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WO2025188074A1 - Method for reporting channel state information with reduced number of ports and device implementing said method - Google Patents

Method for reporting channel state information with reduced number of ports and device implementing said method

Info

Publication number
WO2025188074A1
WO2025188074A1 PCT/KR2025/002940 KR2025002940W WO2025188074A1 WO 2025188074 A1 WO2025188074 A1 WO 2025188074A1 KR 2025002940 W KR2025002940 W KR 2025002940W WO 2025188074 A1 WO2025188074 A1 WO 2025188074A1
Authority
WO
WIPO (PCT)
Prior art keywords
synchronization signal
csi
index
antenna array
terminal
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
PCT/KR2025/002940
Other languages
French (fr)
Other versions
WO2025188074A8 (en
Inventor
Davydov Alexei
Denis ESIUNIN
Dikarev DMITRY
Ermolaev GREGORY
Morozov GREGORY
Pestretsov VLADIMIR
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Samsung Electronics Co Ltd
Original Assignee
Samsung Electronics Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from RU2024105888A external-priority patent/RU2824879C1/en
Application filed by Samsung Electronics Co Ltd filed Critical Samsung Electronics Co Ltd
Publication of WO2025188074A1 publication Critical patent/WO2025188074A1/en
Publication of WO2025188074A8 publication Critical patent/WO2025188074A8/en
Pending legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/0413—MIMO systems
    • H04B7/0456—Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
    • H04B7/0478—Special codebook structures directed to feedback optimisation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0686—Hybrid systems, i.e. switching and simultaneous transmission
    • H04B7/0691—Hybrid systems, i.e. switching and simultaneous transmission using subgroups of transmit antennas

Definitions

  • 5G mobile communication technologies define broad frequency bands such that high transmission rates and new services are possible, and can be implemented not only in “Sub 6GHz” bands such as 3.5GHz, but also in “Above 6GHz” bands referred to as mmWave including 28GHz and 39GHz.
  • 6G mobile communication technologies referred to as Beyond 5G systems
  • terahertz bands for example, 95GHz to 3THz bands
  • IIoT Industrial Internet of Things
  • IAB Integrated Access and Backhaul
  • DAPS Dual Active Protocol Stack
  • 5G baseline architecture for example, service based architecture or service based interface
  • NFV Network Functions Virtualization
  • SDN Software-Defined Networking
  • MEC Mobile Edge Computing
  • multi-antenna transmission technologies such as Full Dimensional MIMO (FD-MIMO), array antennas and large-scale antennas, metamaterial-based lenses and antennas for improving coverage of terahertz band signals, high-dimensional space multiplexing technology using OAM (Orbital Angular Momentum), and RIS (Reconfigurable Intelligent Surface), but also full-duplex technology for increasing frequency efficiency of 6G mobile communication technologies and improving system networks, AI-based communication technology for implementing system optimization by utilizing satellites and AI (Artificial Intelligence) from the design stage and internalizing end-to-end AI support functions, and next-generation distributed computing technology for implementing services at levels of complexity exceeding the limit of UE operation capability by utilizing ultra-high-performance communication and computing resources.
  • FD-MIMO Full Dimensional MIMO
  • OAM Organic Angular Momentum
  • RIS Reconfigurable Intelligent Surface
  • 6G 6th Generation
  • 6G technology involves the widespread use of extremely massive antenna arrays containing multiple transceiver Antenna Elements (AE), which effectively implement xMIMO (extreme Multiple Input Multiple Output) when for data transmission (for example, Physical Downlink Shared Channel (PDSCH)) a number of simultaneously transmitted spatial MIMO streams or MIMO layers are generated.
  • AE transceiver Antenna Elements
  • xMIMO Extreme Multiple Input Multiple Output
  • PDSCH Physical Downlink Shared Channel
  • Fig. 1 clearly shows a comparison of the dimensions of the antenna array supporting massive MIMO (mMIMO) in 5th Generation (5G) communicationswith the antenna array supporting the aforementioned xMIMO technology in 6G communications.
  • mMIMO massive MIMO
  • 5G 5th Generation
  • 6G 6th Generation
  • the space in which the UE needs to perform optimization when carrying out such a search also becomes large since the number of matrices in the codebook generally increases with the number of ports.
  • the disclosure is to enable a device to generate and reporting Channel State Information (CSI) calculated on an equivalent channel obtained over a reduced number of antenna array ports.
  • CSI Channel State Information
  • BS - implemented method for receiving CSI (for communicating with the UE) calculated over a reduced number of antenna array ports comprising the steps of: transmitting at least one synchronization signal, wherein each of the at least one synchronization signal has an associated set of preconfigured codebook parameter values, which is applied at the UE to determine a matrix for reducing the number of antenna array ports, obtain an equivalent channel with the reduced number of ports based on said matrix, and calculate CSI over the equivalent channel; receiving from the UE an index of each of one or more synchronization signals selected by the UE from the previously transmitted at least one synchronization signal, and received power of each of the one or more synchronization signals, the one or more synchronization signals being selected by the UE as having received power values at the UE, which fall within a predetermined range of power values (for example, the highest L1-RSRP measurements); selecting from the one or more synchronization signals indicated by the indices received from the UE, a synchronization signal
  • a certain matrix for reducing the number of ports allows to virtualize a large antenna array, on which the CSI is calculated, into a set of collectively equivalent subarrays with a reduced number of ports (in this case, virtual ports).
  • the use of the virtualized antenna array at the UE reduces the computational complexity of CSI calculation at the UE, because at least the dimension of the multiplied matrices is reduced.
  • the accuracy of beamforming at the BS and, as a consequence, the quality and speed of data transmission between the BS and the UE do not suffer, because the BS, knowing that the UE calculated CSI over the equivalent channel with the reduced number of ports, performs the reverse operation on its side, reapplying the same port reduction matrix that was previously applied at the UE to reconstruct the full precoding matrix on the basis of the CSI received from the UE, and subsequently uses the reconstructed full matrix in beamforming to the UE.
  • the received power of the synchronization signal measured at the UE is Layer 1 Reference Signal Received Power (L1-RSRP).
  • L1-RSRP Layer 1 Reference Signal Received Power
  • receiving from the UE the index of each of the one or more synchronization signals selected by the UE is performed through Media Access Control (MAC) layer signaling, in case more than one synchronization signal is selected by the UE, the indices of these selected synchronization signals are received as an ordered list or an unordered list, in the case of receiving the indices of the selected synchronization signals as the ordered list: the indices are ordered in the list according to the measured received power values of the respective synchronization signals, said list starting with an index of that synchronization signal of the synchronization signals selected by the UE for which the received power measurement obtained at the UE is the highest, wherein the bit value in the DCI field signaling the index of the synchronization signal selected by the BS specifies the ordinal number of the selected synchronization signal index in said list.
  • MAC Media Access Control
  • the ordinal numbering used here to refer to a synchronization signal in the list is relative (i.e. being relative to other synchronization signals indicated by indices in the list), and not absolute, i.e. being not the end-to-end indexing of all possible synchronization signals between the BS and the UE.
  • the index of each selected synchronization signal is reported along with the absolute value of the received power of the corresponding synchronization signal, wherein the bit value in the DCI field signaling the index of the synchronization signal selected by the BS specifies the index of the selected synchronization signal in said list.
  • absence of selected synchronization signal index signaling with a bit value in the DCI field or signaling a predetermined bit value in the DCI field causes the UE to perform CSI calculation over the entire antenna array.
  • a single bit value indicates the synchronization signal (explicitly using the index together with L1-RSRP in the unordered list, or implicitly using the ordinal number of signal index in the ordered list) and a request to calculate CSI with or without reduction in the number of antenna array ports. Therefore, the particular bit value in the DCI field can signal, if necessary, skipping the calculation of CSI with a reduction in the number of antenna ports. If skipping the calculation of CSI with a reduction in the number of antenna ports is signaled, the CSI calculation may be performed by the UE over the entire antenna array.
  • a BS comprising a transceiver antenna unit and a processor configured to perform the method according to the first aspect of the present invention or according to any possible development of the first aspect of the present invention.
  • a storage medium storing instructions executable by a processor, which, when executed by the processor of a device equipped with a transceiver antenna unit, cause the execution of the method according to the first aspect of the present invention or according to any possible development of the first aspect of the present invention.
  • a UE - implemented method for transmitting CSI for communication with BS calculated over a reduced number of antenna array ports, the method comprising the steps of: receiving at least one synchronization signal, wherein each of the at least one synchronization signal has an associated set of preconfigured codebook parameter values, which is applied at the UE to determine a matrix for reducing the number of antenna array ports, obtain an equivalent channel with the reduced number of ports based on said matrix, and calculate CSI over the equivalent channel; measuring received power of each of the at least one synchronization signal; selecting from said at least one synchronization signal, respectively, one or more synchronization signals for which the obtained received power measurements are the highest; transmitting to a BS an index of each of the one or more selected synchronization signals and the received power of each of the one or more selected synchronization signals; receiving from the BS at least one CSI-RS and a request to calculate CSI on the at least one CSI-RS received by the UE, wherein a bit
  • the above-described UE - implemented method according to the fourth aspect of the present invention has the same inventive concept with the first aspect of the present invention in that they share, among others, specific technical features.
  • the above-described UE - implemented method according to the fourth aspect of the present invention provides technical advantages similar to the first aspect of the present invention, which are briefly described above where the essence of the first aspect of the present invention is discussed.
  • the at least one synchronization signal is a Synchronization Signal / Physical Broadcast Channel (SS/PBCH) block.
  • each synchronization signal received from the BS has its own associated set of preconfigured codebook parameter values, containing values of the following parameters: a number of antenna array ports along a first dimension and a number of antenna array ports along a second dimension; an oversampling factor of precoding vectors for the first dimension and an oversampling factor of precoding vectors for the second dimension; and parameters of precoding vectors, which define or approximate a receive beam of the corresponding synchronization signal.
  • the measured received power of the synchronization signal is Layer 1 Reference Signal Received Power (L1-RSRP).
  • L1-RSRP Layer 1 Reference Signal Received Power
  • a UE - implemented method for transmitting CSI calculated over a reduced number of antenna array ports comprising the steps of: receiving at least one synchronization signal, wherein each of the at least one synchronization signal has an associated set of preconfigured codebook parameter values, which is applied at the UE to determine a matrix for reducing the number of antenna array ports, obtain an equivalent channel with the reduced number of ports based on said matrix, and calculate CSI over the equivalent channel; measuring received power of each of the at least one synchronization signal; selecting, from said at least one synchronization signal, respectively, one or more synchronization signals for which the obtained received power measurements are the highest; transmitting to a BS an index of each of the one or more selected synchronization signals and the received power of each of the one or more selected synchronization signals; receiving from the BS at least one CSI-RS and a request to calculate CSI on the at least one CSI-RS received by the UE; determining, based on the
  • the UE-implemented method according to the fifth aspect of the present invention has the same inventive concept with both the first aspect of the present invention and the fourth aspect of the present invention, since they share, among others, specific technical features. Therefore, the above-described UE-implemented method according to the fifth aspect of the present invention provides the technical advantages similar to that in the first and fourth aspects of the present invention, which are briefly described above where the essence of the first aspect of the present invention is discussed. Additionally, the fifth aspect of the present invention allows to reduce the overhead at the BS, i.e. to reduce signaling overhead, because in this alternative embodiment there is no need to signal the BS-selected best synchronization signal to the UE.
