Flexible adaptation of transmission power spectral density based on channel state information (CSI)

Abstract

The present disclosure relates to a 5G communication system or a 6G communication system for supporting higher data rates beyond a 4G communication system such as long term evolution (LTE). The present invention relates, in general, to wireless communications and, more particularly, to methods of obtaining and transmitting channel state information (CSI) and applying an energy-efficient (EE) mode for downlink (DL) data transmission with flexible adaptation of transmission power spectral density (PSD) based on the CSI, as well as to respective communication devices.

Description

FLEXIBLE ADAPTATION OF TRANSMISSION POWER SPECTRAL DENSITY BASED ON CHANNEL STATE INFORMATION (CSI)

[0001] The present invention relates, in general, to wireless communications and, more particularly, to methods of obtaining and transmitting channel state information (CSI) and applying an energy-efficient (EE) mode for downlink (DL) data transmission with flexible adaptation of transmission power spectral density (PSD) based on the CSI, as well as to respective communication devices.

[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 bit per second (bps) and a radio latency less than 100μsec, 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 (THz) band (for example, 95 gigahertz (GHz) 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 collision 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 mechanisms 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 drawbacks of the prior art discussed above, 6G xMIMO systems require new approaches to implementing EE modes of a base station with more flexible, dynamic PSD adaptation, without relying on a predefined set of PSD reduction values, as well as with lower computational complexity when calculating CSI at the side of a user equipment (which in the 5G NR approach substantially has to recalculate RI, PMI, CQI newly for each of configured powerOffset-r18's) and with lower overhead on UL transmission of the CSI report (i.e. the CSI report should be preferably made more compact). The main object of the present invention is to provide such an approach to implementing the EE modes.

[0008] In the context of addressing this technical object, according to the first aspect of the present invention A method of obtaining channel state information (CSI) in a wireless communication system. The method provided hereby comprises, in a user equipment: based on measurements of channel state information reference signals (CSI-RSs) transmitted from a base station (BS) of the wireless communication system, the measurements performed by the user equipment, determining a number of MIMO layers preferred for the user equipment, and selecting, from a predefined codebook, spatial beam vectors in a number corresponding to the preferred number of MIMO layers; calculating a primary channel quality indicator (CQI) by using the spatial beam vectors selected for the preferred number of MIMO layers, and calculating at least one additional channel quality indicator, each of the at least one additional channel quality indicator being calculated by using a respective part of the selected spatial beam vectors, wherein a number of spatial beam vectors in said part corresponds to a number of MIMO layers which is respectively less than the preferred number of MIMO layers; and generating CSI, wherein, at least, the preferred number of MIMO layers, indices of the selected spatial beam vectors, and the calculated channel quality indicators are included into the CSI.

[0009] The technical result achievable by the present invention relates, in general, to enabling to implement a EE mode(s) of the base station with flexible, dynamic adaptation of DL transmission PSD while minimizing the negative impact on the system performance, and also to reducing the computational complexity at the user equipment side when obtaining the CSI report and reducing the overhead on UL transmission of the CSI report for performing, by the base station, said flexible PSD adaptation.

[0010] Figure　1 is the illustration of interaction between a base station and a user equipment in the general context of obtaining and applying CSI according to 5G NR.

[0011] Figure　2 is the general illustration of approaches to reducing energy consumption of the base station according to 5G NR.

[0012] Figure　3 is the illustration of problems arising in implementation of an EE mode of the base station based on reducing PSD of a transmitted signal according to 5G NR.

[0013] Figure　4 is the illustration of configuring PSD reduction values for the user equipment according to 5G NR.

[0014] Figure　5 is the illustration of interaction between the base station and the user equipment in the context of adapting DL transmission PSD according to 5G NR.

[0015] Figure　6 is the illustrative diagram of a wireless communication system in which embodiments of the present invention can be implemented.

[0016] Figure　7 is the general illustration of usage of the approach to stretching an allocated frequency resource to compensate for losses due to reducing PSD of DL data transmission.

[0017] Figure　8 is the illustration of negative effects when directly applying the approach of stretching the allocated frequency resource to implement transition to a EE mode of the base station based on reducing PSD according to 5G NR.

[0018] Figure　9 is the general illustration of the aspect of the technical object of the present invention to develop a flexible approach to PSD adaptation.

[0019] Figure　10 is the illustrative representation of 5G NR Type　1 codebook.

[0020] Figure　11a, 11b are the illustrations of precoding matrices for RI = 1 and RI = 2, respectively.

[0021] Figure　12a, 12b are the illustrations of precoding matrices for RI = 3 and RI = 4, respectively.

[0022] Figure　13 is the flowchart of a method for obtaining a CSI report according to an embodiment of the present invention.

[0023] Figures　14a to 16 illustrate implementations of arrangement of the CSI report according to an embodiment of the present invention that relates to transmitting CSI via UCI.

[0024] Figure　17 illustrates an implementation of arrangement of the CSI report according to the present invention that relates to transmitting CSI via MAC CE.

[0025] Figure　18 is the flowchart of a method for flexibly adapting DL transmission PSD based on the CSI report, according to an embodiment of the present invention.

[0026] Figure　19a is the illustration of DL transmission PSD adaptation in the base station according to an embodiment of the present invention without the ability to change the precoding matrix.

[0027] Figure　19b is the illustration of DL transmission PSD adaptation in the base station according to an embodiment of the present invention with the ability to change the precoding matrix.

[0028] Figure　20 is the illustration of interaction between the base station and user equipment in the context of flexible adaptation of DL transmission PSD according to the present invention.

[0029] Figure　21 is a block diagram of a terminal or user equipment (UE) according to an embodiment of the disclosure.

[0030] Figure　22 is a block diagram of a base station (BS) according to an embodiment of the disclosure.

[0031] In the context of addressing this technical object, according to the first aspect of the present invention A method of obtaining channel state information (CSI) in a wireless communication system. The method provided hereby comprises, in a user equipment: based on measurements of channel state information reference signals (CSI-RSs) transmitted from a base station (BS) of the wireless communication system, the measurements performed by the user equipment, determining a number of MIMO layers preferred for the user equipment, and selecting, from a predefined codebook, spatial beam vectors in a number corresponding to the preferred number of MIMO layers; calculating a primary channel quality indicator (CQI) by using the spatial beam vectors selected for the preferred number of MIMO layers, and calculating at least one additional channel quality indicator, each of the at least one additional channel quality indicator being calculated by using a respective part of the selected spatial beam vectors, wherein a number of spatial beam vectors in said part corresponds to a number of MIMO layers which is respectively less than the preferred number of MIMO layers; and generating CSI, wherein, at least, the preferred number of MIMO layers, indices of the selected spatial beam vectors, and the calculated channel quality indicators are included into the CSI.

[0032] In accordance with an embodiment, the method provided herein further comprises: transmitting, by the user equipment, the CSI to the base station.

[0033] A spatial beam vector represents a Kronecker product of a Discrete Fourier Transform (DFT) vector by a DFT vector , where

[0034]

[0035] is a number of CSI-RS ports of an antenna array of the base station along a first spatial dimension and is a respective oversampling factor, is a spatial beam vector index in the codebook along the first spatial dimension, is a number of CSI-RS ports of the antenna array of the base station along a second spatial dimension and is a respective oversampling factor, is a spatial beam vector index in the codebook along the second spatial dimension, is imaginary unit, denotes transposing.

[0036] According to an embodiment, the selecting spatial beam vectors comprises: based on the measurements of the CSI-RSs, determining a receive quality metric corresponding to each spatial beam vector from at least part of a set of spatial beam vectors defined by the codebook; selecting, from the at least part of the set of spatial beam vectors, spatial beam vectors with larger corresponding receive quality metrics, where is said number of spatial beam vectors corresponding to the preferred number of MIMO layers; and ordering the selected spatial beam vectors according to the corresponding receive quality metrics. Preferably, , where is the preferred number of MIMO layers, denotes rounding to the closest greater integer.

[0037] In according with a preferred embodiment, the selected spatial beam vectors are mutually orthogonal, wherein, among the spatial beam vectors, a spatial beam vector with the largest corresponding receive quality metric defines an orthogonal basis in the codebook, wherein other of the spatial beam vectors are selected in said orthogonal basis.

[0038] According to an embodiment, each of the primary channel quality indicator and the at least one additional channel quality indicator represents a wideband channel quality indicator (wCQI). Said calculating a primary channel quality indicator comprises: generating a primary precoding matrix based on the ordered spatial beam vectors, wherein a number of precoding vectors which the primary precoding matrix is comprised of equals ; and calculating a primary wCQI for the generated primary precoding matrix. Said calculating at least one additional channel quality indicator comprises, for each from a set { }, where is a -th number of MIMO layers less than , , is a number of s in the set { }: selecting, from the ordered spatial beam vectors, spatial beam vectors with larger corresponding receive quality metrics according to said ordering of the spatial beam vectors, wherein corresponds to the number of MIMO layers, preferably ; generating a -th precoding matrix based on the selected spatial beam vectors; and calculating a -th additional wCQIkfor the generated -th precoding matrix. A number of precoding vectors which the -th precoding matrix is comprised of equals .

[0039] In accordance with an embodiment, the generating CSI comprises: ordering the indices of the spatial beam vectors in the CSI according to said ordering of the spatial beam vectors, where ; further including into the CSI, for each of the spatial beam vectors, a respective polarization co-phasing factor , wherein the polarization co-phasing factors are ordered within the CSI according to the ordering of the indices of the spatial beam vectors; and ordering the calculated wCQIs within the CSI according to a format preset in the base station and signaled in advance to the user equipment. The preset format can correspond to ordering the calculated wCQIs in such a way that each of the calculated wCQIs is ordered within the CSI according to a number of MIMO layers for which said wCQI was calculated, wherein said signaling of the preset format from the base station to the user equipment is performed via radio resource control (RRC) signaling.

[0040] According to an embodiment, the receive quality metric is an indicator of received power of a respective beam, said indicator obtained based on the measurements of the CSI-RSs and a corresponding spatial beam vector.

[0041] In accordance with one embodiment, each in the set { } corresponds to a pair of integer values of a number of MIMO layers, wherein, in the set { }, , , where .

[0042] In one implementation of the one embodiment, . In this case, can be equal to 8 or 7, can be equal to 6 or 5, can be equal to 4 or 3, can be equal to 2 or 1.

[0043] In another implementation of said one embodiment, is preset in the base station and signaled in advance to the user equipment via RRC signaling. In this case, can be equal to 8 or 7, can be equal to 1 or 2.

[0044] According to another embodiment, a combination of values of a number of MIMO layers is signaled in advance from the base station to the user equipment via RRC signaling, wherein all values from said combination which are less that are included into the set { } in the user equipment.

[0045] In according to one embodiment, the CSI is transmitted via UCI. The CSI in the UCI comprises a CSI part　1 and a CSI part　2, wherein a payload size of the CSI part　1 is fixed, and a payload size of the CSI part　2 is variable and dependent on contents of the CSI part　1.

[0046] According to one implementation of the one embodiment, the CSI part　1 includes and the primary wCQI. The CSI part　2 can include the indices of the spatial beam vectors, followed by the respective polarization co-phasing factors , followed by the additional wCQIks, where , . Otherwise, the CSI part　2 can include the indices of the spatial beam vectors, followed by the additional wCQIks, followed by the polarization co-phasing factors , where , .

[0047] According to another implementation of said one embodiment, the CSI part　1 includes . The CSI part　2 can include the indices of the spatial beam vectors, followed by the respective polarization co-phasing factors , followed by the primary wCQI and the additional wCQIks, where , . Otherwise, the CSI part　2 can include pairs "a spatial beam vector index - a respective polarization co-phasing factor ", where , followed by the primary wCQI and the additional wCQIks, where .

[0048] According to yet another implementation of the one embodiment, the CSI part　1 includes , the primary wCQI, an index of the first spatial beam vector, and a respective polarization co-phasing factor , while the CSI part　2 includes the indices of the spatial beam vectors, followed by the respective polarization co-phasing factors , followed by the additional wCQIks, where , .

[0049] In accordance with another embodiment, the CSI is transmitted via a medium access control (MAC) control element (CE), wherein the MAC CE includes, respectively ordered over octets: , the primary wCQI, the indices of the spatial beam vectors, the respective polarization co-phasing factors , the additional wCQIks, where , .

[0050] According to an embodiment, a bit field size for is , wherein a bit field size for each of , , is .

[0051] In accordance with an embodiment, the method further comprises: receiving, from the base station, a CSI request, the CSI request comprising a bit field whose value indicates, to the user equipment, to obtain the CSI for two or more numbers of MIMO layers.

[0052] According to an embodiment, the method provided herein further comprising, in the base station: receiving the CSI transmitted by the user equipment; for each of at least part of the channel quality indicators comprised in the CSI, calculating a value of reduction of transmission power spectral density (PSD) based on at least a frequency resource available for a downlink (DL) transmission being scheduled, and applying the calculated PSD reduction value to determine a modulation and coding scheme (MCS) for the DL transmission; based on, at least, an energy efficient (EE) mode and a data rate for the DL transmission, selecting an MCS from the determined MCSs and selecting a number of MIMO layers for which a channel quality indicator which the selected MCS corresponds to was calculated; obtaining a precoding matrix based on spatial beam vectors from the spatial beam vectors indicated by the ordered spatial beam vector indices from the received CSI, wherein a number of the spatial beam vectors based on which the precoding matrix is obtained corresponds to the selected number of MIMO layers; and performing the DL transmission to the user equipment by using the obtained precoding matrix, the selected MCS, and the calculated PSD reduction value corresponding to the selected MCS. Polarization co-phasing factors from the received CSI, which correspond to said spatial beam vectors corresponding to the selected number of MIMO layers, can be further used for said obtaining a precoding matrix.

[0053] In this embodiment, said applying the calculated PSD reduction value for a respective channel quality indicator comprises, in the base station: based on the respective channel quality indicator, determining an estimated signal-to-interference-and-noise ratio (SINR) at a side of the user equipment; applying the calculated PSD reduction value to scale the estimated SINR; and determining the MCS based on the scaled SINR. The PSD reduction value is preferably calculated as

[0054] ,

[0055] where is a frequency resource initially allocated for the DL transmission, is the frequency resource stretched according to the available frequency resource, is the estimated SINR. The stretching of the resource can be performed further with account of at least a current number of active user equipments being served by the base station.

[0056] According to the second aspect of the present invention a user equipment in a wireless communication system is provided, the user equipment comprising, at least: transceiving units; data processing units; and data storage units, wherein the data storage units have computer-executable codes stored therein which, when executed by the data processing units, cause the method according to any one of the embodiments of the first aspect of the present invention to be performed.

[0057] In accordance with the third aspect of the present invention a computer-readable storage medium is provided, the computer-readable storage medium having computer-executable codes stored therein which, when executed by at least one data processing unit of a user equipment (UE), cause the user equipment to perform the method according to any one of the embodiments of the first aspect of the present invention.

[0058] According to the fourth aspect of the present invention a method of requesting CSI is provided, the method being performed by a base station of a wireless communication system. The method provided hereby comprises: transmitting, to a user equipment (UE), a CSI request comprising an indication, to the user equipment, to calculate a CSI report for two or more numbers of MIMO layers, including a number of MIMO layers preferred for the user equipment and at least one number of MIMO layers which is less than the preferred number of MIMO layers.

[0059] In accordance with a preferred embodiment, the CSI request is transmitted via DCI, wherein the CSI request comprises a bit field, wherein said indication is represented by a first value of the bit field, wherein the first value is selected in the base station form a predefined set of bit values. The first value of the bit field can be further indicative of signaling by which the CSI report is to be transmitted by the user equipment to the base station. The indicated signaling can be RRC or MAC CE. The set of bit values can further comprise a second value for indicating, to the user equipment, to calculate the CSI report only for the preferred number of MIMO layers. Selection between the first value and the second value for the bit field in the CSI request can be performed in the base station depending on a current network load.

