(12) United States Patent
`(10) Patent N0.:
`US 6,542,556 B1
`
`Kuchi et al.
`(:45) Date of Patent:
`Apr. 1, 2003
`
`U5006542556B1
`
`(54) SPACE-TIME CODE FOR MULTIPLE
`ANTENNA TRANSMISSION
`
`(75)
`
`..
`Inventors: Kiran Kuchi, Irving, TX (US); Jyri K.
`Hamalamen’ oulu (F1)
`
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`WO 00/51265
`WO 01/19013 A1
`WO 01/54305 A1
`
`,
`$8 81/22::2 :1
`WO 01/69814 A1
`
`8/2000
`3/2001
`7/2001
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`333%
`9/2001
`
`(73)
`
`ASSTgHCCI Nokia Mobile Phones Ltd., ESpOO (F1)
`
`OTIIER PUBLICATIONS
`
`(*) NOtiCCI
`
`SubjeCtIO any disclaimer, the term Of this
`patent 15 extended or adjusted under 35
`U.S.C~ 154(b) by 0 days.
`
`(21) Appl. No.: 09/539,319
`.
`Mar. 31: 2000
`Flledi
`(22)
`Int. C1.7 ............................. H04B 7/06, H04J 11/00
`(51)
`(52) Us. Cl.
`....................... 375/299 375/146 370/204
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`’ 370/209,
`h ................................. 375 133 135
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`0 wags/116 141 146 147 260 /267’ 299?
`' 3'70/50’4 208 20’9 21’0. 453/101’ 103’
`
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`
`58
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`(
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`(56)
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`References Cited
`UHS PATENT DOCUMENTS
`
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`’
`/
`050 “11 et a ‘
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`2 237 706 A
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`W0 00/11806
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`
`GB
`W0
`$8
`W0
`W0
`W0
`
`transmit
`Guey .liann—Ching: “Concatenated coding for
`diversity systems” Proceedings of the 1999 VTC—Fall
`IEEE VTS 50th Vehicular Technology Conference ‘Gate-
`way to 21st Century Communications Village’; Amsterdam,
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`8, Oct.
`1998, pp.
`1451—1458, XP002100058,
`ISSN:
`0733—8716, cited in the applicaion the Whole document.
`
`(List continued on next page.)
`Prlmary Examiner—Young v1‘. 1‘56
`(74) Attorney, Agent, or Firm—Brian T. Rivers
`
`(57)
`
`ABSTRACT
`
`.
`.
`.
`A method and apparatus for space-time codmg signals for
`transmission on multiple antennasAreceived input symbol
`stream is transformed using a predefined transform and
`transmitted on a first set of N antennas. The same input
`symbol stream is then offset by M symbol periods to
`generate an offset input symbol stream. The offset input
`symbol stream is then transformed using the predefined
`transform and transmitted on a second set of N antennas. A
`third through X‘h set of N antennas may be utilized for
`transmission by successively offsetting the offset input sym—
`bol stream by an additional M symbol periods for each
`additional set of N antennas used, before performing the
`transform and transmitting on the additional set of N anten-
`“5'
`
`24 Claims, 2 Drawing Sheets
`
`400
`
`406
`
`
`\(
`
`
`
`Filter and
`s1w1
`Modulate
`
`
`-szw1
`
`
`
`Sd1W1 Sd2W2
`Filter and
`Modulate
`
`-Sd2W1 Sd1W2
`
`32w2
`
`S1W1
`
`416
`
`408
`
`412
`
`(cid:36)(cid:51)(cid:51)(cid:47)(cid:40)(cid:3)(cid:20)(cid:19)(cid:19)(cid:23)
`APPLE 1004
`
`

`

`US 6,542,556 B1
`
`Page 2
`
`OTHER PUBLICATIONS
`
`Tarokh V et al: “SpaceiTime Block Coding for Wireless
`Communications: Performance Results”, IEEE Journal on
`Selected Areas in Communications, IEEE Inc. New York,
`US, v01. 17, N0. 3, Mar. 1999, pp. 451—460, XP000804974
`ISSN: 0733—8716 equations (6) and (7).
`A. Hiroike, F. Adachi, N. Nakajima “Combined Eifects of
`Phase Sweeping Transmitter Diversity and Channel Cod-
`ing”, IEEE Transactions on Vehicular Technology, vol. 41,
`No. 2, May 1992.
`L. Jalloul, K. Rohani, K. Kuchi, J. Chien “Performance
`Analysis of CDMA Transmit Diversity Methods” IEEE
`Vehicular Technology Conference,
`Fall
`1999;
`pp.
