Devices and methods of beamforming for uplink reception

Abstract

The disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. The present invention relates, in general, to wireless communications and, more particularly, to devices and methods of beamforming for reception of data in uplink (UL).

Description

DEVICES AND METHODS OF BEAMFORMING FOR UPLINK RECEPTION

[0001] The present invention relates, in general, to wireless communications and, more particularly, to devices and methods of beamforming for receiving data in uplink (UL).

[0002] 5G mobile communication technologies define broad frequency bands such that high transmission rates and new services are possible, and can be implemented not only in "Sub 6GHz" bands such as 3.5GHz, but also in "Above 6GHz" bands referred to as mmWave including 28GHz and 39GHz. In addition, it has been considered to implement 6G mobile communication technologies (referred to as Beyond 5G systems) in terahertz bands (for example, 95GHz to 3THz bands) in order to accomplish transmission rates fifty times faster than 5G mobile communication technologies and ultra-low latencies one-tenth of 5G mobile communication technologies.

[0003] At the beginning of the development of 5G mobile communication technologies, in order to support services and to satisfy performance requirements in connection with enhanced Mobile BroadBand (eMBB), Ultra Reliable Low Latency Communications (URLLC), and massive Machine-Type Communications (mMTC), there has been ongoing standardization regarding beamforming and massive MIMO for mitigating radio-wave path loss and increasing radio-wave transmission distances in mmWave, supporting numerologies (for example, operating multiple subcarrier spacings) for efficiently utilizing mmWave resources and dynamic operation of slot formats, initial access technologies for supporting multi-beam transmission and broadbands, definition and operation of BWP (BandWidth Part), new channel coding methods such as a LDPC (Low Density Parity Check) code for large amount of data transmission and a polar code for highly reliable transmission of control information, L2 pre-processing, and network slicing for providing a dedicated network specialized to a specific service.

[0004] Currently, there are ongoing discussions regarding improvement and performance enhancement of initial 5G mobile communication technologies in view of services to be supported by 5G mobile communication technologies, and there has been physical layer standardization regarding technologies such as V2X (Vehicle-to-everything) for aiding driving determination by autonomous vehicles based on information regarding positions and states of vehicles transmitted by the vehicles and for enhancing user convenience, NR-U (New Radio Unlicensed) aimed at system operations conforming to various regulation-related requirements in unlicensed bands, NR UE Power Saving, Non-Terrestrial Network (NTN) which is UE-satellite direct communication for providing coverage in an area in which communication with terrestrial networks is unavailable, and positioning.

[0005] Moreover, there has been ongoing standardization in air interface architecture / protocol regarding technologies such as Industrial Internet of Things (IIoT) for supporting new services through interworking and convergence with other industries, IAB (Integrated Access and Backhaul) for providing a node for network service area expansion by supporting a wireless backhaul link and an access link in an integrated manner, mobility enhancement including conditional handover and DAPS (Dual Active Protocol Stack) handover, and two-step random access for simplifying random access procedures (2-step RACH for NR). There also has been ongoing standardization in system architecture / service regarding a 5G baseline architecture (for example, service based architecture or service based interface) for combining Network Functions Virtualization (NFV) and Software-Defined Networking (SDN) technologies, and Mobile Edge Computing (MEC) for receiving services based on UE positions.

[0006] As 5G mobile communication systems are commercialized, connected devices that have been exponentially increasing will be connected to communication networks, and it is accordingly expected that enhanced functions and performances of 5G mobile communication systems and integrated operations of connected devices will be necessary. To this end, new research is scheduled in connection with eXtended Reality (XR) for efficiently supporting AR (Augmented Reality), VR (Virtual Reality), MR (Mixed Reality) and the like, 5G performance improvement and complexity reduction by utilizing Artificial Intelligence (AI) and Machine Learning (ML), AI service support, metaverse service support, and drone communication.

[0007] Furthermore, such development of 5G mobile communication systems will serve as a basis for developing not only new waveforms for providing coverage in terahertz bands of 6G mobile communication technologies, multi-antenna transmission technologies such as Full Dimensional MIMO (FD-MIMO), array antennas and large-scale antennas, metamaterial-based lenses and antennas for improving coverage of terahertz band signals, high-dimensional space multiplexing technology using OAM (Orbital Angular Momentum), and RIS (Reconfigurable Intelligent Surface), but also full-duplex technology for increasing frequency efficiency of 6G mobile communication technologies and improving system networks, AI-based communication technology for implementing system optimization by utilizing satellites and AI (Artificial Intelligence) from the design stage and internalizing end-to-end AI support functions, and next-generation distributed computing technology for implementing services at levels of complexity exceeding the limit of UE operation capability by utilizing ultra-high-performance communication and computing resources.

[0008] The object of the present invention is, on one hand, to preserve the advantages achieved by the 6G xMIMO oriented approach according to [3] in relation to 5G NR, and, on the other hand, to provide flexible adaptability of the UL beamforming procedure depending on load of time-frequency resources in UL and, accordingly, reduce the associated computational complexity in the base station.

[0009] In the context of addressing said technical object, according to the first aspect of the present invention a method of beamforming for uplink (UL) reception in a wireless communication system is provided. The method comprises, in a base station of the wireless communication system: defining one or more CSI-RS port group configurations; and transmitting, to a user equipment, configuration parameters for transmitting CSI. The configuration parameters comprise, at least: for each of the one or more CSI-RS port group configurations, parameters of a codebook corresponding to said CSI-RS port group configuration, wherein the codebook is formed by a respective set of DFT vectors. Then, according to the method provided hereby, the base station transmits CSI-RSs.

[0010] The method provided herein comprises, in the user equipment: based on measurements of the CSI-RSs, for each of at least one CSI-RS port group configuration from the one or more CSI-RS port group configurations, selecting a subset of DFT vectors from a set of DFT vectors of a codebook corresponding to said CSI-RS port group configuration, wherein the corresponding codebook is determined in the user equipment by using the received configuration parameters; generating the CSI, wherein, for each of the at least one CSI-RS port group configuration, information about the subset of DFT vectors is included into the CSI; and transmitting the generated CSI to the base station. At least one beamforming (BF) matrix for the UL reception is obtained in the base station, the BF matrix being obtained based on the information about the subset of DFT vectors from the CSI received from the user equipment.

[0011] In accordance with an embodiment, the method provided herein can further comprise, after the transmitting CSI-RSs: transmitting, by the base station to the user equipment, a CSI request, the CSI request comprising an indication of the at least one CSI-RS port group configuration. The at least one CSI-RS port group configuration can be selected in the base station, at least, depending on load of time-frequency resources in UL.

[0012] The CSI request is preferably transmitted via DCI. Said indication preferably represents a bit field. A value of the bit field is accordingly selected in the base station from a preset plurality of bit values, wherein each value of the bit field from at least part of the plurality of bit values has a combination of one or several CSI-RS port group configurations corresponding thereto. According to an embodiment, the plurality of bit values is preset in the base station and signaled in advance from the base station to the user equipment via radio resource control (RRC) signaling, wherein the method further comprises, prior to said selecting a subset of DFT vectors: in the user equipment, determining, based on the value of the bit field comprised in the received CSI request, a combination corresponding to the at least one CSI-RS port group configuration.

[0013] In accordance with an embodiment of the method provided herein, an antenna array of the base station has N1CSI-RS ports along a first spatial dimension by N2CSI-RS ports along a second spatial dimension implemented therein, N1≥N2. The base station is configured to perform, on each CSI-RS port, transmission and reception of a signal with one of a first polarization and a second polarization, wherein the first polarization and the second polarization are orthogonal. According to this embodiment, said defining one or more CSI-RS port group configurations comprises: defining each r-th CSI-RS port group configuration, among the one or more CSI-RS port group configurations being defined, by virtually dividing CSI-RS ports of the base station into Nrpgidentical groups of CSI-RS ports, wherein each group has sizes N1'rCSI-RS ports along the first spatial dimension by N2'rCSI-RS ports along the second spatial dimension, where N1'r≥N2'r, . The parameters of the codebook which are included in the configuration parameters for each r-th CSI-RS port group configuration of the one or more CSI-RS port group configurations can comprise: a number N1'rof CSI-RS ports along the first spatial dimension in a group of CSI-RS ports of said CSI-RS port group configuration and a respective oversampling factor O1r, and a number N2'rCSI-RS ports along the second spatial dimension in the group of CSI-RS ports and a respective oversampling factor O2r. The set of DFT vectors of the codebook corresponding to said CSI-RS port group configuration is the same for said first and second orthogonal polarizations.

[0014] In accordance with the considered embodiment, said selecting a subset of DFT vectors comprises, in the user equipment: determining at least one channel matrix based on the measurements of the CSI-RSs; based on the determined at least one channel matrix, calculating a quality metric for each DFT vector from at least part of the set of DFT vectors of the corresponding codebook; and, based on the calculated quality metrics, selecting the subset of DFT vectors by using a threshold quantization parameter. The quality metric is preferably a relative received power associated with a DFT vector, the relative received power being calculated as

[0015]

[0016] , is a DFT vector from the at least part of the set of DFT vectors; Hs,i,pis a channel matrix for an i-th subcarrier among NSCsubcarriers, an s-th group of CSI-RS ports from the Nrpggroups of CSI-RS ports in the r-th CSI-RS port group configuration, and a p-th polarization among said first and second orthogonal polarizations; the dimension of the matrix Hs,i,pis the number of CSI-RS ports in the group of CSI-RS ports by the number of receiving ports of the user equipment. DFT vectors in the subset of DFT vectors can be sorted in the user equipment according to associated relative received powers.

[0017] In accordance with the considered embodiment, the method provided herein can further comprise: setting, in the base station, the threshold quantization parameter, wherein the set threshold quantization parameter can be included either into the configuration parameters or into the CSI request. In one possible implementation, a target number of DFT vectors is set as the threshold quantization parameter, and in this case said selecting a subset of DFT vectors comprises: selecting the target number of DFT vectors with larger associated relative received powers. In another possible implementation, a relative power threshold value is set as the threshold quantization parameter, and in this case said selecting a subset of DFT vectors comprises: selecting DFT vectors with associated relative received powers equal to or greater than the relative power threshold value.

[0018] In accordance with an embodiment, the method further comprises: in the base station, determining a number L of streams of the UL reception, wherein the number of beamforming vectors which the BF matrix is comprised of is defined based on L. The number L of streams of the UL reception can be determined depending on load of time-frequency resources in UL.

[0019] According to this embodiment, L can be further included in the configuration parameters, and in this case the method further comprises, prior to said generating the CSI: in the user equipment, reducing the selected subset of DFT vectors to L / P DFT vectors with larger associated relative received powers, where P=2 when for the transmission of the CSI-RSs the base station uses CSI-RS ports corresponding to both the first polarization and the second polarization, and P=1 when for the transmission of the CSI-RSs the base station uses CSI-RS ports corresponding to only one of the first polarization and the second polarization.

[0020] According to one implementation, said generating the CSI comprises: including, into the information about the subset of DFT vectors, indices of DFT vectors of the subset of DFT vectors, said indices being encoded by combinatorial encoding, wherein the indices of the DFT vectors are from a plurality of DFT vector indices along each of the spatial dimensions of the corresponding codebook.

[0021] According to another implementation, said generating the CSI comprises: determining indices of DFT vectors of the subset of DFT vectors by using a first bitmap whose values indicate DFT vectors of the subset of DFT vectors among DFT vectors along the first spatial dimension of the corresponding codebook, and a second bitmap whose values indicate DFT vectors of the subset of DFT vectors among DFT vectors along the second spatial dimension of the corresponding codebook. The values of the first bitmap and the second bitmap which indicate the DFT vectors of the subset of DFT vectors can be 1s, while the other values of the first bitmap and the second bitmap are 0s in such a case. According to this implementation, the first bitmap and the second bitmap are included into the information about the subset of DFT vectors, or, for each DFT vector of the subset of DFT vectors, a binary representation of an index accordingly obtained by common inner indexing over the values of the first bitmap and the second bitmap which indicate the DFT vectors of the subset of DFT vectors is included into the information about the subset of DFT vectors.

[0022] According to yet another implementation corresponding to the embodiment where DFT vectors are sorted according to associated relative received powers, said generating the CSI comprises: determining indices of DFT vectors of the subset of DFT vectors along the first spatial dimension of the corresponding codebook and indices of said DFT vectors along the second spatial dimension of the corresponding codebook, wherein i=0, ... , M-1, where M is a number of DFT vectors in the subset of DFT vectors. The DFT vector indicated by indices has the largest relative received power corresponding thereto. In accordance with this implementation, a binary representation of a pair of indices of each DFT vector of the subset of DFT vectors is included into the information about the subset of DFT vectors.

[0023] According to an embodiment of the method provided herein, said generating the CSI further comprises, in the user equipment: quantizing each of the relative received powers associated with the DFT vectors of the subset of DFT vectors by rounding to one of values preset in the user equipment; and including, into the information about the subset of DFT vectors, a binary representation of an associated quantized relative received power for each DFT vector of the subset of DFT vectors.

[0024] In accordance with an embodiment of the method provided herein, the CSI is transmitted via uplink control information (UCI). UCI comprises UCI part　1, wherein a payload size of UCI part　1 is fixed. UCI further comprises UCI part　2, wherein a payload size of UCI part　2 is variable and dependent on UCI contents in UCI part　1. The UCI transmission is performed in the physical level (L1) or in the medium access control (MAC) level (L2)

[0025] According to one implementation, information about the indices of the DFT vectors of the subset of DFT vectors for each of the at least one CSI-RS port group configuration can be placed into UCI part　1. According to another implementation, information about the indices of the DFT vectors of the subset of DFT vectors for each of the at least one CSI-RS port group configuration can be placed into UCI part　2. Moreover, the binary representations of the quantized relative received powers for the subset of DFT vectors for each of the at least one CSI-RS port group configuration can be placed either into UCI part　1 or into UCI part　2.