[0060] According to an embodiment, the method provided herein further comprises, before the transmitting a CSI request: transmitting, to the user equipment via RRC signaling, a message comprising a combination of values of a number of MIMO layers or a number of numbers of MIMO layers, for being used in the calculation of the CSI report.

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

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

[0063] Hereinafter, embodiments of the disclosure will be described in detail with reference to the accompanying drawings.

[0064] In describing the embodiments, descriptions related to technical contents well-known in the art and not associated directly with the disclosure will be omitted. Such an omission of unnecessary descriptions is intended to prevent obscuring of the main idea of the disclosure and more clearly transfer the main idea.

[0065] For the same reason, in the accompanying drawings, some elements may be exaggerated, omitted, or schematically illustrated. Further, the size of each element does not completely reflect the actual size. In the drawings, identical or corresponding elements are provided with identical reference numerals or different reference numerals.

[0066] The advantages and features of the disclosure and ways to achieve them will be apparent by making reference to embodiments as described below in detail in conjunction with the accompanying drawings. However, the disclosure is not limited to the embodiments set forth below, but may be implemented in various different forms. The following embodiments are provided only to completely disclose the disclosure and inform those skilled in the art of the scope of the disclosure, and the disclosure is defined only by the scope of the appended claims. Throughout the specification, the same or like reference numerals designate the same or like elements. Furthermore, in describing the disclosure, a detailed description of known functions or constitution incorporated herein will be omitted in the case that it is determined that the description may make the subject matter of the disclosure unnecessarily unclear. The terms which will be described below are terms defined in consideration of the functions in the disclosure, and may be different according to users, intentions of the operators, or customs. Therefore, the definitions of the terms should be made based on the contents throughout the specification.

[0067] Herein, it will be understood that each block of the flowchart illustrations, and combinations of blocks in the flowchart illustrations, may be performed based on computer program instructions. These computer program instructions may be loaded collectively onto at least one processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which perform through any one of, or in any combination of, the at least one processor of the computer or other programmable data processing apparatus, create means for performing the functions specified in the flowchart block(s). These computer program instructions may also be stored in a non-transitory computer usable or computer-readable memory that may direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer usable or computer-readable memory produce an article of manufacture including instruction means that perform the function specified in the flowchart block(s). The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable data processing apparatus to produce a computer executed process such that the instructions that perform on the computer or other programmable data processing apparatus provide steps for executing the functions specified in the flowchart block(s).

[0068] Further, each block may represent a module, segment, or portion of code, which includes one or more executable instructions for executing the specified logical function(s). It should also be noted that in some alternative implementations, the functions noted in the blocks may occur out of the order. For example, two blocks(or functions) shown in succession may in fact be performed substantially concurrently or the blocks may sometimes be performed in the reverse order, depending upon the functionality involved.

[0069] As used in embodiments of the disclosure, a "~unit" may refer to a software element or a hardware element, such as a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC), which performs a predetermined function. However, the term including the word "~unit" does not always have a meaning limited to software or hardware. The "~unit" may be constructed either to be stored in an addressable storage medium or to execute one or more processors. Therefore, the "~unit" includes, for example, software elements, object-oriented software elements, components such as class elements and task elements, processes, functions, properties, procedures, sub-routines, segments of a program code, drivers, firmware, micro-codes, circuits, data, database, data structures, tables, arrays, and parameters. The components and functions provided by the "~unit" may be either combined into a smaller number of components and a "~unit," or divided into additional components and a "~unit." Moreover, the components and "~units" may be implemented to reproduce one or more central processing units (CPUs) within a device or a security multimedia card. Further, in the embodiments, the "～unit" may include one or more processors.

[0070] It should be appreciated that the blocks in each flowchart and combinations of the flowcharts may be performed by one or more computer programs which include instructions. The entirety of the one or more computer programs may be stored in a single memory device or the one or more computer programs may be divided with different portions stored in different multiple memory devices.

[0071] Any of the functions or operations described herein can be processed by one processor or a combination of processors. The one processor or the combination of processors is circuitry performing processing and includes circuitry like an application processor (AP, e.g. a CPU), a communication processor (CP, e.g., a modem), a graphics processing unit (GPU), a neural processing unit (NPU) (e.g., an artificial intelligence (AI) chip), a Wi-Fi chip, a Bluetooth® chip, a global positioning system (GPS) chip, a near field communication (NFC) chip, connectivity chips, a sensor controller, a touch controller, a finger-print sensor controller, a display driver integrated circuit (IC), an audio CODEC chip, a universal serial bus (USB) controller, a camera controller, an image processing IC, a microprocessor unit (MPU), a system on chip (SoC), an IC, or the like.

[0072] It will be appreciated that various embodiments of the disclosure according to the claims and description in the specification can be realized in the form of hardware, software or a combination of hardware and software.

[0073] Any such software may be stored in non-transitory computer readable storage media. The non-transitory computer readable storage media store one or more computer programs (software modules), the one or more computer programs include computer-executable instructions that, when executed by one or more processors of an electronic device individually or collectively, cause the electronic device to perform a method of the disclosure.

[0074] Any such software may be stored in the form of volatile or non-volatile storage such as, for example, a storage device like read only memory (ROM), whether erasable or rewritable or not, or in the form of memory such as, for example, random access memory (RAM), memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a compact disk (CD), digital versatile disc (DVD), magnetic disk or magnetic tape or the like. It will be appreciated that the storage devices and storage media are various embodiments of non-transitory machine-readable storage that are suitable for storing a computer program or computer programs comprising instructions that, when executed, implement various embodiments of the disclosure. Accordingly, various embodiments of the present disclosure may provide a program comprising code for implementing apparatus or a method as claimed in any one of the claims of this specification and a non-transitory machine-readable storage storing such a program.

[0075] Hereinafter, the determination of priority between A and B in the present disclosure may refer to various actions such as selecting the one having a higher priority based on a predefined priority rule and performing an operation corresponding thereto, or omitting or dropping an operation corresponding to the one having a lower priority.

[0076] Hereinafter, "A or B" as described in the present disclosure may be understood as "A and / or B," which may include A, or B, or both A and B.

[0077] In addition, "at least one of A, B, and C" as described in the present disclosure may be understood to include A, or B, or C, or any combination of A, B, and C.

[0078] In addition, "at least one of A, B, or C" as described in the present disclosure may be understood to include A, or B, or C, or any combination of A, B, and C.

[0079] Furthermore, "A / B" as described in the present disclosure may be understood as "A and / or B," which may include A, or B, or both A and B.

[0080] Furthermore, "A, B" as described in the present disclosure may be understood as "A and / or B," which may include A, or B, or both A and B.

[0081] Furthermore, "A and B" as described in the present disclosure may be understood as "A and / or B," which may include A, or B, or both A and B.

[0082] Furthermore, "if condition A and condition B are satisfied," as described in the present disclosure, may not be limited to a case where both condition A and condition B are satisfied, but may be understood to include a case where either condition A or condition B is individually satisfied, both condition A and condition B are satisfied, or one or more additional conditions are satisfied in combination.

[0083] Furthermore, throughout this disclosure, ordinal terms such as "first," "second," "third," etc., (and similar qualifiers) are used merely to distinguish between different instances, occurrences, configurations, messages, stages, or aspects of elements, operations, or information as described herein. Unless the context clearly dictates otherwise, the use of such ordinal terms does not itself require that the elements, operations, or information distinguished by these terms be structurally different, numerically distinct, or substantively dissimilar. For example, a "first signal" and a "second signal" may refer to instances of the same signal transmitted at different times or containing the same core information despite minor variations, or they may refer to signals with different content or characteristics, depending on the specific context. Similarly, a "first value" and a "second value" may represent the same magnitude but measured or applied in different circumstances, or they may represent different magnitudes. The interpretation should be guided by the specific technical context, function, and relationship described in the relevant portion of the specification and claims.

[0084] Furthermore, the terms "first ~", "second ~", etc., as described in the present disclosure with respect to various elements (e.g., information, objects, operation, sequences, or the like), should not limit those elements. These terms may only be intended to distinguish one element from another, and may not be intended to indicate a specific order. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element.

[0085] Furthermore, even if "first ~" and "second ~" are described in the present disclosure, it may be understood that element(s) referred to by "first ~" and "second ~" may be the same or different. For example, in case of element(s) being information, first information and second information may both be same information and, in some cases, are separate and different information.

[0086] In addition, the terms "if ~" and "in case that ~" as used in the disclosure or claims may be interpreted to include the meanings of "when (or upon) ~," "in response to ~," "based on ~," or "according to ~," and may be used interchangeably with these expressions. In addition, expressions other than those exemplified herein may also be used, as long as they have substantially the same meaning and do not impair the technical features of the present disclosure.

[0087] For example, the physical layer signaling may be referred to as Layer 1 (L1) signaling and may include downlink control information (DCI). In addition, the higher layer signaling may include a medium access control (MAC) control message, a radio resource control (RRC) signaling message, a non-access stratum (NAS) signaling message, or an application layer message. The RRC signaling message may be referred to as L3 (layer 3) signaling. It should be noted, however, that the higher layer signaling is not limited to the aforementioned examples.

[0088] In addition, the term "not perform" as used in the present disclosure or claims may, in context, be understood to mean that the corresponding step is omitted or skipped. Such a term may be replaced with other terms having the same or substantially equivalent meaning.

[0089] In addition, "transmitting a message including A and B" as described in the present disclosure, may be understood as encompassing both (i) transmitting A and B in a single message, and (ii) transmitting A and B separately via multiple messages (e.g., transmitting a first message including A and a second message including B). This interpretation may also apply to messages that include two or more items (e.g., A, B, C), transmitted either together or separately.

[0090] In addition, "transmitting a message including A and transmitting a message including B" may also be interpreted as transmitting a message including A and B in a single message.

[0091] In the specific embodiments of the present disclosure described below, terms or components included in the disclosure may be expressed in singular or plural form depending on the specific embodiments presented. However, such singular or plural expressions are selected appropriately for convenience of description, and the present disclosure is not limited to a singular or plural number of components. A component expressed in the plural form may be implemented as a single component, and a component expressed in the singular form may be implemented as multiple components.

[0092] The drawings or flowcharts described below illustrate exemplary methods that may be implemented according to the principles of the present disclosure, and various modifications may be made to the methods illustrated in the flowcharts of the present disclosure. For example, although illustrated as a series of steps, various steps in each drawing or flowchart may overlap, occur in parallel, occur in a different order, or be repeated. In other examples, any step may be omitted or replaced with another step.

[0093] The methods and apparatuses proposed in the embodiments of the present disclosure are not limited to each embodiment individually, but may also be applied in combination of all or some of the embodiments proposed in the disclosure. Therefore, the embodiments of the present disclosure may be modified and applied without significantly departing from the scope of the present disclosure, as would be understood by those skilled in the art.

[0094] In this case, even if certain wordings are described differently across embodiments, they may be used interchangeably or in substitution or in combination if their underlying concepts are equivalent. For example, for the same or equivalent concept, even if one embodiment uses the expression "A" and another embodiment uses the expression "B", such expressions may be understood interchangeably, in substitution, or in combination.

[0095] The terms used in the following description to refer to access nodes, network entities, messages, interfaces between network entities, various types of identification information, and the like, are provided merely for the convenience of explanation by way of example. Therefore, the present disclosure is not limited to the terms described below, and other terms having equivalent technical meanings may also be used. Such terms may also be interchangeable with terms defined in any 3rd generation partnership project　(3GPP) technical specifications (TS) where appropriate.

[0096] Hereinafter, a base station is an entity that allocates resources to terminals, and may be at least one of a gNode B, an eNode B, a Node B, a base station (BS), a wireless access unit, a BS controller, or a node on a network.

[0097] Furthermore, the base station of the present disclosure may include a split architecture comprising a central unit (CU) and a distributed unit (DU). In this structure, the CU is configured to process the higher layers of the control and user planes, while the DU is configured to process lower-layer radio resource functions. The embodiments of the present disclosure may be equally applicable to 5G base station architectures in which such CU and DU functional splits are implemented.

[0098] A terminal may include a UE, a mobile station (MS), a cellular phone, a smartphone, a computer, or a multimedia system capable of performing communication functions.

[0099] In the disclosure, a downlink (DL) refers to a radio link through which a BS transmits a signal to a UE, and an uplink (UL) refers to a radio link through which a UE transmits a signal to a BS.

[0100] Furthermore, hereinafter, 5th generation (5G) mobile communication technologies (e.g., 5G new radio (NR)), 6th generation (6G) mobile communication technologies may be described by way of example, but the embodiments of the present disclosure may also be applied to other communication systems having similar technical backgrounds or channel types. For example, newly evolved mobile communication systems developed after 5G and 6G may be included. Furthermore, based on determinations by those skilled in the art, the embodiments of the present disclosure may also be applied to other communication systems (e.g., Wi-Fi systems) through some modifications without significantly departing from the scope of the present disclosure

[0101] In the following description, the terms physical channel and signal may be used interchangeably with data or control signal. For example, the term physical downlink shared channel (PDSCH) refers to a physical channel through which data is transmitted, but the term PDSCH may also be used to refer to the data itself. That is, in the present disclosure, the expression "transmit a physical channel" may be interpreted as being equivalent to the expression "transmit data or a signal via a physical channel."

[0102] Hereinafter, in the context of the present disclosure, higher layer signaling may refer to signaling corresponding to at least one or any combination of the following: master information block (MIB), system information block (SIB) or SIB M (M = 1, 2, ...), radio resource control (RRC), or medium access control (MAC) control element (CE), or a non-access stratum (NAS) signaling message, or an application layer message. The RRC signaling message may be referred to as L3 (layer 3) signaling.

[0103] In addition, L1 signaling may refer to signaling corresponding to at least one or any combination of signaling techniques using the at least one or any combination of the following physical layer channels or signaling: physical downlink control channel (PDCCH), downlink control information (DCI), user equipment (UE)-specific DCI, group-common DCI, common DCI, scheduling DCI (e.g., DCI used for scheduling downlink or uplink data), non-scheduling DCI (e.g., DCI not used for scheduling downlink or uplink data) physical uplink control channel (PUCCH), or uplink control information (UCI). The L1 signaling message may be referred to as a physical layer signaling.

[0104] Hereinafter, the expression that information is configured by the BS, as used in the present disclosure or claims, may, in context, be understood to mean that the terminal receives the corresponding information from the BS via a physical layer signaling or a higher layer signaling. Such an expression may be replaced with other terms having the same or substantially equivalent meaning.

[0105] Hereinafter, the operational principle of the present disclosure will be described in detail with reference to the accompanying drawings.

[0106] Nowadays more and more active deployment of 5th Generation (5G) New Radio (NR) networks takes place, whose advantages and capabilities are broadly known.

[0107] Base stations (BSs) in a 5G NR system use massive antenna arrays (Massive MIMO (mMIMO)) comprising multiple transceiver antenna elements (AEs). Such antenna arrays enable to efficiently implement a multiple-input multiple-output (MIMO) technology, when several spatial MIMO layers can be transmitted to transmit data (e.g. physical downlink shared channel (PDSCH)) to a user equipment(s) (UE).

[0108] An antenna array of a base station is divided into groups of antenna elements, or subarrays, where the number of antenna elements in a subarray is set in manufacturing of the base station and, therefore, is constant during operation of the base station. In a transceiving device of the base station, each subarray of the antenna array has its own transmission chain connected thereto. The transmission chain comprises, in particular, a digital-to-analog converter (DAC) whose input is provided with a respective signal from the digital part of the base station, a power amplifier (PA), and a band-pass filter whose output the subarray is connected to. Therefore, the subarray is a single physical emitting element of the antenna array of the base station. Since the antenna array of the base station operates for reception as well and, accordingly, the subarray is a single receiving element of the antenna array, the abovementioned chain of transmission elements can be implemented as part of a transceiving chain. The term 'transmission chain' used throughout the text of the application may be assumed as referring to 'transceiving chain' as well, without limitations.

