111111
`
`1111111111111111111111111111111111111111111111111111111111111111111111111111
`US 20030043928Al
`
`(19) United States
`(12) Patent Application Publication
`Ling et al.
`
`(10) Pub. No.: US 2003/0043928 Al
`Mar. 6, 2003
`(43) Pub. Date:
`
`(54) CODING SCHEME FORA WIRELESS
`COMMUNICATION SYSTEM
`
`(76)
`
`Inventors: Fuyun Ling, San Diego, CA (US);
`Nagabhushana T. Sindhushayana, San
`Diego, CA (US); Jay R. Walton,
`Westford, MA (US); Mark Wallace,
`Bedford, MA (US); Ivan Fernandez,
`San Diego, CA (US)
`
`Correspondence Address:
`QUALCOMM Incorporated
`Attn: Patent Department
`5775 Morehouse Drive
`San Diego, CA 92121-1714 (US)
`
`(21) Appl. No.:
`
`09/776,073
`
`(22) Filed:
`
`Feb. 1,2001
`
`Publication Classification
`
`(51)
`
`Int. CI? ....................................................... H04B 7/02
`
`(52) U.S. Cl. ............................................ 375/267; 375/347
`
`(57)
`
`ABSTRACT
`
`Coding techniques for a (e.g., OFDM) communication sys(cid:173)
`tem capable of transmitting data on a number of "transmis(cid:173)
`sion channels" at different information bit rates based on the
`channels' achieved SNR. Abase code is used in combination
`with common or variable puncturing to achieve different
`coding rates required by the transmission channels. The data
`(i.e., information bits) for a data transmission is encoded
`with the base code, and the coded bits for each channel (or
`group of channels with the similar transmission capabilities)
`are punctured to achieve the required coding rate. The coded
`bits may be interleaved (e.g., to combat fading and remove
`correlation between coded bits in each modulation symbol)
`prior to puncturing. The unpunctured coded bits are grouped
`into non-binary symbols and mapped to modulation symbols
`(e.g., using Gray mapping). The modulation symbol may be
`"pre-conditioned" and prior to transmission.
`
`110
`~
`
`112
`
`114
`
`116
`
`117
`
`150
`,...-
`
`SONY EX. 1004
`Page 1
`
`

`
`00
`N
`'0
`~
`c c
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`'JJ. =(cid:173)~
`8
`N c
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`~
`
`~ ..... .... 0 =
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`~
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`~ = .....
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`""C
`
`I")
`
`I")
`
`FIG.1
`
`DE MOD
`
`: 154r
`•
`
`: 122t
`•
`
`DEMOD r-:::1 p MIMO 1-+1 Calculatio
`
`158
`
`rocessor
`
`·~ 156
`
`152a
`
`v
`
`Processor
`
`MIMO
`
`120
`
`118
`
`124a
`
`164
`
`162
`
`~
`150
`
`Deinterleaver
`
`Puncturer
`
`Channel
`
`160
`
`De-
`
`159
`
`117
`
`116
`
`114
`
`112
`
`100
`
`~
`110
`
`SONY EX. 1004
`Page 2
`
`

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`ts 9
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`ts 8
`
`ts 7
`
`ts 6
`
`ts 5
`
`ts 4
`
`ts 3
`
`ts 2
`
`ts 1
`
`FIG. 2
`
`sub-channel 16
`sub-channel15
`
`sub-channel 14
`
`sub-channel13
`sub-channel 12
`
`sub-channel 11
`sub-channel 1 0
`sub-channel 9
`sub-channel 8
`sub-channel 7
`
`sub-channel 6
`
`sub-channel 5
`
`sub-channel 4
`
`sub-channel 3
`sub-channel 2
`
`sub-channel1
`
`____,. OFDM symbol..--
`
`~
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`~ c:
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`"'Tl
`
`SONY EX. 1004
`Page 3
`
`

`
`Patent Application Publication Mar. 6, 2003 Sheet 3 of 10
`
`US 2003/0043928 Al
`
`114x
`r---------C---------1
`:
`312a
`I
`I
`lnformation_..._ __ ,__ __ 4>1 Constituent
`Bits
`Encoder 1
`
`1
`I
`~~~~
`1
`......,...._ ....
