United States Patent
`(12)
`(10) Patent No.:
`US 6,542,556 B1
`Kuchiet al.
`(45) Date of Patent:
`Apr. 1, 2003
`
`
`US006542556B1
`
`(54) SPACE-TIME CODE FOR MULTIPLE
`ANTENNA TRANSMISSION
`
`(75)
`
`Inventors: Kiran Kuchi, Irving, TX (US); Jyri K.
`specs
`Haméailainen, Oulu (FI)
`(73) Assignee: Nokia Mobile Phones Ltd., Espoo (FT)
`
`wo
`wo
`WoO
`wo
`we
`
`WO 00/51265
`8/2000
`WO 01/19013 Al
`3/2001
`WO 01/54305 Al
`7/2001
`wo phsae “ Sonat
`/
`WO 01/69814 Al
`9/2001
`OTIIER PUBLICATIONS
`
`(*) Notice:
`
`Subjectto any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C, 154(b) by 0 days.
`
`transmit
`Guey Jiann—Ching: “Concatenated coding for
`diversity systems” Proceedings of the 1999 VT'C—Fall
`ILLE VTS 50th Vehicular Technology Conference ‘Gate-
`way to 21st Century Communications Village’; Amsterdam,
`Neth. Sep. 19-Sep. 22, 1999, vol. 5, 1999 pp. 2500-2504,
`(21) Appl. No.: 09/539,819
`XP002181329 IEEE Veh. Technol. Conf. , IEEE Vehicular
`:
`Technology Conference 1999 IEEE, Piscataway, NJ, USA—
`Mar.31, 2000
`(22) Tiled:
`Whole document.
`(51)
`Int C17 caceccsscssesseceesen HO4B 7/06; Ho4s 11/00
`
`(52) UWS. Ce vascessescseeeeeeee 375/299: 375/146; 370/204;|AlamoutiS M: “A Simple Transmit Diversity Technique for
`°
`° 370/209
`Wireless Communications”, IEEE Journal on Selected Areas
`Field of Search .....cccccccsssessenen 3950133, 135,
`i. Communications, IEEE.Ine. New York, US, vol. 16, No,
`0 TSS TAL kG, LET 260 Jey 306,
`8: Oct.
`1998, pp. 1451-1458, XP002100058,
`ISSN:
`Field
`3 °aei ate 508 aa; 455/101 103
`0733-8716, cited in the applicaion the whole document.
`References Cited
`(List continued on next page.)
`U.S. PATENT DOCUMENTS
`Primary Examiner—Young 'T. ‘Tse
`(74) Attorney, Agent, or Firm—BrianT. Rivers
`
`58)
`(58)
`
`(56)
`
`GB
`wo
`Wo
`wo
`WO
`wo
`
`5,170,413 A * 12/1992 Hess et al. cc. 375/260
`... 375/143
`5,859,870 A *
`1/1999 Tsujimoto .........
`
`8/1999 Alamouti et al. 0... 370/330
`5,933,421 A *
`5,943,372 A
`3/1999 Gansetal.
`6,031,474 A *
`2/2000 Kayet al. vce 341/106
`6,088,408 A *
`7/2000 Calderbank etal. ........ 374/347
`6,097,771 A
`8/2000 Foschini
`6,115,427 A *
`9/2000 Calderbank Cb al.
`ieevines 375/207
`
`6,178,196 B1 :
`1/2001 Naguib et al.
`........
`+. 375/148
`Oetee Bt
`toot Whinnett el ‘il
`cesemeneaes 370/204
`ae
`/
`oschint et al.
`FOREIGN PATENT DOCUMENTS
`-
`5/1991
`11/1997
`31000
`3/2000
`3/2000
`8/2000
`
`2 237 706 A
`WO 97/41670
`WO ee x
`WO 00/11806
`WO 00/18056
`WO00/49780
`
`ABSTRACT
`(57)
`.
`.
`.
`A method and apparatus for space-time coding signals for
`transmission on multiple antennas. 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 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™ set of N antennas may beutilized 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-
`mae
`
`24 Claims, 2 Drawing Sheets
`
`
`
`400
`
`~~}
`
`
`
`406
`
`Filter and
`Modulate
`
`
`
`402
`x(t)
`
`
`
`
`-SdoW1 Sd,W2
`
`412
`
`Sd,W1 SdoW2
`
`Filter and
`Modulate
`
`408
`
`(cid:36)(cid:51)(cid:51)(cid:47)(cid:40)(cid:3)(cid:20)(cid:19)(cid:19)(cid:23)
`APPLE1004
`
`