[0109] In 5G NR, virtualization of subarrays of an antenna array of a base station (i.e. substantially of physical antennas) into logical ports is implemented. Depending on implementation, each subarray can be virtualized into one logical port, or more than one (for example, two) subarrays can correspond to one logical port. Each such logical port has its own channel state information (CSI) reference signal (RS) port associated therewith; accordingly, this logical port is referred to as a CSI-RS port of the base station. Generally speaking, in 5G NR, CSI-RSs are transmitted from the base station to a user equipment(s), while the user equipment performs DL channel state measurement based on CSI-RSs received from the base station and transmits to the base station, in the form of CSI, a report on the completed DL channel estimation, so that the base station, based on said report, could perform an appropriate adjustment of parameters of subsequent DL data transmission to the user equipment. It should be noted that communication of the user equipment with the base station is carried out specifically in the level of CSI-RS ports of the base station, i.e. the user equipment may not be aware of a specific number of subarrays of the antenna array represented by a CSI-RS port.

[0110] The general description of the mechanism of obtaining, transmitting, and applying CSI, as used in 5G NR, is given thereafter in order to provide more full understanding of the technical context of the present invention.

[0111] As briefly recited earlier, in 5G NR, CSI-RSs are transmitted from a base station to a user equipment(s), so that the user equipment performs, based on the received CSI-RSs, determination of the DL channel state with respect to all or required part of CSI-RS ports. Appropriate analog beamforming (A-BF) can be applied in the analog part of the base station to the CSI-RSs transmitted by the base station at a certain time instance, said A-BF setting a specific direction of the DL transmission or, in other words, an analog beam. In this regard, two A-BF strategies are supported in 5G NR. Analog beams corresponding to the first strategy are highly spatially-directed, with steering of transmission power in a preset direction (i.e. narrow beams with a high gain), and are optimized for the single-user MIMO (SU-MIMO) mode, along with providing maximum throughput for individual user equipments. Analog beams corresponding to the second strategy are wider with a lower gain and, accordingly, are aimed at providing simultaneous data transmission to multiple user equipments, i.e. such beams are optimized for the multi-user MIMO (MU-MIMO) mode. Of course, CSI-RSs can be transmitted by the base station without applying A-BF thereto.

[0112] For transmission of CSI-RSs, for example, performed at a certain time in a certain analog beam, respective orthogonal multiplexing of the CSI-RSs over frequency domain and time domain resources is applied in 5G NR. More specifically, the base station uses a specific CSI-RS configuration according to which time-frequency resources are divided into a predefined number of code division multiplexing groups (CDM groups) of a predefined size, said CDM groups being regularly arranged in frequency and time (for example, the distance between adjacent CDM groups in frequency can be one subcarrier, and the distance between adjacent CDM groups in time can be one OFDM symbol); furthermore, in each of the predefined number of CDM groups, multiplexing of CSI-RSs is provided by applying respective orthogonal cover codes (OCC) in the frequency domain and in the time domain. Such CSI-RS configuration basically implements mapping of CSI-RS ports to time-frequency resources.

[0113] The 5G NR aspects related to mapping of base station CSI-RS ports to time-frequency resources of the CSI-RS configuration, as well as to multiplexed transmission of CSI-RSs, are disclosed in specification TS 38.211, v.18.1.0 which is entirely included in the present application by reference. In particular, this specification provides the table of CSI-RS configurations supported in 5G NR, along with their respective characteristics.

[0114] When connecting a user equipment(s) to the cell served by the base station, a number of configurations are transmitted to the user equipment from the base station, the configurations, in general, defining parameters for transmitting signals in said cell. In particular, one or more CSI-RS resources are configured for the user equipment via radio resource control (RRC) (L3) signaling. Each CSI-RS resource is encoded with a certain number of respective parameters, as defined in specification TS 38.331, v18.1.0, which is entirely included in the present application by reference. In particular, one of these parameters in the CSI-RS resource sets specific mapping of CSI-RS ports to time-frequency resources for a respective CSI-RS configuration. More than one CSI-RS resource can be similarly configured for the user equipment, each of the CSI-RS resources corresponding to one of analog beams used by the base station. In particular, in such configuring, a set of CSI-RS resources can be encoded for the user equipment - for example, a set of CSI-RS resources for a respective set of beams optimized for SU-MIMO can be configured for the user equipment.

[0115] According to 5G NR, CSI-RSs can be transmitted by a base station in the following modes:

[0116] ● aperiodically, when the base station transmits CSI-RSs as needed, and a user equipment(s) is informed in advance (for example, via downlink control information (DCI)) about the CSI-RS transmission in a specific slot;

[0117] ● periodically, and in this case periodicity of the transmission is configured in the base station and signaled in advance to the user equipment(s);

[0118] ● semi-persistently, when configuring is performed similarly to the periodic mode, but the base station uses DL control signaling (for example, a medium access control (MAC) message) to activate / deactivate specific CSI-RS resources.

[0119] The aperiodic mode will be discussed below, for illustrative purposes, with reference to the generalized scheme of the embodiment of interaction between a wireless communication network (NW) and a user equipment (UE) shown in Figure 1.

[0120] A base station, which is part of the NW, transmits a CSI request to the user equipment (action 1 in Figure 1), the CSI request, as an example, indicating a CSI-RS resource set, and performs respective transmission of CSI-RSs (action 2).

[0121] The user equipment performs measurements of the received CSI-RSs and, based on the measurements, selects one CSI-RS resource. A report in the form of CSI will be generated in the user equipment in relation to the selected CSI-RS resource (action 3); accordingly, an identifier (CRI) of the selected CSI-RS resource can be included into the CSI.

[0122] The CSI report also includes a number of parameters that are calculated in the user equipment based on the results of the measurements. In particular, the user equipment selects a preferred number of MIMO layers corresponding to the number of spatial data streams simultaneously transmitted from the base station for being received by the user equipment. This number of MIMO layers is reflected by the parameter RI as part of the CSI. In addition, the user equipment obtains a precoding matrix by using spatial beam vectors that define directions recommended by the user equipment for transmitting said number of MIMO layers to the user equipment. The spatial beam vectors are selected from a predefined codebook, the parameters of the codebook can be signaled to the user equipment when configuring the CSI discussed above. The obtained precoding matrix is reflected by the parameter PMI as part of the CSI. Moreover, the user equipment determines a channel quality indicator (CQI) which is also included into the CSI and which should inform the base station about noise robustness of the DL channel between the base station and the user equipment and, accordingly, a modulation and coding scheme (MCS) that should be chosen.

[0123] The 5G NR aspects related, in particular, to implementation of the codebook, channel estimation based on CSI-RSs and obtaining a precoding matrix at the user equipment side, the specifics of representing and transmitting CRI, RI, PMI, CQI, and other parameters within CSI, are disclosed in specifications TS 38.212 (see, in particular, section 6.3.2.1.2), TS 38.214 (see, in particular, section 5.2.2.1). In particular, 5G NR Type　1 codebook (see Table 5.2.2.2.1-2 from TS 38.214) can be used as the codebook.

[0124] The obtained CSI, including inter alia RI, PMI, CQI for the selected CSI-RS resource, is transmitted from the user equipment to the base station (action 4). This transmission is typically performed via uplink control information (UCI) which is multiplexed into Physical Uplink Control Channel (PUCCH).

[0125] Upon reception of the CSI, the base station, in particular, uses the CQI to select the MCS and applies the obtained precoding matrix to carry out respective digital beamforming (D-BF) (action 5) to perform DL transmission (for example, of PDSCH) to the user equipment (action 6). The parameters included in the received CSI are substantially used by the base station to optimally adapt parameters of the subsequent DL data transmission to the reported DL channel state.

[0126] It should be also explained herein that, in 5G NR wireless communication systems two approaches to DL beamforming are used for dynamically steering a transmitted signal in one or more preset directions: A-BF and D-BF. D-BF is performed in the digital part of the base station when generating a DL signal and can be applied in both the time domain and the frequency domain; A-BF is performed in the analog part of the base station and is applied to the already generated signal, and only in the time domain. 5G NR supports adaptive methods of beamforming using A-BF and D-BF (i.e. hybrid beamforming (H-BF)).

[0127] Nowadays reduction of operating expenses associated with wireless communication systems is an important goal, inter alia - in the context of developing next generation communication systems. A significant contribution to the operating expenses of an operator of a wireless communication network is made by energy consumption of the network; accordingly, in the context of addressing this important goal, the general motivation is to use various power saving technologies in order to ensure high energy efficiency of the network.

[0128] As practice shows, energy consumption of power amplifiers of transceiver devices of base stations constitutes a significant portion of total energy consumed by the radio access network in the process of operation. Accordingly, this fact motivates development of a general approach to reducing power consumption of a base station(s).

[0129] One such approach is in transitioning the base station to a reduced energy consumption mode, or, in other words, energy-efficient (EE) mode, by temporarily transitioning some power amplifiers in transmission chains of the base station to the off state in cases where activity of all power amplifiers is not required. In 5G NR, implementation of this general approach is the antenna muting (AM) technology according to which, depending on a number of characteristics, such as the current network traffic load, current wireless channel state, location of active user equipments relative to the base station, the base station dynamically or semi-statically disables some transmission chains along with transitioning respective power amplifiers of said chains to the off state. As a result, transmission from subarrays whereto the disabled transmission chains are connected is not performed - in other words, these subarrays become muted. In one of possible implementations of the AM technology according to 5G NR, when part of the power amplifiers are disabled, part of subarrays of the antenna array will stop transmitting respective CSI-RSs, and such muting of the part of the CSI-RS ports may negatively affect the DL channel estimation quality at the user equipment side.

[0130] Another approach, which is more flexible as compared to the AM technology described above, relies on adapting the transmission power spectral density (PSD) level of a signal transmitted from the base station. Generally speaking, according to this approach, depending on a number of characteristics such as the current network traffic load, current wireless channel state, available frequency band, the base station transitions to an EE mode by accordingly reducing PSD for the DL transmission. This PSD adaptation is performed in the base station based on CSI received from a user equipment(s). In this case, all the power amplifiers of the base station are assumed to be in the active state.

[0131] The approaches to reducing energy consumption of the base station, as briefly outlined above, are schematically illustrated in Figure　2.

[0132] The diagram in the left part of Figure　2 corresponds to PDSCH transmission in the primary (i.e. non-energy-saving) operation mode of the base station. The PSD level of PDSCH transmitted by the base station is shown along the ordinate axis, and CSI-RS port indices of the base station antenna array are shown along the abscissa axis. The right part of Figure　2 corresponds to implementations of the EE operation mode of the base station.

[0133] The diagram in the lower right part of Figure　2 schematically shows transmission of PDSCH in the EE operation mode of the base station that is based on the AM technology. As seen from this diagram, the PDSCH transmission is not performed from a half of subarrays of the base station antenna array, i.e. a half of CSI-RS ports are muted, while the PSD level of PDSCH transmitted from the other half of the subarrays is equal to PSD of the primary mode. Therefore, in this implementation of the EE mode, the twofold reduction in the total transmission power of the base station is provided.

[0134] The diagram in the upper right part of Figure　2 schematically depicts transmission of PDSCH in the EE operation mode of the base station that is based on PSD reduction. As shown in the considered diagram, the PDSCH transmission is performed from all the subarrays, i.e. all the CSI-RS ports of the base station are active, while PSD of the transmitted PDSCH is twice less than PSD of the primary mode. Therefore, in this implementation of the EE mode of the base station, the twofold reduction in the total transmission power is again provided.

[0135] Figures 3a, 3b illustrate one of the main problems arising when implementing the EE mode of the base station based on reducing PSD of the transmitted signal.

[0136] Figure 3a shows the primary operation mode of the base station wherein high transmission power is ensured (obviously, at the expense of power saving), as well as high system performance. Figure 3b shows, substantially in comparison with Figure 3a, the EE operation mode of the base station in which PSD of the DL transmission is reduced (see the upper right portion of Figure 2). As illustrated by Figure 3b, the reduction of PSD in the EE mode may lead to reduction in coverage of the cell served by the base station and to deterioration of the system performance (in particular, to decreased interference resistance at the user equipment side).

[0137] Therefore, the general goal in such implementation of the EE mode of the base station is in selecting a transmission PSD reduction in a flexible way, along with minimizing deterioration of performance at the user equipment side. More specifically, it is desirable to control transmission power at the base station side as flexibly as possible, so that it is feasible to adapt transmission PSD depending on a specific user equipment being served. For example, if the user equipment is located at the edge of the cell served by the base station, then it is desirable not to reduce PSD when transmitting data by the base station to said user equipment; if, on the contrary, the user equipment is closer to the base station, then a EE mode with reduced PSD can be used.

[0138] It should be noted that the reduction of coverage, as illustrated in Figure 3b, and the associated deterioration in the system performance are similarly typical to usage of the AM technology according to 5G NR.

[0139] A more detailed general description of the PSD-based approach of implementation of EE modes of the base station according to 5G NR is provided hereinbelow, improvement of said approach being addressed by the present invention.

[0140] Among the abovementioned configurations transmitted from the base station to the user equipment upon the user equipment having been connected to the cell served by the base station, the following RRC container is transmitted to the user equipment:

[0141]

[0142] Parameters to subsequently perform power control at the base station side are encoded in said container.

[0143] The main problem is in that, when the base station intends to reduce PSD of a transmitted signal, signal-to-noise-and-interference ratio (SINR) at the user equipment side will also change respectively, and the goal arises to adapt parameters of subsequent transmission to the current PSD level, in particular - to adapt the choice of the following parameters: the number of MIMO layers and MCS which are both directly related to SINR. Said CSI-ReportSubConfig-r18 container has been introduced to support the required adaptation of parameters in 5G NR, said container including inter alia the parameter powerOffset-r18 which the user equipment is to apply upon measurements of CSI-RSs transmitted from the base station to emulate, at the user equipment side, PSD reduction by the base station. The parameter powerOffset-r18 takes quantized values in the range from 0 to 23 dB. Since the container CSI-ReportSubConfig-r18 is a sequence (SEQUENCE), multiple values of the parameter powerOffset-r18 can be set for the user equipment in said container; therefore, the user equipment should independently calculate the CSI parameters (RI, PMI, CQI) for each of the set values of powerOffset-r18, thereby emulating application of the respective PSD reduction at the base station side.

[0144] The aspects associated with the container CSI-ReportSubConfig-r18 are described in 5G NR specification TS 38.331, v18.1.0.

[0145] The implementation of the 5G NR approach to adapting PSD based on the container CSI-ReportSubConfig-r18 is illustrated below with reference to Figures 4 and 5.

[0146] Figure 4 illustrates the case where three PSD reduction values are configured for the user equipment in the sequence container CSI-ReportSubConfig-r18 by using the parameter powerOffset-r18: |P1| < |P2| < |P3|. Accordingly, the value P3 corresponds to more aggressive reduction of transmission PSD in the base station, P2 corresponds to medium PSD reduction, and P1 corresponds to small PSD reduction (or to absence of such reduction at all). Moreover, Figure 4 illustratively shows the reduction in coverage of the base station in DL data transmission for each of the configured PSD reduction values P1, P2, P3.

[0147] Figure 5, in the format similar to Figure 1, generally shows the respective communication between the wireless network (NW) and the user equipment (UE) in the context of the PSD adaptation illustrated in Figure 4.

