(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2005/0163081 A1
`(43) Pub. Date:
`Jul. 28, 2005
`Aoki et al.
`
`US 20050163081A1
`
`(54) WIRELESS TRANSMITTING AND
`RECEIVING DEVICE AND METHOD
`
`(76) Inventors: Tsuguhide Aoki, KaWasaki-shi (JP);
`Daisuke Takeda, Tokyo (JP); Takahiro
`Kobayashi, KaWasaki-shi (JP);
`Yasuhiko Tanabe, KaWasaki-shi (JP)
`
`Correspondence Address:
`OBLON, SPIVAK, MCCLELLAND, MAIER &
`NEUSTADT, RC.
`1940 DUKE STREET
`ALEXANDRIA, VA 22314 (US)
`
`Appl. No.:
`
`(21)
`(22) Filed:
`
`11/018,251
`
`Dec. 22,
`2004
`
`(30)
`
`Foreign Application Priority Data
`
`Dec. 26, 2003
`Dec. 9,2004
`
`(JP) .................................... .. 2003-43334?
`
`(JP) .................................... .. 2004-357097
`
`Publication Classi?cation
`
`(51) Int. Cl? ..................................................... ..H04Q 7/00
`(52) Us. 01. ............................................................ ..370/334
`
`(57)
`
`ABSTRACT
`
`AWireless device, method, and signal for use in communi
`cation of a Wireless packet betWeen transmitting device and
`a Wireless receiving device via a plurality of antennas,
`Wherein a signal generator generates Wireless packet includ
`ing a short-preamble sequence used for a ?rst automatic gain
`control (AGC), a ?rst long-preamble sequence, a signal ?eld
`used for conveying a length of the Wireless packet, an AGC
`preamble sequence used for a second AGC to be performed
`after the ?rst AGC, a second long-preamble sequence, and a
`data ?eld conveying data. The AGC preamble sequence is
`transmitted in parallel by the plurality of antennas.
`
`202
`2
`Memory
`
`203
`2
`Digital
`modulator
`
`204A
`
`Transmitting 7» unit
`
`/ 2048
`
`L» Transmitting unit
`
`205A
`
`2058
`
`i / 2040 J 2050
`» Transmitting
`unit
`/ 204D
`
`_>_ Transmitting unrt
`
`2050
`
`Transmission data
`
`201
`
`Exhibit 2001
`IPR2015-00221
`1 of 22
`
`

`

`Patent Application Publication Jul. 28, 2005 Sheet 1 0f 11
`
`US 2005/0163081 A1
`
`<50 5 E. n_._. 5
`
`Q2? 5% £2 Q2 Q2 Q2
`
`ma? 5% 5% ~ E2 H £2 H $2
`
`~ ~ ~ ~ ~ ~ ~ ~ f 4 <
`
`
`
`
`
`as? Home a? 55 5&2 68F
`
`
`
`<0: <02 $2 <5 $2 $2 #2 we we §
`
`
`
`
`
`5.3 n_._ n: E n: “.2205 ._<zo_w 1m ,6
`
`0:
`
`3:.
`
`Exhibit 2001
`IPR2015-00221
`2 of 22
`
`

`

`Patent Application Publication Jul. 28, 2005 Sheet 2 0f 11
`
`US 2005/0163081 A1
`
`202
`9
`
`Memory
`
`203 D' 't I?
`
`d t
`'
`'
`T
`> |g| a
`ransmrsslon aa
`—;————-> modulator h"
`201
`
`204A.
`\ Transmltting
`’ unit
`/204B
`
`
`
`‘ Transmitting unit
`
`/204C
`‘ Transmitting
`’ unit
`/204D
`
`\ Transmitting ’ unit
`
`205A
`
`205B
`
`205C
`
`205D
`
`301A
`
`301B
`
`3010
`
`I
`
`i
`
`3010 T
`
`302
`
`30?‘
`;
`_
`Receiving
`“""k L Channel impulse >
`3028 1
`303A
`response
`_
`H _
`”“ estlmation unit
`eceivmg
`_
`-
`um‘
`L Channel impulse ‘
`Received data
`305C 1‘ 303B
`response
`_
`' ‘ Digital
`Receiving
`‘
`estlmatlon unit
`r demodulator T
`BM}
`L Channel impulse \
`res onse
`I
`_ 303C
`estimation unit
`Recewlng _
`>
`“m
`L Channel impulse ‘
`‘
`303D
`response
`_
`'
`estlmatlon unlt
`
`304
`
`z
`
`>
`
`’
`
`F I 6.3
`
`Exhibit 2001
`IPR2015-00221
`3 of 22
`
`

