US007233625B2
`
`(12) United States Patent
`Ma et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7,233,625 B2
`Jun. 19, 2007
`
`(54) PREAMBLE DESIGN FOR MULTIPLE
`INPUT MULTIPLE OUTPUT (MIMO),
`ORTHOGONAL FREQUENCY DIVISION
`MULTIPLEXING (OFDM) SYSTEM
`(75) Inventors: Jianglei Ma, Ottawa (CA); Wen Tong,
`Ottawa (CA); Shiquan Wu, Nepean
`(CA)
`(73) Assignee: Nortel Networks Limited, St. Laurent,
`Quebec (CA)
`Subject to any disclaimer, the term of this
`y
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 665 days.
`(21) Appl. No.: 09/819,957
`
`*) Notice:
`
`(22) Filed:
`
`Mar. 28, 2001
`
`(65)
`
`Prior Publication Data
`US 2002/0041635 A1
`Apr. 11, 2002
`Related U.S. Application Data
`(63) Continuation-in-part of application No. 09/751,879,
`filed on Dec. 29, 2000.
`(60) Provisional application No. 60/229,972, filed on Sep.
`1, 2000.
`
`(51) Int. Cl.
`H04L 27/28
`
`(2006.01)
`
`(58) Field of Classification Search ................ 375/130,
`375/146, 261,260, 267,298, 299, 347, 377;
`455/25, 101, 103,104, 112: 370/327, 330,
`370/465, 477,478,482
`See application file for complete search history.
`References Cited
`
`(56)
`
`U.S. PATENT DOCUMENTS
`6,442,214 B1* 8/2002 Boleskei et al. ............ 375,299
`6,704,370 B1* 3/2004 Chheda et al. ....
`... 375,299
`6,731,668 B2 *
`5/2004 Ketchum ..........
`... 375/130
`2002/O122381 A1
`9/2002 Wu et al. ................... 370,208
`OTHER PUBLICATIONS
`Jones, V.K.; Raleigh, Gregory G.; Channel Estimation For Wireless
`OFDM Systems; IEEE, Nov. 8, 1998, pp.980-985.
`Cimini, Leonard J. et al., Clustered OFDM With Transmitter
`Diversity And Coding: IEEE; Nov. 18, 1996, pp. 703-707.
`Daneshrad, Babak et al; Clustered-OFDM Transmitter Implemen
`tation; IEEE: 1996, pp. 1064-1068.
`Matsumoto, Yoichi et al.; OFDM Subchannel Space-Combining
`Transmission Diversity; IEEE, 1998, pp. 137-141.
`* cited by examiner
`Primary Examiner Dac V. Ha
`
`ABSTRACT
`(57)
`One or more preambles are inserted into frames of Orthogo
`nal Frequency Multiplexing (OFDM)-Multiple Input, Mul
`tiple Output (MIMO) signals. The preamble is received by
`the antennas of a receiver, decoded and compared to known
`values to provide synchronization, framing, channels esti
`mation, offsets and other corrections to the transmitted
`signal.
`
`(52) U.S. Cl. ...................... 375/260; 375/267; 375/299;
`375/347; 455/101; 455/112; 370/330; 370/465
`
`26 Claims, 7 Drawing Sheets
`
`
`
`
`
`105
`STC coding
`OFDM
`modulation
`
`Modulated data
`For Tx antenna A
`
`QAM
`modulator
`interleaver
`
`
`
`
`
`
`
`Preamble
`insertion
`
`109
`/
`
`
`
`Input
`Ele Encoder Rate
`Data
`matching
`interleaver
`
`
`
`
`
`
`
`STC coding
`OFDM
`modulation
`
`
`
`107
`
`Modulated data
`For Tx antenna B
`
`APPLE 1011
`
`

`

`U.S. Patent
`
`Jun. 19, 2007
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`Jun. 19, 2007
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`U.S. Patent
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`Jun. 19, 2007
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`U.S. Patent
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`Jun. 19, 2007
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`Sheet 6 of 7
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`US 7,233,625 B2
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`

`

`U.S. Patent
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`Jun. 19, 2007
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`US 7,233,625 B2
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`US 7,233,625 B2
`
`1.