[0148] The base station (BS in Figure　4), which is part of the NW, transmits, to the user equipment, the container CSI-ReportSubConfig-r18 wherein the three PSD reduction values reflected by the parameter powerOffset-r18 (|P1| < |P2| < |P3| in Figure　4) are configured for the user equipment (action 1 in Figure　5). The base station requests CSI from the user equipment by transmitting a CSI request to the user equipment (action 2 in Figure　5). The user equipment performs measurements with respect to CSI-RSs received from the base station, and performs calculations to obtain the CSI for being reported to the base station (action 3 in Figure　5). When obtaining the CSI, the user equipment performs respective calculations of RI, PMI, CQI independently for each of the three values of powerOffset-r18; that is, the user equipment calculates an optimal combination of RI, PMI, CQI under assumption of reducing PSD according to the values P1, P2, P3, individually for each of them (each of these values substantially corresponds to a separate hypothesis of PSD reduction emulation at the user equipment side). Accordingly, the user equipment generates and transmits to the base station three CSI reports (CSI1, CSI2, CSI3) each containing the respective optimal combination of RI, PMI, CQI for the respective configured PSD reduction value (action 4 in Figure　5). Based on the CSI1, CSI2, CSI3reports received from the user equipment and information about the current traffic load (inter alia - about the current frequency resource load), the base station determines an appropriate EE mode, i.e. whether to transition to the EE mode and by which value PSD of scheduled DL transmission can be reduced (action 5 in Figure　5). According to the illustration of Figure 5, the base station selects the value of powerOffset-r18 equal to P2 (i.e. the moderate EE mode), and the base station performs, inter alia based on the parameters comprised in the respective report CSI2, scheduling of resources for the subsequent DL data transmission, and transmission of Downlink Control Channel (PDCCH) by which the user equipment is, in particular, informed of the scheduled resources and the selected powerOffset-r18 and the scheduled transmission of PDSCH are performed to the user equipment (action 6 in Figure　5). The user equipment then receives PDSCH (action 7 in Figure　5).

[0149] The following drawbacks are typical to the 5G NR approach to implementation of EE operation modes of the base station, said approach being based on adapting PSD, as illustrated above.

[0150] First, as initially assumed in the base station, the base station can apply PSD reduction only based on the predefined set of values; in other words, quantized values of the PSD reduction are implied hereby. As a result, when considering as an example the scenario according to Figures 4 and 5, the reduction of PSD by the value P3 may lead to excessive deterioration of the system performance; the reduction of PSD by the smaller value P2 may result in insufficient reduction of energy consumption of the base station. Additional specifics related to this drawback will be described below.

[0151] Second, the fact that the user equipment has to independently obtain and transmit multiple CSI reports leads to significant computational overhead at the user equipment side and high overhead on uplink (UL) transmission from the user equipment, and these overheads scale linearly with the number of configured values of powerOffset-r18 for the user equipment. For example, if the user equipment is at the edge of the cell served by the base station, it may be difficult for the user equipment to transmit a message with a large number of multiplexed CSI reports to the base station due to power limitations on the UL transmission.

[0152] Third, a consequence of the first and second drawbacks mentioned above is the base station scheduler limitation according to which only a limited number of PSD reduction values can be used from the quantized set thereof. At the same time, selection of values of powerOffset-r18 to configure CSI to be reported by the user equipment is not itself a trivial task at the base station side.

[0153] Though deployment of 5G NR systems in the world is only spinning up, 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.

[0154] In particular, for the 6G operating range of 7-13 GHz (UPPER MID BAND), it is planned to support, at base stations, extremely large antenna arrays (for instance, comprised of 3072 antenna elements), with hybrid analog and digital beamforming with a large number of antenna ports (≤256). Therefore, support of up to 64 simultaneously transmitted spatial MIMO layers in UPPER MID BAND communication systems will bring the concept of radio interface with extremely large antenna array (xMIMO) to a principally new level. Moreover, support of a set of reference signals similar to the one used in 5G NR, such as DMRS, CSI-RS, SRS, PT-RS, PSS / SSS, is planned in 6G.

[0155] At the same time, approaches used in 5G NR may not be always directly extended to next generation communication systems. In particular, the drawbacks discussed above that are associated with implementation of EE modes based on reducing DL transmission PSD in 5G NR are not substantial for operation of the 5G NR system, but they may become more significant for 6G wireless communication systems where, due to xMIMO, support for a much greater number of CSI-RS ports will be provided, along with providing support for greater spatial directionality of beams, while the requirements on energy efficiency of the system operation will be at least not less than the ones acting in 5G NR. In other words, the known technologies can not provide sufficiently flexible and efficient adaptation of data transmission PSD for implementing an EE operation mode(s) of a base station in the next generation communication systems.

[0156] Figure 6 generally illustrates a wireless communication system in which various aspects of the present invention can be implemented. As shown in Figure 6, user equipments (UE) 601 communicate with base station (BS) 602 in a radio access network (RAN) 600. The UEs 601 (e.g. UE 601-1, 601-2, 601-3, ...) are distributed over the RAN 600, and each of the UEs 601 can be fixed or mobile. Broadly known examples of UEs are smartphones, tablets, modems, etc.

[0157] The base stations 602 (e.g. BSs 602-A, 602-B, 602-C) can provide coverage for a specific geographic area commonly referred to as 'cell'. The base stations 602 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 602-A, 602-B, 602-C in Figure 6), as well as pico base stations for pico-cells or femto base stations for femto-cells. Cells in turn can be divided into sectors.

[0158] Coordination and management of operating the base stations 602 can be provided by a network controller which is in communication therewith (for instance, via a backhaul connection). The RAN 600 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 602 in the RAN 600 can also connect to each other, for instance, via a direct physical connection, which is preferably a high-speed connection.

[0159] When a user equipment is moving within the RAN 600, handover of the user equipment from one base station to another base station can be performed. For example, the UE 601-3 can be handed over from the BS 602-B to the BS 602-A. While performing this, respective communication system parameters are reconfigured in the user equipment for operation with the new base station. The user equipment can be also handed over between sectors of one base station.

[0160] The OpenRAN (O-RAN) architecture is implemented in 5G NR - in particular, O-RAN 7-2x - which comprises splitting the base station into two parts and using a fronthaul (FH) interface defined for exchanging information between these functional parts. More specifically, according to this architecture, the base station is split into a radio unit (RU) and a distributed unit (DU) that are connected to each other via the FH interface. Support for the O-RAN architecture is expected in 6G xMIMO wireless communication systems.

[0161] Each of the BSs 602 shown in Figure 6 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.

[0162] In a similar way, each of the UEs 601 shown in Figure 6 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.

[0163] 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.

[0164] The hardware and software elements of the base station and the user equipment, as listed above, are configured to provide execution, in the base station and in the user equipment, of the methods according to the present application which are described below. Implementation of the component hardware of the base station and user equipment and specialized configuring thereof, including by respective logical means, are known in the technical field which the present application relates to. Furthermore, various functions according to the present application can be executed in multiple separate elements or in one or more integral elements, which is defined by design structural characteristics.

[0165] Hereinafter the approach is described that underlies the solution of the important technical problem outlined above when discussing the prior art according to the present invention.

[0166] As recited earlier, reduction, by a base station, of DL transmission PSD leads to decrease of SINR at the user equipment side and, consequently, to deterioration in performance - in particular, to reduction of data transmission rate or, in other words, throughput in the user equipment. The primary idea of the considered approach is in that, if there is a sufficient amount of the available frequency resource, then it can be used, despite the PSD reduction, to efficiently compensate for the drawback of reduced data transmission rate by utilizing the available frequency resource. This compensation is based on the Shannon formula

[0167]

[0168] which generally approximates well operation of the entire communication system. In formula (1): C is the maximum achievable data transmission rate at the user equipment side; B is the frequency resource allocated to the user equipment (FDRA); SRxis PSD of the received signal; STxis PSD of the transmitted signal; N is PSD of noise and inter-cell interference; CL is the coupling loss between the base station and the user equipment; and is SINR at the user equipment side. The characteristic of the Shannon formula (1) is that the bandwidth (B) is included thereby as a linear coefficient, while SINR ( ) is under the logarithm, and, as known, at large values of the argument the logarithmic function increases slower than the linear one. Therefore, reduction of the transmitted signal PSD (STx↓) (and the respective reduction of SINR) can be compensated based on the Shannon formula by stretching the transmitted signal bandwidth (B↑).

[0169] This stretching procedure for the sake of maintaining throughput at the user equipment side in PDSCH transmission with PSD reduction is mathematically reflected by the following expression:

[0170]

[0171] where C1is the data transmission rate at the user equipment side before the PSD reduction and bandwidth stretching, and C2is the data transmission rate at the user equipment side after the PSD reduction and bandwidth stretching. Using formula (1), equation (2) takes the following form:

[0172]

[0173] where B1is the frequency resource allocated to the user equipment before the PSD reduction and stretching, and B2is the frequency resource allocated to the user equipment after stretching thereof in the frequency domain and the respective PSD reduction, i.e. B1<B2,

[0174]

[0175] Since , then according to equation (4) .

[0176] The right part of equation (3) shows the transmission PSD reduction by the factor and the bandwidth stretching to B2- an attempt to render the transmission with the reduced PSD equivalent in terms of throughput by stretching the bandwidth is made by means of this equation. This aspect is illustrated in Figure　7.

[0177] It should be explained herein that equations (3), (4) are basically used to determine an amount by which PSD of the signal transmitted by the base station can be reduced. In particular, as clearly seen from these equations, if there is a sufficient amount of the available bandwidth (B2), then it is possible to achieve a significant level of PSD reduction expressed by the factor , without substantial negative impact on throughput. The exponent of is a negative number (see equation (4)), and if is large, then decreases sufficiently quickly as the bandwidth B2increases. This indicates that if there is the sufficient available bandwidth B2, it is possible to significantly reduce (by the factor ) the transmitted signal PSD without loss of throughput. This approach is more preferable for user equipment with high SINR (i.e. ), allowing to efficiently compensate for losses associated with the PSD reduction.

[0178] The approach described above with reference to equations (1)-(4) and Figure　7 substantially represents a tool that motivates to maximally effectively utilize the available frequency resource allocated to the user equipment when implementing a EE operation mode(s) of the base station based on reducing DL transmission PSD, and this tool will be used accordingly in the present invention, which will be described in detail below.

[0179] Thereafter, in continuation of the example disclosed with reference to Figures　4, 5, the illustration is given, with reference to Figure　8, of problems arising when potentially applying the abovementioned tool, which is based on the bandwidth stretching, to the scenario where the three PSD reduction values - P1, P2, P3 - are configured for two user equipments UE1, UE2 by using the parameter powerOffset-r18 in the RRC container CSI-ReportSubConfig-r18. In the considered example, without loss of generality, P1 is assumed to be indicative of no PSD reduction.

[0180] In the upper part of Figure　8, the grey rectangle for each of UE1, UE2 respectively shows a frequency resource for P1, i.e. substantially the initially allocated frequency resource due to the absence of PSD reduction according to the value P1. According to the middle part of Figure　8, the PSD reduction from P1 to P2 (shown by the arrow) occurs, and, at the same time, for each of UE1 and UE2 the bandwidth is accordingly stretched (the wider grey rectangles in the corresponding part of Figure　8) to compensate for the losses in throughput at the side of said user equipment, in view of the presence of the available frequency resource. According to the lower part of Figure　8, the greater PSD reduction from P1 to P3 (shown by an arrow) occurs, and it is required to perform, for each of UE1 and UE2, the greater stretching of the used bandwidth allocated to the user equipment.

[0181] The drawbacks of applying the bandwidth stretching tool for the PSD reduction approach according to 5G NR are directly visible in Figure　8. Upon reduction by the fixed value P2, the bandwidth for each of UE1, UE2 is stretched, but the available frequency resource is utilized not entirely; upon reduction by the greater value P3 and respectively stretching the bandwidth for each of UE1, UE2, competition for the resource occurs between them, and the problem arises at the base station side how to simultaneously serve said two user equipments, since the used frequency resource for each of them becomes significantly larger than the available one. As follows from the aforesaid, it is rather difficult for the base station to select the levels P2, P3 to efficiently adapt PSD of the transmitted signal, since these levels are not related anyhow with specific conditions of data transmission to a user equipment(s) particularly in view of the quantized nature of PSD reduction levels which are predefined according to 5G NR.

[0182] Figure 9, basically in comparison with Figure 8, illustrates the aspect of the technical object of the present invention, in particular, development of the approach of flexible ("soft") PSD adaptation when implementing EE operation modes of the base station, without using predefined quantized reductions of PSD of the transmitted signal, as in 5G NR. According to the illustration of Figure 9, in accordance with this approach of the present invention, it is required to dynamically calculate the level P4 of PSD reduction in such a way that it is possible to maximally efficiently use the available frequency resource, without the competition (see the lower part of Figure　8) and without unused intermediate portions (see the middle part of Figure　8).

[0183] The primary idea of the present invention is to reformat the CSI report based on which the base station inter alia takes a decision on transitioning to a specific EE mode. As previously noted, in 5G NR the user equipment is to recalculate the entire CSI report, including RI, PMI, CQI (reflecting the optimal MCS), for each configured PSD reduction value (powerOffset-r18) and accordingly report the CSI separately for each powerOffset-r18. The present invention, generally speaking, provides for reporting, by the user equipment within the CSI, an optimal MCS, which is reflected by the parameter CQI, for a different number of MIMO layers (reflected by the parameter RI in the CSI); accordingly, in the present invention, the user equipment, based on measurements of CSI-RSs received from the base station, determines the number of MIMO layers which is preferred for the user equipment and calculates a precoding matrix and CQI for this preferred number of MIMO layers (RI), and the user equipment also obtains a precoding matrix and calculates CQI for at least one number of MIMO layers which is respectively less than the preferred RI. In other words, the present invention provides for calculating CQIs reflecting respective optimal MCSs, not for different values of powerOffset-r18 predefined in the base station (as in 5G NR), but for different numbers of MIMO layers. Respective rearrangement of the CSI report is required at the user equipment side to implement said concept of the present invention, as generally outlined above.

[0184] Hereinafter obtaining of a precoding matrix at the user equipment side according to an embodiment of the present invention is disclosed with reference to Figures　10 to 12b. This disclosure is provided, without limitation, in relation to the abovementioned Type　1 codebook according to specification TS 38.214, however, it should be clear to a skilled artisan that a different codebook can be used to implement the present invention.

[0185] Figure　10 provides the illustrative representation of Type　1 codebook. Each of possible spatial beams in which the base station can perform directional data transmission upon having performed respective D-BF is represented in the codebook by a beamforming spatial beam vector (shown schematically as circles in the 2D grid in Figure　10).

[0186] A spatial beam vector is the Kronecker product of a Discrete Fourier Transform (DFT) vector by a DFT vector , i.e.

[0187]

[0188] where

[0189]

[0190]

[0191] is the number of CSI-RS ports of the antenna array (or its part) of the base station along the first spatial dimension and is the respective oversampling factor, is an index of the spatial beam vector in the codebook along the first spatial dimension, is the number of CSI-RS ports of the base station antenna array along the second spatial dimension and is the respective oversampling factor, is an index of the spatial beam vector in the codebook along the second spatial dimension, is the imaginary unit, and denotes transposing. By using the oversampling factors ( , ), a sequential linear phase shift is provided per each DFT vector in the directions , , respectively; as a consequence, the overall density of the considered beam structure is significantly increased. As a result, the size of the codebook is along the first spatial dimension (in horizontal direction in the non-limiting illustration of Figure　10) and along the second spatial dimension (in vertical direction in Figure　10), i.e. the total number of spatial beam vectors defined by the codebook is . According to TS 38.214, .

[0192] When the user equipment calculates the precoding matrix based on said codebook, the capability of each CSI-RS port of the base station antenna array to transmit a signal with one of two different, orthogonal polarizations is taken into account. These orthogonal polarizations can be linear (vertical and horizontal) polarizations, as well as circular (right-hand and left-hand) polarizations. Three dimensions are substantially involved in said calculation: the first spatial dimension (N1), the second spatial dimension (N2), and the polarization dimension (P). Accordingly, the total number of CSI-RS ports in the base station antenna array is . Moreover, the above discussion of Figure　10, including equations (5)-(7), is given not taking polarization into account (i.e. under implicit assumption of one specific polarization (P=1)).

[0193] It is assumed in the text of the application and figures, that P=2, i.e. both orthogonal polarizations are used for DL transmission by the base station.

[0194] The possible supported configurations of Type　1 codebook are shown in below Table　1 which substantially represents Table　5.2.2.2.1-2 from TS　38.214:

[0195]

[0196] In the illustrative example shown in Figure　10, O1=O2=4.