`1326—1330.
`Alberto Gutierrez et al., “An Introduction to PSTD for 18—95
`and CDMA 2000”, Wireless Communications and Network-
`ing Conference, WCNC, pp. 1358—1362, vol. 3, 1999.
`Two Signaling Schemes for Improving the Error Perfor—
`mance of Frequency—Division—Duplex (FDD) Transmission
`Systems Using Transmitter Antenna Diversity, Seshadri, et
`al. 1993 IEEE; pp. 508—511.
`A Simple Transmit Diversity Technique for Wireless Com-
`munications, S. M. Alamouti, 1998 IEEE; pp. 1451—1458.
`Space—Time Block Codes
`from Orthogonal Designs,
`Tarokh, et al., 1999 IEEE; pp. 1456—1467.
`Downlink Improvement
`through Space—Time Spreading,
`Kogiantis, et al., Proposal for 3PP2/TSG—C3—19990805—xx.
`Link Performance Comparison of OTD and STTD/STS for
`Voice Applications, Kuchi,
`et
`al.,
`Proposal
`for
`3GPP2—C30—19990826—i.
`Open and Closed Loop Transmit Diversity at High Data
`Rates on 2 and 4 Elements, Harrison, et al., Proposal for
`3GPP2—C30—19990817—017, 1999.
`Seshadri, N. et al; SpaceiTime Codes for Wireless Com—
`munication: Code Construction: 1997 IEEE; pp. 637—641;
`0—7803—3659—3/97.
`Tarokh, V., et al.; The Application of Orthogonal Designs to
`Wireless Communication;
`1998
`IEEE;
`pp.
`46—47;
`0—7803—4408—1/98.
`Tarokh, V. et al; Space—Time Codes for High Data Rate
`Wireless Communication: Performance Criteria;
`1999
`IEEE; pp. 299—303.
`Tarokh, V. et al; A Differential Detection Scheme for Trans-
`mit Diversity; 1999 IEEE; pp. 1043—1047; 0—7803—5668—3/
`99.
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`Foschini, G.; Layered Space—Time Architecture for Wireless
`Communication in a Fading Environment When Using
`Multi—Element Antennas; Bell Labs Technical Journal,
`1996; p. 41—p59.
`Tirkkonen, O. et al.; Complex SpaceiTime Block Codes for
`Four TX Antennas;
`IEEE;
`2000;
`p.
`1005—p.
`1009;
`0—7803—6451—1/10.
`Hottinen, A. et al.; Closediloop transmit diversity tech—
`niques for multi—element transceivers; IEEE 2000; p. 70—73;
`0—7803—6507—0/00.
`Tirkkonen, O. et al.; Minimal Non—Orthogonality Rate 1
`Space—Time Block Code for 3+ TX Antennas; IEEE Sep.
`6—8, 2000; 6th Int. Symp. on Spread—Spectrum Tech. &
`Appli., NJIT, New Jersey, USA; p. 429—p. 432.
`Sweatman, C. et al.; A Comparison of Detection Algorithms
`including BLAST for Wireless Communication using Mul-
`tiple Antennas; IEEE 2000; p. 698—p. 703; 0—7803—6465—5/
`00.
`
`Damen, O. et al.; Lattice Code Decoder for Space—Time
`Codes; IEEE 2000; p. 161—p. 163; 1089—7798/00; IEEE
`Communications Letters, vol. 4, No. 5, May 2000.
`
`Calderbank, A. et al.; Space—Time Codes for Wireless
`Communication; 19997 IEEE; ISIT 1997, Ulm, Germany,
`Jun. 29—Jul. 4; p. 146.
`Tarokh, V. et al.; Recent Progress in Space—Time Block and
`Trellis Coding; 1998 IEEE; ISIT 1998, Cambridge, MA,
`USA; Aug. 16—Aug. 21; p. 314.
`Rohani, K. et al.; A Comparison of Base Station Transmit
`Diversity Methods for Third Generation Cellular Standards;
`1999 IEEE; 0—7803—5565—2/99; p. 351—p. 355.
`Jalloul, L. et al.; Performance Analysis of CDMA Transmit
`Diversity Methods; 1999 IEEE; 0—7802—5435—4/99; p.
`1326—p. 1330.
`
`Raitola, M. et al.; Transmission Diversity in Wideband
`CDMA; 1999 IEEE; 0—7803—5565—2/99; p. 1545—1549.
