0
`
`(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`
`(19) World Intellectual Property Organization
`International Bureau
`
`'
`
`(43) International Publication Date
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`21 October 2010 (21.10.2010)
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`|l||||ll|||1|||||||||||||||||I||lllllllllHl|||1||l|l|||||||||||l||||||||||||||||1||||||||l||||
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`(10) International Publication Number
`WO 2010/120692 A1
`
`(51)
`
`(21)
`
`International Patent Classification:
`H04I. 12/28 (2006.01)
`H04]. 29/08 (2006.01)
`H041. 12/56 (2006.01)
`H04W28/06 (2009.01)
`.
`2
`H041. 29/06 (2006.01)
`[104L 27/..6 (2006.01)
`International Application Number:
`PCT/U82010/030750
`
`(22) International Filing Date:
`
`(71) Applicant (for all designated States except US): MAR-
`VELL WORLD TRADE LTD.
`[BB/I313]; L'horizon,
`Gunsite Road, Brittons Hill, St. Michael, BB14027 (BB).
`Inventors; and
`(72)
`(71) Applicants : YU, Mao [US/US]; 3319 Loire Court, San
`Jose, CA 95135 (US). BANERJEA, Raja [US/US]; 970
`Corte Madera Ct, Apt. 203, Sunnyvale, CA 94085 (US).
`
`12 April 2010 (12.04.2010)
`
`(72)
`(75)
`
`bnghsh
`English
`
`(30)
`
`(25) brllng Language:
`(26) Publication Language:
`.
`,
`'
`:3?g'8t3;?zata'
`61/181'518
`61/227:360
`61/228,911
`61/229,900
`61/232,724
`giggi‘gzg
`61/240,604
`61/240,945
`61/241,760
`61/244,779
`61/252,290
`61/319,773
`
`13 April 2009 (13 O4 2009)
`27 May 2009 (27052009)
`21 July 2009 (21072009)
`27 July 2009 (27.07.2009)
`30 July 2009 (30.07.2009)
`10 August 2009 (10.08.2009)
`i: 2323:: 3333 82323333;
`8 September 2009 (08.09.2009)
`9 September 2009 (09.09.2009)
`11 September 2009 (11.09.2009)
`22 September 2009 (22.09.2009)
`16 October 2009 (16.10.2009)
`31 March 2010 (31.03.2010)
`
`Inventors; and
`ZHANG,
`only:
`US
`(for
`Inventors/Applicants
`Hongyuan [CN/US]; 4707 Pasco Padre Pkwy, Fremont,
`CA 94555 (US). LOU, Hui-Ling [US/US]; 1485 Firebird
`Way, Sunnyvale, CA 94807 (US). NABAR, Rohit. U.
`[IN/US]; 730 E. Evelyn Ave., Apt. 525, Sunnyvale, CA
`US
`94.086
`(US) S-RmWASA’
`sudhlr
`[IN/U81‘
`'030
`US
`M1che1angelo Drive, Sunnyvale, CA 94087 (US).
`US
`us (74) Agent: STANTON, Gregory, E.; Marshall, Gerstein &
`US
`Borun LLP, 233 S. Wackcr Drive, 6300 Willis Tower,
`US
`Chicago, IL 60606-6357 (US).
`3:
`(81) Designated States (unless otherwise indicated, for every
`US
`land ofnational protection available): AE, AG, AL, AM,
`us
`A0) AT, AU’ Ala “A, BR“, ”G, “E" 31’3" BW’ “J, “2'
`US
`S? g: E: $2 E? E1 ’GCBU’GCD , GF’ 85 2M, 2?,
`US
`HN' PIR' PIU' ID'II: 'IN 'IS 1i) K12 KG KM KN' KP,
`US
`KR, KZ' LA, LC' LR LR ’LS 'LT 'LU 'LY MA ’MD'
`US
`’
`’
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`ME, MG, MK, MN, MW, MX, MY, MZ, NA, NG, NI,
`NO, NZ, OM, PE, PG, PH, PL, PT, RO, RS, RU, SC, SD,
`
`(54) Title: PHYSICAL LAYER FRAME FORMAT FOR WLAN
`
`[Continued on next page]
`
`FIG. 6
`
`LEGACV
`For: now
`
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`(57) Abstract: In a method for generating a data unit for transmission via a communication channel, wherein the data unit con-
`forms to a first communication protocol, a preamble of the data unit is generated. The preamble includes a first field having infor-
`mation that indicates a duration of the data unit, the first field being formatted such that the first field is decodable by a receiver
`device that conforms to a second communication protocol but does not conform to the first communication protocol to determine
`the duration of the data unit based on the first field. Additionally, the preamble is formatted such that a portion of the preamble is
`decodable by a receiver device that conforms to a third communication protocol but does not conform to the first communication
`protocol. Also, the preamble is formatted such that a receiver device that conforms to the first communication protocol can deter-
`mine that the data unit conforms to the first communication protocol. A data portion of the data unit that conforms to the first
`communication protocol and does not conform to either (i) the second communication protocol or (ii) the third communication
`protocol is gcncratcd.