[0197] At the same time, it should be clear to a skilled artisan that the present invention also applies to the case where signal transmission is carried out with only one polarization, i.e. when P=1.

[0198] Figures 11a, 11b provide illustrations of possible precoding matrices for cases when one spatial beam vector is selected from the codebook ( in Figures　11a and 11b), where Figure　11a refers to the case when the preferred number of MIMO layers determined by the user equipment is equal to one, and Figure　11b refers to the case when the preferred number of MIMO layers for the user equipment equals two. In Figures　11a, 11b, is the antenna polarization coefficient defined by the following equation:

[0199]

[0200] the parameter NCSI-RScomprised by the normalization multiplier by which the precoding matrix is multiplied represents the number of CSI-RS ports, and the application of said normalization multiplier to the precoding matrix is basically aimed at uniformly distributing the base station transmission power over all the respective number of MIMO layers.

[0201] Therefore, in Figure　11a (RI=1) the selected one spatial beam vector (which is shown schematically by the vertical arrow within the circle) is used to obtain the precoding matrix; in Figure　11b (RI=2) the same single spatial beam vector (which is again shown schematically by the vertical arrow within the circle) and both orthogonal polarizations , (which is schematically shown by the horizontal dashed arrow within the circle) are used to obtain the precoding matrix. That is, in the case of Figure　11b the polarization space is fully utilized; in fact, this means that both MIMO layers will be transmitted from the base station to the user equipment in the one spatial beam, but with the different polarizations.

[0202] Figures　12a, 12b, in the format similar to Figures　11a, 11b, provide illustrations of precoding matrices for cases when two spatial beam vectors ( and in Figures　12a, 12b) are selected from the codebook (Figures　12a and 12b), where Figure　12a refers to the case when the preferred number of MIMO layers determined by the user equipment is equal to three (RI=3), and Figure　12b refers to the case when the preferred number of MIMO layers for the user equipment equals four (RI=4). The usage of the spatial beam vectors and and the polarization space is illustrated in Figures　12a, 12b by the respective arrows in two circles, similarly to Figures　11a, 11b.

[0203] In general, a precoding matrix is formed by precoding vectors (in Figures　11a to 12b, the precoding vectors are shown as column vectors without limitations). The number of precoding vectors in the precoding matrix is equal to the respective preferred number of MIMO layers, and the size of each precoding vector is equal to the number of CSI-RS ports according to the codebook (see Table　1). It should be noted that, in accordance with 5G NR, the base station can support at most 8 MIMO layers per user equipment. It should be also noticed that that the normalization factor by which the precoding matrix is multiplied (see Figures　11a to 12b) is generally expressed as ; the preferred number RI of MIMO layers and the respective number L of spatial beam vectors selected from the codebook are related by the following equation:

[0204] ,

[0205] where denotes rounding to the closest greater integer; i.e.

[0206]

[0207] in the considered case where both orthogonal polarizations are used.

[0208] Specification TS　38.214 defines strict requirements with respect to combinations of spatial beam vectors that can be used for subsequent DL transmission of a respective number of MIMO layers (RI=3, 4, 5), furthermore, according to said specification, joint encoding of indices of selected spatial beam vectors is to be used for reporting them in PMI within the CSI report.

[0209] In the present invention, in general, it is proposed to provide a user equipment with greater freedom in selecting spatial beam vectors from the codebook and to avoid the joint encoding of their indices for the CSI report, unlike 5G NR.

[0210] More particularly, according to the considered embodiment of the present invention, the user equipment determines the preferred number of MIMO layers (RI) based on measurements of CSI-RSs received from the base station, as performed by the user equipment. Based on said measurements, the user equipment determines a receive quality metric corresponding to each spatial beam vector from the set of spatial beam vectors defined by the codebook (see Figure　10), and selects (see equation (9)) spatial beam vectors with larger corresponding receive quality metrics.

[0211] According to a possible implementation, the receive quality metric is an indicator of received power of the respective beam, said indicator being obtained based on the CSI-RS measurements and the corresponding spatial beam vector. The respective received power is calculated as follows:

[0212]

[0213] where , , is a spatial beam vector;Hi,pis a channel matrix for an i-th subcarrier among NSCsubcarriers and a p-th polarization from the two orthogonal polarizations, the channel matrix being calculated by the user equipment based on the CSI-RS measurements; denotes Hermitian conjugation.

[0214] Therefore, in the considered implementation, selection of spatial beam vectors will be performed by the user equipment according to corresponding larger received power indicators determined, for example, by equation (10). It should be clear to a skilled artisan that not the entire set of spatial beam vectors of the codebook can be used when selecting the required number of spatial beam vectors - for example, the user equipment may be aware in advance that some spatial beam vectors of said set will not be relevant for the selection being performed.

[0215] Other receive quality metrics can be used for selecting spatial beam vectors in the considered embodiment. For example, according to an alternative implementation of this embodiment, predicted spectral efficiency values of respective DL data transmissions can be used as the receive quality metrics.

[0216] In the context of the task of rearranging the CSI report according to the present invention, the selection of L spatial beam vectors is performed as follows. The user equipment first selects, from the codebook, a spatial beam vector with the largest receive quality metric (for example, with the highest relative received power). Hereinafter in the text of the application, such a selected vector may be referred to as "the strongest spatial beam vector" without limitations. The strongest spatial beam vector is symbolically shown by the black circle for the sake of illustration in Figure　10.

[0217] The structure of the considered codebook is such that the selected strongest spatial beam vector, due to the usage of oversampling, defines an orthogonal basis in the codebook. In accordance with the present invention, selection of other of the L spatial beam vectors should be primarily performed in this orthogonal basis. In Figure　10, the dashed circles symbolically depict the subset of options of selection of spatial beam vectors in the orthogonal basis defined by the strongest spatial beam vector. Furthermore, in Figure　10 the arrows show illustrative lobes for said orthogonal basis, the lobes schematically depicting DL transmission directions along the respective spatial dimensions. Therefore, the spatial beam vectors selected in such a way are mutually orthogonal. For further illustration, the grey circles in Figure　10 show the subset of options of selection of spatial beam vectors in the orthogonal basis defined by the vector in the codebook.

[0218] Then, in accordance with the consideration embodiment, the user equipment orders the selected L spatial beam vectors according to the corresponding receive quality metrics. As a result, the precoding matrix calculated by the user equipment will have the nested structure, and, provided said precoding matrix is appropriately reported in the CSI to the base station, the base station will be aware of spatial beams which are preferable for the user equipment for the respective number of MIMO layers.

[0219] The CSI report arrangement according to the present invention is underlain by the nested property of the precoding matrix obtained according to the approach described above with reference to Figures　10 to 12 and equations (5)-(10), in relation to different numbers of MIMO layers preferable for the user equipment. Thereafter, with reference to Figure　13, the disclosure is provided for a respective embodiment of a method 1300 of calculating CSI parameters based on measurements of CSI-RSs transmitted by a base station of the wireless communication system (e.g. such as the BS 602-A, 602-B, 602-C in Figure　6), the measurements being performed by a user equipment (e.g. such as the UE 601-1, 601-2, 601-3, ... in Figure　6).

[0220] In step 1310, the user equipment determines the number of MIMO layers preferred for the user equipment according to the current DL channel state. This determination can be carried out by using 5G NR techniques. As in 5G NR, the calculated preferred number of MIMO layers is reflected by the parameter RI in the CSI report according to the present invention, and thereafter in the text of the present application, said preferred number of MIMO layers may be denoted as RI without limitations.

[0221] In step 1320, the user equipment selects, for the preferred number of MIMO layers determined in step 1310, a respective number of spatial beam vectors from the codebook and calculates a precoding matrix according to the approach disclosed with reference to Figures　10 to 12b and equations (5)-(10). More specifically, according to said approach, spatial beam vectors (see equations (5)-(7), (9)) selected from the codebook (see Figure　10) are ordered according to receive quality metrics corresponding thereto (see equation (10)), and the precoding matrix is calculated based on the ordered L spatial beam vectors (see Figures　11a to 12b, equations (5)-(8)). The precoding matrix obtained by the user equipment for the preferred number of MIMO layers (RI) may be referred to hereafter in the text of the application as "the primary precoding matrix" without limitations.

[0222] In step 1330, the user equipment calculates, for the primary precoding matrix obtained in step 1320, a channel quality indicator (CQI) reflecting an MCS optimal for the user equipment according to the current DL channel state. This calculation can be performed in accordance with 5G NR techniques. In the preferred implementation of the considered embodiment, the CQI relates to wideband (WB) report, i.e. it is calculated for the entire frequency band for which the CSI is to be obtained. Accordingly, the CQI corresponding to the WB report context is denoted throughout the text of the present application and in the figures as "wCQI." The wCQI calculated by the user equipment for the preferred number of MIMO layers (RI) may be referred to hereinafter in the text of the application as "the primary wCQI" without limitations.

[0223] In step 1340, the user equipment calculates at least one additional wCQI for at least one number of MIMO layers which is less than RI. In the considered embodiment, the calculation in step 1340 is performed for a set { }, where denotes a k-th number of MIMO layers which is respectively less than , , is the number of s in the set { }. The set of numbers of MIMO layers for which a respective additional wCQI is to be calculated may contain only one smaller less of MIMO layers ( ) or several sequentially less numbers of MIMO layers ( ). The preferred implementation of calculating an additional wCQI for each from the set{ } according to step 1340 of the method 1300 is described below; such an additional wCQI may be respectively denoted as "wCQIk" in the text of the present application and in the figures.

[0224] In sub-step 1341, the user equipment selects, from the ordered L spatial beam vectors obtained in step 1320 and keeping said ordering thereof, a required number

[0225]

[0226] of spatial beam vectors with larger corresponding receive quality metrics, i.e. Zkstronger spatial beam vectors. For example, if , then only the strongest spatial beam vector is selected from the L spatial beam vectors (Zk=1) in sub-step 1341.

[0227] In sub-step 1342, the user equipment generates a k-th precoding matrix based on the selected Zkspatial beam vectors. Accordingly, the number of precoding vectors which the k-th precoding matrix is comprised of equals . Due to the abovementioned nested property of the primary precoding matrix obtained according to the present invention (step 1320), the k-th precoding matrix is substantially a submatrix of the primary precoding matrix.

[0228] In sub-step 1343, the user equipment, similarly to step 1330, calculates a k-th additional wCQIkfor the k-th precoding matrix obtained in sub-step 1342.

[0229] In one possible implementation, the user equipment generates the set { } for step 1340 according to the following principle: each in the set { } corresponds to a pair of integer values of the number of MIMO layers, i.e.

[0230]

[0231] In equation (12), is RI determined in step 1310. In this implementation, the user equipment can itself determine the entire set { }, from

[0232]

[0233] or can be preset in the base station and signaled in advance to the user equipment via RRC signaling.

[0234] For instance, if the preferred number of MIMO layers is determined in step 1310 as equal to 8 (i.e. the maximum value according to 5G NR) or 7, then, in view of equations (9) and (13), the number of less numbers of MIMO layers in the considered set thereof will be equal to 3, and, respectively, can be equal to 6 or 5, can be equal to 4 or 3, can be equal to 2 or 1 according to equation (12).

[0235] In another possible implementation, a combination of values of numbers of MIMO layer is signaled in advance from the base station to the user equipment via RRC signaling, and the user equipment includes, into the set { } for step 1340, all values from said combination which are less than RI. For example, the combination {8, 6, 4, 2} can be transmitted from the base station, and in step 1310 the user equipment determined that RI=6; accordingly, the set { } in this case will have the following form: {4, 2}.

[0236] It should be appreciated that the approach to calculating the CSI parameters for multiple numbers of MIMO layers, as described above, is applicable even for a preferred number of MIMO layers greater than eight. In this case more than one orthogonal basis in the codebook (see Figure　10) can be used in a similar way to select a required number of MIMO layers.

[0237] It should be emphasized herein that, unlike 5G NR where the CSI report is entirely recalculated for each of PSD reduction values (powerOffset-r18) preconfigured for a user equipment, according to the present invention the user equipment recalculates the precoding matrix and the optimal MCS for one or more less numbers of MIMO layers (see sub-steps 1342, 1343).

[0238] In order to generate the CSI based on the parameters calculated for the multiple numbers of MIMO layers in steps 1310-1340 of the method 1300, the approach to reporting the precoding matrix to the base station is used according to the present invention that is different from the joint encoding used in 5G NR. Therefore, according to the approach corresponding to the preferred embodiment of the present invention, in order to inform the base station about the precoding matrix in the CSI report, it is proposed to separately report indices BIiof the L spatial beam vectors selected by the user equipment from the codebook for the preferred number of MIMO layers (steps 1310, 1320), and respective polarization co-phasing factors PLZi, where . Here, BI is a binary representation of a spatial beam vector index for the 2D codebook grid (i.e. jointly for the first and second spatial dimensions (see equations (5)-(7), Figure　10)), and PLZ is a binary representation of a polarization coefficient index (see equation (8)).

[0239] In accordance with said preferred embodiment of the present invention, the user equipment includes the following into the single CSI report: the parameter RI reflecting the preferred number of MIMO layers (step 1310); the spatial beam vector indices BIiwhich are ordered according to the abovementioned ordering of the L spatial beam vectors (step 1320), the respective polarization co-phasing factors PLZiordered according to the ordering of the indices BIi, , and the calculated wCQIs, in particular, the primary wCQI (step 1330) and the additional wCQIks, (sub-step 1343). Accordingly, while considering the example of Figures　10 to 12b with reference to equations (5)-(10), the bit field size for the index of the strongest spatial beam vector will be

[0240]

[0241] and the bit field size for each of the indices of the spatial beam vectors, , selected according to the orthogonal basis defined in the codebook by the strongest spatial beam vector will be

[0242]

[0243] The calculated wCQIs are ordered within the CSI according to a format predefined in the base station and signaled in advance to the user equipment, for example, via RRC signaling. According to the preferred embodiment of the present invention, said predefined format corresponds to the ordering of the calculated wCQIs in the CSI according to the numbers of MIMO layers corresponding thereto, i.e. each of the calculated wCQIs is ordered within the CSI according to the number of MIMO layers for which said wCQI was calculated. For example, the CSI report can comprise first the primary wCQI calculated for the preferred number of MIMO layers, followed by the additional wCQI calculated for the closest less number of MIMO layers, and so on; i.e., in this example, the calculated wCQIs are ordered in descending order of the respective numbers of MIMO layers. It should be clear to a skilled artisan that other options ordering wCQIs within the CSI can be used, e.g. in ascending order of respective numbers of MIMO layers. It is essential that the base station and the user equipment are in advance aware of the wCQI representation format in the CSI report according to the present invention, and, therefore, the base station will know, from the received CSI report, which number of MIMO layers a specific reported wCQI corresponds to.

[0244] As a result, having received from the user equipment the CSI report arranged, in general, in the abovementioned way, and knowing in advance the nested nature of the reported precoding matrix, the base station will be able to determine which precoding matrix will be used for a respective less number of MIMO layers (by using a respectively less number of stronger precoding vectors from their ordered set indicated in the CSI by using the indices and using the respective PLZis), and the base station will know which wCQI (i.e. which optimal MCS) of the reported wCQIs corresponds to said less number of MIMO layers. Based on the information received in the CSI report, the base station can perform the flexible PSD adaptation of the transmitted signal the embodiments of which will be described below.

[0245] Thereafter, with reference to Figures　14a to 17, the description is provided with respect to embodiments of how the CSI report can be arranged according to the present invention.

[0246] In one embodiment, as in 5G NR, the CSI report is transmitted via UCI, UL transmission of UCI is scheduled in advance in the base station. Two parts are allocated in UCI for transmitting CSI: CSI part　1 with a fixed payload size (in bits), and CSI part　2 with a variable payload size, where the payload size of CSI part　2 depends on contents of CSI part　1. Parameters comprised by the CSI are accordingly distributed over CSI part　1 and CSI part　2 in UCI. The payload of CSI part　2 can be obtained in the base station only after decoding of the payload of CSI part　1.