`

`US 6,542,556 B1
`
`Page 2
`
`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).
`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.
`L. Jalloul, K. Rohani, K. Kuchi, J. Chien “Performance
`Analysis of CDMA Transmit Diversity Mcthods” IEEE
`Vehicular Technology Conference,
`Fall
`1999;
`pp.
`1326-1330.
`Alberto Gutierrez et al., “An Introduction to PSTD for IS—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—lime 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—_.
`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; Space-Time 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 Designsto
`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
`TEEE; pp. 299-303.
`Tarokh, V. et al; A Differential Detection Scheme for Trans-
`mit Diversity; 1999 IEEE; pp. 1043-1047; 0-7803-5668-3/
`oo;
`
`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.
`Tirkkonen,O. et al.; Complex Space-Time Block Codesfor
`Four Tx Antennas;
`IEEE;
`2000;
`p. 1005-p.
`1009;
`0-7803-645 1-1/10.
`Hottinen, A. et al.; Closed—loop transmit diversity tech-
`niques for multi-elementtransceivers; 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; TEEE
`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. ct al.; A Comparison of Base Station Transmit
`Diversity Methods for Third Generation Cellular Standards;
`1999 TEEE; 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. ct 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 [EEE; 0—-7803-5668-3/99; p.
`1043-p. 1047.
`
`Ionescu; New Results on Space-Time Code
`D. Mihai
`Design Criteria; 1999 IEEE; pp. 684-687; 0—-7803-5668—3/
`99.
`
`Tarokh, V., et al.; Space-Time Codes for High Data Rate
`Wireless Communication: Performance Criterion and Code
`Construction; 1998 TERE; 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, PO19 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. No.
`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 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.
`Alamouti, S.M. et al; Trellis-Coded Modulation and Trans-
`mit Diversity: Design Criteria and Performance Evaluation;
`1998 TEEE; 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.; “High—Rate Linear Space—Time 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
`
`

`

`U.S. Patent
`
`Apr.1, 2003
`
`Sheet 1 of 2
`
`US 6,542,556 B1
`
`
` Filter and
`Modulate
`
`
`
`
`Spread,
`
`Filter and
`Modulate
`
`
`112
`
`202
`
`
`
`206 204
`:
`
`
`
`
`Filter
`r(t1),r(t2)...r(tn)
`208
`Despread and
`
`
`Demodulate
`
`
`
`Processor
`
`FIG. 2
`
`States Output Symbols (Ant.1, Ant. 2)
`0
`1
`2
`8
`(0,0)
`(0,1)
`(0,2)
`(0,3)
`
`0
`
`300
`
`x
`
`1
`
`2
`
`3
`
`(1,0)
`
`(1,1)
`
`(1,2)
`
`(1,3)
`
`(2,0)
`
`(2,1)
`
`(2,2)
`
`(2,3)
`
`(3,0)
`
`(3,1)
`
`(3,2)
`
`(3,3)
`
`FIG. 3
`
`

`

`U.S. Patent
`
`Apr.1, 2003
`
`Sheet 2 of 2
`
`US 6,542,556 B1
`
`
`
` S4W1
`
`SoW2
`Filter and
`-SoW1
`Modulate
`
`
`S.W1
`
`
`
`SdiW1 Sd2W2
`-Sd2W1 Sd4W2
`
`Filter and |
`Modulate
`
`412
`
`408
`
`FIG. 4
`
`500 “a
`506
`
`
`Spread,
`Biotinel
`Filter and
`
`
`
`Spread,
`cheekede
`Filter and
`
`Modulate
`
`512
`
`Modulate
`
`508
`
`FIG. 5
`
`

