(12) United States Patent
`Kaiser et al.
`
`US006188717B1
`US 6,188,717 B1
`Feb. 13, 2001
`
`(10) Patent N0.:
`(45) Date of Patent:
`
`(54) METHOD OF SIMULTANEOUS RADIO
`TRANSMISSION OF DIGITAL DATA
`BETWEEN A PLURALITY 0F SUBSCRIBER
`STATIONS AND A BASE STATION
`(75) Inventors: Stefan Kaiser, Munich; Khaled Fazel,
`Wessling, both of (DE)
`
`_
`(73) Asslgnee: Deutsche Forschungsanstalt #:ur
`Luft-und Raumfahrt E.V., Koln (DE)
`
`OTHER PUBLICATIONS
`
`Chouly, A; Brajal, A; Jourdan, S; Orthogonal Multicarrier
`Techniques Applied to Direct Sequence Spread Spectrum
`1C7D21;A_A172S8y:temS; 1993: IEEE’ New York’ NY; pp'
`'
`K. FaZel et al., “On the Performance of Convolutionally—
`Coded CDMA/OFDM for Mobile Communication System”,
`pp‘ 465F472‘
`
`( * ) Notice:
`
`Under 35 U.S.C. 154(b), the term of this
`patent shall be extended for 0 days.
`
`*
`
`_
`_
`cued by exammer
`
`(21) Appl' NO‘: 08/971’583
`(22) Filed;
`Nov_ 17, 1997
`(30)
`Foreign Application Priority Data
`
`Primary Examiner—Stephen Chin
`Assistant Examiner—Thomas E McKiernan
`(74) Attorney, Agent, or Firm—BroWdy & Neimark
`
`Nov. 19, 1996
`
`(DE) ............................................ .. 196 47 833
`
`(57)
`
`ABSTRACT
`
`"""""""""""""" "
`
`(51) Int Cl 7
`'
`'
`52 U S C]
`(
`)
`I.
`.
`. ............................................................ ..
`Fleld Of Search ................................... ..
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`H04B 15/00 H04K 1/00
`’ H04L 27/36
`375/148
`'
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`370/200
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`(56)
`
`,
`References Clted
`U_S_ PATENT DOCUMENTS
`*
`2,227,226 * 11/1992 ch61 .................................. .. 372/232
`{262L253 *
`5
`370/404
`5:487:069 * 1/1996
`370/210
`575047775 * 4/1996 Chouly et aL
`5,548,582 * 8/1996 Brajal et al. ....................... .. 370/206
`FOREIGN PATENT DOCUMENTS
`
`The method of the invention is based on an optimum
`combination of multi-carrier modulation With the spread
`spectrum technique. The data of a subscriber station are
`Spread, With the data of a Subscriber Station being modulated
`on a Set of Orthogonal Spread Sequences and Superirnposed~
`The data of a subscriber station are transmitted to a partial
`quantity of subcarriers in the frequency band, With the
`partial quantity of sub-carriers associated With the individual
`subscriber stations being disjunct and distributed over the
`entire transmission band. A channel estimation required for
`receiving_side data detection is performed by means of
`?ltering in the time and/or frequency direction of reference
`symbols.
`low-complexity maximum-likelihood sequence
`est1ma't1on~1s possible for data detection. The method of the
`lnventlon 1S Well-511K601 for use for both the upstream and
`doWnlinks in future cellular mobile-radio systems.
`
`0717505
`
`6/1996 (EP) .
`
`37 Claims, 12 Drawing Sheets
`
`10.46 kb/s Conv- encoder
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`
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`1 reference symbol after 4 chips
`
`I
`
`lmerleaver
`[192 chips]
`\
`(
`38
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`Feb. 13, 2001
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`Sheet 3 0f 12
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`US 6,188,717 B1
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`Digital data
`(e.g. from the output of the voice encoder)
`
`1
`
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`D / A converter
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`
`(Figs. 5 and 6)
`
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`Sheet 4 0f 12
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`Sheet 7 0f 12
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`US 6,188,717 B1
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`Sub-carrier of
`Subscriber 1
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`Sub-carrier oi
`Subscriber 2
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`Feb. 13, 2001
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`US 6,188,717 B1
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`US 6,188,717 B1
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`1
`METHOD OF SIMULTANEOUS RADIO
`TRANSMISSION OF DIGITAL DATA
`BETWEEN A PLURALITY OF SUBSCRIBER
`STATIONS AND A BASE STATION
`
`FIELD OF THE INVENTION
`
`The invention relates to a method of simultaneous radio
`transmission of digital data betWeen a plurality of subscriber
`stations and a base station.
