Methods and apparatus for downlink beamforming in a wireless communication system

Abstract

The disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. A method performed by a terminal includes receiving, from a base station, information on an association between SS (synchronization signal) / PBCH (physical broadcast channel) blocks (SSBs) and CSI (channel state information)-RSs (reference signals); receiving, from the base station, one or more SSBs; performing a measurement of the one or more SSBs; based on the measurement, identifying at least one SSB; and transmitting, to the base station, a first message comprising information on the at least one SSB.

Description

METHODS AND APPARATUS FOR DOWNLINK BEAMFORMING IN A WIRELESS COMMUNICATION SYSTEM

[0001] The present invention relates, in general, to wireless communications and, more specifically, to devices and methods for downlink (DL) beamforming.

[0002] Considering the development of wireless communication from generation to generation, the technologies have been developed mainly for services targeting humans, such as voice calls, multimedia services, and data services. Following the commercialization of 5G (5th-generation) communication systems, it is expected that the number of connected devices will exponentially grow. Increasingly, these will be connected to communication networks. Examples of connected things may include vehicles, robots, drones, home appliances, displays, smart sensors connected to various infrastructures, construction machines, and factory equipment. Mobile devices are expected to evolve in various form-factors, such as augmented reality glasses, virtual reality headsets, and hologram devices. In order to provide various services by connecting hundreds of billions of devices and things in the 6G (6th-generation) era, there have been ongoing efforts to develop improved 6G communication systems. For these reasons, 6G communication systems are referred to as beyond-5G systems.

[0003] 6G communication systems, which are expected to be commercialized around 2030, will have a peak data rate of tera (1,000 giga)-level bps and a radio latency less than 100 sec, and thus will be 50 times as fast as 5G communication systems and have the 1 / 10 radio latency thereof.

[0004] In order to accomplish such a high data rate and an ultra-low latency, it has been considered to implement 6G communication systems in a terahertz band (for example, 95GHz to 3THz bands). It is expected that, due to severer path loss and atmospheric absorption in the terahertz bands than those in mmWave bands introduced in 5G, technologies capable of securing the signal transmission distance (that is, coverage) will become more crucial. It is necessary to develop, as major technologies for securing the coverage, radio frequency (RF) elements, antennas, novel waveforms having a better coverage than orthogonal frequency division multiplexing (OFDM), beamforming and massive multiple input multiple output (MIMO), full dimensional MIMO (FD-MIMO), array antennas, and multiantenna transmission technologies such as large-scale antennas. In addition, there has been ongoing discussion on new technologies for improving the coverage of terahertz-band signals, such as metamaterial-based lenses and antennas, orbital angular momentum (OAM), and reconfigurable intelligent surface (RIS).

[0005] Moreover, in order to improve the spectral efficiency and the overall network performances, the following technologies have been developed for 6G communication systems: a full-duplex technology for enabling an uplink transmission and a downlink transmission to simultaneously use the same frequency resource at the same time; a network technology for utilizing satellites, high-altitude platform stations (HAPS), and the like in an integrated manner; an improved network structure for supporting mobile base stations and the like and enabling network operation optimization and automation and the like; a dynamic spectrum sharing technology via collison avoidance based on a prediction of spectrum usage; an use of artificial intelligence (AI) in wireless communication for improvement of overall network operation by utilizing AI from a designing phase for developing 6G and internalizing end-to-end AI support functions; and a next-generation distributed computing technology for overcoming the limit of UE computing ability through reachable super-high-performance communication and computing resources (such as mobile edge computing (MEC), clouds, and the like) over the network. In addition, through designing new protocols to be used in 6G communication systems, developing mecahnisms for implementing a hardware-based security environment and safe use of data, and developing technologies for maintaining privacy, attempts to strengthen the connectivity between devices, optimize the network, promote softwarization of network entities, and increase the openness of wireless communications are continuing.

[0006] It is expected that research and development of 6G communication systems in hyper-connectivity, including person to machine (P2M) as well as machine to machine (M2M), will allow the next hyper-connected experience. Particularly, it is expected that services such as truly immersive extended reality (XR), high-fidelity mobile hologram, and digital replica could be provided through 6G communication systems. In addition, services such as remote surgery for security and reliability enhancement, industrial automation, and emergency response will be provided through the 6G communication system such that the technologies could be applied in various fields such as industry, medical care, automobiles, and home appliances.

[0007] In view of the problems existing in the art, as discussed above, the primary object of the present invention is to provide an automatic procedure of reconfiguring CSI-RS resources in DL beamforming, not involving L3 signaling thereby.

[0008] In line with development of the communication systems, there is a need for method of DL beamforming.

[0009] The technical subjects pursued in the disclosure may not be limited to the above mentioned technical subjects, and other technical subjects which are not mentioned may be clearly understood, through the following descriptions, by those skilled in the art to which the disclosure pertains.

[0010] The present invention relates, in general, to wireless communications and, more specifically, to devices and methods for downlink (DL) beamforming in a wireless communication system. According to the method provided herein, an association between synchronization signals (SS / PBCHs) and channel state information reference signals (CSI-RSs) is preconfigured in a base station (BS), wherein each SS / PBCH corresponds to one of beams that are usable by the base station for DL transmission, and the preconfigured association is transmitted from the base station to a user equipment (UE). Corresponding SS / PBCHs are transmitted from the base station in at least some of the beams. In the user equipment, measurements of received SS / PBCHs are performed, one or more SS / PBCHs are selected based on results of the measurement, and a message about the one or more selected SS / PBCHs (a MAC CE report) is transmitted to the base station by L2 signaling. Upon reception, from the base station, of control information identifiable as an ACK of reception of the MAC CE report, a first UE timer of a first predefined duration (T1) is started in the user equipment, wherein, upon transmission of the control information to the user equipment, a first BS timer of the duration T1 has been started in the base station. Upon expiration of T1, the user equipment performs, based on the preconfigured association, switching to subsequent estimation of CSI-RSs corresponding to the selected SS / PBCHs, and the base station performs, based on the preconfigured association, reconfiguring, for the user equipment, of the CSI-RSs corresponding to the selected SS / PBCHs as CSI-RSs to be used by the user equipment for the estimation. CSI-RSs transmitted from the base station are received in the user equipment. Upon having received a CSI request from the base station, the user equipment generates CSI based on the estimation of received CSI-RSs, and transmits the generated CSI to the base station. The present invention enables to reduce signaling overhead due to significantly decreased usage of high-level signaling (RRC) during DL beamforming, and respectively reduce implementation complexity at the base station side.

[0011] In the context of said technical object, according to the first object of the present invention, a method of DL beamforming in a wireless communication system is provided.

[0012] The method provided hereby comprises: in a base station of the wireless communication system: preconfiguring an association between synchronization signals and channel state information reference signals (CSI-RSs), wherein each synchronization signal corresponds to one of spatial beams usable by the base station to perform DL transmission; and transmitting, by the base station, the preconfigured association to a user equipment (UE) in the wireless communication system.

[0013] Then, said method comprises: transmitting, from the base station in at least some of the spatial beams, corresponding synchronization signals.

[0014] Thereafter the method comprises: in the user equipment, performing measurements of the synchronization signals received from the base station; on results of the measurements, selecting one or more synchronization signals; and transmitting to the base station, by using L2 signaling, a message about the selected one or more synchronization signals (L2 message).

[0015] The method provided herein comprises: upon having received, from the base station, control information identifiable as a positive acknowledgement (ACK) of reception of the L2 message, in the user equipment, with account of round-trip time, starting a first UE timer of a first predefined duration; wherein, upon having transmitted the control information to the user equipment, a first BS timer of the first predefined duration has been started in the base station. Upon expiration of the first predefined duration, the method comprises: in the user equipment, based on the preconfigured association, switching to subsequent estimation of CSI-RSs which correspond to the selected synchronization signals; and, in the base station, based on the preconfigured association, reconfiguring, for the user equipment, the CSI-RSs corresponding to the selected synchronization signals as CSI-RSs to be used by the user equipment for the estimation.

[0016] Then, the method provided herein comprises: in the user equipment, receiving CSI-RSs from the base station. The method comprises: upon having received from the base station a CSI request, generating, in the user equipment, CSI based on the estimation of the CSI-RSs received from the base station, and transmitting the generated CSI to the base station; and, in the base station, performing DL precoding based on the CSI received from the user equipment.

[0017] According to one alternative embodiment, the method provided herein further comprises: upon having transmitted the L2 message, in the user equipment, starting a second UE timer of a second predefined duration; and, upon having received the L2 message, in the base station, with account of the round-trip time, starting a second BS timer of the second predefined duration, wherein the second predefined duration is greater than the first predefined duration. In accordance with this alternative embodiment, at absence of reception of the control information identifiable as the ACK within the second predefined duration, the method comprises: continuing, in the user equipment, to use for the estimation CSI-RSs which were used directly before said measurements of the synchronization signals.

[0018] According to another alternative embodiment, the method provided herein further comprises: upon having received the L2 message, transmitting, from the base station to the user equipment via L3 signaling, preferably via RRC signaling, configuration information indicating one or more CSI-RSs with respect to which the user equipment is to actually perform the estimation. In accordance with this alternative embodiment, the control information identifiable as the ACK is not transmitted from the base station to the user equipment. Said one or more CSI-RSs can be CSI-RSs which were used by the user equipment for the estimation directly before said measurements of the synchronization signals.

[0019] According to an embodiment, said performing measurements of the synchronization signals comprises: measuring, in the user equipment, received power of each synchronization signal; and selectingMsynchronization signals with larger received powers, whereMis a predefined natural number; wherein the L2 message comprises: indices of the selected synchronization signals, and parameters indicating respective received power values of the selected synchronization signals.