  • the BS in this case assumes that the UE will use the port reduction matrix that will be determined unambiguously at both the UE and the BS based on the set of preconfigured codebook parameter values, which is associated with the UE-reported synchronization signal index for which the UE obtained the best received power measurement.
  • a UE comprising a transceiver antenna unit and a processor configured to perform the method according to the fourth aspect of the present invention or according to any possible development of the fourth aspect of the present invention or the method according to the alternative fifth aspect of the present invention having the same purpose but slightly different implementation.
  • a storage medium storing instructions executable by a processor, which, when executed by the processor of a device equipped with a transceiver antenna unit, cause the execution of the method according to the fourth aspect of the present invention or according to any possible development of the fourth aspect of the present invention or the method according to the alternative fifth aspect of the present invention having the same purpose but slightly different implementation.
  • a communication system comprising one or more base stations according to the second aspect of the present invention or according to any possible development of the second aspect of the present invention and one or more user equipments according to the sixth aspect of the present invention or according to any possible development of the sixth aspect of the present invention.
  • CSI Channel State Information
  • Fig. 1 schematically illustrates the antenna array supporting 5G mMIMO, and the antenna array supporting 6G xMIMO.
  • Fig. 2 schematically illustrates how interaction occurs between BS and UE, during which the BS performs the method according to the first aspect of the present invention and the UE performs the method according to the fourth aspect of the present invention.
  • Fig. 3 illustrates in more detail how the UE performs steps S108-S111 illustrated in the flowchart of Fig. 2.
  • Fig. 4 illustrates the representation of the codebook and the related other features.
  • Fig. 5a schematically illustrates the exemplary beamforming for simultaneous emission of eight synchronization signals.
  • Fig. 5b schematically illustrates the exemplary beamforming for simultaneous emission of eight synchronization signals.
  • Fig. 5c schematically illustrates the exemplary beamforming for simultaneous emission of eight synchronization signals.
  • Fig. 6 schematically illustrates the other example of beamforming for simultaneous emission of sixteen synchronization signals with a large number of sub-regions in the vertical emission plane.
  • Fig. 7 illustrates three examples of using different matrices for reducing the number of antenna array ports to virtualize the antenna array with reduced number of antenna ports.
  • Fig. 8a illustrates three other examples of virtualized antenna arrays with reduced number of antenna ports.
  • Fig. 8b illustrates three other examples of virtualized antenna arrays with reduced number of antenna ports.
  • Fig. 8c illustrates three other examples of virtualized antenna arrays with reduced number of antenna ports.
  • Fig. 9 illustrates the schematic diagram of the BS according to the second aspect of the present invention.
  • Fig. 10 illustrates the schematic diagram of the UE according to the sixth aspect of the present invention.
  • Fig. 11 illustrates the schematic diagram of the communication system according to the eighth aspect of the present invention.
  • a digital signal is transmitted through one or more digital ports associated with the antenna elements of the BS by the Radio Frequency (RF) unit that performs the function of converting the digital signal to analog and vice versa.
  • RF Radio Frequency
  • up to 64 digital antenna ports can be used, allowing BSs to use various digital signal spatial processing schemes (precoding).
  • precoding For example, using Spatial Multiplexing (SM) technology, it is possible to reuse the same time-frequency resources for DL transmission of multiple signals (MIMO layers) to one or more UEs, and using adaptive beamforming (BF) technology provides dynamic focusing of the power of the transmitted signal in one or more specified directions.
  • modulation techniques such as Orthogonal Frequency Division Multiplexing (OFDM) modulation, efficient wideband signal transmission is achieved.
  • OFDM Orthogonal Frequency Division Multiplexing
  • BS being a part of the network broadcasts synchronization signals (e.g., SS/PBCH) on all or part of the spatial beams, where SS is the Synchronization Signal, PBCH is Physical Broadcast Channel containing Demodulation Reference Signals (DMRS).
  • synchronization signals e.g., SS/PBCH
  • PBCH Physical Broadcast Channel containing Demodulation Reference Signals (DMRS).
  • DMRS Demodulation Reference Signals
  • these beams may be referred to as receive/transmit beams, depending on whether they are used in the context of receiving or transmitting data, respectively.
  • Each synchronization signal is received/transmitted using a corresponding receive/transmit beam, i.e. to each synchronization signal, the base station applies one predefined beam.
  • the UE evaluates the received synchronization signals; more specifically, the UE measures the RSRP of each synchronization signal, selects a required number of synchronization signals with the highest RSRP (hereinafter such synchronization signals may be referred to as the best synchronization signalsfor brevity, and the corresponding transmit/receive beams as the best beamsor the highest quality beams) and reports the selected beams in the form of a measurement report to the BS.
  • Said report indicates the indices (e.g., SS/PBCH Resource Block Indicators, abbreviated as SSB-RI) of the selected synchronization signals and information about the corresponding RSRPs; thereafter, the generated report is transmitted by the UE to the BS via uplink (UL).
  • SSB-RI SS/PBCH Resource Block Indicators
  • the base station may use the information contained in the received report to carry out beamforming for subsequent DL transmission to the UE.
  • the BS transmits (e.g., on a periodic or aperiodic basis) CSI-RS, to which analog beamforming is typically applied in the analog part of the base station; more specifically, the base station preferably uses one or more best beams according to the report previously received from the UE to transmit CSI-RS to the UE.
  • each CSI-RS port may correspond to one digital antenna port, or, if additional virtualization is performed, each CSI-RS port may correspond to more than one (e.g., four) digital antenna ports.
  • the portion of the antenna array corresponding to more than one (e.g., four) digital antenna ports will define a subarray (i.e., a smaller portion) of the antenna array, and the essence of the above virtualization process will be to obtain for the entire antenna array an equivalent set of subarrays to reduce the number of antenna array ports, which will be described in detail below.
  • a virtualized representation of the antenna elements of the base station antenna array in the form of CSI-RS antenna ports is ultimately enabled.
  • the UE when communicating with the BS, the UE is not aware of the actual structure of the BS antenna array - this communication, in fact, is carried out at the level of the CSI-RS antenna ports of the BS, i.e. each CSI-RS antenna port is treated at the UE as a single emitting element, regardless of the number of antenna elements in the physical antenna array it covers.
  • a CSI request (which may also be referred to as a 'a request to calculate CSI'), which may be transmitted by the BS on a periodic or aperiodic basis, and whose transmission may be via DCI, the UE performs calculations to obtain CSI using CSI-RS measurements that are being performed or already performed.
  • the calculation of the CSI at the UE comprises the calculation of a number of parameters that are included in the generated CSI.
  • the UE selects a preferred number of MIMO layers corresponding to the number of simultaneous data streams transmitted from the BS that the UE intends to receive. This number of MIMO layers is reflected by the Rank Indicator (RI) parameter in the CSI.
  • the UE also generates a precoding matrix from precoding vectors (e.g., vectors of a mathematical structure such as Discrete Fourier Transform (DFT), but not limited to such structure) that are selected from a predetermined codebook.
  • the generated precoding matrix is reflected by the PMI parameter as part of the CSI.
  • the UE determines the Channel Quality Indicator (CQI), which is included in the CSI as well.
  • CQI Channel Quality Indicator
  • the generated CSI thus including RI, PMI, CQI, is transmitted from the UE to the BS as channel feedback information in response to said CSI request.
  • the BS uses the CQI to select a modulation and error correction coding scheme (MCS) and applies the resulting precoding matrix to perform digital beamforming of the DL transmission (e.g., PDSCH) to the UE.
  • MCS modulation and error correction coding scheme
  • the BS broadcasts synchronization signals on all or part of the beams, and the BS uses a corresponding specified transmit beam to transmit each synchronization signal.
  • the UE measures the received power (e.g., L1-RSRP) of each synchronization signal, selects a predetermined number M of synchronization signals with the largest RSRP, i.e. M best synchronization signals, and generates a report (e.g., in the form of an ordered or unordered list of selected synchronization signals) indicating the indices of the selected synchronization signals or their ordinal numbers in the list and the corresponding measurements of the received power of the corresponding selected synchronization signals.
  • Received power measurements in the list can be indicated by absolute values (for example, L1-RSRP values) or relative values relative to the listed synchronization signal whose received power measurement is the highest.
  • M is a natural number that is typically preconfigured by the BS for the UE and accordingly signaled in advance by the BS to the UE, for example, through Radio Resource Control (RRC) protocol signaling.
  • RRC Radio Resource Control
  • the BS indicates to the UE what required number of its best synchronization signals the UE should report to the BS.
  • M can take the values 1, 2, 4, but is not limited to these values.
  • the indices of the selected synchronization signals are reported by bit values of a given length.
  • the following describes a non-restrictive approach by which appropriate RSRPs for SSB-RI may be reported.
  • a quantization-based implementation may be used for the RSRP report. Namely, a set of ranges of absolute values of received power in the corresponding units of measurement is preset, and a unique index value is assigned to each range. This configuration is summarized in illustrative Table 1 below.
  • the right column indicates the unit of measurements of Synchronization Signal Received Power (SS-RSRP), namely dBm; the two middle columns list the ranges of absolute values of the L3 and L1 synchronization signal received powers, respectively in dBm; the left column lists index values, each of which uniquely defines a corresponding range of absolute power values.
  • SS-RSRP Synchronization Signal Received Power
  • a differential approach can be used, which is also based on a quantized representation.
  • Table 2 specifies the range of received power values relative to the largest RSRP.
  • the middle column lists the difference ranges of the corresponding RSRP values with respect to the largest RSRP, and the unit of these difference, relative ⁇ RSRP values, as indicated by the right column of Table 2 , is dB; the left column lists index values, each of which uniquely defines a corresponding range of relative power values.
  • the M synchronization signals are ordered in the list reported to the BS in descending order of the corresponding measured RSRP. That is, first, the synchronization signal with the largest RSRP and the index value RSRP_i of the corresponding range of absolute received power values are indicated, and then, indicated in descending order of the corresponding difference RSRP values are the remaining (M - 1) synchronization signals with index values DIFFRSRP_j of the corresponding relative received power ranges (according to Table 2 ) or index values RSRP_i of absolute received power values (according to Table 1 ).