`
`REVIEW OF THE RELATED TECHNOLOGY
`
`In modern radio-transmission systems, particularly in
`cellular mobile-radio systems, a transmission method for
`digital signal transmission is required to be able to supply a
`large number of active subscriber stations With variable data
`rates for multimedia services (audio, video, text, data, etc.)
`must be used for digitally transmitting signals (data). Cur
`rent and future mobile-radio systems should include mobile
`subscriber stations that are small, ?exible, reliable and
`robust, and consume little energy to permit long battery
`operation.
`In particular, future cellular mobile-radio systems must be
`designed to possess a high spectral-e?iciency With respect to
`the transmission method used, despite mobile-radio channel
`disturbances and the intended high number of subscribers,
`so a plurality of active subscriber stations can transmit on the
`available mobile-radio channel. To avoid extreme
`complexity, and to use identical components, the transmis
`sion method should also be applicable for both an uplink,
`i.e., in the direction from a subscriber station to the base
`station, and a doWnlink, i.e., in the direction from a base
`station to the subscriber station.
`The modulation method of future mobile-radio systems
`should permit a coherent detection With the use of channel
`state information, at loW cost and With high reliability, and
`prevent interference (MAI, Multiple Access Interference)
`betWeen the subscriber stations of a base station.
`The detection method of a future cellular mobile-radio
`system should further permit a loW-cost maximum
`likelihood sequence estimation (optimum estimation) for
`common detection of the data of a subscriber station.
`The different data streams (audio, video, text, data, etc.)
`must be transmitted virtually error-free at a variable data rate
`(a feW kbit/s to about 2 Mbit/s) on the available mobile-radio
`channel.
`Different knoWn digital radio-transmission methods
`already include measures for meeting these requirements,
`Which are expected to be especially required in future
`cellular mobile-radio systems. The multi-carrier modulation
`method OFDM (Orthogonal Frequency-Division
`Multiplexing) With a guard interval can be used as a modu
`lation method having a high spectral e?iciency; this method
`is knoWn from the essay by S.
`Weinstein and P. M. Ebert, “Data Transmission by
`Frequency-Division Multiplexing using the Discrete Fourier
`Transform” in IEEE Trans. Commun. Tech., Vol. COM-19,
`pp. 628—634, October 1971.
`With a given signal-to-noise ratio and the respective
`channel properties, channel encoding permits the reception
`of the signal With the desired biterror probability. Moreover,
`it has been proposed to combine the multi-carrier modula
`tion method OFDM With the CDMA (Code-Division Mul
`tiple Access) method (refer to K. FaZel and L. Papke, “On
`the performance of convolutionally-coded CDMA/OFDM
`for mobile communication system” in Proc. IEEE Int. Symp.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`2
`on Personal, Indoor and Mobile Radio Commun.
`(PIMRC’93), pp. D3.2.1—D3.2.5, September 1993).
`It is knoWn that signal-level ?uctuations frequently occur
`during transmission on radio channels, particularly on
`mobile-radio channels; these ?uctuations can be caused by
`multi-path propagation, temporal change in the channel
`transmission behavior and, particularly in mobile radio, by
`movement of a subscriber station. The time-varying multi
`path propagation causes intersymbol interferences (ISI) in
`the received signal because of different signal arrival times
`over the individual re?ection paths and, consequently, signal
`fading due to destructive signal superposition. The channel
`fading has correlations in the time and frequency range. The
`errors on such channels are therefore frequently bundled and
`statistically-dependent.
`A number of options for eliminating channel disturbances
`are knoWn. A narroW-band system having equaliZation can
`be used. A system of this type With the TDMA (Time
`Division Multiple Access) method is already in use in
`cellular mobile-radio standard GSM (Global System for
`Mobile Communication). In GSM, the entire transmission
`bandWidth of 25 MHZ is subdivided into 125 channels of
`200 kHZ. In each 200 kHz-Wide channel, the TDMA method
`is used With GMSK (Gaussian Minimum Shift Keying)
`modulation. The maximum number of active subscribers per
`channel is 8 (at a data rate of 13 kbit/s). As a result, each
`channel has a spectral e?iciency of about 0.52 bit/s/HZ.
`A second knoWn option for eliminating channel distur
`bances consists of using a broadband system With spread
`spectrum and rake receivers based on the CDMA method.
