(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2004/0190598A1
`Seki et al.
`(43) Pub. Date:
`Sep. 30, 2004
`
`US 2004O190598A1
`
`(54) MULTICARRIER CDMA TRANSMISSION
`SYSTEMAND TRANSMISSION METHOD
`
`(76) Inventors: Hiroyuki Seki, Kawasaki (JP); Daisuke
`Jitsukawa, Kawasaki (JP); Yoshinori
`Tanaka, Kawasaki (JP)
`Correspondence Address:
`KATTEN MUCHIN ZAVIS ROSENMAN
`575 MADSON AVENUE
`NEW YORK, NY 10022-2585 (US)
`
`(21) Appl. No.:
`
`10/783,893
`
`(22) Filed:
`
`Feb. 20, 2004
`Related U.S. Application Data
`
`(63) Continuation of application No. PCT/JP01/07451,
`filed on Aug. 30, 2001.
`
`Publication Classification
`
`(51) Int. Cl." ..................................................... H04B 1/707
`(52) U.S. Cl. .............................................................. 375/141
`
`(57)
`
`ABSTRACT
`
`-
`0
`In multicarrier transmission for multiplying transmit data
`individually by each code constituting orthogonal codes and
`transmitting each result of multiplication by a prescribed
`Subcarrier, a plurality of different Subcarriers are assigned
`exclusively to each user and each user performs multicarrier
`transmission of the transmit data by the Subcarriers assigned.
`Further, a base Station assigns a plurality of different Sub
`carriers to each user exclusively, applies beam-forming
`processing on a per-user basis and performs multicarrier
`transmission of transmit data to each user by the Subcarriers
`assigned.
`
`ORTHOGONAL CODE 1 C-CN
`
`NPUT DATA OF
`USER 1
`
`51
`
`
`
`DATA
`MODULATOR
`
`PILOT
`
`
`
`
`
`
`
`s
`t
`3 go
`E-
`23.
`i 2 gts
`
`S
`
`-->
`
`H
`
`2.
`
`S2
`e
`
`a
`t a
`
`"
`.
`.
`
`58 OFDM SIGNAL
`
`
`
`FFT
`
`GUARD
`NTERWAL
`NSERTION
`UNIT
`
`1
`
`GM 1019
`
`

`

`Patent Application Publication Sep. 30, 2004 Sheet 1 of 17
`
`US 2004/0190598 A1
`
`F/G 7
`
`SPREADING
`CODE
`
`
`
`
`
`;
`
`SCN
`
`SC21
`SC SC12
`/ - SC2
`("(
`uSER 2 (CODE 2)
`USER 1 (CODE 25
`*USER 1 (CODE 1) YUSER2 (CODE 1) :
`
`SC2N
`/
`
`USER 1
`FADING FLUCTUATION
`
`F1
`
`F2
`
`USER 2
`
`SPREADING
`CODE
`
`
`
`
`
`
`
`SC
`SC 2N
`SC 11 SC 12
`SIN
`( w
`SC 22
`as /
`(, -(
`(
`USER 4 (CODE.2)
`;
`USER 2 (CODE 2)
`;
`: USER 1 (CODE 1) YUSER3 (CODE 1)
`
`W .
`
`FREQUENCY
`
`USER 12
`FADING FLUCTUATION
`
`F12
`
`USER 3, 4
`
`F34
`
`2
`
`

`

`Patent Application Publication Sep. 30, 2004 Sheet 2 of 17
`
`US 2004/0190598A1
`
`
`
`
`
`
`
`s
`
`s
`
`s
`
`
`
`
`
`SERIAL/
`PARALLEL
`CONVERTER
`
`
`
`
`
`
`
`
`
`
`
`S
`
`TIME
`MULTIPLEXER
`
`spa
`ld
`
`-
`Cd
`Cl
`H
`So
`
`H sR
`Cl
`2
`
`1.
`
`-
`
`Se S Y
`s
`o
`t
`> -
`as
`-
`2.
`
`e
`
`3
`
`

`

`Patent Application Publication Sep. 30, 2004 Sheet 3 of 17
`
`US 2004/0190598A1
`
`PARALLEL/
`SERIAL
`CONVERTER
`
`FREQUENCY DENTERLEAVER
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`4
`
`

`

`Patent Application Publication Sep. 30, 2004 Sheet 4 of 17
`
`US 2004/0190598A1
`
`
`
`
`
`5
`
`

`

`Patent Application Publication Sep. 30, 2004 Sheet 5 of 17
`
`US 2004/0190598A1
`
`
`
`VIVO 1/id100 || ||
`
`PARALLEL/
`SERAL
`CONVERTER
`
`FREQUENCY DENTERLEAVER
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`6
`
`