  • Arranging this order of information reported to the BS in the RSRP report allows the BS to subsequently indicate the synchronization signal selected by the BS by means of a corresponding bit value in the DCI field signaling the ordinal number of the selected synchronization signal according to the order of the synchronization signals in the list.
  • the UE then performs UL transmission of the generated report to the BS via physical layer (L1) channels.
  • This report can be further referred to in the text as RSRP report, and the synchronization signal received power can be namely L1-RSRP.
  • FIG. 4 illustrating a non-restrictive representation of the applicable type 1 codebook and other beamforming-related features.
  • each antenna port in this case corresponds to a subset of three adjacent antenna elements.
  • the same considerations can be applied without limitations to antenna arrays with other required dimensions ( , ).
  • Fig. 4 illustrates the representation of a codebook with reference to the antenna array discussed above with reference to the illustration in the upper left corner of Fig. 4 .
  • Each of the possible spatial beams in which the BS can carry out directional data transmission is represented in the codebook by a precoding vector.
  • the codebook is illustrated in Fig. 4 with a two-dimensional (horizontal and vertical) grid of beams. Each beam, and hence its corresponding precoding vector, is shown as a circle on this grid.
  • the dimension of the codebook is ⁇ in horizontal direction and ⁇ in vertical direction, i.e. the total number of precoding vectors in the codebook is ( ⁇ ) ⁇ ( ⁇ ).
  • precoding vectors i.e., codebook vectors
  • codebook vectors codebook vectors
  • the darkest circle conventionally shows a specific beam (i.e., a specific transmission direction) selected from the codebook.
  • Top and center in Fig. 4 shows standard, usually 4 phases, the values of which can be taken by the phasing coefficient. Physically, the phasing coefficient can form vertical, horizontal, left circular, and right circular polarizations.
  • FIG. 4 shows the general processing scheme implemented at the BS when forming transmission beam pattern.
  • the BS performs baseband processing to obtain virtual ports and corresponding transmitted spatial streams (MIMO layers).
  • MIMO layers transmitted spatial streams
  • digital beamforming is performed at the BS, the result of which are the digital ports of the antenna array formed with the required configuration and the corresponding CSI-RSs to be transmitted to the UE.
  • the BS then performs digital-to-analog conversion on the signal obtained from the digital beamforming step.
  • the analog signal undergoes analog beamforming and is emitted by the physical antennas towards the UE.
  • the UE Upon receiving such a signal, the UE can calculate the channel per each digital port of the BS antenna array, and in fact, the UE, using the codebook, finds and signals to the BS the best vector, which allows the signal transmitted from the digital ports of the BS to said UE to be phased in the most optimal way.
  • the codebook illustrated in Fig. 4 essentially corresponds to the simplest type 1 codebook, but the present invention should not be limited to this type of codebook because the present disclosure also applies to other types of codebook, such as type 2 codebook.
  • Possible codebook configurations supported in 6G can be determined from Table 3 below:
  • the first column in Table 3 above specifies the total number of CSI-RS antenna ports, .
  • the maximum number of digital antenna ports supported in 6G is 256.
  • the maximum number of digital antenna ports supported in 5G NR is only 32.
  • Codebook configurations for 5G NR can be determined from the lines in above Table 3 for any ⁇ 32.
  • the second column of the Table specifies possible configurations of digital antenna ports, i.e. how this total number of digital antenna ports can be arranged in the two-dimensional antenna array.
  • the number of digital antenna ports is 16, they can be arranged as 4x2 or 8x1 subarray grids without regard to polarization; the actual product is two times less, because different polarizations are used additionally.
  • the third column specifies the applicable oversampling factors to provide denser coverage and more flexible configuration.
  • the fourth column indicates the total number of PMI matrices in the codebook. According to the fourth column of Table 3 , the pattern is observed that the number of PMI matrices generally increases with the total number of digitalantenna ports .
  • Precoding matrix is calculated according to the following equation 1.
  • the matrix in equation1 is the precoding matrix ordered in a predefined way. From equation1 it is clear that the entire precoding matrix is multiplied by the normalization factor , where is the number of CSI-RS antenna ports, which essentially corresponds to a uniform distribution of the BS transmit power to all MIMO layers. That is, the use of each new MIMO layer proportionally reduces the power allocation per MIMO layer.
  • Each column vector of the precoding matrix specifies a specific precoding vector for the corresponding MIMO layer.
  • the number of column vectors of the precoding matrix corresponds to the required number of MIMO layers, each of which may represent a transmission from the BS to the UE of a corresponding signal. For example, if the number of transmitted signals from the BS to the UE is 3, then (the number of column vectors in the precoding matrix) will also be 3.
  • the number of elements of each column vector (vertically) corresponds to the number of CSI-RS antenna ports.
  • the first half of each column vector corresponds to the first polarization
  • the second half of each column vector, where the polarization-phasing coefficient is applied additionally, corresponds to the second polarization.
  • the column vectors are strictly ordered in the precoding matrix in such a way that they are first specified for an antenna of one polarization from the entire antenna array, and then for an antenna of a different polarization.
  • the precoding vectors are ordered similarly.
  • Each precoding vector is the Kronecker product of a column vector to a column vector , where equation 2 and equation 3 are as below.
  • - imaginary unit denotes transposition.
  • the precoding vector actually specifies the plane wave wavefront characterized by the indices and , i.e. by changing the index values , it is possible to actually control the direction of the precoding vector.
  • the number of elements in the vector is equal to the number of antenna ports along one spatial dimension (in this case - horizontal), i.e.
  • the number of elements in the vector is equal to the number of antenna ports along the other spatial dimension (in this case - vertical), i.e. ; wherein should be greater than or equal to , which determines the choice of the specific spatial dimension as the mentioned one and the other dimensions (see Fig. 4 for the illustration). Accordingly, the number of elements in any precoding vector will be ⁇ .
  • the possible values of the parameters , , , , see Table 3 above .
  • precoding matrices that can be constructed based on type 1 codebook, sequentially for a selectable number of MIMO layers from being equal to the number from 1 to 8 in this example.
  • precoding matrices can be constructed by analogy.
  • the general principle underlying the construction of the precoding matrix becomes clear: namely, first, the polarization dimension is used to the maximum, and only then a new precoding vector from the codebook is used (i.e., the DFT dimension).
  • This essentially means that both MIMO layers will be transmitted from the BS to the UE in the same spatial beam, but with different, orthogonal polarizations.
  • the same principle is observable for and applicable to other values as well.
  • the sequence of polarization priority engagement is shown above with circled arrows, wherein orthogonal polarizations are shown as vertical and horizontal only as the non-limiting example.
  • the precoding matrix thus generated is applied at the BS to perform appropriate beamforming for data transmission.
  • the UE having the codebook, can search for the optimal precoding matrix and the optimal number of layers, indicated respectively by the PMI and RI parameters included in the CSI calculated at the UE side, without reducing the number of antenna array ports (general case), based on the reception of the CSI-RS from the BS.
  • the UE receives CSI-RSs from the BS and, if there is the CSI request from the BS, performs channel estimation based on each of the received CSI-RS to obtain a channel matrix having the dimension for each frequency subband, where is the number of UE receiving antennas, which is usually 2 or 4, but, in rare cases, can be 8; and is the number of CSI-RS antenna ports.
  • the UE typically determines several channel matrices , each having a relatively large dimension defined by the product and .
  • the authors of the present invention proposed to reduce the computational complexity of the CSI calculation at the UE by reducing the dimension of the channel matrix up to reduced dimension of the (equivalent) channel matrix using the matrix for reducing the number of antenna array ports, which will be described in detail below with reference to Figs. 2 and 3 .
  • the PMI/RI search problem can be reduced to the following optimization problem:
  • the UE measures the channel matrix , applies the precoding matrix to it and obtains the equivalent channel using the product of the specified terms. In other words, the UE is actually emulating what a specific channel will look like after applying the precoding matrix to it.
  • the UE's task at it is to iterate over all codebook indices and and all ranks, find the optimal value optimizing the above-mentioned function , and select the optimal precoding matrix and the most optimal rank specified by the PMI and RI, respectively.
  • Application of equations13-14 given above as the non-limiting example in particular allows to maximize the objective function, which, in this example, is the throughput function for MIMO systems.
  • Fig. 2 shows schematically how the interaction between the BS and the UE occurs according to the present invention.
  • What is shown on the left in Fig. 2 under the abbreviation 'BS' corresponds to the BS-implemented method for receiving CSI calculated over a reduced number of antenna array ports, and what is shown on the right in Fig. 2 under the abbreviation 'UE' corresponds to UE-implemented method for generating and transmitting said CSI.
  • the interaction of the BS and the UE begins at step S100 of transmitting by the BS at least one synchronization signal (e.g.
  • each of the at least one synchronization signal having an associated set of preconfigured codebook parameter values applied at the UE to determine the matrix for reducing the number of antenna array ports, obtain an equivalent channel with the reduced number of ports based on said matrix, and calculate CSI over such an equivalent channel.
  • said at least one synchronization signal is received by the UE.
  • Each specific synchronization signal transmitted by the BS in step S100 has its own set of preconfigured codebook parameter values associated with it.
  • Said set of preconfigured codebook parameter values comprises, for the corresponding synchronization signal, its values of the following parameters: the number of antenna array ports in the first dimension and the number of antenna array ports in the second dimension; precoding vectors oversampling factor for the first dimension and precoding vectors oversampling factor for the second dimension; and indices and of the precoding vectors defining the transmit beam of the corresponding synchronization signal.
  • step S102 the UE measures the received power of each synchronization signal of the at least one synchronization signal it receives.
  • the synchronization signal can be namely SS/PBCH
  • the measured received power can be L1-RSRP.
  • step S103 the UE selects from the received and measured signals, respectively, the M (M is a configurable parameter) synchronization signals for which the obtained measurements of received power are the highest.
  • the division into steps S102 and S103, illustrated in Fig. 2 is the logical division based on the different functions performed. This division is made only for the purpose of a more consistent and detailed description of the present invention.
  • This reporting can be carried out as described above with reference to Tables 1 and 2 , indicating the indexes of the M best synchronization signals and the index values of the absolute and/or relative values of the measured received power, reported, for example, in the form of the list ordered from the selected synchronization signal with the highest received power to the selected synchronization signal with the lowest received power, or unordered list in which each selected synchronization signal is reported with its corresponding absolute L1-RSRP value.
  • This information may be signaled from the UE to the BS in MAC Control Element (MAC CE).
  • MAC CE MAC Control Element
  • the MAC CE message including SSB-RI/L1-RSRP (instead of an L1 message in 5G NR) provides reliable reception of SSB-RI at the BS, subject to an agreed understanding of the SSB-RIs between the BS and the UE, which can be achieved by pre-configuring them to use a specific sets of synchronization signals with strictly defined SSB-RIs.
