11 of 20
`
`

`

`U.S. Patent
`
`Aug. 19, 2008
`
`Sheet 11 of 11
`
`US 7415,074 B2
`
`so
`
`-20
`
`-10
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`10
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`20
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`30
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`F. G. 14D
`
`Exhibit 1036
`Panasonic v. UNM
`IPR2024-00364
`Page 12 of 20
`
`

`

`US 7,415,074 B2
`
`1.
`MIMO TRANSMISSION AND RECEPTION
`METHODS AND DEVICES
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`This application is based upon and claims the benefit of
`priority from prior Japanese Patent Application No. 2004
`004848, filed Jan. 9, 2004, the entire contents of which are
`incorporated herein by reference.
`
`10
`
`BACKGROUND OF THE INVENTION
`
`2
`from a plurality of antennas, as different subcarriers divided
`from one OFDM signal. Likewise, the signal field is trans
`mitted, from the plurality of antennas, as subcarriers divided
`from one OFDM signal. Since the long preamble sequence is
`transmitted by dividing one OFDM signal into subcarriers as
`described above, the receiving side can simultaneously esti
`mate channel impulse response.
`In the OFDM receiver apparatus, a received signal is gen
`erally demodulated by digital signal processing, so an analog
`to digital converter is prepared to convert an analog received
`signal into a digital signal. This analog to digital converter has
`an allowable level range (called an input dynamic range)
`permitted to an analog signal to be converted. Therefore,
`AGC by which the level of a received signal falls within the
`input dynamic range of the analog to digital converter is
`essential.
`In the preamble by Jan Boer et al., channel estimation is
`performed by using the long preamble. Since this channel
`estimation is done by digital signal processing, AGC must be
`performed by using the short preamble sequence which is a
`signal before the long preamble sequence. That is, the
`received level of the short preamble sequence is measured by
`a receiver connected to each receiving antenna, and the input
`level of the analog to digital converter is adjusted on the basis
`of this received level.
`Unfortunately, other transmit antennas than the transmit
`antenna which transmits the short preamble sequence trans
`mit nothing before the long preamble sequence. To receive
`the long preamble sequence, therefore, AGC must be per
`formed by using the short preamble transmitted from the
`single transmit antenna. Accordingly, when the receiving side
`receives the long preamble sequence transmitted from the
`other transmission antennas or receives a data signal, the
`received level becomes much higher or lower than the level
`adjusted by AGC using the short preamble sequence trans
`mitted from the single transmit antenna. If the received level
`is higher than the upper limit of the input dynamic range of the
`analog to digital converter, the analog to digital converter
`saturates. If the received level is lower than the lower limit of
`the input dynamic range, the analog to digital converter pro
`duces a large quantization error. In either case, the analog to
`digital converter cannot appropriately convert a signal, and
`this adversely affects processing after the conversion.
`Also, since a data signal is transmitted from the plurality of
`transmit antennas, the changing range of the received level in
`the interval of the data signal further increases. Accordingly,
`the problems of the Saturation and quantization error of the
`analog to digital converter described above become signifi
`cant, and the receiving performance greatly deteriorates.
`Generally, a wireless apparatus desirably holds the output
`level of a transmission signal constant. Assume that the num
`ber of transmit antennas is N, and the transmission output is C.
`watts. In a wireless communication system obtained by
`combining the MIMO technique and OFDM, i.e., in a so
`called MIMO-OFDM system, the transmission output of a
`single antenna must be C. Watts for the short preamble
`sequence because the signal is transmitted from a single
`antenna. In contrast, for the long preamble sequence, signal
`field, and data signal, the transmission output of each antenna
`is C/N watts because these signals are transmitted from all
`antennas.
`Accordingly, in a path which transmits the short preamble
`sequence by using a single antenna, N-fold transmission out
`put is required only to transmit the short preamble. That is, a
`transmission path for the short preamble produces the redun
`dancy that the specifications of an up converter and power
`amplifier are required to be able to control the transmission
`
`15
`
`25
`
`30
`
`35
`
`40
`
`1. Field of the Invention
`The present invention relates particularly to a wireless
`transmitting device, wireless receiving device, wireless trans
`mitting method and wireless receiving method by which pre
`amble are transmitted before data.
