(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY(PCT)
`
`(19) World Intellectual Property Organization
`International Bureau
`
`(43) International Publication Date
`13 June 2002 (13.06.2002)
`
`
`
`PCT
`
`(10) International Publication Number
`WO 02/47286 A2
`
`(51) International Patent Classification’:
`
`HO04B 7/00
`
`(81) Designated States (national): AE, AG, AL, AM,AT, AU,
`AZ, BA, BB, BG, BR, BY, BZ, CA, CH, CN, CR, CU, CZ,
`DE, DK, DM,DZ, EE, ES, FI, GB, GD, GE, GH, GM,HR,
`(21) International Application Number:©PCT/EP00/12269
`HU,ID,IL,IN, IS, JP, KE, KG, KP, KR, KZ, LC, LK, LR,
`LS, LT, LU, LV, MA, MD, MG, MK, MN, MW, MX, MZ,
`NO, NZ, PL, PT, RO, RU, SD, SE, SG, SL, SK, SL, TJ, TM,
`TR, TI, TZ, UA, UG, US, UZ, VN, YU, ZA, ZW.
`
`(22) International Filing Date: 6 December 2000 (06.12.2000)
`
`(25) Filing Language:
`
`English
`
`(26) Publication Language:
`
`English
`
`(71) Applicant (for all designated States except US): NOKIA
`CORPORATION[FI/FI]; Keilalahdentie 4, FIN-02150
`Espoo (FD).
`
`(72) Inventors; and
`HOTTINEN,
`(for US only):
`(75) Inventors/Applicants
`Ari [FI/FI]; Ristiniementie 4 0 30, FIN-02320 Espoo
`(FID. WICHMAN,Risto [FI/FI]; Viipurinkatu 10 A 20,
`FIN-00510 Helsinki (FD. TIRKKONEN, Olav [FI/FI],
`Puroniitynpolku 5 A 6, FIN-00720 Helsinki (FID.
`
`(74) Agent: COHAUSZ & FLORACK; Kanzlcrstrasse 8a,
`40472 Diisseldorf (DE).
`
`(84) Designated States (regional): ARIPO patent (GH, GM,
`KF, LS, MW, MZ, SD, SL, SZ, TZ, UG, ZW), Eurasian
`patent (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), European
`patent (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR,IE,
`IT, LU, MC, NL, PT, SE, TR), OAPI patent (BF, BJ, CF,
`CG, CL, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG).
`
`Published:
`
`without international search report and to be republished
`upon receipt of that report
`
`For two-letter codes and other abbreviations, refer to the "Guid-
`ance Notes on Codes andAbbreviations" appearing at the begin-
`ning ofeach regular issue ofthe PCT Gazette.
`
`A2
`(54) Title: METHOD FOR CONTROLLING THE WEIGHTING OF A DATA SIGNAL IN THE AT LEAST TWO ANTENNA
`ELEMENTS OF A RADIO CONNECTION UNIT, RADIO CONNECTION UNIT, MODULE AND COMMUNICATIONSSYS-
`oO TEM
`
`(57) Abstract: The invention relates to a method for controlling the weighting of a data signal in the at least two antenna elements
`of a first radio connection unit of a radio communications system, which data signal is to be distributed for parallcl transmission to a
`second radio connectionunit to at least two beams. In orderto improve such a method, it comprises: determining in the second radio
`connection unit a weight information enablingthe first radio connection unit to determine the sets of weights for suitable beams for
`transmission and transmitting it to the first radio connection unit; and distributing the data signal in thefirst radio connection unit to
`those sets of weights and transmitting the data signals simultaneously via the formed beams. Alternatively or additionally, the second
`unit determines the number of beams to be used and informsthefirst unit about it. ‘The invention equally relates to corresponding
`radio connection units, radio connection unit modules and radio communications systems.
`
`1
`
`AMAZON.COM,INC.,et al.
`
`EXHIBIT 1011
`
`8N
`
`O02/47
`
`S
`
`1
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`

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`WO 02/47286
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`PCT/EP00/12269
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`Method for controlling the weighting of a data signal in the
`
`at least two antenna elements of a radio connection unit,
`
`radio connection unit, module and communications system
`
`FIELD OF THE INVENTION
`
`The invention relates to a method for controlling the
`
`weighting of a data signal in the at least two antenna
`
`elements of a first radio connection unit of a radio
`
`communications system, which data signal is to be
`
`distributed to at least two beams for parallel transmission
`
`of the data signal in at least two at least partly different
`
`streams to a second radio connection unit with at least one
`
`antenna element,
`
`the beams being formed by weighting the
`
`data signal in the antenna elements with a set of weights
`
`for each beam. The invention equally relates to a radio
`
`connection unit, a radio connection unit module and a radio
`
`communications system to be employed for such a method.