  • the value of M i.e., the number of synchronization signals selected at the UE side out of the total number of SS/PBCHs transmitted by the BS
  • M the number of synchronization signals selected at the UE side out of the total number of SS/PBCHs transmitted by the BS
  • the UE has determined that the best synchronization signals are the synchronization signals with indexes ⁇ k0, k1, k3, k4 ⁇ .
  • this synchronization signal is indicated first in the list (i.e.
  • the power of the second and subsequent signals in the list is indicated relative to the absolute power of the signal k1 with the index values as determined according to Table 2.
  • the signal with index k2 was not included in the list, because its RSRP turned out to be less than the RSRP of signals with indices k1, k3, k4 and k0.
  • the particular synchronization signal selected in step S106 by the BS is transmitted subsequently in step S107 to the UE by the bit value in DCI field reflecting, among other things, the ordinal number m of the entry of the selected synchronization signal according to the list, which will be described in detail below.
  • the example of the alternative list structure used according to Table 5 differs from the example list structure described above with reference to Table 4 in that the entries in the list according to Table 5 do not need to be ordered according to received power values, but instead the index of each of the selected signals is reported together with the index value of the corresponding absolute L1-RSRP power. Moreover, in comparison with the list structure illustrated in Table 4 , the list structure illustrated in Table 5 provides more accurate information about the power of the received synchronization reference signal, because absolute values allow a wider L1-RSRP range to be quantized. At the same time, the list structure illustrated in Table 4 reduces the number of used bits required to transmit the relative L1-RSRP power.
  • the example of the alternative list structure described above with reference to Table 5 should not be interpreted as any limitation of the present invention as well.
  • the UE transmits in step S104 to the BS the list comprising the indices of the selected synchronization signals and the received powers corresponding to the selected synchronization signals.
  • step S105 the selected synchronization signals and their received powers at the UE are received by the BS.
  • the BS performs beam selection procedure selecting one of the M synchronization signals (and the corresponding beam) previously selected by the UE.
  • the beam that the BS uses to transmit the synchronization signal may not exactly match the beam that the UE uses to reduce the number of ports.
  • beam selection occurs at the BS, but on the UE side its approximation, for example, in the direction of maximum gain can be used.
  • the beam selection procedure performed at the BS may be carried out in any manner known in the art, including a method based on machine learning, and based on any criteria and data that the base station may be aware of.
  • the BS may select the strongest beam
  • MU-MIMO multi-user data transmission mode
  • the BS may select a beam that will provide maximum transmit power between the BS and the UE, while causing minimal interference to other users.
  • SU-MIMO single-user data transmission mode
  • MU-MIMO multi-user data transmission mode
  • the BS transmits at step S107 to the UE at least one CSI-RS and the request to calculate the CSI at the UE side on the at least one CSI-RS received by the UE.
  • the CSI calculation request may be signaled in the DCI.
  • the index of the synchronization signal selected by the BS (and the corresponding beam) is additionally signaled by the bit value in the DCI field.
  • the CSI calculation request field in the DCI may include a reference to or direct indication of a specific SSB-RI from the indexes previously received in step S105 from the UE.
  • Non-limiting examples of allocating specific bit values to perform such signaling are given in Table 6 below.
  • the UE receives from the BS the at least one CSI-RS and the CSI request signaled in the DCI according to the exemplary scheme shown above in Table 6 . If the bit value in the DCI field of the received CSI request indicates that the UE should calculate the CSI and thereby use a particular synchronization signal to reduce the number of antenna array ports, the UE proceeds to step S109, where the UE determines, as shown in Fig. 3 in more detail, from the synchronization signal signaled by the index and the associated set of preconfigured codebook parameter values, the matrix to be used by the UE to reduce the number of BS antenna array ports in CSI calculation.
  • This step S109 may be performed at the UE side according to the following non-limiting implementation.
  • the bit value in the DCI field signals a particular synchronization signal by reflecting its index (e.g., SSB-RI).
  • each specific synchronization signal transmitted by the BS at step S100 has its own associated set of preconfigured codebook parameter values, containing specific values, corresponding to a given synchronization signal, of the following parameters: , , , , and .
  • the UE accesses a predefined function or mapping table of at least the index of the synchronization signal to the predefined values of the parameters , , , , and .
  • Said function or mapping table may be preconfigured in the same manner for both the BS and the UE.
  • the mapping itself can be performed according to any rule that is subject to determination by the network operator and/or equipment manufacturers and inclusion in the appropriate specification.
  • the particular values of the associated set of parameter values may be selected so as to, for example, match the width (parameters , ) and direction of the beam (parameters , , and ) used to transmit the synchronization signal, and an effective beam used to reduce the number of CSI-RS ports.
  • the supported complexity of the UE's receiver may be taken into account to calculate the CSI.
  • the parameters ( , ) should be selected appropriately so that the UE is able to perform the CSI calculation. Other options are possible as well.
  • the UE may, according to the present non-limiting implementation, find some equivalent in the form of the matrix for reducing the number of antenna array ports, which is essentially a (coarse) precoding matrix, with the help of which it would be possible to reduce the dimension of the channel matrix obtained by the UE as the result of channel measurements (between the BS and the given UE) performed by the UE based on the at least one CSI-RS received in step S108 from the BS.
  • the channel matrix itself can be calculated by the UE in the present invention by any method known in the art, without any limitation, therefore, a detailed description of the calculation of the channel matrix is not given here.
  • the PR-PMI (Port Reduction - Precoding Matrix Indicator) unit shown in Fig. 3 may be responsible for implementing this step S109 in the UE.
  • the PR-PMI unit may have a software and/or hardware implementation (e.g., as a processor or a part thereof).
  • Obtainment of the matrix for reducing the number of antenna array ports in the PR-PMI unit can be performed according to the following equation 15.
  • the number of column vectors (i.e., horizontal dimension) of this matrix for reducing the number of antenna array ports corresponds to the number of virtual antenna array ports for CSI once the port number is reduced, i.e. this matrix dimension actually defines to what number the BS wishes/allows the UE to reduce the channel dimension; this parameter is a parameter configured by the network operator or equipment manufacturer.
  • the number of elements in each column vector (i.e., vertical dimension) of the matrix for reducing the number of antenna array ports corresponds to the total number of antenna array ports (for example, 256, 128, 64 according to the possible configurations in Table 3 , i.e., to the original number of antenna array ports before the reduction).
  • the first half of each column vector of the matrix for reducing the number of antenna array ports corresponds to the first polarization
  • the second half of each column vector corresponds to the second polarization.
  • the column vectors are strictly ordered in the matrix for reducing the number of antenna array ports in such a way that they are first specified for an antenna of one polarization from the entire reduced antenna array, and then for an antenna of a different polarization.
  • the elements of the matrix for reducing the number of antenna array ports are ordered in a manner similar to how the corresponding elements are arranged in the applicable codebook (e.g., in type 1 codebook).
  • Upper half of the matrix for reducing the number of antenna array ports is applied to the first polarization
  • the lower half of the matrix for reducing the number of antenna array ports is applied to the second polarization.
  • Said two halves of the matrix for reducing the number of antenna array ports are identical, i.e. the reduction in the number of ports will apply equally to both the first polarization of the antenna array and the second (orthogonal) polarization of the antenna array.
  • the matrix for reducing the number of antenna array ports which will be applied in the same way to each subarray from the set of subarrays generated by reducing the number of antenna array ports, will have the structure defined according to the following equation 16.
  • the precoding vectors defining the transmit beam of the corresponding synchronization signal for the virtualized antenna array are determined in the associated set of preconfigured parameter values by the and parameters of the precoding vector direction angles along the two dimensions.
  • PR-PMI is specified by said parameters and
  • the structure of the codebook and the partitioning of the antenna array into the equivalent set of subarrays is defined by the parameters , , , .
  • PR-PMI is approximated by said indices and , and the structure of the codebook and the partitioning of the antenna array into the equivalent set of subarrays is defined by the parameters , , , .
  • the beam that the BS uses to transmit the synchronization signal and the beam that is to be used by the UE for port reduction may be completely identical beams, defined directly, or substantially identical beams (i.e., beams having essentially identical directions), one of which is obtained by approximating the other.
  • the beams are the same (i.e. they have the DFT type structure and are specified directly); 2. the beams match approximately, i.e. the DFT type mathematical structure may be used for port reduction, and a mathematical structure of a different type may be used for the synchronization signals (or the DFT type mathematical structure, but with different parameters that would be obvious to one of ordinary skill in the art based on the examples above).
  • the approximation is related to option 2, since this option can provide an approximate match in the direction of the beams, or an approximate match in the direction of the beams and the angular width at a certain level (for example, at the 3 dB level).
  • a certain level for example, at the 3 dB level.
  • step S110 illustrated in Figs. 2 and 3 , on which the UE obtains an equivalent channel with a reduced number of ports by applying the matrix for reducing the number of antenna array ports to the channel matrix according to the following equation 21.
  • step S111 is performed, on which the UE performs CSI calculation with the search for optimal RIs/PMIs from said equivalent channel matrix .
  • This calculation is performed according to the following equations 22, 23 being the respectively modified versions of the above equations 13, 14, which use the equivalent channel and the matrix of reduced dimensions to make the operations performed by the UE at this step S111 simpler in terms of computational complexity, because the number of PMI candidates, among which the search for the optimal PMI is carried out, and the dimensions of the matrices involved in the calculations are reduced.
  • steps S109, S110 and S111 illustrated in Fig. 2 is the logical division based on the different functions performed. This division is made only for the purpose of a more consistent and detailed description of the present invention. However, such a division into steps should not be interpreted as any limitation of the present invention, since similar functions in an actual implementation may be performed in fewer (including as a single step) or more (>3) steps.
  • step S112 the UE performs UL transmission to the BS of the CSI calculated over said equivalent channel with the reduced number of antenna array ports in response to the CSI request received in step S108.
  • step S113 the BS receives said CSI from the UE and in step S114 it reconstructs the full (complete) precoding matrix by applying said matrix for reducing the number of antenna array ports previously applied at the UE for reducing the number of antenna array ports to the precoding matrix indicated by the PMI contained in the received CSI.
  • the matrix for reducing the number of ports of the antenna array applied at the UE is either known to the BS in advance (preconfigured), or the BS can easily derive such a matrix in the same way as the UE derives it using the above equations15-20, based on the same set of preconfigured codebook parameter values associated with the synchronization signal indicated from the BS to the UE in step S107. Therefore, reconstruction of the full precoding matrix is performed according to the following equation 24.
  • the BS performs in step S115 a subsequent transmission to the UE of any data and/or signals while beamforming the transmission based on said full precoding matrix.
  • the UE respectively receives the transmission of data and/or signals from the BS. Therefore, the present invention reduces the CSI-calculation-related computational load on the UE, but does not subsequently negatively impact the efficiency and quality of communication between the BS and the UE.
