US00724.8559B2
`
`(12) United States Patent
`Ma et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7,248.559 B2
`Jul. 24, 2007
`
`(54) SCATTERED PILOT PATTERN AND
`CHANNEL ESTMLATION METHOD FOR
`MIMO-OFDM SYSTEMS
`
`(75) Inventors: Jianglei Ma, Kanata (CA); Ming Jia,
`Ottawa (CA); Peiying Zhu, Kanata
`(CA); Wen Tong, Ottawa (CA)
`
`(73) Assignee: Nortel Networks Limited, St. Laurent,
`Quebec (CA)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 898 days.
`
`(*) Notice:
`
`1-1.
`(22) Filed:
`
`Jan. 8, 2002
`
`6,473,393 B1 * 10/2002 Ariyavisitakul et al. .... 370/203
`6,654,429 B1 * 1 1/2003 Li .............................. 375.316
`2002/0003774 A1* 1/2002 Wang et al. ................ 370,208
`2002/0034213 A1* 3/2002 Wang et al. ......
`... 375,132
`2002/0080887 A1* 6/2002 Jeong et al. ................ 375,295
`2002/O122383 A1* 9, 2002 Wu et al. ................... 370/210
`2002/0144.294 A1* 10, 2002 Rabinowitz et al. ........ 725,139
`2002/0181390 A1* 12/2002 Mody et al. ................ 370,208
`2003/0016621 A1
`1/2003 Li .............................. 370,203
`
`OTHER PUBLICATIONS
`Fernández-Getino Garcia, M. Julia et al; Efficient Pilot Patterns for
`Channel Estimation in OFDM Systems Over HF Channels; pp.
`
`Jones, V.K.; Raleigh, Gregory G.; Channel Estimation for Wireless
`OFDM Systems; pp.980-985.
`
`* cited by examiner
`Primary Examiner Chi Pham
`Assistant Examiner Melanie Jagannathan
`
`(57)
`
`ABSTRACT
`
`(65)
`
`(56)
`
`Prior Publication Data
`US 2003 FOOT2254A1
`Apr. 17, 2003
`Related U.S. Application Dat
`elated U.S. Application Uata
`(60) Provisional application No. 60/329.509, filed on Oct.
`17, 2001.
`A method and app
`provided for reducing th
`(51) Int. Cl.
`method and apparatus are orOV1Cled Or reduc1ng the
`number of pilot symbols within a MIMO-OFDM commu
`(2006.01)
`HO4. IIM
`nication system, and for improving channel estimation
`(2006.01)
`H04O 700
`within Such a system. For each transmitting antenna in an
`(2006.01)
`H04B 7/26
`OFDM transmitter, pilot symbols are encoded so as to be
`(2006.01)
`H04B 7/02
`unique to the transmitting antenna. The encoded pilot sym
`(2006.01)
`H04L 27/00
`bols are then inserted into an OFDM frame to form a
`370/208: 370/328: 370/335:
`(52) U.S. Cl
`diamond lattice, the diamond lattices for the different trans
`AV
`370,343.370,441: 375,299. 375,316. 455/101
`mitting antennae using the same frequencies but being offset
`.
`.
`.
`.
`.
`.
`s
`s
`(58) Field of Classislist Sh 5 437.465 ... from each other by a single symbol in the time domain. At
`S
`lication file f s
`s let s
`h hist
`s
`the OFDM receiver, a channel response is estimated for a
`ee appl1cauon Ille Ior complete searcn n1story.
`symbol central to each diamond of the diamond lattice using
`References Cited
`a two-dimensional interpolation. The estimated channel
`responses are Smoothed in the frequency domain. The chan
`U.S. PATENT DOCUMENTS
`nel responses of remaining symbols are then estimated by
`interpolation in the frequency domain.
`
`5,867.478 A * 2/1999 Baum et al. ................ 370,203
`6,298,035 B1 * 10/2001 Heiskala ..................... 370,206
`6,359,938 B1* 3/2002 Keevill et al. .............. 375.316
`
`44 Claims, 7 Drawing Sheets
`
`OFDM TRANSMITTERTTTTTTTTTTTTTTTTTTTT
`
`1O
`
`- - - - - - - - - - - - - - - -
`
`
`
`
`
`CODENG
`MODULATION
`12
`
`
`
`16
`
`
`
`
`
`18
`
`
`
`
`
`
`
`
`
`
`
`PLOT
`INSERTER
`24
`
`PILOT STBC
`23
`
`P1, P2
`
`
`
`
`
`
`
`PILOT
`NSEER
`40
`
`GUARD
`INSERTER
`30
`
`GUARD
`INSERTER
`30
`
`
`
`Ford Motor Co.
`Exhibit 1008
`Page 001
`
`

