US006542556B1
`
`United States Patent
`
`(12) (10) Patent No.: US 6,542,556 B1
`Kuchi et al. 5) Date of Patent: Apr. 1, 2003
`(54) SPACE-TIME CODE FOR MULTIPLE WO WO 00/51265 8/2000
`ANTENNA TRANSMISSION WO WO 01/19013 Al 3/2001
`WO WO 01/54305 Al 7/2001
`(75) Inventors: Kiran Kuchi, Irving, TX (US); Jyri K. gg xg 852;;2 ii ggggi
`Hamaléinen, Oulu (FI) WO WO 01/69814 Al 9/2001
`(*) Notice: Subject to any disclaimer, the term of this Guey Jiann—Ching: “Concatenated coding for transmit
`patent is extended or adjusted under 35 diversity systems” Proceedings of the 1999 VTC—Fall
`U.S.C. 154(b) by 0 days. IEEE VTS 50th Vehicular Technology Conference ‘Gate-
`way to 21st Century Communications Village’; Amsterdam,
`(21) Appl. No.: 09/539,819 Neth. Sep. 19-Sep. 22, 1999, vol. 5, 1999 pp. 2500-2504,
`. XP002181329 IEEE Veh. Technol. Conf. , IEEE Vehicular
`(22) Filed: Mar. 31, 2000 Technology Conference 1999 IEEE, Piscataway, NJ, USA—
`(51) It CL7 oo HO4B 7/06; H04J 11/00 ~ Whole document.
`(52) US.CL .o 375/299: 375/146: 370/204: Alamouti S M: “A Simple Transmit Diversity Technique for
`’ ’ 370 /209’ Wireless Communications”, IEEE Journal on Selected Areas
`58) Field of S o 375/133. 135 in Communications, IEEE Inc. New York, US, vol. 16, No.
`370 /20’4 208. 200. 210 45’5/‘101’ 103 0733-8716, cited in the applicaion the whole document.
`(56) References Cited (List continued on next page.)
`(74) Attorney, Agent, or Firm—3Brian T. Rivers
`5,170,413 A * 12/1992 Hess et al. .....cccoveuueees 375/260
`5859,870 A * 1/1999 Tsujimoto 375143 (57) ABSTRACT
`5,933,421 A * 8/1999 Alamouti et al. ........... 370/330 . . .
`5043372 A 8/1999 Gans et al. A method and apparatus for space-time coding signals for
`6,031,474 A * 2/2000 Kay et al. ...coooccovvvnnenn. 341/106 transmission on multiple antennas. A received input symbol
`6,088,408 A * 7/2000 Calderbank et al. ........ 374/347 stream is transformed using a predefined transform and
`6,097,771 A 8/2000 Foschini transmitted on a first set of N antennas. The same input
`6,115427 A * 9/2000 Calderbank et al. ........ 375/267 symbol stream is then offset by M symbol periods to
`6,178,196 Bl : 1/2001 Naguib et al. s 375/148 generate an offset input symbol stream. The offset input
`6,317,411 B * 11/2001 Wh“;l‘}eFt et 211' """""" 370/204 symbol stream is then transformed using the predefined
`6,317,466 B 11/2001 Foschini et al. transform and transmitted on a second set of N antennas. A
`FOREIGN PATENT DOCUMENTS third through X7 set of N antennas may be utilized for
`transmission by successively offsetting the offset input sym-
`GB 2237706 A 5/1991 bol stream by an additional M symbol periods for each
`WO WO 97/41670 11/1997 additional set of N antennas used, before performing the
`‘\xg xg 332‘3‘%; . ;figgg transform and transmitting on the additional set of N anten-
`WO WO 00/11806 3/2000 nas.
`WO WO 00/18056 3/2000
`WO WO 00/49780 8/2000 24 Claims, 2 Drawing Sheets
`400~y 406y 411\ ’\414
`. 416
`SWT - SW21 | Filter and ’
`4 -S;W1 SqW1 Modulate
`02
`x(t) 418
`404
`Sdq{W1 SdW2 Eil d 420
`oT || Filteran
`-SdoW1 SdqW2 Modulate
`408”7 4127/
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`US 6,542,556 Bl
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`OTHER PUBLICATIONS
`
`Tarokh V et al: “Space—Time Block Coding for Wireless
`Communications: Performance Results”, IEEE Journal on
`Selected Areas in Communications, IEEE Inc. New York,
`US, vol. 17, No. 3, Mar. 1999, pp. 451-460, XP000804974
`ISSN: 0733-8716 equations (6) and (7).
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`A. Hiroike, F. Adachi, N. Nakajima “Combined Effects of
`Phase Sweeping Transmitter Diversity and Channel Cod-
`ing”, IEEE Transactions on Vehicular Technology, vol. 41,
`No. 2, May 1992.