`
`BACKGROUND OF THE INVENTION
`
`It is known from wireless communications systems of the
`
`state of the art to transmit data signals between two radio
`
`connection units,
`
`in particular from a base station to a
`
`terminal,
`
`in parallel via several transmit antenna elements.
`
`When using multiple antennas with adapted transmission and
`
`detection techniques,
`
`the spatial dimension can be exploited
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`at the terminal and the spectral efficiency of fading
`
`wireless channels can be increased significantly compared to
`
`conventional single antenna links. A terminal receiving
`
`signals from such a transceiver can be designed to
`
`distinguish several channels,
`
`if they are sufficiently
`
`uncorrelated.
`
`The document "Link-Optimal BLAST Processing With Multiple-
`
`Access Interference" by F.R. Farrokhi, G.J. Foschini, A.
`
`Lozano, R.A. Valenzuela, Bell Laboratories (Lucent
`
`Technologies)
`
`in IEEE Vehicular Technology Conference,
`
`Boston, Massachussets, USA, Sept. 24-28, 2000, proceeds from
`a wireless communications system with antenna arrays at
`|
`
`both,
`
`transmitter and receiver. The system transmits
`
`parallel data streams simultaneously and in the same
`
`frequency band, using the multiple antennas. With rich
`
`propagation,
`
`the different streams can be separated at the
`
`receiver because of their distinct spatial signatures. It is
`
`proposed to make the channel and the interference covariance
`
`available to the transmitter. The transmitter finds the
`
`channel eigenmodes in the presence of the interference and
`
`sends multiple independent data streams through those
`
`eigenmodes. The total transmitted power is distributed among
`
`the eigenmodes according to an optimal water-fill process.
`
`Thereby,
`
`the maximised capacity is supposed to be achieved.
`
`The method, as described above, always assumes that the
`
`receiver has at least two antenna elements. Preferably,
`
`in
`
`the aforementioned concept,
`
`the number of transmit and
`
`receive elements is the same.
`
`3
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`The parallel transmission via a plurality of antenna
`elements in transceiver and terminal enables a reduction of
`
`Eb/No (Eb = energy per bit; No = noise power density per Hz)
`
`requirements for achieving data rates associated with higher
`
`order constellations like 8PSK,
`
`16QAM, or 64QAM. Moreover,
`
`it enables the expansion of the number of rate options for
`
`adaptive modulation and coding (AMC) and an increase of the
`
`maximum rate.
`
`SUMMARY OF THE INVENTION
`
`It is an object of the invention to provide a further
`
`improved method for controlling the weighting of a data
`
`signal in the at least two antenna elements of a transceiver
`
`of a wireless communications system which allows for high
`
`data rates in the downlink matched to channel conditions.
`
`This object is reached on the one hand by a first method for
`
`controlling the weighting of a data signal in the at least
`
`two antenna elements of a first radio connection unit of a
`
`radio communications system, which data signal is to be
`
`distributed to at least two beams for parallel transmission
`
`of the data signal in at least two at least partly different
`streams to a second radio connection unit with at least one |
`antenna element,
`the beams being formed by weighting the
`data signal in the antenna elements with a set of weights
`for each beam,
`the method comprising:
`
`- determining in the second radio connection unit a weight
`
`information enabling the first radio connection unit to
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`determine the sets of. weights for at least two suitable
`
`beams for transmission of a data signal from the first
`
`radio connection unit to the second radio connection
`
`unit;
`
`-~
`
`transmitting the determined weight
`
`information to the
`
`first radio connection unit; and
`
`in the first radio
`- distributing the data signal
`connection unit to at least two sets of weights
`
`determined from the received weight
`
`information and
`
`transmitting the data signals simultaneously via the at
`
`least two formed beams.