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

[0248] The UCI transmission itself is carried out in the physical layer (L1).

[0249] The disclosure of possible implementations of said embodiment with reference to Figures　14a to 17 is led under the non-limiting assumption that four (L=4) spatial beam vectors for the preferred number of MIMO layers (RI) equal to eight (or seven) should be reported in the CSI report from by the user equipment; therefore, the CSI report will contain four ordered spatial beam vector indices BI, four respectively ordered polarization co-phasing factors PLZ, and four channel quality indicators wCQI ordered in descending order of the respective MIMO layer numbers.

[0250] In accordance with the implementation illustrated in Figures　14a, 14b, RI and the primary wCQI (denoted as wCQI4in all of Figures　14a to 17) calculated for the number of MIMO layers reflected by RI (see step 1330) are included into CSI part　1.

[0251] According to one option of the considered implementation illustrated in Figure　14a, CSI part　2 includes the spatial beam vector indices BIi, followed by the respective polarization co-phasing factors PLZi, where , followed by the additional channel quality indicators wCQI3, wCQI2, wCQI1. As noted earlier, the spatial beam vector indices BIiare ordered ― therefore, BI1is the index of the strongest spatial beam vector, BI2, BI3, BI4are the indices of spatial beam vectors with successively lower receive quality metrics; the polarization co-phasing factors PLZ1, PLZ2, PLZ3, PLZ4are ordered according to the ordering of the spatial beam vector indices. wCQI3corresponds to the precoding matrix obtained by using the spatial beam vectors with the indices BI1, BI2, BI3(and accordingly the polarization co-phasing factors PLZ1, PLZ2, PLZ3), i.e. for the number of MIMO layers equal to 6 (or 5); wCQI2corresponds to the precoding matrix obtained by using the spatial beam vectors with the indices BI1, BI2(and accordingly the polarization co-phasing factors PLZ1, PLZ2), i.e. for the number of MIMO layers equal to 4 (or 3); and wCQI1corresponds to the precoding matrix obtained by using the spatial beam vector with the index BI1(and accordingly the polarization co-phasing factor PLZ1), i.e. for the number of MIMO layers equal to 2 (or 1).

[0252] In another option of the considered implementation illustrated in Figure　14b, CSI part　2 includes the spatial beam vector indices BIi, where , followed by the additional channel quality indicators wCQI3, wCQI2, wCQI1, followed by the respective polarization co-phasing factors PLZi, where . The aspects of ordering parameter in the CSI report precisely match the ones reflected in consideration of the abovementioned one implementation option with reference to Figure　14a.

[0253] This other option substantially relies on the fact that 5G NR mMIMO systems are satisfactorily operational without information on polarization, though said information is important. That is, if at least some of the polarization co-phasing factors are lost due to applying the omission mechanism, the base station can employ respective mechanisms (e.g. pseudo-random switching of polarizations) to compensate for said loss and ensure operating the system with acceptable characteristics. Similar mechanisms are planned to be used in 6G xMIMO systems as well.

[0254] In the implementation of the considered one embodiment, as illustrated in Figures　15a, 15b, only RI is included into CSI part　1.

[0255] In one option of said implementation, as illustrated in Figure　15a, CSI part　2 includes the spatial beam vector indices BIi, followed by the respective polarization co-phasing factors PLZi, where , followed by the primary wCQI (wCQI4) and the additional wCQI3, wCQI2, wCQI1. In accordance with another option thereof, as illustrated in Figure　15b, CSI part　2 includes pairs "the spatial beam vector index BIi- the respective polarization co-phasing factor PLZi" where , followed by the primary wCQI (wCQI4) and the additional wCQI3, wCQI2, wCQI1. In both options, the aspects of ordering the parameter within the CSI report precisely match the ones reflected in the consideration of the implementation options with reference to Figures　14a, 14b.

[0256] According to the implementation of the considered embodiment, as illustrated in Figure　16, CSI part　1 includes RI, the primary wCQI (wCQI4), the index BI1of the strongest spatial beam vector, and the respective polarization co-phasing factor PLZ1, while CSI part　2 includes the spatial beam vector indices BIi, followed by the respective polarization co-phasing factors PLZi, where , followed by the additional wCQI3, wCQI2, wCQI1.

[0257] In all of the implementations considered above with reference to Figures　14a to 16 it is assumed that the bit field size in UCI for the index BI1is defined by equation (14), and the bit field size for each of the indices BI2, BI3, BI4is defined by equation (15). It should also be emphasized that the considered implementations are illustrative but not limiting, and other options of arranging the reported parameters within the CSI report can be used in a way apparent to a skilled artisan.

[0258] In another embodiment, alternative with respect to UCI, as illustrated in Figure　17, the CSI report is transmitted via a Medium Access Control (MAC) Control Element (CE), i.e. in the L2 level. According to the structure of the MAC CE message, the parameters reported within the CSI are arranged in octets. As shown in Figure　17 in the standard record format for a bit structure in octets, the MAC CE includes, respectively ordered in octets: RI, the primary wCQI (wCQI4), the spatial beam vector indices BIiand the respective polarization co-phasing factors PLZi, where , and the additional wCQI3, wCQI2, wCQI1. The index BI1, whose bit size is defined by equation (14), is illustratively shown as occupying three octets (i.e. 12 bits in total), and each of the indices BI2, BI3, BI4whose smaller bit size is defined by equation (15), are respectively shown as occupying one octet (i.e. 4 bits). The MAC CE octets following the additional channel quality indicator octets can be used to report other CSI parameters ― for example, as shown in Figure　17, sub-band (SB) report channel quality indicators which are denoted as sCQI in Figure　17. It should be explained herein that in 5G NR sub-bands refer to frequency blocks into which the entire frequency band, for which the CSI is to be obtained, is divided and each comprised of several neighboring physical resource blocks (PRBs).

[0259] It should be clear to a skilled artisan that the embodiment shown in Figure　17 is illustrative but not limiting, and other options of arranging the parameters being reported within the CSI report, over octets in the MAC CE, can be used.

[0260] Thereafter, the illustration is provided, with reference to Figure　18 and with additional reference to Figures　19a, 19b, for an embodiment of a method 1800 of applying, in the base station, the CSI report arranged according to the present invention (see disclosures according to Figures　10 to 17 above) and transmitted by the user equipment, for taking, by the base station, a decision on transitioning to an EE mode with flexible adaptation of DL transmission PSD.

[0261] In step 1810, the base station receives from the user equipment the CSI report the structure of which is illustrated in Figures　14a to 17. More particularly, the CSI report includes the parameter RI reflecting the number of MIMO layers preferred for the user equipment, the ordered set of spatial beam vector indices for RI, and the respective set of polarization co-phasing factors, as well as the set of channel quality indicators (CQIs) ordered according to respective numbers of MIMO layers, including the channel quality indicator for RI and at least one additional channel quality indicator for at least one less number of MIMO layers.

[0262] In step 1820, the flexible PSD adaptation is performed in the base station according to the approach of the present invention in order to implement transition to a required EE operation mode of the base station, and, in step 1830, the base station accordingly schedules and performs DL data transmission (PDSCH). This approach is described in more detail below with references to Figures　19a, 19b.

[0263] A quantized channel quality indicator (CQI) can be used in the base station as an implicit characteristic of SINR at the user equipment side when applying, by the base station, a respective precoding matrix to carry out D-BF of a transmitted signal. The adaptation of PSD of the transmitted signal at the base station side according to the present invention is generally based on the fact that the base station, knowing the CQI for each of the precoding matrices reported using the spatial beam vector indices and polarization co-phasing factors, in further view of the respective ordering and the nested structure of the information about the precoding matrix, can select a modulation and coding scheme (MCS) for said precoding matrix, provided DL transmission PSD will change in the base station.

[0264] Figure 19a schematically shows the sequence of actions performed by the base station in the context of the flexible PSD adaptation according to the present invention, under assumption that the base station uses only one precoding matrix determined for the preferred number of MIMO layers (RI), i.e. the primary precoding matrix in the terminology of the present application. As follows from Figure　19a, the base station obtains, from the received CSI, the CQI calculated by the user equipment for the primary precoding matrix (i.e. the primary CQI in terminology of the present application), and, in accordance with the aforesaid, determines based thereon, e.g. by using techniques available in 5G NR, quantized approximation of SINR at the user equipment side, where said quantized approximation may be referred to as the estimated SINR in the user equipment in the text of the present application and in the figures, without limitations. Then, the base station calculates the PSD reduction value based on equation (4) (i.e. based on stretching the allocated frequency resource (FDRA) based on the available frequency resource and, preferably, taking into account the current number of active user equipments served by the base station), applies to scale the estimated SINR (see equation (3)), and accordingly calculates the MCS optimal for the obtained scaled SINR. The approach inverse to the abovementioned technique of calculating the estimated SINR based on the CQI reported in the CSI report can be used for said calculation of the optimal MCS. Finally, having performed step 1820 in said way, according to Figure　19a the base station schedules and performs PDSCH transmission by using the primary precoding matrix (and, accordingly, RI), the calculated MCS, and the calculated PSD reduction value, i.e. performs step 1830. In other words, in accordance with the disclosure of Figure　19a, if the base station intends to reduce PSD of the transmitted signal without changing the precoding matrix, the base station can estimate how SINR will change at the user equipment side due to said reduction, and accordingly recalculate the DL transmission parameters.

[0265] The limitation of the scheme disclosed above with reference to Figure　19a is that it works well for high SINRs, i.e. when the DL channel state allows the base station to use a larger number of MIMO layers for PDSCH transmission. At the same time, the number of MIMO layers preferable for the user equipment also depends on SINR in the DL channel at the user equipment side. Accordingly, at low SINRs it may be more advantageous to use a less number of MIMO layers for DL transmission, since the base station can distribute all transmission power over less number (e.g. one or two) of spatial streams. That is, when reducing PSD (and accordingly reducing the estimated SINR in the user equipment), at some time instance it may turn out to be optimal for the base station to use a different precoding matrix corresponding to a less number of MIMO layers.

[0266] Hereinafter the embodiment of adaptation of DL transmission PSD is described with reference to Figure 19b, where the parameters contained in the CSI report according to the present invention are fully utilized. In particular, due to the arrangement of the CSI report according to the present invention, as described above, and, in particular, due to the nested structure of the information about the precoding matrix, precoding (sub)matrices for different numbers of MIMO layers and channel quality indicators corresponding thereto are available in the base station. Therefore, the base station can select, for the number RI' of MIMO layers which is less than the preferred number of MIMO layers reported by the user equipment by the parameter RI, the respective less number (see equation (11)) of stronger spatial beam vectors indicated by the ordered indices BI within the CSI (see Figures　14a to 17), and calculate the precoding matrix for RI' also using the respective polarization co-phasing factors, and the base station, having the channel quality indicator for the calculated precoding matrix from the CSI report (see sub-step 1343; Figures　14a to 17), can make an attempt to adapt PSD within the scope of said smaller RI'. In essence, in order to implement said adaptation according to the considered embodiment, the approach described above with reference to Figure　19a is independently used for each of the required numbers of MIMO layers, along with subsequently selecting, by the base station, the optimal number of MIMO layers.

[0267] The upper part of Figure　19b corresponds to Figure　19a, i.e. the PSD adaptation is performed by the base station for the number of MIMO layers which is preferred for the user equipment and reported by the parameter RI in the CSI report (see Figures　14a to 17).

[0268] The lower part of Figure　19b corresponds to the independent execution of the sequence of actions according to Figure　19a for the number RI' of MIMO layers less than RI. For example, if the user equipment has reported RI = 8, then the base station can select RI' equal to 6. As noted previously, the decision to select a less number of MIMO layers can be taken by the base station due to a significant decrease of the estimated SINR in the user equipment at a greater number of MIMO layers (RI). Therefore, the base station obtains, from the received CSI, the channel quality indicator CQI' respectively calculated by the user equipment for RI', and, based on CQI', determines the estimated SINR' in the user equipment. Then, the base station calculates the PSD reduction value based on equation (4), applies to scale the estimated SINR', and accordingly calculates MCS' for DL transmission that is optimal for the resulting scaled SINR'.

[0269] In accordance with the embodiment illustrated in Figure　19b, based on at least the preferred EE mode (i.e. whether medium or more aggressive PSD reduction is required), as well as on the estimated spectral efficiency at the user equipment side upon having applied the respective PSD reduction or, in other words, the respective data transmission rate for DL transmission, the base station selects an optimal modulation and coding scheme from the calculated MCS and MCS' and selects the respective number of MIMO layers, i.e. RI or RI', thereby completing execution of step 1820.

[0270] Thereafter, according to the considered embodiment, the base station obtains the precoding matrix for the selected number of MIMO layers by using the information about precoding matrix arranged in the CSI according to the present invention. For instance, if the base station selects RI' = 6, then the base station selects stronger spatial beam vectors, in the number defined by equation (11) (i.e. three in this case), the spatial beam vectors being respectively indicated by the ordered indices BI1, BI2, BI3and calculates the precoding matrix by using the respective polarization co-phasing factors PLZ1, PLZ2, PLZ3from the CSI report (see Figures　14a to 17). In a similar way, if the base station selected RI = 8, then all the reported spatial beam vectors and polarization co-phasing factors would be used to calculate the precoding matrix, as in the case of Figure　19a.

[0271] Finally, according to Figure　19b, the base station schedules and performs PDSCH transmission using the calculated precoding matrix (and the respectively selected number of MIMO layers), the selected modulation and coding scheme, and the calculated PSD reduction value, thereby completing step 1830.

[0272] Figure 19b shows independent execution, by the base station, of the sequence of actions according to the considered embodiment for two values of the number of MIMO layers. It should be appreciated that this aspect does not impose any limitations onto the present invention, and the proposed approach can be similarly applied to a greater number of values of the number of MIMO layer ― for example, when considering the CSI report arranged according to any of the illustrations of Figures　14a to 17, said approach can be equally applied for the number of MIMO layers equal to 4 or 3, and for the number of MIMO layers equal to 2 or 1. At the same time, in practical implementation, it is unlikely that if, for example, the user equipment reported the preferred number of MIMO layers equal to 8 in the CSI report, the base station would need to reduce the number of MIMO layers to two or one; i.e. the base station may apply the process of flexibly adapting PSD according to the considered embodiment of Figure　19b not for all the possible less numbers of MIMO layers provided for by the CSI report according to the present invention.

[0273] It should be emphasized that, according to the embodiments of step 1820 described above with reference to Figures　19a, 19b, the base station determines the PSD reduction value not from a predefined set, as in 5G NR, but in the adaptive, flexible manner depending on the current DL channel state and available frequency resource.

[0274] In accordance with the embodiment of the present invention, the base station indicates in advance to the user equipment, via a respectively arranged CSI request according to the present invention, to calculate the CSI report for two or more numbers of MIMO layers, including the number of MIMO layers preferred for the user equipment and at least one number of MIMO layers which is less than the preferred number of MIMO layers, thereby substantially being indicative of the intention of the base station to perform adaptation of DL transmission PSD according to the approach of the present invention described with reference to Figure　19b, or indicates to calculate the CSI report only for the preferred number of MIMO layers, thereby essentially being indicative of the intention of the base station to perform DL transmission PSD adaptation according to the approach described with reference to Figure　19a. More detailed disclosure of the aspect of the present invention according to this embodiment will be provided hereinbelow.

[0275] Thereafter, interaction between the wireless network (NW) and the user equipment (UE) in the context of the flexible PSD adaptation of a transmitted signal according to the present invention is described with reference to the illustrative diagram of Figure　20, in the format similar to Figure　5.

[0276] The base station, which is part of the NW, similarly to 5G NR, transmits in advance CSI configuration information to the user equipment via RRC signaling (action 1 in Figure　20), including inter alia parameters of the codebook (see e.g. Table 1). The configuration information can also include the maximum number of less numbers of MIMO layers for which additional channel quality indicators should be calculated, or a set of such less numbers of MIMO layers, as well as information about a format of ordering of calculated CQIs in CSI, as described above. One or more RRC messages can be used to transmit the configuration information from the base station according to action 1.