[0026] In accordance with an embodiment of the method provided herein, the BF matrix is obtained further based on information about a subset of DFT vectors from CSI received in the base station from each of one or more other user equipments, wherein the obtained BF matrix is applied for UL reception from said user equipment and from said other user equipments.

[0027] According to the second aspect of the present invention, a method of beamforming for UL reception in a wireless communication system is provided. The method comprises, in a base station of the wireless communication system, wherein the base station comprises a radio unit (RU) and a distributed unit (DU) connected to each other via an FH interface: defining one or more CSI-RS port group configurations; and transmitting, to a user equipment through the radio unit, configuration parameters for transmitting CSI. The configuration parameters comprise, at least: for each of the one or more CSI-RS port group configurations, parameters of a codebook corresponding to said CSI-RS port group configuration, wherein the codebook is formed by a respective set of DFT vectors. Then, according to the method provided hereby, CSI-RSs are transmitted from the base station through the radio unit.

[0028] In accordance with the method provided herein, in the user equipment: based on measurements of the CSI-RSs, for each of at least one CSI-RS port group configuration from the one or more CSI-RS port group configurations, selecting a subset of DFT vectors from a set of DFT vectors of a codebook corresponding to said CSI-RS port group configuration, wherein the corresponding codebook is determined in the user equipment by using the received configuration parameters; generating the CSI, wherein, for each of the at least one CSI-RS port group configuration, information about the subset of DFT vectors is included into the CSI; and transmitting the generated CSI to the base station. At least one BF matrix for the UL reception is obtained in the base station, the BF matrix being obtained based on the information about the subset of DFT vectors from the CSI received from the user equipment. Said obtaining a BF matrix can be performed in the distributed unit or in the radio unit

[0029] According to an embodiment, the method provided herein can further comprise, after the transmitting CSI-RSs: transmitting, from the base station through the radio unit to the user equipment, a CSI request, the CSI request comprising an indication of the at least one CSI-RS port group configuration. The at least one CSI-RS port group configuration can be selected in the base station, at least, depending on load of the FH interface.

[0030] The CSI request is preferably transmitted via DCI. Said indication preferably represents a bit field. A value of the bit field is accordingly selected in the base station from a preset plurality of bit values, wherein each value of the bit field from at least part of the plurality of bit values has a combination of one or several CSI-RS port group configurations corresponding thereto. In accordance with an embodiment, the plurality of bit values is preset in the base station and signaled in advance from the base station to the user equipment via RRC signaling, wherein the method further comprises, prior to said selecting a subset of DFT vectors: in the user equipment, determining, based on the value of the bit field comprised in the received CSI request, a combination corresponding to the at least one CSI-RS port group configuration.

[0031] According to an embodiment of the method provided herein, an antenna array of the radio unit has N1CSI-RS ports along a first spatial dimension by N2CSI-RS ports along a second spatial dimension implemented therein, N1≥N2. The base station is configured to perform, on each CSI-RS port, transmission and reception of a signal with one of a first polarization and a second polarization, wherein the first polarization and the second polarization are orthogonal. According to this embodiment, said defining one or more CSI-RS port group configurations comprises: defining each r-th CSI-RS port group configuration, among the one or more CSI-RS port group configurations being defined, by virtually dividing CSI-RS ports of the base station into Nrpgidentical groups of CSI-RS ports, wherein each group has sizes N1'rCSI-RS ports along the first spatial dimension by N2'rCSI-RS ports along the second spatial dimension, N1'r≥N2'r, . The parameters of the codebook which are included in the configuration parameters for each r-th CSI-RS port group configuration of the one or more CSI-RS port group configurations can comprise: a number N1'rof CSI-RS ports along the first spatial dimension in a group of CSI-RS ports of said CSI-RS port group configuration and a respective oversampling factor O1r, and a number N2'rCSI-RS ports along the second spatial dimension in the group of CSI-RS ports and a respective oversampling factor O2r. The set of DFT vectors of the codebook corresponding to said CSI-RS port group configuration is the same for the first and second orthogonal polarizations.

[0032] In accordance with the considered embodiment, said selecting a subset of DFT vectors comprises, in the user equipment: determining at least one channel matrix based on the measurements of the CSI-RSs; based on the determined at least one channel matrix, calculating a quality metric for each DFT vector from at least part of the set of DFT vectors of the corresponding codebook; and, based on the calculated quality metrics, selecting the subset of DFT vectors by using a threshold quantization parameter. The quality metric is preferably a relative received power associated with a DFT vector, the relative received power being calculated as

[0033]

[0034] , is a DFT vector from the at least part of the set of DFT vectors; Hs,i,pis a channel matrix for an i-th subcarrier among NSCsubcarriers, an s-th group of CSI-RS ports from the Nrpggroups of CSI-RS ports in the r-th CSI-RS port group configuration, and a p-th polarization among said first and second orthogonal polarizations; the dimension of the matrix Hs,i,pis the number of CSI-RS ports in the group of CSI-RS ports by the number of receiving ports of the user equipment. DFT vectors in the subset of DFT vectors can be sorted according to associated relative received powers.

[0035] In accordance with the considered embodiment, the method provided herein can further comprise: setting, in the base station, the threshold quantization parameter, wherein the set threshold quantization parameter can be included either into the configuration parameters or into the CSI request. In one possible implementation, a target number of DFT vectors is set as the threshold quantization parameter, and in this case said selecting a subset of DFT vectors comprises: selecting the target number of DFT vectors with larger associated relative received powers. In another possible implementation, a relative power threshold value is set as the threshold quantization parameter, and in this case said selecting a subset of DFT vectors comprises: selecting DFT vectors with associated relative received powers equal to or greater than the relative power threshold value.

[0036] According to an embodiment, the method further comprises: in the base station, determining a number L of streams of the UL reception, wherein the number of beamforming vectors which the BF matrix is comprised of is defined based on L. The number L of streams of the UL reception can be determined depending on load of the FH interface.

[0037] In accordance with this embodiment, L can be further included in the configuration parameters, and in this case the method further comprises, prior to said generating the CSI: in the user equipment, reducing the selected subset of DFT vectors to L / P DFT vectors with larger associated relative received powers, where P=2 when for the transmission of the CSI-RSs the base station uses CSI-RS ports corresponding to both the first polarization and the second polarization, and P=1 when for the transmission of the CSI-RSs the base station uses CSI-RS ports corresponding to only one of the first polarization and the second polarization.

[0038] According to one implementation, said generating the CSI comprises: including, into the information about the subset of DFT vectors, indices of DFT vectors of the subset of DFT vectors, said indices being encoded by combinatorial encoding, wherein the indices of the DFT vectors are from a plurality of DFT vector indices along each of the spatial dimensions of the corresponding codebook.

[0039] According to another implementation, said generating the CSI comprises: determining indices of DFT vectors of the subset of DFT vectors by using a first bitmap whose values indicate DFT vectors of the subset of DFT vectors among DFT vectors along the first spatial dimension of the corresponding codebook, and a second bitmap whose values indicate DFT vectors of the subset of DFT vectors among DFT vectors along the second spatial dimension of the corresponding codebook. The values of the first bitmap and the second bitmap which indicate the DFT vectors of the subset of DFT vectors can be 1s, while the other values of the first bitmap and the second bitmap are 0s in such a case. In accordance with this implementation, the first bitmap and the second bitmap are included into the information about the subset of DFT vectors, or, for each DFT vector of the subset of DFT vectors, a binary representation of an index accordingly obtained by common inner indexing over the values of the first bitmap and the second bitmap which indicate the DFT vectors of the subset of DFT vectors is included into the information about the subset of DFT vectors.

[0040] According to another implementation corresponding to the embodiment where DFT vectors are sorted according to associated relative received powers, said generating the CSI comprises: determining indices of DFT vectors of the subset of DFT vectors along the first spatial dimension of the corresponding codebook and indices of said DFT vectors along the second spatial dimension of the corresponding codebook, wherein i=0, ... , M-1, where M is a number of DFT vectors in the subset of DFT vectors. The DFT vector indicated by indices has the largest relative received power corresponding thereto. In accordance with this implementation, a binary representation of a pair of indices of each DFT vector of the subset of DFT vectors is included into the information about the subset of DFT vectors.

[0041] According to an embodiment of the method provided herein, said generating the CSI further comprises, in the user equipment: quantizing each of the relative received powers associated with the DFT vectors of the subset of DFT vectors by rounding to one of values preset in the user equipment, and including, into the information about the subset of DFT vectors, a binary representation of an associated quantized relative received power for each DFT vector of the subset of DFT vectors.

[0042] In accordance with an embodiment of the method provided herein, the CSI is transmitted via UCI. UCI comprises UCI part　1, wherein a payload size of UCI part　1 is fixed. UCI further comprises UCI part　2, wherein a payload size of UCI part　2 is variable and dependent on UCI contents in UCI part　1. The UCI transmission can be performed in the physical level (L1) or in the MAC level (L2).

[0043] According to one implementation, information about the indices of the DFT vectors of the subset of DFT vectors for each of the at least one CSI-RS port group configuration can be placed into UCI part　1. According to another implementation, information about the indices of the DFT vectors of the subset of DFT vectors for each of the at least one CSI-RS port group configuration can be placed into UCI part　2. Moreover, the binary representations of the quantized relative received powers for the subset of DFT vectors for each of the at least one CSI-RS port group configuration can be placed either into UCI part　1 or into UCI part　2.

[0044] In accordance with an embodiment of the method provided herein, the BF matrix is obtained further based on information about a subset of DFT vectors from CSI received in the base station from each of one or more other user equipments. The obtained BF matrix is applied for UL reception from said user equipment and from said other user equipments.

[0045] According to the third aspect of the present invention, a method of obtaining CSI for beamforming for UL reception in a wireless communication system is provided, the method being performed in a user equipment. The method comprises: receiving, from a base station of the wireless communication system, configuration parameters for transmitting the CSI, wherein the configuration parameters comprise, at least: for each of one or more CSI-RS port group configurations defined in the base station, parameters of a codebook corresponding to said CSI-RS port group configuration, wherein the codebook is formed by a respective set of DFT vectors; receiving CSI-RSs from the base station; based on measurements of the CSI-RSs, for each of at least one CSI-RS port group configuration from the one or more CSI-RS port group configurations, selecting a subset of DFT vectors from a set of DFT vectors of a codebook corresponding to said CSI-RS port group configuration, wherein the corresponding codebook is determined in the user equipment by using the received configuration parameters; generating the CSI, wherein, for each of the at least one CSI-RS port group configuration, information about the subset of DFT vectors is included into the CSI; and transmitting the generated CSI to the base station for obtaining, by the base station, at least one BF matrix for the UL reception.

[0046] In accordance with an embodiment, the method provided hereby can further comprise, after the receiving CSI-RSs: receiving, from the base station, a CSI request, the CSI request comprising an indication of the at least one CSI-RS port group configuration. The CSI request is preferably received from the base station in DCI. Said indication preferably represents a bit field. A value of the bit field is accordingly selected in the base station from a preset plurality of bit values, wherein each value of the bit field from at least part of the plurality of bit values has a combination of one or several CSI-RS port group configurations corresponding thereto. According to an embodiment, the plurality of bit values is preset in the base station and signaled in advance from the base station to the user equipment via RRC signaling, wherein the method further comprises, prior to said selecting a subset of DFT vectors: in the user equipment, determining, based on the value of the bit field comprised in the received CSI request, a combination corresponding to the at least one CSI-RS port group configuration.

[0047] In accordance with an embodiment, an antenna array of the base station has N1CSI-RS ports along a first spatial dimension by N2CSI-RS ports along a second spatial dimension implemented therein, N1≥N2, wherein the base station is configured to perform, on each CSI-RS port, transmission and reception of a signal with one of a first polarization and a second polarization, wherein the first polarization and the second polarization are orthogonal. According to this embodiment, each r-th CSI-RS port group configuration among the one or more CSI-RS port group configurations is defined in the base station by virtually dividing CSI-RS ports of the base station into Nrpgidentical groups of CSI-RS ports, wherein each group has sizes N1'rCSI-RS ports along the first spatial dimension by N2'rCSI-RS ports along the second spatial dimension, N1'r≥N2'r, .

[0048] The parameters of the codebook which are included in the configuration parameters for each r-th CSI-RS port group configuration of the one or more CSI-RS port group configurations can comprise: a number N1'rof CSI-RS ports along the first spatial dimension in a group of CSI-RS ports of said CSI-RS port group configuration and a respective oversampling factor O1r, and a number N2'rCSI-RS ports along the second spatial dimension in the group of CSI-RS ports and a respective oversampling factor O2r. The set of DFT vectors of the codebook corresponding to said CSI-RS port group configuration is the same for said first and second orthogonal polarizations.

[0049] In accordance with the considered embodiment, said selecting a subset of DFT vectors comprises: determining at least one channel matrix based on the measurements of the CSI-RSs; based on the determined at least one channel matrix, calculating a quality metric for each DFT vector from at least part of the set of DFT vectors of the corresponding codebook; and, based on the calculated quality metrics, selecting the subset of DFT vectors by using a threshold quantization parameter. The quality metric is preferably a relative received power associated with a DFT vector, the relative received power being calculated as

[0050]

[0051] , is a DFT vector from the at least part of the set of DFT vectors; Hs,i,pis a channel matrix for an i-th subcarrier among NSCsubcarriers, an s-th group of CSI-RS ports from the Nrpggroups of CSI-RS ports in the r-th CSI-RS port group configuration, and a p-th polarization among said first and second orthogonal polarizations; the dimension of the matrix Hs,i,pis the number of CSI-RS ports in the group of CSI-RS ports by the number of receiving ports of the user equipment. DFT vectors in the subset of DFT vectors can be sorted in the user equipment according to associated relative received powers.