`PREAMBLE DESIGN FOR MULTIPLE
`INPUT MULTIPLE OUTPUT (MIMO),
`ORTHOGONAL FREQUENCY DIVISION
`MULTIPLEXING (OFDM) SYSTEM
`
`RELATED APPLICATIONS
`
`This application is a continuation-in-part of U.S. appli
`cation Ser. No. 09/751,879, filed Dec. 29, 2000, which
`claims the priority of U.S. Provisional Application No.
`60/229.972, filed Sep. 1, 2000.
`
`10
`
`FIELD OF THE INVENTION
`
`The present invention is directed to the delivery of data
`via a wireless connection and, more particularly, to the
`accurate delivery of data at high rates via a wireless con
`nection.
`
`15
`
`BACKGROUND OF THE INVENTION
`
`The demand for services in which data is delivered via a
`wireless connection has grown in recent years and is
`expected to continue to grow. Included are applications in
`which data is delivered via cellular mobile telephony or
`other mobile telephony, personal communications systems
`(PCS) and digital or high definition television (HDTV).
`Though the demand for these services is growing, the
`channel bandwidth over which the data may be delivered is
`limited. Therefore, it is desirable to deliver data at high
`speeds over this limited bandwidth in an efficient, as well as
`cost effective, manner.
`A known approach for efficiently delivering high speed
`data over a channel is by using Orthogonal Frequency
`Division Multiplexing (OFDM). The high-speed data sig
`nals are divided into tens or hundreds of lower speed signals
`that are transmitted in parallel over respective frequencies
`within a radio frequency (RF) signal that are known as
`sub-carrier frequencies (“sub-carriers'). The frequency
`spectra of the Sub-carriers overlap so that the spacing
`between them is minimized. The sub-carriers are also
`orthogonal to each other so that they are statistically inde
`pendent and do not create crosstalk or otherwise interfere
`with each other. As a result, the channel bandwidth is used
`much more efficiently than in conventional single carrier
`transmission schemes such as AM/FM (amplitude or fre
`quency modulation), in which only one signal at a time is
`sent using only one radio frequency, or frequency division
`multiplexing (FDM), in which portions of the channel
`bandwidth are not used so that the sub-carrier frequencies
`are separated and isolated to avoid inter-carrier interference
`(ICI).
`Further, each block of data is converted into parallel form
`and mapped into each Subcarrier as frequency domain
`symbols. To get time domain signals for transmission, an
`inverse discrete Fourier transform or its fast version, IFFT,
`is applied to the symbols. The symbol duration is much
`longer than the length of the channel impulse response so
`that inter-symbol interference is avoided by inserting a
`cyclic prefix for each OFDM symbol. Thus, OFDM is much
`less Susceptible to data loss caused by multipath fading than
`other known techniques for data transmission. Also, the
`coding of data onto the OFDM sub-carriers takes advantage
`of frequency diversity to mitigate loss from frequency
`selective fading when forward error correction (FEC) is
`applied.
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`In addition to having greater spectral efficiency, i.e. more
`bps/Hz, than conventional transmission schemes, the OFDM
`spectral efficiency is further enhanced because the spectrum
`can be made to look like a rectangular window so that all
`frequencies are similarly utilized. Moreover, OFDM is less
`sensitive to timing errors because the timing errors are
`translated to a phase offset in the frequency domain.
`Another approach to providing more efficient use of the
`channel bandwidth is to transmit the data using a base station
`having multiple antennas and then receive the transmitted
`data using a remote station having multiple receiving anten
`nas, referred to as Multiple Input-Multiple Output (MIMO).
`The data may be transmitted such there is spatial diversity
`between the signals transmitted by the respective antennas,
`thereby increasing the data capacity by increasing the num
`ber of antennas. Alternatively, the data is transmitted Such
`that there is temporal diversity between the signals trans
`mitted by the respective antennas, thereby reducing signal
`fading.
`Presently, MIMO systems either are designed to transmit
`signals having spatial diversity or are designed to transmit
`signals having temporal diversity. It is therefore desirable to
`provide a common system that can deliver signals with
`either spatial diversity or temporal diversity depending on
`the transmission environment.