`
`
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`wo2010/120692A1|l||||llllllllllllllllllll||||||l||||||||l|1|l|||||||||||||||Illlllllllllll|||||||||||||||||||
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`WO 2010/120692 A1 |||||||lllllllllllllllllllllllll|||l||||l|||||||l||||||||||l||||l|ll|||||||||||||||||||||||||||
`
`ES, FI, FR, GB, GR, HR, HU, IE, IS, IT, LT, LU, LV,
`SE, SG, SK, SL, SM, ST, SV, SY, TH, TJ, TM, TN, TR,
`MC, MK, MT, NL, NO, PL, PT, RO, SE, SI, SK, SM,
`TT, TZ, UA, UG, US, UZ, VC, VN, ZA, ZM, ZW.
`:41?,SI?{PII\I§ZBIS,I\?JTSFT8?’ CI’ CM’ GA’ GN’ GQ’ GW’
`(84) Designated States (unless otherwise indicated, for eveiy
`’
`’
`’
`’
`‘
`'
`kind of regional protection available): ARIPO (BW, GH,
`GM, KE, LR, LS, MW, MZ, NA, SD, SL, SZ, TZ, UG, Published:
`.
`.
`ZM, ZW), Eurasian (AM, AZ, BY, KG, KZ, MD, RU, TJ, _
`.
`TM), European (AT, BE, BG, CH, CY, CZ, DE, DK, EE
`With international search report (Ari. 21(3))
`
`

`

`WO 2010/120692
`
`PCT/U52010/030750
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`PHYSICAL LAYER FRAME FORMAT FOR WLAN
`
`Cross-References to Related Applications
`
`[0001]
`
`This disclosure claims the benefit of the following US. Provisional
`
`Patent Applications:
`
`US. Provisional Patent Application No
`
`. 61/168,732, entitled “80 MHz OFDM for
`
`WLAN,” filed on April 13, 2009;
`
`US. Provisional Patent Application No
`
`.61/181,518, entitled “80 MHz OFDM for
`
`WLAN,” filed May 27, 2009;
`
`US. Provisional Patent Application No
`
`. 61/227,360, entitled “80 MHz OFDM for
`
`WLAN,” filed July 21, 2009;
`
`US. Provisional Patent Application No
`
`. 61/228,911, entitled “80 MHZ OFDM for -
`
`WLAN,” filed July 27, 2009;
`
`US. Provisional Patent Application No
`
`. 61/229,900, entitled “80 MHz OFDM for
`
`WLAN,” filed July 30, 2009;
`
`US. Provisional Patent Application No
`
`. 61/232,724, entitled “80 MHz OFDM for
`
`WLAN,” filed August 10, 2009;
`
`US. Provisional Patent Application No
`
`. 61/233,440, entitled “80 MHz OFDM for
`
`WLAN,” filed August 12, 2009;
`
`US. Provisional Patent Application No
`
`. 61/234,943, entitled “80 MHZ OFDM for
`
`WLAN,” filed August 18, 2009;
`
`US. Provisional Patent Application No
`
`. 61/240,604, entitled “80 MHz OFDM for
`
`WLAN,” filed September 8, 2009;
`
`US. Provisional Patent Application No
`
`. 61/240,945, entitled “80 MHz OFDM fog
`
`WLAN,” filed September 9, 2009;
`
`-1-
`
`SUBSTITUTE SHEET (RULE 26)
`
`

`

`WO 2010/120692
`
`PCT/US2010/030750
`
`US. Provisional Patent Application No. 61/241,760, entitled “80 MHz OFDM for
`
`WLAN,” filed September 11, 2009;
`
`US. Provisional Patent Application No. 61/244,779, entitled “80 MHz OFDM for
`
`WLAN,” filed September 22, 2009;
`
`US. Provisional Patent Application No. 61/252,290, entitled “80 MHZ OFDM for
`
`WLAN,” filed October 16, 2009; and
`
`US. Provisional Patent Application No. 61/319,773, entitled “NDP Preamble,”
`
`filed March 31, 2010.