[0052] According to the considered embodiment, the configuration parameters further include the threshold quantization parameter set in the base station, or the CSI request further includes the threshold quantization parameter set in the base station. In one possible implementation, a target number of DFT vectors is set as the threshold quantization parameter, and in this case said selecting a subset of DFT vectors comprises: selecting the target number of DFT vectors with larger associated relative received powers. In another possible implementation, a relative power threshold value is set as the threshold quantization parameter, and in this case said selecting a subset of DFT vectors comprises: selecting DFT vectors with associated relative received powers equal to or greater than the relative power threshold value.

[0053] In accordance with an embodiment of the method provided herein, the configuration parameters further comprise a number L of streams of the UL reception determined in the base station. According to this embodiment, the method further comprises, prior to said generating the CSI: in the user equipment, reducing the selected subset of DFT vectors to L / P DFT vectors with larger associated relative received powers, where P=2 when for transmission of the CSI-RSs the base station uses CSI-RS ports corresponding to both the first polarization and the second polarization, and P=1 when for transmission of the CSI-RSs the base station uses CSI-RS ports corresponding to only one of the first polarization and the second polarization.

[0054] In accordance with one implementation, said generating the CSI comprises: including, into the information about the subset of DFT vectors, indices of DFT vectors of the subset of DFT vectors, said indices being encoded by combinatorial encoding, wherein the indices of the DFT vectors are from a plurality of DFT vector indices along each of the spatial dimensions of the corresponding codebook.

[0055] In accordance with another implementation, said generating the CSI comprises: determining indices of DFT vectors of the subset of DFT vectors by using a first bitmap whose values indicate DFT vectors of the subset of DFT vectors among DFT vectors along the first spatial dimension of the corresponding codebook, and a second bitmap whose values indicate DFT vectors of the subset of DFT vectors among DFT vectors along the second spatial dimension of the corresponding codebook. The values of the first bitmap and the second bitmap which indicate the DFT vectors of the subset of DFT vectors can be 1s, while the other values of the first bitmap and the second bitmap are 0s in such a case. According to this implementation, the first bitmap and the second bitmap are included into the information about the subset of DFT vectors, or, for each DFT vector of the subset of DFT vectors, a binary representation of an index accordingly obtained by common inner indexing over the values of the first bitmap and the second bitmap which indicate the DFT vectors of the subset of DFT vectors is included into the information about the subset of DFT vectors.

[0056] In accordance with yet another implementation corresponding to the embodiment where DFT vectors are sorted according to associated relative received powers, said generating the CSI comprises: determining indices of DFT vectors of the subset of DFT vectors along the first spatial dimension of the corresponding codebook and indices of said DFT vectors along the second spatial dimension of the corresponding codebook, wherein i=0, ... , M-1, where M is a number of DFT vectors in the subset of DFT vectors. The DFT vector indicated by indices has the largest relative received power corresponding thereto. According to this embodiment, a binary representation of a pair of indices of each DFT vector of the subset of DFT vectors is included into the information about the subset of DFT vectors.

[0057] In accordance with an embodiment of the method provided herein, said generating the CSI further comprises: quantizing each of the relative received powers associated with the DFT vectors of the subset of DFT vectors by rounding to one of values preset in the user equipment, and including, into the information about the subset of DFT vectors, a binary representation of an associated quantized relative received power for each DFT vector of the subset of DFT vectors.

[0058] According to an embodiment of the method provided herein, the CSI is transmitted via UCI. UCI comprises UCI part　1, wherein a payload size of UCI part　1 is fixed. UCI further comprises UCI part　2, wherein a payload size of UCI part　2 is variable and dependent on UCI contents in UCI part　1. The UCI transmission can be performed in the physical level (L1) or in the MAC level (L2).

[0059] In accordance with one implementation, information about the indices of the DFT vectors of the subset of DFT vectors for each of the at least one CSI-RS port group configuration can be placed into UCI part　1. According to another implementation, information about the indices of the DFT vectors of the subset of DFT vectors for each of the at least one CSI-RS port group configuration is placed into UCI part　2. Moreover, the binary representations of the quantized relative received powers for the subset of DFT vectors for each of the at least one CSI-RS port group configuration can be placed either into UCI part　1 or into UCI part　2.

[0060] In accordance with the fourth aspect of the present invention, a wireless communication system comprising at least a base station is provided, the base station comprising, at least: transceiving units; data processing units; and data storage units, wherein the base station is in communication with at least one user equipment comprising, at least: transceiving units; data processing units; and data storage units, wherein the data storage units of the base station have computer-executable codes stored therein, and the data storage units of the user equipment have computer-executable codes stored therein, wherein the computer-executable codes, when executed by the data processing units of the base station and the user equipment, cause the method according to any one of the embodiments of the first aspect of the present invention to be performed.

[0061] According to the fifth aspect of the present invention, a user equipment in a wireless communication system is provided, the user equipment comprising, at least: transceiving units; data processing units; and data storage units, wherein the data storage units have computer-executable codes stored therein which, when executed by the data processing units, cause the method according to any one of the embodiments of the third aspect of the present invention to be performed.

[0062] In accordance with the sixth aspect of the present invention, a computer-readable storage medium is provided, the computer-readable storage medium having computer-executable codes stored therein which, when executed by at least one data processing unit of a user equipment (UE), cause the user equipment to perform the method according to any one of the embodiments of the third aspect of the present invention.

[0063] The technical result achievable by the present invention relates, in general, to UL beamforming in the base station with required accuracy and coverage, along with extension to support of communication systems where extremely large antenna arrays are used, and, more specifically, to providing flexible adaptability of the UL beamforming procedure depending on load of time-frequency resources in UL, thereby enabling to reduce associated computational complexity in the base station (in particular, in its radio unit when the O-RAN architecture is used), by using the new codebook structure and respective support of various levels of spatial port compression.

[0064] Figure 1 is an illustrative example of a two-dimensional antenna subarray of a base station.

[0065] Figure 2 is an illustrative diagram of a wireless communication system in which embodiments of the present invention can be implemented.

[0066] Figure 3 is an illustrative diagram of an O-RAN 7-2x base station.

[0067] Figure 4 is a generalized diagram of interaction between a wireless communication network and a user equipment for UL beamforming according to 5G NR.

[0068] Figure 5a is an illustrative block diagram of functional modules of the radio unit and distributed unit of the O-RAN 7-2x base station according to 5G NR.

[0069] Figure 5b is illustrative another block diagram of functional modules of the radio unit and distributed unit of the O-RAN 7-2x base station according to 5G NR.

[0070] Figure 6a is an illustrative representation of the codebook which can be used in the approach according to [3].

[0071] Figure 6b is an illustration of the general structure of the respective BF matrix according to [3].

[0072] Figure 7 is an illustrative block diagram of functional modules of the radio unit and distributed unit of the O-RAN 7-2x base station according to [3].

[0073] Figure 8a is an illustration of dynamic changes in load of the FH interface.

[0074] Figure 8b is another illustration of dynamic changes in load of the FH interface.

[0075] Figure 9a is an illustration of the virtual division of the base station antenna array into groups of CSI-RS ports according to an embodiment of the present invention.

[0076] Figure 9b is another illustration of the virtual division of the base station antenna array into groups of CSI-RS ports according to an embodiment of the present invention.

[0077] Figure 9c is another illustration of the virtual division of the base station antenna array into groups of CSI-RS ports according to an embodiment of the present invention.

[0078] Figure 9d is another illustration of the virtual division of the base station antenna array into groups of CSI-RS ports according to an embodiment of the present invention.

[0079] Figure 10 is an illustration of the general structure of the BF matrix according to the present invention.

[0080] Figure 11 is a flowchart of a method of beamforming for UL reception according to the present invention.

[0081] Figure 12 is an illustration of an embodiment of encoding CDI for being transmitted as part of CSI according to one embodiment of the present invention.

[0082] Figure 13 is an illustration of an embodiment of encoding CDI for being transmitted as part of CSI according to another embodiment of the present invention.

[0083] Figure 14a is an illustration of embodiments of placing information about a quantized subset of DFT vectors in CSI transmitted via UCI.

[0084] Figure 14b is another illustration of embodiments of placing information about a quantized subset of DFT vectors in CSI transmitted via UCI.

[0085] Figure 14c is another illustration of embodiments of placing information about a quantized subset of DFT vectors in CSI transmitted via UCI.

[0086] Figure 14d is another illustration of embodiments of placing information about a quantized subset of DFT vectors in CSI transmitted via UCI.

[0087] Figure 15 is a generalized diagram of interaction between a wireless communication network and a user equipment for UL beamforming according to an embodiment of the present invention;

[0088] Hereinafter, embodiments of the disclosure will be described in detail with reference to the accompanying drawings.

[0089] In describing the embodiments, descriptions related to technical contents well-known in the relevant art and not associated directly with the disclosure will be omitted. Such an omission of unnecessary descriptions is intended to prevent obscuring of the main idea of the disclosure and more clearly transfer the main idea.

[0090] For the same reason, in the accompanying drawings, some elements may be exaggerated, omitted, or schematically illustrated. Furthermore, the size of each element does not completely reflect the actual size. In the respective drawings, the same or corresponding elements are assigned the same reference numerals.

[0091] The advantages and features of the disclosure and ways to achieve them will be apparent by making reference to embodiments as described below in detail in conjunction with the accompanying drawings. However, the disclosure is not limited to the embodiments set forth below, but may be implemented in various different forms. The following embodiments are provided only to completely disclose the disclosure and inform those skilled in the art of the scope of the disclosure, and the disclosure is defined only by the scope of the appended claims. Throughout the specification, the same or like reference signs indicate the same or like elements. Furthermore, in describing the disclosure, a detailed description of known functions or configurations incorporated herein will be omitted when it is determined that the description may make the subject matter of the disclosure unnecessarily unclear. The terms which will be described below are terms defined in consideration of the functions in the disclosure, and may be different according to users, intentions of the users, or customs. Therefore, the definitions of the terms should be made based on the contents throughout the specification.

[0092] In the following description, a base station is an entity that allocates resources to terminals, and may be at least one of a gNode B, an eNode B, a Node B, a base station (BS), a wireless access unit, a base station controller, and a node on a network. A terminal may include a user equipment (UE), a mobile station (MS), a cellular phone, a smartphone, a computer, or a multimedia system capable of performing a communication function. In the disclosure, a "downlink (DL)" refers to a radio link via which a base station transmits a signal to a terminal, and an "uplink (UL)" refers to a radio link via which a terminal transmits a signal to a base station. Furthermore, in the following description, LTE or LTE-A systems may be described by way of example, but the embodiments of the disclosure may also be applied to other communication systems having similar technical backgrounds or channel types. Examples of such communication systems may include 5th generation mobile communication technologies (5G, new radio, and NR) developed beyond LTE-A, and in the following description, the "5G" may be the concept that covers the exiting LTE, LTE-A, and other similar services. In addition, based on determinations by those skilled in the art, the disclosure may also be applied to other communication systems through some modifications without significantly departing from the scope of the disclosure.

[0093] Herein, it will be understood that each block of the flowchart illustrations, and combinations of blocks in the flowchart illustrations, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart block or blocks. These computer program instructions may also be stored in a computer usable or computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer usable or computer-readable memory produce an article of manufacture including instruction means that implement the function specified in the flowchart block or blocks. The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions that execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks.

[0094] Furthermore, each block in the flowchart illustrations may represent a module, segment, or portion of code, which includes one or more executable instructions for implementing the specified logical function(s). It should also be noted that in some alternative implementations, the functions noted in the blocks may occur out of the order. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved.

[0095] As used in embodiments of the disclosure, the term "unit" refers to a software element or a hardware element, such as a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC), and the "unit" may perform certain functions. However, the "unit" does not always have a meaning limited to software or hardware. The "unit" may be constructed either to be stored in an addressable storage medium or to execute one or more processors. Therefore, the "unit" includes, for example, software elements, object-oriented software elements, class elements or task elements, processes, functions, properties, procedures, sub-routines, segments of a program code, drivers, firmware, micro-codes, circuits, data, database, data structures, tables, arrays, and parameters. The elements and functions provided by the "unit" may be either combined into a smaller number of elements, or a "unit", or divided into a larger number of elements, or a "unit". Moreover, the elements and "units" may be implemented to reproduce one or more CPUs within a device or a security multimedia card. Furthermore, the "unit" in embodiments may include one or more processors.

[0096] Hereinafter reference is made to exemplary embodiments of the present invention which are illustrated in the accompanying drawings where the same reference numerals denote similar elements. It should be appreciated that the embodiments of the invention can have various forms and should not be considered to be limited by the descriptions given herein. Therefore, the exemplary embodiments are described hereinbelow with reference to the drawings to elucidate the essence of the aspects of the present invention.

[0097] It should be noted that the diagram according to Figure　2 can also serve as a general illustration of a wireless communication system in which various aspects of the present invention can be implemented. It is necessary to emphasize that the description according to Figure　2 and this figure itself have solely illustrative, non-limiting nature for the purpose of outlining the general operating environment of the present invention. Although Figure　2 illustrates only known basic components of the communication system, it should be appreciated that the communication system can additionally include a plurality of other elements.

[0098] The hardware and software elements of the base station and the user equipment, as listed above, are configured to provide execution, in the base station and in the user equipment, of the methods according to the present application which are described below. Implementation of the component hardware of the base station and user equipment and specialized configuring thereof, including by respective logical means, are known in the technical field which the present application relates to. Moreover, various functions according to the methods of the present application can be performed in multiple separate elements or in one or more integral elements, which is defined by design structural characteristics.

[0099] The present invention is underlain by the concept which, in general, comprises performing, in a base station, virtual division of an antenna array of the base station into various configurations of groups of CSI-RS ports, where each configuration has a different level of spatial port compression corresponding thereto, and associating, with each CSI-RS port group configuration, an own codebook the general structure of which is similar to the one illustrated above with reference to Figure　6a.

[0100] Nowadays more and more active deployment of 5th Generation (5G) New Radio (NR) networks takes place, whose advantages and capabilities are broadly known.