`It is further desirable to provide a system that has the
`advantages of both an OFDM system as well as those of a
`MIMO system. Such a system would transmit the OFDM
`symbols over a plurality of channels with either spatial
`diversity or temporal diversity between the symbols. How
`ever, when the signals are received at the remote station, the
`framing and timing of the received signals and the frequency
`and sampling clock offsets must be determined so that the
`information contained in the received signals may be recov
`ered. Further, the signals may be distorted because of
`transmitter imperfections as well as because of environmen
`tal effects and interference which change the frequencies of
`the channels and may also increase the bit error rate (BER).
`Additionally, the gain of the received signals must be
`controlled.
`Accordingly, it is advantageous to provide a system that
`can efficiently transfer data from a transmitter to a receiver
`over multiple channels.
`
`SUMMARY OF THE INVENTION
`
`The present invention provides a preamble that is inserted
`into a signal frame and which corresponds to a respective
`transmitter antenna. The preamble is matched to known
`values by a respective receiver to decode the signals and
`permit multiple signals to be transferred from the transmitter
`to the receiver.
`In accordance with an aspect of the invention, a preamble
`portion of a data signal is configured for transmission over
`a plurality of Sub-carriers by at least two antennas of a
`transmitter device. A respective pseudo-noise (PN) code is
`assigned to each of the at least two antennas. Each of the
`plurality of sub-carriers is assigned to a respective one of the
`at least two antennas. Each of the plurality of sub-carriers is
`modulated as a function of the respective pseudo-noise (PN)
`code that is assigned to a same one of the at least two
`antennas as the each of the plurality of Sub-carriers such that
`a plurality of modulated sub-carriers are obtained that are
`each assigned to a respective one of the at least two
`antennas. Each of the plurality of modulated sub-carriers is
`delivered to its assigned transmitter. Each the plurality of
`
`

`

`US 7,233,625 B2
`
`3
`modulated Sub-carriers using its assigned transmitter is
`transmitted at Substantially a same time.
`According to another aspect of the invention, a preamble
`portion of a data signal is configured for transmission over
`a plurality of sub-carriers by at least two transmitter devices
`each having at least two antennas. A respective pseudo-noise
`(PN) code is assigned to each of the at least two antennas.
`Each of the plurality of Sub-carriers is assigned to a respec
`tive one of the at least two transmitter devices. Each of the
`plurality of sub-carriers is modulated as a function of the
`respective pseudo-noise (PN) code that is assigned to a same
`one of the at least two transmitter devices to which the each
`of the plurality of Sub-carriers is assigned such that a
`plurality of modulated sub-carriers are obtained that are each
`assigned to a respective one of the at least transmitter
`devices. Each of the plurality of modulated sub-carriers
`using each of the at least two antennas of its assigned
`transmitter device at Substantially a same time.
`Other features and advantages of the present invention
`will become apparent from the following detailed descrip
`tion of the invention with reference to the accompanying
`drawings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`4
`prefix, comprised of the last elements of the vector V, is then
`inserted at the front of the vector V to obtain vector
`V=(v1000, v1001, . . . . v1024, v0, v1,..., v1024). The
`elements of the V are then transmitted serially by a single
`transmitter antenna over the single channel to a receiver
`having a single receiver antenna.
`In an OFDM-MIMO system of the invention, by contrast,
`the OFDM symbols are transmitted in the time domain using
`multiple antennas to concurrently transmit the symbols over
`the same Sub-carriers to multiple receiver antennas. How
`ever, when the signals are detected by the multiple antenna,
`they may be distorted and must also be synchronized and
`framed properly to avoid errors.
`Thus, the invention provides one or more preambles
`which are is inserted between the OFDM data symbols
`within OFDM frames in the time domain. The preamble
`includes training symbols which include a training sequence
`for different antennas, also known as pilot symbols.
`FIG. 1 shows an arrangement an OFDM transmitter
`employed by the invention. An encoder and rate matching
`interleaver 101 receives a stream of data bits and divides the
`stream of data bits into segments of B bits each, such as
`segments of 1024 bits. A block and/or a convolutional
`coding scheme is then carried out on the segments of B bits
`to introduce error correcting and/or error-detecting redun
`dancy. The segments of B bits are then respectively subdi
`vided into 2N sub-segments of m bits each, where m
`typically has a value of from two to six.