`

`
`U.S. Patent Jul. 24, 2007
`
`Sheet 1 of 7 US 7,248,559 B2
`
`PILOT EXTRACTION IN FREQUENCY
`
`DOMAIN
`lA-1
`-
`l
`
`+
`
`INTERPOLATION IN TIME
`lA-2
`
`- I
`
`
`
`,..,
`
`INTERPOLATION IN FREQUENCY
`1A-3
`
`PILOT EXTRACTION IN FREQUENCY
`
`DOMAIN
`1 B-1
`-
`
`J,
`
`INTERPOLATION IN FREQUENCY
`
`1B-2
`
`- J,
`
`
`IFFT
`1 B-3
`-
`
`•
`SMOOTHING/DE-NOISE
`18-4
`
`-
`
`FIG. lA
`(PRIOR ART)
`
`-
`
`J..
`
`FFT
`1B-5
`-
`
`FIG. 1B
`(PRIOR ART)
`
`PILOT EXTRACTION IN FREQUENCY
`
`DOMAIN
`1 C-1
`-
`
`•
`
`INTERPOLATION IN TIME
`1 C-2
`-
`
`+
`
`INTERPOLATION IN FREQUENCY
`1C-3
`
`-
`
`FIG. lC
`(PRIOR ART)
`
`Ford Motor Co.
`Exhibit 1008
`Page 002
`
`

`

`r------ ----------------------------------
`OFDM TRANSMITTER
`1
`r----------- --------------------------------------
`10
`
`ODFM COMPONENT 20
`: :
`:
`GUARD LIMITER : : �37
`:
`INSERTER 32
`I
`- :
`-
`-
`30
`
`------------------------------
`
`I
`
`,......,,,,,.,...,.,,,,..._,,
`
`,.......,,,,,.,..,..,,,,.,,....., .-----,
`
`...._.....,......____,
`
`...__.=-_ ......
`
`I
`I
`I
`
`�
`
`I
`
`I I
`
`I
`I
`
`J
`
`e •
`00 •
`�
`�
`�
`�
`
`�
`=
`
`2'
`:-'
`
`N
`J·
`N
`0
`0
`-...J
`
`rJJ
`=­('D
`('D .....
`
`N
`
`2
`
`0 ....
`
`-...J
`
`COOING/
`ENCODING
`MODULATION
`14
`12
`
`_________________________________________________
`
`21 PILOT STBC [ P1, P2]
`___,_, -► I 23 -Pt p1*
`_ I ODFM COMPONENT 38
`
`:
`-
`-- . - GUARD
`LIMITER
`INSERTER
`30 32
`H
`
`18
`
`L ___________________________
`
`1 I
`1 I
`I -----.i
`�
`11
`
`L ________________________________________________ JI
`_____________________
`______________________
`J
`
`FIG. 2
`
`d
`r.,;_
`
`'-"--...l
`N
`�
`'-"Q/0
`UI
`UI
`\0
`=
`N
`
`Ford Motor Co.
`Exhibit 1008
`Page 003
`
`

`

`•
`
`------------------------------------------------------------
`�
`1
`I
`
`OFDM COMPONENT 56
`�
`OFDM RECEIVER
`�
`�
`50
`
`52
`
`.....__.__I •1 5 9
`
`FREQ.
`DEMUX FFT
`
`RF ADC
`
`CORR.
`60
`68
`70
`64
`
`•
`
`�
`
`N
`�
`...N
`0
`0
`-....J
`
`rJJ
`
`FRAME
`SYNC.
`66
`
`I
`
`5
`
`75
`
`CHANNEL
`ESTIMATOR
`72
`
`75
`
`I I�
`
`=­('D
`DECODE/
`('D .....
`DECODER
`DEMOD
`�
`78
`0
`
`80
`
`....
`-....J
`
`OFDM COMPONENT
`58
`
`'
`I
`I
`I
`I
`I
`d
`
`r.,;_
`-....l
`'N
`�
`00
`
`--------------------------------------------------------
`
`FIG. 3
`
`UI
`\0
`
`=
`N
`
`Ford Motor Co.
`Exhibit 1008
`Page 004
`
`

`

`U.S. Patent Jul. 24, 2007
`
`Sheet 4 of 7
`
`US 7,248,559 B2
`
`
`
`RECEIVE DAT A SYMBOLS
`
`-
`
`100
`i
`
`GENERATE PILOT SYMBOLS
`
`102
`
`
`APPLY STBC ENCODING TO PILOT SYMBOLS
`
`- .1
`
`FIG. 4
`
`104
`
`
`
`INSERT ENCODED PILOT SYMBOLS
`
`- i
`
`106
`
`-
`
`122
`
`126
`
`128
`
`124
`
`FIG. 5
`
`Ford Motor Co.
`Exhibit 1008
`Page 005
`
`