`2. Description of the Related Art
`The institute of Electrical and Electronics Engineers
`(IEEE) is establishing a wireless LAN standard called IEEE
`802.11n which aims at a throughput of 100Mbps or more. In
`IEEE 802.11n, a technique called multi-input multi-output
`(MIMO) which uses a plurality of antennas at transmitters
`and receivers, may be adopted. IEEE 802.11n is required to
`coexist with the existing IEEE 802.11a. In the MIMO tech
`nique, to measure responses (called channel impulse
`responses) of channel impulse response from a plurality of
`transmit antennas to each receiving antenna, a preamble as a
`known sequence must be transmitted from these transmit
`antennas.
`In a preamble proposed by Jan Boer et al. in “Backwards
`compatibility”, IEEE 802.11-03/714r0 (Jan Boer, “Back
`wards compatibility”, IEEE 802.11-03/714r0, Section 2,
`Slide 14 to 19, (URL:ftp://ieee: wireless(aftp. 802wireless
`world.com/)), Paragraph 2 “Diagonally loaded preamble', a
`short preamble sequence for performing timing synchroniza
`tion and automatic gain control (AGC) is transmitted from a
`single transmit antenna. After that, along preamble sequence
`for estimating channel impulse response is transmitted from a
`plurality of transmit antennas. The receiving side performs
`automatic frequency control (AFC) by using the short pre
`amble sequence and long preamble sequence, and estimates
`channel impulse response between the antennas. In this man
`ner, the MIMO technique is used in transmission of data
`45
`signals and the like after that. That is, after the long preamble
`sequence, a signal field indicating the arrangement of a data
`signal, e.g., the modulation coding scheme and length of a
`wireless packet is transmitted, and then the data signal is
`transmitted.
`Jan Boer et al. describe only that the short preamble
`sequence is transmitted from one antenna and the long pre
`amble sequence is divided into Subcarriers and transmitted
`from a plurality of antennas, and do not describe any signal
`field transmission method. The preamble proposed by Jan
`Boer at al. is the same, in a portion from the short preamble
`sequence to the signal field, as the preamble of IEEE 802.11a
`standard based on transmission from a single antenna. There
`fore, a wireless receiver based on IEEE 802.11a standard
`which has received the proposed preamble can recognize that
`the received packet is a wireless packet based on IEEE
`802.11a. Accordingly, the proposed preamble allows IEEE
`802.11n and IEEE 802.11a standards to coexist on a single
`wireless station.
`The short preamble sequence is transmitted as an orthogo
`nal frequency division multiplexing (OFDM) signal from a
`single antenna. The long preamble sequence is transmitted,
`
`50
`
`55
`
`60
`
`65
`
`Exhibit 1036
`Panasonic v. UNM
`IPR2024-00364
`Page 13 of 20
`
`

`

`US 7,415,074 B2
`
`3
`output C. watts only when the short preamble sequence is
`transmitted. On the transmission side as described above, a
`plurality of transmitters corresponding to a plurality of trans
`mit antennas cannot be given equal structures, and this com
`plicates the whole transmitter apparatus. In addition, since the
`power consumption of the transmitter apparatus strongly
`depends on the transmission output level, this is not advanta
`geous in achieving low power consumption.
`
`4
`FIGS. 5A to 5D are views showing the subcarrier arrange
`ments of long preambles and signal fields shown in FIG. 1;
`FIG. 6 is a block diagram showing a receiver shown in FIG.
`3:
`FIG. 7 is a view showing channel impulse response of an
`MIMO-OFDM system according to the embodiment of the
`present invention;
`FIG. 8 is a view showing the received levels of receiving
`antennas for PLCP signals and data signals according to the
`embodiment of the present invention;
`FIG. 9 is a view showing the received levels of the receiv
`ing antennas for PLCP signals and data signals based on IEEE
`802.11a;
`FIG. 10 is a block diagram showing a wireless transmitting
`device according to another embodiment of the present inven
`tion;
`FIGS. 11A and 11B are graphs showing two typical fading
`characteristics used to explain the other embodiment of the
`present invention;
`FIGS. 12A to 12D are views showing the subcarrier
`arrangements of short preambles according to the other
`embodiment of the present invention;
`FIGS. 13A to 13D are views showing the subcarrier
`arrangements of long preambles and signal fields according
`to the other embodiment of the present invention; and
`FIGS. 14A to 14D are views showing the subcarrier
`arrangements of data signals.