`

`Patent Application Publication Sep. 30, 2004 Sheet 6 of 17
`
`US 2004/0190598A1
`
`
`
`
`
`
`
`
`
`7
`
`

`

`Patent Application Publication Sep. 30, 2004 Sheet 7 of 17
`
`US 2004/0190598A1
`
`PARALLEL/
`SERIAL
`CONVERTER
`
`8 9/-/
`
`ff ||
`
`- -+– – – !
`
`Z 3000
`
`TWN000H180ºff?00|
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`8
`
`

`

`LWNNAINV;143|LINSNVYL*
`WNOISWa40}|Nimtly|\902£02
`
`TWNOSOHIYO|OP~2eQz
`|602802L0¢TWNODOH14O|||WNNALNY404Ney~wl2y:24000|LINNWHGO-OW
`
`
`!743009
`
`'LINN
`
`(|
`
`Patent Application Publication Sep. 30,2004 Sheet 8 of 17
`
`US 2004/0190598 A1
`
`
`
`€WNNGINY404LINNVNO9-OW1fs&YNNALNY'uscdJLIWSNVYL=FooLeeeeeee_|5==HOLYINGOWvivdINdN!
` WNNSLNV:|LUWSNVYLmyeMLoudOOee1«—_|
`‘iASAD!LIWSNWYL‘—~---—--—---—--—--—--—--—--—-->
`
`«—_|ZVNNJINYYO4LINNYWO-OW|207Loe
`<—|_¥YNNGINV404LINNYNOO-ON_~®)
`©£02M5Zwasn
`ye?&||=3/012'202
`nn=.é
`
`9
`
`
`

`

`Patent Application Publication Sep. 30, 2004 Sheet 9 of 17
`
`US 2004/0190598A1
`
`f/G 10 pp/OR ART
`
`1
`
`2a
`
`4.
`
`(b)
`
`SUBCARRIERS
`
`- 24
`A/6 11 A/0R AAR
`
`Re
`
`7a
`
`I-ch
`
`8
`
`ORTHOGONAL
`MODULATOR
`
`
`
`
`
`
`
`(b)
`
`?till
`
`. f
`
`10
`
`

`

`Patent Application Publication Sep. 30, 2004 Sheet 10 of 17
`A/6 12 AP/OR AR/
`
`US 2004/0190598A1
`
`O
`
`1
`
`O
`
`1
`
`9
`
`TRANSMT
`DATA
`
`|
`
`-o-
`
`ic, C, C
`cic, c, c,
`c,
`" '
`case io c, FR-t
`
`SPREADING
`
`V 1 V2 V3
`
`NV 1 V2 V3
`
`N
`
`k-Ts — -> <-
`BIT INTERVAL
`TC
`CHIP INTERVAL
`
`A/6 13 AR/OR AAP/
`
`NM
`
`DS
`
`fe--
`
`fo
`
`f
`
`FREQUENCY
`
`11
`
`

`

`Patent Application Publication Sep. 30, 2004 Sheet 11 of 17
`
`US 2004/0190598A1
`
`A/6 14 AP/OR AAP/
`COPY
`C
`-- T.S — -- TS -->
`TRANSMT
`TRANSMT
`DATA D
`DAA D
`
`(x)
`
`91
`
`C2
`
`\,
`
`\,
`
`1- TS -->
`
`D. C.
`
`Ts
`
`TS
`
`f
`
`Af
`
`f
`
`Af
`
`f
`
`Af
`
`
`
`TRANSMT
`DATA D
`
`(X)
`92
`
`CN
`
`TRANSMT
`ENS
`
`(x)
`9N
`A/G 15 AP/OR AAP/
`
`
`
`(a)
`
`- IM
`
`- K
`/
`
`12
`
`

`

`Patent Application Publication Sep. 30, 2004 Sheet 12 of 17
`
`US 2004/0190598A1
`
`01078|-
`
`
`
`61 - || IVNOIS MHO º!
`
`FREQUENCY INTERLEAVER
`
`CODE MULTIPLEXER
`
`SERIAL/PARALLEL CONVERTER
`
`CN
`
`TIME
`MULTIPLEXER
`
`| |
`
`WIWO
`
`
`
`
`
`13
`
`