`
`[0002]
`
`The disclosures of all of the above-referenced patent applications are
`
`hereby incorporated by reference herein in their entireties.
`
`Field of the Disclosure
`
`[0003]
`
`The present disclosure relates generally to communication networks and,
`
`more particularly, to wireless local area networks that utilize orthogonal frequency
`
`division multiplexing (OFDM).
`
`Background
`
`[0004]
`
`The background description provided herein is for the purpose of
`
`generally presenting the context of the disclosure. Work of the presently named
`
`inventors, to the extent it is described in this background section, as well as aspects of the
`
`description that may not otherwise qualify as prior art at the time of filing, are neither
`
`expressly nor impliedly admitted as prior art against the present disclosure.
`
`[0005] When operating in an infrastructure mode, wireless local area networks
`
`(WLANs) typically include an access point (AP) and one or more client stations.
`
`WLANs have evolved rapidly over the past decade. Development of WLAN standards
`
`such as the Institute for Electrical and Electronics Engineers (IEEE) 802.] 1a, 802.] lb,
`
`802.11g, and 802.11n Standards has improved single-user peak data throughput. For
`
`example, the IEEE 802.11b Standard specifies a single-user peak throughput of 11
`
`-2-
`
`

`

`WO 2010/120692
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`PCT/U52010/030750
`
`megabits per second (Mbps), the IEEE 802.1 la and 802.1 lg Standards specify a single-
`
`user peak throughput of 54 Mbps, and the IEEE 802.1 111 Standard specifies a single-user
`
`peak throughput of 600 Mbps. Work has begun on a new standard, IEEE 802.1 lac, that
`
`promises to provide even greater throughput.
`
`Summary
`
`[0006] According to one embodiment, a method for generating a data unit for
`
`transmission via a communication channel, wherein the data unit conforms to a first
`
`communication protocol, includes generating a preamble of the data unit. The preamble
`
`includes a first field having information that indicates a duration of the data unit, the first
`
`field being formatted such that the first field is decodable by a receiver device that
`
`conforms to a second communication protocol but does not conform to the first
`
`communication protocol to determine the duration of the data unit based on the first field.
`
`Additionally, the preamble is formatted such that a portion of the preamble is decodable
`
`by a receiver device that conforms to a third communication protocol but does not
`
`conform to the first communication protocol. Also, the preamble is formatted such that a
`
`receiver device that conforms to the first communication protocol can determine that the
`
`data unit conforms to the first communication protocol. The method further includes
`
`generating a data portion of the data unit that conforms to the first communication
`
`protocol and does not conform to either (i) the second communication protocol or (ii) the
`
`third communication protocol.
`
`[0007]
`
`In other embodiments, one or more of the following features are also
`
`included.
`
`[0008] A portion of the data unit that is decodable by the receiver device that
`
`conforms to the third communication protocol but does not conform to the first
`
`communication protocol includes the first field, and wherein the first field is formatted
`
`such that the first field is decodable by the receiver device that conforms to the third
`
`

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`WO 2010/120692
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`PCT/U52010/030750
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`communication protocol but does not conform to the first communication protocol to
`
`determine the duration of the data unit based on the first field.
`
`[0009]
`
`The first field of the preamble includes a rate subfield and a length
`
`subfield that indicate the duration of the data unit.
`
`[0010]
`
`The first field ofthe preamble includes a subfield that is set to a value
`
`that contradicts the second communication protocol. The value of the first subfield that
`
`contradicts the second communication protocol indicates to the receiver device that
`
`conforms to the first communication protocol that the data unit conforms to the first
`
`communication protocol.
`
`[0011] A second field of the preamble includes a subfield that is set to a value
`
`that contradicts the third communication protocol. The subfield that is set to the value
`
`that contradicts the third communication protocol indicates to the receiver device that
`conforms to the third communication protocol to the wait until the energy of the data unit
`
`drops out before switching to a clear channel assessment (CCA) mode.
`
`[0012] A second field of the preamble includes information that indicates the
`
`duration of the data unit, and wherein the portion of the preamble that is decodable by the
`
`receiver device that conforms to the third communication protocol but does not conform
`
`to the first communication protocol includes the second field.
