USOO7577085B1
`
`(12) Unlted States Patent
`(10) Patent No.:
`US 7,577,085 B1
`
`Narasimhan
`(45) Date of Patent:
`Aug. 18, 2009
`
`(54) MULTICARRIER TRANSMIT DIVERSITY
`
`(75)
`
`Inventor: Ravi Narasimhan, LOSAltOSs CA (US)
`.
`.
`_
`.
`(73) ASSlgnee‘
`121/3316“ Internatlonal Ltd" Hamflmn
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 982 days.
`
`(21) Appl. No.: 10/189,385
`
`(22)
`
`Filed:
`
`Jul. 5, 2002
`
`................ 375/267
`7/2002 Dabak et a1.
`6,424,679 B1*
`8/2002 Boleskeietal.
`............. 375/299
`6,442,214 B1*
`6,501,803 B1* 12/2002 Alamouti etal.
`............ 375/265
`6,731,668 132*
`5/2004 Ketchum .................... 370/209
`7,002,900 B2 *
`2/2006 Walton et al.
`............... 370/208
`
`(Continued)
`OTHER PUBLICATIONS
`
`Lee, King, A space frequency transmitter diversity technique for
`OFDM systems, Dec. 1, 2000, IEEE, pp. 1473-1477.*
`
`Related US. Application Data
`
`(Continued)
`
`(63) Continuation of application No. 10/162,274, filed on
`Jun. 3, 2002, now abandoned.
`
`Primary Examiner7Steven H Nguyen
`
`(57)
`
`ABSTRACT
`
`(51)
`
`Int. Cl.
`(2006.01)
`H04J 11/00
`(2006.01)
`H043 7/216
`(2006.01)
`H043 7/02
`(2006.01)
`H043 15/00
`(2006.01)
`H04K 1/10
`(2006.01)
`H043 7/10
`(52) US. Cl.
`....................... 370/206; 370/335; 370/342;
`375/260; 375/267; 375/285; 375/299; 375/347
`(58) Field of Classification Search ......... 370/2037210,
`370/335, 342; 375/260, 267, 285, 2993 347
`See application file for complete search history.
`_
`References Clted
`U.S. PATENT DOCUMENTS
`
`(56)
`
`.
`
`..... 370/514
`1/1997 Weigand et a1.
`5,598,419 A
`----- 370/514
`9/ 1997 Malek et 31~
`5,668,813 A
`~~~~~ 370/347
`~
`3/1998 Welgand et 31'
`5729543 A
`4/1998 so?“ """""""""" 370/347
`5’745’484 A
`10/1998 Welgand et al'
`‘
`””” 370/280
`5’822’308 A
`2/2000 Flckes et al.
`..... 370/349
`6,031,833 A
`.
`9/2000 Ablven et al.
`..... 370/338
`6,122,267 A
`6,144,711 A * 11/2000 Raleigh et al.
`.............. 375/347
`6,185,258 B1 *
`2/2001 Alamouti et al.
`............ 375/260
`6,351,499 B1 *
`2/2002 Paulraj et a1.
`............... 375/267
`
`
`
`Method, apparatus, and data packet format to implement
`transmit diversity in a multicarrier environment is disclosed.
`For diversity transmission operations,
`space frequency
`encoding techniques are employed creating distinguishable
`first and second time domain signals from a multicarrier
`frequency domain symbol bearing data of interest, which are
`then broadcast in parallel over first and second transmission
`units
`respectively For diversity reception Operations,
`complementary space frequency decoding is used to recover
`a corrected multicarrier frequency domain symbol from a
`time domain signal containing either this symbol, a space
`frequency modified symbol based on the multicarrier symbol,
`or a possible partial/complete combination of both. The data
`packet format 1ncludes portlons defining a transm1ss1on
`diversity semaphore, a preamble enabling training of a
`receiver receiving the data packet, and a payload. This pay-
`load includes plural data symbol pairs, each defining a first
`symbol for transmission by a first transmission unit of a
`diversity transmitter, and a second symbol for transmission
`1‘)
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`US 7,577,085 B1
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`3/2006 Li et a1.
`...................... 370/208
`7,020,072 B1 *
`6/2006 Ryan
`. 370/208
`7,065,036 B1 *
`
`8/2006 Nafie et a1.
`.
`. 375/267
`7,088,785 B2 *
`
`...........