[0101] Base stations (BSs) in a 5G NR system use massive antenna arrays (Massive MIMO (mMIMO)) comprising multiple transceiver antenna elements (AEs). Such antenna arrays enable to efficiently implement a multiple-input multiple-output (MIMO) technology, when for transmission of data several spatial MIMO layers are transmitted (e.g. physical downlink shared channel (PDSCH)) to one or more user equipments (UEs). In a similar way, one or more MIMO layers (for example, of physical uplink shared channel (PUSCH)) can be transmitted from each of the user equipments to a receiving device of a base station.

[0102] Generally speaking, a digital signal is transmitted or received using one or more digital ports connected to antenna elements of the base station, by means of a radio frequency unit that performs the function of digital-to-analog and analog-to-digital signal conversion. For instance, for the 3.5 GHz frequency range, up to 64 digital ports can be utilized enabling usage of various precoding schemes. For example, a spatial multiplexing (SM) technology allows reuse of the same-time frequency resources for downlink (DL) transmission of MIMO layers to one or more user equipments, while an adaptive beamforming (BF) technology enables to dynamically steer transmitted signal power to one or more predefined directions. Usage of the orthogonal frequency division multiplexing (OFDM) modulation provides efficient wideband signal transmission in a multipath channel.

[0103] For illustrative purposes, Figure　1 shows an example of part of a two-dimensional antenna array of a base station, wherein antenna elements (symbolically denoted as Х in this figure) are virtualized into N1= 4 antenna ports along the horizontal direction and N2= 2 antenna ports along the vertical direction. As seen from the illustration, each antenna port in this case corresponds to a subset of three adjacent antenna elements. It is also taken into account that each port is capable of emitting a signal with one of two different, orthogonal polarizations (P = 2). These orthogonal polarizations can be linear (vertical and horizontal) polarizations, as well as circular (right and left) polarizations. As a result, the considered antenna subarray supports N1Х N2Х P = 16 digital ports. N1substantially corresponds to the dimension in one (here, horizontal) spatial direction, N2corresponds to the dimension in another (here, vertical) spatial direction, and P corresponds to the polarization dimension. Naturally, similar considerations apply to subarrays with other required dimensions (N1, N2). Moreover, in general N1≥N2.

[0104] In 5G NR, beamforming is also carried out when receiving uplink (UL) transmissions performed from user equipments to the base station.

[0105] Brief explanation of UL beamforming techniques in accordance with 5G NR is given hereinbelow, for the sake of understanding the technical context of the present invention.

[0106] First of all, Figure　2 generally illustrates a wireless communication system which can be a 5G NR communication system. As shown in Figure　2, user equipments (UE) 201 communicate with base stations (BSs) 202 in a radio access network (RAN) 200. UE 201 (e.g. UE 201-1, 201-2, 201-3, ...) are distributed over the RAN 200, and each of the UEs 201 can be fixed or mobile. Broadly known examples of UEs are smartphones, tablets, modems, etc.

[0107] The base stations 202 (e.g. BSs 202-A, 202-B, 202-C) can provide coverage for a specific geographic area commonly referred to as 'cell'. The base stations 202 basically have fixed structure, but they can have mobile implementation as well. In general, the base stations can represent macro base stations (as illustrated by the BSs 202-A, 202-B, 202-C in Figure　2), as well as pico base stations for pico-cells or femto base stations for femto-cells. Cells in turn can be divided into sectors.

[0108] Coordination and management of operating the base stations 202 can be provided by a network controller which is in communication therewith (for instance, via a backhaul connection). The RAN 200 may communicate with a core network (CN) (for example, via the network controller) which provides various network functions, such as e.g. access and mobility management, session management, authentication server function, application function, etc. Moreover, the base stations 202 in the RAN 200 can also connect to each other, for instance, via a direct physical connection, which is preferably a high-speed connection.

[0109] When a user equipment is moving within the RAN 200, handover of the user equipment from one base station to another base station can be performed. For example, the UE 201-3 can be handed over from the BS 202-B to the BS 202-A. While performing this, respective communication system parameters are reconfigured in the user equipment for operation with the new base station. The user equipment can be also handed over between sectors of one base station.

[0110] The OpenRAN (O-RAN) architecture is implemented in 5G NR - in particular, O-RAN 7-2x - which comprises splitting the base station into two parts and using a fronthaul (FH) interface defined for exchanging information between these functional parts. More specifically, according to this architecture, the base station is split into a radio unit (RU) and a distributed unit (DU) that are connected to each other via the FH interface (see Figure　3). The functionality implemented by the radio unit and the distributed unit in the considered technical context will be described in more detail below.

[0111] Support for the O-RAN architecture is expected in next generation wireless networks.

[0112] Each of the base stations 202 shown in Figure　2 includes hardware and logical means to implement respective functions in the base station. The hardware means refer to, in particular, an antenna array comprised of transceiving antenna elements which have been discussed above, various specially configured processors, controllers, data storage devices, other circuit elements, as well as buses connecting them. The logical means refer to software which is stored in respective memory devices and configures respective circuit elements. Firmware directly hardwired in processors and controllers also refers to the software. The abovementioned hardware means are configured inter alia to perform various processing with respect to transmitted and received signals, including (de)modulation, (de)multiplexing, (de)coding, amplifying, filtering, digitizing, (de)interleaving, resource allocation, reception / transmission scheduling.

[0113] In a similar way, each of the user equipments 201 shown in Figure　2 includes hardware and logical means to implement respective functions in the user equipment. The hardware means refer to, in particular, transceiving devices with respective antenna elements, various specially configured processor(s), controllers, data storage devices, other circuit elements, as well as buses connecting them. The logical means refer to software which is stored in respective memory devices and configures respective circuit elements. Firmware directly hardwired in controllers also refers to the software. The indicated hardware means are configured inter alia to perform various processing with respect to transmitted and received signals, including (de)modulation, (de)multiplexing, (de)coding, amplifying, filtering, digitizing, (de)interleaving. Moreover, the user equipment comprises means to interact with a user, including a touch screen, speakers / microphone, buttons, as well as user applications which are stored in the memory of the user equipment and executed by the processor of the user equipment in a respective operating system.

[0114] Examples of the abovementioned processors / controllers include microprocessors, microcontrollers, digital signal processors (DSPs), field programmable gate arrays (FPGAs), discrete hardware integrated circuits, etc. Firmware / software executed by the processors / controllers should be understood broadly, as referring to computer-executable instructions, instruction sets, program code, code segments, subroutines, program modules, objects, procedures, etc. The software is stored in respective computer-readable media which can be implemented e.g. in the form of random-access memory (RAM), read-only memory (ROM), electrically erasable programmable (EEPROM), solid state storage devices, magnetic storage devices, optical storage devices, etc. which can be recorded with respective program codes and data structures that can be accessed by respective processors / controllers.

[0115] In 5G NR, the following expression is used in the base station to calculate MIMO demodulation weights for received UL signals:

[0116] [Equation 1]

[0117]

[0118] The matrix WRXin equation (1) is referred to as LMMSE-IRC receiver. Thereafter in the text of the application, for the sake of simplicity, this matrix can be referred to as the LMMSE-IRC receiver or simply the receiver.

[0119] In equation (1), HBSis the channel matrix obtained in the base station, the dimension of said matrix is the number of base station receiving digital ports by the number of spatial streams (i.e. MIMO layers) to be received by the base station from one or more user equipments. Let, as one example, the base station have 32 receiving digital ports and let it receive one MIMO layer from one user equipment, i.e. single-user MIMO (SU-MIMO) is taking place - in this case, the dimension of the channel matrix HBSwill be 32Х1. Let, as another example, the base station have 64 receiving digital ports and let it receive two MIMO layers from each of five user equipments, i.e. multi-user MIMO (MU-MIMO) is taking place - in this case, the dimension of the channel matrix HBSwill be 64Х10.

[0120] Furthermore, in equation (1), R is the covariance matrix by which interference and noise is suppressed at the base station receiver; the dimension of said matrix is the number of receiving digital ports by the number of receiving digital ports. That is, in the two examples considered in the preceding paragraph, the dimension of the covariance matrix R will be 32Х32 and 64Х64, respectively.

[0121] Finally, in equation (1), I is the identity matrix, H denotes Hermitian conjugate.

[0122] For 5G mMIMO, where, as noted earlier, the number of digital ports is large, the receiver in the base station according to equation (1) will be rather complex - first, inversion of matrices of a sufficiently large size regularly occurs; second, if the base station has the O-RAN architecture, undesirably high load of the FH interface takes place. This high load is generally associated with transmission of the received wideband signal from each digital port, said transmission requiring high throughput of the FH interface.

[0123] Standard approaches used in 5G NR to reduce receiver complexity are based on uplink (UL) beamforming (BF). In general, the task of UL beamforming is the maximally efficient weighted processing of a received UL signal on different receiving digital ports of the base station. Weights are selected in a (sub)optimal manner, and signals from the receiving digital ports, after applying respective weights thereto, are summed, with obtaining so-called virtual ports the number of which is less than the number of base station digital ports. In other words, UL beamforming in the considered context is applied in the base station to virtualize a large number of receiving digital ports into a smaller number of virtual ports.

[0124] More specifically, beamforming can be reflected by the following equations:

[0125] [Equation 2]

[0126] Heff= Wbf·HBS

[0127] [Equation 3]

[0128] Reff= Wbf·R·WbfH

[0129] In equations (2), (3)

[0130] [Equation 4]

[0131]

[0132] is the beamforming (BF) matrix, wiis an i-th weight or beamforming vector, i = 1, ..., L, its size is the number of base station receiving digital ports; Heffis the equivalent channel matrix after beamforming; Reffis the equivalent noise and interference covariance matrix after beamforming; T denotes transposition.

[0133] The parameter L defines the number of reception streams after applying UL beamforming, i.e. the number of virtual ports, and it is chosen in the base station depending on implementation thereof. For instance, the parameter L can be chosen based on acceptable receiver complexity; also, for the O-RAN architecture, this parameter can be chosen based on the FH interface constraints - in particular, said parameter reflects the number of reception streams to be transmitted through the FH interface. The smaller the value of L, the less information needs to be transmitted from the radio unit to the distributed unit for further processing; on the other hand, usage of a larger number of beamforming vectors is preferable for more efficient (in the sense of interference resistance) subsequent processing of the UL signal. In a typical case, L is chosen to be less than the number of receiving digital ports and not less than the number NMIMOof received MIMO layers. This aspect of 5G NR will be further illustrated in Figure　5b.

[0134] As a result, the dimension of the equivalent channel matrix Heffafter beamforming will be L×NMIMO, and the dimension of the equivalent covariance matrix Reffafter beamforming will be L×L. Namely, these equivalent matrices Heff, Reffof the smaller dimensions are to be used in equation (1), providing reduction in receiver complexity and reduction in load of the FH interface.

[0135] It should be noted herein that equations (1)-(4) have been considered not taking the polarization dimension into account, without loss of generality.

[0136] Thereafter, with references to Figures　4, 5, the description of applying the abovementioned beamforming in a 5G NR wireless communication network (NW) with a base station having the O-RAN 7-2x architecture is provided. The 5G NR approach described herein is based on sounding reference signals (SRSs) received in the base station from one or more user equipments.

[0137] Figure　4 illustratively shows a generalized scheme of interaction between the NW and a user equipment, for beamforming in the base station which is part of the NW, for reception of UL transmission from the user equipment. Figure　5a illustratively shows a block diagram of functional modules of the radio unit and the distributed unit of the base station in the context of interaction according to Figure　4.

[0138] Upon reception of an SRS request (action 1 according to Figure 4) from the base station, the user equipment transmits SRS to the base station (action 2). Based on SRSs received from user equipments, the base station performs channel measurements (action 3) and performs calculations for UL beamforming in accordance with equations (2)-(4) (action 4). Next, the base station allocates UL transmission resources to the user equipment, and notifies the user equipment about this allocation (UL grant) in downlink control information (DCI) (action 5). The user equipment performs scheduled transmission of PUSCH to the base station (action 6). The base station applies the calculated BF matrix and the receiver built accordingly (see equations (1)-(4)) to receive PUSCH (action 7), and performs demodulation of PUSCH (action 8).

[0139] The radio unit of the base station according to Figure 5a receives the UL signal and performs low-level processing thereof (in particular, digitization, fast Fourier transform (FFT)). In this case, the SRSs are extracted as is from the received UL signal, and the extracted SRSs are transmitted to the distributed unit where, based on the SRSs received from the radio unit, the BF matrix is calculated, and the calculated BF matrix is transmitted back to the radio unit so that said matrix is applied therein for reducing the number of ports by means of the virtualization described above (see equations (2)-(4); Figure 5b). Then, the distributed unit accordingly generates the receiver (see equation (1)) and applies it for demodulating the UL signal, and also performs other standard operations during UL reception (in particular, LDPC decoding of data).

[0140] It should be noted herein that approaches to obtaining the BF matrix are known in the technical field which the present invention relates to. Such approaches are disclosed, in particular, in publications [1], [2] which are both entirely incorporated into the present application by reference.

[0141] Though deployment of 5G NR systems in the world is only spinning up, nevertheless active research is being already carried out now in different directions for standardization of next generation wireless communication systems, so called 6G, which will have characteristics superior to 5G NR.

[0142] In particular, for the 6G operating range of 7-13 GHz (UPPER MID BAND), it is planned to support, at base stations, extremely large antenna arrays (for instance, comprised of 3072 antenna elements), with hybrid analog and digital beamforming with a large number of antenna ports (≤256). Therefore, support of up to 64 simultaneously transmitted spatial MIMO layers in UPPER MID BAND communication systems will bring the concept of radio interface with extremely large antenna array (xMIMO) to a principally new level. Moreover, support of a set of reference signals similar to the one used in 5G NR, such as DMRS, CSI-RS, SRS, PT-RS, PSS / SSS, is planned in 6G

[0143] At the same time, approaches used in 5G NR may not be always directly extended to next generation communication systems.