`1
`
`116
`
`Code
`lnterleaver
`
`314
`
`312b
`
`L--.---.....r Constituent
`Encoder2
`1
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`- - - - - - - - - - - _'-_-_-_-_-_-_~ __ I
`FIG. 3A
`
`YiNT
`
`.z;NT
`
`XINT - - - - - - - - - - - - - - - - - - .
`
`YiNT __ __...._
`
`342
`
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`
`Unpunctured
`Coded Bits
`
`346
`
`2 X 1
`MUX
`
`352
`
`p
`
`Q
`
`348
`
`Toggle
`
`356
`
`Decision
`Unit
`
`Reset
`
`354
`
`358
`
`Increment
`Counter
`
`=(0-1)
`
`Q
`
`FIG. 3C
`
`SONY EX. 1004
`Page 4
`
`

`
`Patent Application Publication
`
`Mar. 6, 2003 Sheet 4 of 10
`
`US 2003/0043928 Al
`
`,_
`Q) Q)
`c >
`c
`CIS
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`SONY EX. 1004
`Page 5
`
`

`
`Patent Application Publication Mar. 6, 2003 Sheet 5 of 10
`
`US 2003/0043928 Al
`
`(
`
`Start
`
`+
`
`Determine SNR for each
`transmission channel
`
`+
`
`Determine number of information
`bits per modulation symbol
`supported by each transmission
`channel based on its SNR
`
`•
`Select a modulation scheme for lr 416
`each transmission channel
`+
`
`I' 412
`
`I' 414
`
`lr 418
`
`Determine total number of
`information bits supported by
`all transmission channels
`
`+
`
`Determine total number of
`coded bits for modulation
`schemes selected for all
`transmission channels
`t
`Code total number of
`information bits with encoder
`t
`Puncture parity bits to obtain the lr 424
`required total number of coded bits
`t
`Map the unpunctured coded
`bits to modulation symbols
`for the transmission channels
`J
`End
`
`r 420
`
`II' 422
`
`426
`lr
`
`FIG. 4A
`
`SONY EX. 1004
`Page 6
`
`

`
`Patent Application Publication Mar. 6, 2003 Sheet 6 of 10
`
`US 2003/0043928 Al
`
`Start
`!
`Determine SNR for each
`transmission channel
`
`modulation symbol supported by each
`transmission channel based on its SNR
`
`Select a modulation scheme
`for each transmission channel
`
`+
`Determine number of information bits per v
`+
`..
`
`v 432
`
`434
`
`r 436
`
`lr 438
`
`Group transmission channels belonging
`to the same SNR range into a segment
`
`+
`•
`+
`to each transmission channel of segment i v 444
`+
`
`lr 440
`
`f 442
`
`446
`r
`
`448
`
`r
`
`Determine total number of information
`bits and total number of coded bits that
`can be transmitted in each segment
`
`Code the information bits
`for all segments with encoder
`
`Assign Ni information bits and N/R parity bits
`
`Puncture the N/R parity bits to obtain
`the Pi parity bits required for each
`transmission channel of segment i
`
`+
`
`Map the Ni+Pi coded bits in each transmission
`channel of segment i to form modulation
`symbol for the transmission channel
`
`c
`
`+
`
`End
`
`FIG. 48
`
`SONY EX. 1004
`Page 7
`
`

`
`Patent Application Publication Mar. 6, 2003 Sheet 7 of 10
`
`US 2003/0043928 Al
`
`0000 •
`
`0100 •
`
`• 1100
`
`• 1000
`
`0001 •
`
`0101 •
`
`• 1101
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`0011 •
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`~
`512
`
`• 1111
`
`• 1011
`
`0010 •
`
`0110 •
`
`• 1110
`
`• 1010
`
`FIG. 5
`
`SONY EX. 1004
`Page 8
`
`

`
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`
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`Cyclic Prefix
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`r----------------~-----------------1 1----------_...,!.----------1
`
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`Symbols
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`SONY EX. 1004
`Page 9
`
`

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`FIG. 7
`
`1---
`
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`• •
`--+ DEMUX •
`
`L
`734k
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`lj2k
`
`Sub-Channel XKL
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`
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`SK1
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`r-
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`
`f-
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`Bits
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`
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`
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`
`110y
`
`SONY EX. 1004
`Page 10
`
`

`
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`
`816
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`
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`L:T Bits
`
`FIG. 8
`
`810b
`
`LLR(x')---+{ +)
`
`Decoder
`
`•I Decoder I--+(~ lnterleaver I
`
`Code
`
`d
`
`812b
`
`LLR(z')
`
`814
`
`LLR(x') I
`
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`
`LLR(y')
`
`Decoded
`
`LLR(z)
`,
`LLR(y')
`LLR(x')
`
`818
`
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`
`.