`

`U.S. Patent Jul. 24, 2007
`
`
`Sheet 5 of 7 US 7,248,559 B2
`
`FIG. 6
`
`Ford Motor Co.
`Exhibit 1008
`Page 006
`
`

`

`U.S. Patent Jul. 24, 2007
`Sheet 6 of 7 US 7,248,559
`B2
`
`Q 2D INTERPOLATION
`ESTIMATE
`CHANNEL
`@ PILOT
`
`160
`
`FIG. 7
`
`Q 2D INTERPOLATION
`® PILOT CHANNEL
`ESTIMATE
`
`,,.
`
`--(4---+---+---------
`110···--
`-------------
`-------------
`___ )
`
`... \
`
`-
`
`FILTER
`172
`
`FREQUENCY
`
`FIG. 8
`
`Q 2D INTERPOLATION
`ESTIMATE
`@ PILOT CHANNEL
`.----------�---,
`a) 1D INTERPOLATION
`CUBIC INTERPOLATOR
`LAGRANGE
`175
`
`FREQUENCY
`
`FIG. 9
`
`Ford Motor Co.
`Exhibit 1008
`Page 007
`
`

`

`U.S. Patent Jul. 24, 2007
`
`
`Sheet 7 of 7 US 7,248,559 B2
`
`PILOT EXTRACTION AT FREQUENCY DOMAIN FOR
`
`
`
`
`EACH RECEIVE ANTENNA
`500-
`i
`
`
`
`502-
`.i
`
`BUFFER SCATTERED PILOT FOR 3 STBC BLOCKS
`
`FIG. 10
`503
`
`CHANNEL RESPONSE MATRIX COMPUTING
`
`3-POINT SMOOTHING IN FREQUENCY DOMAIN
`
`i
`
`4-POINT 2-D INTERPOLATION
`-
`504
`.i
`
`
`
`505-
`.i
`
`
`506-
`
`INTERPOLATION IN FREQUENCY DOMAIN
`
`1.00E+OO
`I I
`100Hz
`1.00E-01
`� � ...... "
`t---::. t'---J
`1.00E-02
`� � �
`I.I.I
`co
`1.00E-03
`
`1.00E-04
`
`300Hz
`
`� � � t, � � �)
`
`1.00E-05
`�c§>�c§>�c§>�c§>�c§>�c§>�c§>�
`<r.,· c:o· <:o· I'\. I'\. ct)· Cb' o.,· o.,· c:::,· c:::,· ..._,. ..._,. �-�·
`SNR (dB)
`
`"' "' "" " "
`
`• DPPOLER = 1 OOHz PROPOSED METHOD
`
`
`
`Q DOPPLER=300Hz PROPOSED METHOD
`♦ DPPOLER = 1 OOHz IDEAL CHANNEL
`◊DOPPLER= 300Hz IDEAL CHANNEL
`
`
`FIG. 11
`
`Ford Motor Co.
`Exhibit 1008
`Page 008
`
`