[0144] For instance, direct application of the above approach to UL beamforming, which has proven itself for 5G mMIMO, will generally not be so efficient for the case of 6G xMIMO. As noted earlier, said next generation wireless communication system provides support of up to 256 digital ports and 64 MIMO layers per UE; accordingly, the dimensions of the channel matrices and covariance matrices at the base station side will be significantly larger than in the case of 5G NR. At the same time, usage of SRSs in the context of xMIMO for channel estimation and beamforming becomes difficult for the following reasons. In the UPPER MID BAND operating range, due to wideband signal transmission and transmission power limitations in user equipments, power spectral density significantly decreases, while losses increase, and, accordingly, quality of reception of SRSs in the base station degrades noticeably, whereas, as noticed earlier, the SRSs are received in the base station as is, i.e. without applying beamforming thereto. This is especially fair for user equipments located closer to the boundary of the cell served by the base station. Therefore, accuracy of calculation in the base station of beamforming vectors which the UL beamforming matrix is comprised of also decreases, thereby degradation of reception quality can be in general caused.

[0145] In publication [3], which is fully included in the present application by reference, the concept is proposed to solve the problems discussed above, said concept generally referring to using, for UL beamforming in a base station, - instead of SRSs - channel state information received as feedback from user equipments, the channel state information being calculated by DL channel measurements in the user equipments. Said concept is underlain by implementation in 5G mMIMO of time division duplex (TDD) communication, where one channel is substantially divided in time between DL and UL; accordingly, there is the channel reciprocity property according to which (at proper calibration of base station antennas) the channel information calculated for DL in the user equipment will be also applicable to UL. The usage of TDD is also planned in 6G.

[0146] More specifically, according to [3], in each of user equipments served by the base station, measurements of channel state information (CSI) reference signals (RSs), i.e. CSI-RSs, transmitted from the base station are carried out, and quantization of the obtained information about the channel signal space is performed, thereafter the quantized information is reported to the base station as part of CSI transmitted from the user equipment. The base station, in turn, uses this quantized information received from the user equipments to build the BF matrix.

[0147] It is necessary to explain herein that in 5G NR CSI-RSs are transmitted from a base station to user equipments for estimation of the state of channels corresponding to digital ports of the base station. Depending on implementation, each CSI-RS may correspond to one digital port, or additional virtualization is performed in such a way that each CSI-RS may correspond to more than one (for example, two) digital ports. In other words, taking into account this additional virtualization, the virtualized representation of antenna elements of the base station antenna array in the form of CSI-RS ports is ultimately used. It should be noted that in communication with the base station the user equipment may not be aware of an actual structure of the base station antenna - said communication is basically performed in the level of CSI-RS ports of the base station, i.e. each CSI-RS port is considered as a single emitting element, regardless of antenna elements encompassed thereby.

[0148] Since transmission power of the base station is a priori sufficient to provide coverage of the entire cell served thereby, then quality of reception and, accordingly, accuracy of measurement of CSI-RSs received by each of the served user equipment are high.

[0149] The aforementioned quantization according to [3] is based on usage, in the base station and in the user equipment, of a codebook (CB) which is formed by a set of discrete Fourier transform (DFT) vectors.

[0150] Figure　6a shows an illustrative representation of the codebook with reference to the subarray considered above with reference to Figure　1.

[0151] The codebook is illustrated in Figure　6a by a two-dimensional (along the first spatial dimension and along the second spatial dimension) grid of DFT vectors. Each DFT vector is shown as a circle in this grid. Light grey circles symbolically show DFT vectors directly corresponding to N1×N2= 8 (i.e. in this case four along the horizontal direction, two along the vertical direction) CSI-RS ports. These DFT vectors are mutually orthogonal. In addition, due to usage of oversampling factors (O1, O2), a sequential linear phase shift is provided for each DFT vector in the directions N1, N2, respectively. As a result, the dimension of the codebook is N1·O1in the first spatial dimension and N2·O2in the second spatial dimension, i.e. the total number of DFT vectors in the codebook is equal to N1·O1·N2·O2. DFT vectors in the codebook are indexed along the first spatial dimension by index l, l = 0, ... , N1·O1- 1, and along the second spatial dimension by index m, m = 0, ... , N2·O2- 1. In the case considered in Figure　6a, O1= O2= 4. For the sake of illustration, a specific DFT vector selected from the codebook is symbolically shown in Figure　6a by the black circle.

[0152] Each DFT vector v represents the Kronecker product of a column vector v, where

[0153] [Equation 5]

[0154]

[0155] by a column vector u, where

[0156] [Equation 6]

[0157]

[0158] i.e.

[0159] [Equation 7]

[0160]

[0161] In equations (5), (6), j is the imaginary unit.

[0162] The number of elements in the vector v is equal to the number of CSI-RS ports along the first spatial dimension (in this case, horizontal), i.e. N1, and the number of elements in the vector u is equal to the number of CSI-RS ports along the second spatial dimension (in this case, vertical), i.e. N2. Accordingly, the number of elements in any DFT vector v will be N1·N2.

[0163] [3] proposes to use, as the codebook illustrated in Figure　6a, a codebook based on 5G NR Type　1 codebook which is basically used in 5G NR for DL precoding. Possible supported configurations of Type　1 codebook can be identified according to Table　5.2.2.2.1-2, as given below, from specification [4] which is fully included in the present application by reference:

[0164] Number of CSI-RS ports(N1, N2)(O1, O2)4(2,1)(4,1)8(2,2)(4,4)(4,1)(4,1)12(3,2)(4,4)(6,1)(4,1)16(4,2)(4,4)(8,1)(4,1)24(4,3)(4,4)(6,2)(4,4)(12,1)(4,1)32(4,4)(4,4)(8,2)(4,4)(16,1)(4,1)

[0165] Therefore, possible values of the parameters N1, O1, N2, O2included in equations (5)-(7) can be set in accordance with Table　5.2.2.2.1-2 from specification [4].

[0166] The abovementioned quantization according to [3] is in the following: a user equipment, knowing the structure of the codebook, determines indices {l.m} of DFT vectors which are the most consistent with the DL channel whose state is measured by the user equipment based on CSI-RSs received from the base station. In other words, the user equipment finds, in the two-dimensional grid of DFT vectors, one or more DFT vectors (see Figure　6a) which are consistent to the greatest extent with the DL channel, and the user equipment reports the indices of these DFT vectors (i.e. the quantized subset of DFT vectors) to the base station as part of CSI.

[0167] Figure　6b illustrates the general structure of the BF matrix obtained for UL reception at the base station side based on CSI received from the user equipment. Grey blocks in the BF matrix denote DFT vectors of the quantized subset of DFT vectors for one of the two orthogonal polarizations, white blocks denote the same DFT vectors for the other of the two orthogonal polarizations; that is, the subset of DFT vectors is the same for said two orthogonal polarizations. Accordingly, each beamforming row vector in the BF matrix is applied to N1·N2, i.e. to half of digital ports.

[0168] Figure　7, similarly to Figure　5b, illustratively shows the block diagram of functional modules of the radio unit and the distributed unit of the base station in accordance with [3].

[0169] The CSI-RS based approach proposed in [3] enables to carry out UL beamforming with required accuracy and maintaining acceptable LMMSE-IRC receiver complexity, along with extension to support of communication systems where extremely large antenna arrays are used, thereby in turn ensuring high quality UL reception at the base station side. In particular, unlike the abovementioned SRS based approach according to 5G NR the performance of which may be low for user equipments located at the cell edge, the approach according to [3] is more efficient in terms of coverage and is applicable both for user equipments near the base station and for user equipments at the cell edge.

[0170] At the same time, UL traffic changes dynamically, virtually arbitrarily. As the load of time-frequency resources in UL changes (substantially, as the number of packets transmitted from a user equipment in UL to the base station changes), the load of the FH interface also changes; for example, the more user equipments from which the base station receives UL transmissions at a given time instance, the greater the load onto the FH interface. Accordingly, even taking into account UL beamforming applied in the base station, there are transmission time intervals (TTIs) where the load of the FH interface is high, and there are TTIs in which the load of the FH interface is relatively low. This aspect is illustrated in Figures　8a, 8b.

[0171] Accordingly, flexible adaptation of the UL beamforming procedure depending on the current load of time-frequency resources in UL is desirable, in terms of ensuring, on one hand, that the maximum load of the FH interface is not exceeded, and, on the other hand, maximum utilization of the available throughput of the FH interface.

[0172] At the same time, the BF matrix according to [3] (see Figure　6b) is applied to all digital ports of the base station and is rather dense, with a relatively small number of non-zero elements, thereby causing high computational complexity of the respective UL beamforming procedure in the base station radio unit. In other words, the procedure for converting digital ports into virtual ports (i.e. the spatial compression procedure) in the radio unit according to [3] is expensive. At the same time, the approach proposed in [3] does not provide relevant adaptability of the UL beamforming procedure - for instance, the number L of UL reception streams to be transferred via the FH interface (i.e. the number of virtual ports) set in the base station is substantially the only parameter by which adaptation of the UL beamforming procedure can be executed; however, such adaptation does not allow to flexibly consider the current load of time-frequency resources in UL and does not allow to accordingly reduce computational complexity in the base station.

[0173] The virtual division corresponding to the present invention is illustrated in Figures　9a-9d.

[0174] Figure　9a, similarly to Figure　1, provides the illustration of the base station antenna array (or part thereof) with N1CSI-RS ports along the first spatial dimension (here horizontal) and N2CSI-RS ports along the second spatial dimension (here vertical), where N1≥N2. As in the case of Figure　1, the base station is configured to perform, on each CSI-RS port, transmission and reception of a signal with one of the first polarization and the second polarization, where the first polarization and the second polarization are orthogonal.

[0175] Figure　9b illustrates the division of the antenna array of Figure　9a into sixteen identical groups of CSI-RS ports, where each CSI-RS port group (shown in Figure　9b in the callout) combines N1' = 2 CSI-RS ports in the first spatial dimension and N2'=1 CSI-RS ports in the second spatial dimension. The configuration of CSI-RS port groups of Figure　9b corresponds to a low level of spatial port compression and can be preferably used for relatively low load of time-frequency resources in UL (see Figures　8a, 8b).

[0176] Figure　9c illustrates the division of the antenna array of Figure　9a into eight identical CSI-RS port groups, where each CSI-RS port group (shown in Figure　9c in the callout) combines N1' = 2 CSI-RS ports in the first spatial dimension and N2'=2 CSI-RS ports in the second spatial dimension. The CSI-RS port group configuration of Figure　9c corresponds to a medium level of spatial port compression and can be preferably used for moderate load of time-frequency resources in UL.

[0177] Figure　9d illustrates the division of the antenna array of Figure　9a into four identical CSI-RS port groups, where each CSI-RS port group (shown in Figure　9d in the callout) combines N1' = 4 CSI-RS ports in the first spatial dimension and N2'=2 CSI-RS ports in the second spatial dimension. The CSI-RS port group configuration of Figure　9d corresponds to a high level of spatial port compression and can be preferably used for relatively high load of time-frequency resources in UL.

[0178] In accordance with the present invention, each possible CSI-RS port group configuration has an own codebook associated therewith, said codebook being formed by a respective set of DFT vectors, where, similarly to equations (5)-(7) discussed above, each DFT vector v is the Kronecker product of a column vector v, where

[0179] [Equation 8]

[0180]

[0181] by a column vector u, where

[0182] [Equation 9]

[0183]

[0184] i.e.

[0185] [Equation 10]

[0186]

[0187] The oversampling factors (O1, O2) in equations (8), (9), as in the case with Table　5.2.2.2.1-2 from specification [4] described above, can respectively take values (4,4), (4,1), (1,4).

[0188] As follows from the illustrations according to Figures　9b-9d and equations (8)-(10), N'1defines the size of the CSI-RS port group in the first spatial dimension, N'2defines its size in the second spatial dimension; therefore, the parameters (N'1,N'2) are characteristic parameters of the respective CSI-RS port group configuration and, accordingly, the associated codebook. At the same time, according to equations (8)-(10), the virtualization applied to each CSI-RS port group in the respective CSI-RS port group configuration is the same.

[0189] In Figures　9b-9d, in the lower right corner of each of the CSI-RS port groups, its index in a respective CSI-RS port group configuration is shown. Index q of the CSI-RS port group is defined by the following equation:

[0190] [Equation 11]

[0191]

[0192] where z is an index of a CSI-RS port in the considered antenna array (the indexing is performed according to the principle "first in the first spatial dimension - then in the second spatial dimension"), denotes rounding down to the closest integer, mod(a,b) is the operation of obtaining the remainder from dividing a by b.

[0193] It is emphasized again herein that the options of virtual division shown in Figures　9b-9d are illustrative, and other values of the parameters (N'1,N'2) can be used.

[0194] In accordance with the present invention, the base station signals, to a user equipment(s), parameters for one or more CSI-RS port group configurations, said parameters being set in the base station by means of the respective virtual division of the base station antenna array (see Figures　9a-9d). More specifically, the base station signals to the user equipment for each of said one or more CSI-RS port group configurations, at least the parameters (N'1,N'2) which, as noted above, are parameters of the codebook associated with this CSI-RS port group configuration (see equations (8)-(10)).

[0195] As in [3], according to the present invention, the user equipment performs measurements of CSI-RSs received from the base station and quantization of information about the DL channel signal space obtained based on said measurements. Again, as in [3], said quantization basically comprises performing, in the user equipment, selection from the codebook of a subset of DFT vectors that are most consistent with the DL channel. At the same time, unlike [3], in accordance with the present invention said selection is performed not from a single codebook (see Figure　6a), i.e. not over all digital ports, but from a smaller codebook associated with a specific CSI-RS port group configuration set in the base station (see equations (8)-(10)). Then, the quantized subset of DFT vectors is reported to the base station as part of CSI transmitted from the user equipment. The base station uses the quantized subset of DFT vectors to obtain the BF matrix (see equations (2)-(4)).