`7,149,253 B2* 12/2006 Hosur
`375/267
`9/2002 El-Gamal et a1.
`.
`2002/0131516 A1*
`375/285
`
`4/2003 Tarokh et a1.
`............... 370/210
`2003/0072258 A1*
`
`OTHER PUBLICATIONS
`
`Peichocki R. Performance of space time coding with hiperlan/2 and
`IEEE 802.11a Wlan standards on real channels, Oct. 11, 2001; pp.
`848-852.*
`Peichocki R. Performance of space frequency techniques over mea-
`sured channels in MIMO-Systems, Oct. 11, 2001; pp. 1-9.*
`IEEE P802.11/g/D8.2, Apr. 2003 (Supplement to ANSI/IEEE std
`802.1 1 1999(Reaff2003), SponsoryLANMANStandards Committee
`ofIEEE Computer Society, “Part 1 1: Wireless LAN Medium Access
`Control (MAC) and Physical Layer (PHY) specifications: Further
`Higher Data Rate Extension in the 2.4 GHz Band,” pp. 1-69.
`
`Alamouti, Siavash M., “A Simple Transmit Diversity Technique for
`Wireless Communications”, IEEE Journal on SelectAreas in Com—
`munications, vol. 6, No. 8, Oct. 1998, pp. 1451-1457.
`IEEE std. 802.11a71999, Sponsor LANMAN Standards Committee
`ofIEEE Computer Society, “Part 1 1: Wireless LAN Medium Access
`Control (MAC) and Physical Layer (PHY) Specifications, High-
`Speed Physical Later Extension in the 5 GHz Band,” Sep. 1999, pp.
`1-83.
`
`IEEE std. 802.1 1b71999, Sponsor LANMAN Standards Committee
`ofIEEE Computer Society, “Part 1 1: Wireless LAN Medium Access
`Control (MAC) and Physical Layer (PHY) Specifications, Higher-
`Speed Physical Layer Extension in 2.4 GHz Band,” Sep. 1999, pp.
`1-89.
`
`International Standard, ANSI/IEEE std. 802.1 1, first edition, Sponsor
`LAN MAN Standards Committee ofIEEE Computer Society, “Part
`11: Wireless LAN Medium Access Control (MAC) and Physical
`Layer (PHY) specifications,” 1999.
`
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`U.S. Patent
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`Aug. 18, 2009
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`U.S. Patent
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`Aug. 18, 2009
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`Sheet 6 of 6
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`US 7,577,085 B1
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`2
`
`properly account for multipath distortion and other artifacts
`introduced by having dual proximate RF transmitters operat-
`ing at the same carrier frequency, the receiver must know in
`advance that it will be operating in a diversity environment
`and accommodate for these effects.
`
`The present high speed data wireless transmission stan-
`dards in the 802.11 family,
`including the commercially
`important IEEE 802.11a & 802.1 1g standards do not account
`for transmit diversity. Therefore, it would be advantageous to
`incorporate transmit diversity in a wireless transmission sys-
`tem that is backwards compatible with the IEEE 802.11a &
`802.1 1 g standards, as well as provide for a wireless diversity
`system capable of operating in multicarrier encoding envi-
`ronments generally.
`
`SUMMARY OF THE INVENTION
`
`To address these perceived and related shortcomings, the
`present invention is directed to a method, apparatus, and data
`packet suitable for implementing transmit diversity in a mul-
`ticarrier environment. In diversity transmission consistent
`with the present invention, space frequency encoding tech-
`niques are employed to create distinguishable first and second
`time domain signals from a multicarrier frequency domain
`symbol bearing the data of interest, which are broadcast in
`parallel over first and second transmission units respectively.
`In diversity reception consistent with the present invention,
`complementary space frequency decoding is used to recover
`a corrected multicarrier frequency domain symbol from a
`time domain signal containing either this multicarrier fre-
`quency domain symbol, a space-frequency modified symbol
`based on this multicarrier frequency domain symbol, or a
`possible incomplete or complete combination of both.
`Accordingly, diversity transmission in accordance with an
`embodiment of the invention employs space frequency
`encoding operable on multicarrier frequency domain sym-
`bols which bear the data of interest to provide corresponding
`modified symbols. These multicarrier frequency domain
`symbols and their corresponding modified symbols are con-
`verted into corresponding time domain counterparts and then
`transmitted in parallel by first and second RF transmission
`units. These time domain counterparts may be transmitted at
`approximately the same time on the same frequency channel,
`or, alternatively, in a staggered sequence or on dissimilar
`channels as will be appreciated by those ordinarily skilled in
`the art.