`

`Patent Application Publication Jul. 28, 2005 Sheet 3 0f 11
`
`US 2005/0163081 A1
`
`401
`P
`; Down-
`converter
`
`402
`2
`‘ Variable gain
`amplifier
`
`403
`P
`; A/D
`converter
`
`A
`
`V
`
`Gain
`controller
`
`V
`
`4
`i
`
`@404
`
`—— From digital demodulator 304
`
`
`
`
`
`Receiving power of data (x08~x11)
`
`3.5
`
`0.5
`
`1.5
`Receiving power of short- preamble (X01)
`
`3.5
`
`F|G.5
`
`Exhibit 2001
`IPR2015-00221
`4 of 22
`
`

`

`Patent Application Publication Jul. 28, 2005 Sheet 4 0f 11
`
`US 2005/0163081 A1
`
`3.5
`
`|
`
`I
`
`I
`
`I
`
`|
`
`I
`
`
`
`
`
`Receiving power of data (106~110)
`
`+
`
`+
`
`+
`++,., +
`+ +
`
`+
`
`*H'HH»
`
`_
`
`-
`
`-
`
`3 —
`
`2.5 —
`
`2 -
`
`0.5 —
`
`0
`
`0
`
`|
`0.5
`
`|
`|
`|
`r
`2.5
`2
`1.5
`1
`Receiving power of preamble (105)
`
`3
`
`3.5
`
`401
`P
`
`402
`2
`
`\ Down-
`converter
`
`‘ Variable gain
`ampli?er
`A
`
`403
`P
`
`> A/D
`converter
`
`~302A
`
`>
`
`~ <
`Gain
`> controller @404
`A
`
`v
`Memory F» 405
`
`From digital demodulator 304
`
`Exhibit 2001
`IPR2015-00221
`5 of 22
`
`

`

`Patent Application Publication Jul. 28, 2005 Sheet 5 0f 11
`
`US 2005/0163081 A1
`
`(
`
`Start AGC F31
`
`S4
`
`Calculation gain
`
`r
`
`ls
`preamble 105 being
`ece?rved
`I H NO
`85-» Set rnttral value
`
`.
`
`V SF
`Read data
`from memory
`
`4
`i
`
`V
`
`V
`
`1
`Change gain ~36
`
`r
`Measure level ~87
`
`S8
`Target amplitude
`?
`Yes
`
`Hold memory data N S11
`
`Exhibit 2001
`IPR2015-00221
`6 of 22
`
`

`

`Patent Application Publication Jul. 28, 2005 Sheet 6 0f 11
`
`US 2005/0163081 A1
`
`@
`
`S21
`
`Receive the short-preamble
`sequence 101
`i
`Start first AGC
`i
`Set a gain for variable
`gain ampli?ers 402
`
`k s22
`
`S23
`
`$24
`
`Write the set gain
`to the memory 405
`
`i
`Start the second AGC by
`using AGC preamble sequence ~S25
`105A-105D
`
`Refer to the stored galn rn
`the memory 405
`i
`
`|\S26
`
`Set new gain ‘for variable gain
`amplifiers 402
`
`S27
`
`@
`
`Exhibit 2001
`IPR2015-00221
`7 of 22
`
`

`

`Patent Application Publication Jul. 28, 2005 Sheet 7 of 11
`
`US 2005/0163081 A1
`
`301A
`
`302
`2
`
`FCC C Receiving
`
`301 B
`
`301C
`
`301D
`
`304
`
`Digital
`
`' demodulator
`
`Received data
`__T_,
`305
`
`V
`
`V
`
`V
`
`V
`
`V
`
`V
`
`V
`
`V
`
`‘ ’
`
`Channel impulse
`response
`_
`estlmatlon unlt
`303M
`
`Channel impulse
`response
`_
`estrmatron unlt
`3035f
`
`*——0 Channel impulse
`
`_
`
`response '
`
`estimation unlt
`3030r
`
`i '
`
`Channel impulse
`response
`I
`estlmatron un|t
`303Dr
`
`Exhibit 2001
`IPR2015-00221
`8 of 22
`
`