`
`the invention proceeds
`With regard to this first method,
`from the idea that the second radio connection unit is in
`
`possession of the most comprehensive information relevant
`
`for selecting suitable beams for transmission of the data
`
`signal and for determining sets of weights for the selected
`
`beams. It is therefore proposed to calculate all relevant
`
`information needed for the weighting of the data signals in
`
`the antenna elements of the first radio connection unit
`
`already at the second radio connection unit. The feedback
`
`information includes a weight information from which the
`
`first radio connection unit can determine the set of weights
`
`for each beam that is to be used for transmission of the
`
`data signals from the first radio connection unit to the
`
`second radio connection unit. Each feedback information
`
`indicates the weighting of the data signal for each of the
`
`different antenna elements of the first radio connection
`
`unit. This way,
`
`the information needed for obtaining the
`
`weight sets can be determined with the full information
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`present at the second radio connection unit, while only the
`
`information needed is fed back to the first radio connection
`
`unit.
`
`It is to be noted that the feedback information can include
`
`the set of weights for each selected beam,
`
`the first radio
`
`connection unit only having to apply the received sets for
`
`forming the selected beams. It is not required, however,
`
`that the second radio connection unit determines and
`
`transmits all sets of weights, if there exists an a priori
`
`fixed or negotiated way of calculating multiple weights from
`
`a single feedback known to both, first and second radio
`
`connection unit. Then, a reduced feedback information is
`
`sufficient, which enables the first radio connection unit to
`
`determine the necessary sets of weights. Therefore,
`
`the
`
`second radio connection unit controls the parallel beams
`
`with weight
`
`information either directly using explicit
`
`feedback for all beams or implicitly using reduced feedback
`
`and the knowledge of beam parameterisation at the first
`
`radio connection unit.
`
`On the other hand,
`
`the object is reached by a second method
`
`for controlling the weighting of a data signal in the at
`
`least two antenna elements of a first radio connection unit
`
`of a radio communications system, which data signal is to be
`
`distributed to at least two beams for parallel transmission
`
`of the data signal in at least two at least partly different
`
`streams to a second radio connection unit with at least one
`
`antenna element,
`
`the beams being formed by weighting the
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`data signal in the antenna elements with a set of weights
`
`for each beam, said second method comprising:
`
`- determining in the second radio connection unit the
`
`number of beams to be used for transmission of a data
`
`signal from the first radio connection unit to the second
`
`radio connection unit;
`
`- providing the first radio connection unit with
`
`information about the determined number of beams; and
`
`- distributing the data signal
`
`in the first radio
`
`connection unit to the number of beams corresponding to
`
`the number of beams determined in the second radio
`
`connection unit.
`
`Just like in the first proposed method,
`
`in the second
`
`the second radio
`proposed method according to the invention,
`connection unit makes use of its knowledge in order to
`
`determine an information relevant for beamforming in the
`
`first radio connection unit and transmits this information
`
`to the first radio connection unit. The difference is that
`
`here,
`
`the information may include the number of beams that
`
`are to be formed by the first radio connection unit.
`
`Both methods are aimed at controlling the weighting of a
`
`data signal that is to be divided, usually after encoding
`and modulation,
`into at least two parts for transmission. At
`least partly different symbols are therefore transmitted in
`
`parallel using the at least two formed beams, even though
`
`the symbols transmitted by the two beams do not have to be
`
`completely different.
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`The weight
`
`information for the selected beams and the number
`
`of beams respectively can be signalled to the first radio
`
`connection unit using any feasible technique known in the
`
`state of the art.
`
`The transmitted data signals can be received at the second
`
`radio connection unit by one antenna element or by several
`
`antenna elements.
`
`The above stated object of the invention is equally reached
`by a radio connection unit that can be used as first and/or
`as second radio connection unit, comprising means
`respectively for realising the methods according to the
`invention. Moreover,
`the object is reached by radio
`
`connection unit modules comprising means for realising the
`
`methods according to the invention in a first or second or a
`
`combined first and second radio connection unit. Finally,
`
`also a radio communications system with radio connection
`
`units suitable for realising the methods according to the
`
`invention reaches this object of the invention.
`
`Preferred embodiments of the invention become apparent from
`
`the subclaims.
`
`In the first method according to the invention,
`
`the second
`
`radio connection unit preferably determines the set of
`
`weights for at least two dominant downlink beams that are
`
`spatially sufficiently independent or uncorrelated for
`
`reception at said second radio connection unit. The sets of
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`. weights for forming the downlink beams that are fed back to
`
`the first radio connection unit can be calculated at the
`
`second radio connection unit so that they enable an
`
`efficient signal separation at the receiver. As an example,
`
`if the two most dominant beams are highly correlated,
`
`the
`
`first radio connection unit and the second radio connection
`
`unit can use only one of them for an efficient parallel
`
`transmission.