`

`Patent Application Publication Sep. 30, 2004 Sheet 13 of 17
`
`US 2004/0190598A1
`
`
`
`USER DATA
`
`A/6 17 AP/OR ART
`p
`: P
`USER DATA
`: P
`USER DATA
`32:... laxuk
`SYMBOLS symbols
`
`30 - - - - - - - - - - - - - - - - - - - - - - - - 2 1 4 3 2 1
`
`2
`3
`
`M
`
`USER DATA
`30 XM SYMBOLS
`
`PILOT
`4 XM SYMBOLS
`
`A/G 18 AP/OR AAP/
`
`g
`
`is
`
`COPY
`
`COPY
`
`S
`
`14
`
`

`

`Patent Application Publication Sep. 30, 2004 Sheet 14 of 17
`
`US 2004/0190598 A1
`
`
`
`
`
`PARALLEL/SERAL CONVERTER
`
`No 01' O SHOOO ! TW?000H180
`
`
`
`"901'0 SEGOO
`
`TWN090H180
`
`FREQUENCY DENTERLEAVER
`
`
`
`/NOI IWZ INOMHONAS
`
`–9N||||||
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`15
`
`

`

`Patent Application Publication Sep. 30, 2004 Sheet 15 of 17
`
`US 2004/0190598 A1
`
`A/G 20 AR/0R ART
`SPREADNG CODE
`
`FADING FLUCTUATION WITH
`REGARD TO USERS 1, 2
`
`FIG 21 PRIOR ART
`
`SPREADING CODE
`
`FREQUENCY
`
`FREQUENCY
`
`
`
`FADING FLUCTUATION
`WITH REGARD TO USER 1 F1
`
`
`
`FADING FLUCTUATION
`WITH REGARD TO USER 2 F2
`
`16
`
`

`

`Patent Application Publication Sep. 30, 2004 Sheet 16 of 17
`
`US 2004/0190598A1
`
`FIG 22 PR/O API
`
`--
`
`
`
`33
`
`32
`
`TRANSMT DATA
`
`s
`na
`O
`L
`
`s
`e
`
`H
`s
`cMO
`2
`se
`Ha
`
`
`
`17
`
`

`

`Patent Application Publication Sep. 30, 2004 Sheet 17 of 17
`F/G 24 AR/OR ART
`
`US 2004/0190598 A1
`
`COMMON
`PILOT
`
`
`
`(a)
`
`POWER
`
`USER DATA 1
`
`4.
`
`30 -- -b
`sias'
`SYMBOLS
`
`(b)
`
`SEPARATE PLOT FOR USER 4.
`SEPARATE PILOT FOR USER 3
`
`SEPARATE PILOT FOR USER 2
`SEPARATE PILOT FOR USER 1
`
`
`
`
`
`
`
`P4
`
`USER DATA 4
`USER DATA 3
`USER DATA 2
`USER DATA 1
`4 -> <- -->
`SYMBOLS
`SYMBOLS
`
`|
`
`18
`
`