`

`Patent Application Publication Jul. 28, 2005 Sheet 8 0f 11
`
`US 2005/0163081 A1
`
`301A
`’
`
`3018
`
`301C
`
`T
`
`301D
`
`401A
`f
`converter
`
`‘ Down-
`
`402A
`V , blf
`‘ al'a e
`g?gli?er
`1
`
`4018
`f
`
`Down-
`converter
`
`4010
`I
`
`~
`
`Down-
`converter
`
`4028
`I
`_
`val'able
`g?gli?er
`1
`——$
`4020
`I
`valiable
`ampn?er
`A
`
`\ garn
`
`401D
`
`Down-
`’ converter
`
`'
`
`402D
`
`,
`
`valiable
`g‘giglmer
`1 —J'
`
`302
`I
`
`403A
`I
`converter
`
`‘ A/D
`
`4035
`f
`
`A / D
`’ converter
`
`4030
`I
`
`*
`
`A / 0
`converter
`
`403D
`
`A / D
`converter
`494
`
`'-——>
`
`Gain
`> controller
`
`A
`
`r
`
`Memory ~405
`
`From digital demodulator 304
`
`Hero
`
`Exhibit 2001
`IPR2015-00221
`9 of 22
`
`

`

`Patent Application Publication Jul. 28, 2005 Sheet 9 0f 11
`
`US 2005/0163081 A1
`
`502A
`
`5028
`
`502C 502D
`
`
`
`FIG.11
`
`(a)
`
`Tx 1
`
`(b)
`
`Tx 2
`
`Tx 3
`
`FIG.12
`
`t
`
`Exhibit 2001
`|PR2015-00221
`10 of 22
`
`Exhibit 2001
`IPR2015-00221
`10 of 22
`
`

`

`Patent Application Publication Jul. 28, 2005 Sheet 10 0f 11
`
`US 2005/0163081 A1
`
`f
`
`9
`
`,ZZ/
`
`k/z/M/l/V/?/
`
`31%
`
`?/////////////
`
`Tx1
`
`TX2
`
`Tx4
`
`Exhibit 2001
`IPR2015-00221
`11 of 22
`
`

`

`Patent Application Publication Jul. 28, 2005 Sheet 11 0f 11
`
`US 2005/0163081 A1
`
`202
`P
`Memory
`
`r
`206 ~ [FFT
`
`2%3
`
`’ Digital
`Transmission data
`—)—> modulator —'
`
`.
`
`201
`
`/ 204A
`Transmitting
`unit
`
`V
`
`/ 2045
`
`Transmitting
`ii unit
`
`/ 204C
`Transmitting
`unit
`/ 204D
`Transmitting
`unit
`
`205A
`
`2058
`
`2056
`VJ
`
`vv2osn
`
`Exhibit 2001
`IPR2015-00221
`12 of 22
`
`