`
`In this case, only one of those most dominant
`
`beams is used and in addition another dominant beam with a
`
`smaller eigenvalue but which is sufficiently different from
`
`the two most dominant beams. With sufficient information
`
`about the beamforming at the first radio connection unit,
`
`instead of all needed sets of weights only some
`again,
`reduced weight
`information from which several sets of
`
`weights can be determined can be transmitted to the first
`
`radio connection unit as feedback information.
`
`In a further preferred embodiment of the first of the
`
`proposed methods,
`
`the second radio connection unit not only
`
`determines the downlink beams and the corresponding weight
`
`information indicating the sets of weights that are to be
`used for multiple transmission, but also the data rates to
`be used for each of the selected beams. The data rates are
`
`determined in the second radio connection unit according to
`
`the characteristics of the received channels and information
`
`about the determined data rates is transmitted to the first
`
`radio connection unit. This means,
`
`the data rate mapping to
`
`multiple beams is done at least partially using a second
`
`radio connection unit to first radio connection unit
`
`feedback. Thereby,
`
`the downlink data rate using multiple
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`transmit beams or weight sets can be maximised. In order to
`
`be able to assign the data rates,
`
`the signal-to-noise ratio
`
`(SNR) or signal-to-interference ratio (SIR), or signal-to-
`
`noise-plus-interference ratio (SINR) of the different
`
`channels can be evaluated. Moreover, with correlated
`
`channels,
`
`the data rate should typically be reduced
`
`regardless of the number of transmit or receive antenna
`
`elements. The data rates can be determined in a way that the
`
`total data rate remains constant. Advantageously, however,
`
`the total data rate is determined in a way that it coincides
`
`with a data rate requested by the terminal and that the
`
`associated transmission power supports the quality-of-
`service (QoS) criteria (e.g. SIR, SNR, SINR, Bit Error Ratio
`BER, Frame Error Rate FER, Outage) set for the transmitted
`
`service by the terminal.
`
`The information about changes in the data rates transmitted
`
`from the second to the first radio connection unit can be
`
`differential or absolute.
`
`In the first case, e.g. only a
`
`requested increase or decrease in a data rate has to be
`
`indicated in the feedback, while in the second case,
`
`the
`
`data rate can change arbitrarily, but more feedback is
`
`required.
`
`The determination of multi-rate beams is preferably done in
`
`the second radio connection unit by taking into account the
`
`effective signal-to-noise ratio for parallel beams and by
`
`using in addition the knowledge of the receiver structure in
`
`the second radio connection unit. For example,
`
`some
`
`receivers can be better suited for mitigating inter-beam
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`10
`
`interferences than others. Furthermore,
`
`the inter-beam
`
`interference can be optimised when controlling jointly the
`
`transmit powers, weight coefficients and data rates.
`
`In an equally preferred embodiment of the first method
`
`according to the invention,
`
`the second radio connection unit
`
`determines alternatively or in addition to the data rate
`
`distribution an advantageous power distribution over the
`
`selected downlink beams. Like the data rates, also the power
`
`distribution is determined in the second radio connection
`
`unit according to the characteristics of the received
`
`channels. The second radio connection unit transmits
`information about this distribution to the first radio
`
`connection unit for controlling the antenna elements
`
`accordingly. Equivalent as for the data rates,
`
`the total
`
`power over all used beams can be kept constant.
`
`The optimal power allocation can be determined in a way that
`
`the desired SIR is met after the sets of weights have been
`
`fixed. A downlink power assignment for the power of downlink
`
`beams with fixed beam coefficients from a base station to a
`
`number of terminals is described in "Optimal downlink power
`
`assignment for smart antenna systems" by Weidong Yang;
`
`Guanghan Xu,
`
`in Acoustics, Speech and Signal Processing,
`
`1998; Proceedings of the 1998 IBEE, Vol. 6, pp. 3337-3340.
`
`This approach can be adapted for the first method of the
`
`invention to be used to jointly determine the powers and the
`
`Q0S parameters for each of several parallel downlink beams
`
`from a first radio connection unit to a given second radio
`
`connection unit rather than for the power of downlink beams
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`11
`
`from a base station to multiple users, where to each user
`
`there is assigned one beam.