`
`DETAILED DESCRIPTION OF THE INVENTION
`
`Embodiments of the present invention will be described in
`detail below with reference to the accompanying drawing.
`A preamble according to an embodiment of the present
`invention contains first to fourth physical layer convergence
`protocol (PLCP) signals 11 to 14 transmitted from transmit
`antennas Tx1 to Tx4. The PLCP signals 11 to 14 includes
`short preamble sequences 1A to 1D, long preamble sequences
`2A to 2D, first signal fields (Sig1) 3A to 3D, and second signal
`fields (Sig2) 4A to 4D. The transmit antenna Tx1 transmits
`the short preamble sequence 1A, long preamble sequence 2A,
`first signal field 3A, and second signal field 4A of the first
`PLCP signal 11 in order. Likewise, the antenna Tx2 transmits
`1B, 2B,3B, and 4B of the second PLCP signal 12 in order, the
`antenna Tx3 transmits 1C, 2C, 3C, and 4C of the third PLCP
`signal 13 in order, and the antenna Tx4 transmits 1D, 2D, 3D,
`and 4D of the fourth PLCP signal 14 in order.
`Unit preambles SP contained in the short preamble
`sequences 1A to 1D and unit preambles LP contained in the
`long preamble sequences 2A to 2D are signal sequences
`having predetermined lengths. The length of LP is relatively
`larger than that of SP. After transmitting the PLCP signals 11
`to 14, i.e., the second long preamble sequences 4A to 4D, the
`antennas Tx1 to Tx4 transmit data signals (DATA) 5.
`The short preamble sequences 1A to 1D, long preamble
`sequences 2A to 2D, and first signal fields 3A to 3D are based
`on IEEE 802.11a standard. The second fields 4A to 4D are not
`based on IEEE 802.11a standard, but contain information
`Such as the modulation coding scheme and data length of
`wireless packet for communication by MIMO technique. The
`second signal fields 4A to 4D are desirably based upon IEEE
`802.11n currently being in standardization process.
`Guard intervals GI are arranged between the short pre
`amble sequences 1A to 1D and the long preamble sequences
`2A to 2D, between the long preamble sequences 2A to 2D and
`the first signal fields 3A to 3D, between the first signal fields
`3A to 3D and the second signal fields 4A to 4D, and between
`the second signal fields 4A to 4D and the data signals 5. In the
`
`BRIEF SUMMARY OF THE INVENTION
`
`10
`
`The first aspect of the present invention provides a wireless
`transmitting method of performing transmission by an
`orthogonal frequency division multiplexing (OFDM) using a
`plurality of subcarriers orthogonal to each other, the method
`comprising: transmitting, by using a plurality of transmit
`antennas, a plurality of preambles formed of a plurality of
`different subcarrier groups selected from a plurality of sub
`carriers; and transmitting a data by using the plurality of
`transmit antennas after the preambles are transmitted.
`The second aspect of the present invention provides a wire
`less receiving method for an orthogonal frequency division
`multiplexing (OFDM) using a plurality of subcarriers
`orthogonal to each other, the method comprising: receiving,
`via a plurality of receiving antennas, a plurality of preambles
`containing a plurality of short preamble sequences formed of
`a plurality of different subcarrier groups selected from a
`plurality of Subcarriers, and data following the preambles;
`amplifying the received preambles by a variable gain ampli
`fier having a gain; and controlling the gain in response to
`reception of the short preamble sequences.
`The third aspect of the present invention provides a wire
`less transmitting method with a plurality of antennas, com
`prising: transmitting a plurality of preamble signals with the
`plurality of antennas, the preamble signals being formed of a
`plurality of different subcarrier groups selected from a plu
`rality of Subcarriers orthogonal to each other, using an
`orthogonal frequency division multiplexing (OFDM) system;
`and transmitting a data signal with the plurality of antennas,
`after transmitting the preamble signals.