[0196] Figure　10, similarly to Figure　6b, illustrates the general structure of the BF matrix according to the present invention, the BF matrix being obtained for UL reception at the base station side based on the CSI received from the user equipment. The dimension of the BF matrix of Figure　10 is the number of virtual ports by the number of receiving digital ports of the base station. Grey blocks in the BF matrix in Figure　10 again denote DFT vectors of the quantized subset of DFT vectors for one of the two orthogonal polarizations, white blocks denote the same DFT vectors for the other of the two orthogonal polarizations. That is, the subset of DFT vectors is the same for said two orthogonal polarizations.

[0197] Unlike the BF matrix according to [3], as illustrated in Figure　6b, where, for each of the two orthogonal polarizations, each beamforming row vector is applied to all the N1·N2CSI-RS ports, thereby resulting in the BF matrix having rather dense structure, in the BF matrix according to the present invention, as illustrated in Figure　10, in a similar context each beamforming vector is applied to a small number of N1'·N2' CSI-RS ports, thereby resulting in the BF matrix having sparse structure. As a consequence, due to the approach according to the present invention, it is required to apply calculations to a relatively small set of digital ports in order to obtain a virtual port (i.e. a respective row in the BF matrix illustrated in Figure　10), thereby significantly reducing computational complexity in the base station.

[0198] As follows from the aforesaid, in the illustration of the general structure of the BF matrix according to the present invention, as given in Figure　10, it is generally assumed that the base station uses, for transmitting CSI-RSs, CSI-RS ports corresponding to both the first polarization and the second polarization. At the same time, the present invention provides for an embodiment where the base station will use, for transmitting CSI-RSs, CSI-RS ports corresponding only to one of said two orthogonal polarizations, and the BF matrix corresponding to this embodiment is shown by the dashed line in Figure　10. As seen from the illustration according to Figure　10, for the considered possible embodiment with one polarization, the number of beamforming row vectors in the BF matrix will be half of the respective number for the general case with two polarizations.

[0199] Therefore, the present invention enables, on one hand, to flexibly adapt UL beamforming in the base station, in particular, depending on load of time-frequency resources in UL. For instance, unlike [3] where only the parameter L set in the base station that defines the number of reception streams (i.e. the number of virtual ports) can be used to adapt UL beamforming, the parameters (N1',N2') characterizing the required CSI-RS port group configuration and associated codebook are also used to adapt UL beamforming according to the present invention. On the other hand, the present invention provides reduction in respective computational costs in the base station, where said reduction is expected to be more significant in the context of 6G xMIMO.

[0200] Thereafter, with reference to the flowchart of Figure　11, the description is given of the method 1100 of beamforming for UL reception in the wireless communication system according to the present invention, where the communication system can be, for example, a 6G xMIMO wireless communication system.

[0201] In step 1110, one or more CSI-RS port group configurations are set in the base station (for example, such as the BS 202-A, 202-B, 202-C in Figure　2).

[0202] Embodiments of setting one or more CSI-RS port group configurations on the base station antenna array which, in general, has N1CSI-RS ports along the first spatial dimension by N2CSI-RS ports along the second spatial dimension implemented therein (N1≥N2), and also taking into account the capability of the base station to perform, on each CSI-RS port, transmission and reception of a signal with one of the two orthogonal polarizations, are described above with reference to Figures　9a-9b. In particular, each r-th CSI-RS port group configuration set in the base station can be defined by virtual division of CSI-RS ports of the base station into Nrpgidentical groups of CSI-RS ports; each group has dimensions N1'rCSI-RS ports in the first spatial dimension by N2'rCSI-RS ports in the second spatial dimension, N1'r≥N2'r, . As recited earlier, in accordance with the present invention, each set CSI-RS ports groups configuration has its own codebook associated therewith, the associated codebook is formed by a respective set of DFT vectors (see equations (8)-(10)); the set of DFT vectors of the associated codebook is the same for the first and second orthogonal polarizations.

[0203] In particular, for the embodiment illustrated in Figure　9b, the respective CSI-RS port group configuration (for example, configuration r=1) is set by dividing the CSI-RS ports of the considered antenna array into N1pg=16 CSI-RS port groups, with dimensions of the group N1'1=2 CSI-RS ports in the first spatial dimension by N2'1=1 CSI-RS port in the second spatial dimension. As noted earlier, this CSI-RS port group configuration can be used for relatively low load of time-frequency resources in UL.

[0204] For the embodiment in Figure　9c, the respective configuration of groups of CSI-RS ports (for example, configuration r=2) is set by dividing CSI-RS ports of the antenna array into N2pg=8 CSI-RS port groups, with dimensions of the group N1'2=2 CSI-RS ports in the first spatial dimension by N2'2=2 CSI-RS ports in the second spatial dimension. This CSI-RS port group configuration can be used for moderate load of time-frequency resources in UL.

[0205] Finally, for the embodiment illustrated in Figure　9d, the respective CSI-RS port group configuration (for example, configuration r=3) is set by dividing CSI-RS ports of the antenna array into N3pg=4 CSI-RS port groups, with dimensions of group N1'3=4 CSI-RS ports in the first spatial dimension by N2'3=2 CSI-RS ports in the second spatial dimension. The considered CSI-RS port group configuration can be used for relatively high load of time-frequency resources in UL.

[0206] In step 1110, several CSI-RS port group configurations can be set in the base station (for example, all the three configurations of Figures　9b-9d or any two of them) or one CSI-RS port group configuration can be set (for example, any one of the three configurations according to Figures　9b-9d). This aspect does not impose a limitation onto the present invention.

[0207] According to an embodiment of the present invention, as in the case of [3], in step 1110 the number L of UL reception streams is additionally determined in the base station. As noticed earlier, the parameter L can be determined depending on load of time-frequency resources in UL.

[0208] In step 1120, configuration parameters required by the user equipment for generating and transmitting CSI are transmitted from the base station to the user equipment (for example, such as the UE 201-1, 201-2, ... in Figure　2). For each of the one or more CSI-RS port group configurations set in step 1110, the configuration parameters will comprise, at least, parameters of a codebook associated with said CSI-RS port group configuration. In accordance with the above discussion, the codebook parameters included in the configuration parameters in step 1120 for each r-th CSI-RS port group configuration from the one or more CSI-RS port groups configurations set in step 1110 can comprise: the number N1'rof CSI-RS ports along the first spatial dimension in a CSI-RS port group of said CSI-RS port group configuration and the respective oversampling factor O1r, and the number N2'rof CSI-RS ports along the second spatial dimension in said CSI-RS port group and the respective oversampling factor O2r. It should be obvious to a skilled artisan that the oversampling factors may not be included into the configuration parameters transmitted in step 1120, for example, in the case when the base station and the user equipment have a table similar to Table　5.2.2.2.1-2 given above, and the respective parameters O1r·O2rcan be determined by the user equipment from this table based on N1'r·N2'r. According to an embodiment, the number L of UL reception streams can be also included in the configuration parameters.

[0209] DL transmission of step 1120 can be performed using DCI, MAC signaling, RRC signaling, or a combination thereof.

[0210] In step 1130, the base station performs transmission of CSI-RSs.

[0211] In step 1140, a CSI request can be transmitted by the base station, where the CSI request can comprise an indication of at least one CSI-RS port group configuration from the one or more CSI-RS port group configurations set in step 1110, for the user equipment. Selection of the at least one CSI-RS port group configuration being indicated can be performed in the base station, depending at least on load of time-frequency resources in UL. For example, under assumption that in step 1110 the three CSI-RS port group configurations shown in Figures　9b-9d were set in the base station, the CSI request transmitted in step 1140 can comprise an indication of the configuration according to Figure　9c (r=2) and the configuration according to Figure　9d (r=3) for the user equipment.

[0212] Preferably, DL transmission of the CSI request in step 1140 is performed via DCI. Implementations of said indication in the CSI request transmitted via DCI will be discussed below.

[0213] In step 1150, based on measurements of the CSI-RSs transmitted from the base station in step 1130, said measurements being performed by the user equipment, for each of the at least one CSI-RS port group configuration signaled in step 1140, a subset of DFT vectors is selected in the user equipment from the set of DFT vectors of the codebook associated with said CSI-RS port group configuration. The codebook associated with each of said at least one CSI-RS port group configuration is accordingly determined in the user equipment by using the configuration parameters that were transmitted from the base station in step 1110.

[0214] As noted above, the selection of the subset of DFT vectors in step 1150 substantially corresponds to the quantization according to [3]. In general, as in [3], the following actions can be performed in the user equipment to select the subset of DFT vectors in step 1150: based on the performed measurements of CSI-RSs, at least one channel matrix is determined, and, based on the determined channel matrix, a quality metric is calculated for each DFT vector from the set of DFT vectors of the associated codebook; based on the calculated quality metrics, the subset of DFT vectors is selected by using a set quantization threshold parameter.

[0215] The quality metric in the considered context is preferably a relative received power associated with a DFT vector with indices (l,m), the relative received power being calculated in accordance with the following expression:

[0216] [Equation 12]

[0217]

[0218] In equation (11), pl,mis the received power associated with the DFT vector, and max(pl,m) is its maximum value over the set of DFT vectors (l,m) of the associated codebook.

[0219] According to a preferred embodiment of the present invention, the received power pl,mused in equation (12) is determined as follows:

[0220] [Equation 13]

[0221]

[0222] where , is a DFT vector from the set of DFT vectors; Hs,i,pis a channel matrix for an i-th subcarrier from NSCsubcarriers, an s-th CSI-RS port group among NrpgCSI-RS port groups in an r-th CSI-RS port group configuration and a p-th polarization from the first (p=0) and second (p=1) orthogonal polarizations. The dimension of the channel matrix Hs,i,pis the number of CSI-RS ports in the CSI-RS port group of the r-th CSI-RS port group configuration by the number of receiving digital ports of the user equipment. The aspects of determining the channel matrix are disclosed in [3] and do not directly relate to the subject of the present invention.

[0223] It should be noticed that, according to another embodiment(s), non-normalized received power values, i.e. pl,m, can be used as the quality metrics, or another option of normalization can be used to obtain relative received powers.

[0224] It should be obvious to a skilled artisan that, in the context of the present invention, the quality metrics can be calculated not for all DFT vectors of the associated codebook, but for some predetermined part thereof. For example, with respect to some DFT vectors, it may be known in advance that a quality indicator corresponding thereto will be low, and these vectors are excluded from the analysis according to the method 1100.

[0225] The quantization threshold parameter is set in the base station and can be signaled to the user equipment, for example, by including it in the configuration parameters transmitted in step 1120, or in the CSI request transmitted in step 1140.

[0226] As in [3], in accordance with an embodiment of the present invention, the following can be set by the base station as the quantization threshold parameter: (i) the target number of DFT vectors, and in this case the set target number of DFT vectors with larger respective relative received powers is selected as the quantized subset of DFT vectors from the associated codebook, or (ii) the relative power threshold value, and in this case the DFT vectors with respective relative received powers greater than or equal to the set relative power threshold value are selected as the quantized subset of DFT vectors from the associated codebook.

[0227] It should also be noted that, in accordance with an embodiment of the present invention, selection of a subset of DFT vectors can be additionally constrained by the condition of orthogonality of DFT vectors in the subset to be selected.

[0228] For the embodiment where the number L of UL reception streams set in the base station was included in the configuration parameters in step 1110, in step 1150 each obtained quantized subset of DFT vectors can be reduced to L / P DFT vectors with larger respective relative received powers, where P=2 for the case when the base station uses CSI-RS ports corresponding to both the first polarization and the second polarization for transmitting CSI-RSs, and P=1 for the case when the base station uses CSI-RS ports corresponding only to one of the first polarization and the second polarization for transmitting CSI-RSs (see Figure　10).

[0229] Furthermore, in accordance with an embodiment of the present invention, DFT vectors in each quantized subset of DFT vectors can be sorted according to respective relative received powers.

[0230] In step 1160, CSI is generated in the user equipment, along with including, into the CSI, information about a respective quantized subset of DFT vectors for each of the at least one CSI-RS port group configuration indicated in step 1140. The generated CSI is transmitted in step 1160 to the base station. Embodiments of including information about the subset(s) of DFT vectors into the CSI will be discussed in detail below.

[0231] In step 1170, the base station receives the CSI transmitted by the user equipment in step 1160, and the base station accordingly obtains at least one BF matrix based on the information about the subset of DFT vectors from the received CSI. Said obtaining of the BF matrix performed in step 1170 is substantially similar to the one disclosed in [3].

[0232] In the embodiment of the method 1100 described above, the transmission of the CSI in step 1160 is performed in response to the CSI request transmitted by the base station in step 1140. At the same time, it should be appreciated by a skilled artisan that the CSI transmission can be performed by the user equipment without a CSI request (for example, if the periodic CSI transmission is configured), and in this case said indication of at least one CSI-RS port group configuration can be transmitted by the base station to the user equipment in a control message other than the CSI request. In other words, step 1140 is not mandatory in the UL beamforming method 1100.

[0233] An embodiment of the present invention that relates to implementation of the CSI request transmitted by the base station via DCI (see stage 1140) is described hereinbelow.

[0234] The approach according to this embodiment generally refers to implementation of the CSI request in such a way that it comprises an indication of a CSI-RS port group configuration(s) with respect to which the base station needs to receive feedback from the user equipment in the form of the accordingly generated CSI.

[0235] In the considered embodiment, said indication is encoded by a respective bit field in DCI, and to this end a respective code table, as illustrated below by Table　2, is set in advance in the base station:

[0236] The value of the bit field in the DCI CSI requestA CSI-RS port group configuration(s) for which CSI is requested...00CSI not requested...011st CSI-RS port group configuration / associated codebook...102nd CSI-RS port group configuration / associated codebook...113rd CSI-RS port group configuration / associated codebook......

[0237] The ellipsis before the two digits in the left column of Table　1 shows that the bit field encoding a specific CSI-RS port group configuration or a combination of CSI-RS port group configurations can have different sizes depending on implementation.

[0238] The code table set in the base station is signaled in advance from the base station to the user equipment via RRC signaling.