`
`Correia, A. et al.; Optimised Constellations for Transmitter
`Diversity; 1999 IEEE; 0/7803—5435—4/99; p. 1785—1789.
`Tarokh, V. et al.; A Differential Detection Scheme for
`Transmit Diversity; 1999 IEEE; 0—7803—5668—3/99; p.
`1043—p. 1047.
`
`Ionescu; New Results on Space—Time Code
`D. Mihai
`Design Criteria; 1999 IEEE; pp. 6844687; 0778037566873/
`99.
`
`Tarokh, V., et al.; Space—Time Codes for High Data Rate
`Wireless Communication: Performance Criterion and Code
`Construction; 1998 IEEE; IEEE Transactions on Informa-
`tion Theory, vol. 44, No. 2, Mar. 1998.
`
`Edited by Holma H., et al.; WCDMA for UMTS Radio
`Access for Third Generation Mobile Communications;
`Reprinted Jun. 2000; p. 97; John Wiley & Sons, Ltd., Baffins
`Lane, Chichester, West Sussex, P019 1UD, England.
`
`Tarokh, V., et al.; Space—Time Block Coding for Wireless
`Communications: Performance Results; 1999 IEEE; IEEE
`Journal on Selected Areas in Communications, vol. 17. N0.
`3, Mar. 1999.
`
`Naguib, A.F. et al; Space—Time Coded Modulation for High
`Data Rate Wireless Communications; 1997 IEEE; pp.
`102—109; 0—7803—4198—8/97.
`
`Shiu, D. et al.; “Scalable Layered SpaceiTime Codes for
`Wireless Communications: Performance Analysis
`and
`Design Criteria”; 0—7803—5668—3/99; 159—163 pp.; 1999
`IEEE; University of California at Berkeley USA.
`Alamouti, SM. et al; Trellis—Coded Modulation and Trans-
`mit Diversity: Design Criteria and Performance Evaluation;
`1998 IEEE; pp. 703—707; 0—7803—5 106—1/98.
`
`Shiu, D. et al.; “Layered Space—Time Codes for Wireless
`Communications Using Multiple Transmit Antennas”;
`0—7803—5284—X99; 436—440 pp.; 1999 IEEE; University of
`California at Berkeley USA.
`
`Hassibi, B. et al.; “HighiRate Linear SpaceiTime Codes”;
`IEEE Apr. 2001; p. 2461—p. 2464, 0—7803—7041—04/01.
`
`Lo, T. et al; Space—Time Block Coding—From a Physical
`Perspective; 1999 IEEE; pp. 150—153; 0—7803—5668—3/99.
`
`* cited by examiner
`
`

`

`US. Patent
`
`Apr. 1, 2003
`
`Sheet 1 0f2
`
`US 6,542,556 B1
`
`
`
`
`
` Spread,
`Filter and
`
`Modulate
`
`102
`x(t)
`
`
` Spread,
`
`Filter and
`
`Modulate
`
`
`108
`112
`
`206
`204
`
`
`Filter
`Despread and
`
`Demodulate
`
`FIG. 2
`
`State* Output Symbols (Ant.1, Ant. 2)
`0
`1
`2
`3
`
`300
`
`V
`
`0
`
`1
`
`2
`
`3
`
`(0,0)
`
`(0,1)
`
`(0,2)
`
`(0,3)
`
`(1,0)
`
`(1,1)
`
`(1.2)
`
`(2,0)
`
`(2,1)
`
`(2,2)
`
`(3,0)
`
`(3,1)
`
`(3,2)
`
`(1,3)
`
`(2,3)
`
`(3,3)
`
`

`

`US. Patent
`
`Apr. 1, 2003
`
`Sheet 2 0f 2
`
`US 6,542,556 B1
`
`
`
`s1w1
`52w2
`
`s1w1
`-82W1
`
`Filter and
`Modulate
`
`411
`
`Sd1W1 Sd2W2
`
`
`
`Filter and
`Modulate
`
`-Sd2W1 Sd1W2
`
`412
`
`408
`
`416
`
`420
`
`FIG. 4
`
`
`
`
`502
`
`X(t)
`
`506
`
`3/4 AT&T
`Block Code
`
`3/4 AT&T
`Block Code
`
`508
`
`
`
`Spread,
`Filter and
`Modulate
`
`
`
`
`
`
`Spread,
`Filter and
`Modulate
`
`
`512
`
`FIG. 5
`
`

`

`US 6,542,556 B1
`
`1
`SPACE-TIME CODE FOR MULTIPLE
`ANTENNA TRANSMISSION
`
`FIELD OF THE INVENTION
`
`This invention relates to a method and apparatus for
`achieving transmit diversity in telecommunication systems
`and, more particularly, to a method and apparatus for space—
`time coding signals for transmission on multiple antennas.