[0020] In accordance with a preferred embodiment, each synchronization signal is an SS / PBCH resource block (SSB), an index of the synchronization signal is an SSB resource index (SSB-RI), a parameter indicating a received power (L1-RSRP) value measured for the SSB-RI is a table index corresponding to a preset power range which the L1-RSRP of said SSB-RI belongs to, and the L2 message is a report formed as a MAC control element (CE), whereinMis preset in the base station and signaled in advance to the user equipment. The preconfigured association is preferably represented as a table in which identifiers of SS / PBCH resources are set in correspondence to identifiers of CSI-RS resources.

[0021] According to one embodiment, in the MAC CE report, for an SSB-RI which the largest L1-RSRP corresponds to, a respective index of a table of received power absolute values is indicated, said index indicating a range of received power absolute values which said largest L1-RSRP belongs to, and, for each of the other (M-1) SSB-RIs, a respective index of a table of received power relative values is indicated, said index indicating a range of received power values relative to said largest L1-RSRP which an L1-RSRP of said SSB-RI belongs to, wherein theMSSB-RIs are ordered in the MAC CE report in descending order of the L1-RSRPs.

[0022] According to another embodiment, in the MAC CE report, for each of theMSSB-RIs, a respective index of a table of received power absolute values is indicated, said index indicating a range of received power absolute values which an L1-RSRP of said SSB-RI belongs to.

[0023] In accordance with an embodiment, the CSI request comprises an indication, among the CSI-RSs corresponding to SSB-RIs comprised in the MAC CE report, of a set of CSI-RSs with respect to which the user equipment is to actually perform the estimation to generate the CSI. According to a preferred embodiment, the CSI request is transmitted via downlink control information (DCI), wherein said indication represents a bit field, wherein a value of the bit field is respectively 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 corresponds to a preset combination ofKCSI-RS indices, the combination defining the set of CSI-RSs being indicated, where 1 K M. Said plurality of bit values, along with respective combinations of CSI-RS indices, can be preset in the base station and signaled from the base station to the user equipment via RRC signaling. According to said preferred embodiment, the method further comprises, prior to said estimation of the CSI-RSs: in the user equipment, determining the CSI-RSs, with respect to which the user equipment is to actually perform the estimation to generate the CSI, based on the value of the bit field comprised in the received CSI request. The CSI-RS indices are preferably defined by ordering associated SSB-RIs according to L1-RSRPs.

[0024] In accordance with an embodiment, said control information is DCI with an UL grant, wherein the ACK of the reception of the L2 message is indicated by: the DCI having the same HARQ ID as the L2 message, and a new data indicator (NDI) in the DCI being respectively toggled to a preset value.

[0025] According to the second aspect of the present invention, a wireless communication system is provided, the wireless communication system comprising a base station (BS), the base station comprising, at least: transceiving units; data processing units; and data storage units, wherein the base station is configured to communicate with a user equipment (UE) comprising, at least: transceiving units; data processing units; and data storage units. 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. 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 embodiment of the first aspect of the present invention.

[0026] According to the third aspect of the present invention, a method of DL beamforming in a wireless communication system is provided, wherein the wireless communication system comprises a group of base stations communicatively interconnected. In particular, the base stations of the group can be interconnected by a high-throughput communication link.

[0027] The method provided hereby comprises, in one base station of the group: preconfiguring an association between synchronization signals and CSI-RSs, wherein each synchronization signal corresponds to one of spatial beams usable by the base stations of the group to perform DL transmission; and transmitting, by the one base station, the preconfigured association to a user equipment in the wireless communication system. The preconfigured association is also signaled to each of the other base stations of the group.

[0028] Then, the method provided herein comprises: transmitting, from the base stations of the group in at least some of the spatial beams, corresponding synchronization signals.

[0029] Thereafter, the method comprises, in the user equipment: performing measurements of received synchronization signals; on results of the measurements, selecting one or more synchronization signals; and transmitting to the one base station, by using L2 signaling, a message about the selected one or more synchronization signals, along with respective identification information of base stations from which said synchronization signals were transmitted (L2 message).

[0030] The method provided herein comprises: upon having received, from the one base station, control information identifiable as an ACK of reception of the L2 message, in the user equipment, with account of round-trip time, starting a first UE timer of a first predefined duration; wherein, upon having transmitted the control information to the user equipment, a first BS timer of the first predefined duration has been started in the one base station. The method comprises, upon expiration of the first predefined duration: in the user equipment, based on the preconfigured association, switching to subsequent estimation of CSI-RSs which correspond to the selected synchronization signals; in the one base station, based on the preconfigured association, reconfiguring, for the user equipment, the CSI-RSs corresponding to the selected synchronization signals as CSI-RSs to be used by the user equipment for the estimation; and applying said reconfiguring to at least some of the other base stations of the group.

[0031] Then, the method provided herein comprises: in the user equipment, receiving CSI-RSs from the base stations of the group. Said method comprises: upon having received from the one base station a CSI request, generating, in the user equipment, CSI based on the estimation of the received CSI-RSs, and transmitting the generated CSI for DL precoding being performed based on the CSI.

[0032] Each of the base stations of the group can serve a respective sector or cell in the wireless communication system. The identification information of the base station is preferably a cell identifier (PCID). Said one base station is preferably a serving base station for the user equipment.

[0033] According to one alternative embodiment, the method further comprises: upon having transmitted the L2 message, in the user equipment, starting a second UE timer of a second predefined duration; and, upon having received the L2 message, in the one base station, with account of the round-trip time, starting a second BS timer of the second predefined duration, wherein the second predefined duration is greater than the first predefined duration. In accordance with this embodiment, at absence of reception of the control information identifiable as the ACK within the second predefined duration, the method comprises: continuing, in the user equipment, to use for the estimation CSI-RSs which were used directly before said measurements of the synchronization signals.

[0034] According to another alternative embodiment, the method further comprises: upon having received the L2 message, transmitting, from the one base station to the user equipment via L3 signaling, preferably via RRC signaling, configuration information indicating one or more CSI-RSs with respect to which the user equipment is to actually perform the estimation. In accordance with this embodiment, the control information identifiable as the ACK is not transmitted from the base station to the user equipment. Said one or more CSI-RSs can be CSI-RSs which were used by the user equipment for the estimation directly before said measurements of the synchronization signals.

[0035] According to an embodiment, said performing measurements of the synchronization signals comprises: measuring, in the user equipment, received power of each synchronization signal; and selectingMsynchronization signals with larger received powers, whereMis a predefined natural number; wherein the L2 message comprises: indices of the selected synchronization signals, respective PCIDs of the base stations from which said synchronization signals were transmitted, and parameters indicating respective received power values of said synchronization signals.

[0036] In accordance with a preferred embodiment, each synchronization signal is an SS / PBCH resource block (SSB), an index of the synchronization signal is an SSB-RI, a parameter indicating a received power (L1-RSRP) value measured for the SSB-RI is a table index corresponding to a preset power range which the L1-RSRP of said SSB-RI belongs to, and the L2 message is a MAC CE report, whereinMis preset in the base station and signaled in advance to the user equipment. The preconfigured association is preferably represented as a table in which identifiers of SS / PBCH resources are set in correspondence to identifiers of CSI-RS resources.

[0037] According to one embodiment, in the MAC CE report, for an SSB-RI which the largest L1-RSRP corresponds to, a respective index of a table of received power absolute values is indicated, said index indicating a range of received power absolute values which said largest L1-RSRP belongs to, and, for each of the other (M-1) SSB-RIs, a respective index of a table of received power relative values is indicated, said index indicating a range of received power values relative to said largest L1-RSRP which an L1-RSRP of said SSB-RI belongs to, wherein theMSSB-RIs are ordered in the MAC CE report in descending order of the L1-RSRPs.

[0038] According to another embodiment, in the MAC CE report, for each of theMSSB-RIs, a respective index of a table of received power absolute values is indicated, said index indicating a range of received power absolute values which an L1-RSRP of said SSB-RI belongs to.

[0039] In accordance with an embodiment, the CSI request comprises an indication, among the CSI-RSs corresponding to SSB-RIs comprised in the MAC CE report, of a set of CSI-RSs with respect to which the user equipment is to actually perform the estimation to generate the CSI. According to a preferred embodiment, the CSI request is transmitted via DCI, wherein said indication represents a bit field, wherein a value of the bit field is respectively selected in the one 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 corresponds to a preset combination ofKCSI-RS indices, the combination defining the set of CSI-RSs being indicated, where 1 K M. Said plurality of bit values, along with respective combinations of CSI-RS indices, can be preset in the base stations of the group and signaled in advance to the user equipment. In accordance with this preferred embodiment, the method further comprises, prior to said estimation of the CSI-RSs: in the user equipment, determining the CSI-RSs, with respect to which the user equipment is to actually perform the estimation to generate the CSI, based on the value of the bit field comprised in the received CSI request. The CSI-RS indices are preferably defined by ordering associated SSB-RIs according to L1-RSRPs.

[0040] According to an embodiment, said control information is DCI with an UL grant, wherein the ACK of the reception of the L2 message is indicated by: the DCI having the same HARQ ID as the L2 message, and an NDI in the DCI being respectively toggled to a preset value.

[0041] According to the fourth aspect of the present invention, a wireless communication system is provided, the wireless communication system comprising a group of base stations, each base station of the group comprising, at least: transceiving units; data processing units; and data storage units, wherein the base stations are communicatively interconnected, and at least some base stations are in communication with a user equipment comprising, at least: transceiving units; data processing units; and data storage units. The data storage units of the base stations have computer-executable codes stored therein, and the data storage units of the user equipment have computer-executable codes stored therein. The computer-executable codes, when executed by the data processing units of the base stations and the user equipment, cause the method according to any embodiment of the third aspect of the present invention.