[0239] Table　3 below provides the example of implementation of the code table, as generally illustrated by Table　1, for the case where the DCI bit field (the left column of Table　1) has size of 2 bits.

[0240] The value of the bit field in the DCI CSI requestA CSI-RS group configuration(s) for which CSI is requested00CSI not requested011st CSI-RS port group configuration102nd CSI-RS port group configuration111st and 2nd CSI-RS port group configurations

[0241] Therefore, the base station, for example, depending on the current load of time-frequency resources in UL (see Figures　8a, 8b), selects the value of the bit field in the code table, and this value is signaled to the user equipment in the DCI CSI request. Based on the bit field value comprised in the received CSI request, the user equipment determines from its code table the CSI-RS port group configuration or combination of CSI-RS port group configurations with respect to which the user equipment is to provide feedback to the base station within CSI.

[0242] For example, for the above illustrations of Figures　9b-9d, in the case of pre-configuring the code table in the form of Table　2, if the base station, based on the current load of time-frequency resources in UL, selects the second (r=2) CSI-RS port group configuration, then the base station will set the value of the bit field in the CSI request to '10', and if the base station selects the first (r=1) and second (r=2) CSI-RS port group configurations, then the base station will set the value of the bit field in the CSI request to '11'. The user equipment, based on the bit field value in the received DCI CSI request, in step 1150 determines with respect to which CSI-RS port group configuration(s) from the CSI-RS port group configurations set in step 1110 a quantized subset of DFT vectors should be determined and reported within CSI to the base station. For example, according to the bit field value in the received CSI request equal to '11', the user equipment will determine that the subset of DFT vectors should be calculated with respect to each of the configurations r=1 and r=2 (see Figures　9b, 9c), and in step 1160 the user equipment will include the information about these subsets of DFT vectors into the CSI being generated.

[0243] The considered embodiment of the present invention provides, on one hand, compact encoding of the indication of a CSI-RS port group configuration(s) and, on the other hand, the capability to flexibly switch between the set CSI-RS port group configurations and combinations thereof, i.e. the capability, by means of accordingly setting the value of the bit field in the DCI CSI request, of dynamically requesting the user equipment for feedback regarding the required CSI-RS port group configuration(s).

[0244] It should be appreciated that, although Table　2 shows the example with the bit field size equal to 2, other values of the size of this bit field can be used (for example, 3 bits), with the capability to encode a greater number of CSI-RS port group configurations and combinations thereof. Then, as noted earlier, transmission of the CSI request (i.e. step 1140) is not mandatory; nevertheless, the approach according to the considered embodiment of the present invention can be also applied in a different control message in which a respective indication can be transmitted from the base station to the user equipment.

[0245] Embodiments of encoding the information about the subset(s) of DFT vectors included by the user equipment into the CSI in step 1150 are described hereinafter with reference to Figures　12, 13.

[0246] It should be explained herein that, in accordance with 5G NR, CSI is transmitted via uplink control information (UCI) the UL transmission of which is scheduled in advance in the base station. Two parts are allocated within UCI for transmitting CSI: part　1 with a fixed payload size (in bits) and part　2 with a payload size that can be variable, where the payload size of part　2 depends on UCI contents of part　1. The parameters included in the CSI are accordingly distributed between UCI part　1 and UCI part　2. In this case, payload of UCI part　2 can be obtained in the base station only upon payload of UCI part　1 has been decoded.

[0247] The omission mechanism is provided for UCI part　2, and according to said mechanism, if the total payload of the CSI parameters exceeds the payload size initially allocated by the base station when scheduling transmission of UCI part　2, then some of the CSI parameters assigned for being placed into UCI part　2 are excluded from UCI to be transmitted in order to match its allocated size. To implement the omission mechanism, the CSI parameters are ordered within UCI part　2 in such a way that parameters which are less important for operating the system are placed at the end of part　2.

[0248] Application of the UCI based approach to CSI transmission, as outlined above, is also planned in 6G xMIMO systems.

[0249] For each q-th CSI-RS port group configuration of the at least one CSI-RS port group configuration indicated in step 1140, the user equipment includes information about indices of DFT vectors (Channel Directional Information, CDI) of a respective quantized subset of DFT vectors obtained in step 1150 into the information about the subset of DFT vectors which is included into the CSI generated in step 1160.

[0250] According to the first embodiment, combinatorial encoding is used to encode the information about the DFT vector indices. In this case, under assumption that the respective (q-th) subset of DFT vectors includes L DFT vectors (see step 1150), their indices from the set , of DFT vector indices along the first spatial dimension of the associated (q-th) codebook are encoded in the form of the code point p1q:

[0251] [Equation 13a]

[0252]

[0253] and indices from the set of DFT vector indices along the second spatial dimension of the associated codebook are encoded in the form of the code point p2q:

[0254] [Equation 13b]

[0255]

[0256] In equations (13a), (13b)

[0257]

[0258] In accordance with the considered first embodiment, a pair of code points is included into the CSI as CDI for each q-th quantized subset of DFT vectors reported by the user equipment. This embodiment is characterized by relatively low bit overhead in UCI. It should be noticed that it is possible to implement this embodiment by performing combinatorial encoding of DFT vector indices from the total set of indices in the number in both spatial dimensions of the associated codebook, with accordingly obtaining one code point pqto be included as CDI into the CSI.

[0259] According to the second embodiment which corresponds to implementation of step 1150 with sorting of DFT vectors in the respective (q-th) quantized subset of DFT vectors selected from the associated codebook according to respective received powers, indices of the DFT vectors of said subset along the first spatial dimension of the associated codebook and indices of the DFT vectors of said subset along the second spatial dimension of the associated codebook are determined, where i=0, ... , L-1, again under assumption, as in the first embodiment, that the number of DFT vectors in the subset of DFT vectors is equal to L. Therefore, the DFT vector indicated by the indices will have the largest relative received power correspond thereto.

[0260] In this embodiment, for each q-th quantized subset of DFT vectors reported by the user equipment, a binary representation of pairs of indices of the DFT vectors of said subset is included as CDI into the CSI. This embodiment is characterized by moderate bit overhead in UCI.

[0261] The considered second embodiment is illustrated in Figure　12, where the codebook of size 8 DFT vectors along the first spatial dimension by 4 DFT vectors along the second spatial dimension is schematically shown, and, according to the illustration of Figure　12, the quantized subset of DFT vectors (black squares) is represented as {χ(1)}=(2, 1, 6, 6), {χ(2)}=(3,1,3,1). In accordance with the aforesaid, the first DFT vector indicated by indices (2,3) corresponds to the largest relative received power, the second DFT vector indicated by indices (1, 1) corresponds to the second largest relative received power, and so on.

[0262] According to the third embodiment, a first bitmap is used whose values indicate DFT vectors of the respective quantized subset of DFT vectors obtained by the user equipment in step 1150 for the q-th CSI-RS port group configuration, among DFT vectors along the first spatial dimension in the associated codebook, and a second bitmap whose values indicate DFT vectors of the respective subset of DFT vectors among DFT vectors along its second spatial dimension. In this case, the encoded representation of the subset of DFT vectors selected by the user equipment in step 1150 from the associated codebook can have the following form:

[0263] [Equation 14a]

[0264]

[0265] [Equation 14b]

[0266]

[0267] where in equations (14a), (14b) bitakes the value 1 for a selected DFT vector and 0 for a DFT vector which is not selected.

[0268] In the considered third embodiment, for each q-th subset of DFT vectors reported by the user equipment, respective bitmaps p(1)q, p(2)qare included as CDI into the CSI. This embodiment is characterized, on one hand, by high flexibility, that is, it enables to encode any combination of indices of selected DFT vectors, but, on the other hand, by relatively high bit overhead in UCI. It should be noted that this embodiment can be implemented by using one bitmap for both spatial dimensions of the associated codebook with common indexing; in this case, CDI can have the following form:

[0269] [Equation 14c]

[0270]

[0271] In the considered third embodiment, other bit values in the bitmaps can be used in a way obvious to a skilled artisan (for example, 0 can indicate a selected DFT vector, and 1 - a DFT vector which is not selected).

[0272] The fourth embodiment is also provided, which is development of the third embodiment, where two bitmaps are used. According to this embodiment, based on the generated bitmaps p(1)q, p(2)q, the quantized subset of DFT vectors is encoded into the final representation by inner indexing over the selected DFT vectors in said first and second bitmaps.

[0273] The considered fourth embodiment is illustrated in Figure　13. The upper part of Figure　13 shows the preliminary representation of the selected DFT vectors by bitmaps p(1)= (0, 1, 1, 0, 0, 0, 1, 0) and p(2)= (0, 1, 0, 1) (see equations (14a), (14b)), which corresponds to dashed gray squares in this figure. As illustrated in the lower part of Figure　13, the DFT vectors selected into the quantized subset of DFT vectors are represented by indexing over said preliminary representation, namely as =(1, 4, 5, 6). This indexing may be referred to as 'common inner indexing' in the text of this application, without limitations. These selected DFT vectors are shown in Figure　13 as black squares.

[0274] Accordingly, in the considered fourth embodiment, for each q-th quantized subset of DFT vectors reported by the user equipment, binary representations of indices of the DFT vectors of said subset are included as CDI into the CSI.

[0275] It should be noted that in the above four embodiments of representing the information about the indices of the DFT vectors of the subset(s) of DFT vectors in CSI, which enable to report this information with different bit overheads in UCI, other options for indexing DFT vectors over codebooks and bitmaps can be used in a way obvious to a skilled artisan.

[0276] In accordance with a possible embodiment of the present invention, in step 1160, for each q-th CSI-RS port group configuration of the at least one CSI-RS port group configuration indicated in step 1140, information about relative received power (Beam Power Information, BPI) for DFT vectors of the respective quantized subset of DFT vectors obtained in step 1150 is additionally included by the user equipment into the information about the subset of DFT vectors, besides CDI the implementations of which have been considered above. This additional inclusion of BPI enables to directly inform the base station about the contribution made by each DFT vector to the reported signal space.

[0277] According to the considered possible embodiment, quantization of values of relative received power accordingly calculated for DFT vectors of each q-th quantized subset of DFT vectors in step 1150 is performed first. More specifically, each calculated value of relative received power , i=0, ... , L-1 (under assumption that the q-th subset of DFT vectors includes L DFT vectors (see step 1150)) is rounded to one of values preset in the user equipment (for example, 1 / 2, 1 / 4, 1 / 8, 1 / 16), each mapped to a binary value of a bit sequence (for example, '00', '01', '10', '11').

[0278] Accordingly, in this possible embodiment, binary representations of the relative received power quantized values are included as BPI into the CSI for the DFT vectors of each q-th quantized subset of DFT vectors reported by the user equipment. As recited earlier (see equations (12), (13)), a relative received power is calculated relative to the received power maximum value, i.e. relative to the received power of the strongest DFT vector; accordingly, in the considered case, the quantized value of the relative received power of the first DFT vector (i.e. the strongest one) from the sorted subset of DFT vectors may not be included into the CSI transmitted by the user equipment.

[0279] Illustrative embodiments of placing the information about the subset of DFT vectors within the CSI transmitted by the user equipment to the base station via UCI (see stage 1160) are described hereinafter with reference to the diagrams of Figures　14a-14d.

[0280] The embodiments according to Figures　14a, 14b correspond to the case where only CDI of a quantized set(s) of DFT vectors is included into the CSI. In accordance with the aforesaid, BPI may not be included into the CSI, for example, when DFT vectors of each reported set of DFT vectors are sorted according to received power.

[0281] In accordance with the illustration of Figure　14a, {CDIi}, i = 1, ..., K, respectively for K quantized sets of DFT vectors reported by the user equipment as part of the CSI, are placed into UCI part　1; in accordance with the illustration in Figure　14b, {CDIi}, i = 1, ..., K, are placed into UCI part　2.

[0282] The embodiments according to Figures　14c, 14d correspond to the case where BPI is included into the CSI in addition to CDI. These embodiments are characterized by higher bit overhead in UCI, as compared to the embodiments according to Figures　14a, 14b.

[0283] In accordance with the illustration of Figure　14c, {CDIi} and {BPIi}, i = 1, ..., K, respectively for K quantized sets of DFT vectors reported by the user equipment as part of the CSI are placed into UCI part　1. Options for combined placing of {CDIi} and {BPIi} within UCI part　1 that are different in relation to Figure　14c should be clear to a skilled artisan. It should be also obvious to a skilled artisan from the illustration of Figure　14c that {CDIi} and {BPIi}, i = 1, ..., K, can be similarly placed into UCI part　2.

[0284] According to the illustration of Figure　14d, {CDIi}, i = 1, ..., K, similarly to Figure　14a, are placed into UCI part　1, and {BPIi} are placed into UCI part　2 in a manner similar to Figure　14b. When using the omission mechanism discussed above, some of the {BPIi} can be excluded from UCI part　2, if necessary. In view of the aforesaid, according to an embodiment of the present invention, BPI for the first DFT vector (i.e. BPI1) may not be included into the CSI; therefore, for the implementations illustrated with reference to Figure　14c, Figure　14d, in this case {BPIi}, i = 2, ..., K will be accordingly transmitted as part of the CSI.

[0285] Thereafter, similarly to the consideration of Figure　4 above, the description of applying UL beamforming according to the embodiment of the present invention in a wireless communication network (NW) with a base station having an architecture similar to O-RAN 7-2x is given hereinbelow with references to Figure　15 and Figure　5. The wireless communication network may be a 6G xMIMO network.

[0286] Figure　15, similarly to Figure　4, illustratively shows the generalized diagram of interaction between the NW and a user equipment to carry out, in the base station which is part of the NW, beamforming for receiving UL transmission from the user equipment.

[0287] The base station sets one or more CSI-RS port group configurations (action 1 in Figure　15; step 1110) and transmits, by the radio unit to the user equipment, configuration parameters for transmitting CSI, the configuration parameters comprising, at least: for each (r-th) CSI-RS port group configuration of the set one or more CSI-RS port group configurations, parameters of a codebook (for example, N1'r, N2'r) associated with the r-th CSI-RS port group configuration (action 2; step 1120).