`BACKGROUND OF THE INVENTION
`
`5
`
`10
`
`2
`sity for two antennas that offers second order diversity for
`complex valued signals. S. Alamouti, “A Simple Transmit
`Diversity Technique for Wireless Communications, ” IEEE
`Journal on Selected Areas of Communications, pp.
`1451—1458, October 1998. The Alamouti method involves
`simultaneously transmitting two signals from two antennas
`during a symbol period. During one symbol period, the
`signal transmitted from a first antenna is denoted by S0 and
`the signal transmitted from the second antenna is denoted by
`S1. During the next symbol period,
`the signal —sl* is
`transmitted from the first antenna and the signal 50* is
`transmitted from the second antenna, where * is the complex
`conjugate operator. The Alamouti method may also be done
`in space and frequency coding. Instead of two adjacent
`symbol periods, two orthogonal Walsh codes may be used to
`realize space—frequency coding.
`Extension of the Alamouti method to more than two
`antennas is not straightforward. Tarokh et al. have proposed
`a method using rate=1/2, and 3/4 SpaceTime Block codes for
`transmitting on three and four antennas using complex
`signal constellations. V. Tarokh, H. Jafarkhani, and A.
`Calderbank, “Space-Time Block Codes from Orthogonal
`Designs, ” IEEE Transactions on Information Theory, pp.
`1456—1467, July 1999. This method has a disadvantage in a
`loss in transmission rate and the fact that the multi-level
`
`nature of the ST coded symbols increases the peak-to-
`average ratio requirement of the transmitted signal and
`imposes stringent requirements on the linear power amplifier
`design. Other methods proposed include a rate=1, orthogo—
`nal transmit diversity (OTD)+space-time transmit diversity
`scheme (STTD) four antenna method. L. Jalloul, K. Rohani,
`K. Kuchi, and J. Chen, “Performance Analysis of CDA/IA
`Transmit Diversity Alethoa's, ” Proceedings ofIEEE Vehicu-
`lar Technology Conference, Fall 1999, and M. Harrison, K.
`Kuchi, “Open and Closed Loop Transmit Diversity at High
`Data Rates on 2 and 4 Elements, ” Motorola Contribution to
`3GPP-C30-19990817—017. This method requires an outer
`code and offers second order diversity due to the STTD
`block (Alamouti block) and a second order interleaving gain
`from use of the OTD block. The performance of this method
`depends on the strength of the outer code. Since this method
`requires an outer code,
`it
`is not applicable to uncoded
`systems. For the case of rate=1,/3 convolutional code, the
`performance of the OTD+STTD method and the Tarokh
`rate=% method ST block code methods are about the same.
`
`SUMMARY OF THE INVENTION
`
`The present invention presents a method and apparatus for
`space—time coding signals for transmission on multiple
`antennas. In the method and apparatus, a received input
`symbol stream is transformed using a predefined transform
`and transmitted on a first set of N antennas. The same input
`symbol stream is then offset in time by M symbol periods to
`generate an oifset input symbol stream. The oifset input
`symbol stream may be offset so as to lead or lag the input
`symbol stream. The offset
`input symbol stream is then
`transformed using the predefined transform and transmitted
`on a second set of N antennas. Athird through X’h set of N
`antennas may be utilized for transmission by successively
`offsetting the offset input symbol stream by an additional M
`symbol periods for each additional set of N antennas used,
`before performing the transform and transmitting on the
`additional set of N antennas. The transform may be applied
`in either the time domain or Walsh code domain.
`
`At the receiver, the transmitted symbols may be recovered
`using a maximum likelihood sequence estimator (MLSE)
`decoder implemented with the Viterbi algorithm with a
`decoding trellis according to the transmitter.
`
`As wireless communication systems evolve, wireless sys-
`tem design has become increasingly demanding in relation
`to equipment and performance requirements. Future wire-
`less systems, which will be third and fourth generation
`systems compared to the first generation analog and second
`generation digital systems currently in use, will be required
`to provide high quality high transmission rate data services
`in addition to high quality voice services. Concurrent with ,
`the system service performance requirements will be equip—
`ment design constraints, which will strongly impact
`the
`design of mobile terminals. The third and fourth generation
`wireless mobile terminals will be required to be smaller,
`lighter, more power-efficient units that are also capable of
`providing the sophisticated voice and data services required
`of these future wireless systems.