`This system is included in US Mobile-Radio Standard IS-95,
`in Which all subscriber stations of a cell use the entire
`channel bandWidth of 1.25 MHZ. Each subscriber station has
`its oWn code. QPSK (Quadrature Phase Shift Keying) and
`offset QPSK are used as modulation method. The maximum
`number of active subscriber stations in a cell, that is, in the
`region of a base station, is less than 60 (at a data rate of 9.6
`kbit/s). Consequently, each channel as a spectral e?iciency
`of less than 0.46 bit/s/HZ.
`A third knoWn option for eliminating channel distur
`bances consists of using a broadband system With Orthogo
`nal Frequency-Division Multiplexing (OFDM). A system
`this type, having a guard interval, has already been selected
`for digital audio and terrestrial video broadcasting standards
`DAB (Digital Audio Broadcasting) and DVB-T (Digital
`Video Broadcasting Terrestrial)in Europe. The DQPSK
`(Differentially-Encoded Quadrature Phase Shift Keying)
`modulation method With robust channel encoding is used in
`DAB. The spectral e?iciency in DAB is about 0.75 bit/s/HZ
`per channel. In DVB-T, a multi-resolution QAM
`(Quadrature Amplitude Modulation). is used, With Which a
`?exible selection of up to a 64-QAM constellation can be
`made. A spectral e?iciency of up to 4.5 bit/s/HZ per channel
`results.
`A fourth knoWn option for eliminating channel interfer
`ence lies in the combination of the broadband spread
`spectrum system With the OFDM and COMA methods, as
`mentioned in the literature references. The spectral e?i
`ciency of this method, With BPSK (Binary Phase Shift
`Keying) modulation, is about half the spectral e?iciency of
`DAB. With QPSK the same spectral e?iciency as in DAB
`can be obtained.
`Of the four aforementioned options for eliminating chan
`nel disturbances, the narroW-band system With equaliZation
`(GSM) and the broadband system With spread spectrum and
`rake receivers (IS-95) having the draWback of requiring an
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`3
`extremely complex estimation of the channel-state informa
`tion in the case of coherent detection. To reduce costs,
`coherent estimation Was only used for the doWnlink in IS-95 .
`For the uplink, a higher transmission poWer must be used.
`The spectral ef?ciency of these tWo systems is fairly loW,
`namely 0.52 bit/s/HZ and loWer.
`The advantage of combining the broadband spread
`spectrum system With multi-carrier modulation having a
`guard interval is that no intersymbol interference (ISI)
`equalization and no rake receiver are required, and the
`embodiment is relatively simple. The knoWn spread
`spectrum multiple-access systems employing the OFDM
`multi-carrier modulation method and a guard interval are
`nevertheless only designed for the doWnlink of a cellular
`mobile-radio system, because the channel estimation is not
`problematic in this case.
`At this time there is no knoWn method or apparatus that
`alloWs the use of synchronous spread-spectrum multiple
`access systems having multi-carrier modulation and a guard
`interval in the uplink With coherent detection, because it is
`very dif?cult to estimate the channel-state information of the
`different transmission channels of all active mobile subscrib
`ers simultaneously in the base station.
`
`15
`
`SUMMARY OF THE INVENTION
`
`25
`
`Accordingly, the present invention has an object, among
`others, to overcome de?ciencies in the prior art such as
`noted above.
`It is an object of the.invention to provide a digital radio
`transmission method (or apparatus) that can be used for both
`the uplink and the doWnlink, particularly for cellular mobile
`radio, the method has a high spectral ef?ciency so that a very
`large number of active subscriber stations can transmit on
`the available radio channel; Where its modulation method
`permits a coherent detection With a loW complexity and high
`reliability; that prevents interference betWeen the subscriber
`stations of a base station; and that ensures virtually error-free
`transmission of different data streams (audio, video, text,
`data, etc.) on the available radio channel. In addition, the
`transmission method is intended to permit at the receiving
`side a detection method based on maximum-likelihood
`sequence estimation (optimum estimation) for common
`detection of the data of a subscriber station at loW cost.
`ToWard this object the method of the invention optimally
`combines the multi-carrier modulation method With the
`spread-spectrum technique. This combination permits a
`maximum-likelihood sequence estimation With loW com
`plexity for coherent detection of the data in the receiver, and
`can be used for both the upstream and doWnlinks. The
`necessary channel estimation can be realiZed suitably With a
`simple Wiener ?lter.