`The encoder and rate matching interleaver 101 then
`delivers the Sub-segments of data to a quadrature amplitude
`modulation (QAM) modulator and interleaver 103 which
`maps the Sub-segments onto corresponding complex-valued
`points in a 2"-ary constellation. A corresponding complex
`valued 2"-ary QAM Sub-symbol, c a+b that represent
`a discrete value of phase and amplitude, where -Nsks N.
`is assigned to represent each of the Sub-segments such that
`a sequence of frequency-domain Sub-symbols is generated.
`The QAM modulator and interleaver 103 also assigns the
`value c. Oto the Zero-frequency sub-carrier and interleaves
`any additional Zeroes that may be required for later inter
`polation into the sequence of frequency-domain Sub-sym
`bols.
`The QAM modulator and interleaver 103 then delivers the
`sequence of frequency-domain sub-symbols to one of space
`time coding (STC) and OFDM modulation circuits 105 and
`107 which employs an inverse fast Fourier transform (IFFT)
`to modulate the phase and amplitude of the Sub-carriers and
`also space time code the Sub-carriers to incorporate either
`spatial diversity or temporal diversity between the sub
`carriers. Each of the complex-valued, frequency-domain
`Sub-symbols c is used to modulate the phase and amplitude
`of a corresponding one of 2N-1 Sub-carrier frequencies over
`a symbol interval T. The sub-carriers are each represented
`by change value e', and have baseband frequencies of
`fk/T, where k is the frequency and is an integer in the
`range-Nsks N. A plurality of digital time-domain OFDM
`symbols of duration T. are thus generated according to the
`relation:
`
`W
`
`where 0sts.T.
`
`10
`
`15
`
`25
`
`30
`
`35
`
`The invention will now be described in greater detail in
`the following detailed description with reference to the
`drawings in which:
`FIG. 1 is a block diagram showing an example of trans
`mitter arrangement for generating OFDM-MIMO signals
`that include preambles according to the invention.
`FIG. 2 is a diagram showing an example of a frame, slot
`and symbol structure for signals of the invention.
`FIG. 3 is a diagram showing an arrangement of preamble,
`pilot and data symbols according to Sub-carrier frequency
`and time in accordance with the invention.
`FIG. 4 is a diagram showing an example of an arrange
`ment in the frequency domain of pilot carriers transmitted by
`a pair of transmitter antennas according to the invention.
`FIG. 5 is a diagram showing an example of an arrange
`ment in the frequency domain of pilot carriers transmitted by
`plural base stations according to the invention.
`FIG. 6 is a diagram showing an arrangement of preambles
`and data within one or more frames in accordance with the
`invention.
`FIG. 7 is a block diagram showing an example of a
`receiver arrangement for receiving and decoding OFDM
`MIMO signals that include preambles according to the
`invention.
`
`40
`
`45
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`50
`
`The present invention provides an Orthogonal Frequency
`Divisional Multiplexing (OFDM) signal that is delivered
`using Multiple-Input and Multiple-Output (MIMO) trans
`mitter and receiver antennas. In a conventional OFDM
`system, a block of data is represented by a frequency domain
`signal vector S that may be comprised of real or complex
`values. The vector S may be comprised of, for example,
`1024 elements, namely S=(s0, s1, ... .s 1024). Each element
`of the frequency domain signal vector S is used to modulate
`a respective Sub-carrier frequency of the carrier signal to
`obtain OFDM symbols. The frequency domain signal vector
`S is then converted into the time domain, Such as using a
`inverse fast Fourier transform (IFFT), to obtain a time
`domain vector V=IFFT(S)=(v0, v1,...,v1024). A cyclic
`
`55
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`

`US 7,233,625 B2
`
`5
`The modulated Sub-carriers are each modulated according
`to a sinc X (sin x)/x function in the frequency domain, with
`a spacing of 1/T between the primary peaks of the Sub
`carriers, so that the primary peak of a respective Sub-carrier
`coincides with a null the adjacent sub-carriers. Thus, the
`modulated Sub-carriers are orthogonal to one another though
`their spectra overlap.