`

`US 6,542,556 B1
`
`1
`SPACE-TIME CODE FOR MULTIPLE
`ANTENNA TRANSMISSION
`
`FIELD OF THE INVENTION
`
`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
`This invention relates to a method and apparatus for
`during a symbol period. During one symbol period, the
`achieving transmit diversity in telecommunication systems
`signal transmitted fromafirst antenna is denoted by s, and
`and, more particularly, to a method and apparatus for space-
`the signal transmitted from the second antennais denoted by
`time coding signals for transmission on multiple antennas.
`S,. During the next symbol period,
`the signal -s,* is
`transmitted from the first antenna and the signal s,* is
`BACKGROUND OF THE INVENTION
`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
`symbolperiods, 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=4, and #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
`
`15
`
`As wireless communication systems evolve, wireless sys-
`tem design has become increasingly demanding in relation
`to equipment and performance requirements. [‘uture wire-
`less systems, which will be third and fourth generation
`systems comparedto 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 knownfor
`overcoming the effects of multi-path fading, such as time
`interleaving with error correction coding,
`implementing
`frequencydiversity byutilizing 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 fecdback
`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.
`
`nature of the ST coded symbols increases the peak-to-
`average ratio requirement of the transmitted signal and
`imposesstringent 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 Contributionto
`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
`dependson 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=’ convolutional code, the
`performance of the OTD+STTD method and the Tarokh
`rate=*4 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 inpul
`symbolstream is transformed using a predefined transform
`and transmitted on a first set of N antennas. The same input
`symbolstreamis then offset in time by M symbolperiods to
`generate an offset input symbol stream. The offset input
`symbolstream 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
`symbolperiods 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.
`
`Atthe 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.
`
`,
`
`40
`
`45
`
`Antennadiversityis another technique for overcoming the
`effects of multi-path fading in wireless systems.In diversity
`reception,
`two or more physically separated antennas are 5
`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 s
`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 systemsin that it is easier
`to implement multiple antennas in the base station than in
`the mobile terminal.
`
`60
`
`65
`
`Transmit diversity for the case of two antennas is well
`studied. Alamouti has proposed a method of transmit diver-
`
`

`

`US 6,542,556 B1
`
`3
`In an embodiment, 4 antennas are used for transmission.
`Every 2 input symbols in a received input symbolstream 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 MLSEreceiver. The method
`and apparatus provides diversity of order four and outper-
`forms other proposcd extensions of the Alamouti method to
`more than two antennas by approximately % 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 WI and :
`W2 span two symbol periods, which maintains the trans-
`mission rate at
`two symbol periods. The received input
`symbolstream 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=% S'l 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 symbolstream is also
`delayed for four symbol periods, and this delayed input
`symbolstream 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
`symbolperiods.
`BRIEF DESCRIPTION OF THE FIGURES
`
`40
`
`45
`
`60
`
`FIG. 1 showsa 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 showsa trellis structure used to process signals in
`the receiver of FIG. 2;
`FIG. 4 showsa block diagram ofportions of a transmitter
`according to an alternative embodiment of the invention;
`and
`
`FIG. 5 showsa block diagram ofportions of a transmitter
`according to a further alternative embodiment of the inven-
`ion.
`
`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
`embodimentof 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 symbolstream X(t) at input 102. X(t) is split into two
`
`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:
`
`Iss |~Sz
`
`ST
`
`Equation 1
`
`The rows in the matrix indicate the antenna the symbolis
`transmitted on, and the columnsindicate the instant they are
`transmitted. Symbols $1 and S2 are transmitted on antenna
`114 and antenna 116 at instants tl 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:
`
`Say |
`
`-Sdj Sdj
`
`Equation 2
`
`The output of the transform from transform block 108is 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,
`ra)= 7 [Sjal — S3a2 + Sy,a3 — S04] + n(zl)
`
`Equation 3
`
`and, for the time duration (t1,t2) as,
`
`Ec
`r(t2)= x [Spal + Sja2 + Sna3 + 53,04] + n(22)
`
`Equation 4
`
`where S,, and S,, are the transmitted symbols on the
`delayed branchand n(t) is the additive white Gaussiannoise.
`The transmitted signal power E, may be evenly distrib-
`uted across the four antennas and the channelcoefficients a
`
`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 embodimentof 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 signalin filter, despread and demodulate block 204.
`Processor block 206 then decodes the sequence that mini-
`mizes the Eucledian distance D betweenthe transmitted and
`received signals and outputs the sequence at output 208
`according to the following:
`
`D=|rQ) - @() + x@—27))Il
`= |lritJ) - (Spal -— S302 + Syja3 — Spa4)|| +
`
`Equation 5
`
`