[0277] The base station transmits to the user equipment, via DCI, a CSI request arranged according to the present invention (action 2 in Figure　20).

[0278] According to the preferred implementation of the considered aspect of the present invention, a set of bit values is preset in the base station, and said set of bit values is signaled in advance from the base station to the user equipment via RRC signaling (e.g. during execution of action 1 in Figure　20). A non-limiting example of the code table is generally presented below in Table 2, where, by means of bit values, encoding of respective instructions to the user equipment with respect to obtaining the CSI report is implemented in the CSI request.

[0279]

[0280] Table 2Accordingly, a code table similar to Table 2 is preset in the base station and sent in advance to a user equipment(s) via RRC signaling.

[0281] When requesting CSI, the base station, based on the current network load, sets a value of said bit field of the CSI request. For example, if the network load is low or medium and there is an opportunity to reduce DL transmission PSD along with respective bandwidth stretching to compensate for throughput losses, the base station will choose the value "...01". If the network load is sufficiently high, then the base station will select the value "...10" in order to save uplink control channel (UCI) resources.

[0282] The ellipses in Table 2 indicate that, depending on implementation, different numbers of bits may be used to represent a relevant bit value, as well as different numbers of options for the relevant bit value. For example, for the indication to calculate the CSI report for two or more numbers of MIMO layers, two bit combination options for the bit value can be used, where the one bit combination indicates to calculate the CSI report for the two or more numbers of MIMO layers and transmit it via UCI (see Figures　14a to 16), and the other one indicates to calculate the CSI report for the two or more MIMO layer numbers and transmit it via MAC CE (see Figure　17). The same equally applies to the value denoted in Table 1 as "...10".

[0283] Based on measurements of CSI-RSs received from the base station, the user equipment obtains and transmits the CSI report according to the present invention (actions 3, 4 in Figure　20), in accordance with the indication in the received CSI request. If the bit field value of the CSI request indicates to calculate the CSI report for two or more numbers of MIMO layers (as illustrated by "...01" in Table 2), the user equipment will execute the method 1300 described above with reference to Figures　10 to 17. If the bit field value indicates to calculate the CSI report only for the preferred number of MIMO layers (as illustrated by "...10" in Table 2), then the user equipment will obtains the CSI report generally arranged in the format according to the present invention described above with reference to Figures　14a to 17, but, when executing the method 1300, the user equipment will not determine and include into the CSI report additional channel quality indicators and additional polarization co-phasing factors for respective less numbers of MIMO layers. In other words, in this case the user equipment accordingly will not perform at least step 1340 of said method. The CSI report size when "...10" has been indicated will be less than the CSI report size when "...01" has been indicated.

[0284] Based on the received CSI report, the base station performs the flexible adaptation of transmitted signal PSD in accordance with the approach of the present invention, as disclosed above with reference to Figures　18 to 19b, and scheduling of DL data transmission (action 5 in Figure　20), signals the user equipment about the scheduled DL transmission via PDCCH (action 6 in Figure　20), and carries out transmission of PDSCH to the user equipment (action 7 in Figure　20) in accordance with the performed PSD adaptation, as well as in accordance with the calculated precoding matrix and selected optimal MCS (see steps 1820, 1830 with reference to Figures　19a, 19b). The user equipment performs reception of PDSCH (action 8 in Figure　20).

[0285] The present invention, in general, enables to implement an EE mode(s) of the base station with flexible adaptation of transmitted signal PSD by using the CSI report provided by the user equipment, along with minimizing the negative impact onto the system performance. More specifically, calculation and arrangement of the single CSI report for multiple numbers of MIMO layers according to the present invention reduces computational complexity at the user equipment side by avoiding the necessity to recalculate the entire CSI report for each of preconfigured PSD reduction values (powerOffset-r18), as in 5G NR. Furthermore, the present invention enables, at the base station side, to flexibly calculate the PSD reduction value (again, without relying on the predefined set of values of powerOffset-r18, as in 5G NR) with the capability to dynamically select the optimal number of MIMO layers (and respective DL transmission parameters) and optimal usage of the available frequency resource to compensate for associated throughput losses at the user equipment side. Finally, usage of the flexible requesting of CSI according to the present invention enables to reduce overhead on UL transmission of the CSI report.

[0286] FIG. 21 is a block diagram of a terminal or user equipment (UE) 2100 according to an embodiment of the disclosure.

[0287] The terminal is an electronic device capable of wireless communication, may include a User Equipment (UE), a portable phone, a smartphone, a tablet, an Internet of things (IoT) device, etc., having various form factors, and may perform wireless communication with a base station (BS) through a wireless channel.

[0288] Referring to FIG. 21, the UE 2100 may include at least one transceiver (hereinafter, referred to as simply "transceiver") 2101, at least one processor (hereinafter, referred to as simply "processor") 2102, and at least one memory (hereinafter, referred to as simply "memory") 2103. According to at least one or a combination of methods corresponding to the embodiments described in the present disclosure, the transceiver 2101, the processor 2102, and the memory 2103 of the UE 2100 may operate. However, components of the UE 2100 are not limited to the exemplary components illustrated in FIG. 21. In another embodiment, the UE 2100 may further include additional components in addition to the above-mentioned components, or some components may be omitted. Further, in some embodiments, any combination of the transceiver 2101, the processor 2102, or the memory 2103 may be integrated in the form of one component.

[0289] The transceiver 2101 may be a communication circuit or communication circuitry that enables the UE 2100 to perform wireless communication with a node or an entity of a network. For example, the transceiver 2101 may enable the UE 2100 to transmit or receive a signal to or from a BS through cellular communication, or to transmit or receive a signal to or from another UE through cellular communication. For example, the transceiver 2101 may support at least one of various cellular communication technologies including 3rd generation (3G), 4thgeneration (4G), long term evolution (LTE), 5th generation (5G) NR, 6thgeneration (6G), and various cellular wireless communication technologies supported by the transceiver (2101) may include all subsequent generations of evolved wireless communications.

[0290] According to an embodiment, the UE 2100 may include a plurality of transceivers. For example, in the case of supporting evolved-universal terrestrial radio access-new radio (E-UTRA-NR) sual connectivity (EN-DC), the UE 2100 may include a first transceiver supporting the 4G LTE wireless communication and a second transceiver supporting the 5G NR wireless communication. According to another embodiment, in the case of supporting NR-dual connectivity (NR-DC), the UE 2100 may include a plurality of transceivers supporting the 5G NR wireless communication. According to still another embodiment, in the case of supporting near field wireless communication, the UE 2100 may separately include a transceiver supporting at least one standard in the group of wireless communication protocol standards as defined in the protocol standards for Bluetooth®, wireless local area network (WLAN) network (including institute of electrical and electronics engineers (IEEE) 802.11-2016 standard or its amendments, e.g., 802.11ah, 802.11ad, 802.11ay, 802.11ax, 802.11az, 802.11ba, and 802.11be, without being limited thereto).

[0291] According to an embodiment, the transceiver 2101 may include various circuit structures used to transmit or receive signals to or from a BS through a wireless channel. The signals may include control information and data. For example, the transceiver 2101 may include a radio frequency (RF) transmitter for up-converting and amplifying the frequency of a transmitted signal and an RF receiver for low-noise-amplifying a received signal and down-converting the frequency thereof. The transceiver 2101 may output a signal received through a wireless channel to the processor 2102 and may transmit, through a wireless channel, a signal output from the processor 2102.

[0292] The processor 2102 may control general operations of the UE 2100 according to embodiments of the disclosure. The processor 2102 may be implemented by one or more integrated circuit (or circuitry) (IC) chips and may execute various data processings. The processor 2102 may include at least one electric circuit, and may execute instructions (or a program, codes, data, etc.) stored in the memory 2103, individually, collectively or in any combination thereof. Further, the processor 2102 may include a single-core processor or multi-core processor, and may include a processor assembly including a plurality of processing circuits (circuitry) according to a specific implementation scheme.

[0293] The processor 2102 may be electrically, operatively, or communicatively coupled to the transceiver 2101 to control the transceiver 2101.

[0294] The processor 2102 may include at least one processor (or processing circuitry), and the at least one processor may perform the following operations individually, collectively or in any combination thereof. For example, the processor 2102 may include a communication processor (CP) configured to control communication operations and an application processor (AP) configured to control execution of an upper layer (for example, an application layer) . In a specific embodiment, at least a part of the processor 2102 may be included in one chip and the other part of the processor 2102 may be included in another chip. Otherwise, at least one processor may be included in another component, for example, the transceiver 2101 or the memory 2103.

[0295] The processor 2102 may perform or control or cause an operation of the UE 2100 for executing at least one or a combination of methods according to embodiments of the disclosure. For example, the processor 2102 may control operations of the UE 2100 for processing a downlink signal received from a BS or generating and transmitting an uplink signal to a BS. To this end, the processor 2102 may execute a computer program, codes, or instructions stored in the memory 2103, so as to control other components of the UE 2100 to enable execution of various operations.

[0296] The memory 2103 corresponds to a hardware storage device capable of temporarily or permanently storing information and may include one or more storage media. For example, the memory 2103 may include a memory assembly including one or more storage media. For example, the one or more storage media may include permanent memory, such as a hard drive, flash memory, or read-only memory (ROM), semipermanent memory, such as random access memory (RAM), cache memory, or a combination thereof.

[0297] The memory 2103 may be electrically, operatively, or communicatively coupled to the processor 2102 and may be accessed by the processor 2102.

[0298] The memory 2103 may store a computer program, codes, or instructions executable by the processor 2102. According to an embodiment, a computer program, codes, or instructions executable by the processor 2102 may be either stored in a single memory device or separated and distributedly stored in two or more memory devices. By executing the instructions stored in the memory 2103, the processor 2102 may perform various functions according to an embodiment of the disclosure.

[0299] According to an embodiment of the disclosure, operations of the UE 2100 may be caused to be performed based on execution of instructions (or a computer program or codes) stored in the memory 2103 by at least one processor (or processing circuitry) configured to execute the same individually, collectively, or in any combination thereof, based on processing circuitry that is not configured to execute instructions, and / or based on components of processing circuitry that is not configured to execute instructions.

[0300] FIG. 22 is a block diagram of a base station (BS) 2200 according to an embodiment of the disclosure.

[0301] The BS 2200 may perform wireless communication with at least one user equipment (UE) located within the area of the BS 2200 through a wireless channel.

[0302] Referring to FIG. 22, the BS 2200 may include at least one transceiver (hereinafter, referred to as simply "transceiver") 2201, at least one processor (hereinafter, referred to as simply "processor") 2202, and at least one memory (hereinafter, referred to as simply "memory") 2203. According to at least one or a combination of methods corresponding to the embodiments described in the present disclosure, the transceiver 2201, the processor 2202, and the memory 2203 of the BS 2200 may operate. However, components of the BS 2200 are not limited to the exemplary components illustrated in FIG. 22. In another embodiment, the BS 2200 may further include additional components in addition to the above-mentioned components, or some components may be omitted. Further, in some embodiments, any combination of the transceiver 2201, the processor 2202, or the memory 2203 may be integrated in the form of one component.

[0303] The transceiver 2201 may be a communication circuit or communication circuitry that enables the BS 2200 to perform wireless communication with a node or an entity of a network. For example, the transceiver 2201 may enable the BS 2200 to transmit or receive a signal to or from the UE X00 through cellular communication, or to transmit or receive a signal to or from another network entity through wireless communication. For example, the transceiver 2201 may support various cellular communication technologies including 3rd generation (3G), 4thgeneration (4G), long term evolution (LTE), 5th generation (5G) NR, 6thgeneration (6G), and various cellular wireless communication technologies supported by the transceiver (2201) may include all subsequent generations of evolved wireless communications.. According to an embodiment, the transceiver 2201 may include various circuit structures used to transmit or receive signals to or from a UE through a wireless channel. The signals may include control information and data. For example, the transceiver 2201 may include a radio frequency (RF) transmitter for up-converting and amplifying the frequency of a transmitted signal and an RF receiver for low-noise-amplifying a received signal and down-converting the frequency thereof. The transceiver 2201 may output a signal received through a wireless channel to the processor 2202 and may transmit, through a wireless channel, a signal output from the processor 2202.

[0304] Meanwhile, according to an embodiment of the present disclosure, the BS 2200 may perform communication with a node or an entity of a network through wired or wireless communication. For example, the BS 2200 may perform wired or wireless communication with an adjacent BS, or a node or an entity of a core network through a backhaul network. Although not illustrated in FIG. 22, when the BS 2200 performs wired communication, the BS 2200 may further include a separate network interface for wired communication in addition to the transceiver 2201. The network interface may be referred to as network interface circuitry or communication interface circuitry.

[0305] The processor 2202 may control general operations of the BS 2200 according to embodiments of the disclosure. The processor 2202 may be implemented by one or more integrated circuit (or circuitry) (IC) chips and may execute various data processings. The processor 2202 may include at least one electric circuit, and may execute instructions (or a program, codes, data, etc.) stored in the memory 2203, individually, collectively or in any combination thereof. Further, the processor 2202 may include a single-core processor or multi-core processor, and may include a processor assembly including a plurality of processing circuits (circuitry) according to a specific implementation scheme.

[0306] The processor 2202 may be electrically, operatively, or communicatively coupled to the transceiver 2201 to control the transceiver 2201.

[0307] The processor 2202 may include at least one processor (or processing circuitry), and the at least one processor may perform the following operations individually, collectively or in any combination thereof. In a specific embodiment, at least a part of the processor 2202 may be included in one chip and the other part of the processor 2202 may be included in another chip. Otherwise, at least one processor may be included in another component, for example, the transceiver 2201 or the memory 2203.

[0308] The processor 2202 may perform or control or cause an operation of the BS 2200 for executing at least one or a combination of methods according to embodiments of the disclosure. For example, the processor 2202 may control operations of the BS 2200 for generating and transmitting a downlink signal to a UE or processing an uplink signal received from a UE. Otherwise, the BS 2200 may transmit or receive a signal to or from a neighboring BS, transfer a signal received from a UE to an upper node of the network, or transmit a signal transferred from an upper node of the network to a UE. To this end, the processor 2202 may execute a computer program, codes, or instructions stored in the memory 2203, so as to control other components of the BS 2200 to enable execution of various operations.

[0309] The memory 2203 corresponds to a hardware storage device capable of temporarily or permanently storing information and may include one or more storage media. For example, the memory 2203 may include a memory assembly including one or more storage media. For example, the one or more storage media may include permanent memory, such as a hard drive, flash memory, or read-only memory (ROM), semipermanent memory, such as random access memory (RAM), cache memory, or a combination thereof.

[0310] The memory 2203 may be electrically, operatively, or communicatively coupled to the processor 2202 and may be accessed by the processor 2202.

[0311] The memory 2203 may store a computer program, codes, or instructions executable by the processor 2202. According to an embodiment, a computer program, codes, or instructions executable by the processor 2202 may be either stored in a single memory device or separated and distributedly stored in two or more memory devices. By executing the instructions stored in the memory 2203, the processor 2202 may perform various functions according to an embodiment of the disclosure.

[0312] According to an embodiment of the disclosure, operations of the BS 2200 may be caused to be performed based on execution of instructions (or a computer program or codes) stored in the memory 2203 by at least one processor (or processing circuitry) configured to execute the same individually, collectively, or in any combination thereof, based on processing circuitry that is not configured to execute instructions, and / or based on components of processing circuitry that is not configured to execute instructions.