`
`1
`MULTICARRIER TRANSMIT DIVERSITY
`
`RELATED APPLICATION
`
`This application is a continuation of copending US. patent
`application Ser. No. 10/162,274, filed Jun. 3, 2002, which is
`incorporated herein fully by reference.
`
`TECHNICAL FIELD
`
`This application is directed generally to wireless commu-
`nications, and is specifically concerned with techniques for
`implementing transmit diversity in a multi-carrier environ-
`ment.
`
`BACKGROUND
`
`The past few years has witnessed the ever-increasing avail-
`ability of relatively cheap, low, power wireless data commu-
`nication services, networks and devices, promising near wire
`speed transmission and reliability. One technology in particu-
`lar, described in the IEEE Standard 802.1 1a (1999) and IEEE
`Draft Standard 802.11g (2002) Supplements to the ANSI/
`IEEE Standard 802.11, 1999 edition, collectively incorpo-
`rated herein fully by reference and collectively referenced as
`“IEEE 802.11a & 802.11g”, has recently been commercial-
`ized with the promise of 54 Mbps+ peak data rates, making it
`a strong competitor to traditional wired Ethernet and the more
`ubiquitous “802.11b” or “WiFi” 11 Mbps wireless transmis-
`sion standard.
`
`IEEE 802.11a & 802.11g compliant transmission systems
`achieve their high data transmission rates using a type of
`multicarrier frequency domain symbol encoding or modula-
`tion known as Orthogonal Frequency Division Multiplexing,
`(“OFDM”). In particular, OFDM encoded symbols mapped
`up to 64 QAM multicarrier constellation bear the data
`intended for transmission, though even larger constellations
`are contemplated to further increase data throughput. Before
`final power amplification and transmission, these OFDM
`encoded symbols are converted into the time domain using
`Inverse Fast Fourier Transform techniques resulting in a rela-
`tively high-speed time domain signal with a large peak-to-
`average ratio (PAR).
`One concern with the IEEE 802.11a & 802.11g standards
`is the rather strict power levels compliant transmission equip-
`ment must operate within without running afoul of FCC and
`international intraband and interband interference limits, par-
`ticularly at lower channels within the 5 GHZ band for North
`American operation. Accordingly, standards compliant trans-
`mission equipment designers continue to seek ways to
`improve reception performance without needing to increase
`power output of the transmitter. One cost effective technique
`that has surprisingly not been explored in IEEE 802.11a/
`802.11g, is the concept of transmit diversity used in single
`carrier systems. See e. g., S. M. Alamouti, “A Simple Transmit
`Diversity Technique For Wireless Communications,” IEEE
`Journal on Select Areas in Communications, vol. 16, no. 8,
`October 1998, pp. 1451-1458 which is incorporated herein
`fully by reference. Transmit diversity provides a diversity
`gain without multiple receiver chains as well as reduced
`power output from each transmitter since, for a constant total
`radiated power, the transmitted signals of interest are broad-
`cast over two separately positioned antennas using two dif-
`ferent RF transmission pathways at 1/2 power. This 3-dB
`reduction for each transmitting amplifier permits use of less
`expensive and less linear power amplifiers yet retain if not
`improve overall reception performance. However, in order to
`
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`Diversity aware reception in accordance with an embodi-
`ment of the invention includes utilizing a receiver to receive a
`time domain signal which may define both a multicarrier
`frequency domain symbol and a modified symbol based on
`such multicarrier frequency domain symbol. A conversion
`unit is employed to generate a composite signal in the fre-
`quency domain based on this time domain signal which
`includes at least an incomplete analog sum ofthe multicarrier
`frequency domain symbol and the modified symbol. There-
`after, a space frequency decoder is used to recover a corrected
`multicarrier frequency domain symbol from this composite
`signal.