`

`US 2004/O190598 A1
`
`Sep. 30, 2004
`
`MULTICARRIER CDMA TRANSMISSION SYSTEM
`AND TRANSMISSION METHOD
`0001. This application is a continuation of international
`application number PCT/JP01/07451, filed Aug. 30, 2001
`and is still pending.
`
`BACKGROUND OF THE INVENTION
`0002. This invention relates to a multicarrier CDMA
`transmission System and transmission method. More par
`ticularly, the invention relates to a multicarrier CDMA
`transmission System and transmission method for Subjecting
`transmit data to a Serial-to-parallel conversion, multiplying
`each symbol of the obtained parallel data individually by
`each code constituting orthogonal codes, and multicarrier
`transmitting each result of multiplication by a prescribed
`Subcarrier.
`0.003
`Multicarrier modulation schemes have become the
`focus of attention as next-generation mobile communication
`Schemes. Using multicarrier modulation not only makes it
`possible to implement wideband, high-Speed data transmis
`Sion but also enables the effects of frequency-Selective
`fading to be mitigated by narrowing the band of each
`Subcarrier. Further, using orthogonal frequency division
`multiplexing not only makes it possible to raise the effi
`ciency of frequency utilization but also enables the effects of
`inter-Symbol interference to be eliminated by providing a
`guard interval for every OFDM symbol.
`0004 (a) in FIG. 10 is a diagram useful in describing a
`multicarrier transmission Scheme. A Serial/parallel converter
`1 converts Serial data to parallel data and inputs the parallel
`data to orthogonal modulators 3a to 3d via D/A converter 2a
`to 2d, respectively. In the Figure, the conversion is to
`parallel data comprising four Symbols. Each Symbol
`includes an in-phase component and a quadrature compo
`nent. The orthogonal modulators 3a to 3d subject each of the
`Symbols to orthogonal modulation by Subcarriers having
`frequencies f, to fillustrated in (b) of FIG. 10, a combiner
`4 combines the orthogonally modulated Signals and a trans
`mitter (not shown) up-converts the combined signal to a
`high-frequency Signal and then transmits the high-frequency
`Signal. With the multicarrier transmission Scheme, the fre
`quencies are arranged, as shown at (b), in Such a manner that
`the Spectrums will not overlap in order to Satisfy the
`orthogonality of the Subcarriers.
`0005. In orthogonal frequency division multiplexing, fre
`quency spacing is arranged So as to null the correlation
`between a modulation band Signal transmitted by an nth
`Subcarrier of a multicarrier transmission and a modulation
`band signal transmitted by an (n+1)th Subcarrier. If we
`assume that a symbol (a complex baseband signal) trans
`mitted by the nth Subcarrier (center frequency: fin) is repre
`Sented by Zn (=an+jbn), then we may write modulation band
`Signal Sn(t)=ReZn exp(27tfn t) (where Re represents the
`real part of the complex number). The requirement for the
`(n+1)th Subcarrier to be orthogonal to the nth Subcarrier is
`that the cross correlation between Sn(t) and Sn+1(t) be 0. If
`the frequency spacing between neighboring Subcarriers is fa
`and the period of the symbol Zn is T, then, in order for the
`cross correlation to become 0, it will suffice for fa=k/T (k=1,
`2,...) to hold and the minimum spacing will be fa=1/T. A
`multicarrier multiplexing Scheme having frequency spacing
`is an orthogonal frequency division multiplexing Scheme.
`
`0006 (a) of FIG. 11 is a diagram of the structure of a
`transmitting apparatus that relies upon the Orthogonal fre
`quency division multiplexing Scheme. A Serial/parallel con
`verter 5 converts Serial data to parallel data comprising a
`plurality of Symbols (I-Q, which is a complex number). An
`IDFT (Inverse Discrete Fourier Transform) 6, which is for
`the purpose of transmitting the Symbols as Subcarriers
`having a frequency spacing shown in (b) of FIG. 11, applies
`an inverse discrete Fourier transform to the frequency data
`to effect a conversion to time data, and inputs the real and
`imaginary parts to an Orthogonal modulator 8 through D/A
`converter 7a, 7b. The orthogonal modulator 8 subjects the
`input data to orthogonal modulation, and a transmitter (not
`shown) up-converts the modulated Signal to a high-fre
`quency Signal. In accordance with orthogonal frequency
`division multiplexing, a frequency placement of the kind
`shown in (b) of FIG. 11 becomes possible, thereby enabling
`an improvement in the efficiency with which frequency is
`utilized.
`0007. In recent years, there has been extensive research in
`multicarrier CDMA schemes (MC-CDMA) and application
`thereof to next-generation wideband mobile communica
`tions is being studied. With MC-CDMA, partitioning into a
`plurality of Subcarriers is achieved by Serial-to-parallel
`conversion of transmit data and spreading of orthogonal
`codes in the frequency domain. Owing to frequency-Selec
`tive fading, Subcarriers distanced by their frequency spacing
`experience independent fading on an individual basis.
`Accordingly, by causing code-spread Subcarrier Signals to be
`distributed along the frequency axis by frequency interleav
`ing, a despread signal can acquire frequency-diversity gain.
`0008 An orthogonal frequency/code division multiple
`access (OFDM/CDMA) scheme, which is a combination of
`OFDM and MC-CDMA, also is being studied. This is a
`Scheme in which a signal, which has been divided into
`Subcarriers by MC-CDMA, is subjected to orthogonal fre
`quency multiplexing to raise the efficiency of frequency
`utilization.
`0009 A CDMA (Code Division Multiple Access) scheme
`multiplies transmit data having a bit cycle T by Spreading
`codes C to CN of chip frequency Tc using a multiplier 9, as
`shown in FIG. 12, modulates the result of multiplication and
`transmits the modulated Signal. Owing to Such multiplica
`tion, a 2/T, narrow-band signal NM can be spread-spectrum
`modulated to a 2/Tc wideband signal DS and transmitted, as
`shown in FIG. 13. Here TS/Tc is the spreading ratio and, in
`the illustrated example, is the code length N of the Spreading
`code. In accordance with this CDMA transmission Scheme,
`an advantage acquired is that an interference Signal can be
`reduced to 1/N.
`0010. According to the principles of multicarrier CDMA,
`N-number of items of copy data are created from a single
`item of transmit data D, as shown in FIG. 14, the items of
`copy data are multiplied individually by respective ones of
`codes C to CN, which are spreading codes (orthogonal
`codes), using multipliers 9 to 9, respectively, and products
`DC to DC undergo multicarrier transmission by N-number
`of Subcarriers of frequencies f, to fillustrated in (a) of FIG.
`15. The foregoing relates to a case where a Single item of
`Symbol data undergoes multicarrier transmission. In actual
`ity, however, as will be described later, transmit data is
`converted to parallel data of M symbols, the M-number of
`
`19
`
`