`

`US 2005/0163081 A1
`
`Jul. 28, 2005
`
`WIRELESS TRANSMITTING AND RECEIVING
`DEVICE AND METHOD
`
`control (AGC) for adjusting the levels of received signals
`Within the input dynamic range of the A/D converter.
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`[0001] This application is based upon and claims the
`bene?t of priority from prior Japanese Patent Applications
`No. 2003-433347, ?led Dec. 26, 2003; and No. 2004
`357097, ?led Dec. 9, 2004, the entire contents of both of
`Which are incorporated herein by reference.
`
`BACKGROUND OF THE INVENTION
`
`[0002] 1. Field of the Invention
`
`[0003] The present invention relates to a Wireless trans
`mitting device and Wireless receiving device for respectively
`transmitting and receiving radio signals in mobile commu
`nication system like a Wireless LAN, using a Wireless packet
`including a preamble and data, and a Wireless transmission
`method and Wireless receiving method for use in the devices.
`
`[0004] 2. Description of the Related Art
`[0005] The Institute of Electrical and Electronics Engi
`neers (IEEE) is noW de?ning a Wireless LAN standard called
`IEEE 802.11n, Which aims to achieve a high throughput of
`100 Mbps or more. It is very possible that IEEE 802.11n Will
`employ a technique, called multi-input multi-output
`(MIMO), for using a plurality of antennas in a transmitter
`and receiver. IEEE 802.11n is required to coexist With the
`standard IEEE 802.11a Where OFDM (Orthogonal Fre
`quency Division Multiplex) is used. So, it is required that
`IEEE 802.11n Wireless transmitting device and receiving
`device have so called backWards compatibility.
`[0006] A proposal presented by Jan Boer et al. in “Back
`Wards Compatibility”, IEEE 802.11-03/714r0, introduces a
`Wireless preamble for MIMO. In this proposal, a short
`preamble sequence used for time synchroniZation, frequency
`synchroniZation and automatic gain control (AGC), a long
`preamble sequence used to estimate a channel impulse
`response, a signal ?eld indicating a modulation scheme used
`in the Wireless packet, and another signal ?eld for IEEE
`802.11n are ?rstly transmitted from a single particular
`transmit antenna. Subsequently, long-preamble sequences
`are transmitted from the other three transmit antennas. After
`?nishing the transmission of the preamble, transmission data
`is transmitted from all the antennas.
`
`[0007] From the short-preamble to the ?rst signal ?eld, the
`proposed preamble is identical to the preamble stipulated in
`IEEE 802.11a Where single transmit antenna is assumed.
`Therefore, When Wireless receiving devices that conform to
`IEEE 802.11a receive a Wireless packet containing the
`Boer’s proposed preamble, they recogniZe that the packet is
`based on IEEE 802.11a. Thus, the proposed preamble con
`forming to both IEEE 802.11a and IEEE 802.11n enables
`IEEE 802.11a and IEEE 802.11n to coeXist.
`[0008] Generally, in Wireless receiving devices, demodu
`lation of a received signal is performed by digital signal
`processing. Therefore, an analog-to-digital
`converter
`is provided in the devices for digitiZing a received analog
`signal. A/D converters have an input dynamic range (an
`alloWable level range of analog signals to be converted).
`Accordingly, it is necessary to perform automatic gain
`
`[0009] Since the estimation of a channel impulse response
`using the above-mentioned long preamble sequences is
`performed by digital signal processing, AGC must be per
`formed using the signal transmitted before the long-pre
`amble sequence. In the Boer’s preamble, AGC is performed
`using a short-preamble sequence transmitted before the
`long-preamble sequence from a particular transmit antenna.
`That is, the receiving level of the short-preamble sequence
`is measured, and AGC is performed so that the receiving
`level falls Within the input dynamic range of the A/D
`converter. By virtue of AGC using the short-preamble
`sequence, the long-preamble sequence and data transmitted
`from the particular transmit antenna can be received cor
`rectly. If all the antennas are arranged apart, the receiving
`levels of signals transmitted from the antennas are inevitably
`different from each other. Therefore, When a Wireless receiv
`ing device receives long-preamble sequences transmitted
`from the other three transmit antennas, or data transmitted
`from all the antennas, their receiving levels may be much
`higher or loWer than the level acquired by AGC using the
`short-preamble sequence transmitted from the particular
`transmit antenna. When the receiving level eXceeds the
`upper limit of the input dynamic range of the A/D converter,
`the output of the A/D converter is saturated. On the other
`hand, When the receiving level is loWer than the loWer limit
`of the input dynamic range of the A/D converter, the output
`of the A/D converter suffers a severe quantization error. In
`either case, the A/D converter cannot perform appropriate
`conversion, Which adversely in?uences the processing after
`A/D conversion.
`
`[0010] Further, data is transmitted from all the antennas.
`Therefore, during data transmission, the range of variations
`in receiving level is further increased, Which Worsens the
`above-mentioned saturation of the A/D converter output
`and/or the quantiZation error therein, thereby signi?cantly
`degrading the receiving performance.
`[0011] As described above, in the Boer’s proposed pre
`amble, AGC is performed at the receive side using only the
`short-preamble sequence transmitted from a single transmit
`antenna, Which makes it difficult to deal With variations in
`receiving level that may occur When signals transmitted
`from the other antennas in MIMO mode are received.
`
`BRIEF SUMMARY OF THE INVENTION
`
`[0012] In accordance With an aspect of the invention, there
`is provided a Wireless transmitting device for use in com
`munication With a Wireless receiving device With a Wireless
`packet, comprising: a plurality of antennas; and a signal
`generator generates a signal for the Wireless packet being
`transmitted, the Wireless packet comprising: a short-pre
`amble sequence used for a ?rst automatic gain control
`(AGC); a ?rst long-preamble sequence; a signal ?eld used
`for conveying information regarding a length of the Wireless
`packet; an AGC preamble sequence used for a second AGC
`to be performed after the ?rst AGC; a second long-preamble
`sequence; and a data ?eld conveying data, Wherein the AGC
`preamble sequence being transmitted by the plurality of
`antennas in parallel.
`
`[0013] Since a signal format employed in the invention
`includes preambles for ?ne tune the AGC for MIMO recep
`
`Exhibit 2001
`IPR2015-00221
`13 of 22
`
`