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`L. Jalloul, K. Rohani, K. Kuchi, J. Chien “Performance
`Analysis of CDMA Transmit Diversity Methods” IEEE
`Vehicular Technology Conference, Fall 1999; pp.
`1326-1330.
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`Alberto Gutierrez et al., “An Introduction to PSTD for IS-95
`and CDMA 20007, 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.
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`A Simple Transmit Diversity Technique for Wireless Com-
`munications, S. M. Alamouti, 1998 IEEE; pp. 1451-1458.
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`Tarokh, et al., 1999 IEEE; pp. 1456-1467.
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`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—__.
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`Open and Closed Loop Transmit Diversity at High Data
`Rates on 2 and 4 Elements, Harrison, et al., Proposal for
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`Seshadri, N. et al; Space-Time Codes for Wireless Com-
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`Wireless Communication: Performance Criteria; 1999
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`mit Diversity; 1999 IEEE; pp. 1043-1047; 0-7803-5668-3/
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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-p.59.
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`Tirkkonen, O. et al.; Complex Space—Time Block Codes for
`Four Tx Antennas; IEEE; 2000; p. 1005-p. 1009;
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`niques for multi—element transceivers; IEEE 2000; p. 70-73;
`0-7803—-6507-0/00.
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`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.
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`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.
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`Calderbank, A. et al; Space—Time Codes for Wireless
`Communication; 19997 IEEE; ISIT 1997, Ulm, Germany,
`Jun. 29-Jul. 4; p. 146.
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`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.
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`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.
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`Jalloul, L. et al.; Performance Analysis of CDMA Transmit
`Diversity Methods; 1999 IEEE; 0-7802-5435-4/99; p.
`1326—p. 1330.
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`Raitola, M. et al; Transmission Diversity in Wideband
`CDMA; 1999 IEEE; 0-7803-5565-2/99; p. 1545-1549.
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`Correia, A. et al.; Optimised Constellations for Transmitter
`Diversity; 1999 IEEE; 0/7803-5435-4/99; p. 1785-1789.
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`Tarokh, V. et al.; A Differential Detection Scheme for
`Transmit Diversity; 1999 IEEE; 0-7803-5668-3/99; p.
`1043—p. 1047.
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`D. Mihai Ionescu; New Results on Space-Time Code
`Design Criteria; 1999 IEEE; pp. 684-687; 0-7803-5668-3/
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`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.
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`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, PO19 1UD, England.
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`Tarokh, V., et al.; Space-Time Block Coding for Wireless
`Communications: Performance Results; 1999 IEEE; IEEE
`Journal on Selected Areas in Communications, vol. 17. No.
`3, Mar. 1999.
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`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.
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`Shiu, D. et al.; “Scalable Layered Space—Time 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.
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`Alamouti, S.M. et al; Trellis—Coded Modulation and Trans-
`mit Diversity: Design Criteria and Performance Evaluation;
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`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.
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`Hassibi, B. et al.; “High—Rate Linear Space—Time Codes”;
`IEEE Apr. 2001; p. 2461—p. 2464, 0-7803-7041-04/01.
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`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
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`U.S. Patent Apr. 1, 2003 Sheet 1 of 2 US 6,542,556 B1
`
`100 ’ \114
`\ 106\ 110\
`Si Sy Spread, ‘ \116
`
`s s — Filter and
`102 2 1 Modulate
`x(® 104 ’ s
`Sdy Sd, I:Slpread,d ’ 120
`2T —» Filter an
`-Sdy Sd4 Modulate
`108/ 1127
`FIG. 1
`200\‘
`204 206
`202 ‘ Ffier (t1),r(t2)...r(tn) 2 208
`r(t1),r(t2)...r(tn
`Despread and f——p{ Processor —L>
`Demodulate
`FIG. 2
`
`Statex Output Symbols(Ant.1, Ant. 2) 300
`o 1 2 3 '3
`
`0 (0,0) (0,1) (0,2) (0,3)
`
`1 (1,0) (1,1) (1,2) (1,3)
`
`2 (2,0) (2,1) (2.2) (2,3)
`
`3 (3,0) (3,1) (3,2) (3,3)
`
`FIG. 3
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`U.S. Patent Apr. 1, 2003 Sheet 2 of 2 US 6,542,556 B1
`400 414
`~ 406y 411\ | \ ,
`SIW1 - S;W21 | Filter and ‘ 16
`-S;W1 - SyWiA Modulate
`402 415
`Xt 404 T\ 420
`T SdiW1 SdW2 Filter and ‘
`-Sd,W1 SdqW2 ™ Modulate
`408/ 412/
`FIG. 4
`14
`5 516518
`500 T
`™4 506\ 510\ r 520
`Spread,
`——————— 3/4 AT&T — Filter and
`Block Code Modulate
`522
`502 524
`X(t)L—> 526
`504 T 528
`Spread,
`41— SMAATET L ol Filier and
`Block Code Modulate
`508/ 512/
`FIG. 5
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`US 6,542,556 B1
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`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
`
`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 receiver-to-transmitter 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.