`
`[0013] A second field of the preamble is modulated using a modulation different
`
`than specified by the third communication protocol. The modulation of the second field
`
`different than specified by the third communication protocol indicates to the receiver
`
`device that conforms to the first communication protocol that the data unit conforms to
`
`the first communication protocol.
`
`[0014]
`
`The data portion includes data for only a single receiver device.
`
`[0015]
`
`The data portion includes independent data for a plurality of receiver
`
`devices.
`
`

`

`WO 2010/120692
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`PCT/USZ010/030750
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`[0016]
`
`The data portion has a cumulative bandwidth greater than a bandwidth
`
`specified by the second communication protocol and a maximum bandwidth specified by
`
`the third communication protocol.
`
`[0017]
`
`The second communication protocol is the Institute for Electrical and
`
`Electronics Engineers (IEEE) 802.11a Standard.
`
`[0018]
`
`The third communication protocol is the IEEE 802.11n Standard.
`
`Brief Description of the Drawings
`
`[0019]
`
`Fig.
`
`1 is a block diagram of an example wireless local area network
`
`(WLAN) 10, according to an embodiment;
`
`[0020]
`
`Figs. 2A and 28 are diagrams of a prior art data unit format;
`
`[002]]
`
`Fig. 3 is a diagram of another prior art data unit format;
`
`[0022]
`
`Fig. 4 is a diagram of another prior art data unit format;
`
`[0023]
`
`Fig. 5 is a diagram of an example data unit format, according to an
`
`embodiment;
`
`[0024]
`
`Fig. 6 is a diagram of another example data unit format, according to an
`
`embodiment;
`
`[0025]
`
`Fig. 7A are diagrams of modulation used to modulate symbols in a prior
`
`art data unit;
`
`[0026]
`
`Fig. 7B are diagrams ofmodulation used to modulate symbols in an
`
`example data unit, according to an embodiment;
`
`[0027]
`
`Fig. 7C are diagrams of modulation used to modulate symbols in another
`
`example data unit, according to an embodiment;
`
`[0028]
`
`Fig. 7D are diagrams of modulation used to modulate symbols in another
`
`example data unit, according to an embodiment;
`
`

`

`WO 2010/120692
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`PCT/U52010/030750
`
`[0029]
`
`Fig. 7B is a diagram of modulation used to modulate a symbol in another
`
`example data unit, according to an embodiment;
`
`[0030]
`
`Fig. 8 is a diagram oftones in an orthogonal frequency division
`
`multiplexing (OFDM) symbol, according to an embodiment;
`
`[0031]
`
`Fig. 9 is a diagram of another example data unit format, according to an
`
`embodiment;
`
`[0032]
`
`Fig. 10 is a diagram of another example data unit format, according to an
`
`embodiment;
`
`[0033]
`
`Fig. 11 is a diagram of another example data unit format, according to an
`
`embodiment;
`
`[0034]
`
`Figs. 12A and 12B are diagrams of modulation used to modulate symbols
`
`in two example data units, according to an embodiment;
`
`[0035]
`
`Fig. 13 is a diagram of another example data unit format, according to an
`
`embodiment;
`
`[0036]
`
`Fig. 14 is a diagram of another example data unit format, according to an
`
`embodiment;
`
`[0037]
`
`Fig. 15 is a diagram of another example data unit format, according to an
`
`embodiment;
`
`[0038]
`
`Fig. 16 is a diagram of an example field used in a data unit, according to
`
`an embodiment;
`
`[0039]
`
`Fig. 17 is a diagram of another-example data unit format, according to an
`
`ellibodilncnt;
`
`[0040]
`
`Fig. 18 is a diagram of another example data unit format, according to an
`
`embodiment;
`
`

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`WO 2010/120692
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`PCT/U$2010/030750
`
`[0041]
`
`Fig. 19 is a diagram of another example data unit format, according to an
`
`embodiment;
`
`[0042]
`
`Fig. 20 is a diagram of another example data unit format, according to an
`
`embodiment;
`
`[0043]
`
`Fig. 21A is a diagram of another example data unit, according to an
`
`embodiment;
`
`[0044]
`
`Fi g. 218 are diagrams of modulation used to modulate symbols in the
`
`example data unit of Fig. 21A, according to an embodiment;
`
`[0045]
`
`Fig. 22 is a diagram of another example data unit, according to an
`
`embodiment;
`
`[0046]
`
`Fig. 23 is a diagram of an example sounding data unit, according to an
`
`embodiment; and
`
`.