`

`US 2004/O190598 A1
`
`Sep. 30, 2004
`
`symbols are subjected to the processing shown in FIG. 14,
`and all results of MXN multiplications undergo multicarrier
`transmission using MXN Subcarriers of frequencies f to
`fN. Further, orthogonal frequency/code division multiple
`access can be achieved by using Subcarriers having the
`frequency placement shown in (b) of FIG. 15.
`0.011
`FIG. 16 is a diagram illustrating the structure on
`the transmitting side of MC-CDMA. A data modulator 11
`modulates transmit data and converts it to a complex base
`band signal (symbol) having an in-phase component and a
`quadrature component. A time multiplexer 12 time-multi
`plexes the pilot of the complex symbol to the front of the
`transmit data. A Serial/parallel converter 13 converts the
`input data to parallel data of M Symbols, and each Symbol
`is input to a spreader 14 upon being branched into N paths.
`The spreader 14 has M-number of multipliers 14 to 14.
`The multipliers 14 to 14 multiply the branched symbols
`individually by codes C, C, ..., CN constituting orthogo
`nal codes and output the resulting Signals. As a result,
`Subcarrier Signals S to SMN for multicarrier transmission by
`NXM Subcarriers are output from the spreader 14. That is,
`the spreader 14 multiplies the symbols of every parallel
`Sequence by the Orthogonal codes, thereby performing
`Spreading in the frequency direction. Codes that differ for
`every user are assigned as the orthogonal codes used in
`Spreading.
`0012. In the case of a downlink (transmission by a base
`station), a code multiplexer 15 code-multiplexes the Subcar
`rier Signals generated as Set forth above and the Subcarriers
`of other users generated through a similar method. That is,
`for every subcarrier, the code multiplexer 15 combines the
`Subcarrier Signals of a plurality of users conforming to the
`Subcarriers and outputs the result. A frequency interleaver 16
`rearranges the code-multiplexed Subcarriers by frequency
`interleaving, thereby distributing the Subcarrier Signals
`along the frequency axis, in order to obtain frequency
`diversity gain. An IFFT (Inverse Fast Fourier Transform)
`unit 17 applies an IFFT to the Subcarrier signals that enter in
`parallel, thereby effecting a conversion to an OFDM signal
`(a real-part signal and an imaginary-part Signal) on the time
`axis. A guard-interval insertion unit 18 inserts a guard
`interval into the OFDM signal, an orthogonal modulator
`applies orthogonal modulation to the OFDM signal into
`which the guard interval has been inserted, and a radio
`transmitter 20 up-converts the Signal to a radio frequency,
`applies high-frequency amplification and transmits the
`resulting Signal from an antenna.
`0013 The total number of subcarriers is (spreading ratio
`N)x(number M of parallel sequences). Further, Since fading
`that differs from Subcarrier to Subcarrier is Sustained on the
`propagation path, a pilot is time-multiplexed onto all Sub
`carriers and it is So arranged that fading compensation can
`be performed Subcarrier by Subcarrier on the receiving Side.
`The time-multiplexed pilot is a common pilot that all users
`employ in channel estimation. In case of uplink, the Signals
`of each of the users are combined on the propagation path
`and received at a base Station.
`0.014
`FIG. 17 is a diagram useful in describing a serial
`to-parallel conversion. Here a common pilot P has been
`time-multiplexed to the front of transmit data. If the com
`mon pilot is 4xM symbols and the transmit data is 30xM
`symbols, then M symbols of the pilot will be output from the