`A preamble insertion circuit 109 stores and periodically
`inserts at least one preamble into the modulated Sub-carriers
`respectively generated by the STC and OFDM modulation
`circuits 105 and 107 according to the invention. The STC
`and OFDM modulation circuits 105 and 107 then deliver the
`modulated sub-carriers and the preambles in the time
`domain to their respective antennas (not shown) for trans
`mission.
`Preferably, the pilot symbols of the preamble are initially
`generated in the frequency domain by modulating frequency
`domain Sub-carriers using a pSuedo-noise (PN) code that is
`unique to each transmitter antenna. Then, the frequency
`domain pilot symbol sequence is converted to the time
`domain using an inverse fast Fourier transform (IFFT). The
`time domain pilot symbols are then stored in a memory in
`the pilot insertion circuit 109 and are then periodically
`inserted into the time domain OFDM-MIMO signal, such as
`at the beginning of a frame.
`FIG. 2 shows an example of a structure of the transmitted
`OFDM-MIMO signal in the time domain. The signal is
`formatted as a plurality of frames 201. Each frame includes
`plural slots 203. The first slot of each frame includes a
`preamble that is located at the beginning of the slot. The
`preamble includes two training symbols 205 and plural
`symbols 207.
`FIG. 3 shows the transmitted symbols arranged according
`to increasing time and increasing Sub-carrier frequency. In
`the time domain, the first two symbols of a frame are
`preamble symbols, as described above. Thereafter, data
`symbols or pilot symbols are transmitted, depending on the
`Sub-carrier frequency, until the next preamble symbols are
`transmitted.
`FIG. 4 illustrates, in greater detail, an example of a
`preamble shown in FIG. 3, referred to as Preamble 1. The
`preamble is broadcast by a single base station having at least
`two transmitter antennas. Each transmitter antenna transmits
`respective pairs of identical training symbols, also known as
`pilot carrier symbols, at a given Sub-carrier frequency.
`The Sub-carrier frequencies are divided into groups which
`are each assigned to a respective transmitter antenna. For
`example, FIG. 3 shows two transmitter antennas where, for
`example, the even numbered sub-carriers are assigned to
`Antenna Tx1 and the odd numbered sub-carriers are
`assigned to Antenna TX2. The pilot symbols for each
`antenna are orthogonal in the frequency domain in an
`interlaced transmission patterns, and the pilot symbols are
`Superimposed in the time domain.
`A unique pSuedo-noise (PN) code is assigned to each
`transmitter antenna to define the pilot symbols used to
`modulate the sub-carrier frequencies. The values of the pilot
`symbols that are transmitted are known to the receiver and
`may be used by the receiver to determine the framing of the
`transmitted signal, to determine the timing of the transmitted
`signal, to estimate the frequency and timing clock offsets of
`the receiver, to estimate the distortion in the transmitted
`Sub-carrier channels, and to estimate the carrier-to-interfer
`ence (C/I) ratio of the transmitted signals.
`When more than one base transceiver station (BTS)
`transmits to a receiver, another example of a preamble,
`referred to as Preamble 2, may be used, such as for fast cell
`
`40
`
`45
`
`6
`Switching applications. Two training symbols are used.
`However, the sub-carrier frequencies are divided among the
`BTSs, and each BTS uses a respective PN code to modulate
`its assigned sub-carrier frequencies. The Sub-carrier fre
`quencies assigned to particular BTS, as well as the PN code
`assigned to each BTS, are known to the receiver and may be
`used to provide co-channel interference cancellation
`between the BTSs, may be used to estimate the sub-carrier
`channels used by adjacent BTSs, and may be used as pilot
`symbols to track the Sub-carrier channels.
`FIG. 5 illustrates and example of Preamble 2 in which 6
`BTSS each transmit using two respective antennas. The two
`training symbols are assigned to Antenna Tx1 and Antenna
`Tx2, respectively. The sub-carrier frequencies are divided
`into 6 groups, each as signed to a BTSs.