`Channel
`
`160
`
`Puncturer
`
`-
`
`Calculation
`
`159
`
`1
`
`15Bx
`
`Received --1 B'lt LLR H De
`
`Symbols
`Modulation
`·
`
`.
`
`SONY EX. 1004
`Page 11
`
`

`
`US 2003/0043928 Al
`
`Mar. 6, 2003
`
`1
`
`CODING SCHEME FOR A WIRELESS
`COMMUNICATION SYSTEM
`
`BACKGROUND
`
`[0001]
`
`I. Field
`
`[0002] The present invention relates to data communica(cid:173)
`tion. More particularly, the present invention relates to a
`novel, flexible, and efficient coding scheme for encoding
`data for transmission on multiple transmission channels with
`different transmission capabilities.
`
`[0003]
`
`II. Description of the Related Art
`
`[0004] Wireless communication systems are widely
`deployed to provide various types of communication such as
`voice, data, and so on. These systems may be based on code
`division multiple access (CDMA), time division multiple
`access (TDMA), orthogonal frequency division modulation
`(OFDM), or some other modulation techniques. OFDM
`systems may provide high performance for some channel
`environments.
`
`[0005]
`In an OFDM system, the operating frequency band
`is effectively partitioned into a number of "frequency sub(cid:173)
`channels", or frequency bins. Each subchannel is associated
`with a respective subcarrier upon which data is modulated,
`and may be viewed as an independent "transmission chan(cid:173)
`nel". Typically, the data to be transmitted (i.e., the informa(cid:173)
`tion bits) is encoded with a particular coding scheme to
`generate coded bits. For a high-order modulation scheme
`(e.g., QPSK, QAM, and so on), the coded bits are grouped
`into non-binary symbols that are then used to modulate the
`subcarriers.
`
`[0006] The frequency subchannels of an OFDM system
`may experience different link conditions (e.g., different
`fading and multipath effects) and may achieve different
`signal-to-noise-plus-interference
`ratio
`(SNR). Conse(cid:173)
`quently, the number of information bits per modulation
`symbol (i.e., the information bit rate) that may be transmit(cid:173)
`ted on each subchannel for a particular level of performance
`may be different from subchannel to subchannel. Moreover,
`the link conditions typically vary with time. As a result, the
`supported bit rates for the subchannels also vary with time.
`
`[0007] The different transmission capabilities of the fre(cid:173)
`quency subchannels plus the time-variant nature of the
`capabilities make it challenging to provide an effective
`coding scheme capable of encoding the supported number of
`information bits/modulation symbol to provide the required
`coded bits for the subchannels
`
`[0008] Accordingly, a high performance, efficient, and
`flexible coding scheme that may be used to encode data for
`transmission on multiple subchannels with different trans(cid:173)
`mission capabilities is highly desirable.