`
`serial/parallel converter 13 as parallel data the first four
`times, and thereafter M symbols of the transmit data will be
`output from the Serial/parallel converter 13 as parallel data
`30 times. As a result, the pilot can be time-multiplexed into
`all Subcarriers and transmitted. By using this pilot on the
`receiving Side, fading compensation becomes possible on a
`per-Subcarrier basis.
`0015 FIG. 18 is a diagram useful in describing insertion
`of a guard interval. If an IFFT output Signal conforming to
`MSymbols is taken as one unit, then guard-interval insertion
`Signifies copying the tail-end portion of this symbol to the
`leading-end portion thereof. Inserting a guard interval GI
`makes it possible to eliminate the effects of inter-symbol
`interference ascribable to multipath.
`0016 FIG. 19 is a diagram showing structure on the
`receiving side of MC-CDMA. A radio receiver 21 subjects
`a received multicarrier Signal to frequency conversion pro
`cessing, and an Orthogonal demodulator Subjects the receive
`Signal to Orthogonal demodulation processing. A timing
`Synchronization/guard-interval removal unit 23 establishes
`receive-signal timing Synchronization, removes the guard
`interval GI from the receive signal and inputs the result to an
`FFT (Fast Fourier Transform) unit 24. The FFT unit 24
`converts a signal in the time domain to NXM-number of
`Subcarrier Signals. A frequency deinterleaver 25 rearranges
`the Subcarrier Signals in an order opposite that on the
`transmitting Side and outputs the Signals in the order of the
`Subcarrier frequencies.
`0017. After deinterleaving is carried out, a fading com
`pensator 26 performs channel estimation on a per-Subcarrier
`basis using the pilot time-multiplexed on the transmitting
`Side and applies fading compensation. In the Figure, a
`channel estimation unit 26a is illustrated only in regard to
`one Subcarrier. However, Such a channel estimation unit is
`provided for every Subcarrier. The channel estimation unit
`26a, estimates the influence exp(jp) of fading on phase using
`the pilot Signal, and a multiplier 26b multiplies the Subcar
`rier signal of the transmit Symbol by exp(-jp) to compensate
`for fading. A despreader 27 has M-number of multipliers 27
`to 27. The multiplier 27 multiplies N-number of Subcar
`riers individually by codes C, C2, . .
`. , CN constituting
`orthogonal codes assigned to users and outputs the results.
`The other multipliers also execute Similar processing. AS a
`result, the fading-compensated Signals are despread by
`Spreading codes assigned to each of the users, and Signals of
`desired users are extracted from the code-multiplexed Sig
`nals by despreading.
`each add the N-number of
`0.018 Combiners 28 to
`results of multiplication that are output from respective ones
`of the multipliers 27 to 27M, thereby creating parallel data
`comprising M-number of Symbols. A parallel/serial con
`verter 29 converts this parallel data to Serial data, and a data
`demodulator 30 demodulates the transmit data.
`0019 FIG.20 is an explanatory view illustrating the state
`of MC-CDMA fading fluctuation in a downlink from a base
`Station. A Subcarrier Signal of a prescribed user that has been
`Spread along the frequency axis is code-multiplexed onto the
`Subcarrier Signal of another user and Sustains fading that
`differs for every Subcarrier on the propagation path. In the
`case of an outgoing call from a base Station, however, a
`code-multiplexed Subcarrier Signal of a different user SuS
`tains the same fading FD12 on each Subcarrier. As a result,
`
`20
`
`