`FIG. 6 illustrates an example of the insertion of preambles
`into one or more frames 601. A preamble, shown here as
`Preamble 1, is inserted at the beginning of the frame. Then,
`depending on the length of the frame and the channel
`conditions, additional preambles may be inserted at loca
`tions within the frame. As an example, Preamble 2 is
`inserted in the middle of the frame. A further preamble may
`be inserted at the end of the frame or at the beginning of the
`next frame.
`FIG. 7 is an example of a receiver that receives and
`decodes the preambles of the present invention. The receiver
`may be an Internet network terminal, cellular or wireless
`telephone, or other device that is able to receive OFDM
`MIMO signals.
`RF signals received by receiver antennas A and B (not
`shown) are delivered to respective circuits 701, 703 which
`convert the analog OFDM signals into digital signals and
`use the preamble of the signal to synchronize the signal and
`determine the frame boundaries of the transmitted data, such
`as by using sliding correlation. The framed data is then
`converted into vector form.
`To obtain better framing synchronization, a fine synchro
`nization stage is used by checking the correlation between
`received signals with known signals that are stored in the
`OFDM receiver memory. The orthogonal property of PN
`pilots in the training symbols is utilized to separate MIMO
`channels and perform the fine synchronization. The synchro
`nization may be performed either in the time domain or in
`the frequency domain. The MIMO system makes the fine
`synchronization more robust to multi-path fading due to the
`separation of the MIMO channel correlators.
`The synchronization operation is described in greater
`detail in U.S. application Ser. No. 09/751,881, titled “Syn
`chronization in a Multiple-input/multiple-output (MIMO)
`Orthogonal Frequency Division Multiplexing (OFDM) Sys
`tem. For Wireless Applications', filed Dec. 29, 2000 by the
`applicants of the present application, and incorporated
`herein by reference.
`After timing synchronization, the FFT window is deter
`mined, and the received OFDM signals are framed and are
`transferred into the frequency domain. The pilot channel can
`be used to estimate the frequency and sampling clock. The
`performance can be improved by averaging the results
`obtained from the different MIMO channels.
`The digital signals are also corrected for any differences
`between the oscillation frequency of the local oscillator of
`the transmitter system and the oscillation frequency of the
`local oscillator of the receiver system. A correction signal is
`used in generating the data vectors.
`The circuits 701 and 703 then deliver the data vectors to
`their demodulators 705, 707 which removes unneeded cycli
`cal extensions in the data vector and performs a discrete
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`OFourier transform (DFT) or a Fast Fourier Transform (FFT)
`that demodulates the data vectors to recover the original
`sequences of frequency domain Sub-symbols. The demodu
`lators 705, 707 then deliver the frequency domain sub
`symbols to a STC decoder 713 which decodes the sub
`symbols. The STC decoder also uses the preamble portion of
`the sub-symbols to correct for co-channel interference.
`The demodulators 705, 707 also deliver the preamble
`portion of the frequency domain Sub-symbols to their
`respective channel estimators 709, 711 which use the
`detected sub-symbols and the known values of the sub
`symbols to estimate the values of channel responses vectors
`that are delivered to the STC decoder 713 to compensate for
`distortions in the received signal.
`The STC decoder 713 then delivers the decoded Sub
`symbols to circuit 715 which performs a QAM demodula
`tion and de-interleaving, and further decodes the Sub-sym
`bols to obtain the original raw bit stream.
`The operation of the MIMO-OFDM receiver system and
`the channel estimation are described in greater detail in U.S.
`application Ser. Nos. 09/750,804 titled "Adaptive Time
`Diversity and Spatial Diversity for OFDM and 09/751,166
`titled “Channel Estimation for a MIMO OFDM System’,
`both filed Dec. 29, 2000 and incorporated herein by refer
`CCC.
`Although the present invention has been described in
`relation to particular embodiments thereof, many other
`variations and modifications and other uses may become
`apparent to those skilled in the art. It is preferred, therefore,
`that the present invention be limited not by this specific
`disclosure herein, but only by the appended claims.