`

`US 2005/0163081 A1
`
`Jul. 28, 2005
`
`tion transmitted from multiple antennas, the input level of an
`A/D converter can be appropriately adjusted With a short
`time, thereby enhancing the receiving performance of a
`Wireless receiving device and reducing the number of reso
`lution bits of the A/D converter.
`
`[0031] FIG. 1 shoWs a format for a Wireless packet
`employed in a ?rst embodiment of the invention. This
`format is a physical layer protocol data unit format for the
`MIMO mode and provides interoperability and coexistence
`With IEEE802.11a Wireless stations.
`
`BRIEF DESCRIPTION OF THE SEVERAL
`VIEWS OF THE DRAWING
`[0014] The accompanying draWings, Which are incorpo
`rated in and constitute a part of the speci?cation, illustrate an
`embodiment of the invention, and together With the general
`description given above and the detailed description of the
`embodiment given beloW, serve to eXplain the principles of
`the invention.
`
`[0015] FIG. 1 is a vieW illustrating a format for a Wireless
`packet including the AGC preambles for Wireless commu
`nication used in an embodiment of the invention;
`[0016] FIG. 2 is a block diagram illustrating the con?gu
`ration of a Wireless transmitting device according to the
`embodiment;
`[0017] FIG. 3 is a block diagram illustrating the con?gu
`ration of a Wireless receiving device according to the
`embodiment;
`[0018] FIG. 4 is a block diagram illustrating a con?gu
`ration eXample of a receiving unit incorporated in the device
`of FIG. 3;
`[0019] FIG. 5 is a graph illustrating the distribution of the
`receiving poWer of short preambles and data in the prior art;
`[0020] FIG. 6 is a graph illustrating the distribution of the
`receiving poWer of short preambles and data in the embodi
`ment;
`[0021] FIG. 7 is a block diagram illustrating another
`con?guration eXample of the receiving unit;
`[0022] FIG. 8A is a ?oWchart in explaining the operation
`of a gain controller;
`
`[0023] FIG. 8B is a ?oWchart shoWing a ?rst AGC opera
`tion and second AGC operation.
`
`[0024] FIG. 9 is a block diagram illustrating a Wireless
`receiving device according to a modi?cation of the embodi
`ment;
`[0025] FIG. 10 is a block diagram illustrating a con?gu
`ration eXample of a receiving unit incorporated in the
`Wireless receiving device of FIG. 9;
`[0026] FIG. 11 is a block diagram illustrating a con?gu
`ration eXample of the propagation path estimation unit
`appearing in FIG. 3;
`[0027] FIG. 12 is a vieW illustrating structural eXamples
`of the AGC preambles appearing in FIG. 1;
`[0028] FIG. 13 is a vieW illustrating other structural
`eXamples of the AGC preambles appearing in FIG. 1; and
`[0029] FIG. 14 is a vieW illustrating a Wireless transmit
`ting device according to another embodiment of the inven
`tion.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`[0030] Embodiments of the invention Will be described in
`detail With reference to the accompanying draWings.
`
`[0032] As seen from FIG. 1, a preamble includes a
`physical layer convergence protocol (PLCP) signal trans
`mitted from an antenna TX1. The PLCP signal includes a
`short-preamble sequence 101, ?rst long-preamble sequence
`102, ?rst signal ?eld (SIGNAL) 103 and second signal ?eld
`(SIGNAL 2) 104. The short-preamble sequence 101 con
`tains several unit preambles SP. The long-preamble
`sequence 102 contains the unit preambles LP having respec
`tive predetermined lengths. The preambles LP are longer
`than the preambles SP.
`[0033] The short-preamble sequence 101, ?rst long-pre
`amble sequence 102 and ?rst signal ?eld 103 conform to
`IEEE 802.11a, While the second signal ?eld 104 is necessary
`for the neW Wireless LAN standard IEEE 802.11n. First
`signal ?eld 103 conforming to IEEE 802.11a may be called
`“legacy signal ?eld”. Since the second signal ?eld 104 is
`provided for neW high throughput Wireless LAN standard, it
`may be called “high throughput signal ?eld”. A guard
`interval GI is inserted betWeen the short-preamble sequence
`101 and the long-preamble sequence 102.
`[0034] After the PLCP signal, AGC preambles 105A to
`105D that are transmitted in parallel from a plurality of
`antennas TX1 to TX4 are positioned. The AGC preambles
`105A to 105D are transmitted simultaneously from a plu
`rality of antennas TX1 to TX4. The AGC preambles 105A to
`105D are used to enable the receiving device to perform ?ne
`AGC When performing MIMO communication. These pre
`ambles are unique to perform ?ne tune the AGC for recep
`tion of MIMO mode in accordance With IEEE802.11n.
`Therefore, the AGC preambles 105A to 105D may be called
`“high throughput short trainings ?eld”. On the other hand,
`since the short-preamble sequence 101 conforms to IEEE
`802.11a, being used for coarse AGC operation, it may be
`called “legacy short training ?eld”.
`
`[0035] After the AGC preambles 105A to 105D, second
`long-preamble sequences 106A to 109A, 106B to 109B,
`106C to 109C and 106D to 109D are positioned. In the
`embodiment, the same signal sequences are used as the AGC
`preambles 105A to 105D. HoWever, different signal
`sequences may be used as the AGC preambles 105A to
`105D. A guard interval GI is inserted betWeen each pair of
`adjacent ones of the unit preambles LP that form the second
`long-preamble sequences 106A to 109A, 106B to 109B,
`106C to 109C and 106D to 109D. As described later, the
`second long-preamble sequences 106A to 109A, 106B to
`109B, 106C to 109C and 106D to 109D are in an orthogonal
`relationship. The number of unit preambles LP 106-109 for
`each transmit antenna is equal to the number of transmit
`antennas in MIMO mode. In order to distinguish betWeen
`tWo kinds of long-preamble sequences, ?rst long-preamble
`sequence 102 conforming to IEEE 802.11a may be called
`“legacy long training ?eld”. Since the second long pre
`ambles sequences 106-109 are provided for neW high
`throughput Wireless LAN standard, it may be called “high
`throughput long training ?eld”.
`[0036] After each of the second long-preamble sequences
`106A to 109A, 106B to 109B, 106C to 109C and 106D to
`
`Exhibit 2001
`IPR2015-00221
`14 of 22
`
`