[0313] In the context of addressing this technical object, according to the first aspect of the present invention A method of obtaining channel state information (CSI) in a wireless communication system. The method provided hereby comprises, in a user equipment: based on measurements of channel state information reference signals (CSI-RSs) transmitted from a base station (BS) of the wireless communication system, the measurements performed by the user equipment, determining a number of MIMO layers preferred for the user equipment, and selecting, from a predefined codebook, spatial beam vectors in a number corresponding to the preferred number of MIMO layers; calculating a primary channel quality indicator (CQI) by using the spatial beam vectors selected for the preferred number of MIMO layers, and calculating at least one additional channel quality indicator, each of the at least one additional channel quality indicator being calculated by using a respective part of the selected spatial beam vectors, wherein a number of spatial beam vectors in said part corresponds to a number of MIMO layers which is respectively less than the preferred number of MIMO layers; and generating CSI, wherein, at least, the preferred number of MIMO layers, indices of the selected spatial beam vectors, and the calculated channel quality indicators are included into the CSI.

[0314] In accordance with an embodiment, the method provided herein further comprises: transmitting, by the user equipment, the CSI to the base station.

[0315] A spatial beam vector represents a Kronecker product of a Discrete Fourier Transform (DFT) vector by a DFT vector , where

[0316]

[0317] is a number of CSI-RS ports of an antenna array of the base station along a first spatial dimension and is a respective oversampling factor, is a spatial beam vector index in the codebook along the first spatial dimension, is a number of CSI-RS ports of the antenna array of the base station along a second spatial dimension and is a respective oversampling factor, is a spatial beam vector index in the codebook along the second spatial dimension, is imaginary unit, denotes transposing.

[0318] According to an embodiment, the selecting spatial beam vectors comprises: based on the measurements of the CSI-RSs, determining a receive quality metric corresponding to each spatial beam vector from at least part of a set of spatial beam vectors defined by the codebook; selecting, from the at least part of the set of spatial beam vectors, spatial beam vectors with larger corresponding receive quality metrics, where is said number of spatial beam vectors corresponding to the preferred number of MIMO layers; and ordering the selected spatial beam vectors according to the corresponding receive quality metrics. Preferably, , where is the preferred number of MIMO layers, denotes rounding to the closest greater integer.

[0319] In according with a preferred embodiment, the selected spatial beam vectors are mutually orthogonal, wherein, among the spatial beam vectors, a spatial beam vector with the largest corresponding receive quality metric defines an orthogonal basis in the codebook, wherein other of the spatial beam vectors are selected in said orthogonal basis.

[0320] According to an embodiment, each of the primary channel quality indicator and the at least one additional channel quality indicator represents a wideband channel quality indicator (wCQI). Said calculating a primary channel quality indicator comprises: generating a primary precoding matrix based on the ordered spatial beam vectors, wherein a number of precoding vectors which the primary precoding matrix is comprised of equals ; and calculating a primary wCQI for the generated primary precoding matrix. Said calculating at least one additional channel quality indicator comprises, for each from a set { }, where is a -th number of MIMO layers less than , , is a number of s in the set { }: selecting, from the ordered spatial beam vectors, spatial beam vectors with larger corresponding receive quality metrics according to said ordering of the spatial beam vectors, wherein corresponds to the number of MIMO layers, preferably ; generating a -th precoding matrix based on the selected spatial beam vectors; and calculating a -th additional wCQIkfor the generated -th precoding matrix. A number of precoding vectors which the -th precoding matrix is comprised of equals .

[0321] In accordance with an embodiment, the generating CSI comprises: ordering the indices of the spatial beam vectors in the CSI according to said ordering of the spatial beam vectors, where ; further including into the CSI, for each of the spatial beam vectors, a respective polarization co-phasing factor , wherein the polarization co-phasing factors are ordered within the CSI according to the ordering of the indices of the spatial beam vectors; and ordering the calculated wCQIs within the CSI according to a format preset in the base station and signaled in advance to the user equipment. The preset format can correspond to ordering the calculated wCQIs in such a way that each of the calculated wCQIs is ordered within the CSI according to a number of MIMO layers for which said wCQI was calculated, wherein said signaling of the preset format from the base station to the user equipment is performed via radio resource control (RRC) signaling.

[0322] According to an embodiment, the receive quality metric is an indicator of received power of a respective beam, said indicator obtained based on the measurements of the CSI-RSs and a corresponding spatial beam vector.

[0323] In accordance with one embodiment, each in the set { } corresponds to a pair of integer values of a number of MIMO layers, wherein, in the set { }, , , where .

[0324] In one implementation of the one embodiment, . In this case, can be equal to 8 or 7, can be equal to 6 or 5, can be equal to 4 or 3, can be equal to 2 or 1.

[0325] In another implementation of said one embodiment, is preset in the base station and signaled in advance to the user equipment via RRC signaling. In this case, can be equal to 8 or 7, can be equal to 1 or 2.

[0326] According to another embodiment, a combination of values of a number of MIMO layers is signaled in advance from the base station to the user equipment via RRC signaling, wherein all values from said combination which are less that are included into the set { } in the user equipment.

[0327] In according to one embodiment, the CSI is transmitted via UCI. The CSI in the UCI comprises a CSI part　1 and a CSI part　2, wherein a payload size of the CSI part　1 is fixed, and a payload size of the CSI part　2 is variable and dependent on contents of the CSI part　1.

[0328] According to one implementation of the one embodiment, the CSI part　1 includes and the primary wCQI. The CSI part　2 can include the indices of the spatial beam vectors, followed by the respective polarization co-phasing factors , followed by the additional wCQIks, where , . Otherwise, the CSI part　2 can include the indices of the spatial beam vectors, followed by the additional wCQIks, followed by the polarization co-phasing factors , where , .

[0329] According to another implementation of said one embodiment, the CSI part　1 includes . The CSI part　2 can include the indices of the spatial beam vectors, followed by the respective polarization co-phasing factors , followed by the primary wCQI and the additional wCQIks, where , . Otherwise, the CSI part　2 can include pairs "a spatial beam vector index - a respective polarization co-phasing factor ", where , followed by the primary wCQI and the additional wCQIks, where .

[0330] According to yet another implementation of the one embodiment, the CSI part　1 includes , the primary wCQI, an index of the first spatial beam vector, and a respective polarization co-phasing factor , while the CSI part　2 includes the indices of the spatial beam vectors, followed by the respective polarization co-phasing factors , followed by the additional wCQIks, where , .

[0331] In accordance with another embodiment, the CSI is transmitted via a medium access control (MAC) control element (CE), wherein the MAC CE includes, respectively ordered over octets: , the primary wCQI, the indices of the spatial beam vectors, the respective polarization co-phasing factors , the additional wCQIks, where , .

[0332] According to an embodiment, a bit field size for is , wherein a bit field size for each of , , is .

[0333] In accordance with an embodiment, the method further comprises: receiving, from the base station, a CSI request, the CSI request comprising a bit field whose value indicates, to the user equipment, to obtain the CSI for two or more numbers of MIMO layers.

[0334] According to an embodiment, the method provided herein further comprising, in the base station: receiving the CSI transmitted by the user equipment; for each of at least part of the channel quality indicators comprised in the CSI, calculating a value of reduction of transmission power spectral density (PSD) based on at least a frequency resource available for a downlink (DL) transmission being scheduled, and applying the calculated PSD reduction value to determine a modulation and coding scheme (MCS) for the DL transmission; based on, at least, an energy efficient (EE) mode and a data rate for the DL transmission, selecting an MCS from the determined MCSs and selecting a number of MIMO layers for which a channel quality indicator which the selected MCS corresponds to was calculated; obtaining a precoding matrix based on spatial beam vectors from the spatial beam vectors indicated by the ordered spatial beam vector indices from the received CSI, wherein a number of the spatial beam vectors based on which the precoding matrix is obtained corresponds to the selected number of MIMO layers; and performing the DL transmission to the user equipment by using the obtained precoding matrix, the selected MCS, and the calculated PSD reduction value corresponding to the selected MCS. Polarization co-phasing factors from the received CSI, which correspond to said spatial beam vectors corresponding to the selected number of MIMO layers, can be further used for said obtaining a precoding matrix.

[0335] In this embodiment, said applying the calculated PSD reduction value for a respective channel quality indicator comprises, in the base station: based on the respective channel quality indicator, determining an estimated signal-to-interference-and-noise ratio (SINR) at a side of the user equipment; applying the calculated PSD reduction value to scale the estimated SINR; and determining the MCS based on the scaled SINR. The PSD reduction value is preferably calculated as

[0336] ,

[0337] where is a frequency resource initially allocated for the DL transmission, is the frequency resource stretched according to the available frequency resource, is the estimated SINR. The stretching of the resource can be performed further with account of at least a current number of active user equipments being served by the base station.

[0338] According to the second aspect of the present invention a user equipment in a wireless communication system is provided, the user equipment comprising, at least: transceiving units; data processing units; and data storage units, wherein the data storage units have computer-executable codes stored therein which, when executed by the data processing units, cause the method according to any one of the embodiments of the first aspect of the present invention to be performed.

[0339] In accordance with the third aspect of the present invention a computer-readable storage medium is provided, the computer-readable storage medium having computer-executable codes stored therein which, when executed by at least one data processing unit of a user equipment (UE), cause the user equipment to perform the method according to any one of the embodiments of the first aspect of the present invention.

[0340] According to the fourth aspect of the present invention a method of requesting CSI is provided, the method being performed by a base station of a wireless communication system. The method provided hereby comprises: transmitting, to a user equipment (UE), a CSI request comprising an indication, to the user equipment, to calculate a CSI report for two or more numbers of MIMO layers, including a number of MIMO layers preferred for the user equipment and at least one number of MIMO layers which is less than the preferred number of MIMO layers.

[0341] In accordance with a preferred embodiment, the CSI request is transmitted via DCI, wherein the CSI request comprises a bit field, wherein said indication is represented by a first value of the bit field, wherein the first value is selected in the base station form a predefined set of bit values. The first value of the bit field can be further indicative of signaling by which the CSI report is to be transmitted by the user equipment to the base station. The indicated signaling can be RRC or MAC CE. The set of bit values can further comprise a second value for indicating, to the user equipment, to calculate the CSI report only for the preferred number of MIMO layers. Selection between the first value and the second value for the bit field in the CSI request can be performed in the base station depending on a current network load.

[0342] According to an embodiment, the method provided herein further comprises, before the transmitting a CSI request: transmitting, to the user equipment via RRC signaling, a message comprising a combination of values of a number of MIMO layers or a number of numbers of MIMO layers, for being used in the calculation of the CSI report.

[0343] According to the fifth aspect of the present invention a base station of a wireless communication system is provided, the base station comprising, at least: transceiving units; data processing units; and data storage units, wherein the data storage units have computer-executable codes stored therein which, when executed by the data processing units, cause the method according to any one of the embodiments of the fourth aspect of the present invention to be performed.

[0344] In accordance with the sixth aspect of the present invention a computer-readable storage medium is provided, the computer-readable storage medium having computer-executable codes stored therein which, when executed by at least one data processing unit of a base station (BS), cause the base station to perform the method according to any one of the fourth aspect of the present invention.

[0345] Meanwhile, although specific embodiments of the present disclosure have been described in detail, various modifications may be made without departing from the scope of the present disclosure. Therefore, the scope of the present disclosure should not be limited to the described embodiments, but should be defined by the claims and equivalents thereof.

Claims

1.A method of obtaining channel state information (CSI) in a wireless communication system, the method comprising, in a user equipment (UE):based on measurements of channel state information reference signals (CSI-RSs) transmitted from a base station (BS) of the wireless communication system, the measurements performed by the user equipment,determining a number of MIMO layers preferred for the user equipment, andselecting, from a predefined codebook, spatial beam vectors in a number corresponding to the preferred number of MIMO layers;calculating a primary channel quality indicator (CQI) by using the spatial beam vectors selected for the preferred number of MIMO layers, and calculating at least one additional channel quality indicator, each of the at least one additional channel quality indicator being calculated by using a respective part of the selected spatial beam vectors, wherein a number of spatial beam vectors in said part corresponds to a number of MIMO layers which is respectively less than the preferred number of MIMO layers; andgenerating CSI, wherein, at least, the preferred number of MIMO layers, indices of the selected spatial beam vectors, and the calculated channel quality indicators are included into the CSI.2.The method of claim　1, further comprising: transmitting, by the user equipment, the CSI to the base station.3.The method of claim　1, wherein a spatial beam vector represents a Kronecker product of a Discrete Fourier Transform (DFT) vector by a DFT vector , whereis a number of CSI-RS ports of an antenna array of the base station along a first spatial dimension andis a respective oversampling factor,is a spatial beam vector index in the codebook along the first spatial dimension,is a number of CSI-RS ports of the antenna array of the base station along a second spatial dimension andis a respective oversampling factor,is a spatial beam vector index in the codebook along the second spatial dimension,is imaginary unit,denotes transposing;the selecting spatial beam vectors comprises:based on the measurements of the CSI-RSs, determining a receive quality metric corresponding to each spatial beam vector from at least part of a set of spatial beam vectors defined by the codebook;selecting, from the at least part of the set of spatial beam vectors,spatial beam vectors with larger corresponding receive quality metrics, whereis said number of spatial beam vectors corresponding to the preferred number of MIMO layers; andordering the selected spatial beam vectors according to the corresponding receive quality metrics.4.The method of claim　3,wherein, whereis the preferred number of MIMO layers,denotes rounding to the closest greater integer,wherein the selectedspatial beam vectors are mutually orthogonal,wherein, among thespatial beam vectors, a spatial beam vector with the largest corresponding receive quality metric defines an orthogonal basis in the codebook, andwherein other of thespatial beam vectors are selected in said orthogonal basis.5.The method of claim　4,wherein each of the primary channel quality indicator and the at least one additional channel quality indicator represents a wideband channel quality indicator (wCQI),wherein the calculating a primary channel quality indicator comprises:generating a primary precoding matrix based on the orderedspatial beam vectors, wherein a number of precoding vectors which the primary precoding matrix is comprised of equals, andcalculating a primary wCQI for the generated primary precoding matrix,the calculating at least one additional channel quality indicator comprises, for eachfrom a set {}, whereis a-th number of MIMO layers less than,,is a number ofs in the set {}:selecting, from the orderedspatial beam vectors,spatial beam vectors with larger corresponding receive quality metrics according to said ordering of the spatial beam vectors, whereincorresponds to the numberof MIMO layers,generating a-th precoding matrix based on the selectedspatial beam vectors; andcalculating a-th additional wCQIkfor the generated-th precoding matrix.6.The method of claim　5,wherein, andwherein a number of precoding vectors which the-th precoding matrix is comprised of equals.7.The method of claim　5, wherein the generating CSI comprises:ordering the indicesof thespatial beam vectors in the CSI according to said ordering of the spatial beam vectors, where;further including into the CSI, for each of thespatial beam vectors, a respective polarization co-phasing factor, wherein the polarization co-phasing factors are ordered within the CSI according to the ordering of the indices of the spatial beam vectors; andordering the calculated wCQIs within the CSI according to a format preset in the base station and signaled in advance to the user equipment.8.The method of claim　7, wherein the preset format can correspond to ordering the calculated wCQIs in such a way that each of the calculated wCQIs is ordered within the CSI according to a number of MIMO layers for which said wCQI was calculated, wherein said signaling of the preset format from the base station to the user equipment is performed via radio resource control (RRC) signaling.9.The method of claim　3, wherein the receive quality metric is an indicator of received power of a respective beam, said indicator obtained based on the measurements of the CSI-RSs and a corresponding spatial beam vector.10.The method of claim　5, wherein each in the set { } corresponds to a pair of integer values of a number of MIMO layers, wherein, in the set { }, , , where .11.The method of claim　10, wherein .12.The method of claim　11, wherein is equal to 8 or 7, can be equal to 6 or 5, can be equal to 4 or 3, can be equal to 2 or 1.13.The method of claim　5, wherein is preset in the base station and signaled in advance to the user equipment via RRC signaling.14.The method of claim　13, wherein can be equal to 8 or 7, can be equal to 1 or 2.15.The method of claim　5, a combination of values of a number of MIMO layers is signaled in advance from the base station to the user equipment via RRC signaling, wherein all values from said combination which are less that are included into the set { } in the user equipment.

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