`The fourth aspect of the present invention provides a wire
`less receiver apparatus comprising: a plurality of antennas; a
`receiver, associated with the plurality of antennas, which
`receives a plurality of preamble signals containing a plurality
`of short preamble strings formed of a plurality of different
`subcarrier groups selected from the plurality of subcarriers
`being orthogonal to each other, and a data signal following the
`preamble signal, using an orthogonal frequency division mul
`tiplexing (OFDM) system; a variable gain amplifier which
`amplifies signals received by the receiver, and again control
`ler which controls a gain of the variable gain amplifier
`depending upon the short preamble strings of the preamble
`signals.
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`BRIEF DESCRIPTION OF THE SEVERAL
`VIEWS OF THE DRAWING
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`FIG. 1 is a view showing a wireless packet format includ
`ing a preamble according to an embodiment of the present
`invention;
`FIG. 2 is a block diagram showing a wireless transmitting
`device according to the embodiment of the present invention;
`FIG. 3 is a block diagram showing a wireless receiving
`device according to the embodiment of the present invention;
`FIGS. 4A to 4D are views showing the subcarrier arrange
`ments of short preambles shown in FIG. 1;
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`Exhibit 1036
`Panasonic v. UNM
`IPR2024-00364
`Page 14 of 20
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`US 7,415,074 B2
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`preamble based on IEEE 802.11a, GIT having a double length
`is placed before each of the long preamble sequences 2A to
`2D.
`The short preamble sequences 1A to 1D are mainly used in
`timing synchronization, AGC, and coarse adjustment of AFC
`for frequency synchronization. The long preamble sequences
`2A to 2D are mainly used in fine adjustment of AFC, and
`signal processing for channel estimation. The first signal
`fields 3A to 3D are based on IEEE 802.11a, and transmitted as
`OFDM symbols. In the first signal fields 3A to 3D, the modu
`lation coding scheme of the data signals 5 following the PLCP
`signals 11 to 14, the length of a wireless packet, and the like
`are described. Therefore, a wireless receiving device based on
`IEEE 802.11a can perform a normal receiving operation.
`During the interval of the data signals 5 following the PLCP
`signals 11 to 14, no other wireless transmitting device based
`on IEEE 802.11a starts transmission and destroys wireless
`packets.
`The PLCP signals 11 to 14 can meet IEEE 802.11a stan
`dard during the interval from the short preamble sequences
`1A to 1D to the first signal fields 3A to 3D. This makes it
`possible to construct an MIMO-OFDM system capable of
`matching both IEEE 802.11a and another wireless LAN stan
`dard (e.g., IEEE 802.11n).
`In this embodiment, the second signal fields 4A to 4D
`describing the modulation coding scheme for communication
`by using MIMO and the length of a wireless packet are
`inserted in the endmost portions of the PLCP signals 11 to 14.
`The receiving side demodulates the second signal fields 4A to
`4D, and recognizes, e.g., the modulation coding scheme of
`signals transmitted from the antennas Tx1 to TX4, the wireless
`packet length, and the MIMO operation. Therefore, the
`receiving side can recognize that the data signals 5 following
`the PLCP signals 11 to 14 are wireless packets based on a
`wireless LAN standard (e.g., IEEE 802.11n) other than IEEE
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`802.11a, and perform a receiving operation as the MIMO
`OFDM system.
`FIGS. 2 and 3 show a wireless transmitting device 200 and
`wireless receiving device 300 according to this embodiment
`which implements the MIMO-OFDM system. The wireless
`transmitting device 200 shown in FIG. 2 includes transmit
`antennas 205A to 205D, wireless transmitters 204A to 204D,
`a digital modulator 203, and a memory 202. The wireless
`receiving device 300 shown in FIG. 3 includes receiving
`antennas 301A to 301D, wireless receivers 302A to 302D,
`channel estimators 303 A to 303D for performing channel
`impulse response estimation (channel estimation) on the
`basis of information from the wireless receivers 302A to
`302D, and a digital demodulator 304.