`

`US 2005/0163081 A1
`
`Jul. 28, 2005
`
`109D, a ?eld for transmission data (DATA) 110A to 110C
`transmitted from the antennas TX1 to TX4, respectively, is
`positioned. The second long-preamble sequences 106A to
`109A, 106B to 109B, 106C to 109C and 106D to 109D are
`transmitted simultaneously from a plurality of antennas TX1
`to TX4 respectively.
`
`[0037] Referring noW to FIG. 2, the Wireless transmitting
`device according to the embodiment Will be described.
`Firstly, digital modulator 203 forms a signal for Wireless
`packet by combining transmission data 201 and the above
`described preamble outputted from a memory 202. The
`thus-obtained signal for Wireless packet is sent to transmit
`ting units 204A to 204D, Where they are subjected to
`processing needed for transmission, for eXample, digital-to
`analog (D/A) conversion, frequency conversion into a radio
`frequency (RF) band (up-conversion) and poWer ampli?ca
`tion. Thereafter, the resultant signal is sent to a plurality of
`antennas 205A to 205D corresponding to the antennas TX1
`to TX4 described With reference to FIG. 1, Where an RF
`signal is sent from each transmit antenna 205A to 205D to
`the Wireless receiving device shoWn in FIG. 3. In the
`description beloW, the antennas TX1 to TX4 shoWn in FIG.
`1 are referred to as the antennas 205A to 205D, respectively.
`
`[0038] In the embodiment, the PLCP signal shoWn in FIG.
`1, Which includes the short-preamble sequence 101, ?rst
`long-preamble sequence 102, ?rst signal ?eld 103 and
`second signal ?eld 104, is transmitted from the transmit
`antenna 205A of the transmission unit 204A shoWn in FIG.
`2. The AGC preambles 105A to 105D, second long-pre
`amble sequences 106A to 109A, 106B to 109B, 106C to
`109C and 106D to 109D, Which are positioned after the
`PLCP signal as shoWn in FIG. 1, and the data 110A to 110D
`are transmitted across all the transmit antennas 205A to
`205D.
`
`[0039] In the Wireless receiving device shoWn in FIG. 3,
`a plurality of receiving antennas 301A to 301D receive RF
`signals transmitted from the Wireless transmitting device
`shoWn in FIG. 2. The Wireless receiving device may have
`one receiving antenna or multiple receiving antennas. The
`RF signals received by the receiving antennas 301A to 301D
`are sent to receiving units 302A to 302D, respectively. The
`receiving units 302A to 302D each perform various types of
`receiving processing, such as frequency conversion (doWn
`conversion) from the RF band to BB (baseband), automatic
`gain control (AGC), analog-to-digital conversion, etc.,
`thereby generating a baseband signal.
`[0040] The baseband signals from the receiving units
`302A to 302D are sent to channel impulse response estima
`tion units 303A to 303D and digital demodulator 304. These
`units 303A to 303D estimate the impulse responses of the
`respective propagation paths betWeen the Wireless transmit
`ting device of FIG. 2 and the Wireless receiving device of
`FIG. 3. The channel impulse response estimation units 303A
`to 303D Will be described later in detail. The digital demodu
`lator 304 demodulates the baseband signals based on the
`estimated channel impulse response provided by units 303A
`to 303D, thereby generating received data 305 correspond
`ing to the transmission data 201 shoWn in FIG. 2.
`
`[0041] More speci?cally, the digital demodulator 304 has
`an equaliZer of the channel impulse response at its input
`section. The equaliZer performs equaliZation for correcting
`the received signal distorted in the propagation path, based