`

`US 2004/O190598 A1
`
`Sep. 30, 2004
`
`if fading compensation is carried out using channel estima
`tion information estimated for every carrier by means of the
`pilot Symbol, fading Sustained by each user can be compen
`Sated for Simultaneously, as indicated by FD12", orthogo
`nality of the spreading codes of each of the users can be
`maintained and user Signals will not interfere with one
`another. Accordingly, using a code having a high degree of
`orthogonality as the Spreading code is extremely effective in
`an MC-CDMA Scheme.
`0020. In the uplink, however, each user experiences dif
`ferent degrees of fading F1, F2 as shown in FIG. 21.
`Consequently, each Subcarrier Signal experiences indepen
`dent fading user by user and Orthogonality of the Spreading
`code of each user is lost completely. For example, even if
`fading fluctuation F1 with respect to user 1 is compensated
`for by a fading compensator in the manner indicated at F1',
`fading fluctuation F2 with respect to user 2 becomes as
`indicated at F2'. Accordingly, in a case where the MC
`CDMA Scheme for performing spreading in the frequency
`domain is applied to the uplink, a large deterioration in
`characteristics occurs.
`0021
`Further, there are instances where a directional
`beam is emitted from a base Station toward each user to
`transmit data. In Such an instance it is necessary to provide
`an antenna array and carry out beam forming by causing a
`beam former to apply an array weight, which differs for
`every user, to the transmit data. FIG. 22 is a simple
`Structural view of beam forming and illustrates an array
`antenna 31, a transmit beam former 32 for controlling the
`directivity of the beam by changing the array weight, and
`transmitters 33 to 33N for inputting transmit Signals to
`antenna elements ATT to ATTN that construct the array
`antenna. The transmit beam former 32 controls the array
`weight in accordance with the direction of the user (mobile
`Station), thereby transmitting the beam toward the user upon
`changing the magnitude and phase of the transmit Signal
`applied to each antenna element.
`0022. In a case where a signal to which a weight that
`differs for every user has been applied is code-multiplexed
`in order to implement beam forming, each Subcarrier will
`Sustain fading that differs for every user, in a manner Similar
`to that the uplink in FIG. 21, if this signal traverses a
`propagation path that experiences multipath fading. In par
`ticular, the larger the angular spread of multipath, the more
`the fading experienced by each user is different from and
`independent of that of other users. Even when beam forming
`is carried out, therefore, the orthogonality of Spreading
`codes is lost and the characteristic deteriorates Significantly.
`If the array weight of each user has been decided in Such a
`manner that the beam will not be directed toward other users
`in this case, the interference component toward other users
`is Suppressed and therefore the problem of loSS of spreading
`code orthogonality is eliminated. In actuality, however, the
`Side lobes of the beam interfere with other users and, hence,
`the influence of deterioration of characteristics due to loSS of
`orthogonality is great.
`0023. As shown in FIG. 23, there are also cases where a
`Sector is divided into a plurality, e.g., three, of directional
`Zones A1, A2, A3, and a beam having the same directivity
`is transmitted by being directed toward those mobile Stations
`MS11 to MS12, MS21 to MS22, MS31 to MS32 present in
`the same directional Zone. In the case of Such beam forming,
`
`it is necessary to use an array weight that differs for every
`directional Zone. However, if a signal to which a weight that
`differs for every directional Zone is code-multiplexed and
`the code-multiplexed signal traverses a propagation path that
`experience multipath fading, then, in a manner Similar to
`that of FIG. 21, each subcarrier will Sustain fading that
`differs for every directional Zone. In Such case, fading
`Sustained by users in different directional Zones becomes
`independent, orthogonality of spreading codes is lost and
`characteristics deteriorate markedly. In this case also, if the
`array weight of each directional Zone has been decided in
`Such a manner that the beam will not be directed toward
`other directional Zones, the interference component toward
`other users is Suppressed and therefore the problem of loSS
`of Spreading-code orthogonality is eliminated. In actuality,
`however, side lobes SB of the beam BM interfere with other
`users, as shown in FIG. 23, and, hence, the influence of
`deterioration of characteristics due to loSS of Orthogonality is
`great.
`Furthermore, in a case where each subcarrier has
`0024.
`Sustained fading that differs for every user, channel estima
`tion must be performed using an individual pilot for each
`user in order to compensate for fading. With MC-CDMA,
`channel estimation must be carried out with regard to each
`Subcarrier before despreading is performed. To Separate an
`individual pilot of each user, there is a method of utilizing
`the pattern of a pilot and a method of shifting the position
`along the frequency and time axes of the pilot user by user
`to thereby effect separation. In either case, power allocated
`to individual channels decreaseS as the number of individual
`channels increases. (a) in FIG. 24 illustrates a case where a
`common pilot is used and (b) of FIG. 24 a case where
`individual pilots are used. The power of each individual pilot
`is one-fourth that of the common pilot. The greater the
`number of individual pilots, therefore, the greater the decline
`in the accuracy of channel estimation. Further, depending
`upon the placement and position of the pilot pattern, the
`channel of each Subcarrier must be estimated as by finding
`channel information between pilots (channel estimation
`information) by interpolation.
`
`SUMMARY OF THE INVENTION
`0025. Accordingly, an object of the present invention is to
`So arrange it that the orthogonality of a spreading code will
`not be lost even when MC-CDMA transmission is per
`formed on an uplink (i.e., in call origination from a mobile
`Station).
`0026. Another object of the present invention is to avoid
`loSS of the Orthogonality of a spreading code even when
`MC-CDMA transmission is performed by applying beam
`forming in a downlink (i.e., in call origination from a base
`Station).
`0027 A further object of the present invention is to
`realize excellent channel estimation accuracy even when
`individual pilots are used.
`0028. A further object of the present invention is to so
`arrange it that a narrow-band receiver can be used in
`MC-CDMA transmission.
`0029. In multicarrier transmission in which transmit data
`is converted to Serial data, each Symbol of parallel data
`obtained is output upon being multiplied individually by
`
`21
`
`