[0042] The technical result achievable by the present invention is in enabling to reduce signaling overhead due to significantly decreased usage of high-level signaling (RRC) during DL beamforming, and in enabling to respectively reduce implementation complexity at the base station side.

[0043] The present disclosure provides an effective and efficient method for DL beamforming. Advantageous effects obtainable from the disclosure may not be limited to the above mentioned effects, and other effects which are not mentioned may be clearly understood, through the following descriptions, by those skilled in the art to which the disclosure pertains.

[0044] Fig. 1 is a general scheme of interaction between a wireless communication network and a user equipment to perform DL beamforming according to 5G NR.

[0045] Fig. 2 is a part of the scheme of Fig. 1 that illustrates operations by which subsequent performing of A-BF according to 5G NR is provided at the base station side.

[0046] Fig. 3 is an illustration of the base station scheduler constraint according to 5G NR.

[0047] Fig. 4 is an illustration of performing, over time, H-BF according to 5G NR.

[0048] Fig. 5 is an illustrative diagram of a wireless communication system in which embodiments of the present invention can be implemented.

[0049] Fig. 6 is an illustration of interaction between a user equipment and a group of base stations.

[0050] Fig. 7 is an illustration of performing, over time, H-BF according to an embodiment of the present invention.

[0051] Fig. 8 is a part of the scheme of Fig. 1 that illustrates operations by which subsequent performing of A-BF according to the present invention is provided at the base station side.

[0052] Fig. 9 is an illustration of embodiments of the present invention that are alternative to the embodiment of Figs. 7, 8.

[0053] Fig. 10 is a flowchart of a method of DL beamforming according to one embodiment of the present invention.

[0054] Fig. 11 is a flowchart of a method of DL beamforming according to another embodiment of the present invention.

[0055] 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.

[0056] Nowadays more and more active deployment of 5th Generation (5G) New Radio (NR) networks takes place, whose advantages and capabilities are broadly known.

[0057] Base stations (BSs) in a 5G NR system use massive antenna arrays containing multiple transceiver antenna elements, which enable efficient implementation of multiple-input multiple-output (MIMO) technology, where a number of simultaneously transmitted spatial MIMO layers are generated to transmit data (e.g. physical downlink shared channel (PDSCH)) to one or more user equipments (UEs).

[0058] Generally speaking, a digital signal is transmitted 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 converting the digital signal into an analog one and vice versa. For example, for the 3.5 GHz frequency range, up to 64 digital antenna ports can be used which enable to use, in base stations, various precoding schemes. For example, the spatial multiplexing (SM) technology enables to reuse of the same frequency-time resources for DL transmission of multiple signals (MIMO layers) to one or more user equipments, and the adaptive beamforming (BF) technology enables to dynamically steer power of a transmitted signal to one or more predefined directions. Advanced modulation techniques, such as orthogonal frequency-division multiplexing (OFDM), provide efficient broadband signal transmission.

[0059] More specifically, two approaches to DL beamforming are presently known to be used in wireless communication systems: analog beamforming (A-BF) and digital beamforming (D-BF). The combined implementation of these approaches is referred to as hybrid beamforming (H-BF).

[0060] A-BF is performed in the analog part of the base station and is applied, in the time domain, to a signal which has been already generated; this approach is characterized by relatively low computational costs, but also less flexibility. D-BF is performed in the digital part of the base station and can be applied in the frequency domain as well; this approach is much more flexible than A-BF, but also more computationally expensive.

[0061] Adaptive beamforming methods using A-BF and D-BF (i.e. H-BF) are supported in 5G NR. The general scheme of interaction between a wireless communication network (NW) and a user equipment (UE) is described below with illustrative reference to Fig. 1, where H-BF is used for DL data transmission according to 5G NR.

[0062] A base station, which is part of the NW, broadcasts SS / PBCH block resources (SSBs) in all or some of spatial beams, where SS is a synchronization signal, PBCH is a physical broadcast channel (action 1). Such broadcasting can be performed by the base station periodically. In the left part of Fig. 1, the set of possible beams is illustrated by contours; hereinafter, these beams may be referred to as "analog beams" without limitation, in order to indicate for the sake of clarity that digital DL precoding has not been yet applied to signals transmitted therein. Each SSB corresponds to one of the analog beams, i.e. for each SSB the base station uses one predefined analog beam.

[0063] The user equipment performs estimation of received SSBs; more specifically, the user equipment measures a level of received power (RSRP) of each SSB, selects a required number of SSBs with larger RSRP (hereinafter, such SSBs may be referred to as "best SSBs" for brevity, while analog beams corresponding thereto may be referred to as "best beams" or "higher quality beams"), and generates a report on the measurements, the report indicating SSB-RI indices of the selected SSBs and information about the respective RSRPs (action 2); thereafter, the generated report is transmitted by the user equipment to the base station over uplink (UL) (action 3).

[0064] A more detailed explanation regarding execution of the operations corresponding to action 2 will be given below.

[0065] The base station can use the information included by the received report for analog beamforming, for the purpose of performing subsequent DL transmission to the user equipment. In particular, the base station performs transmission (e.g. periodically) of channel state information (CSI) reference signals (RSs) (action 4) whereto A-BF is applied in the analog part of the base station; more specifically, the base station preferably uses the one or more best beams according to the report for the transmission of CSI-RSs to the user equipment.

[0066] CSI-RSs are, in general, transmitted for obtaining, by user equipments, information about the channel state of digital antenna ports of the base station. Depending on implementation, each CSI-RS port can correspond to one digital antenna port, or additional virtualization is performed in such a way that each CSI-RS port can correspond to more than one (e.g. two) digital antenna ports. In other words, taking this additional virtualization into account, the virtualized representation of antenna elements of the base station antenna array in the form of CSI-RS antenna ports is ultimately used. It should be noted that, when communicating with the base station, the user equipment considers each CSI-RS antenna port as a single emitting element, regardless of antenna elements encompassed thereby.

[0067] The user equipment performs measurements with respect to received CSI-RSs (action 5).

[0068] Upon reception of a CSI request from the base station (action 6), which can be transmitted by the base station periodically and the transmission of which can be performed by means of downlink control information (DCI), the user equipment performs calculations to generate CSI by using the performed CSI-RS measurements (step 7). The user equipment calculates a number of parameters which are included in the CSI being generated. In particular, the user equipment selects a preferred number of MIMO layers, corresponding to a number of data streams simultaneously transmitted from the base station, which the user equipment intends to receive. This number of MIMO layers is reflected by a parameter RI in the CSI. The user equipment also generates a precoding matrix from discrete Fourier transform vectors (DFT vectors) which are selected from a predefined code book. The generated precoding matrix is reflected by a parameter PMI in the CSI. In addition, the user equipment determines a channel quality indicator (CQI) which is also included into the CSI.

[0069] The generated CSI, includinginter aliaRI, PMI, CQI, is transmitted from the user equipment to the base station as the channel state feedback in reply to said CSI request (action 8). Upon reception of the CSI, the base station, in particular, uses CQI to select a modulation and coding scheme (MCS) and applies the received precoding matrix for digital beamforming (action 9) to perform DL transmission (e.g. PDSCH) to the user equipment (action 10).

[0070] The aspects according to 5G NR, which relate, in particular, to implementation of the code book, estimation of CSI-RSs, and calculation of the precoding matrix at the user equipment side, the specificity of representation of RI, PMI, CQI, and other parameters in the CSI, are disclosed in specification TS 38.214, v.17.4.0 and also reflected in publication RU 2811989 which are both incorporated herein by reference in their entirety. In particular, the 5G NR Type 1 code book can be used as the code book (see Table 5.2.2.2.1-2 of said specification). It should be noted that RU 2811989 also discloses advanced technologies for implementing DL precoding.

[0071] The more detailed description of the operations performed according to actions 1-3 of Fig. 1, by which subsequent A-BF according to 5G NR is performed at the base station side, is provided hereinbelow with reference to Fig. 2.

[0072] As discussed above with reference to Fig. 1, the base station broadcasts SS / PBCH block resources (SSBs) in all or some of the analog beams, where the base station uses one corresponding predefined analog beam for transmitting each SSB (action 1). The user equipment measures RSRP of each SSB, selects a predefined numberMof SSBs with larger RSRPs, i.e.Mbest SSBs, and generates a report indicating SSB-RIs of the selected SSBs and information about RSRPs corresponding to the selected SSBs (action 2).

[0073] Mis a natural number that is typically preconfigured by the base station for the user equipment and accordingly presignaled by the base station to the user equipment, for example, by means of Radio Resource Control (RRC) signaling. By means of the parameterM, the base station substantially indicates to the user equipment what required number of its best SSBs (i.e. analog beams) the user equipment is to signal to the base station in the report. In particular,Mcan take values 1, 2, 4, ....

[0074] SSB-RIs are indicated in the report by means of bit values of a preset length. The approach according to 5G NR by which corresponding RSRPs for SSB-RIs are signaled in the report is described hereinbelow.

[0075] 5G NR uses the quantization-based implementation for reporting RSRPs. In particular, a set of ranges of absolute receive power values is preset in respective units, and a unique index value is assigned to each range. This configuration is summarized in the illustrative Table 1 below.