  • Fig. 5 schematically illustrating the non-limiting example of the beam radiation pattern applied by the BS when transmitting in this example eight synchronization signals, each of which is transmitted by its transmit/receive beam 0-7, which corresponds to the pre-configuration provided in advance in the same way for both the BS and the UE.
  • the number of synchronization signals, as well as the shown radiation pattern (i.e., the configuration and the number of transmit/receive beams) of the synchronization signals are configurable parameters, i.e. in an actual implementation, the number of synchronization signals and the radiation pattern may differ from those shown in Fig. 5.
  • codebook parameters For each synchronization signal transmitted by the corresponding transmit/receive beam 0-7, a unique set of values of codebook parameters , , , , and is configured in advance, which is applied at the UE to determine the matrix for reducing the number of antenna array ports, obtain the equivalent channel with the reduced number of ports based on said matrix, and calculate CSI over the equivalent channel.
  • the preconfigured set of values of codebook parameters , , , , and for each synchronization signal (e.g. SS/PBCH) emitted by the BS becomes known due to said pre-configuration of both the BS and all UEs supporting a particular communication standard, which will be served by the BS in the mobile communications network of the corresponding communication standard.
  • synchronization signal e.g. SS/PBCH
  • the UE receives, at step S101, the synchronization signal 0 transmitted from the BS with the corresponding transmit beam 0, the UE will be able to determine, due to said pre-configuration, the following set of codebook parameter values: , , , , and as said preconfigured set of parameter values, and perform, in the steps S109, S110, S111 described above, CSI calculation over the equivalent channel using that particular set of values.
  • the UE if the UE receives, at step S101, the synchronization signal 1 transmitted from the BS with the corresponding transmit beam 1, the UE will be able to determine, due to said pre-configuration, the following set of codebook parameter values: , , , , and as said preconfigured set of parameter values, etc.
  • Forming patterns of beams (beamforming) of synchronization signals shown in Fig. 5 or 6 is carried out as determined by the BS.
  • the specific radiation pattern(s) depends on the particular implementation of the BS.
  • the specific radiation pattern(s) depends on the specific location of the BS in the area.
  • a particular radiation pattern(s) may be dynamically adjusted depending on current network operating conditions (e.g., but not limited to, the number of active users, etc.).
  • General approaches to forming radiation patterns of synchronization signals on the BS side may be as follows.
  • Several hierarchy levels (two in the example of Fig. 5a and four in the example of Fig. 6 ) can be formed to serve both UEs that may be located close to the BS, and UEs that may be located at a greater distance from the BS.
  • the BS typically configures beam(s) that, in terms of vertical angle (i.e., elevation angle), is(are) emitted with a large absolute deviation from the horizon, and in terms of azimuthal angle, is(are) wide in the azimuthal plane and is emitted with a lower gain, because it makes no sense to form such a beam(s) with a narrow radiation pattern and high gain.
  • the beam that serves nearby UEs is beam 0, and in the example of Fig. 6 with a larger number of hierarchies, which can be applicable for larger cells, the beams that serve nearby UEs are beams 1, 2, 3.
  • the reverse logic is typically applied, namely, to serve UEs that are farther away, the BS typically configures beam(s) that, in terms of vertical angle (i.e., elevation angle) is(are) emitted in directions that have a smaller absolute deviation from the horizon, and in terms of azimuthal angle, is(are) narrower in the azimuthal plane and emitted with a higher gain, because it makes sense to design such beam(s) with the narrow beam pattern and high gain (i.e., with higher energy concentration) given the greater distance to the possible location of the UEs.
  • vertical angle i.e., elevation angle
  • azimuthal angle is(are) narrower in the azimuthal plane and emitted with a higher gain
  • the total number of individual beams increases as the gain increases, because a beam with a higher gain becomes narrower in the azimuthal plane and more beams are required to cover the entire area served by the BS.
  • the beams that serve UEs located further away are beams 1-7
  • the beams that serve further-away UEs are beams 4-16.
  • Non-limiting examples of configurations of subarrays of antenna array which are listed above in Table 7 , configure the radiation pattern of eight beams 0-7 for transmitting eight synchronization signals shown in Fig. 5a .
  • Each precoding vector for each synchronization signal has a strictly defined directionality horizontally and vertically, which is clearly demonstrated by the illustrations of Fig. 5 .
  • the BS can control this direction by changing the values of the indices (parameters) and , which are contained for particular synchronization signals in the corresponding configurations as illustrated on the basis of the example related to Table 7 given above. Knowing the association of indices and with the corresponding synchronization signal (e.g.
  • precoding vectors of the direction of the beam with which the BS transmits the corresponding synchronization signal can be determined.
  • Fig. 5a which should not be interpreted as limiting the present invention, there are eight precoding vectors defining transmit/receive beams 0-7 in total.
  • the values of these parameters are defined in the third column in the second row of Table 7 ; thus, the first dimension is oversampled by the factor of 16 to allow granular (fine) tuning of the beam in the vertical plane, and
  • the UE Knowing the specific values of the above parameters associated with synchronization signal 0 transmitted by beam 0, the UE will be able, if necessary (if the L1-RSRP measurement of this synchronization signal appeared to be one of the largest or largest one, or if the BS indicated at step S107 this synchronization signal 0 transmitted by beam 0), to obtain the equivalent radiation pattern that will match with the radiation pattern used to transmit this synchronization signal 0 by the BS by substituting this set of values into the equations15-20 described above and performing subsequent CSI calculation according to equations21-23.
  • each of the beams 1-7 is characterized by the different direction in the azimuthal plane (i.e. all these beams have different values of the index , see columns 4-10 in the last row of Table 7 above), but the same direction in the vertical plane (i.e. all these beams have the same value '31' of the index , see columns 4-10 in the last row of Table 7 above).
  • each of the beams 1-7 is narrow in the azimuthal plane, so unlike beam 0 shown in Fig.
  • each beam of beams 1-7 is '4',and not '1', see second column in the last row of Table 7 above.
  • the width of each beam of beams 1-7 in the vertical plane is similar to the width of beam 0 in the vertical plane, so the value for both each beam of beams 1-7 and beam 0 is configured equal to '2', see rows 2-3 in the second column of Table 7 .
  • the parameters , , , and can be configured, and index values can be reported, so that the UE knows and can determine some equivalent of the radiation pattern used to transmit the synchronization signal of each SSB-RI. This allows the UE to essentially emulate the radiation pattern for a specific synchronization signal and use it to reduce the dimensionality of the channel matrix according to equation21 described above.
  • Figs. 7 and 8 let us describe the non-limiting example of the technical implementation of constructing a synchronization signal precoding matrix, and also illustrate various examples of partitioning an antenna array into multiple subarrays that can be achieved in the given technical implementation.
  • the BS can apply a procedure according to which the antenna array is partitioned into subarrays, and certain directivity is formed in each of the subarrays with the use of precoding vectors .
  • Phasing vector can then be used to phase the signals from the subarrays.
  • Application of the phasing vector provides an omni- or quasi-omni radiation pattern that co-phases the virtual ports of the subarrays into a single port without substantially changing the radiation pattern previously provided by the precoding vectors.
  • the application of the co-phasing vector is necessary due to the need to obtain single port from all subarrays of the antenna array to transmit the synchronization signal, since the synchronization signal is single-port.
  • the non-limiting example of applicable here implementation of how the co-phasing vector should be applied when constructing a synchronization signal precoding vector is described in detail in C. -Y. Pai, Z. Liu, Y. -Q. Zhao, Z. -M. Huang and C. -Y. Chen, "Designing Two-Dimensional Complete Complementary Codes for Omnidirectional Transmission in Massive MIMO Systems," 2022 IEEE International Symposium on Information Theory (ISIT), Espoo, Finland, 2022, pp.
  • the synchronization signal precoding matrix may be determined and applied at the BS according to the following equation 25.
  • precoding vectors specified by the indices are precoding vectors specified by the indices and ,
  • the BS partitions its antenna array into subarrays in an appropriate manner.
  • the UE upon receipt of the corresponding synchronization signal, the UE attempts to emulate such a partitioning to reduce the number of antenna array ports in calculation of CSI.
  • said partitioning is logical and represents only one of the possible options.
  • Other beamforming techniques may be used to transmit the synchronization signal.
  • the UE-side partitioning will be an approximation of beams used by the BS to transmit synchronization signals.
  • Non-limiting examples of antenna array partitioning and virtualization are shown in Figs. 7 and 8 .
  • Fig. 8a shows the way of partitioning/virtualizing the antenna array into two subarrays, each of which covers 16 antenna elements.
  • Each of these two subarrays is large enough both horizontally and vertically so that applying a precoding vector to them will result in a sufficiently narrow beam both horizontally and vertically.
  • beams like the beams 1-7 in Fig. 5a or like the beams 9-16 in Fig. 6 can be obtained.
  • the specific direction of the beam within the subarray can be adjusted by changing the values of the indices , .
  • the wider the beam needs to be made the fewer the number of antenna elements the BS includes in the corresponding subarray; and vice versa, the narrower the beam needs to be made, the BS includes a larger number of antenna elements in the corresponding subarray.
  • Fig. 8b shows the other non-limiting example of partitioning/virtualizing the antenna array into eight subarrays.
  • Each subarray in this example has 1 antenna element horizontally, which will give a wide lobe in the azimuthal plane, i.e. the beam will not be given any specific direction in the azimuthal plane; such a beam will correspond to the beam 0 in Fig. 5a .
  • each subarray in this example has 4 antenna elements vertically, which provides a sufficiently large aperture to form a sufficiently narrow beam like the beam 1 in Fig. 5a .
  • Other non-limiting examples of antenna array partitioning/virtualization are shown in Fig. 7 and Fig. 8c .
  • Fig. 9 illustrates a schematic diagram of the BS 300 according to the second aspect of the present invention, which is configured to perform the method according to the first aspect of the present invention due to that it comprises at least a transceiver antenna unit 305 configured to communicate with the UE and any other devices within the coverage area of the corresponding cell; and a processor 310 operably coupled to the transceiver antenna unit 305 and configured to perform the method of the first aspect of the present invention or any possible implementation of the first aspect of the present invention.
  • the BS may be, but is not limited to, a Transmit-Receive Point (TRP), an Access Point (AP) or a NodeB, an eNodeB, a gNodeB (gNB).
  • TRP Transmit-Receive Point
  • AP Access Point
  • gNB gNodeB
  • the BS 300 is shown in Fig. 9 in a relatively simplified, schematic form, so this figure does not show all the components actually contained in the BS 300, but only those through which the present invention is implemented.
  • the BS may comprise other components not shown in Fig. 9 , such as a power supply, various interfaces, I/O means, interconnects, random access and read only memory storing instructions executable by the processor 310 to carry out the method of the first aspect of the present invention or any possible implementation of the first aspect of the present invention, and an operating system, etc.