`A data packet according to an embodiment ofthe invention
`includes a first portion defining a transmission diversity
`semaphore, a second portion adjacent to the first portion and
`including a preamble to enable training of a receiver receiving
`the data packet, and a third portion following the second
`portion defining a payload. Here the payload includes a plu-
`rality of data symbol pairs with at least one ofthe data symbol
`pairs defining a first symbol capable of being transmitted by
`a first transmission unit of a diversity transmitter, and a sec-
`
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`

`

`US 7,577,085 B1
`
`3
`ond symbol capable of being transmitted by a second trans-
`mission unit of the diversity transmitter, wherein the second
`symbol is derived from the first symbol.
`In accordance with these embodiments, a given multicar-
`rier frequency domain symbol or first symbol may conve-
`niently include an OFDM encoded symbol encoded in com-
`pliance with at least one of the IEEE Standard 802.11a and
`IEEE Standard 802.11g Supplements to the IEEE Standard
`802.11 (1999) for wireless communications. The correspond-
`ing modified symbol or second symbol may conveniently
`include a re-ordered subcarrier complex conjugate of the
`given multicarrier frequency domain symbol to enable rela-
`tively fast and predictable space frequency encoding and
`decoding activities.
`Additional aspects and advantages of this invention will be
`apparent from the following detailed description of embodi-
`ments thereof, which proceeds with reference to the accom-
`panying drawings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a known PLCP frame format compliant with IEEE
`802.11a & 802.11g standards.
`FIG. 2 is a data packet format according to an embodiment
`of the invention.
`
`FIG. 3 is a simplified block diagram of a transmitter
`capable oftransmitting a data packet formatted in accordance
`with FIG. 2.
`
`FIG. 4 is a simplified block diagram ofa receiver capable of
`receiving a data packet formatted in accordance with FIG. 2.
`FIG. 5 is a block diagram of a wireless transceiver incor-
`porating the transmitter and receiver described in FIG. 3 and
`FIG. 4 respectively.
`FIG. 6 is a flowchart illustrating transmit processing con-
`sistent with the transmitter of FIG. 3.
`
`FIG. 7 is a flowchart illustrating receive processing consis-
`tent with the receiver of FIG. 4.
`
`DETAILED DESCRIPTION OF THE
`EMBODIMENTS
`
`In order to better understand transmit diversity according
`to the present invention, discussion of the Physical Layer
`Control Protocol (“PLCP”) frame format used to convey data
`in packet form (i.e. a type of data packet) in a IEEE 802.11a
`and/or 802.11g environment is deemed appropriate. FIG. 1.
`illustrates the general organization or format of a PLCP frame
`according to the IEEE 802.1 1a & 802.1 1 g standards. The
`PLCP preamble 110 includes 10 short training symbols in
`order for an incident receiver to self-adjust the gain of the
`received baseband signal so that the received signal’s ampli-
`tude is within the optimal range for analog-to-digital conver-
`sion, recover OFDM symbol timing and initiate coarse carrier
`signal frequency acquisition as is well known in the art. PLCP
`preamble 110 also includes two long training symbols fol-
`lowing the 10 short training symbols which again allows the
`receiver to estimate the carrier channel being used, as well as
`any needed fine frequency acquisition.
`In essence,
`the
`receiver uses these long symbols for fine tuning ofthe training
`occurring during the previous 10 short symbols. With this
`preamble, it takes approximately 16 microseconds to train the
`receiver after first receiving the frame.
`Still referring to FIG. 1, following the PLCP preamble 110
`is the Signal field 115, which encodes the data rate ofthe data
`field 135 portion of the frame, followed by a Reserved bit set
`to zero under the existing IEEE 802.1 1a & 802.1 1g standards,
`a 12-bit Link field which identifies the number of octets in the
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`
`frame, a parity bit to ensure that the first 17 bits of the frame
`Signal field (Rate, Reserved, and Link fields) have even parity
`and a 6-bit tail which is set to all zeroes. The Signal field 115
`forms a first portion ofthe PLCP header 155 ofthe frame 100.
`As will be discussed in more detail below, for backwards
`compatibility purposes in accordance with the embodiment
`of the invention shown in FIG. 2, the Signal field 215 of data
`packet format 200 differs from the Signal field 115 in that the
`Reserved bit will contain a transmit diversity semaphore indi-
`cating to a transmit diversity aware receiver consistent with
`the present invention (herein “TX diversity receiver”) such as
`receiver 400 discussed below whether or not transmit diver-
`
`sity has been enabled. The Signal field 115 is convolutionally
`encoded at 6 megabits per second using Binary Phase-Shift
`Keying (BPSK) no matter what the data rate the Signal field
`indicates.