[0076]

[0077]

[0078] Table 1

[0079] In Table 1, the right column indicates the unit for receive power of synchronization signals (SS-RSRP), namely dBm; the middle column lists ranges of absolute values of synchronization signal receive powers, also in dBm; the left column lists index values each uniquely identifying a respective range of power absolute values. For example, if a measured RSRP value for one of best SSBs is -31.3 dBm, then, according to Table 1, the index RSRP125 corresponding to the range [-32; -31] is indicated in the report.

[0080] In addition, 5G NR uses the differential approach which is also based on the quantized representation. An SSB having the largest RSRP corresponding thereto is determined among theMbest SSBs, and a respective index from the table of receive power absolute values (for example, RSRP_iaccording to Table 1 above) is indicated in the report along with the SSB-RI for said SSB, the respective index indicating a range of receive power absolute values that said largest RSRP belongs to. A respective index of the table of receive power relative values is indicated in the report for each of the other (M-1) SSB-RIs, the respective index indicating a range of receive power values, relative to said largest highest RSRP, that RSRP of said SSB-RI belongs to. Such a table is illustrated below by Table 2.

[0081]

[0082] Table 2

[0083] In Table 2, the middle column lists ranges of the difference of respective RSRP values with respect to the largest RSRP, and the unit of these difference, relative values RSRP, as indicated by the right column of Table 2, is dB; the left column lists index values each uniquely identifying a respective range of relative power values.

[0084] For each of said remaining (M-1) SSBs, an index DIFFRSRP_j,j={0, 1, ..., 15}, is indicated in the report for a respective range of relative receive power values according to Table 2. In a typical implementation of the considered approach, theMSSB-RIs are arranged in the report in descending order of respective measured RSRPs. That is, an SSB-RI with the largest RSRP and an index RSRP_iof a respective range of absolute receive power values are indicated first, and then, in descending order of respective difference values RSRP, SSB-RIs of the remaining (M-1) SSBs with indices DIFFRSRP_jof respective ranges of relative receive power values are indicated.

[0085] Then, the user equipment performs UL transmission of the generated report to the base station over physical layer (L1) channels (action 3 of Fig. 1). This report may be referred to hereinafter as "L1-RSRP report", and a receive power of an SSB may be accordingly referred to as "L1-RSRP".

[0086] The aspects of generating and transmitting the L1-RSRP report according to 5G NR are reflected in specification TS 38.133; in particular, Tables 1 and 2, given above as an illustration, basically correspond to similar tables given in TS 38.133 (see Section 10.1.6). This specification is incorporated in the present application by reference in its entirety.

[0087] Next, the aspect relating to implementation of DL H-BF according to 5G NR is described hereinafter with reference to Fig. 3, said aspect referring to implementation of a respective constraint in a scheduler of the base station. As known, the main purpose of the base station scheduler is, in general, to decide which user equipment(s) to serve in a particular time resource (e.g. slot).

[0088] For illustration purposes, in the leftmost diagram of Fig. 3, the hexagon pictorially shows a cell sector which is served by a base station and in which a plurality of user equipments are located; the base station itself is assumed to be located in the hexagon vertex, which is encircled in the diagram, and configured to use, in general, several analog beams for DL transmission. As discussed above with reference to Figs. 1 and 2, respective A-BF is applied to CSI-RSs transmitted from the base station to the user equipments, i.e. the CSI-RS transmission to each of the user equipments is performed in one or more of the several analog beams.

[0089] In the case considered in Fig. 3, it is assumed that the base station currently intends to use only one analog beam from the illustrative number of usable analog beams (equal to three) to serve the user equipments; and this beam will be symbolically referred to as the first beam. Based on results of measuring L1-RSRPs of respective SSBs, the first analog beam will be the best one for one user equipments in the sector (i.e., among the three analog beams, the largest measured RSRP will correspond to the SSB of this first beam), and these user equipments are denoted by triangles in Fig. 3. For other user equipments, the first beam will be the second best (i.e., among the three analog beams, the second largest RSRP will correspond to the SSB of the first beam), and these user equipments are denoted by circles in Fig. 3. Finally, for the remaining user equipments in the sector, the first beam will be the third best (i.e., among the three usable analog beams, the third highest RSRP will correspond to the SSB of the first beam), and these user equipments are denoted by squares in Fig. 3.

[0090] A parameterKis used in the base station to configure the scheduler restriction, said parameter substantially indicating a number of analog beams for which the base station should have the feedback in the form of CSI from user equipments in the served sector, and, accordingly, scheduling of DL transmission can be performed for said user equipments.

[0091] In the context of discussing the second left drawing in Fig. 3, it is assumed that the parameterKequal to 1 is preconfigured in the base station. In this case, the base station scheduler will schedule resources for DL transmission only to those user equipments for which the first analog beam is the best; accordingly, CSI (including at least RI, PMI, CQI) from these user equipments is to be available in the base station. The case withK=1 corresponds to the strongest scheduler restriction; this case is illustrated in the drawing under consideration by presence of triangles only, i.e. those user equipments for which the first beam is the best one. Such user equipments, as shown in Fig. 3 in accordance with the current scheduler restriction, will be symbolically referred to as "served" in the description of this figure; the other user equipments, which are not shown in Fig. 3 in accordance with the current scheduler restriction, will be symbolically referred to as "unserved" in this description. It can be seen from the illustration of the considered drawing that the served user equipments for which resource scheduling will be performed are concentrated basically in the area of the sector to the left of the base station, said area corresponding to the coverage area provided by the first beam.

[0092] The user equipments are informed about said preconfigured restriction by means of a CSI request transmitted by the base station in DCI (see action 6 in Fig. 1). To this end, the base station sets a respective bit field in the DCI CSI request with respect to identifiers of the CSI-RSs for which the served user equipments (i.e., in this case, the user equipments for which the first beam is the best one) should perform the estimation to transmit the feedback to the base station in the form of the required CSI. It should be emphasized that the identifiers are implied herein by which CSI-RS resources are uniquely identified in the 5G NR communication system; hereinafter, such identifiers may be referred to as "absolute CSI-RS indices".

[0093] Then, in the context of discussing the second right drawing the in Fig. 3, let us suppose that the parameterKequal to 2 is preconfigured in the base station. In this case, the scheduler will schedule resources only for user equipments for which the first beam is either the best or the second best; accordingly, CSI reported from such user equipments should be available in the base station. The case withK=2 corresponds to a moderate scheduler restriction; this case is illustrated in the drawing under consideration by presence in the sector of triangles and circles only, i.e. the served user equipments for which the first beam is the best and second best; the other user equipments are not shown as unserved in accordance with the current moderate scheduler restriction. Accordingly, for this restriction option, the base station will set the bit field in the CSI request different from the case withK=1.

[0094] Finally, in the context of discussing the rightmost drawing in Fig. 3, it is assumed that the parameterKequal to 3 is preconfigured in the base station. In this case, CSI from all the user equipments in the sector can be available in the base station. The case withK=3 corresponds to the absence of a restriction in the base station scheduler, which is illustrated in the drawing under consideration by the presence of triangles, circles, and squares. In other words, DL transmissions (e.g. PDSCH) can be scheduled by the scheduler for any of the user equipments in the sector, regardless of the fact that the base station intends to use only the first beam, and, therefore, all the user equipments in the sector can be considered as served ones in the above sense. Accordingly, for the case under consideration, the base station will set the bit field in the CSI request differently from those for the cases withK=1 andK=2 discussed above.

[0095] Thus, the arrows in Fig. 3 indicate the direction of relaxation of the base station scheduler restriction.

[0096] Accordingly, the more channel information is reported by user equipments to the base station, the more flexibility the scheduler has in terms of scheduling PDSCH transmissions to a greater number of user equipments. Therefore, CSI should be provided for multiple analog beams (K> 1) in order to relax the abovementioned restriction imposed on the base station scheduler in the context of H-BF.

[0097] Fig. 4 schematically shows the implementation of H-BF according to 5G NR over time; in this figure, the time axis is assumed to be directed from left to right, the upper horizontal dashed line relates to a base station, the lower horizontal dashed line relates to a user equipment, transmissions from the base station to the user equipment are shown by downward vertical arrows, and transmissions from the user equipment to the base station are accordingly shown by upward vertical arrows.

[0098] In the illustrative case described with reference to Fig. 4, the base station is assumed to generally use seven analog beams to serve user equipments in the sector. The left part of Fig. 4 shows transmission by the base station of CSI-RSs CSI-RS0to CSI-RS6to the user equipments by using the respective seven analog beams. As repeatedly noted above, respective A-BF is applied to the CSI-RSs transmitted from the base station to the user equipments. In this case, signals CSI-RS3, CSI-RS4, CSI-RS6are transmitted to the considered user equipment in the analog beams, as indicated by thick arrows, which could have been previously selected by the user equipment based on measurements of L1-RSRPs of respective SSBs and reported to the base station in the L1-RSRP report, as described above with reference to Figs. 1, 2. The three analog beams mentioned are also respectively shown with solid contours among the contours which pictorially show the seven analog beams usable by the base station. CSI-RS3, CSI-RS4, CSI-RS6are currently considered to be the so-called "active" CSI-RSs for the user equipment.

[0099] The user equipment then transmits, to the base station, CSI generated by the user equipment by using the estimation of the received active CSI-RS3, CSI-RS4, CSI-RS6, which corresponds to actions 5-8 of Fig. 1. The base station processes the CSI received from the user equipment and transmits PDSCH to the user equipment based on, in particular, the MCS selected and the DL precoding performed based on the results of this processing (steps 9, 10 of Fig. 1).

[0100] Next, it is assumed that the user equipment has moved to a new location within the sector.