`
`[0047]
`
`Fig. 24 is a diagram of another example sounding data unit, according to
`
`an embodiment.
`
`Detailed Description
`
`[0048]
`
`In embodiments described below, a wireless network device such as an
`
`access point (AP) of a wireless local area network (WLAN) transmits data streams to one
`
`or more client stations. The AP is configured to operate with client stations according to
`
`at least a first communication protocol. Similarly, different client stations in the vicinity
`
`of the AP may be configured to operate according to different communication protocols.
`
`When the AP transmits a data unit according to a first protocol, a preamble of the data is
`
`formatted such that a client station that operates according to a second protocol, and not
`
`the first protocol, is able to determine certain information regarding the data unit, such as
`
`a duration of the data unit, and/or that the data unit does not conform to the second
`
`protocol. Additionally, a preamble of the data unit is formatted such that a client station
`
`that operates according to the first protocol is able to determine the data unit conforms to
`
`-7-
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`

`WO 2010/120692
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`the first protocol. Similarly, a client station configured to operate according to the first
`
`protocol also transmits data units such as described above.
`
`[0049] Data units formatted such as described above may be useful, for example,
`
`with an AP that is configured to operate with client stations according to a plurality of
`
`different communication protocols and/or with WLANs in which a plurality of client
`
`stations operate according to a plurality of different communication protocols.
`
`Continuing with the example above, a communication device configured to operate
`
`according to both the first communication protocol and the second communication
`
`protocol is able to determine that the data unit is formatted according to the first
`
`communication protocol and not the second communication protocol. Similarly, a
`
`communication device configured to operate according to the second communication
`
`protocol but not the first communication protocol is able to determine that the data unit is
`
`not formatted according to the second communication protocol and/or determine a
`
`duration of the data unit.
`
`[0050]
`
`Fig. l is a block diagram of an example wireless local area network
`
`(WLAN) 10, according to an embodiment. An AP 14 includes a host processor 15
`
`coupled to a network interface 16. The network interface 16 includes a medium access
`
`control (MAC) unit 18 and a physical layer (PHY) unit 20. The PHY unit 20 includes a
`
`plurality of transceivers 21, and the transceivers are coupled to a plurality of antennas 24.
`
`Although three transceivers 21 and three antennas 24 are illustrated in Fig. 1, the AP 14
`
`can include different numbers (e.g., 1, 2, 4, 5, etc.) of transceivers 21 and antennas 24 in
`
`other embodiments.
`
`In one embodiment, the MAC unit 18 and the PHY unit 20 are
`
`configured to operate according to a first communication protocol (e.g., the IEEE
`802.1 lac Standard, now in the process of being standardized). In another embodiment,
`
`the MAC unit 18 and the PHY unit 20 are also configured to operate according to a
`
`second communication protocol (e.g., the IEEE 802.11n Standard). Inlyet another
`
`embodiment, the MAC unit 18 and the PHY unit 20 are additionally configured to
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`WO 2010/120692
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`PCT/U52010l030750
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`operate according to the second communication protocol and a third communication
`
`protocol (cg, the IEEE 802.11a Standard).
`
`[0051]
`
`The WLAN 10 includes a plurality ofclient stations 25. Although four
`
`client stations 25 are illustrated in Fig. 1, the WLAN 10 can include different numbers
`
`(e.g., 1,2, 3, 5, 6, etc.) ofclient stations 25 in various scenarios and embodiments. At
`
`least one ofthe client stations 25 (e.g., client station 25-1) is configured to operate at least
`
`according to the first communication protocol.
`
`In some embodiments, at least one of the
`
`client stations 25 is not configured to operate according to the first communication
`
`protocol but is configured to operate according to at least one of the second
`
`communication protocol or the third communication protocol (referred to herein as a
`
`“legacy client station”).
`
`[0052]
`
`The client station 25-1 includes a host processor 26 coupled to a network
`
`interface 27. The network interface 27 includes a MAC unit 28 and a PHY unit 29. The
`
`PHY unit 29 includes a plurality of transceivers 30, and the transceivers 30 are coupled to
`
`a plurality of antennas 34. Although three transceivers 30 and three antennas 34 are
`
`illustrated in Fig. 1, the client station 25-1 can include different numbers (e.g., 1, 2, 4, 5,
`
`etc.) of transceivers 30 and antennas 34 in other embodiments.