`
`SUMMARY
`
`[0009] Various aspects of the present invention provides
`efficient and effective coding techniques for a communica(cid:173)
`tion system capable of transmitting data on a number of
`"transmission channels" at different information bit rates
`based on the channels achieved SNR. A number of coding/
`puncturing schemes may be used to generate the required
`coded bits (i.e., the information, tail, and parity bits, if a
`Turbo code is used). In a first coding/puncturing scheme, a
`
`particular base code and common puncturing is used for all
`transmission channels (e.g., all frequency subchannels in an
`OFDM system, or spatial subchannels of all frequency
`subchannels in an OFDM svstem with multiple input/mul(cid:173)
`tiple output antennas (MIMO), as described below). In a
`second coding/puncturing scheme the same base code but
`variable puncturing is used for the transmission channels.
`The variable puncturing can be used to provide different
`coding rates for the transmission channels. The coding rate
`for each transmission channel is dependent on the informa(cid:173)
`tion bit rate and the modulation scheme selected for the
`channel.
`
`[0010] An embodiment of the
`invention provides a
`method for preparing data for transmission on a number of
`transmission channels in a communication system. e.g., an
`orthogonal frequency division modulation (OFDM) system.
`Each transmission channel is operable to transmit a respec(cid:173)
`tive sequence of modulation symbols. In accordance with
`the method, the number of information bits per modulation
`symbol supported by each transmission channel is deter(cid:173)
`mined (e.g., based on the channel's SNR). A modulation
`scheme is then identified for each transmission channel such
`that the determined number of information bits per modu(cid:173)
`lation symbol is supported. Based on the supported number
`of information bits per modulation symbol and the identified
`modulation scheme, the coding rate for each transmission
`channel is determined. At least two transmission channels
`are associated with different coding rates because of differ(cid:173)
`ent transmission capabilities.
`
`[0011] Thereafter, a number of information bits is encoded
`in accordance with a particular encoding scheme to provide
`a number of coded bits. If a Turbo code is used a number of
`tail and parity bits are generated for the information bits (the
`coded bits include the information bits, tail bits, and parity
`bits). The coded bits may be interleaved in accordance with
`a particular interleaving scheme. For ease of implementa(cid:173)
`tion, the interleaving may be performed prior to puncturing.
`The coded bits (e.g., the tail and parity bits, if a Turbo code
`is used) are then punctured in accordance with a particular
`puncturing scheme to provide a number of unpunctured
`coded bits for the transmission channels. The puncturing is
`adjusted to achieve different coding rates needed by the
`transmission channels. As an alternative, the puncturing may
`also be performed prior to interleaving.
`[0012] Non-binary symbols are then formed for the trans(cid:173)
`mission channels. Each non-binary symbol includes a group
`of interleaved and unpunctured coded bits and is mapped a
`respective modulation symbol. The specific number of
`coded bits in each non-binary symbol is dependent on the
`channel's modulation scheme. For a multiple-input mul(cid:173)
`tiple-output (MIMO) system capable of transmitting on a
`number of spatial subchannels for each frequency subchan(cid:173)
`nel, the modulation symbols for each frequency subchannel
`may be pre-conditioned prior to transmission, as described
`below.