`
`A first portion ofthe data field 135 immediately follows the
`Signal field 115. This data field referred to in the figure as
`DATAl 120. More commonly known as the Service field, this
`field consists of 16 bits, with the first seven bits as zeros to
`synchronize the descrambler in the IEEE 802.11a & 802.1 1g
`compliant receiver and the remaining nine bits reserved for
`future use and set to zero. Together with the Signal field 115,
`the DATAl/Service field 120 form the PLCP header 155.
`DATA2 125, DATA3 130 .
`.
`. DATAN 140 represent the
`payload or PSDU (“PLCP Service Data Unit”) 150 portion of
`the PLCP frame. It should be noted that DATA2 125, DATA3
`130 .
`.
`. DATAN 140 each comprise an OFDM symbol trans-
`mitted using BPSK and QAM depending on the chosen data
`rate as presented in the following table:
`
`Data
`Coding
`Rate Modu-
`Rate
`(Mbps) lation
`1/2
`6
`BPSK
`3/4
`9
`BPSK
`1/2
`12
`QPSK
`3/4
`18
`QPSK
`24
`16-QAM 1/2
`36
`16-QAM 3/4
`48
`64—QAM 2/3
`54
`64—QAM 3/4
`
`Coded Bits
`per Sub-
`carrier
`1
`1
`2
`2
`4
`4
`6
`6
`
`Data Bits
`Code Bits
`per OFDM per OFDM
`Symbol
`Symbol
`48
`24
`48
`3 6
`96
`48
`96
`72
`192
`96
`192
`144
`288
`192
`288
`216
`
`During actual transmission a data scrambler using 127-bit
`sequence generator scrambles all the bits in the data field 135
`to randomize the bit patterns in order to avoid long streams of
`ones and zeros.
`
`Immediately following the payload or PSDU 150 is a tail
`and pad portion 145 ofthe PLCP frame. The tail field includes
`a bit string of 6 “zero” bits to return the convolutional encoder
`to a “zero” state. (The 6 scrambled “zero” bits in the tail field
`are replaced by 6 nonscrambled “zero” bits.) Subsequently, a
`variable length pad field is appended in order to extend the
`resulting bit string so that the resulting length will correspond
`to an integer number of OFDM symbols for transmission at
`the established data rate.
`
`In contrast to FIG. 1, a data packet format 200 (proposed as
`an “alternative” PLCP frame format to accommodate trans-
`
`mit diversity according to the present invention) according to
`an embodiment of the invention will now be detailed with
`
`respect to FIGS. 2, 3 and the flowchart of FIG. 6. Turning first
`to FIG. 2, the novel packet format 200 begins with a standards
`compliant PLCP preamble 110. The PLCP preamble 110 in
`this embodiment is used for the same receiver training pur-
`poses as described above with reference to FIG. 1. The Signal
`field 215, which immediately follows the standards compliant
`
`
`
` AZX-I
`%
` T 1009
`HUAW 4'.
`
`
`
`VS.
`SPI—I
`HUAW 4'.
`
`
`
`000010
`
`HUAWEI EXHIBIT 1009
`HUAWEI VS. SPH
`
`000010
`
`

`

`US 7,577,085 B1
`
`6
`In the present embodiment, though not required, the sec-
`ond preamble 218 includes two long training symbols in
`sequence. In particular, the first long training symbol is con-
`templated to be used by a TX diversity receiver for coarse
`AGC adjustment to quickly attenuate the received signal
`broadcast by the second transmission unit of an originating
`TX diversity transmitter in case there may be strong differ-
`ence in experienced gain between it and that previously
`encountered when receiving from the first transmission unit
`of such transmitter. The second long training symbol of the
`second preamble 218 is used to help this receiver estimate the
`channel transfer function from the second transmission unit
`
`5
`PLCP preamble 110, is generally similar to the Signal field
`115 described above. However, the Signal field 215 also
`includes a binary semaphore or flag TXDIV 217, which occu-
`pies the currently Reserved bit of the standards compliant
`Signal field 115. A TXDIV:TRUE setting indicates that the
`data packet follows the diversity data packet format 200. The
`advantage of using the Reserved bit ensures that legacy stan-
`dards compliant transceivers encountering or intercepting a
`data packet formatted in accordance with the format 200 will
`correctly train to the PLCP preamble 110 and perceive the
`Signal field 215, but ignore it if the TXDIV flag 217 is set,
`because these legacy devices will perceive such packet as
`being erroneous and, consistent with existing IEEE 802.1 la
`& 802.1 lg standards, will not attempt further decoding or
`recovery operations. At
`the same time, a TX diversity
`receiver, such as receiver 400 discussed below, will include
`appropriate logic to watch for and correctly interpret the
`TXDIV semaphore 217.