`
`on the estimated channel impulse response. The digital
`demodulator 304 also demodulates the equaliZed signal at
`appropriate timing determined by the time synchroniZation,
`thereby reproducing data.
`
`[0042] The receiving units 302A to 302D shoWn in FIG.
`3 Will noW be described. FIG. 4 shoWs the con?guration of
`the receiving unit 302A in detail. Since the other receiving
`units 302B to 302D have the same con?guration as the unit
`302A, only the receiving unit 302A Will be described. The
`RF received signal received by the receiving antenna 301A
`is doWn-converted by a doWn-converter 401 into a baseband
`signal. At this time, The RF signal may be directly converted
`into a baseband signal, or may be ?rstly converted into an
`intermediate frequency (IF) signal and then into a baseband
`signal.
`[0043] The baseband signal generated by the doWn-con
`verter 401 is sent to a variable gain ampli?er 402, Where it
`is subjected to perform AGC, i.e., signal level adjustment.
`The signal output from the variable gain ampli?er 402 is
`sampled and quantiZed by an A/D converter 403. The digital
`signal output from the A/D converter 403 is sent to the
`outside of the receiving unit 302 and to a gain controller 404.
`The gain controller 404 performs gain calculation based on
`the digital signal output from the A/D converter 403, and
`controls the gain of the variable gain ampli?er 402. The
`speci?c procedure for the gain control Will be described
`later.
`
`[0044] The operation of the Wireless receiving device
`shoWn in FIGS. 3 and 4 eXecuted for receiving the Wireless
`packet including the preamble Whose format is shoWn in
`FIG. 1 is as folloWs. Firstly, the Wireless receiving device
`receives a short-preamble sequence 101 transmitted from the
`transmit antenna 205A of FIG. 2, and then performs packet
`edge detection, time synchroniZation, auto frequency control
`(AFC) and AGC, using a baseband signal corresponding to
`the short-preamble sequence 101. AFC is also called fre
`quency synchroniZation. Packet edge detection, time syn
`chroniZation and AFC can be performed using knoWn tech
`niques, therefore no description Will be given thereof. Only
`AGC Will be explained beloW.
`
`[0045] The baseband signal corresponding to the short
`preamble sequence 101 is ampli?ed by the variable gain
`ampli?er 402 in accordance With a predetermined initial
`gain value. The signal output from the variable gain ampli
`?er 402 is input to the gain controller 404 via the A/D
`converter 403. The gain controller 404 calculates a gain
`from the level of the received signal corresponding to the
`short-preamble sequence 101, Which is acquired after A/D
`conversion, and controls the gain of the variable gain
`ampli?er 402 in accordance With the calculated gain.
`
`[0046] Assume here that the level of the baseband signal
`corresponding to the short-preamble sequence 101, Which is
`acquired before A/D conversion, is X. If level X is high, the
`baseband signal input to the A/D converter 403 eXceeds the
`upper limit of the input dynamic range of the A/D converter
`403. As a result, the signal (digital signal) output from the
`A/D converter 403 is saturated and degraded the quality of
`signal reception. On the other hand, if level X is extremely
`loW, the signal output from the A/D converter 402 (i.e., the
`digital signal acquired by A/D conversion) suffers a severe
`quantiZation error. Thus, When level X L is very high or loW,
`
`Exhibit 2001
`IPR2015-00221
`15 of 22
`
`