`
`[0053]
`
`In an embodiment, one or both of the client stations 25-2 and 25-3, has a
`
`structure the same as or similar to the client station 25-1. In an embodiment, the client
`
`station 25-4, has a structure similar to the client station 25-1. In these embodiments, the
`
`client stations 25 structured the same as or similar to the client station 25-1 have the same
`
`or a different number of transceivers and antennas. For example, the client station 25—2
`
`has only two transceivers and two antennas, according to an embodiment.
`
`[0054] According to an embodiment, the client station 25-4 is a legacy client
`
`station, i.e., the client station 25-4 is not enabled to receive and fully decode a data unit
`
`that is transmitted by the AP 14 or another client station 25 according to the first
`
`communication protocol. Similarly, according to an embodiment, the legacy client
`
`-9.
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`WO 2010/120692
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`
`station 25-4 is not enabled to transmit data units according to the first communication
`
`protocol. On the other hand, the legacy client station 25-4 is enabled to receive and fully
`
`decode and transmit data units according to the second communication protocol and/or
`
`the third communication protocol.
`
`[0055]
`
`In various embodiments, the PHY unit 20 ofthe AP 14 is configured to
`
`generate data units conforming to the first communication protocol and having formats
`described hereinafter. The transceiver(s) 21 is/are configured to transmit the generated
`
`data units via the antenna(s) 24. Similarly, the transceiver(s) 24 is/are configured to
`
`receive the data units via the antenna(s) 24. The PHY unit 20 of the AP 14 is configured
`
`to process received data units conforming to the first communication protocol and having
`
`formats described hereinafter and to determine that such data units conform to the first
`
`communication protocol, according to various embodiments.
`
`[0056]
`
`In various embodiments, the PHY unit 29 ofthe client device 25-1 is
`
`‘
`
`configured to generate data units conforming to the first communication protocol and
`
`having formats described hereinafter. The transceiver(s) 30 is/are configured to transmit
`
`the generated data units via the antenna(s) 34. Similarly, the transceiver(s) 30 is/are
`
`configured to receive data units via the antenna(s) 34. The PHY unit 29 of the client
`
`device 25-1 is configured to process received data units conforming to the first
`
`communication protocol and having formats described hereinafter and to determine that
`
`such data units conform to the first communication protocol, according to various
`
`embodiments.
`
`[0057]
`
`Fig. 2A is a diagram ofa prior art data unit 60 that the legacy client
`
`station 25-4 is configured to transmit to the AP 14 via orthogonal frequency domain
`
`multiplexing (OFDM) modulation, according to an embodiment. The data unit 60
`
`conforms to the IEEE 802.1 la Standard and occupies a 20 Megahertz (MHz) band. The
`
`data unit 60 includes a preamble having a legacy short training field (L-STF) 62, a legacy
`
`long training field (L-LTF) 64, and a legacy signal field (L-SIG) 66. The data unit 60
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`also includes a data portion 68. Fig. 2B is a diagram of an example data portion 68 (not
`low density parity check encoded), which includes a service field, a scrambled physical
`
`layer service data unit (PSDU), tail bits, and padding bits, ifneeded.
`
`[0058]
`
`Fig. 3 is a diagram ofa prior art OFDM data unit 78 that the legacy client
`
`station 25-4 is configured to transmit to the AP 14, according to an embodiment. The
`
`data unit 78 conforms to the IEEE 802.11n Standard, occupies a 20 MHz band, and is
`
`designed for mixed mode situations, i.e., when the WLAN includes one or more client
`
`stations that conform to the IEEE 802.11a Standard but not the IEEE 802.11n Standard.
`
`The data unit 78 includes a preamble having an L-STF 80, an L-LTF 81, an L-SlG 82, a
`
`high throughput signal field (HT-SIG) 83, a high throughput short training field (I-IT-
`
`STF) 84, N data high throughput long training fields (HT-LTFs) 85, where N is an
`
`integer, and M extension HT-LTFS 86, where M is an integer. The data unit 78 also
`
`includes a data portion 87.
`
`[0059]
`
`Fig. 4 is a diagram ofa prior art OFDM data unit 90 that the legacy client
`
`station 25-4 is configured to transmit to the AP 14, according to an embodiment. The
`
`data unit 90 conforms to the IEEE 802.11n Standard, occupies a 20 MHz band, and is
`
`designed for “Greenfield” situations, i.e., when the WLAN does not include any client
`
`stations that conform to the IEEE 802.1 ]a Standard but not the IEEE 802.11n Standard.