`The transmit antennas 205A, 205B, 205C, and 205D
`shown in FIG. 2 correspond to Tx1, Tx2, Tx3, and Tx4,
`respectively, shown in FIG.1. In this embodiment, the num
`bers of the transmit antennas and receiving antennas are four.
`However, the number of the transmit antennas is not limited to
`four and can be any plural number. The number of the receiv
`ing antennas may also be one or any plural number other than
`four. The numbers of the transmit antennas and receiving
`antennas need not be equal.
`A practical operation of the wireless transmitting device
`200 shown in FIG. 2 will be explained below. First, the digital
`modulator 203 modulates transmission data 201 and an out
`put preamble from the memory 202 to assemble a wireless
`packet. The output preamble from the memory 202 corre
`sponds to the first to fourth PLCP signals 11 to 14 shown in
`FIG 1.
`The assembled wireless packet undergoes processing nec
`essary for transmission performed by the transmitters 204A
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`to 204D, e.g., digital to analog conversion, frequency conver
`sion (up conversion) to the radio frequency (RF) band, and
`power amplification. After that, the wireless packet is Sup
`plied to the transmitantennas 205A to 205D corresponding to
`the antennas Tx1 to TX4 shown in FIG.1. As a consequence,
`the RF signal is transmitted from the transmit antennas 205A
`to 205D to the wireless receiving device shown in FIG. 3. In
`the following explanation, the transmit antennas 205A to
`205D are Tx1 to TX4 shown in FIG. 1.
`The transmitted RF signal is based on an OFDM signal,
`and contains a plurality of subcarriers of the OFDM signal.
`The first to fourth PLCP signals 11 to 14 shown in FIG. 1 are
`simultaneously transmitted from the transmit antennas 205A
`to 205D as subcarriers allocated to the transmit antennas
`205A to 205D while frequency orthogonal conditions are
`maintained.
`Generally, in the OFDM signal based on IEEE 802.11a, the
`short preamble sequences 1A to 1D contain 12 Subcarriers,
`and the long preamble sequences 2A to 2D, the first signal
`fields 3A to 3D, second signal fields 4A to 4D, and data
`signals 5 contain 52 Subcarriers.
`As shown in FIGS. 4A to 5D, the first to fourth PLCP
`signals 11 to 14 are transmitted as different Subcarrier groups
`from the transmit antennas 205A to 205D (corresponding to
`Tx1 to Tx5 in FIG. 1). FIGS. 4A to 4D illustrate the arrange
`ments of 12 Subcarriers in the short preamble sequences 1A to
`1D shown in FIG. 1. FIGS. 5A to 5D illustrate the arrange
`ments of 52 Subcarriers in the long preamble sequences 2A to
`2D and first signal fields 3A to 3D in FIG. 1. Referring to
`FIGS. 4A to 5D, the abscissa indicates the positions where the
`Subcarriers are arranged, and the ordinate indicates the Sub
`carrier numbers. The dotted lines indicate subcarrier posi
`tions where Subcarriers can be arranged, and the Solid por
`tions represent that Subcarriers are actually arranged.
`The subcarrier numbers are 0 in the center of the signal
`band of the OFDM signal, negative numbers on the lower
`sideband side, and positive numbers on the upper sideband
`side. No subcarrier is placed in a position where the subcarrier
`number is “0”, and 52 subcarriers are arranged in the posi
`tions of subcarrier numbers +1 to +26. For example, as shown
`in FIGS. 4A to 4D, 12 subcarriers of the short preamble
`sequences 1A to 1D are arranged in the positions of Subcarrier
`numbers +24, +20, it 16, it 12, +8, and +4 on the basis of IEEE
`802.11a.
`As a Subcarrier dividing method, i.e., as a method of allo
`cating a plurality of subcarriers of the OFDM signal to the
`first to fourth PLCP signals 11 to 14, the embodiment of the
`present invention uses a method, as shown in FIGS. 4A to 5D,
`by which subcarriers are sequentially selected and allocated
`one by one to the PLCP signals 11 to 14 in order of subcarrier
`arrangement (order of Subcarrier number).