`The parameters for the physical layer (modulation, chan
`nel encoding, access method, etc.) of a system operating in
`accordance With the method of the invention can be advan
`tageously selected such that signi?cantly more data can be
`transmitted per transmission channel than are necessary for
`pure voice transmission. In the case of voice transmission
`(9.6 kbit/s), the TDMA (Time-Division Multiple Access)
`method can be used per transmission channel to accommo
`date a plurality of voice channels in the transmission chan
`nel.
`
`BRIEF DESCRIPTION OF THE DRAWING
`
`The above and other objects and the nature and advan
`tages of the present invention Will become more apparent
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`from the folloWing detailed description of the method of the
`invention and its essential advantages Which are explained in
`detail beloW by Way of an embodiment for a cellular
`mobile-radio system taken in conjunction With draWings,
`Wherein:
`FIG. 1a is a schematic vieW of a transmission scenario for
`an uplink in a cell of a mobile-radio system;
`FIG. 1b is a schematic vieW of a transmission scenario for
`a doWnlink in a cell of a mobile-radio system;
`FIG. 2 is a block diagram of a transmission side for the
`transmission of the data of a subscriber station;
`FIG. 3 is a block diagram of a receiving side for receiving
`the data of a subscriber station;
`FIG. 4 is a block diagram of a transmission-side spreading
`of the data symbols and subsequent superimposing of
`sequences;
`FIG. 5 is a block diagram of a transmission-side multi
`carrier modulation With frequency mapping, including the
`insertion of reference symbols that serve for channel esti
`mation;
`FIG. 6 is a spectral schematic vieW over the Width of the
`transmission band for K subscriber stations to explain a
`transmission-side frequency mapping and the corresponding
`frequency demapping on the receiver side;
`FIG. 7 is a block diagram of a receiving-side multi-carrier
`demodulation With frequency demapping, including detec
`tion of the received reference symbols for the channel
`estimation;
`FIG. 8 is a block diagram of the principle of maximum
`likelihood sequence estimation, including data-symbol
`demapping;
`FIG. 9a is a block diagram of the transmission side for an
`actual, number-speci?c embodiment and application
`example of the transmission method of the invention for a
`TDMA time slot;
`FIG. 9b is a block diagram of the receiving side for an
`actual, number-speci?c embodiment and application
`example of the transmission method of the invention for a
`DMA time slot; and
`FIG. 10 is a tabular vieW of the principle of DMA in the
`application example of FIGS. 9a and 9b.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENT
`A cellular netWork according to the OSI (Open-system
`Interconnection) reference model comprises a plurality of
`levels or layers: ?rstly, the netWork administrator, secondly,
`the protocol layer (or level), and thirdly, the physical layer
`(or level). The protocol level is made up of different syn
`chronisation levels such as multiple-access synchronisation
`and frame synchronisation.
`The aforementioned GSM and IS-95 systems contain
`synchronisation channels Which are speci?ed for them. Only
`the physical level (modulation, channel encoding, access
`method, etc.) is discussed here in connection With the
`invention; the present discussion assumes that the synchro
`nisation and netWork administrator are present.
`FIG. 1a illustrates a transmission scenario for an uplink
`from a mobile subscriber station T1, T2, .
`.
`, TK,
`respectively, to a base station B. While FIG. 1b shoWs a
`transmission scenario for the doWnlink from the base station
`B to one of the mobile subscriber stations T1, T2, .
`.
`. , TK,
`respectively.
`In the case of the uplink (FIG. 1a), the data transmitted by
`the subscriber stations T1, T2, .
`.
`.
`, TK via antennas are
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`received in the base station B by an antenna A, then detected,
`subscriber-speci?cally, by detection devices D1, D2, .
`.
`.
`,
`DK. In the case of the doWnlink (FIG. 1b), the subscriber
`speci?c data originating from the signal transmitters S1,
`S2 , .
`.
`. , SK are collected by a superimposing device U in
`the base station B. and transmitted from there via the
`antenna A and received by the subscriber stations T1,
`T2 ,
`.
`.
`.
`, TK and evaluated there for each individual
`subscriber.
`Because the transmission method of the invention avoids
`interferences betWeen the signals of the different subscriber
`stations of a base station, it can be used for both the upstream
`and doWnlinks of a cellular mobile-radio netWork. The
`folloWing description of the radio-transmission method of
`the invention therefore applies to both the upstream and
`doWnlinks.