[0101] As noted earlier, the base station transmits, in each of the analog beams, corresponding SS / PBCH resource blocks which are denoted in Fig. 4 as SSB0-SSB6in the vertical arrows directed downwards. The user equipment performs measurements with respect to the received SSB0-SSB6and generates the L1-RSRP report indicating SSB-RIs of three selected best SSBs with L1-RSRP values corresponding thereto (i.e. the preconfigured value ofMis equal to 3 according to the description of Fig. 2), and transmits the generated L1-RSRP report to the base station (actions 1-3 of Fig. 1). It is assumed that the three best beams corresponding to the selected SSBs are different from the analog beams that were the best ones for the user equipment before the said movement (see left side of Fig. 4).

[0102] The base station processes the L1-RSRP report received from the user equipment. Based on the results of this processing, the base station determines that the new active CSI-RSs for the user equipment are CSI-RS0, CSI-RS1, CSI-RS3. The base station is reconfigured to receive, from the user equipment, CSI with respect to CSI-RS0, CSI-RS1, CSI-RS3, and also transmits to the user equipment the RRC reconfiguration message (RRC reconfig) indicating said three new active CSI-RSs for which the user equipment is to perform the estimation now. The respective switch to the subsequent estimation of the CSI-RSs indicated in the RRC reconfiguration message is performed in the user equipment.

[0103] The right part of Fig. 4, similarly to the left part thereof, shows transmission, by the base station, of CSI-RSs CSI-RS0to CSI-RS6to user equipments by using the respective seven analog beams. In this case, the signals CSI-RS0, CSI-RS1, CSI-RS3are transmitted to the considered user equipment in the analog beams, as indicated by thick arrows, which were reported to the base station in the recent L1-RSRP report (action 4 of Fig. 1). Said three analog beams are also shown by solid contours among the contours of the seven analog beams usable by the base station.

[0104] Thereafter, in a similar manner, the user equipment transmits, to the base station, CSI generated by using the estimation of received CSI-RS0, CSI-RS1, CSI-RS3which are now active, and the base station processes the CSI received from the user equipment and, accordingly, performs PDSCH transmission with applied D-BF (actions 5-10 of Fig. 1).

[0105] Although the approach to performing H-BF, as described above with reference to Figs. 1-4, is operational in 5G NR wireless communication systems, nevertheless, increased signaling overhead and higher implementation complexity at the base station side are associated with usage of RRC signaling, which is L3 signaling, for reconfiguring the user equipment to new active CSI-RSs.

[0106] 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.

[0107] In particular, for the 6G operating range of 8-13 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, by supporting, in particular, up to 64 simultaneously transmitted spatial MIMO layers in UPPER MID BAND communication systems, the concept of radio interface with extremely large antenna array (xMIMO) will be rendered 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.

[0108] At the same time, approaches used in 5G NR may not be always directly extended to next generation communication systems. In particular, the abovementioned problem in implementing H-BF, which is in the increased signaling overhead and high implementation complexity at the base station side, may become noticeably more significant in 6G wireless communication systems.

[0109] Fig.5 shows a general view of a wireless communication system, in which various aspects of the present invention can be implemented. As shown in Fig.5, user equipments (UE) 501 communicate with base station (BS) 502 in a radio access network (RAN) 500. UE 501 (e.g. UE 501-1, 501-2, 501-3, ...) are distributed over the RAN 500, and each of the UEs 501 can be fixed or mobile. Broadly known examples of UEs are smartphones, tablets, modems, etc.

[0110] The base stations 502 (e.g. BSs 502-A, 502-B, 502-C) can provide coverage for a specific geographic area commonly referred to as 'cell'. The base stations 502 basically have fixed structure, but they can have mobile implementation as well. In general, the base stations can represent macro-BSs (as illustrated by the BSs 502-A, 502-B, 502-C in Fig.5), as well as pico-BSs for pico-cells or femto-BSs for femto-cells. Cells in turn can be divided into sectors.

[0111] Coordination and management of operating the base stations 502 can be provided by a network controller which is in communication therewith (for instance, via a backhaul connection). The RAN 500 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 502 in the RAN 500 can also connect to each other, for instance, via a direct physical connection, which is preferably a high-speed connection.

[0112] When a user equipment is moving within the RAN 500, handover of the user equipment from one BS to another BS can be performed. For example, the UE 501-3 can be handed over from the BS 502-B to the BS 502-A. While performing this, respective communication systems 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.

[0113] In the considered wireless communication system, interaction is possible between a user equipment and a group of interconnected base stations, and such interaction can occur not only in the case of handing over the user equipment. One base station of the group of base stations is a serving base station for the user equipment, and various aspects of coordinating joint operation of the base stations of the group during such interaction can be performed in a centralized way (e.g. by the network controller) and / or by the serving base station.

[0114] The concept of Cloud RAN (C-RAN) implemented in the 5G NR wireless communication system, where said concept is in dividing a base station into three parts and using a special interface defined for information exchange between these functional parts. In particular, the base station can be divided into a radio unit (RU) which performs radio transceiver functions, a distributed unit (DU) for L1 (physical layer) computations and L2 (MAC layer) computations, and a centralized unit (CU) for L2 and L3 (RRC layer) computations. Such a division enables to centralize CU units in a respective central network node, while DUs can be distributed to a greater extent, at cell nodes. In this case, switching of connections between cell sites can be performed at L1 layer, i.e. with relatively low latency. Support for this concept is also expected in 6G wireless communication networks.

[0115] It should be noticed that the description according to Fig.5 and the figure itself have exclusively illustrative, non-limiting nature with the aim of outlining the general operation environment of the present invention. Though only known basic components of the communication system are illustrated in Fig.5, it should be appreciated that the communication system can further include plural other elements.

[0116] Each of the BSs 502 shown in Fig.5 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.

[0117] In a similar way, each of the UEs 501 shown in Fig.5 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.

[0118] 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.

[0119] The hardware and software elements of base stations and user equipments, as listed above, are configured to enable performing, in the base stations and user equipments, the methods according to the present application which are described hereinbelow. Implementation itself of the component hardware means of the base stations and user equipments and specific configuring thereof, including by respective logical means, is 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 plural separate elements or in one or more integral elements, as defined by design structural characteristics.

[0120] The technical problem, which is addressed by the present invention and relates to minimizing the usage of RRC signaling to reconfigure a user equipment to new active CSI-RSs during DL beamforming (see the description of Figs. 1, 2, 4 above for reference), is solved based on automation of execution of such reconfiguring in a base station(s) and in the user equipment, as the basic implementation.

[0121] This automation is underlain by initially preconfiguring, in the base station, an association between SS / PBCH resources and CSI-RS resources. According to an embodiment of the present invention, this association is represented by means of a table in which SS / PBCH resource identifiers and CSI-RS resource identifiers are in correspondence. As an illustration, such tabular representation of the preconfigured association is presented in Table 3 below, where rIDidenotes an identifier of a respective resource,i=1, 2, ...,N, whereNis a natural number:

[0122]

[0123] Table 3

[0124] It should be reminded herein that each SSB corresponds to one of spatial beams that can be used by the base station to perform DL transmission, and CSI-RSs inform about CSI-RS ports of the base station antenna array. Accordingly, the parameterN, which denotes the total number of associated elements in the table, is determined by the configuration of the spatial beams / antenna ports in the base station. This table does not imply that each rID of a SS / PBCH reference signal in the left column of the table and each rID of a CSI-RS reference signal in the right column of the table are unique identifiers - in particular (but not necessarily), according to the preconfigured association, several different SS / PBCH rIDs may correspond to one CSI-RS rID. That is, in the considered case,i= 1, 2, ...,Nshould be preferably interpreted, without limitation, as a sequence number of an element of the association table. CSI-RS identifiers mentioned in the discussion of Fig. 3 can be used as CSI-RS rIDs.

[0125] The preconfigured association is transmitted by the base station to the user equipment. This transmission is preferably performed by RRC signaling.

[0126] The scenario of preconfiguring the SSB-CSI-RS association between one base station and the user equipment has been considered above. At the same time, as noted above in the discussion of Fig. 5, interaction between a user equipment and a group of interconnected base stations is possible in a wireless communication system. This case is illustrated in Fig. 6, which shows a group of three base stations that are implied to be interconnected by a high-speed link. As should be known to a skilled in artisan, each base station in the wireless communication system has a unique cell / sector identifier associated therewith, denoted as PCID. For each of the base stations of the group shown in Fig. 6, the PCID associated therewith is given in this figure: PCID 1, PCID 2, PCID 3, respectively. The user equipment, while receiving signals from different base stations of the considered group, nevertheless knows which base station the transmission is received from, due to the presence of a respective PCID in the transmission. Since, as shown in Fig. 6, the user equipment is within (although near the boundary of) the coverage area of the base station with PCID 1, this base station will be considered as a serving base station for the user equipment. The NW-Ctrl block in Fig. 6 denotes the network controller (see the discussion of Fig. 5 above).

[0127] In the considered scenario, the preconfiguring of the association between SS / PBCH resources and CSI-RS resources according to the present invention is performed in the serving base station with PCID 1. The preconfigured association for the considered scenario associates SS / PBCH reference signals, identification information of the base stations of the group, and CSI-RS reference signals. A tabular representation of the preconfigured association for the scenario with the group of base stations is illustrated below in Table 4, similarly to Table 3:

[0128]

[0129] Table 4

[0130] As in the case of Table 3, according to the preconfigured association of Table 4, several different PCIDs and / or several different SS / PBCH rIDs can correspond to one CSI-RS rID.