  • the transceiver antenna unit 305 may include a transceiver and an antenna coupled to each other.
  • the antenna can be implemented as a massive or extremely massive MIMO antenna array with a large number of antenna ports, which supports hybrid analog and digital beamforming capabilities.
  • the processor 310 of the BS 300 may be a central processing unit, a special purpose processor, another processing unit such as a Graphics Processing Unit (GPU), or a combination thereof.
  • the processor 310 may be implemented as an integrated circuit, such as Field Programmable Gate Array (FPGA), Application-Specific Integrated Circuit (ASIC), System-on-Chip (SoC), etc.
  • FPGA Field Programmable Gate Array
  • ASIC Application-Specific Integrated Circuit
  • SoC System-on-Chip
  • Fig. 10 illustrates a schematic diagram of the UE 400 according to sixth aspect of the present invention, which is configured to implement the method according to fourth or fifth aspect of the present invention due to that it comprises at least a transceiver antenna unit 405 configured to communicate with BS and any other devices within the coverage area of the corresponding cell, and the processor 410 operatively coupled to the transceiver antenna unit 405 and configured to perform the method of the fourth or fifth aspect of the present invention or any possible implementation of these aspects of the present invention.
  • the UE may include, but is not limited to, a mobile phone, tablet, laptop, PC, wearable electronic device (e.g.
  • the UE may be referred to differently, e.g. as user terminal, terminal, user device, terminal device, subscriber device and so on.
  • the UE 400 is shown in Fig. 10 in a relatively simplified, schematic form, so the figure does not show all of the components actually contained in the UE 400, but only those that enable the present invention to be implemented.
  • the UE may comprise other components not shown in Fig. 10 , such as a power supply, a battery, various interfaces, I/O means, interconnects, random access and read only memory storing instructions executable by the processor 410 to carry out the method of the fourth or fifth aspects of the present invention or any possible implementation of these aspects of the present invention, as well as an operating system, etc.
  • the transceiver antenna unit 405 may include a transceiver and an antenna coupled to each other.
  • the antenna can be implemented as a massive or extremely massive MIMO antenna array with a large number of antenna ports, which supports hybrid analog and digital beamforming capabilities.
  • the processor 410 of the UE 400 may be a central processing unit, a special purpose processor, another processing unit such as GPU, or a combination thereof.
  • the processor 410 may be implemented as an integrated circuit, such as an FPGA, ASIC, SoC, etc.
  • Fig. 11 illustrates a schematic diagram of the communication system 500 according to eighth aspect of the present invention.
  • the communications system 500 includes one BS 300 that is installed to serve UEs 400 in three deployed cells 1, 2, 3.
  • the BS may correspond to the BS 300 that is described in detail above with reference to Fig. 9
  • each UE 400 may correspond to the UE 400 that is described in detail with reference to Fig. 10 , therefore detailed descriptions of the BS 300 and UE 400 are not repeated here.
  • the communication system 500 may simultaneously support two active Radio Access Technologies (RATs) of, e.g., 4G LTE, 5G NR, 6G.
  • RATs Radio Access Technologies
  • each cell of cell 1, cell 2, cell 3 may have its own BS 300, the number of UEs 400 in the cells may differ from what is shown, cells 1, 2, 3 may be a single larger cell, the shape and space covered by the cells may differ from those shown and so on.
  • the number of cells can be more or less than 3.
  • the present invention may further be implemented as a storage medium storing processor-executable instructions that, when executed by a processor of a device equipped with a transceiver antenna unit, perform a method of any aspect of the disclosed invention or any possible implementation of the corresponding aspect.
  • the storage medium may be any non-transitory computer readable medium, media, storage area, storage device, etc., such as, but not limited to, HDD, optical medium, semiconductor medium, SSD and so on.
  • the technical solutions disclosed herein are methods for communicating between BS and UE, namely for requesting CSI, calculating CSI with less computational complexity for the UE, and reporting the obtained CSI to the BS to enable subsequent efficient communication between the BS and the UE.
  • the present invention can be used in 3GPP compliant communication networks comprising BSs and UEs supporting xMIMO antenna technology for up to 256 digital ports / 3072 antenna elements.
  • the proposed frequency range for use of the disclosed invention is the upper portion of the mid-frequency range (9-13 GHz).
  • the solutions of the present disclosure may be implemented with analog/digital single-beam/multi-beam beamforming and TDD (unpaired spectrum) and/or FDD duplex modes. Other applications of the technology disclosed herein will become apparent to those of ordinary skill in the art upon reading this detailed application disclosure.
  • At least one aspect of the disclosed technical solution may be implemented by an AI model.
  • An AI-related function can be performed through ROM, RAM, and processor(s) (CPU, GPU, NPU).
  • the processor(s) controls the processing of input data according to a predefined operating rule or artificial intelligence (AI) model stored in ROM and RAM.
  • the predefined operating rule or artificial intelligence model is provided through learning.
  • "provided through learning” means that by applying a learning algorithm to a set of training data, the predefined operating rule or AI model with a desired characteristic is created.
  • an AI model may be created to determine, from the synchronization signal signaled by the index and its associated set of preconfigured codebook parameter values, the matrix for reducing the number of antenna array ports; and/or AI model to obtain the equivalent channel with reduced number of ports or CSI based on the matrix for reducing the number of antenna array ports or based on the set of preconfigured codebook parameter values.
  • the set of preconfigured codebook parameter values or any other data describing the possible interaction of the UE and BS in a particular communication network and/or the current operating conditions of the communication network can be used as training data for training such an AI model.
  • the training may be performed on the device itself (i.e., online) that uses the AI model of the embodiment and/or may be implemented through a separate server/system (i.e., offline).
  • the AI model may be a decision tree-based algorithm or consist of multiple neural network layers. Each layer has a plurality of weights and performs the operation of the layer through a calculation based on the result of the calculation in the previous layer and the application of a plurality of weights and other parameter values.
  • decision tree-based algorithms include random forest, ensemble trees, etc.
  • neural networks include, but are not limited to, Convolutional Neural Network (CNN), Deep Neural Network (DNN), Recurrent Neural Network (RNN), Restricted Boltzmann Machine (RBM), Deep Belief Network (DBN), Bidirectional Recurrent Deep Neural Network (BRDNN), Generative Adversarial Network (GAN), Transformer Networks, Deep Q Network, Large Language Models and so on.
  • a learning algorithm is a method of training a predetermined target device or target function based on a corresponding set of training data that causes, enables, controls, or provides an output of the target device or target function.
  • Examples of learning algorithms include, but are not limited to, supervised learning, unsupervised learning, semi-supervised learning or reinforcement learning, and so on.
  • any disclosed method is not strict because some one or more steps may be rearranged in the actual order of execution and/or combined with another one or more steps, and/or divided into a larger number of sub-steps, as discussed above.

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Abstract

The disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. The present invention relates generally to wireless communications and, more particularly, to devices and methods for generating and reporting Channel State Information (CSI) calculated over an equivalent channel obtained over a reduced number of BS antenna array ports. Thus, a technical result of the present invention consists in reduced the computational complexity associated with CSI calculation and optimal precoding matrix search operations at the UE, without compromising the efficiency of subsequent communication between the UE and the BS.

Description

METHOD FOR REPORTING CHANNEL STATE INFORMATION WITH REDUCED NUMBER OF PORTS AND DEVICE IMPLEMENTING SAID METHOD
The present invention relates generally to wireless communications and, more particularly, to devices and methods for generating and reporting Channel State Information (CSI) calculated on an equivalent channel obtained over a reduced number of antenna array ports.
5G mobile communication technologies define broad frequency bands such that high transmission rates and new services are possible, and can be implemented not only in "Sub 6GHz" bands such as 3.5GHz, but also in "Above 6GHz" bands referred to as mmWave including 28GHz and 39GHz. In addition, it has been considered to implement 6G mobile communication technologies (referred to as Beyond 5G systems) in terahertz bands (for example, 95GHz to 3THz bands) in order to accomplish transmission rates fifty times faster than 5G mobile communication technologies and ultra-low latencies one-tenth of 5G mobile communication technologies.
At the beginning of the development of 5G mobile communication technologies, in order to support services and to satisfy performance requirements in connection with enhanced Mobile BroadBand (eMBB), Ultra Reliable Low Latency Communications (URLLC), and massive Machine-Type Communications (mMTC), there has been ongoing standardization regarding beamforming and massive MIMO for mitigating radio-wave path loss and increasing radio-wave transmission distances in mmWave, supporting numerologies (for example, operating multiple subcarrier spacings) for efficiently utilizing mmWave resources and dynamic operation of slot formats, initial access technologies for supporting multi-beam transmission and broadbands, definition and operation of BWP (BandWidth Part), new channel coding methods such as a LDPC (Low Density Parity Check) code for large amount of data transmission and a polar code for highly reliable transmission of control information, L2 pre-processing, and network slicing for providing a dedicated network specialized to a specific service.
Currently, there are ongoing discussions regarding improvement and performance enhancement of initial 5G mobile communication technologies in view of services to be supported by 5G mobile communication technologies, and there has been physical layer standardization regarding technologies such as V2X (Vehicle-to-everything) for aiding driving determination by autonomous vehicles based on information regarding positions and states of vehicles transmitted by the vehicles and for enhancing user convenience, NR-U (New Radio Unlicensed) aimed at system operations conforming to various regulation-related requirements in unlicensed bands, NR UE Power Saving, Non-Terrestrial Network (NTN) which is UE-satellite direct communication for providing coverage in an area in which communication with terrestrial networks is unavailable, and positioning.
Moreover, there has been ongoing standardization in air interface architecture/protocol regarding technologies such as Industrial Internet of Things (IIoT) for supporting new services through interworking and convergence with other industries, IAB (Integrated Access and Backhaul) for providing a node for network service area expansion by supporting a wireless backhaul link and an access link in an integrated manner, mobility enhancement including conditional handover and DAPS (Dual Active Protocol Stack) handover, and two-step random access for simplifying random access procedures (2-step RACH for NR). There also has been ongoing standardization in system architecture/service regarding a 5G baseline architecture (for example, service based architecture or service based interface) for combining Network Functions Virtualization (NFV) and Software-Defined Networking (SDN) technologies, and Mobile Edge Computing (MEC) for receiving services based on UE positions.
As 5G mobile communication systems are commercialized, connected devices that have been exponentially increasing will be connected to communication networks, and it is accordingly expected that enhanced functions and performances of 5G mobile communication systems and integrated operations of connected devices will be necessary. To this end, new research is scheduled in connection with eXtended Reality (XR) for efficiently supporting AR (Augmented Reality), VR (Virtual Reality), MR (Mixed Reality) and the like, 5G performance improvement and complexity reduction by utilizing Artificial Intelligence (AI) and Machine Learning (ML), AI service support, metaverse service support, and drone communication.