`

`US 2005/0163081 Al
`
`Jul. 28, 2005
`
`the A/D converter 403 cannot perform appropriate conver
`sion, thereby signi?cantly degrading the quality of signal
`reception.
`[0047] To overcome this problem, the gain controller 404
`controls the gain of the variable gain ampli?er 402 so that
`the level X of the baseband signal corresponding to the
`short-preamble sequence 101, is adjusted to a target value Z.
`If the input baseband signal has such a very high level as
`makes the output of the A/D converter 403 limited to its
`upper limit level, or if it has a very loW level, the gain of the
`variable gain ampli?er 402 may not appropriately be con
`trolled by one control process. In this case, gain control is
`performed repeatedly. As a result, the level of the baseband
`signal input to the A/D converter 403 can be adjusted to a
`value that falls Within the input dynamic range of the A/D
`converter 403. Thus, the gain of the variable gain ampli?er
`402 is appropriately controlled using the baseband signal
`corresponding to the short-preamble sequence 101, thereby
`performing appropriate A/D conversion to avoid a reduction
`in the quality of signal reception.
`[0048] In the above-described embodiment, the reception
`level needed for calculating the gain of the variable gain
`ampli?er 402 is measured using a digital signal output from
`the A/D converter 403. HoWever, such level measurement
`can be eXecuted using an analog signal acquired before A/D
`conversion. Furthermore, the reception level may be mea
`sured in the IF band or RF band, instead of BB.
`[0049] The Wireless receiving device receives a ?rst long
`preamble sequence 102 transmitted from the transmit
`antenna 205A, and performs the estimation of channel
`impulse response , i.e., estimates the response (frequency
`transfer function) of the propagation path betWeen the
`Wireless transmitting device to the Wireless receiving device,
`using a baseband signal corresponding to the long-preamble
`sequence 102. Since the signal transmitted from the transmit
`antenna 205A has already been subjected to AGC as
`described above, the level of an input to the A/D converter
`403 is appropriately adjusted When the estimation of channel
`impulse response is performed. Accordingly, concerning the
`signal transmitted from the transmit antenna 205A, a highly
`accurate digital signal is acquired from the A/D converter
`403. The estimation of channel impulse can be performed
`accurately With the acquired digital signal.
`[0050] The Wireless receiving device receives a ?rst signal
`?eld 103 transmitted from the transmit antenna 205A, and
`demodulates a baseband signal corresponding to the ?rst
`signal ?eld 103, using the digital demodulator 304 and the
`above-mentioned propagation path estimation result. The
`?rst signal ?eld 103 contains information indicating the
`modulation scheme and Wireless packet length of data to be
`sent after the preamble. The ?rst signal ?eld 103 is a ?eld
`that conveys a kind of attribute information regarding the
`Wireless packet. The Wireless receiving device continues
`demodulation using the digital demodulator 304 during the
`duration of a Wireless packet recogniZed from the Wireless
`packet length information contained in the ?rst signal ?eld
`103.
`
`[0051] Since the packet format from the short-preamble
`sequence 101 to the ?rst signal ?eld 103 provides interop
`erability With IEEE802.11a stations, IEEE 802.11a station is
`able to perform normal receiving operation Without destroy
`ing the Wireless packet. In other Words, another IEEE
`
`802.11a Wireless transmitting and receiving device conform
`ing to the IEEE 802.11a standard (a legacy station), upon
`receiving the ?rst signal ?eld 103, is prohibited to transmit
`a signal until the Wireless packet ends so as not to destroy the
`Wireless packet.
`[0052] Subsequently, the Wireless receiving device
`receives a second signal ?eld 104 transmitted from the
`transmit antenna 205A. The second signal ?eld 104 contains
`identi?cation information indicating a Wireless packet that
`corresponds to a standard other than IEEE 802.11a, e.g.,
`IEEE 802.11n. In other Words, the second signal ?eld 104
`indicates that subsequent AGC preambles 105A to 105D,
`second long-preamble sequences 106A to 109A, 106B to
`109B, 106C to 109C and 106D to 109D are signals corre
`sponding to, for eXample, IEEE 802.11n.
`[0053] The Wireless receiving device receives AGC pre
`ambles 105A to 105D transmitted from the transmit anten
`nas 205A to 205D in parallel. The AGC preambles 105A to
`105D are transmitted from the transmit antenna 205A that
`has transmitted the short-preamble sequence 101, ?rst long
`preamble sequence 102, ?rst signal ?eld 103 and second
`signal ?eld 104, and from the transmit antennas 205B to
`205D that have transmitted no signal so far. Accordingly,
`While the signals transmitted from the transmit antenna
`205A (i.e., the short-preamble sequence 101, ?rst long
`preamble sequence 102, ?rst signal ?eld 103 and second
`signal ?eld 104) are received With a certain receiving level,
`the AGC preambles 105A to 105D are received With differ
`ent receiving levels from the level of the reception signal
`coming from the transmit antenna 205A. In other Words, the
`reception level is changed after the MIMO transmission
`using the multiple transmit antenna.
`[0054] As described above, the Wireless receiving device
`receives the second signal ?eld 104 and demodulates it using
`the digital demodulator 304, thereby recogniZing that the
`present Wireless packet corresponds to IEEE 802.11n. After
`that, the digital demodulator 304 issues an instruction to
`restart AGC for ?ne tune to the receiving units 302A to
`302D, thereby re-eXecuting AGC on the AGC preambles
`105A to 105D. As a result, the signals transmitted from the
`transmit antennas 205A to 205D via the MIMO channel and
`received at the receiving units 302A to 302D, are input to the
`A/D converter 403 With an appropriately adjusted receiving
`level.
`
`[0055] That is, using the level of baseband signals corre
`sponding to the AGC preambl