[0131] The preconfigured association is transmitted by the serving base station to the user equipment. In addition, the preconfigured association is also signaled to each of the base stations with PCID 2 and PCID 3. This signaling can be performed directly by the serving base station, or this signaling can be performed through the network controller - this aspect does not impose limitations onto the present invention.

[0132] Next, without limitation, interaction between one base station and a user equipment in DL beamforming according to an embodiment of the present invention for DL data transmission will be considered in detail. Fig. 1 will be used as an illustration of the general scheme of such interaction. Hereinafter, with reference to Fig. 7 whose format is similar to Fig. 4, performing, over time, of DL beamforming according to an embodiment of the present invention is schematically shown. In parallel, with reference to Fig. 8 whose format is similar to Fig. 2, the detailed description of operations performed according to actions 1-3 of Fig. 1, by which the subsequent performing of A-BF in the base station is provided according to this embodiment of the present invention, is given. It is assumed hereby that the SSB - CSI-RS association is preconfigured in the base station (see e.g. Table 3 above), and this preconfigured association is transmitted to the user equipment in advance (said transmission is denoted by the vertical arrow in the left part of Fig. 7 and by the horizontal arrow in the upper part of Fig. 8). That is, according to the considered embodiment, the presence of Table 3 in the base station and in the user equipment of Figs. 7, 8 is initially assumed.

[0133] The left part of Fig. 7, similarly to Fig. 4, shows transmission, by the base station, of CSI-RSs CSI-RS0- CSI-RS6to user equipments by using the respective seven analog beams. As noted earlier, the mention of spatial beams as "analog beams" in the context of H-BF indicates, for the sake of clarity, that digital DL precoding has not been applied yet to signals transmitted therein; however, said mention does not imply anyhow that no other digital processing can be performed with respect to said spatial beams. This aspect does not impose a limitation onto the present invention.

[0134] Respective A-BF is applied to the CSI-RSs transmitted from the base station to the user equipments. In this case, signals CSI-RS3, CSI-RS4, CSI-RS6are transmitted to the considered user equipment in the analog beams indicated by thick arrows. Said three analog beams are also shown by solid contours among the contours pictorially showing the seven analog beams usable by the base station. As noted in the description of Fig. 4, CSI-RS3, CSI-RS4, CSI-RS6are currently considered as active CSI-RSs for the user equipment.

[0135] Then, upon reception of a CSI request from the base station (not shown in the considered part of Fig. 7), the user equipment transmits, to the base station, CSI generated by using the estimation of the received active CSI-RS3, CSI-RS4, CSI-RS6. The base station processes the CSI received from the user equipment and transmits PDSCH to the user equipment based, in particular, on the MCS selected and the DL precoding performed based on results of this processing.

[0136] Next, it is assumed that the user equipment has moved to a new location within the sector.

[0137] In accordance with the aforesaid, the base station periodically broadcasts SS / PBCH resource blocks (SSBs) in all or some of the analog beams, where the base station uses one corresponding predefined analog beam for transmitting each SSB. Similarly to Fig. 4, the broadcasted SS / PBCH resource blocks are designated in Fig. 7 as SSB0-SSB6in the vertical downward arrows.

[0138] The user equipment measures L1-RSRP of each of the received SSB0-SSB6, selects a predefined numberMof SSBs with larger L1-RSRPs, i.e.Mbest SSBs, and generates a report indicating the SSB-RIs of the selected SSBs and information about L1-RSRPs corresponding to the selected SSBs. As noted earlier,Mis typically preconfigured by the base station for the user equipment and accordingly presignaled by the base station to the user equipment. According to the description of Fig. 7, the preconfigured value ofMis 3. Next, the user equipment performs UL transmission of the generated report to the base station, wherein the SSB-RIs of the three selected best SSBs with the L1-RSRP values corresponding thereto are indicated.

[0139] Unlike 5G NR, where the L1-RSRP report is transmitted, according to a preferred embodiment of the present invention, said report about the best SSBs is transmitted to the base station in the form of a medium access control (MAC) control element (CE), i.e., according to the present invention, this transmission is performed by means of L2 signaling rather than L1 signaling, as in the case of 5G NR. Hereinafter, such an L2 report according to the present invention may be referred to as a "MAC CE report" without limitation. The aspect of why namely the L2 message is used according to the present invention to transmit the report on measurements will be explained below.

[0140] According to one implementation of the present invention, for the case considered with reference to Figs. 7 and 8, the MAC CE report may have the following form illustrated by Table 5:

[0141]

[0142] Table 5

[0143] In Table 5, kmis a bit value of a reported SS / PBCH (SSB-RI) resource index for a corresponding selected best SSB, where m, in general, is equal to 0, 1, ...,M- 1, and in this particular case m = 0, 1, 2. The 5G NR quantization-based approach described above with reference to Tables 1 and 2 can be used to report respective measured L1-RSRPs in the MAC CE report. In the considered case, it is assumed that the SSB with SSB-RI k0corresponds to the largest value of L1-RSRP, and for this SSB-RI a respective absolute value of L1-RSRP (abs. L1-RSRP in Table 5) is indicated in the MAC CE report. This absolute value can be indicated by an index RSRP_i,i={0, 1, ..., 126}, from Table 1 for a respective range of receive power absolute values.

[0144] The values of respective measured L1-RSRPs for the other two SSBs among the three best SSBs, in particular, for the SSBs with SSB-RI k1and SSB-RI k2, are indicated in the MAC CE report in the differential way, relative to the abs. L1-RSRP for SSB-RI k0. Each of the relative values L1-RSRP1, L1-RSRP2for said other two SSB-RI k1, SSB-RI k2can be indicated by an index DIFFRSRP_j,j={0, 1, ..., 15}, from Table 2 for a respective range of receive power relative values. It is implied in Table 5 that L1-RSRP1> L1-RSRP2; i.e., according to this embodiment, for the three best SSBs selected by the user equipment, the reported SSB-RIs km, m=0, 1, 2, are arranged in the MAC CE report in descending order of the respective reported L1-RSRPs.

[0145] According to another embodiment of the present invention, for the case considered with reference to Figs. 7 and 8, the MAC CE report can have the following form illustrated by Table 6:

[0146]

[0147] Table 6

[0148] According to this embodiment, in Table 6, for each of theM=3 SSB-RIs km, m = 0, 1, 2, a respective absolute value L1-RSRPmof the measured receive power is indicated. Each of these absolute values can again be indicated by a respective index RSRP_ifrom Table 1.

[0149] The base station receives the MAC CE report from the user equipment. It is assumed that the MAC CE report is correctly received by the base station, and the base station performs processing of the received MAC CE report.

[0150] In the illustrative case considered with reference to Figs. 7 and 8, it is assumed that the three best beams corresponding to the selected SSBs reported in the MAC CE report (see, for example, Tables 5 and 6) are different from the analog beams that were the best for the user equipment before said movement (see the left part of Fig. 7). Accordingly, based on the results of said processing, the base station determines that the new active CSI-RSs for the user equipment are CSI-RS0, CSI-RS1, and CSI-RS3.

[0151] In modern wireless communication systems, including 5G NR, for any L2 message transmitted from a user equipment, a responsive communication from a base station is implied, the communication being identifiable by the user equipment as an acknowledgement of said transmission. Therefore, in the considered embodiment, the base station acknowledges the correct reception of the MAC CE report by sending, to the user equipment, some control information that will be unambiguously identified by the user equipment as a positive acknowledgement (ACK) for the transmitted MAC CE report (see Fig. 8). According to a preferred embodiment, such control information is DCI with an uplink (UL) grant (e.g. of PUSCH) to the user equipment. As an option, such DCI with the UL grant in the considered case can be without data, i.e. substantially virtual. In this preferred embodiment, the ACK of the reception of the MAC CE report is indicated for the user equipment by the DCI having the same HARQ ID as the transmitted MAC CE report and by the new data indicator (NDI) in the DCI respectively toggled to a preset bit value. The aspects related to implementation of the hybrid automatic repeat request (HARQ) procedure are disclosed in specification TS 38.213.

[0152] Hereinafter, without limitation, such control information (DCI) identifiable as the ACK for the MAC CE report, may be referred to simply as "ACK" for brevity.

[0153] Immediately upon the ACK has been transmitted to the user equipment, the base station starts a first timer of a predefined duration. Hereinafter, for the sake of clarity, timers used in the base station will be referred to as "BS timers". Upon reception of the ACK from the base station, a first timer of the same predefined duration is started in the user equipment, with account of round-trip time. Hereinafter, for the sake clarity, timers used in the user equipment will be referred to as "UE timers."

[0154] Upon expiration of the first predefined duration of the UE timer, the user equipment, based on the preconfigured SSB - CSI-RS association (see Table 3), performs automatic switching to subsequent estimation of the new active CSI-RSs, namely CSI-RS0, CSI-RS1, CSI-RS3. Upon expiration of said predefined duration of the BS timer, the base station, based on the same preconfigured association, performs, for the user equipment, automatic reconfiguring of CSI-RS0, CSI-RS1, CSI-RS3as CSI-RSs to be used by the user equipment for the estimation. That is, the base station is automatically reconfigured to receive, from the user equipment, CSI with respect to CSI-RS0, CSI-RS1, CSI-RS3. Said predefined duration of the BS timer and the UE timer is designated in Figs. 7 and 8 as T1. Accordingly, T1 can be preconfigured in the base station and presignaled to the user equipment, for example, by means of RRC signaling.