`
`Alternatively,
`
`the transmit powers for the downlink beams
`
`can be determined jointly with the determination of the set
`
`of weights or corresponding weight information for the
`
`optimal beams. In the document "Joint Optimal Power Control
`
`and Beamforming in Wireless Networks Using Antenna Arrays",
`
`by F. Rashid-Farrokhi, L. Tassiulas, and K. J. Ray Liu,
`
`IEEE
`
`Transactions On Communications, vol. 46, no. 10, October
`
`1898, pp. 1313-1323, an algorithm is provided for computing
`
`transmission powers and beamforming weight vectors, such
`
`that a target SINR is achieved for each link from one base
`
`station to a plurality of terminals with minimal
`
`transmission power.
`In the documents, it is proposed that
`for a fixed power allocation, each base station maximises
`the SINR using the minimum variance distortionless response
`(MVDR) beamformer. Next,
`the mobile powers are updated to
`reduce the cochannel interference. This operation is done
`
`iteratively until the vector of transmitter powers and the
`
`weight coefficients of the beamformers converge to the
`
`jointly optimal value. Assuming that at least two spatial
`
`channels have been estimated for the second radio connection
`
`unit,
`
`the sets of weights and the power optimisation
`
`techniques proposed by Farrokhi et al. can be used in the
`
`first method of the invention to determine multiple beams
`
`for parallel transmission from the first to the (single)
`
`second radio connection unit instead of from a base station
`
`to multiple users. As a result,
`
`the second radio connection
`
`unit has all relevant information for optimising the beams
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`12
`
`and for distributing the signals to at least two parallel
`
`beams.
`
`Furthermore, for determining the at least two suitable
`
`downlink beams, channel
`
`information and/or interference
`
`information can be used in the second radio connection unit.
`
`A possibility for determining an interference covariance
`
`matrix that can be used in the method according to the
`
`invention to calculate the optimal eigenvectors at the
`
`second radio connection unit,
`
`is described e.g.
`
`in "Maximum
`
`bikelihood Multipath Channel Parameter Estimation in CDMA
`
`Systems", by C. Sengupta, A. Hottinen, J.R. Cavallaro, and
`B. Aazhang, 32nd Annual Conference on Information Sciences
`
`and Sysetms (CISS), Princeton, March 1998,
`
`information, which may include the sets of
`The weight
`weights, and/or the data rates and/or the power distribution
`can be determined in the second radio connection unit either
`
`based on short term variations of the received channels or
`
`based on the stationary structure of the received channels
`
`or on a combination of both.
`
`In a slowly fading channel,
`
`short term variations can be used to determine the weight
`
`information and related data rate information.
`
`Alternatively, short term information can be used for
`
`signalling only the data rate and/or the power information
`
`for beams that are determined by using the stationary
`structure of the received channels. With short term
`
`variations, high resolution beams can be calculated such
`
`that the instantaneous data rate ig maximised. This, of
`
`course, works only in slowly fading environments.
`
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`13
`
`In case the stationary structure of the received channels is
`
`used for determining the weight
`
`information for the at least
`
`two downlink beams, preferably the eigenvectors of the
`
`Spatial signal covariance matrices are calculated. However,
`
`the weight information for the preferred beams can be
`
`calculated in any other suitable way. For example,
`
`the
`
`subspace weight vectors can be tracked with a singular value
`
`decomposition and subspace tracking, which does not require
`
`the calculation of the correlation matrix and a subsequent
`
`eigenvalue decomposition. Such a tracking can be taken e.g.
`
`from "Solving the SVD Updating Problem for Subspace Tracking
`on a Fixed Sized Linear Array of Processors" by C.
`Sengupta,J.R. Cavallaro, and B. Aazhang, International
`
`Conference on Acoustics, Speech, and Signal Processing
`
`(ICASSP), Volume 5, pp. 4137-4140, Munich, April 1997.
`
`Alternatively, an independent component analysis can be
`
`applied, as described e.g. by U.F. Cardoso and P. Comon in:
`
`"Independent Component Analysis, a Survey of Some Algebraic
`
`methods", Proc.
`
`ISCAS Conference, volume 2, pp. 93-96,
`
`Atlanta, May 1996.
`
`In this case,
`
`the beams transmitted in
`
`parallel are typically non-orthogonal.