`

`US 6,542,556 B1
`
`5
`-continued
`\lr@2) - (Sad + Sja2 + Su2a3 + S4,04)l
`
`Further optimization of the branch metrics can be obtained
`with the following simplification. Using the equations,
`
`P(t1)=r(#1)-($,0.1-S5*a2)
`
`P(t2)=r(#2)-(S3014+8,*a2)
`
`Equation 6
`
`Equation 7
`
`the following metric can be obtained:
`
`D* = [[rtel) - Sa103 - Spo)+ ||r@2)- (S203 + 83,04) Equation 8
`
`This maybe further simplified as:
`
`D? = |[rie)(a3y + (2)04 in| +
`reed)" = Fay03 + S%p||"
`
`
`Equation 9
`
`Symbols S,,, S;. may be found separately. In the simplifi-
`cation given by equation 9, only the values S,, and S_,. need
`to be modified at each computation stage. This reduces the
`number of multiplications in the calculation.
`The input to the Viterbi decoder is the sampled received
`signal observed over “n” time epochs or n symbol periods,
`where n=2 for 4 antenna ST codes. The state transitions in
`
`the Viterbi decoder occur every “n” time epochs.
`Referring now to FIG. 3,
`thercin is shown a trellis
`structure 300 used to process the ST code of the received
`signal in receiver 200, according to an embodiment of the
`invention. Trellis structure 300 is the binary phase shift
`keying (BPSK)trellis diagram for a 4 antenna space-time
`(ST) code. Trellis 300 can be described using the following
`state labelling:
`
`Next state=input symbols ($,,5>)
`
`Equation 10
`
`Output={previous state, input symbols}={(S4.,S40), (
`S482)}
`
`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 shownintrellis 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 rememberall possible 2 previous symbols (i¢., 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 symbolperiods inthis
`case maintaining the total transmissionrate. ‘his method is
`knownas space-time spreading (STS). A delayed copyofthe
`input signal is STS transformed again and transmitted via
`the other two antennas.
`In the embodiment of FIG. 4, transmitter 400 receives an
`input symbolstream 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
`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 ew|
`
`-SjWwi stw2
`
`Equation 12
`
`The rows in the matrix indicate the antenna on which the
`symbolis 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) inputto offset
`block 404 is delayed by two symbolperiods and transformed
`in transform block 408 using the Alamouti transformation as
`shown below:
`
` Sd,W2
`Sd,WI
`-SdjWi Sdjw2
`
`Equation 13
`
`The rows in the matrix indicate the antenna on which the
`
`symbolis 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 embodimentof the transmitter of FIG.
`
`4 may be implemented in the same manneras 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 embodimentof 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 embodimentof 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 $1, S2
`
`a
`
`10
`
`15
`
`40
`
`45
`
`60
`
`65
`
`

`

`US 6,542,556 B1
`
`8
`performing a secondtransform onat 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.
`
`7
`and S3 are processed in transform block 506 using a % rate
`block code transform 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.
`
`10
`
`15
`
`Sy
`St
`-S, S;
`-S3
`0
`0
`S;
`
`S3
`0
`ST
`-S3
`
`9
`-S3
`Sp
`Sy
`
`Equation 14
`
`described using the following state labelling.
`Next slate=inpul symbols (S1,55,53)
`
`2. The method of claim 1, wherein each of said step of
`performing said first transform and said step of performing
`said second transform comprises the step of performing an
`Alamouti transform.
`3. The method of claim 2, wherein said step ofoffsetting
`comprises offsetting said first input symbol stream to gen-
`erate said 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 by two
`symbol periods, and wherein said step of performing said
`first
`transform and said step of performing said second
`transform each comprises performing said Alamouti trans-
`form on two symbols over a time period of two symbol
`periods.
`4. The method of claim 3, wherein said step of transmit-
`ting comprises transmitting said first transform result on a
`first and second antenna and said second transform result on
`Output label={previous state, input symbols }={(64,,5..543), (Si,
`a third and fourth antenna.
`S5'3)}
`Equation 16
`5. The method of claim 2, wherein said Alamouti trans-
`A receiver for the embodimentof the transmitter of FIG.
`form is performed in a time domain.
`6. The method of claim 5, wherein said step of offsetting
`5 may be implemented in the same manneras the receiver
`comprises delaying said first input symbol stream to gener-
`ot FIG. 2, with the filter, despread and demodulate block 204
`ate said second input symbol stream, wherein said second
`modified to receive the *%4 rate block code symbols. It is
`input symbol stream is offset from said first input symbol
`assumed that
`the Viterbi decoder has knowledge of the
`esimated channel coefficients. For the 8-antenna case of
`stream by two symbol periods, and wherein said step of
`performing said first transform and said step of performing
`FIG. 5, the decoder has to rememberall possible 3 previous
`said second transform each comprises performing said
`symbols at each state (i.c., M® states for M-psk). The branch 4
`Alamouti transform on two symbols overa first time period
`metrics given for the 4-antenna ST code for FIG.1 may be
`of said two symbol periods, and said stcp of transmitting
`generalized to the 8-antenna case.
`comprises transmitting said first transform result onafirst
`‘The described and other embodiments could be imple-
`and second antenna and said second transform result on a
`mented in systems using any type of multiple access
`third and fourth antenna over a second time period of said
`technique, such as time division multiple access (TDMA),
`two symbol