`[0013] The invention provides methods and system ele(cid:173)
`ments that implement various aspects, embodiments, and
`features of the invention, as described in further detail
`below.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`[0014] The features, nature, and advantages of the present
`invention will become more apparent from the detailed
`
`SONY EX. 1004
`Page 12
`
`

`
`US 2003/0043928 Al
`
`Mar. 6, 2003
`
`2
`
`description set forth below when taken in conjunction with
`the drawings in which like reference characters identify
`correspondingly throughout and wherein:
`[0015] FIG. 1 is a diagram of a multiple-input multiple(cid:173)
`output (MIMO) communication system capable of imple(cid:173)
`menting various aspects and embodiments of the invention;
`[0016] FIG. 2 is a diagram that graphically illustrates an
`OFDM transmission from one of NT transmit antennas in the
`MIMO system;
`[0017] FIGS. 3A and 3B are diagrams of a parallel
`concatenated convolutional encoder;
`[0018] FIG. 3C is a diagram of an embodiment of a
`puncturer and multiplexer, which may be used to provide
`variable puncturing of coded bits;
`[0019] FIGS. 4A and 4B are flow diagrams of two coding/
`puncturing schemes for generating the required coded bits
`for a data transmission, which utilize a particular base code
`but common and variable puncturing schemes, respectively;
`[0020] FIG. 5 is a diagram of a signal constellation for
`16-QAM and a specific Gray mapping scheme;
`[0021] FIG. 6 is a block diagram of an embodiment of a
`MIMO processor;
`[0022] FIG. 7 is a block diagram of an embodiment of a
`system capable of providing different processing for differ(cid:173)
`ent transmissions; and
`[0023] FIG. 8 is a block diagram of an embodiment of the
`decoding portion of a receiving system.
`
`DETAILED DESCRIPTION OF THE SPECIFIC
`EMBODIMENTS
`
`[0024] FIG. 1 is a diagram of a multiple-input multiple(cid:173)
`output (MIMO) communication system 100 capable of
`implementing various aspects and embodiments of the
`invention. Communication system 100 can be designed to
`implement the coding schemes described herein. System
`100 can further be operated to employ a combination of
`antenna, frequency, and temporal diversity to increase spec(cid:173)
`tral efficiency, improve performance, and enhance flexibil(cid:173)
`ity. Increased spectral efficiency is characterized by the
`ability to transmit more bits per second per Hertz (bps/Hz)
`when and where possible to better utilize the available
`system bandwidth. Improved performance may be quanti(cid:173)
`fied, for example, by a lower bit-error-rate (BER) or frame(cid:173)
`error-rate (FER) for a given link signal-to-noise-plus-inter(cid:173)
`ference
`ratio
`(SNR). And enhanced
`flexibility
`is
`characterized by the ability to accommodate multiple users
`having different and typically disparate requirements. These
`goals may be achieved, in part, by employing a high
`performance and efficient coding scheme, multi-carrier
`modulation, time division multiplexing (TDM), multiple
`transmit and/or receive antennas, other techniques, or a
`combination thereof. The features, aspects, and advantages
`of the invention are described in further detail below.
`[0025] As shown in FIG. 1, communication system 100
`includes a first system 110 in communication with a second
`system 150. Within system 110, a data source 112 provides
`data (i.e., information bits) to an encoder 114 that encodes
`the data in accordance with a particular coding scheme. The
`encoding increases the reliability of the data transmission.
`
`The coded bits are then provided to a channel interleaver 116
`and interleaved (i.e., reordered) in accordance with a par(cid:173)
`ticular interleaving scheme. The interleaving provides time
`and frequency diversity for the coded bits, permits the data
`to be transmitted based on an average SNR for the subchan(cid:173)
`nels used for the data transmission, combats fading, and
`further removes correlation between coded bits used to form
`each modulation symbol, as described below. The inter(cid:173)
`leaved bits are then punctured (i.e., deleted) to provide the
`required number of coded bits. The encoding, channel
`interleaving, and puncturing are described in further detail
`below. The unpunctured coded bits are then provided to a
`symbol mapping element 118.
`[0026]
`In an OFDM system, the operating frequency band
`is effectively partitioned into a number of "frequency sub(cid:173)
`channels" (i.e., frequency bins). At each "time slot" (i.e., a
`particular time interval that may be dependent on the band(cid:173)
`width of the frequency subchannel), a "modulation symbol"
`may be transmitted on each frequency subchannel. As
`described in further detail below, the OFDM system may be
`operated in a MIMO mode in which multiple (NT) transmit
`antennas and multiple (N~ receive antennas are used for a
`data transmission. The MIMO channel may be decomposed
`into Nc independent channels, with Nc~NT and Nc~NR.