`
`In a preferred embodiment of the second method according to
`
`the invention,
`
`the second radio connection unit determines
`
`the number of beams to be used for transmission of a data
`
`signal from the first radio connection unit to the second
`
`radio connection unit based on channel and/or interference
`
`information.
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`14
`
`As one possibility for transmitting the information about
`
`the determined number of beams in the second method
`
`according to the invention,
`
`the determined number of beams
`
`to be used for transmission of a data signal from the first
`
`radio connection unit to the second radio connection unit
`
`can simply be indicated by the number of beams that are
`
`transmitted from the second radio connection unit to the
`
`first radio connection unit. As mentioned above,
`
`the number
`
`of beams can also be included in the number of sets of
`
`weights determined and transmitted as proposed for the first
`
`method according to the invention.
`
`In the second method according to the invention,
`
`the first
`
`radio connection unit can signal in addition to the number
`
`of beams beam indices selected for transmission, enumerated
`
`in some way.
`
`The first method according to the invention can, but does
`
`not necessarily,
`
`include the second method according to the
`
`invention. That means,
`
`in the first method according to the
`
`invention,
`
`the number of beams to be used can be determined
`
`first in the second radio connection unit and for this
`
`number of beams, sets of weights are determined and
`
`transmitted to the first radio connection unit, or the
`
`number is included in the weight
`
`information if this weight
`
`information does not include the complete set of weights to
`
`be used. Alternatively,
`
`the number of sets of weights
`
`determined in the second radio connection unit can be fixed.
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`In both methods according to the invention,
`
`the second radio
`
`connection unit should recover the data signals distributed
`
`to the at least two beams in the first radio connection unit
`
`and transmitted in at least two at least partly different
`
`streams to the second radio connection unit. This means,
`
`the
`
`parts transmitted by different streams have to be combined
`
`again in the correct symbol/bit order.
`
`In a preferred embodiment of both methods according to the
`
`invention,
`
`the first radio connection unit transmits weight
`
`information used for beamforming to the second radio
`connection unit and the second radio connection unit uses
`
`the received weight information for evaluation of the
`
`received data signals. With this knowledge,
`
`the quality and
`
`the speed in determining information to be transmitted to
`
`the first radio connection unit can be improved.
`
`In an
`
`alternative embodiment for the first method of the
`
`invention,
`
`the second radio connection unit can make use of
`
`its own knowledge included in the weight information
`
`transmitted to the first radio connection unit for
`
`recovering the data signals.
`
`In both embodiments,
`
`the second
`
`radio connection unit can use the channel estimates obtained
`
`for each antenna element,
`
`the transport format information,
`
`and the used beam coefficients for each beam in order to
`
`detect and decode the information most efficiently. The
`
`receiver can use any techniques known in the art to that
`
`end,
`
`including joint detection,
`
`joint decoding,
`
`joint
`
`detection/decoding and channel estimation implemented either
`
`iteratively, or non-iteratively. As an example,
`
`techniques
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`analogous to those described in A. Hottinen and 0.
`
`Tirkkonen, "Iterative decoding and detection in a high data
`
`rate downlink channel," Proc. NORSIG, Kolmorden, Sweden,
`
`June 2000, can be used.
`
`In both methods of to the invention,
`
`the first radio
`
`connection unit can be a base station and the second radio
`
`connection unit a terminal,
`
`the formed beams being downlink
`
`beams. Equally,
`
`the first radio connection unit can be a
`
`terminal and the second radio connection unit a base
`
`the formed beams being uplink beams. Consequently,
`station,
`the methods can also be employed with a base station and a
`terminal which can both form the first radio connection unit
`
`and the second radio connection unit.
`
`The proposed method is of particular advantage when used in
`
`FDD systems.
`
`The first and second radio connection units are preferably
`base stations and user equipments, where base station and
`
`user equipment can include either only means for one of the
`
`first and the second radio connection unit or means for
`
`both.
`
`DETAILED DESCRIPTION OF THE INVENTION
`
`In the following,
`
`the invention is explained in more detail
`
`for three embodiments.
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`All three embodiments of a method according to the invention
`
`relate to a WCDMA FDD wireless communications system,
`
`in
`
`which data signals are to be transmitted with a very high
`
`data rate from a base station to a user equipment. The base
`
`station comprises an antenna array with M antenna elements
`
`and the user equipment comprise an antenna array with N
`
`antenna elements. The data signals are transmitted in
`
`parallel and with the same frequency, but with different
`
`beams from the base station to the user equipment.