`Time-varying multi-path fading is an effect in wireless
`systems whereby a transmitted signal propagates along
`multiple paths to a receiver causing fading of the received
`signal due to the constructive and destructive summing of
`the signals at the receiver. Several methods are known for
`overcoming the effects of multi—path fading, such as time
`interleaving with error correction coding,
`implementing
`frequency diversity by utilizing spread spectrum techniques,
`or transmitter power control
`techniques. Each of these
`techniques, however, has drawbacks in regard to use for
`third and fourth generation wireless systems. Time inter-
`leaving may introduce unnecessary delay, spread spectrum
`techniques may require large bandwidth allocation to over-
`come a large coherence bandwidth, and power control
`techniques may require higher transmitter power than is
`desirable for sophisticated rccciver-to-transmittcr feedback
`techniques that increase mobile terminal complexity. All of
`these drawbacks have negative impact on achieving the
`desired characteristics for third and fourth generation mobile
`terminals.
`
`15
`
`40
`
`45
`
`Antenna diversity is another technique for overcoming the
`effects of multi-path fading in wireless systems. In diversity
`reception,
`two or more physically separated antennas are
`used to receive a signal, which is then processed through
`combining and switching to generate a received signal. A
`drawback of diversity reception is that the physical separa-
`tion required between antennas may make diversity recep-
`tion impractical for use on the forward link in the new
`wireless systems where small mobile terminal size is
`desired. A second technique for
`implementing antenna
`diversity is transmit diversity. In transmit diversity a signal
`is transmitted from two or more antennas and then processed
`at
`the receiver by using maximum likelihood sequence
`estimator (MLSE) or minimum mean square error (MMSE)
`techniques. Transmit diversity has more practical applica-
`tion to the forward link in wireless systems in that it is easier
`to implement multiple antennas in the base station than in
`the mobile terminal.
`
`Transmit diversity for the case of two antennas is well
`studied. Alamouti has proposed a method of transmit diver-
`
`60
`
`65
`
`

`

`US 6,542,556 B1
`
`3
`In an embodiment, 4 antennas are used for transmission.
`Every 2 input symbols in a received input symbol stream are
`transformed in the time domain by an Alamouti transform
`and the result is transmitted on antennas 1 and 2 during the
`time of two symbol periods. The received input symbol
`stream is also delayed for two symbol periods, and this
`delayed input symbol stream is input to an Alamouti trans-
`form where every two symbols are transformed and the
`delayed result is transmitted on antennas 3 and 4 during the
`time of two symbol periods. The transmitted signal may be
`received and decoded using an MLSE receiver. The method
`and apparatus provides diversity of order four and outper-
`forms othcr proposed extensions of the Alamouti method to
`more than two antennas by approximately 1/2 to 1 dB for
`uncoded transmissions.
`
`In an alternative embodiment using 4 antennas, every 2
`input symbols in a received input symbol stream are trans-
`formed in the Walsh code domain. The Alamouti coded
`
`10
`
`15
`
`symbols are transmitted on two orthogonal Walsh codes, W1
`and W2 simultaneously on antennas 1 and 2. Both W1 and '
`W2 span two symbol periods, which maintains the trans-
`mission rate at
`two symbol periods. The received input
`symbol stream is also delayed for two symbol periods and
`the Alamouti transform is also applied in the Walsh code
`domain to the delayed input symbol stream. This delayed ’
`result is transmitted on antennas 3 and 4 during the time of
`two symbol periods.
`In a further alternative embodiment using 8 antennas for
`transmission, a rate=3/i: ST block code is combined with a 4
`symbol delay. Every three symbols in an input symbol
`stream are transformed by the ST block code and transmitted
`on antennas 1—4. The received input symbol stream is also
`delayed for four symbol periods, and this delayed input
`symbol stream is input to the ST block code transform where
`every three symbols are transformed and the delayed result
`is transmitted on antennas 4—8 during the time of four
`symbol periods.