`Each of the Nc independent channels is also referred to as a
`"spatial subchannel" of the MIMO channel, which corre(cid:173)
`sponds to a dimension. In the MIMO mode, increased
`dimensionality is achieved and Nc modulation symbols may
`be transmitted on Nc spatial subchannels of each frequency
`subchannel at each time slot. In an OFDM system not
`operated in the MIMO mode, there is only one spatial
`subchannel. Each frequency subchannel/spatial subchannel
`may also be referred to as a "transmission channel". The
`MIMO mode and spatial subchannel are described in further
`detail below.
`[0027] The number of information bits that may be trans(cid:173)
`mitted for each modulation symbol for a particular level of
`performance is dependent on the SNR of the transmission
`channel. For each transmission channel, symbol mapping
`element 118 groups a set of unpunctured coded bits to form
`a non-binary symbol for that transmission channel. The
`non-binary symbol is then mapped to a modulation symbol,
`which represents a point in a signal constellation corre(cid:173)
`sponding to the modulation scheme selected for the trans(cid:173)
`mission channel. The bit grouping and symbol mapping are
`performed for all transmission channels, and for each time
`slot used for data transmission. The modulation symbols for
`all transmission channels are then provided to a MIMO
`processor 120.
`[0028] Depending on the particular "spatial" diversity
`being implemented (if any), MIMO processor 120 may
`demultiplex, pre-condition, and combine the received modu(cid:173)
`lation symbols. The MIMO processing is described in fur(cid:173)
`ther detail below. For each transmit antenna, MIMO pro(cid:173)
`cessor 120 provides a stream of modulation symbol vectors,
`one vector for each time slot. Each modulation symbol
`vector includes the modulation symbols for all frequency
`subchannels for a given time slot. Each stream of modula(cid:173)
`tion symbol vectors is received and modulated by a respec(cid:173)
`tive modulator (MOD) 122, and transmitted via an associ(cid:173)
`ated antenna 124.
`[0029]
`In the embodiment shown in FIG. 1, receiving
`system 150 includes a number of receive antennas 152 that
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`
`3
`
`receive the transmitted signals and provide the received
`signals to respective demodulators (DEMOD) 154. Each
`demodulator 154 performs processing complementary to
`that performed at modulator 122. The demodulated symbols
`from all demodulators 154 are provided to a MIMO pro(cid:173)
`cessor 156 and processed in a complementary manner as that
`performed at MIMO processor 120. The received symbols
`for the transmission channels are then provided to a bit
`calculation unit 158 that performs processing complemen(cid:173)
`tary to that performed by symbol mapping element 118 and
`provides values indicative of the received bits. Erasures
`(e.g., zero value indicatives) are then inserted by a de(cid:173)
`puncturer 159 for coded bits punctured at system 110. The
`de-punctured values are then deinterleaved by a channel
`deinterleaver 160 and further decoded by a decoder 162 to
`generate decoded bits, which are then provided to a data sink
`164. The channel deinterleaving, de-puncturing, and decod(cid:173)
`ing are complementary to the channel interleaving, punc(cid:173)
`turing, and encoding performed at the transmitter.
`
`[0030] FIG. 2 is a diagram that graphically illustrates an
`OFDM transmission from one of NT transmit antennas in a
`MIMO system. In FIG. 2, the horizontal axis represents time
`and the vertical axis represents frequency. In this specific
`example, the transmission channel includes 16 frequency
`subchannels and is used to transmit a sequence of OFDM
`symbols, with each OFDM symbol covering all 16 fre(cid:173)
`quency subchannels. A time division multiplexing (TDM)
`structure is also illustrated in which the data transmission is
`partitioned into time slots, with each time slot having a
`particular duration. For the example shown in FIG. 2, the
`time slot is equal to the length of one modulation symbol.