`

`
`
`US 7,248,559 B2
`
`1
`SCATTERED PILOT PATTERN AND
`CHANNEL ESTIMATION METHOD FOR
`MIMO-OFDM SYSTEMS
`
`RELATED APPLICATION
`
`
`
`FIELD OF THE INVENTION
`
`
`
`BACKGROUND OF THE INVENTION
`
`2
`The variations in phase and amplitude resulting from
`
`
`
`
`
`
`
`
`propagation along the channel are referred to as the channel
`
`
`
`response. The channel response is usually frequency and
`
`
`
`
`time dependent. If the receiver can determine the channel
`
`
`
`to compensate 5 response, the received sign al can be corrected
`
`
`
`
`
`for the channel degradation. The determination of the chan­
`
`
`
`
`
`nel response is called channel estimation. The inclusion of
`This application claims the benefit of U.S. provisional
`
`
`
`
`pilot symbols in each OFDM symbol allows the receiver to
`
`
`application No. 60/329,509 filed Oct. 17, 2001.
`
`
`
`carry out channel estimation. The pilot symbols are trans-
`
`
`10 mitted with a value known to the receiver. When the receiver
`
`
`
`
`receives the OFDM symbol, the receiver compares the
`
`
`received value of the pilot symbols with the known trans­
`
`
`
`This invention relates to OFDM communication systems,
`
`
`mitted value of the pilot symbols to estimate the channel
`
`
`
`and more particularly to a more efficient use of pilot symbols
`response.
`within such systems.
`15 The pilot symbols are overhead, and should be as few in
`
`
`
`
`
`number as possible in order to maximize the transmission
`
`
`rate of data symbols. Since the chamiel response can vary
`
`
`with time and with frequency, the pilot symbols are scattered
`
`
`
`
`Multiple Input Multiple Output-Orthogonal Frequency
`
`
`
`
`amongst the data symbols to provide as complete a range as
`
`
`
`Division Multiplexing (MIMO-OFDM) is a novel highly
`
`
`
`
`20 possible of channel response over time and frequency. The
`
`
`
`
`spectral efficient technology used to transmit high-speed
`
`
`set of frequencies and times at which pilot symbols are
`
`data through radio chamiels with fast fading both in fre­
`
`
`
`inserted is referred to as a pilot pattern. The optimal tem­
`quency and in time.
`
`
`
`poral spacing between the pilot symbols is usually dictated
`In wireless communication systems that employ OFDM,
`
`
`
`
`
`
`by the maximum anticipated Doppler frequency, and the
`
`
`
`
`
`a transmitter transmits data to a receiver using many sub­
`
`
`
`25 optimal frequency spacing between the pilot symbols is
`
`
`
`
`carriers in parallel. The frequencies of the sub-carriers are
`
`
`
`usually dictated by the anticipated delay spread of multi­
`
`
`
`orthogonal. Transmitting the data in parallel allows the
`path fading.
`
`
`
`symbols containing the data to be of longer duration, which
`The existing pilot-assisted OFDM channel estimation
`
`
`
`
`
`
`
`reduces the effects of multi-path fading. The orthogonality
`
`
`
`approaches are designed for conventional one transmitter
`
`
`of the frequencies allows the sub-carriers to be tightly
`
`
`
`30 system. With a scattered pilot arrangement, there are three
`
`
`
`
`spaced, while minimizing inter-carrier interference. At the
`
`classes of algorithms:
`
`
`
`transmitter, the data is encoded, interleaved, and modulated
`
`1-D frequency interpolation or time interpolation
`
`
`
`to form data symbols. Overhead information is added,
`
`
`Transformed frequency 1-D interpolation
`
`
`
`including pilot symbols, and the symbols ( data plus over­
`
`
`Independent time and frequency 1-D interpolation
`head) are organized into OFDM symbols. Each OFDM 35
`
`
`
`
`
`The first class of algorithms is based on the pilot OFDM
`symbol typically uses 2n frequencies. Each symbol is allo­
`
`
`symbol (all the sub-carriers are used as the pilots) or
`cated to represent a component of a different orthogonal
`
`
`
`
`