Furthermore, such development of 5G mobile communication systems will serve as a basis for developing not only new waveforms for providing coverage in terahertz bands of 6G mobile communication technologies, multi-antenna transmission technologies such as Full Dimensional MIMO (FD-MIMO), array antennas and large-scale antennas, metamaterial-based lenses and antennas for improving coverage of terahertz band signals, high-dimensional space multiplexing technology using OAM (Orbital Angular Momentum), and RIS (Reconfigurable Intelligent Surface), but also full-duplex technology for increasing frequency efficiency of 6G mobile communication technologies and improving system networks, AI-based communication technology for implementing system optimization by utilizing satellites and AI (Artificial Intelligence) from the design stage and internalizing end-to-end AI support functions, and next-generation distributed computing technology for implementing services at levels of complexity exceeding the limit of UE operation capability by utilizing ultra-high-performance communication and computing resources.
Currently, active work is underway on 6th Generation (6G) wireless communication technologies, which will provide higher data transfer speeds, reduce latency and increase communication reliability.
6G technology involves the widespread use of extremely massive antenna arrays containing multiple transceiver Antenna Elements (AE), which effectively implement xMIMO (extreme Multiple Input Multiple Output) when for data transmission (for example, Physical Downlink Shared Channel (PDSCH)) a number of simultaneously transmitted spatial MIMO streams or MIMO layers are generated.
Fig. 1 clearly shows a comparison of the dimensions of the antenna array supporting massive MIMO (mMIMO) in 5th Generation (5G) communicationswith the antenna array supporting the aforementioned xMIMO technology in 6G communications. As shown in this figure, the maximum number of digital ports of the antenna array will be increased from 32 digital ports in 5G to 256 digital ports in 6G. This increase in the number of digital ports will allow for more efficient beamforming, but will inevitably involve increased computational complexity at the BS and/or UE as the number of possible PMI (Precoding Matrix Indicator) values increases with the number of ports used to transmit CSI-RS signals, .
More specifically, the problem of seriously increasing computational complexity in calculating the CSI, including searching the optimal precoding matrix defined by the PMI parameter, arises on the UE side, since, firstly, for each possible matrix, UE has to calculate the product, i.e. calculate how the channel will look if the corresponding precoding matrix is applied, which, given the expected multiple increase in the 6G antenna array dimension, becomes difficult, since it requires the calculation of products of matrices of large sizes. Secondly, due to the large number of ports, the space in which the UE needs to perform optimization when carrying out such a search also becomes large since the number of matrices in the codebook generally increases with the number of ports. Thus, it would be desirable to solve the above problems, i.e. reduce the computational complexity associated with performing the operations of calculating CSI and searching the optimal precoding matrix.
The disclosure is to enable a device to generate and reporting Channel State Information (CSI) calculated on an equivalent channel obtained over a reduced number of antenna array ports.
Provided in the first aspect of the present invention is BS - implemented method for receiving CSI (for communicating with the UE) calculated over a reduced number of antenna array ports, the method comprising the steps of: transmitting at least one synchronization signal, wherein each of the at least one synchronization signal has an associated set of preconfigured codebook parameter values, which is applied at the UE to determine a matrix for reducing the number of antenna array ports, obtain an equivalent channel with the reduced number of ports based on said matrix, and calculate CSI over the equivalent channel; receiving from the UE an index of each of one or more synchronization signals selected by the UE from the previously transmitted at least one synchronization signal, and received power of each of the one or more synchronization signals, the one or more synchronization signals being selected by the UE as having received power values at the UE, which fall within a predetermined range of power values (for example, the highest L1-RSRP measurements); selecting from the one or more synchronization signals indicated by the indices received from the UE, a synchronization signal to be used at the UE side to obtain a corresponding set of preconfigured codebook parameter values; transmitting to the UE at least one CSI-RS and a request to calculate CSI (CSI request) at the UE side on the at least one CSI-RS received by the UE, wherein a bit value in the Downlink Control Information (DCI) field additionally signals an index of the selected synchronization signal; receiving from the UE the CSI calculated by the UE over the equivalent channel with the reduced number of antenna array ports, wherein the equivalent channel is obtained by accessing the set of preconfigured codebook parameter values, which is associated with the synchronization signal signaled by the index of the selected synchronization signal, and defines the matrix for reducing the number of antenna array ports, and applying said matrix to a channel matrix; reconstructing a full precoding matrix by applying said matrix for reducing the number of antenna array ports applied previously at the UE to reduce the number of antenna array ports to a precoding matrix indicated by PMI parameter contained in the received CSI; and transmitting data and/or signals to the UE, said transmission being subjected to beamforming based on the reconstructed full precoding matrix.
Application of the above described method reduces the computational complexity at the UE by defining the port number reduction matrix depending on both the BS- and UE- preconfigured specific information associated with a particular transmitted/received synchronization signal (e.g., SS/PBCH), the received power (for example, L1-RSRP) of which appeared to be the highest at the UE. In this sense, the concept sometimes referred to herein as "best synchronization signal" should be understood as the receive/transmit beam (for example, the primary beam of the receive/transmit beam pattern) with which the received power of the corresponding synchronization signal appeared to be the highest at the UE. A certain matrix for reducing the number of ports allows to virtualize a large antenna array, on which the CSI is calculated, into a set of collectively equivalent subarrays with a reduced number of ports (in this case, virtual ports). The use of the virtualized antenna array at the UE reduces the computational complexity of CSI calculation at the UE, because at least the dimension of the multiplied matrices is reduced. In this case, the accuracy of beamforming at the BS and, as a consequence, the quality and speed of data transmission between the BS and the UE do not suffer, because the BS, knowing that the UE calculated CSI over the equivalent channel with the reduced number of ports, performs the reverse operation on its side, reapplying the same port reduction matrix that was previously applied at the UE to reconstruct the full precoding matrix on the basis of the CSI received from the UE, and subsequently uses the reconstructed full matrix in beamforming to the UE. The above described operations and advantageous technical effects are described in detail below and illustrated in the accompanying drawings with the completeness sufficient to enable one of ordinary skill in the art to practice the disclosed invention.
In the possible implementation of the first aspect of the present invention, the at least one synchronization signal is a Synchronization Signal / Physical Broadcast Channel (SS/PBCH) block. In the other possible implementation of the first aspect of the present invention, each synchronization signal transmitted by the BS has its own associated set of preconfigured codebook parameter values, containing values of the following parameters: a number of antenna array ports along a first dimension and a number of antenna array ports along a second dimension; an oversampling factor of precoding vectors (for example, but not limited to, DFT vectors) for the first dimension and an oversampling factor of precoding vectors for the second dimension; and parameters of precoding vectors, which define or approximate a transmit beam of the corresponding synchronization signal.
In the possible implementation of the first aspect of the present invention, the received power of the synchronization signal measured at the UE is Layer 1 Reference Signal Received Power (L1-RSRP).
In the other possible implementation of the first aspect of the present invention, receiving from the UE the index of each of the one or more synchronization signals selected by the UE is performed through Media Access Control (MAC) layer signaling, in case more than one synchronization signal is selected by the UE, the indices of these selected synchronization signals are received as an ordered list or an unordered list, in the case of receiving the indices of the selected synchronization signals as the ordered list: the indices are ordered in the list according to the measured received power values of the respective synchronization signals, said list starting with an index of that synchronization signal of the synchronization signals selected by the UE for which the received power measurement obtained at the UE is the highest, wherein the bit value in the DCI field signaling the index of the synchronization signal selected by the BS specifies the ordinal number of the selected synchronization signal index in said list. In this sense, the ordinal numbering used here to refer to a synchronization signal in the list is relative (i.e. being relative to other synchronization signals indicated by indices in the list), and not absolute, i.e. being not the end-to-end indexing of all possible synchronization signals between the BS and the UE. In the alternative implementation, in the case of receiving the indices of the selected synchronization signals as the unordered list: the index of each selected synchronization signal is reported along with the absolute value of the received power of the corresponding synchronization signal, wherein the bit value in the DCI field signaling the index of the synchronization signal selected by the BS specifies the index of the selected synchronization signal in said list.
In the other possible implementation of the first aspect of the present invention, absence of selected synchronization signal index signaling with a bit value in the DCI field or signaling a predetermined bit value in the DCI field causes the UE to perform CSI calculation over the entire antenna array. According to this implementation, a single bit value indicates the synchronization signal (explicitly using the index together with L1-RSRP in the unordered list, or implicitly using the ordinal number of signal index in the ordered list) and a request to calculate CSI with or without reduction in the number of antenna array ports. Therefore, the particular bit value in the DCI field can signal, if necessary, skipping the calculation of CSI with a reduction in the number of antenna ports. If skipping the calculation of CSI with a reduction in the number of antenna ports is signaled, the CSI calculation may be performed by the UE over the entire antenna array.
Provided in the second aspect of the present invention is a BS comprising a transceiver antenna unit and a processor configured to perform the method according to the first aspect of the present invention or according to any possible development of the first aspect of the present invention.
Provided in the third aspect of the present invention is a storage medium storing instructions executable by a processor, which, when executed by the processor of a device equipped with a transceiver antenna unit, cause the execution of the method according to the first aspect of the present invention or according to any possible development of the first aspect of the present invention.
Provided in the fourth aspect of the present invention is a UE - implemented method for transmitting CSI (for communication with BS) calculated over a reduced number of antenna array ports, the method comprising the steps of: receiving at least one synchronization signal, wherein each of the at least one synchronization signal has an associated set of preconfigured codebook parameter values, which is applied at the UE to determine a matrix for reducing the number of antenna array ports, obtain an equivalent channel with the reduced number of ports based on said matrix, and calculate CSI over the equivalent channel; measuring received power of each of the at least one synchronization signal; selecting from said at least one synchronization signal, respectively, one or more synchronization signals for which the obtained received power measurements are the highest; transmitting to a BS an index of each of the one or more selected synchronization signals and the received power of each of the one or more selected synchronization signals; receiving from the BS at least one CSI-RS and a request to calculate CSI on the at least one CSI-RS received by the UE, wherein a bit value in the DCI field additionally signals an index of the synchronization signal selected by the BS from the synchronization signals whose indices were previously transmitted by the UE to the BS; determining on the synchronization signal signaled by the index and the associated set of preconfigured codebook parameter values the matrix for reducing the number of antenna array ports; obtaining the equivalent channel with the reduced number of ports by applying said matrix for reducing the number of antenna array ports to a channel matrix; calculating the CSI over said equivalent channel; in response to the request to calculate CSI, transmitting to the BS the CSI calculated over said equivalent channel with the reduced number of antenna array ports; and receiving data and/or signals transmission from the BS, wherein for said transmission the beam pattern is formed on the basis of a full precoding matrix reconstructed at the BS on the basis of the transmitted CSI calculated over said equivalent channel with the reduced number of antenna array ports.