`
`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-
`
`10
`
`20
`
`40
`
`45
`
`65
`
`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 s, and
`the signal transmitted from the second antenna is denoted by
`S,. During the next symbol period, the signal —s,* is
`transmitted from the first antenna and the signal sy* 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=Y%:, and % 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 CDMA
`Transmit Diversity Methods,” Proceedings of IEEE 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='5 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 offset input symbol stream. The offset 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. A third through X™ 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.
`
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`US 6,542,556 B1
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`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 other proposed extensions of the Alamouti method to
`more than two antennas by approximately %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
`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=¥ 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
`
`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
`
`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.
`
`In the embodiment of FIG. 1, transmitter 100 receives an
`input symbol stream X(t) at input 102. X(t) is split into two
`
`15
`
`20
`
`25
`
`40
`
`45
`
`55
`
`65
`
`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
`S2 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:
`
`[ 5]
`=5 S
`
`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:
`
`Equation 1
`
`[ Sdy Sdz] Equation 2
`
`-Sd; Sdy
`
`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:
`
`E. Equation 3
`r(tl) = T [Siaf —S302 + S4 a3 — Spad] + n(t])
`and, for the time duration (t1,t2) as,
`Equation 4
`
`| E,
`r2) = Tc [Saad + 5702 + Spad + Sy04) + n(i2)
`
`where S, and S, are the transmitted symbols on the
`delayed branch and n(t) is the additive white Gaussian noise.
`
`The transmitted signal power E_ may be evenly distrib-
`uted across the four antennas and the channel coefficients o
`may be modelled as complex Gaussian.
`
`This received signal can be decoded using an MLSE
`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 demodu-
`lates 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 = lr() = (x() + x(t = 2D)|
`=|lr(e]) — (S1af = S302 + Sz a3 — ShHad)|| +
`
`Equation 5
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`US 6,542,556 B1
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`5
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`-continued
`IF(2) = (S22 + S} a2 + Su2a3 + S5;04)||
`
`Further optimization of the branch metrics can be obtained
`
`with the following simplification. Using the equations,
`Hl)=r(t1)-(S,a1-S,*a2) Equation 6
`H2)=r(12)-(S,al1+S,*a2) Equation 7
`
`the following metric can be obtained:
`
`D? =|[fel) - (Swad - Spad)|| +|[f(2) - (a3 + 53,04 Equation 8
`
`This may be further simplified as:
`D? = [[Fun@3) + 72 a4 = Sul| + Equation 9
`
`[Feniedy - a2y a3 +sg|
`
`Symbols S, S, may be found separately. In the simplifi-
`cation given by equation 9, only the values S, and S, 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 “n” 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 (S,.5,) Equation 10
`Output={previous state, input symbols}={(S1,5.2), (
`S50} Equation 11
`
`The number of states in the trellis 300 is given by M?
`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.
`Other 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 gpsk, 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). A delayed 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
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`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
`S2 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:
`
`[ SIwi SZWZ] Equation 12
`
`—S3Wi Spw2
`
`The rows in the matrix indicate the antenna on which the
`symbol is transmitted. The symbols S1 and S2 are transmit-
`ted simultaneously on antenna 414 during the same two
`symbol periods in which the symbols—S2* and S1* 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:
`
`Sdy Wi SdyW2
`—SdyWI Sd;w2
`
`Equation 13
`
`The rows in the matrix indicate the antenna on which the
`symbol is transmitted. The symbols Sd1 and Sd2 are trans-
`mitted simultaneously on antenna 418 during the same two
`symbol periods in which the symbols—Sd2* and Sd1* 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 S1, S2
`
`Nintendo Exhibit 1032
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`US 6,542,556 B1
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`and S3 are processed in transform block 506 using a % rate
`block code transtorm and the output of transform block 506
`is transmitted on antennas 514, 516, 518 and 520. The % 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 % 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 % rate ST block code is given by the following
`transformation.
`
`St S S 0 Equation 14
`-S3 S] 0 -S3
`=53 0 S] 5
`
`0 S5 -5 S
`
`The trellis structure for the 8-antenna ST code can be
`described using the following state labelling.
`
`Next state=input symbols (5,.5,.55) Equation 15
`
`Output label={previous state, input symbols }={(Sy1:5u2:543), (S1s
`S5.85)} 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 % rate block code symbols. It is
`assumed that the Viterbi decoder has knowledge of the
`estimated channel coefficients. For the 8-antenna case of
`FIG. 5, the decoder has to remember all possible 3 previous
`symbols at each state (i.e., M> 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;
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`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 simultancously, 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, wh