`

`US 2004/O190598 A1
`
`Sep. 30, 2004
`
`each code constituting orthogonal codes, and each result of
`multiplication is transmitted by a prescribed Subcarrier, a
`plurality of Subcarriers are assigned on a per-user basis and
`transmit data of a user is Subjected to multicarrier transmis
`Sion by the Subcarriers assigned. If this arrangement is
`adopted, use is made of Subcarriers having frequencies that
`differs for every user. As a result, interference on other users
`is eliminated and excellent multicarrier transmission
`becomes possible.
`0.030. In this case, M-number of orthogonal codes are
`assigned to a user, parallel data comprising M-number of
`Symbols is output by a Serial-to-parallel conversion, an ith
`symbol of the parallel data is multiplied individually by each
`code constituting ith Orthogonal codes, corresponding
`results of multiplication from among the results of multi
`plication of multiplication obtained for every symbol are
`added, and each result of addition is transmitted by the
`Subcarrier assigned. If multicode multiplexing is thus per
`formed, excellent multicarrier transmission that will not
`interfere with other users can be performed even with few
`Subcarriers assigned to a user or even if the data transmission
`rate is high.
`0.031
`Further, multicarrier transmission is carried out
`upon assigning a plurality of SubcarrierS eXclusively to each
`user. If this arrangement is adopted, interference upon other
`users is eliminated and excellent multicarrier transmission
`becomes possible even in a case where, in a downlink, a base
`Station executes transmit beam-forming processing user by
`user and transmits the transmit data of each user upon
`performing frequency multiplexing. Further, in an uplink,
`interference upon other users is eliminated and excellent
`multicarrier transmission becomes possible by having the
`user transmit the transmit data to a base Station by multi
`carrier transmission using the Subcarriers assigned.
`0032. Further, the same subcarriers are assigned to a
`plurality of users, different orthogonal code is assigned to
`each of these users and code multiplexing is performed on
`the same Subcarriers to Send the transmit data of each user.
`If this arrangement is adopted, interference upon other users
`is eliminated and excellent multicarrier transmission
`becomes possible even in a case where beam forming is
`applied to a plurality of users present in the same directional
`Zone and a multicarrier transmission is made from a base
`Station using the same Subcarriers.
`0033. Further, in a multicarrier transmission, a user
`extracts, by filtering, a receive Signal component of a
`frequency domain of Subcarriers that have been assigned to
`this user and performs demodulation processing using the
`extracted receive signal component. If this arrangement is
`adopted, multicarrier reception can be performed using a
`narrow-band receiver. Further, by performing transmission
`by dispersing SubcarrierS along the frequency axis using
`frequency interleaving, it can be So arranged that errors will
`not concentrate. This makes it possible to improve error
`correction performance.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`0034 FIG. 1 is a diagram useful in describing a first
`principle of the present invention;
`0.035
`FIG. 2 is a diagram useful in describing a second
`principle of the present invention;
`
`0036 FIG. 3 is a block diagram of the transmitting side
`of a mobile Station in the case of an uplink when Subcarriers
`are assigned exclusively on a per-user basis,
`0037 FIG. 4 is a block diagram of the receiving side of
`a base Station according to a first embodiment;
`0038 FIG. 5 is a block diagram of the transmitting side
`of a base Station in a case where beam forming is used in a
`downlink;
`0039 FIG. 6 is a block diagram of the receiving side of
`a mobile Station in a case where a base Station transmits data
`by an MC-CDMA scheme using transmit beam forming;
`0040 FIG. 7 is a modification of FIG.5 for a case where
`a frequency interleaver on the transmitting Side has been
`deleted;
`0041 FIG. 8 is a modification of FIG. 6 for a case where
`a frequency deinterleaver on the receiving Side has been
`deleted;
`0042 FIG. 9 is a block diagram of a base station accord
`ing to a third embodiment;
`0043 FIG. 10 is a diagram useful in describing a mul
`ticarrier transmission Scheme;
`0044 FIG. 11 is a diagram useful in describing an
`orthogonal frequency division multiplexing Scheme;
`004.5
`FIG. 12 is a diagram useful in describing code
`spreading modulation in CDMA;
`0046 FIG. 13 is a diagram useful in describing spreading
`of a band in CDMA;
`0047 FIG. 14 is a diagram useful in describing the
`principle of a multicarrier CDMA scheme;
`0048 FIG. 15 is a diagram useful in describing place
`ment of Subcarriers,
`0049 FIG. 16 is a block diagram of a transmitting side
`in MC-CDMA according to the prior art;
`0050 FIG. 17 is a diagram useful in describing a serial
`to-parallel conversion;
`FIG. 18 is a diagram useful in describing a guard
`0051)
`interval;
`0052 FIG. 19 is a block diagram of a receiving side in
`MC-CDMA according to the prior