`comb-type of pilots. This approach shown in the flow chart
`frequency. An inverse Fast Fourier Transform (IFFT) is
`
`
`
`
`
`
`
`for channels with high of FIG. lA is simple but only suitable
`
`
`applied to the OFDM symbol (hence the preference of 2n
`
`
`
`
`frequency selectivity or channels with high time fading. The
`frequencies) to generate time samples of a signal. Cyclic
`
`
`
`
`
`
`
`40 method involves pilot extraction in the frequency domain
`
`extensions are added to the sign al, and the sign al is passed
`
`
`
`or (step lA-1) followed by interpolation in time (step lA-2),
`
`
`
`
`
`through a digital-to-analog converter. Finally, the transmitter
`
`
`interpolation in frequency (step lA-3).
`
`
`
`
`transmits the signal to the receiver along a channel.
`The second method shown in the flow chart of FIG. 1B is
`
`
`
`
`When the receiver receives the signal, the inverse opera­
`aimed for chamiels with slow Doppler fading and fast
`
`
`
`tions are performed. The received signal is passed through
`45
`
`
`
`
`frequency fading. It improves the first method by using FFT
`
`
`
`an analog-to-digital converter, and timing information is
`
`
`to reconstruct the chamiel response back to time domain for
`
`
`
`then determined. The cyclic extensions are removed from
`
`
`
`noise reduction processing at the expense of FFT/IFFT
`
`
`
`the signal. The receiver performs an FFT on the received
`
`
`
`
`computing for the chamiel estimation separately. The
`
`
`
`signal to recover the frequency components of the sign al,
`
`
`method begins with pilot extraction in the frequency domain
`
`
`
`
`that is, the data symbols. Error correction may be applied to 50
`
`
`in (step 1B-1), which may be followed by interpolation
`
`
`
`the data symbols to compensate for variations in phase and
`
`
`
`
`trans-fast Fourier Then an inverse frequency (step 1B-2).
`
`
`
`
`amplitude caused during propagation of the signal along the
`
`
`form (step 1B-3), smoothing/de-noise processing (step
`
`
`
`channel. The data symbols are then demodulated, de-inter­
`
`
`
`and finally a fast Fourier transform steps are
`1B-4),
`(1B-5)
`
`
`
`leaved, and decoded, to yield the transmitted data.
`executed.
`
`
`
`
`
`In systems employing differential detection, the receiver 55
`The third method shown in the flow chart of FIG. lC can
`
`
`
`
`compares the phase and/or amplitude of each received
`
`
`
`be used to estimate channel for mobile applications, where
`
`
`
`symbol with an adjacent symbol. The adjacent symbol may
`
`
`
`both fast time fading and frequency fading exist. However
`
`
`
`be adjacent in the time direction or in the frequency direc­
`
`
`
`it needs a relatively high density of pilots and a completed
`
`
`
`tion. The receiver recovers the transmitted data by measur­
`
`
`
`interpolator. This method involves pilot extraction in the
`
`
`
`
`ing the change in phase and/or amplitude between a symbol 60
`
`
`by interpo­frequency domain (step lC-1) this is followed
`
`
`
`
`and the adjacent symbol. If differential detection is used,
`
`
`in frequency lation in time (step lC-2) and interpolation
`(step lC-3).
`
`
`
`channel compensation need not be applied to compensate for
`
`
`
`variations in phase and amplitude caused during propagation
`In the propagation environment with both high frequency
`
`
`
`
`
`
`
`of the signal. However, in systems employing coherent
`
`
`
`dispersion and temporal fading, the chamiel estimation
`
`
`
`
`detection the receiver must estimate the actual d phase and 65
`
`
`
`performance can be improved by the increase of pilot
`
`
`
`amplitude of the channel response, and channel compensa­
`
`
`
`
`symbol density at the price of the reduction of the spectral
`tion must be applied.
`
`
`
`
`efficiency of the data transmission. To interpolate and recon-
`
`Ford Motor Co.
`Exhibit 1008
`Page 009
`
`