`BRIEF DESCRIPTION OF THE FIGURES
`
`40
`
`FIG. 1 shows a block diagram of portions of a transmitter
`according to an embodiment of the invention;
`FIG. 2 shows a block diagram of portions of a receiver
`according to an embodiment of the invention;
`FIG. 3 shows a trellis structure used to process signals in
`the receiver of FIG. 2;
`FIG. 4 shows a block diagram of portions of a transmitter
`according to an alternative embodiment of the invention;
`and
`
`FIG. 5 shows a block diagram of portions of a transmitter
`according to a further alternative embodiment of the inven-
`tion.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`4
`
`identical symbol streams, with one symbol stream X(t)
`being input to transform block 106 and a second identical
`symbol stream X(t) being input to offset block 104. Offset
`block 104 causes a 2 symbol period delay in the second
`symbol stream and then the delayed second symbol stream
`is input to transform block 108. Every two symbols S1 and
`82 are processed in transform block 106 using the Alamouti
`method and the output of the transform is transmitted on
`antenna 114 and antenna 116. The input signal may be
`complex valued and of arbitrary constellation size. The
`Alamouti transformation performed in transform block 106
`can be written in a matrix form as shown below:
`
`[St ”I
`-53 SI
`
`Equation 1
`
`The rows in the matrix indicate the antenna the symbol is
`transmitted on, and the columns indicate the instant they are
`transmitted. Symbols S1 and S2 are transmitted on antenna
`114 and antenna 116 at instants t1 and t2, respectively.
`The second identical symbol stream X(t) input to offset
`block 104 is offset by two symbol periods and transformed
`in transform block 108 using the Alamouti transformation as
`shown below:
`
`[ Sdl
`Sdz]
`—Sd§ Sdf
`
`Equation 2
`
`The output of the transform from transform block 108 is then
`transmitted on antenna 118 and antenna 120. The transmitted
`
`signal as it will be received during the time period (0,t1) can
`be written as follows:
`
`Er
`r(tI) = 4 [51111—53112 +Sd1113 —S§2a4] + n(t])
`
`Equation 3
`
`and, for the time duration (t1,t2) as,
`
`Er
`r(tZ) = 4 [$111+ 5:112 + 51,203 + 531114] + n02)
`
`Equation 4
`
`45
`
`where SM and Sd2 are the transmitted symbols on the
`delayed branch and 11(t) is the additive white Gaussian noise.
`The transmitted signal power EC may be evenly distrib-
`uted across the four antennas and the channel coefficients (X
`
`may be modelled as complex Gaussian.
`This received signal can be decoded using an MISE
`receiver. Referring now to FIG. 2,
`therein is shown a
`receiver 200 according to an embodiment of the invention.
`Receiver 200 includes antenna 202, filter, despread and
`demodulate block 204, processor block 206, and output 208.
`In the embodiment, receiver 200 receives the transmitted
`signal r(t) at antenna 202, and filters, despreads and dem odu-
`latcs the signal in filter, despread and demodulate block 204.
`Processor block 206 then decodes the sequence that mini-
`mizes the Eucledian distance D between the transmitted and
`received signals and outputs the sequence at output 208
`according to the following:
`
`D = “r(t) - (X(t) +360 — 2D)”
`=||r(tI)—(S1111—S3112 +de113 —S§2a4)|| +
`
`Equation 5
`
`Referring now to FIG. 1, therein is illustrated a block
`diagram of portions of a transmitter 100 according to an
`embodiment of the invention. Transmitter 100 includes input
`102, offset block 104, transform block 106, transform block
`108, spread, filter and modulate (SFM) block 110, spread,
`filter and modulate (SFM) block 112, antenna 114, antenna
`116, antenna 118 and antenna 120. Transmitter 100 may be
`implemented into any type of transmission system that
`transmits coded or uncoded digital
`transmissions over a
`radio interface.
`
`60
`
`65
`
`In the embodiment of FIG. 1, transmitter 100 receives an
`input symbol stream X(t) at input 102. X(t) is split into two
`
`

`

`US 6,542,556 B1
`
`5
`-continued
`||r(1‘2)—(Sza'1 + Sill/2 + 542113 + 53,114)”
`
`Further optimization of the branch metrics can be obtained
`with the following simplification. Using the equations,
`
`r'(t1)=r(t1)—(Sl(x1—Sz*a2)
`
`f(t2)=r(t2)— (S20t1+S1 * (12)
`
`Equation 6
`
`Equation 7
`
`the following metric can be obtained:
`
`02 = HM) — (dewj‘ — s3214,)||2 +t|?(12)—(sd2a3 + nga'4)||2 Equation 3
`
`This may be further simplified as:
`
`D2 = ||}(t1)(a3)* +;(12)*ar4 isdj||2 +
`
`Equation 9
`
`H;(II)((14)* — ;(1‘2)*a3 + 3;, 2
`
`Symbols S41, Sd2 may be found separately. In the simplifi-
`cation given by equation 9, only the values $41 and Sd2 need
`to be modified at each computation stage. This reduces the
`number of multiplications in the calculation.