`
`[0031] The available frequency subchannels may be used
`to transmit signaling, voice, packet data, and so on. In the
`specific example shown in FIG. 2, the modulation symbol at
`time slot 1 corresponds to pilot data, which may be peri(cid:173)
`odically transmitted to assist the receiver units synchronize
`and perform channel estimation. Other techniques for dis(cid:173)
`tributing pilot data over time and frequency may also be
`used. Transmission of the pilot modulation symbol typically
`occurs at a particular rate, which is usually selected to be fast
`enough to permit accurate tracking of variations in the
`communication link.
`
`[0032] The time slots not used for pilot transmissions can
`be used to transmit various types of data. For example,
`frequency subchannels 1 and 2 may be reserved for the
`transmission of control and broadcast data to the receiver
`units. The data on these subchannels is generally intended to
`be received by all receiver units. However, some of the
`messages on the control channel may be user specific, and
`may be encoded accordingly.
`
`[0033] Voice data and packet data may be transmitted in
`the remaining frequency subchannels. For the example
`shown, subchannel 3 at time slots 2 through 9 is used for
`voice call 1, subchannel 4 at time slots 2 through 9 is used
`for voice call 2, subchannel 5 at time slots 5 through 9 is
`used for voice call 3, and subchannel 6 at time slots 7
`through 9 is used for voice call 5.
`
`[0034] The remaining available frequency subchannels
`and time slots may be used for transmissions of traffic data.
`A particular data transmission may occur over multiple
`subchannels and/or multiple time slots, and multiple data
`transmissions may occur within any particular time slot. A
`data transmission may also occur over non-contiguous time
`slots.
`
`In the example shown in FIG. 2, data 1 transmis(cid:173)
`[0035]
`sion uses frequency subchannels 5 through 16 at time slot 2
`and subchannels 7 through 16 at time slot 7, data 2 trans(cid:173)
`mission uses subchannels 5 through 16 at time slots 3 and 4
`and subchannels 6 through 16 at time slots 5, data 3
`transmission uses subchannels 6 through 16 at time slot 6,
`data 4 transmission uses subchannels 7 through 16 at time
`slot 8, data 5 transmission uses subchannels 7 through 11 at
`time slot 9, and data 6 transmission uses subchannels 12
`through 16 at time slot 9. Data 1 through 6 transmissions can
`represent transmissions of traffic data to one or more
`receiver units.
`
`[0036] To provide the transmission flexibility and achieve
`high performance and efficiency, each frequency subchannel
`at each time slot for each transmit antenna may be viewed
`as an independent unit of transmission (a modulation sym(cid:173)
`bol) that may be used to transmit any type of data such as
`pilot, signaling, broadcast, voice, traffic data, some other
`data type, or a combination thereof. Flexibility, perfor(cid:173)
`mance, and efficiency may further be achieved by allowing
`for
`independence among the modulation symbols, as
`described below. For example, each modulation symbol may
`be generated from a modulation scheme (e.g., M-PSK,
`M-QAM, or some other scheme) that results in the best use
`of the resource at that particular time, frequency, and space.
`
`[0037] MIMO System
`
`In a terrestrial communications system (e.g., a
`[0038]
`cellular system, a broadcast system, a multi-channel multi(cid:173)
`point distribution system (MMDS) system, and others), an
`RF modulated signal from a transmitter unit may reach the
`receiver unit via a number of transmission paths. The
`characteristics of the transmission paths typically vary over
`time due to a number of factors. If more than one transmit
`or receive antenna is used, and if the transmission paths
`between the transmit and receive antennas are linearly
`independent (i.e., one transmission is not formed as a linear
`combination of the other transmissions), which is generally
`true to at least an extent, then the likelihood of correctly
`receiving the transmitted signal increases as the number of
`antennas increases. Generally, as the number of transmit and
`receive antennas increases, diversity increases and perfor(cid:173)
`mance improves.