`As discussed above, the data packet format 200 of the
`present embodiment as well as the transmitter 300 and
`receiver 400 described below attempt to accommodate legacy
`devices compliant with the IEEE 802.1 la & 802.11 g stan-
`dards. To that end, as noted in FIG. 6, a preliminary determi-
`nation is made whether a transmitter incorporating transmit
`diversity consistent with the present invention (“TX diversity
`transmitter”), such as transmitter 300 shown in FIG. 3, should
`transmit a frame/packet using the data packet format 200
`(Step 610). This may be accomplished through appropriate
`application of user pre-selection, negotiation or handshaking
`techniques as is well known in the art. Alternatively, a default
`action would be to assume that the intended receiver is
`
`arranged in accordance with transmit diversity techniques
`consistent with the present invention, and if no acknowledge-
`ment is received of the packet transmitted in accordance with
`FIG. 2, the data will be retransmitted in accordance with the
`known format 100, and further transmission attempts will
`remain standards compliant using a single transmission unit
`such as the first transmission unit 350 of the transmitter 300,
`unless overridden in the future through e.g. specific device
`request or user selection.
`It should be noted that in accordance with the packet format
`200 shown in FIG. 2, both the PLCP preamble and the Signal
`field 215 are contemplated for transmission on the first of two
`transmission units of a TX diversity transmitter, such as the
`first one 350 of the transmission units 350 and 360 of the
`
`transmitter 300 shown in FIG. 3, again for backwards com-
`patibility reasons. In the packet format 200 shown in FIG. 2,
`the notation “TX I” in a given field or portion of the data
`packet 200 means that this portion will be transmitted on a
`first transmission unit of a TX diversity transmitter, such as
`transmission unit 350 shown in FIG. 3, whereas the notation
`“TX2” means that so-labeled portions will be transmitted by
`a second transmission unit of such TX diversity transmitter,
`such as transmission unit 360.
`
`Immediately following the Signal field 215 in the packet
`format 200 is a second training preamble 218. It should be
`noted that the second preamble 218 has no analogue in the
`standards compliant format 100. This second preamble 218 is
`contemplated for transmission by a second transmission unit
`of a TX diversity transmitter (e.g. second transmission unit
`360 of the transmitter 300 shown in FIG. 3). The purpose of
`this second preamble 200 is to permit a TX diversity receiver
`(e.g. receiver 400, FIG. 4) to re-estimate the potentially dif-
`ferent signal characteristics between the second transmission
`unit and the receiver (step 625, FIG. 6) relative to the first
`transmission unit.
`
`10
`
`15
`
`20
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`25
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`30
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`40
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`45
`
`50
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`65
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`to the receiving antenna.
`Referring to FIG. 2, immediately following the second
`preamble is the data field 250 of the data packet 200 of the
`present embodiment. It should be noted that OFDM encoded
`symbols presented in the data field are modulated at the rate
`specified in the Signal field 215 in a manner similar to that
`specified for the standards compliant Signal field 115. As
`shown in FIG. 2 and as referenced in step 630 of FIG. 6, the
`Service field/DATAl 120 and its space-frequency analogue
`DATAlN 220 are transmitted twice in succession by both the
`first and second transmission units of the TX diversity trans-
`mitter in parallel. In this embodiment, the data symbol pair
`DATA1 120 and DATA1' 220 are transmitted at approximately
`the same time. The first transmitted pair is used by a TX
`diversity receiver such as receiver 400 to further refine auto-
`matic gain control after the coarse adjustment with reference
`to the first long training symbol of the second preamble 218
`has been performed. The second or retransmitted pair of the
`Service field 120 and its space-frequency analogue DATAlN
`220 is actually demodulated according to the space-fre-
`quency decoding technique noted below and its contents
`recovered by this receiver.