`
`The data unit 90 includes a preamble having a high throughput Greenfield short training
`
`field (HT-GF-STF) 91, a first high throughput long training field (HT-LTFI) 92, a HT-
`
`SIG 93, N data HT~LTFs 94, where N is an integer, and M-extension HT-LTFs 95, where
`
`M is an integer. The data unit 90 also includes a data portion 98.
`
`[0060]
`
`Fig. 5 is a diagram of an OFDM data unit 100 that the AP 14 is
`
`configured to transmit to the client station 25—1, according to an embodiment. In an
`
`embodiment, the client station 25-1 is also configured to transmit the data unit 100 to the
`
`AP 14. The data unit 100 conforms to the first communication protocol and occupies an
`
`80 MHz band. In other embodiments, data units similar to the data unit 100 occupy
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`different bandwidths such as 20 MHZ, 40 MHZ, 120 MHZ, 160 MHZ, or any suitable
`
`bandwidth. Additionally, the 80 MHZ band need not be contiguous, but may include two
`
`or more smaller bands, such as two 40 MHZ bands, separated in frequency. The data unit
`
`100 is suitable for “mixed mode” situations, i.e., when the WLAN 10 includes a client
`
`station (i.e., the legacy client station 25-4) that conforms to the IEEE 802.11a Standard
`
`and/or the IEEE 802.1 In Standard, but not the first communication protocol. The data
`
`unit 100 can be utilized in other situations as well. The data unit 100 includes a preamble
`
`having four L—STFs 104, four L-LTFs 108, four L—SIGs 1 12, four first very high
`
`throughput signal fields (VHT-SIGI) 116, four second very high throughput signal fields
`
`(VHT-SIGZ) 120, a very high throughput short training field (VHT-STF) 124, and N very
`
`high throughput long training fields (VHT-LTFS) 128, where N is an integer. The data
`
`unit 100 also includes a data portion 140. The L-STFs 104, the L-LTFs 108, and the L-
`SIGs 112 form a legacy portion. The VHT-STF 124, the VHT-LTFS 128, and the data
`
`portion 140 form a very high throughput (VIIT) portion.
`
`[0061]
`
`In the embodiment of Fig. 5, each of the L-STFs 104, each of the L—LTFs
`
`108, each ofthe L—SIGs 112, each ofthe VHT-SlGls, and each ofthe VHT-SIGZs
`
`occupy a 20 MHZ band. In the present disclosure, several example data units, including
`
`the data unit 100, having an 80 MHZ contiguous bandwidth are described for the
`
`purposes of illustrating embodiments of frame formats, but these frame format
`
`embodiments and other embodiments are applicable to other suitable bandwidths
`
`(including noncoutiguous bandwidths). For instance, although the preamble of big. 5
`
`includes four of each ofthe L-STFs 104, the L-LTFs 108, the L-SIGs 112, the VHT-
`
`81615, and the VHT-SIGZs, in other embodiments in which the OFDM data unit
`
`occupies a cumulative bandwidth other than 80 MHZ, such as 20 MHZ, 40 MHZ, 120
`
`MHZ, 160 MHZ, etc, a different suitable number of the L-STFs 104, the L-LTFS 108, the
`
`L-SIGs 112, the VHT-SIGls, and the VHT-SIG2S is utilized accordingly (e.g., one of
`each ofthe L-STFs 104, the L—LTFs i08, the L-SIGs 112, the VHT-SIGls, and the VHT-
`
`SIGZS for an OFDM data unit occupying 20 MHZ, two of each ofthe fields for a 40 MHZ
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`bandwidth OFDM data unit, six of each ofthe fields for a 120 MHZ bandwidth OFDM
`
`data unit, and eight of each ofthe fields for a 160 MHZ bandwidth OFDM data unit).
`
`Also in 80 MHZ and 160 MHZ bandwidth OFDM data units, for example, the band is not
`
`contiguous in frequency, in some embodiments and situations. Thus, for example, the L-
`
`STFs 104, the L-LTFS 108, the L-SIGs 1 12, the VHT-SIGls, and the VHT-SIGZS occupy
`
`two or more bands that are separated from each other in frequency, and adjacent bands
`
`are separated in frequency by at least one MHZ, at least five MHZ, at least 10 MHZ, at
`
`least 20 MHZ, for example, in some embodiments.