[0155] It should be emphasized herein that the reconfiguring to the new active CSI-RSs in the base station and the user equipment is performed autonomously according to the present invention, i.e. without transmitting the RRC reconfiguration message, as in the case of 5G NR. As follows from the aforesaid, the usage of the ACK is essential to consistently perform such autonomous automatic reconfiguration. Accordingly, if the L1-RSRP report, as in 5G NR, were used instead of the MAC CE report according to the present invention, such usage could significantly reduce robustness of the communication system, since no default acknowledgement is provided for such an L1 report message; accordingly, incorrect reception of the L1-RSRP report by the base station in the considered embodiment of the present invention could lead to the user equipment switching to new active CSI-RSs, assuming that the base station would do the same, but the base station, due to the incorrect reception, would still be waiting for reception, from the user equipment, of CSI with respect to the previous active CSI-RSs.

[0156] The right part of Fig. 7, similarly to the left part thereof, shows transmission, by the base station, of CSI-RSs CSI-RS0- CSI-RS6to user equipments by using the respective seven analog beams. In this case, the transmission of the signals CSI-RS0, CSI-RS1, CSI-RS3is performed to the considered user equipment in the analog beams, as indicated by thick arrows, which were reported to the base station in the recent MAC CE report. Said three analog beams are also respectively shown by solid contours among the contours of the seven analog beams usable by the base station.

[0157] Hereinafter, in a similar manner, upon reception, from the base station, of a CSI request the user equipment transmits, to the base station, CSI generated by using the estimation of the received CSI-RS0, CSI-RS1, CSI-RS3which are now active, and the base station performs processing of the CSI received from the user equipment and accordingly performs PDSCH transmission with the applied D-BF scheme.

[0158] An embodiment of the present invention is described below that relates to implementation of the CSI request which, as mentioned earlier, is transmitted by the base station by means of DCI.

[0159] The approach corresponding to this embodiment is in implementing the CSI request in such a way that it comprises an indication of a set of CSI-RSs with respect to which the user equipment is to actually perform the estimation in order to generate the CSI, specifically among active CSI-RSs, i.e. CSI-RSs corresponding to SSB-RIs included by the MAC CE report from the user equipment, according to the disclosure of Fig. 7 and 8 above.

[0160] As in the case of 5G NR, in the considered embodiment, said indication is encoded by a respective bit field in the DCI. However, unlike 5G NR, according to this embodiment of the present invention, a respective code table, which is illustrated below by Table 7, is preconfigured in the base station:

[0161]

[0162] Table 7

[0163] The ellipsis before two digits in the left column of Table 7 indicates that a bit field encoding a particular set of active CSI-RSs may have different lengths depending on implementation. In Table 7, each bit field value (except for the one encoding "CSI is not requested") corresponds to a predefined combination ofKCSI-RS indices, from 1 toM, and this corresponding combination defines a set of CSI-RSs indicated by said value. The CSI-RS indices can be denoted as , where = 1, 2, ...,M. According to a preferred embodiment, the first CSI-RS index corresponds to the SSB-RI that identifies the best SSB (i.e. the SSB with the largest L1-RSRP) and that was reported in the MAC CE report; the second CSI-RS index corresponds to the reported SSB-RI identifying the second best SSB (i.e. the SSB with the second largest L1-RSRP); the third CSI-RS index corresponds to the reported SSB-RI identifying the third best SSB; and so on. Accordingly, such CSI-RS indices used in the considered embodiment of the present invention may hereinafter be referred to as "relative CSI-RS indexes."

[0164] The code table preconfigured in the base station is presignaled from the base station to the user equipment by RRC signaling.

[0165] Tables 8, 9 below provide exemplary implementations of the code table, as generally illustrated by Table 7, for the case ofM=3 (which corresponds to the above disclosure of Fig. 7, 8), where the DCI bit field (the left column of Table 7) has length 2 and length 3, respectively.

[0166]

[0167] Table 8

[0168]

[0169] Table 9

[0170] Thus, the base station, at its discretion (for example, depending on the current network load), selects a bit field value in the code table, and this value is signaled to the user equipment in the DCI CSI request. Based on the value of the bit field comprised in the received CSI request, the user equipment determines, from its code table, CSI-RSs among the active CSI-RSs with respect to which the user equipment is to actually perform the estimation to generate the CSI. In particular, in this way, the user equipment can be notified of the base station scheduler restriction discussed above with reference to Fig. 3.

[0171] For example, for the embodiment disclosed above with reference to Fig. 7, 8 according to which the CSI transmitted from the user equipment to the base station in reply to the CSI request was generated based on the estimation of CSI-RS0, CSI-RS1, CSI-RS3, i.e. all of the active CSI-RSs, it can be assumed that the CSI request accordingly transmitted from the base station comprised the bit value "11" for the case of preconfiguring the code table in the form of Table 8 or the bit value "111" for the case of preconfiguring the code table in the form of Table 9.

[0172] The proposed embodiment of the present invention further provides more flexible and compact encoding of sets of CSI-RSs for which CSI is requested, as compared to 5G NR where the configuring of the bit field value is performed every time with respect to absolute CSI-RS indices, while in this embodiment, for each of the bit field values, a preset combination of relative CSI-RS indices is preconfigured only for active CSI-RSs.

[0173] The embodiment of the present invention has been described in detail above with reference to Fig. 7, 8 according to which the autonomous reconfiguring to new active CSI-RSs recommended by the user equipment is automatically carried out in the base station and in the user equipment. This embodiment is the basic one and corresponds to the general case.

[0174] Two alternative embodiments, which correspond to less general cases and according to which reconfiguring to CSI-RSs different from those recommended by the user equipment is performed, are discussed below with reference to Fig. 9.

[0175] In accordance with the first of the less general embodiments considered with reference to Fig. 9 (denoted as "Case a" in this figure), upon transmission of the MAC CE report, a second UE timer of a predefined duration is started in the user equipment, and, upon reception of the MAC CE report, a second BS timer of the predefined duration is started in the base station with account of the round-trip time. It is necessary to emphasize herein that the predefined duration of the second BS timer and the second UE timer is longer than the predefined duration of the first BS timer and the first UE timer which, in accordance with the description of Fig. 7 and 8, were respectively started upon transmitting / receiving the ACK. If, upon expiration of this predefined duration (designated as T2 in Fig. 9), the ACK from the base station is not received in the user equipment, the user equipment will continue to use for the estimation the CSI-RSs that were used directly prior to block "Measurements of L1-RSRP" in the considered part of Fig. 9. The base station will accordingly expect, from the user equipment, CSI with respect to the same previous CSI-RSs. As in the case with T1, T2 can be predefined in the base station and presignaled to the user equipment.

[0176] The considered embodiment provides the fallback for the case of the MAC CE report not received / incorrectly received by the base station, thereby enabling to avoid existence of different currently active CSI-RSs in the base station and in the user equipment.

[0177] In accordance with another of the less general embodiments considered with reference to Fig. 9 (designated as "Case b" in this figure), the base station applies the 5G NR approach described above for directly configuring for the user equipment the active CSI-RSs required to the base station. More specifically, despite correct reception of the MAC CE report, the base station transmits to the user equipment the RRC reconfiguration (RRC reconfig) message indicating one or more active CSI-RSs with respect to which the user equipment is to actually perform the estimation. The ACK in this case is of course not transmitted from the base station to the user equipment. As an option, these active CSI-RSs prescribed by the base station through RRC signaling can be the CSI-RSs that were used directly prior to block "Measurements of L1-RSRP" in the considered part of Fig. 9.

[0178] The embodiment b provides backward compatibility with 5G NR.

[0179] Next, the method 1000 of DL beamforming according to one embodiment of the present invention is described with reference to the flowchart of Fig. 10, where the respective interaction takes place between one base station, e.g. such as BS 502-A, 502-B, 502-C of Fig. 5, and a user equipment, e.g. such as UE 501-1, 501-2, ... of Fig. 5. This interaction has been described in detail above with reference to Figs. 1, 7, 8.

[0180] In step 1010, an association between synchronization signals in the form of SS / PBCH block resources (SSBs) and CSI-RS signals is preconfigured in the base station, and the preconfigured association is transmitted from the base station to the user equipment, preferably by means of RRC signaling. The illustrative representation of the preconfigured SSB - CSI-RS association for the considered embodiment is provided in Table 3.

[0181] In step 1020, corresponding SSBs are transmitted from the base station in at least some of the analog beams.

[0182] In step 1030, the user equipment performs measurements of received SSBs, selects one or more SSBs based on results of the measurement, and transmits to the base station, by means of L2 signaling, a report message about the one or more selected SSBs.

[0183] As described in detail above with reference to the embodiment of Figs. 7, 8, when performing the measurements of SSBs in step 1030, the user equipment measures receive power (L1-RSRP) of each SSB, selects the predefined numberMof SSBs with larger L1-RSRPs, and generates the L2 report message in the form of the MAC CE report comprising SSB-RI indices of the selected SSBs and an indication of respective L1-RSRP values for the selected SSBs. The illustrative representations of the MAC CE report are provided in Tables 5, 6. As noted above,Mis preferably preconfigured in the base station and presignaled to the user equipment, for example, by means of RRC signaling.

[0184] In step 1040, upon having received, from base station, control information identifiable by the user equipment as an ACK of reception of the MAC CE report, the user equipment, with account of the round-trip time, starts a first UE timer of a first predefined duration T1. As discussed above in the description of Figs. 7, 8, such control information is preferably DCI with an UL grant, wherein the ACK for the MAC CE report is indicated by the DCI having the same HARQ ID as the MAC CE report and by the NDI in the DCI toggled to a predefined value. Directly upon transmission such DCI to the user equipment, a first BS timer of the same predefined duration T1 has also been started in the base station.