`

`
`
`US 7,248,559 B2
`
`periodically at all frequencies simultaneously. However, SUMMARY OF THE INVENTION
`
`4
`3
`
`
`struct the channel response function from the limited pilots ting antenna typically blinks its pilot pattern on and off. This
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`to achieve reliable channel estimation with the minimum increases the temporal separation of the pilot symbols for
`
`
`overhead is a challenging task.
`
`
`
`each transmitter, reducing the accuracy of the interpolation
`
`
`
`used to estimate the channel response. In MIMO-OFDM
`
`
`
`
`
`There are a variety of existing standard pilot patterns. In
`
`
`
`
`5 systems a simple and fast channel estimation method is
`
`environments in which the channel varies only slowly with
`
`
`
`
`
`
`
`
`
`particularly crucial because of the limitation of the compu­
`time and frequency, the pilot symbols may be inserted
`
`
`
`
`
`
`tational power for estimating MxN channels, while in SISO­
`cyclically, being inserted at an adjacent frequency after each
`
`
`
`
`
`OFDM system only one channel needs to be estimated.
`time interval. In environments in which the channel is highly
`
`
`
`
`frequency dependent, the pilot symbols may be inserted
`
`
`
`
`
`10
`
`
`such a pilot pattern is only suitable for channels that vary
`
`
`very slowly with time. In environments in which the channel
`Channel estimation methods are provided which are based
`
`
`
`
`
`
`
`is highly time dependent, the pilot symbols may be inserted
`
`
`
`on the partial interpolation of a scattered pilot by using true
`
`
`
`
`continuously at only specific frequencies in a comb arrange­
`
`
`
`2-D interpolation; and additionally, simple 1-D interpolation
`
`
`
`ment to provide a constant measurement of the channel
`
`
`
`
`is used reconstruct the entire channels. This method has a
`15
`
`
`
`response. However, such a pilot pattern is only suitable for
`
`
`
`reduced scattered pilot overhead, and is at least an order of
`
`
`
`channels that vary slowly with frequency. In environments
`
`
`
`some existingmagn itude less computationally complex than
`
`
`
`in which the channel is both highly frequency and highly
`
`
`
`
`methods. In general, the proposed method of channel esti­
`
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`time dependent (for example, mobile systems with much
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`mation is more robust in channels with high Doppler spread,
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`multi-path fading), the pilot symbols may be inserted peri-20
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`and provides better performance than some existing methods
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`odically in time and in frequency so that the pilot symbols
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`and requires the less buffering of the OFDM symbols for the
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`form a rectangular lattice when the symbols are depicted in
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`coherent detection at the receiver than in some methods.
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`a time-frequency diagram.
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`The methods allow fewer pilot symbols to be placed
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`In OFDM communication systems employing coherent
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`within each OFDM symbol, while still allowing accurate
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`modulation and demodulation, the receiver must estimate
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`interpolation of the channel response. The data rate of an
`25
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`the channel response at the frequencies of all sub-carriers
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`MIMO-OFDM system is thereby improved.
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`and at all times. Although this requires more processing than
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`A first broad aspect of the invention provides a method of
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`in systems that employs differential modulation and
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`inserting pilot symbols into Orthogonal Frequency Division
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`demodulation, a significant gain in signal-to-noise ratio can
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`Multiplexing (OFDM) frames at an OFDM transmitter hav­
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`be achieved using coherent modulation and demodulation.
`30
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`ing at least one transmitting antenna, the OFDM frames
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`The receiver determines the channel response at the times
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`having a time domain and a frequency domain, each OFDM
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`and frequencies at which pilot symbols are inserted into the
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`frame comprising a plurality of OFDM symbols. The
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`OFDM symbol, and performs interpolations to estimate the
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`method involves, for each antenna, inserting scattered pilot
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`channel response at the times and frequencies at which the
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`symbols in an identical scattered pattern in time-frequency.
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`data symbols are located within the OFDM symbol. Placing
`35
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`In some embodiments, the identical scattered pattern is a
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`pilot symbols more closely together (in frequency if a comb
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`regular diagonal-shaped lattice.
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`pattern is used, in time if a periodic pattern is used, or in both
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`In some embodiments, inserting pilot symbols in an
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`frequency and in time if a rectangular lattice pattern is used)
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`identical diagonal-shaped lattice involves for each point in
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`within a pilot pattern results in a more accurate interpolation.
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`the identical diagonal shaped lattice inserting a number of
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`However, because pilot symbols are overhead, a tighter pilot
`40
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`pilot symbols on a single sub-carrier for N consecutive
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`pattern is at the expense of the transmitted data rate.
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`OFDM symbols, where N is the number of transmitting
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`Existing pilot patterns and interpolation techniques are
`antennae.
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`usually sufficient if the channel varies slowly with time (for
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`example for nomadic applications). However, if the channel
`mond shaped lattice.
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`varies quickly with time (for example, for mobile applica-
`45
`In some embodiments for each point in the diagonal­
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`tions ), the time interval between pilot symbols must be
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`shaped lattice, L uncoded pilot symbols are generated. Space
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`reduced in order to allow an accurate estimation of the
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`time block coding (STBC) is performed on the group of L
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`channel response through interpolation. This increases the
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`uncoded pilot symbols to produce an NxN STBC block, L
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`overhead in the signal.
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`and N determining an STBC code rate. Then, one row or
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`The problem of minimizing the number of pilot symbols
`50
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`column of the STBC block is transmitted on each antenna on
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`while maximizing the accuracy of the interpolation is also
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`a specific sub-carrier.
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`particularly cumbersome in Multiple-Input Multiple-Output
`In some embodiments, transmitting the pilot symbols is
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`(MIMO) OFDM systems. In MIMO OFDM systems, the
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`done with a power level greater than a power level of data
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`transmitter transmits data through more than one transmit­
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`symbols, depending upon a value reflective of channel
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`ting antenna and the receiver receives data through more 55
`conditions.
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`than one receiving antenna. The binary data is usually
`In some embodiments, transmitting the pilot symbols is
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`divided between the transmitting antennae, although the
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`done with a power level which is dynamically adjusted to
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`same data may be transmitted through each transmitting
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`ensure sufficiently accurate reception as a function of a
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`antenna if spatial diversity is desired. Each receiving
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`modulation type applied to the sub-carriers carrying data.
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`antenna receives data from all the transmitting antennae, so 60
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`if there are M transmitting antennae and N receiving anten­
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`In some embodiments, the diagonal shaped lattice pattern
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`each nae, then the sign al will propagate over MxN channels,
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`has a first plurality of equally spaced sub-carrier positions,
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`of which has its own channel response. Each transmitting
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`and a second plurality of equally spaced sub-carrier posi­
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`antenna inserts pilot symbols into the same sub-carrier
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`tions offset from said first plurality. The pilot symbols are
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`location of the OFDM symbol which it is transmitting. In
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`inserted alternately in time using the first plurality of equally
`65
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`order to minimize interference at the receiver between the
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`spaced sub-carrier positions and the second plurality of
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`pilot symbols of each transmitting antenna, each transmit-
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`equally spaced sub-carrier positions.
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`In some embodiments, diagonal shaped lattice is a dia­
`
`Ford Motor Co.
`Exhibit 1008
`Page 010
`
`