`
`In the embodiment of Fig. 5, each of
`
`the STF 124, the VHT-[.TFs 128, and the data portion 140 occupy an 80 MHz band. If
`
`the data unit conforming to the first communication protocol is an OFDM data unit that
`
`occupies a cumulative bandwidth such as 20 MHZ, 40 MHZ, 120 MHZ, or 160 MHZ
`
`OFDM, the VHT-STF, VHT-LTFS and VHT data portion occupy the corresponding
`
`whole bandwidth of the data unit, according to an embodiment.
`
`[0062]
`
`In an embodiment, each of the L-STFs 104 and each of the L-LTFS 108
`
`have a format as specified in the IEEE 802.1 la Standard and/or the IEEE 802.1 1n
`
`Standard. In an embodiment, each of the L-SIGs 112 has a format at least substantially
`
`as specified in the IEEE 802.1 la Standard and/or the IEEE 802.11n Standard. The length
`
`and rate subfields in the L-SIGs 112 are set to indicate the duration T corresponding to
`
`remainder of the data unit 100 after the legacy portion. This permits client devices that
`
`are not configured according to the first communication protocol to determine an end of
`
`the data unit 100, for carrier sense multiple access/collision avoidance (CSMA/CA)
`
`purposes, for example. For instance, a legacy client device configured according to the
`
`IEEE 802.11a Standard will detect a data error from VHT-SlGl field, according to the
`
`receiver state machine specified in the IEEE 802.1 la Standard. Further according to the
`
`IEEE 802.11a Standard, the legacy client device will wait until the end of a computed
`
`packet duration (T) before performing clear channel assessment (CCA).
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`[0063]
`
`The frequency domain symbols of the legacy portion are repeated over
`
`four 20 MHZ sub-bands of the 80 MHZ band. Legacy client devices that are configured
`
`according to the IEEE 802.1 1a Standard and/or the IEEE 802.1 In Standard with 20 MHZ
`
`bandwidth will recognize a legacy IEEE 802.1 1a Standard preamble in any of the 20
`
`MHZ sub-bands. In some embodiments, the modulation of different 20 MHZ sub-bands
`
`signals is rotated by different angles. For example, in one embodiment, a first subband is
`
`rotated 0-degrees, a second subband is rotated 90-degrees, a third sub—band is rotated
`
`180-degrees, and a fourth sub-band is rotated 270—degrees.
`
`In other embodiments,
`
`different suitable rotations are utilized. As just one example, a first sub-band is rotated
`
`45-degrees, a. second sub-band is rotated 90-degrees, a third sub—band is rotated -45-
`
`degrees, and a fourth sub-band is rotated -90-degrees.
`
`[0064]
`
`In one embodiment, each of the L-SIGs l 12 has a format at least
`
`substantially as specified in the IEEE 802.11a Standard and/or the IEEE 802.11n
`
`Standard except that the “reserved” bit is set to 1, whereas the IEEE 802.11a Standard
`
`and the IEEE 802.11n Standard specify that the “reserved” bit is set to 0. By setting the
`
`“reserved” bit to 1, this signals devices that conform to the first communication protocol
`
`that the data unit 100 conforms to the first communication protocol, for example. In
`
`other embodiments, the “reserved” bit to O.
`
`[0065]
`
`In one embodiment, each of the VHT-SIGls, and each of the VHT—SIGZS
`
`has a format at least substantially the same as the HT-SIGl and the HT-SIGZ fields
`
`specified in the IEEE 802.11n Standard. For example, a modulation and coding scheme
`
`(MCS) field in VHT-SIGI and/or VHT—SIG2 is the same as the MCS field in HT—SIG,
`
`but applied to an 80 MHZ band. In one embodiment, MCS 32 is disallowed for VHT data V
`
`units such as the data unit 100. In other embodiments, MCS 32 is allowed for VHT data
`
`units such as the data unit 100.
`
`[0066]
`
`In some embodiments, the format and/or modulation of VHT-SIGl
`
`and/or VHT-SIG2 is at least different to cause a legacy device operating according to the
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`IEEE 802.1 ln Standard to detect an error, such as a cyclic redundancy check (CRC)
`
`error. Further according to the IEEE 802,] In Standard, the legacy client device will wait
`
`until the energy of the data unit 100 drops out before switching to CCA idle mode.
`
`[0067]
`
`In some embodiments, the