`For example, the allocation of subcarriers to the short pre
`amble sequences 1A to 1D of the first to fourth PLCP signals
`11 to 14 is as shown in FIG. 4A to 4D. That is, subcarriers
`having Subcarrier numbers -24, -8, and +12 are allocated to
`the short preamble 1A. Subcarriers having subcarrier num
`bers -20, -4, and +16 are allocated to the short preamble
`sequence 1B. Subcarriers having Subcarrier numbers -16, +4.
`and +20 are allocated to the short preamble sequence 1C.
`Subcarriers having Subcarrier numbers -12, +8, and +24 are
`allocated to the short preamble sequence 1D. In this manner,
`the phases of subcarriers allocated to the short preambles 1A
`to 1D are shifted by four waves.
`The allocation of subcarriers to the long preamble
`sequences 2A to 2D of the first to fourth PLCP signals 11 to
`14 is basically the same as the allocation of subcarriers to the
`short preamble sequences 1A to 1D described above, except
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`Exhibit 1036
`Panasonic v. UNM
`IPR2024-00364
`Page 15 of 20
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`US 7,415,074 B2
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`that the phases of those subcarriers allocated to the long
`preambles 2A to 2D are shifted by one wave as shown in
`FIGS 5A to SD.
`The PLCP signals 11 to 14 containing the subcarrier
`groups divided as shown in FIGS. 4A to 5D are transmitted
`from the transmit antennas 205A to 205D. The data signals 5
`following the PLCP signals 11 to 14 are transmitted by
`MIMO channels. That is, the transmitters 204A to 204D
`generate different OFDM signals corresponding to the indi
`vidual data signals 5. These OFDM signals are transmitted as
`four RF signals, corresponding to the number of the transmit
`ters 204A to 204D, from the transmit antennas 205A to 205D.
`In the wireless transmitting device according to this
`embodiment as described above, the four PLCP signals 11 to
`14 are transmitted, from the transmit antennas 205A to 205D
`by the transmitters 204A to 204D, as four subcarrier groups
`obtained by dividing a plurality of subcarriers of one OFDM
`signal. On the other hand, the four data signals 5 are trans
`mitted as different OFDM signals generated by the transmit
`ters 204A to 204D from the transmit antennas 205A to 205D.
`When subcarriers are uniformly divided in accordance
`with the transmit antennas 205A to 205D, the PLCP signals
`11 to 14 are transmitted at equal levels (transmission powers)
`from the transmit antennas 205A to 205D. Even when sub
`carriers are not uniformly divided, the PLCP signals 11 to 14
`are transmitted at Substantially equal levels. For example,
`when the number of the transmit antennas 205A to 205D is
`four as in this embodiment, the transmit antennas 205A to
`205D transmit three subcarriers for each of the short pre
`amble sequences 1A to 1D, and transmit 13 subcarriers for
`each of the long preamble sequences 2A to 2D and signal
`fields 3A to 3D and 4A to 4D. When the number of the
`transmit antennas is three, each transmit antenna transmits
`four subcarriers for each of the short preamble sequences 1A
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`to 1C, and 17 or 18 subcarriers for each of the long preamble
`sequences 2A to 2C and signal fields 3A to 3C and 4A to 4C.
`Since the data signals 5 are not divided into subcarriers
`unlike the PLCP signals 11 to 14, the data signals 5 have a
`subcarrier arrangement different from the PLCP signals 11 to
`14. However, a total of 52 subcarriers are transmitted as the
`data signals 5 from the transmit antennas 205A to 205D, so
`the transmission level of the data signals 5 is equivalent to that
`of the PLCP signals 11 to 14. As described above, the trans
`mission levels of the transmit antennas 205A to 205D are
`equal between the PLCP signals 11 to 14 and the data signals
`5, and Substantially equal between the transmit antennas
`205A to 205D. Therefore, the transmitters 204A to 204D can
`have identical structures having the same output level. Fur
`thermore, the output level of each of the transmitters 204A to
`204D can be decreased in proportion to the number of anten
`nas, against the total output level of the transmitter apparatus
`200. This makes it possible to reduce the current consumption
`by Suppressing the output power of the power amplifiers used
`in the transmitters 204A to 204D, and alleviate the distortion
`characteristics. That is, it