`
`The beams are formed by assigning a different set of weights
`
`the set of weights
`to the data signals assigned to one beam,
`determining the weighting with which each data bit is
`
`transmitted from each antenna element of the base station.
`
`To each beam,
`
`there is assigned a data rate with which bits
`
`are to be transmitted and an output power. The number of
`
`beams to be used,
`
`the beam weights,
`
`the data rates and the
`
`power for the selected beams are determined in the user
`
`equipment .
`
`The first embodiment of a method according to the invention
`
`is proposed for correlated spatial channels. A specific
`
`parameterised weight set for the base station antenna array
`
`is assumed. That is, it is assumed that the base station has
`
`an uniform linear array (ULA);
`
`the antennas have equal
`
`spacing, which spacing is small enough to allow significant
`
`(but not necessarily close to unit) correlation between
`
`neighbouring antennas. Under those assumptions, a particular
`
`parameterised beam-forming concept is used at the user
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`equipment in which the transmit weight/array vector,
`
`parameterised by 9, is given by:
`
`w(0) = fe? get? f 4M
`
`The feedback can be calculated e.g. using the eigenvectors
`
`corresponding to the two largest eigenvalues of the channel
`matrix H"H, where H=(h,,..., h,) and where h, is the impulse
`response between the m™ array element and all antennas of
`
`the user equipment. When denoting these vectors
`= 1,2) and solving
`
`by e,,,;
`
`(1
`
`G= argmax|w(4)" emax_i
`
`
`
`2
`
`’
`
`the phases at the transmit element m are w, = Ql ner
`
`some (not
`If the user equipment finds it advantageous,
`necessarily orthogonal)
`linear combinations of the
`
`eigenvectors may be used as a basis for directing the beams
`from the ULA,
`instead of the eigenvectors e
`For example,
`max_ie
`if the data rates that may be assigned to the beams are such
`that the beam with the highest eigenvalue may support more
`
`data than can be transmitted with the highest supportable
`
`data rate,
`
`the user equipment may choose to select
`
`correlating beams, where a suitable mixture of orthogonal
`
`beams are used to reach the maximal data rate with an
`
`acceptable Quality of Service.
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`The set of parameters 0i for parallel transmission is fed
`
`back to the base station applying e.g. Mode 1 feedback
`
`signalling.
`
`In Mode 1,
`
`the feedback bit signals in
`
`successive slots the real and the imaginary parts of the
`
`feedback weights, or the angular parameters Oi in this case.
`
`It is also possible to parameterise the gains of the
`
`antennas with one or more parameters. One parameterisation
`
`would be to have the gains linearly increasing or decreasing
`
`along the linear array. Other parameterisation would enhance
`
`or suppress the central antenna elements, or every second
`
`element. If antenna gains are parameterised,
`
`the
`
`maximisation above chooses the best angular and gain
`
`parameters to match the eigenvectors. This information can
`
`be transmitted e.g. by closed-loop Mode 2 signalling.
`
`In
`
`closed-loop Mode 2,
`
`the feedback weight is signalled as a
`
`Gray coded message with 3 phase bits and 1 gain bit. The
`
`gain bit,
`
`transmitted every fourth slot, selects the
`
`relative gain between the two transmit elements. Here, Mode
`
`2 signalling would convey information of the angular
`
`parameter @i
`
`in the phase bits, and one gain parameter in
`
`the gain bit.
`
`In addition,
`
`the feedback from the terminal to the
`
`transmitter can be reduced, if the terminal knows the method
`
`the transmitter uses in determining the coefficients for the
`
`parallel beams. For example, it is possible that the
`
`terminal sends the coefficients or parameters for one beam
`only, and the base station then determines two or more
`
`parallel beams using w(9-A) and w(6+A), where A is a priori
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`fixed or negotiated between the transmitter and the
`
`terminal, and where §@ is the parameter for the two beams.
`
`Then,
`
`the terminal can optimise 90 jointly for w(@-A) and
`
`w(8+A),
`
`so that there are two parameterised beams
`
`transmitted, but with only one feedback signal
`
`(0). This
`
`generalises naturally to multiple parallel beams and
`different ways to calculate the multiple parallel beams from
`
`single feedback