`
`[0039] A MIMO communication system such as the one
`shown in FIG. 1 employs antennas at both the transmit and
`receive ends of the communication link. These transmit and
`receive antennas may be used to provide various forms of
`"spatial diversity",
`including "transmit" diversity and
`"receive" diversity. Spatial diversity is characterized by the
`use of multiple transmit antennas and one or more receive
`antennas. Transmit diversity is characterized by the trans(cid:173)
`mission of data over multiple transmit antennas. Typically,
`additional processing is performed on the data transmitted
`from the transmit antennas to achieved the desired diversity.
`For example, the data transmitted from different transmit
`antennas may be delayed or reordered in time, coded and
`interleaved across the available transmit antennas, and so on.
`Receive diversity is characterized by the reception of the
`transmitted signals on multiple receive antennas, and diver(cid:173)
`sity is achieved by simply receiving the signals via different
`signal paths.
`
`[0040] Spatial diversity may be used to improve the reli(cid:173)
`ability of the communication link with or without increasing
`the link capacity. This may be achieved by transmitting or
`receiving data over multiple paths via multiple antennas.
`Spatial diversity may be dynamically selected based on the
`
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`4
`
`characteristics of the communication link to provide the
`required performance. For example, higher degree of spatial
`diversity may be provided for some types of communication
`(e.g., signaling), for some types of services (e.g., voice), for
`some communication link characteristics (e.g., low SNR), or
`for some other conditions or considerations.
`
`[0041] The data may be transmitted from multiple anten(cid:173)
`nas and/or on multiple frequency subchannels to obtain the
`desired diversity. For example, data may be transmitted on:
`(1) one subchannel from one antenna, (2) one subchannel
`(e.g., subchannel 1) from multiple antennas, (3) one sub(cid:173)
`channel from all NT antennas, ( 4) a set of subchannels (e.g.,
`subchannels 1 and 2) from one antenna, (5), a set of
`subchannels from multiple antennas, ( 6) a set of subchannels
`from all NT antennas, or (7) a set of channels from a set of
`antennas (e.g., subchannel1 from antennas 1 and 2 at one
`time slot, subchannels 1 and 2 from antenna 2 at another
`time slot, and so on). Thus, any combination of subchannels
`and antennas may be used to provide antenna and frequency
`diversity.
`
`In the MIMO communication system, the multi(cid:173)
`[0042]
`input multi-output channel can be decomposed into a set of
`Nc independent spatial subchannels. The number of such
`spatial subchannels is less than or equal to the lesser of the
`number of the transmitting antennas and the number of
`receiving antennas (i.e., Nc~NT and Nc~N~. If H is the
`N xNT matrix that gives the channel response for the NT
`tr~nsmit antennas and the NR receive antennas at a specific
`time, and x is the NT-vector inputs to the channel, then the
`received signal can be expressed as:
`
`[0043] where !! is an NR-vector representing noise plus
`interference. In one embodiment, the eigenvector decompo(cid:173)
`sition of the Hermitian matrix formed by the product of the
`channel matrix with
`its conjugate-transpose can be
`expressed as:
`
`[0044] where the symbol"*" denotes conjugate-transpose,
`E is the eigenvector matrix, and A is a diagonal matrix of
`eigenvalues, both of dimension NTxNT.
`
`[0045] The transmitter converts (i.e., pre-conditions) a set
`of NT modulation symbols b using the eigenvector matrix E.
`The transmitted modulation symbols from the NT transmit
`antennas can be expressed as:
`
`[0046] For all antennas, the pre-conditioning of the modu(cid:173)
`lation symbols can be achieved by a matrix multiply opera(cid:173)
`tion expressed as:
`
`Xj
`
`x2
`
`M
`
`eu,
`
`ell,
`
`e21,
`
`e22,
`
`elNr
`
`e2Nr
`
`bt
`
`b2
`
`M
`
`XNT
`
`eNrl• eNrl•
`
`eNrNr
`
`bNT
`
`Eq (1)
`
`[0048] E=is the eigenvector matrix related to the
`transmission characteristics from transmit antennas
`to the receive antennas; and
`[0049] Xl, x2 . . . XNT are