`The input to the Viterbi decoder is the sampled received
`signal observed over “11” time epochs or n symbol periods,
`where n=2 for 4 antenna ST codes. The state transitions in
`
`the Viterbi decoder occur every “n” time epochs.
`Referring now to FIG. 3,
`therein is shown a trellis
`structure 300 used to process the ST code of the received
`signal in receiver 200, according to an embodiment of the
`invention. Trellis structure 300 is the binary phase shift
`keying (BPSK) trellis diagram for a 4 antenna space-time
`(ST) code. Trellis 300 can be described using the following
`state labelling:
`
`Next state=input symbols (S1,52)
`
`Equation 10
`
`Output={previous state, input symbols}={(Sd1,Sdz), (
`51:52)}
`
`Equation 1 1
`
`The number of states in the trellis 300 is given by M2
`where M is the signal constellation size. The total number of
`states shown in trellis 300 is 4. Trellis 300 may be decoded
`using the Viterbi algorithm. FIG. 3 shows the bpsk case.
`()ther modulation may be used in alternative embodiments.
`Generally, for the case of a 4-antenna ST code, the decoder
`has to remember all possible 2 previous symbols (i.e., 4
`states for bpsk, and 16 states for qpsk, 64 states for 8-psk and
`so on) at each state.
`Referring now to FIG. 4, therein are shown portions of a
`transmitter according to an alternative embodiment of the
`invention. FIG. 4. shows transmitter 400, which includes
`input 402, offset block 404, space—time spreading (STS)
`transform block 406, STS transform block 408, filter and
`modulate block 410, filter and modulate block 412 and
`antennas 414, 416, 418 and 420. In transmitter 400, the
`Alamouti transformation is applied in Walsh code domain
`instead of time domain. The Alamouti coded symbols are
`transmitted on two orthogonal Walsh codes W1, W2 simul-
`taneously. Both W1 and W2 span two symbol periods in this
`case maintaining the total transmission rate. This method is
`known as space-time spreading (STS). Adelayed copy of the
`input signal is STS transformed again and transmitted via
`the other two antennas.
`In the embodiment of FIG. 4, transmitter 400 receives an
`input symbol stream X(t) at input 402. X(t) is split into two
`
`6
`identical symbol streams, with one symbol stream X(t)
`being input to transform block 406 and a second identical
`symbol stream X(t) being input to offset block 404. Offset
`block 404 causes a 2 symbol period delay in the second
`symbol stream and then the delayed second symbol stream
`is input to transform block 408. Every two symbols S1 and
`82 are processed in transform block 406 using the Alamouti
`method and the output of the transform is transmitted on
`antenna 414 and antenna 416. The input signal may be
`complex valued and of arbitrary constellation size. The
`Alamouti transformation performed in STS transform block
`406 can be written in a matrix form as shown below:
`
`[ 51W]
`SgWZ]
`—S§W1 SIWZ
`
`Equation 12
`
`The rows in the matrix indicate the antenna on which the
`symbol is transmitted. The symbols SI and 82 are transmit—
`ted simultaneously on antenna 414 during the same two
`symbol periods in which the symbols—82* and 81* are
`transmitted simultaneously on antenna 416.
`The second identical symbol stream X(t) input to offset
`block 404 is delayed by two symbol periods and transformed
`in transform block 408 using the Alamouti transformation as
`shown below:
`
`Sd2 W2
`Sd1W1
`—Sd§ W] m; m
`
`Equation 13
`
`The rows in the matrix indicate the antenna on which the
`
`symbol is transmitted. The symbols Sdl and Sd2 are trans-
`mitted simultaneously on antenna 418 during the same two
`symbol periods in which the symbols—Sd2* and Sdl* are
`transmitted simultaneously on antenna 420.
`A receiver for the embodiment of the transmitter of FIG.
`
`4 may be implemented in the same manner as the receiver
`of FIG. 2, with the filter, despread and demodulate block 204
`modified to receive the Alamouti coded symbols that are
`transmitted simultaneously on the Walsh codes W1 and W2.