`The transmission path of the multiple-access method
`according to the invention, employing the spread-spectrum
`technique and multi-carrier modulation, is illustrated in
`FIGS. 2 and 3 for the transmission of the data of a subscriber
`station. FIG. 2 shoWs a block diagram of the transmission
`side, and FIG. 3 shoWs a block diagram of the receiving side.
`As shoWn in FIG. 2, on the transmission side, a channel
`encoder 1 provides the digital data coming from, for
`example, the output of a voice encoder With error protection
`against channel disturbances. Convolution codes, turbo
`codes or block codes, for example, can be used as channel
`codes. The code bits are scrambled in blocks or pseudo
`randomly, for example, With an interleaver 2 to avoid long
`error bursts at the input of the channel decoder in the
`receiver, Which Will be described later. The scrambled code
`bits are mapped into complex data symbols in a data-symbol
`mapper 3, for example With a BPSK (Binary Phase Shift
`Keying) or a QPSK (Quadrature Phase Shift Keying).
`Each complex data symbol is then multiplied by a spread
`sequence of length L (L chips) in an assembly 4 shoWn in
`detail in FIG. 4. One chip is one element of the spread
`sequence. As FIG. 4 shoWs, ?rst the complex data symbols
`coming serially from the data-symbol mapper 3 are con
`verted in blocks into a parallel form in a serial/parallel
`converter 9. Then, the data symbols k, k+1, .
`.
`.
`, k+L are
`multiplied by the spread sequences of length L in the
`multipliers 10.
`Orthogonal Walsh-Hadamard sequences, for example, are
`used as spread sequences; of these, L orthogonal spread
`sequences of length L exist. Amaximum of L parallel spread
`sequences modulated With data symbols is superimposed,
`symbol- and thus chip-synchronously, in the assembly 4
`(FIG. 2) by means of an adder 11 shoWn in FIG. 4, resulting
`in a transmission sequence comprising L chips containing
`the information of a maximum of L data symbols.
`The robustness of the transmission method of the inven
`tion With respect to intercell interferences can be increased
`if less than L spread sequences having length L and having
`been modulated With data symbols are superimposed. In
`FIG. 4 the case is shoWn, Where L spread sequences having
`length L and having been modulated With ata symbols are
`superimposed.
`A frequency and time interleaver 5 then crambles the
`chips of a plurality of transmission equences coming from
`the assembly 4, in blocks or pseudo-randomly, for example,
`in the frequency and time direction using a plurality of
`multi-carrier-modulated OFDM symbols in order to avoid
`large error bursts through timeselective fading (Which
`results from Doppler shifts) and frequency-selective fading
`(Which results from re?ections in the channel).
`In a doWnstream frequency mapper and multi-carrier
`modulator 6, Whose principle is shoWn in detail in FIG. 5, M
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`chips coming from the output of the interleaver 5 are
`converted serial/parallel in a serial/parallel converter 12. It
`is not absolutely necessary for the number M of sub-carriers
`of a subscriber station to be a multiple of the spread-code
`length L, Which permits ?exible utilisation of the transmis
`sion capacity With respect to different data rates, for example
`variable data rates, of the individual subscriber stations.
`Reference data 14, Which are required for channel estimation
`and synchronisation in the receiver, are inserted into each of
`the M data streams by means of a multiplexer 13.
`The loWer portion of FIG. 5 shoWs an exemplary data
`stream, With the information-carrying chips being shoWn as
`White boxes and the inserted reference symbols being shoWn
`as black boxes. The reference symbols serving for channel
`estimation are knoWn in the receiver. After the multiplexer
`13, each of the M data streams noW provided With reference
`symbols is modulated on its oWn sub-carrier frequency in a
`multi-carrier modulator 15, With the frequency allocation
`being subscriber station-speci?c.
`FIG. 6 shoWs the transmission-side subscriber station
`speci?c frequency mapping, and the corresponding,
`receiving-side frequency demapping, in a spectral vieW over
`the Width of the transmission-frequency band for K sub
`scriber stations. The partial quantities of sub-carriers asso
`ciated With the individual subscriber stations are disjunct (or,
`disjoint), Which avoids interferences betWeen the subscriber
`stations of a base station.
`The frequency mapper distributes the subcarriers of a
`subscriber station over the entire transmission-frequency
`band for increasing the diversity gain through spreading in
`the receiver; the spacing betWeen adjacent sub-carriers of a
`subscriber station remains equidistant, but can also be
`selected pseudo randomly. The spacing betWeen adjacent
`sub-carriers of a subscriber station must be a multiple factor
`of the reciprocal value of the duration of a multi-carrier
`modulated symbol to ensure the orthogonality betWeen the
`sub-carriers of a subscriber station and that of all subscriber
`stations.