[0185] In step 1050, upon expiration of T1, the user equipment, based on the preconfigured association, switches to subsequent estimation of CSI-RSs corresponding to the selected SSBs, and the base station, based on the preconfigured association, performs reconfiguring, for the user equipment, of the CSI-RSs corresponding to the selected SSBs as CSI-RSs to be used by the user equipment for the estimation. In other words, the autonomous consistent automatic reconfiguring of the base station and the user equipment to the new active CSI-RSs is carried out.

[0186] The alternative implementations of such reconfiguring, not associated with transmission / reception of the ACK, are described above with reference to Fig. 9.

[0187] In step 1060, the user equipment receives CSI-RSs from the base station.

[0188] In step 1070, upon having received, from the base station, a CSI request, CSI (includinginter aliaRI, PMI, CQI) is generated in the user equipment based on the estimation of the received CSI-RSs. As noted above with reference to Tables 7-9, said request preferably comprises an indication, among the active CSI-RSs corresponding to the SSB-RIs comprised in the MAC CE report, of a set of CSI-RSs with respect to which the user equipment is to actually perform the estimation to generate the CSI. In step 1080, the user equipment transmits the generated CSI to the base station.

[0189] In step 1090, the base station performs DL precoding based on the received CSI to perform DL transmission (e.g. PDSCH) to the user equipment.

[0190] In accordance with the detailed description of Figs. 7, 8, steps 1020-1090 of the method 1000 can be performed on a periodic basis.

[0191] Next, the method 1100 of DL beamforming according to another embodiment of the present invention is described provided with reference to the flowchart of Fig. 11, where the corresponding interaction takes place between a group of base stations of the wireless communication system (see Fig. 6) and a user equipment.

[0192] In step 1110, similarly to step 1010, an association between SSBs and CSI-RSs is preconfigured in one base station of the group, and the preconfigured association is transmitted from said base station to the user equipment. This one base station is preferably a serving base station for the user equipment. Also, in step 1110, the preconfigured SSB - CSI-RS association is signaled to each of the other base stations of the group. The illustrative representation of the preconfigured association for the considered embodiment is provided in Table 4.

[0193] In step 1120, corresponding SSBs are transmitted from the base stations of the group in at least some of the analog beams.

[0194] In step 1130, similarly to step 1030, the user equipment performs measurements of received SSBs, selects one or more SSBs based on results of the measurements, and transmits to the serving base station, by L2 signaling, a report message about the one or more selected SSBs.

[0195] When performing the measurements of SSBs in step 1130, the user equipment measures L1-RSRP of each SSB, selects the predefined numberMof SSBs with the larger L1-RSRPs, and generates the MAC CE report comprising SSB-RI indices of the selected SSBs, respective PCIDs of the base stations which said SSBs were transmitted from, and an indication of respective values of L1-RSRP for the selected SSBs. The exemplary representations of the MAC CE report for the considered embodiment are given in Tables 10 and 11 below:

[0196]

[0197] Table 10

[0198] In Table 10, similarly to Table 5, kmis a bit value of a reported SSB-RI, and Pmis a bit value of a reported PCID for a respective selected best SSB, where m is, in general, equal to 0, 1, ...,M-1, and in this particular case m = 0, 1, 2. For the case of Fig. 6, PCIDs are respectively selected from PCID 1, PCID 2, PCID 3. As in Table 5, Table 10 uses the 5G NR quantization-based approach to report respective measured L1-RSRPs in the MAC CE report.

[0199]

[0200] Table 11

[0201] Then, similarly to Table 6, in Table 11, for each of theM=3 SSB-RIs kmand PCIDs Pm, m = 0, 1, 2, a respective absolute value L1-RSRPmis indicated.

[0202] In step 1140, similarly to step 1040, upon having received, from the serving base station, control information identifiable as an ACK of reception of the MAC CE report (preferably, DCI with an UL grant, where the DCI has the same HARQ ID as the MAC CE report and the NDI in the DCI is toggled to a preset value), the user equipment, with account of the round-trip time, starts a first UE timer of a first predefined duration T1. Immediately upon transmission of such DCI to the user equipment, a first BS timer of the same predefined duration T1 has been also started in the serving base station.

[0203] In step 1150, similarly to step 1050, upon expiration of T1, the user equipment, based on the preconfigured association, switches to subsequent estimation of CSI-RSs corresponding to the selected SSBs, and the serving base station, based on the preconfigured association, performs reconfiguring, for the user equipment, of the CSI-RSs that correspond to the selected SSBs as CSI-RSs to be used by the user equipment for the estimation. This reconfiguring is also applied to at least some of the other base stations of the group. Thus, the autonomous consistent automatic reconfiguring of the base stations of the group and the user equipment to the new active CSI-RSs is carried out. The beams used to transmit the new active CSI-RSs to the user equipment are shadowed darker in Fig. 6 for the sake of illustration.

[0204] As noted earlier, the alternative implementations of such reconfiguring, not associated with transmitting / receiving the ACK, are disclosed above with reference to Fig. 9, where, in the considered embodiment, the serving base station acts as the base station mentioned in this disclosure.

[0205] In step 1160, the user equipment receives CSI-RSs from the base stations of the group.

[0206] In step 1170, similarly to step 1070, upon having received a CSI request from the serving base station, the user equipment generates CSI based on the estimation of received CSI-RSs. As noted above with reference to Tables 7-9, said request preferably comprises an indication, among the active CSI-RSs, of a set of CSI-RSs with respect to which the user equipment is to actually perform the estimation to generate the CSI. In step 1180, similarly to step 1080, the user equipment transmits the generated CSI to the serving base station to perform DL precoding at the network side.

[0207] Similarly to the method 1000, steps 1120-1180 of the method 1100 can be performed on a periodic basis.

[0208] As follows from the aforesaid, the present invention provides reduction in signaling overhead due to significantly decreased usage of high-level signaling (RRC) during DL beamforming and respective reduction in implementation complexity at the base station side.

[0209] It should also be understood 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.

Claims

1.A method performed by a terminal in a wireless communication system, the method comprising:receiving, from a base station, information on an association between SS(synchronization signal) / PBCH(physical broadcast channel) blocks (SSBs) and CSI(channel state information)-RSs(reference signals);receiving, from the base station, one or more SSBs;performing a measurement of the one or more SSBs;based on the measurement, identifying at least one SSB; andtransmitting, to the base station, a first message comprising information on the at least one SSB.2.The method of claim 1, further comprising:as a response to the first message, receiving, from the base station, a second message;starting a first timer with a first duration; andin case that the first timer is expired, based on the information on the association, performing switching to an estimation associated with at least one CSI-RS.3.The method of claim 1, further comprising:starting a second timer with a second duration; andin case that the second timer is expired and the terminal has not received a second message from the base station, using an estimation associated with a previous CSI-RS.4.The method of claim 1, further comprising:receiving, from the base station, information on at least one of a first timer or a second timer,wherein the first message comprises an MAC(medium access control) CE(control element).5.A method performed by a base station in a wireless communication system, the method comprising:transmitting, to a terminal, information on an association between SS(synchronization signal) / PBCH(physical broadcast channel) blocks (SSBs) and CSI(channel state information)-RSs(reference signals);transmitting, to the terminal, one or more SSBs; andreceiving, from the terminal, a first message comprising information on at least one SSB.6.The method of claim 5, further comprising:as a response to the first message, transmitting, to the terminal, a second message;starting a first timer with a first duration; andin case that the first timer is expired, based on the information on the association, performing a reconfiguration associated with at least one CSI-RS.7.The method of claim 5, further comprising:transmitting, to the terminal, information on at least one of a first timer or a second timer; andstarting a second timer with a second duration,wherein the first message comprises an MAC(medium access control) CE(control element).8.A terminal in a wireless communication system, the terminal comprising:a transceiver; andat least one processor coupled with the transceiver and configured to:receive, from a base station, information on an association between SS(synchronization signal) / PBCH(physical broadcast channel) blocks (SSBs) and CSI(channel state information)-RSs(reference signals),receive, from the base station, one or more SSBs,perform a measurement of the one or more SSBs,based on the measurement, identify at least one SSB, andtransmit, to the base station, a first message comprising information on the at least one SSB.9.The terminal of claim 8, wherein the at least one processor is further configured to:as a response to the first message, receive, from the base station, a second message,start a first timer with a first duration, andin case that the first timer is expired, based on the information on the association, perform switching to an estimation associated with at least one CSI-RS.10.The terminal of claim 8, wherein the at least one processor is further configured to:start a second timer with a second duration, andin case that the second timer is expired and the terminal has not received a second message from the base station, use an estimation associated with a previous CSI-RS.11.The terminal of claim 8, wherein the at least one processor is further configured to:receive, from the base station, information on at least one of a first timer or a second timer,wherein the first message comprises an MAC(medium access control) CE(control element).12.A base station in a wireless communication system, the base station comprising:a transceiver; andat least one processor coupled with the transceiver and configured to:transmit, to a terminal, information on an association between SS(synchronization signal) / PBCH(physical broadcast channel) blocks (SSBs) and CSI(channel state information)-RSs(reference signals),transmit, to the terminal, one or more SSBs, andreceive, from the terminal, a first message comprising information on at least one SSB.13.The base station of claim 12, wherein the at least one processor is further configured to:as a response to the first message, transmit, to the terminal, a second message,start a first timer with a first duration, andin case that the first timer is expired, based on the information on the association, perform a reconfiguration associated with at least one CSI-RS.14.The base station of claim 12, wherein the at least one processor is further configured to:transmit, to the terminal, information on at least one of a first timer or a second timer, andstart a second timer with a second duration.15.The base station of claim 12,wherein the first message comprises an MAC(medium access control) CE(control element).

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