`

`
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`US 7,248,559 B2
`
`6
`5
`In some embodiments, the second plurality of sub-carriers in the frequency direction to estimate the charmel responses
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`is offset from the first plurality of equally spaced-sub-carrier corresponding to remaining OFDM sub-carriers within each
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`positions by half the spacing between adjacent sub-carriers OFDM symbol.
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`of the first plurality of sub-carrier positions thereby forming
`In some embodiments, estimating the channel response of
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`a diamond shaped lattice pattern.
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`5 a plurality of points not on the scattered pattern by perform­
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`ing a two-dimensional (time direction, frequency direction)
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`In some embodiments, the pilot pattern is cyclically
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`interpolation of channel responses determined for points in
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`offset, both in a time direction and in a frequency direction,
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`the scattered pattern lattice involves for each sub-carrier to
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`for at least one adjacent base station to form re-use patterns.
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`be estimated averaging charmel responses of the given
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`Another broad aspect of the invention provides an OFDM
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`channel estimation period of a sub-carrier before the sub­
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`transmitter. The OFDM transmitter has a plurality of trans-10
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`carrier to be estimated in frequency (when present) and a
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`mit antennas, and is adapted to insert pilot symbols into
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`sub-carrier after the sub-carrier to be estimated in frequency
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`Orthogonal Frequency Division Multiplexing (OFDM)
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`(when present) and the channel response for a previous
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`frames having a time domain and a frequency domain, each
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`estimation period (when present) and a following estimation
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`OFDM frame comprising a plurality ofOFDM symbols by,
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`period (when present).
`15
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`for each antenna, inserting pilot symbols in an identical
`In some embodiments, the method is applied to a single
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`scattered pattern in time-frequency.
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`transmitter, single receiver system.
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`In some embodiments, the identical scattered pattern is a
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`In other embodiments the method is applied to a single
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`diagonal-shaped lattice.
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`transmitter system wherein each point in the scattered pat­
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`In some embodiments, inserting pilot symbols in an
`20
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`tern contains a single pilot symbol.
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`identical scattered pattern involves for each point in the
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`In some embodiments, the method is applied to a system
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`identical scattered pattern inserting a number of pilot sym­
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`in which there are N>=2 antennas, and each point in the
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`bols on a single sub-carrier for N consecutive OFDM
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`scattered pattern contains a number N of consecutive
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`symbols, where N is the number of transmitting antennae,
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`encoded pilot symbols transmitted on a sub-carrier, a single
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`where N>=l.
`25
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`channel estimate being determined for each N encoded pilot
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`In some embodiments, the scattered pattern is a diamond
`symbols.
`shaped lattice.
`In some embodiments, the N encoded pilot symbols
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`In some embodiments, for each point in the scattered
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`contain L pilot symbols which were STBC block coded,
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`pattern, the OFDM transmitter is adapted to generate L
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`where N and L together determine a STBC code rate.
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`uncoded pilot symbols, perform space time block coding
`30
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`Other aspects and features of the present invention will
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`(STBC) on the group of L pilot symbols to produce an N xN
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`become apparent to those ordinarily skilled in the art upon
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`STBC block, and transmit one row or colunm of the STBC
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`
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`review of the following description of specific embodiments
`block on each antenna.
`
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`of the invention in conjunction with the accompanying
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`
`In some embodiments, the OFDM transmitter is further
`Figures.
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`adapted to transmit the pilot symbols with a power level
`35
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`greater than a power level of data symbols depending on a
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`value reflective of channel conditions.
`
`In some embodiments in which the diamond shaped
`The invention will now be described in greater detail with
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`lattice pattern is employed, the diamond shaped lattice
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`reference to the accompanying Figures, in which:
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`pattern has a first plurality of equally spaced sub-carrier
`40
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`
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`FIG. 1 illustrates flow-charts for three examples of con­
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`positions and a second plurality of equally spaced sub­
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`ventional OFDM Charmel Estimation;
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`carrier positions offset from said first plurality. The pilot
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`FIG. 2 is a block diagram of a Multiple-Input Multiple­
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`symbols are inserted alternately in time using the first
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`Output Orthogonal Frequency Division Multiplexing
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`plurality of equally spaced sub-carrier positions and the
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`(OFDM) transmitter provided by an embodiment of the
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`second plurality of equally spaced sub-carrier positions.
`45
`invention;
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`
`
`Another broad aspect of the invention provides a method
`FIG. 3 is a block diagram of an OFDM receiver;
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`of estimating a plurality of charmel responses at an Orthogo­
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`FIG. 4 is a flowchart of a method by which an OFDM
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`nal Frequency Division Multiplexing (OFDM) receiver hav­
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`transmitter inserts pilot symbols into an OFDM frame
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`ing at least one receive antenna. The method involves at each
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`according to one embodiment of the invention;
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`receive antenna receiving OFDM frames transmitted by at 50
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`FIG. 5 is a diagram of a pilot pattern generated using the
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`least one transmitting antenna, the OFDM frames having a
`method of FIG. 4;
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`time domain and a frequency domain, the OFDM frames
`FIG. 6 is a block diagram of a MIMO system showing the
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`transmitted by each antenna having pilot symbols inserted in
`
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`channel transfer functions between two transmit antennas
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`an identical scattered pattern in time-frequency, each OFDM
`
`and two receive antennas;
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`frame comprising a plurality of OFDM symbols. For each 55
`FIG. 7 is a time frequency diagram showing channel
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`transmit antenna, receive antenna combination: a) the pilot
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`estimate positions for pilot channel estimation;
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`symbols of the received OFDM frames are used to estimate
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`FIG. 8 schematically illustrates a step of filtering esti­
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`a channel response for each point in the scattered pattern; b)
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`mated and interpolated pilot channel estimates;
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`the charmel response is estimated for of a plurality of points
`
`FIG. 9 shows schematically the step of interpolating
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`not on the scattered pattern by performing a two-dimen-
`60
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`between the charmel estimates previously determined to
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`sional (time direction, frequency direction) interpolation of
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`
`
`provide charmel estimates for all sub-carriers and all times;
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`
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`channel responses determined for points in the scattered
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`pattern; c) an interpolation is performed in the frequency
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`
`FIG. 10 is a flow chart summarizing the overall channel
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`direction to estimate the charmel responses corresponding to
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`
`estimation method provided by an embodiment of the inven­
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`remaining OFDM sub-carriers within each OFDM symbol.
`tion; and
`65
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`In some embodiments, a filtering function is performed on
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`
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`the channel responses prior to performing the interpolation
`
`
`obtained using the method of FIG. 10.
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`FIG. 11 is an example of a set of performance results
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`
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`BRIEF DESCRIPTION OF THE DRAWINGS
`
`Ford Motor Co.
`Exhibit 1008
`Page 011
`
`