`The orthogonal frequency-division method OFDM can be
`used, for example, Which is relatively simple to realiZe in
`practice With an Inverse Fast Fourier Transformation IFFT
`and a Fast Fourier Transformation FFT for the modulation
`and demodulation performed in the multi-carrier modulator
`15. In a device 16, the multi-carriermodulated data symbols
`are cyclically extended by a guard interval ~ for avoiding
`intersymbol interferences (ISI) betWeen adjacent multi
`carriermodulated OFDM symbols due to multi-path propa
`gation. The M modulated data streams are then added in a
`summation device 17. Prior to transmission on the trans
`mission channel, the respectively added digital data streams
`are converted into an analog transmission form in a digital/
`analog converter 7.
`The aforementioned protection interval ~ is additionally
`necessary for alloWing greater tolerances in synchronous
`transmission of the subscriber stations, because the mobile
`subscriber stations are at different distances from the asso
`ciated base station, and therefore have different signal arrival
`times to and from the base station.
`As shoWn in FIG. 3, on the receiving side the received
`data are multi-carrier-demodulated and frequency
`demapped in a multi-carrier demodulator 19 folloWing their
`conversion into digital form in an analog/digital converter
`18. The functions of the multi-carrier demodulator 19 are
`shoWn in detail in FIG. 7. The data coming from the
`analog/digital converter 18 are ?rst extracted from the guard
`interval 0t in a guard interval-extraction device, and then
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`multiple-carrier-demodulated in a multi-carrier demodula
`tion device 26 and frequency-demapped speci?cally to the
`subscriber station.
`The receiving-side frequency demapping is effected
`analogously to the transmission-side frequency mapping;
`details about the process can be inferred from the description
`of FIG. 6. The reference symbols needed for channel esti
`mation in the channel estimator 20 (FIG. 3, are extracted
`from the information-carrying data in a demultiplexer 27.
`The information-carrying data, Which are present in parallel
`form, are brought into a serial form by means of a parallel/
`serial converter 28.
`The channel estimator 20 shoWn as a block in FIG. 3 uses,
`for example, a Wiener ?lter, Which is relatively simple, to
`?lter the received reference symbols for each sub-carrier to
`be detected over time. From this, it determines the channel
`state information for the information-carrying data. In con
`nection With the channel estimation, it is pointed out here
`that groups (or one group) of sub-carriers can be formed in
`the transmitter, in Which instance the sub-carriers of a group
`are adjacent in the transmission-frequency band, and can
`additionally be ?ltered in the frequency direction in the
`receiver during channel estimation, resulting in more precise
`channel-state information or less redundancy through refer
`ence symbols. The channel-state information itself that is
`obtained through the channel estimation is required for
`receiving-side data detection and channel decoding.
`After deinterleaving in the frequency and time direction in
`a frequency and time de-interleaver 21, the received
`information-carrying data are detected in a data detector 22.
`For data detection, a maximum-likelihood sequence estima
`tor is advantageously used, for example, that determines the
`most probable of all transmitted sequences and provides the
`associated data as soft decisions. In the use of QPSK
`modulated data symbols, for example, the maximum
`likelihood sequence estimation can be performed separately
`in the I and Q signal components.
`FIG. 8 illustrates the principle of maximum-likelihood
`sequence estimation. Here 2L possible transmitted sequences
`are stored in a memory component 29 and compared to the
`respectively received sequence 31 in a circuit 30 for metric
`calculation. Then the maximum metric is determined in a
`device 32; from this metric, a conclusion can be reached
`regarding the most probable of all 2L possible transmitted
`sequences.
`In the maximum-likelihood sequence estimation accord
`ing to FIG. 8, the channel-state information 33 is required
`for the metric calculation. Instead of the maximum
`likelihood sequence estimator, a conventional detection
`method can also be used, Which employs despreading to
`detect all of the data symbols of a subscriber station after a
`equaliZation, and further transmits soft decisions to the
`symbol demapper.
`The code bits detected and demodulated in the data
`detector 22 With symbol demappers are unscrambled in a
`de-interleaver 23, and the information data are detected from
`them in a channel decoder 24 (Viterbi decoder, SOVA
`(Soft-Output Viterbi Algorithm) for iterative turbo decoding
`or block decoder).
`If conventional detection methods are used in the method
`of the invention, they can also be used iteratively to attain a
`reduction in interference in the