`Various alternative embodiments of the invention are
`
`possible. For example, in the case of three transmit antennas,
`the output of any two of the Alamouti/STS branches can be
`mapped to the same antenna to obtain a diversity gain of
`order three. Also, for 6 and 8 antennas the given method can
`be generalized by using Alamouti transform block combined
`with 3 and 4 delay diversity branches, respectively,
`A further alternative embodiment may also be used for 8
`transmit antennas. Referring now to FIG. 5,
`therein is
`illustrated a block diagram of portions of a transmitter 500
`according to a further alternative embodiment of the inven-
`tion. Transmitter 500 includes input 502, offset block 504,
`transform block 506, transform block 508, spread, filter and
`modulate (SFM) block 510, spread, filter and modulate
`(SFM) block 512, antenna 514, antenna 516, antenna 518,
`antenna 520, antenna 522, antenna 524, antenna 526 and
`antenna 528. Transmitter 500 may be implemented into any
`type of transmission system that transmits coded or uncoded
`digital transmissions over a radio interface.
`In the embodiment of FIG. 5, transmitter 500 receives an
`input symbol stream X(t) at input 502. X(t) is split into two
`identical symbol streams, with one symbol stream X(t)
`being input to transform block 506, and a second identical
`symbol stream X(t) being input to offset block 504. Offset
`block 504 causes a 4 symbol period delay in the second
`symbol stream and then the delayed second symbol stream
`is input to transform block 508. Every three symbols SI, 52
`
`5
`
`10
`
`15
`
`40
`
`45
`
`60
`
`65
`
`

`

`US 6,542,556 B1
`
`7
`and 53 are processed in transform block 506 using a 3A: rate
`block code transform and the output of transform block 506
`is transmitted on antennas 514, 516, 518 and 520. The 3A: rate
`block code may be as described in the paper by V. Tarokh,
`H. Jafarkhani, and A. Calderbank, “Space-Time Block
`Orthogonal Codes from Orthogonal Designs, ” IEEE Trans-
`actions on Information Theory, pp. 1456—1467, July 1999.
`The delayed second input symbol stream is processed in
`block 508 using the same 3/4 rate block code transform and
`the output of transform block 508 is transmitted on antennas
`522, 524, 526 and 528. The input signal may be complex
`valued and of arbitrary constellation size.
`The 3/4 rate ST block code is given by the following
`transformation.
`
`S3
`Si
`SI
`0
`—SE SI
`S}
`—S§
`O
`0
`S; —S§
`
`0
`—S3
`52
`51
`
`Equation 14
`
`The trellis structure for the 8-antenna ST code can be
`
`described using the following state labelling.
`Next state=input symbols (51,5253)
`
`Equation 15
`
`Output label={previous state, input symbols}={(Sd1,Sd2,Sd3), (Sl,
`$253)}
`Equation 16
`A receiver for the embodiment of the transmitter of FIG.
`5 may be implemented in the same manner as the receiver
`of FIG. 2, with the filter, despread and demodulate block 204
`modified to receive the 3A: rate block code symbols. It is
`assumed that
`the Viterbi decoder has knowledge of the
`estimated channel coellicients. For the 8-antenna case of
`FIG. 5, the decoder has to remember all possible 3 previous
`symbols at each state (i.e., M3 states for M-psk). The branch
`metrics given for the 4—antenna ST code for FIG.1 may be
`generalized to the 8-antenna case.
`The described and other embodiments could be imple-
`mented in systems using any type of multiple access
`technique, such as time division multiple access (TDMA),
`code division multiple access (CDMA), frequency division
`multiple access (FDMA), orthogonal frequency division
`multiple access (OFDM), or any combination of these, or
`any other type of access technique. This could also include
`systems using any type of modulation to encode the digital
`data.
`Thus, although the method and apparatus of the present
`invention has been illustrated and described with regard to
`presently preferred embodiments thereof, it will be under-
`stood that numerous modifications and substitutions may be
`made to the embodiments described, and that numerous
`other embodiments of the invention may be implemented
`without departing from the spirit and scope of the invention
`as defined in the following claims.
`What is claimed is:
`1. A method for transmitting a signal from a plurality of
`antennas, the signal formed of symbols, sequenced together
`to form a first input symbol stream, said method comprising
`the steps of:
`receiving the first input symbol stream at a transmitter;
`offsetting said first input symbol stream to generate a
`second input symbol stream, wherein said second input
`symbol stream is identical to said first input symbol
`stream but offset from said first input symbol stream M
`symbol periods;
`performing a first transform on at least two symbols of
`said first input symbol stream over a time period to
`generate a first transform result;
`
`8
`performing a second transform on at least two symbols of
`said second input symbol stream, substantially simul-
`taneously over said time period, to generate a second
`transform result, the second transform identical to the
`first transform, and
`transmitting, substantially simultaneously, said first trans-
`form result on a first at least one antenna and said
`second transform result on a second at
`least one
`antenna.
`
`2. The method of claim 1, wherein each of said step