`The actual payload or PSDU portion 255 ofthe data packet
`format 200 will now be discussed with reference to FIGS. 2,
`3 and 6. Similar to the known PLCP frame 100, the present
`PLCP frame 200 includes the payload transmitted in modu-
`lated, OFDM symbol encoded form. It should be noted that
`OFDM symbols DATA2 125, DATA3 130 .
`.
`. DATAN 140, as
`well as the Service field/DATA1 120, are transmitted by a first
`transmission unit of a TX diversity transmitter unmodified
`from their presentation in accordance with known format
`100. However, unlike PLCP frame format 100,
`the data
`packet format 200 also envisions at least substantially parallel
`transmission of modified DATA2N 225, DATA3N 230 .
`.
`.
`DATANN 240, as well as the modified Service field or
`DATAlN 220 at approximately the same time as their
`unmodified counterpart symbols by the second transmission
`unit of a this TX diversity transmitter. Thus, generally, in the
`payload 255 of the data packet format 200, each data symbol
`pair consisting of an OFDM encoded symbol (e.g. a given
`OFDM symbol DATAK) and its corresponding space fre-
`quency modified symbol (e.g. DATAK') is transmitted at
`approximately the same time over the first and second trans-
`mission units of a TX diversity transmitter.
`According to FIG. 2, assuming the given OFDM symbol
`DATAK is to be transmitted in the Data field 250 of a packet
`conforming to packet format 200 by the transmitter 300, the
`first transmission unit 350 would transmit DATAK unmodi-
`fied. The modified form of the symbol, DATAKN will be
`transmitted over the second transmission unit 360 approxi-
`mately the same time if not concurrently. Herein, DATAKN
`differs from DATAK in that the 52 frequency domain subcar-
`rier constellation points forming the OFDM encoded symbol
`DATAK are presented in complex conjugate form and are
`resequenced in pairs. Finally, the magnitude of the first sub-
`
`
`
`
` AZX-I
`%
`I-IUAW 4'.
`T 1009
`
`
`
`HUAW 4'.
`
`000011
`
`
`
`VS.
`
`SPI—I
`
`HUAWEI EXHIBIT 1009
`HUAWEI VS. SPH
`
`000011
`
`

`

`US 7,577,085 B1
`
`7
`carrier constellation point ofeach pair is multiplied by —l . For
`example, if DATAK comprises the following sequence of sub-
`carrier symbols:
`
`subcarrier
`subsymbol of DATAK
`
`l
`A
`
`2
`B
`
`3
`C
`
`4
`D
`
`The subsymbols of DATAKN would be transformed as fol-
`lows:
`
`subcarrier
`constellationpointofDATAKN
`
`l
`—B*
`
`2
`A*
`
`3
`—D*
`
`4
`C*
`
`...52
`...AY*
`
`As shown in FIG. 3, a space frequency encoder 315 such as
`that detailed in the aforementioned Alamouti_reference is
`used to accomplish this transformation. This transformation
`is believed necessary in order for a TX diversity receiver to
`receive and recover both symbols DATAK and DATAKN pre-
`sented simultaneously on a common channel/carrier fre-
`quency, since in many instances both DATAK and DATAKN
`will be perceived as part of a composite signal. As shown in
`Alamouti, transmission ofthe same data points A, B, .
`.
`. ,AZ
`according to the this space-frequency code can achieve a
`second order diversity gain with one receive antenna. Thus,
`the reliability of the transmission is increased.
`It should be noted that a corresponding space frequency
`decoder provided within the receiver 400 in order to recover
`the OFDM encoded symbol DATAK from a possible compos-
`ite signal combining DATAK and DATAKN. In accordance
`with the data packet format 200 shown in FIG. 2, the space
`frequency encoding and parallel transmission of DATAK and
`DATAKN continues until the end of the Data field 250 has
`been reached. See e.g., step 637, step 645 through 655 shown
`in FIG. 6 (note that step 655 and 660 are executed in a
`substantially parallel manner).
`The data packet format 200 according to the present
`embodiment of the invention terminates with the tail and pad
`field discussed above.
`
`Turning now to FIG. 3, it should be noted that the trans-
`mitter 300 receives baseband OFDM symbols for RF trans-
`mission from the symbol encoder 520 shown in FIG. 5. These
`OFDM symbols are encoded in the freque