`

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`US 7,248,559 B2
`
`8
`
`7
`DETAILED DESCRIPTION OF THE
`
`The data symbols sent along the second processing path
`
`
`PREFERRED EMBODIMENTS
`
`18 are sent to a second OFDM component 38 which includes
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`
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`processors similar to those included in the first OFDM
`The following sections describe a MIMO-OFDM trans­
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`
`the pilot inserter component 20. However, 40 inserts
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`mitter/receiver and scattered pilot insertion. By way of 5
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`encoded pilot symbols from the second row of the STBC
`
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`introduction, a OFDM frame consists of the preamble
`
`
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`block produced by the pilot STBC function 23. The symbols
`
`
`
`OFDM symbols and regular OFDM symbols. Each OFDM
`
`
`sent along the second processing path 18 are ultimately
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`symbol uses a set of orthogonal sub-carriers. When there are
`
`transmitted as a signal through a second transmitting
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`
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`two transmit antennas, two OFDM symbols form a STTD
`antenna
`42.
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`block. For regular OFDM symbols, some sub-carriers are 10
`of an MIMO­Referring now to FIG. 3, a block diagram
`
`
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`
`
`used as pilot sub-carriers to carry pilot symbols while the
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`OFDM receiver is shown. An OFDM receiver a 50 includes
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`others are used as data sub-carriers to carry data symbols.
`
`
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`
`antenna first receiving antenna 52 and a second receiving 54
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`
`
`
`The pilot sub-carriers are modulated by pilot symbols gen­
`
`
`( although more generally there will be one or more receiving
`
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`erated by QPSK. The data sub-carriers are modulated by
`
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`a first antennae). The first receiving antenna 52 receives
`
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`complex data symbols generated by Q AM mapping. STTD 15
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`of is a combination received signal received sign al. The first
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`coding is applied to the pilot sub-carrier pairs located at the
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`the two signals transmitted by the two transmitting antennae
`
`same frequency within one STTD block.
`
`
`
`each of the 37 and 42 of FIG. 2, although two sign als will
`
`
`of a Multiple-Input Referring to FIG. 2, a block diagram
`
`
`
`Multiple-Output (MIMO) Orthogonal Frequency Division
`
`
`have been altered by a respective channel between the
`
`
`
`Multiplexing (OFDM) transmitter provided by an embodi-20
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`respective transmitting antenna and the first receiving
`
`
`ment of the invention is shown. The OFDM transmitter
`
`
`
`a antenna antenna 52. The second receiving 54 receives
`
`
`
`though shown in FIG. 2 is a two-output OFDM transmitter,
`
`
`
`second received signal. The second received sign al is a
`
`
`more generally there may be a plurality of M transmitting
`
`
`
`combination of the two signals transmitted by the two
`
`
`antennae. An OFDM transmitter 10 takes binary data as
`
`
`
`each of transmitting antennae 37 and 42 of FIG. 2, although
`
`input but data in other forms may be accommodated. The 25