[0288] Then, the base station performs, by the radio unit, transmission of CSI-RSs (action 3; step 1130) with respect to which measurements are performed by the user equipment (action 4 in Figure　15).

[0289] Next, the base station transmits a CSI request by the radio unit (action 5; step 1140). As noticed earlier, an indication of at least one CSI-RS port group configuration from the set one or more CSI-RS port group configurations can be included into the CSI request (see Tables 1, 2). Selection of the indicated at least one CSI-RS port group configuration can be performed in the base station, at least, depending on load of time-frequency resources in UL, i.e. respectively depending on load of the FH interface.

[0290] Based on the performed measurements of the CSI-RSs, the user equipment obtains, for each of the indicated at least one CSI-RS port group configuration, a quantized subset of DFT vectors from a set of DFT vectors of a codebook associated with said CSI-RS port group configuration (action 6; step 1150, equations (12), (13)). Then, the user equipment generates the CSI, along with including, into the CSI, information about a respective quantized subset of DFT vectors for each of the indicated at least one CSI-RS port group configuration (action 7; step 1160). As noted earlier, CDI (see equations (13a)-(14c), Figures　12, 13) and, optionally, BPI are accordingly included as the information about the quantized subset(s) of DFT vectors into the CSI. Next, the user equipment transmits the generated CSI in UCI to the base station (action 8; step 1160, Figures　14a-14d). The UCI transmission can be performed in the physical level (L1) or MAC level (L2).

[0291] Based on the CSI received from the user equipment through the radio unit, the base station obtains a BF matrix to be applied for the UL reception (action 9; step 1170). As noted earlier, the obtaining itself of the BF matrix in the base station does not directly relate to the subject of the present invention - in particular, the approach disclosed in [3] can be used.

[0292] The above disclosure has been given in the context of obtaining the BF matrix for the case when the CSI with the quantized subset(s) of DFT vectors is provided to the base station by one user equipment. At the same time, the present invention provides for the scenario where such quantized sets are provided by each user equipment from a certain plurality of user equipments served by the base station. That is, each of these user equipments performs steps 1130-1160 of the method 1100, actions 4, 6-8 according to Figure　15. At the same time, based on CSI received from the user equipments, the base station obtains one BF matrix and, accordingly, one receiver to be applied to UL transmissions from the entire plurality of user equipments. This scenario is described in [3].

[0293] The obtaining of the BF matrix can be performed in the distributed unit or in the radio unit of the base station.

[0294] Thereafter, the base station allocates, to the user equipment, resources for UL transmission and signals said allocation to the user equipment in DCI (action 10). The user equipment performs the scheduled transmission of PUSCH to the base station (action 11). The base station applies the obtained BF matrix and the accordingly built receiver (see equations (1)-(4)) for reception of PUSCH (action 12) and performs demodulation of PUSCH (action 13).

[0295] It should be clear to a skilled artisan that action 9 can be performed by the base station at any time after the CSI has been received, before performing action 12.

[0296] As follows from the aforesaid, the present invention provides, in general, UL beamforming in the base station with required accuracy and coverage, along with extension to support of communication systems where extremely large antenna arrays are used, and, more specifically, provides flexible adaptability of the UL beamforming procedure, thereby enabling to reduce associated computational complexity in the base station, due to usage of the new codebook structure and respective support of various levels of spatial port compression, which, in turn, ensures high quality of UL reception at the base station side.

[0297] It should be also appreciated that the illustrated exemplary embodiments are only preferred, but not the only possible implementations of the invention. Specifically, the scope of the present invention is defined by the claims and equivalents thereof.

[0298] LIST OF CITED PUBLICATIONS

[0299] [1] Y. Huang, W. Lei, C. Lu, M. Berg, "Fronthaul Functional Split of IRC-Based Beamforming for Massive MIMO Systems", 2019 IEEE 90thVehicular Technology Conference (VTC2019-Fall), Honolulu, HI, USA, 2019, pp. 1-5, doi: 10.1109 / VTCFall.2019.8891191.

[0300] [2] Y. Huang, C. Lu, M. Berg, P. Odling, "Functional Split of Zero-Forcing Based Massive MIMO for Fronthaul Load Reduction", IEEE Access, vol. 6, pp. 6350-6359, 2018, doi: 10.1109 / ACCESS.2017.2788451.

[0301] [3] RU　2817678, 18 April 2024.

[0302] [4] TS　38.214, v.17.4.0

Claims

1.A method performed by a base station of beamforming for uplink (UL) reception in a wireless communication system, the method comprising:defining one or more CSI-RS port group configurations;transmitting, to a user equipment, configuration parameters for receiving channel state information (CSI), wherein the configuration parameters comprise, at least: for each of the one or more CSI-RS port group configurations, parameters of a codebook corresponding to the CSI-RS port group configuration, wherein the codebook is formed by a respective set of discrete Fourier transform (DFT) vectors;transmitting CSI reference signals (CSI-RSs);receiving, from the user equipment, the CSI, wherein, for each of the at least one CSI-RS port group configuration, information about the subset of DFT vectors is included into the CSI; andobtaining at least one beamforming (BF) matrix for the UL reception, the BF matrix being obtained based on the information about the subset of DFT vectors from the CSI received from the user equipment,wherein, based on measurements of the CSI-RSs, for each of at least one CSI-RS port group configuration from the one or more CSI-RS port group configurations, the subset of DFT vectors from a set of DFT vectors of a codebook corresponding to the CSI-RS port group configuration is selected, wherein the corresponding codebook is determined in the user equipment by using the received configuration parameters.2.The method of claim　1, further comprising, after the transmitting CSI-RSs:transmitting, to the user equipment, a CSI request, the CSI request comprising an indication of the at least one CSI-RS port group configuration.3.The method of claim　2, wherein the CSI request is transmitted via downlink control information (DCI), wherein the indication represents a bit field, wherein a value of the bit field is accordingly selected in the base station from a preset plurality of bit values, wherein each value of the bit field from at least part of the plurality of bit values has a combination of one or several CSI-RS port group configurations corresponding thereto.4.The method of claim　1,wherein an antenna array of the base station has N1CSI-RS ports along a first spatial dimension by N2CSI-RS ports along a second spatial dimension implemented therein, N1≥N2, wherein the base station is configured to perform, on each CSI-RS port, transmission and reception of a signal with one of a first polarization and a second polarization, wherein the first polarization and the second polarization are orthogonal,wherein the defining one or more CSI-RS port group configurations comprises: defining each r-th CSI-RS port group configuration, among the one or more CSI-RS port group configurations being defined, by virtually dividing CSI-RS ports of the base station into Nrpgidentical groups of CSI-RS ports, wherein each group has sizes N1'rCSI-RS ports along the first spatial dimension by N2'rCSI-RS ports along the second spatial dimension, N1'r≥N2'r,.5.A method performed by a user equipment of beamforming for uplink (UL) reception in a wireless communication system, the method comprising:receiving, from a base station, configuration parameters for transmitting channel state information (CSI), wherein the configuration parameters comprise, at least: for each of one or more CSI-RS port group configurations, parameters of a codebook corresponding to the CSI-RS port group configuration, wherein the codebook is formed by a respective set of Discrete Fourier Transform (DFT) vectors;receiving, from the base station, CSI reference signals (CSI-RSs);based on measurements of the CSI-RSs, for each of at least one CSI-RS port group configuration from the one or more CSI-RS port group configurations, selecting a subset of DFT vectors from a set of DFT vectors of a codebook corresponding to said CSI-RS port group configuration, wherein the corresponding codebook is determined in the user equipment by using the received configuration parameters;generating the CSI, wherein, for each of the at least one CSI-RS port group configuration, information about the subset of DFT vectors is included into the CSI; andtransmitting the generated CSI to the base station,wherein at least one beamforming (BF) matrix for the UL reception is based on the information about the subset of DFT vectors from the CSI.6.The method of claim　5, further comprising, after the receiving CSI-RSs:receiving, from the base station, a CSI request, the CSI request comprising an indication of the at least one CSI-RS port group configuration.7.The method of claim　6, wherein the CSI request is received via downlink control information (DCI), wherein the indication represents a bit field, wherein a value of the bit field is accordingly selected in the base station from a preset plurality of bit values, wherein each value of the bit field from at least part of the plurality of bit values has a combination of one or several CSI-RS port group configurations corresponding thereto.8.The method of claim　5,wherein an antenna array of the base station has N1CSI-RS ports along a first spatial dimension by N2CSI-RS ports along a second spatial dimension implemented therein, N1≥N2, wherein the base station is configured to perform, on each CSI-RS port, transmission and reception of a signal with one of a first polarization and a second polarization, wherein the first polarization and the second polarization are orthogonal,wherein the defining one or more CSI-RS port group configurations comprises: defining each r-th CSI-RS port group configuration, among the one or more CSI-RS port group configurations being defined, by virtually dividing CSI-RS ports of the base station into Nrpgidentical groups of CSI-RS ports, wherein each group has sizes N1'rCSI-RS ports along the first spatial dimension by N2'rCSI-RS ports along the second spatial dimension, N1'r≥N2'r,.9.A base station of beamforming for uplink (UL) reception in a wireless communication system, the base station comprising:a transceiver; andat least one processor configured to:define one or more CSI-RS port group configurations,transmit, to a user equipment, configuration parameters for receiving channel state information (CSI), wherein the configuration parameters comprise, at least: for each of the one or more CSI-RS port group configurations, parameters of a codebook corresponding to the CSI-RS port group configuration, wherein the codebook is formed by a respective set of discrete Fourier transform (DFT) vectors,transmit CSI reference signals (CSI-RSs),receive, from the user equipment, the CSI, wherein, for each of the at least one CSI-RS port group configuration, information about the subset of DFT vectors is included into the CSI, andobtain at least one beamforming (BF) matrix for the UL reception, the BF matrix being obtained based on the information about the subset of DFT vectors from the CSI received from the user equipment,wherein, based on measurements of the CSI-RSs, for each of at least one CSI-RS port group configuration from the one or more CSI-RS port group configurations, the subset of DFT vectors from a set of DFT vectors of a codebook corresponding to the CSI-RS port group configuration is selected, wherein the corresponding codebook is determined in the user equipment by using the received configuration parameters.10.The base station of claim　9, wherein, after the transmitting CSI-RSs, the at least one processor is further configured to transmit, to the user equipment, a CSI request, the CSI request comprising an indication of the at least one CSI-RS port group configuration.11.The base station of claim　10, wherein the CSI request is transmitted via downlink control information (DCI), wherein the indication represents a bit field, wherein a value of the bit field is accordingly selected in the base station from a preset plurality of bit values, wherein each value of the bit field from at least part of the plurality of bit values has a combination of one or several CSI-RS port group configurations corresponding thereto.12.The base station of claim　9,wherein an antenna array of the base station has N1CSI-RS ports along a first spatial dimension by N2CSI-RS ports along a second spatial dimension implemented therein, N1≥N2, wherein the base station is configured to perform, on each CSI-RS port, transmission and reception of a signal with one of a first polarization and a second polarization, wherein the first polarization and the second polarization are orthogonal,wherein the defining one or more CSI-RS port group configurations comprises: defining each r-th CSI-RS port group configuration, among the one or more CSI-RS port group configurations being defined, by virtually dividing CSI-RS ports of the base station into Nrpgidentical groups of CSI-RS ports, wherein each group has sizes N1'rCSI-RS ports along the first spatial dimension by N2'rCSI-RS ports along the second spatial dimension, N1'r≥N2'r,.13.A user equipment of beamforming for uplink (UL) reception in a wireless communication system, the user equipment comprising:a transceiver; andat least one processor configured to:receive, from a base station, configuration parameters for transmitting channel state information (CSI), wherein the configuration parameters comprise, at least: for each of one or more CSI-RS port group configurations, parameters of a codebook corresponding to the CSI-RS port group configuration, wherein the codebook is formed by a respective set of Discrete Fourier Transform (DFT) vectors,receive, from the base station, CSI reference signals (CSI-RSs),based on measurements of the CSI-RSs, for each of at least one CSI-RS port group configuration from the one or more CSI-RS port group configurations, select a subset of DFT vectors from a set of DFT vectors of a codebook corresponding to said CSI-RS port group configuration, wherein the corresponding codebook is determined in the user equipment by using the received configuration parameters,generate the CSI, wherein, for each of the at least one CSI-RS port group configuration, information about the subset of DFT vectors is included into the CSI, andtransmit the generated CSI to the base station,wherein at least one beamforming (BF) matrix for the UL reception is based on the information about the subset of DFT vectors from the CSI.14.The user equipment of claim　13, wherein, after the receiving CSI-RSs, the at least one processor is further configured to receive, from the base station, a CSI request, the CSI request comprising an indication of the at least one CSI-RS port group configuration, andwherein the CSI request is received via downlink control information (DCI), wherein the indication represents a bit field, wherein a value of the bit field is accordingly selected in the base station from a preset plurality of bit values, wherein each value of the bit field from at least part of the plurality of bit values has a combination of one or several CSI-RS port group configurations corresponding thereto.15.The user equipment of claim　13,wherein an antenna array of the base station has N1CSI-RS ports along a first spatial dimension by N2CSI-RS ports along a second spatial dimension implemented therein, N1≥N2, wherein the base station is configured to perform, on each CSI-RS port, transmission and reception of a signal with one of a first polarization and a second polarization, wherein the first polarization and the second polarization are orthogonal,wherein the defining one or more CSI-RS port group configurations comprises: defining each r-th CSI-RS port group configuration, among the one or more CSI-RS port group configurations being defined, by virtually dividing CSI-RS ports of the base station into Nrpgidentical groups of CSI-RS ports, wherein each group has sizes N1'rCSI-RS ports along the first spatial dimension by N2'rCSI-RS ports along the second spatial dimension, N1'r≥N2'r,.

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