`What is claimed is:
`1. A method of configuring a preamble portion of a data
`signal for transmission over a plurality of Sub-carriers by at
`least two antennas of a transmitter device, said method
`comprising:
`assigning a respective pseudo-noise (PN) code to each of
`said at least two antennas;
`assigning each of said plurality of Sub-carriers to a
`respective one of said at least two antennas;
`modulating each of said plurality of Sub-carriers as a
`function of said respective pseudo-noise (PN) code that
`is assigned to a same one of said at least two antennas
`as said each of said plurality of Sub-carriers such that a
`plurality of modulated sub-carriers are obtained that are
`each assigned to a respective one of said at least two
`antennas,
`delivering each of said plurality of modulated sub-carriers
`to its assigned transmitter; and
`transmitting, at Substantially a same time, each said
`plurality of modulated Sub-carriers using its assigned
`transmitter.
`2. The method of claim 1 wherein said data signal
`comprises an Orthogonal Frequency Division Multiplexing
`(OFDM) signal.
`3. The method of claim 1 wherein said data signal is
`comprised of a plurality of frames, each of said plurality of
`frames being comprised of a plurality of time slots, each of
`said plurality of time slots including a plurality of symbols,
`and said method further comprises: inserting said each of
`said plurality of modulated sub-carriers into at least a first
`two of said plurality of symbols within a first one of said
`plurality of time slots prior to delivering said plurality of
`modulated Sub-caters to its assigned antenna.
`4. The method of claim 3 further comprising: inserting
`said each of said plurality of modulated sub-carriers into at
`least a first two of said plurality of symbols within a further
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`one of said plurality of time slots prior to delivering said
`plurality of modulated Sub-carriers to its assigned antenna.
`5. A method of configuring a preamble portion of a data
`signal for transmission over a plurality of Sub-carriers by at
`least two transmitter devices each having at least two
`antennas, said method comprising:
`assigning a respective pseudo-noise (PN) code to each or
`said at least two antennas;
`assigning each of said plurality of Sub-carriers to a
`respective one of said at least two transmitter devices;
`modulating each of said plurality of Sub-carriers as a
`function of said respective pseudo-noise (PN) code that
`is assigned to a same one of said at least two transmitter
`devices to which said each of said plurality of sub
`carriers is assigned such that a plurality of modulated
`Sub-carriers are obtained that arc each assigned to a
`respective one of said at least transmitter two devices;
`and
`transmitting, at Substantially a same time, each of said
`plurality of modulated Sub-carriers using each of said at
`least two antennas of its assigned transmitter device.
`6. The method of claim 5 wherein said signal comprises
`an Orthogonal Frequency Division Multiplexing (OFDM)
`signal.
`7. The method of claim 5 wherein said data signal is
`comprised of a plurality of frames, each of said plurality of
`frames being comprised of a plurality of time slots, each of
`said plurality of time slots including a plurality of symbols,
`and said method further comprises: inserting said each of
`said plurality of modulated sub-carriers into at least a first
`two of said plurality of symbols within a first one of said
`plurality of time slots prior to delivering said plurality of
`modulated Sub-carriers to its assigned transmitter device.
`8. The method of claim 7 further comprising: inserting
`said each of said plurality of modulated sub-carriers into at
`least a first two of said plurality of symbols within a further
`one of said plurality of time slots prior to delivering said
`plurality of modulated Sub-carriers to its assigned transmit
`ter device.
`9. An apparatus for configuring a preamble portion of a
`data signal for transmission over a plurality Sub-carriers by
`at least two antennas of a transmitter device, said apparatus
`comprising:
`a preamble insertion circuit configured to:
`assign a respective pseudo-noise (PN) code to each of said
`at least two antennas;
`assign each of said plurality of Sub-carriers to a respective
`one of said at least two antennas; and
`modulate each of said plurality of Sub-carriers as a
`function of said respective pseudo-noise (PN) code that
`is assigned to a same one of said at least two antennas
`as said each of said plurality of Sub-carriers such that a
`plurality of modulated sub-carriers are obtained that are
`each assigned to a respective one of said at least two
`antennas; and
`a coding circuit configured to deliver each of said plural
`ity of modulated Sub- carriers to its assigned transmit
`ter;
`said transmitter antenna being configured to transmit, at
`Substantially a same time, each said plurality of modu
`lated Sub-carriers using its assigned transmitter.
`10. The apparatus of claim 9 wherein said data signal
`comprises an Orthogona