The above-described UE - implemented method according to the fourth aspect of the present invention has the same inventive concept with the first aspect of the present invention in that they share, among others, specific technical features. Thus, the above-described UE - implemented method according to the fourth aspect of the present invention provides technical advantages similar to the first aspect of the present invention, which are briefly described above where the essence of the first aspect of the present invention is discussed.
In the possible implementation of the fourth aspect of the present invention, the at least one synchronization signal is a Synchronization Signal / Physical Broadcast Channel (SS/PBCH) block. In the other possible implementation of the fourth aspect of the present invention, each synchronization signal received from the BS has its own associated set of preconfigured codebook parameter values, containing values of the following parameters: a number of antenna array ports along a first dimension and a number of antenna array ports along a second dimension; an oversampling factor of precoding vectors for the first dimension and an oversampling factor of precoding vectors for the second dimension; and parameters of precoding vectors, which define or approximate a receive beam of the corresponding synchronization signal.
In the possible implementation of the fourth aspect of the present invention, the measured received power of the synchronization signal is Layer 1 Reference Signal Received Power (L1-RSRP).
In the other possible implementation of the fourth aspect of the present invention, transmitting to the BS the index of each of the one or more selected synchronization signals is performed through Media Access Control (MAC) layer signaling, in case of more than one synchronization signal is selected, the indices of these selected synchronization signals are transmitted as an ordered list or an unordered list. In the case of transmitting the indices of the selected synchronization signals as the ordered list: the indices are ordered in the list according to the measured received power values of the respective synchronization signals, said list starting with an index of that synchronization signal of the selected synchronization signals for which the obtained received power measurement is the highest (i.e. the order used in the list is from the highest received power to lower ones; but the implementation is also possible in which the order is reversed and both the BS and the UE know about this), wherein the bit value in the DCI field signaling the index of the synchronization signal selected by the BS specifies the ordinal number of the selected synchronization signal index in said list. In the case of transmitting the indices of the selected synchronization signals as the unordered list: the index of each selected synchronization signal is reported along with the absolute value of the received power of the corresponding synchronization signal, wherein the bit value in the DCI field signaling the index of the synchronization signal selected by the BS specifies the index of the selected synchronization signal in said list.
Provided in the fifth aspect of the present invention is the alternative embodiment of a UE - implemented method for transmitting CSI calculated over a reduced number of antenna array ports, the method comprising the steps of: receiving at least one synchronization signal, wherein each of the at least one synchronization signal has an associated set of preconfigured codebook parameter values, which is applied at the UE to determine a matrix for reducing the number of antenna array ports, obtain an equivalent channel with the reduced number of ports based on said matrix, and calculate CSI over the equivalent channel; measuring received power of each of the at least one synchronization signal; selecting, from said at least one synchronization signal, respectively, one or more synchronization signals for which the obtained received power measurements are the highest; transmitting to a BS an index of each of the one or more selected synchronization signals and the received power of each of the one or more selected synchronization signals; receiving from the BS at least one CSI-RS and a request to calculate CSI on the at least one CSI-RS received by the UE; determining, based on the set of preconfigured codebook parameter values that is associated with the synchronization signal for which the obtained received power measurement is the highest, from among the synchronization signals whose indices were previously transmitted by the UE to the BS, the matrix for reducing the number of antenna array ports; obtaining the equivalent channel with the reduced number of ports by applying said matrix for reducing the number of antenna array ports to a channel matrix; calculating CSI over said equivalent channel; in response to the request to calculate CSI, transmitting to the BS the CSI calculated over said equivalent channel with the reduced number of antenna array ports, and receiving data and/or signals transmission from the BS, wherein for said transmission the beam pattern is formed on the basis of a full precoding matrix reconstructed at the BS on the basis of the transmitted CSI calculated over said equivalent channel with the reduced number of antenna array ports.
The above-described alternative embodiment according to the fifth aspect of the present invention differs from the UE - implemented method for transmitting CSI according to the fourth aspect of the present invention in that, in the fifth aspect of the present invention, the UE does not wait for signaling from the BS of the best, from the position of the BS, synchronization signal, but determines the matrix for reducing the number of ports autonomously based on a set of preconfigured codebook parameter values, which is associated with the synchronization signal for which the obtained received power measurement is the highest. In other words, the UE reports to the BS the index of the synchronization signal whose received power measurement is found to be the highest, and right away (i.e. autonomously) determines the port reduction matrix based on the corresponding set of preconfigured codebook parameter values, which is associated with this synchronization signal.
Thus, the UE-implemented method according to the fifth aspect of the present invention has the same inventive concept with both the first aspect of the present invention and the fourth aspect of the present invention, since they share, among others, specific technical features. Therefore, the above-described UE-implemented method according to the fifth aspect of the present invention provides the technical advantages similar to that in the first and fourth aspects of the present invention, which are briefly described above where the essence of the first aspect of the present invention is discussed. Additionally, the fifth aspect of the present invention allows to reduce the overhead at the BS, i.e. to reduce signaling overhead, because in this alternative embodiment there is no need to signal the BS-selected best synchronization signal to the UE. The BS in this case assumes that the UE will use the port reduction matrix that will be determined unambiguously at both the UE and the BS based on the set of preconfigured codebook parameter values, which is associated with the UE-reported synchronization signal index for which the UE obtained the best received power measurement.
Provided in the sixth aspect of the present invention is a UE comprising a transceiver antenna unit and a processor configured to perform the method according to the fourth aspect of the present invention or according to any possible development of the fourth aspect of the present invention or the method according to the alternative fifth aspect of the present invention having the same purpose but slightly different implementation.
Provided in the seventh aspect of the present invention is a storage medium storing instructions executable by a processor, which, when executed by the processor of a device equipped with a transceiver antenna unit, cause the execution of the method according to the fourth aspect of the present invention or according to any possible development of the fourth aspect of the present invention or the method according to the alternative fifth aspect of the present invention having the same purpose but slightly different implementation.
Provided in the eighth aspect of the present invention is a communication system comprising one or more base stations according to the second aspect of the present invention or according to any possible development of the second aspect of the present invention and one or more user equipments according to the sixth aspect of the present invention or according to any possible development of the sixth aspect of the present invention.
According to an embodiment of the disclosure, methods and devices for efficiently geerating and reporting Channel State Information (CSI) calculated on an equivalent channel obtained over a reduced number of antenna array ports.
These and other aspects of the present disclosure will be described in detail below with reference to figures in which:
Fig. 1 schematically illustrates the antenna array supporting 5G mMIMO, and the antenna array supporting 6G xMIMO.
Fig. 2 schematically illustrates how interaction occurs between BS and UE, during which the BS performs the method according to the first aspect of the present invention and the UE performs the method according to the fourth aspect of the present invention.
Fig. 3 illustrates in more detail how the UE performs steps S108-S111 illustrated in the flowchart of Fig. 2.
Fig. 4 illustrates the representation of the codebook and the related other features.
Fig. 5a schematically illustrates the exemplary beamforming for simultaneous emission of eight synchronization signals.
Fig. 5b schematically illustrates the exemplary beamforming for simultaneous emission of eight synchronization signals.
Fig. 5c schematically illustrates the exemplary beamforming for simultaneous emission of eight synchronization signals.
Fig. 6 schematically illustrates the other example of beamforming for simultaneous emission of sixteen synchronization signals with a large number of sub-regions in the vertical emission plane.
Fig. 7 illustrates three examples of using different matrices for reducing the number of antenna array ports to virtualize the antenna array with reduced number of antenna ports.
Fig. 8a illustrates three other examples of virtualized antenna arrays with reduced number of antenna ports.
Fig. 8b illustrates three other examples of virtualized antenna arrays with reduced number of antenna ports.
Fig. 8c illustrates three other examples of virtualized antenna arrays with reduced number of antenna ports.
Fig. 9 illustrates the schematic diagram of the BS according to the second aspect of the present invention.
Fig. 10 illustrates the schematic diagram of the UE according to the sixth aspect of the present invention.
Fig. 11 illustrates the schematic diagram of the communication system according to the eighth aspect of the present invention.
Before moving on to a detailed discussion of aspects and embodiments of the present invention, certain technical features of the interaction between the BS and the UE are discussed. As mentioned above, at 6G BS it is assumed to use of extremely massive antenna arrays containing multiple transceiver antenna elements that allow efficient implementation of MIMO technology, whereby a number of simultaneously transmitted spatial MIMO layers are formed to transmit data (for example, Physical Downlink Shared Channel (PDSCH)) to one or more UEs.
Generally speaking, a digital signal is transmitted through one or more digital ports associated with the antenna elements of the BS by the Radio Frequency (RF) unit that performs the function of converting the digital signal to analog and vice versa. Thus, for the 3.5 GHz frequency range, up to 64 digital antenna ports can be used, allowing BSs to use various digital signal spatial processing schemes (precoding). For example, using Spatial Multiplexing (SM) technology, it is possible to reuse the same time-frequency resources for DL transmission of multiple signals (MIMO layers) to one or more UEs, and using adaptive beamforming (BF) technology provides dynamic focusing of the power of the transmitted signal in one or more specified directions. By using modulation techniques such as Orthogonal Frequency Division Multiplexing (OFDM) modulation, efficient wideband signal transmission is achieved.
BS being a part of the network broadcasts synchronization signals (e.g., SS/PBCH) on all or part of the spatial beams, where SS is the Synchronization Signal, PBCH is Physical Broadcast Channel containing Demodulation Reference Signals (DMRS). Such broadcasting may be carried out by the BS on a periodic or aperiodic basis. In the following, without loss of generality, these beams may be referred to as receive/transmit beams, depending on whether they are used in the context of receiving or transmitting data, respectively. Each synchronization signal is received/transmitted using a corresponding receive/transmit beam, i.e. to each synchronization signal, the base station applies one predefined beam.
The UE evaluates the received synchronization signals; more specifically, the UE measures the RSRP of each synchronization signal, selects a required number of synchronization signals with the highest RSRP (hereinafter such synchronization signals may be referred to as the best synchronization signalsfor brevity, and the corresponding transmit/receive beams as the best beamsor the highest quality beams) and reports the selected beams in the form of a measurement report to the BS. Said report indicates the indices (e.g., SS/PBCH Resource Block Indicators, abbreviated as SSB-RI) of the selected synchronization signals and information about the corresponding RSRPs; thereafter, the generated report is transmitted by the UE to the BS via uplink (UL).
The base station may use the information contained in the received report to carry out beamforming for subsequent DL transmission to the UE. In particular, the BS transmits (e.g., on a periodic or aperiodic basis) CSI-RS, to which analog beamforming is typically applied in the analog part of the base station; more specifically, the base station preferably uses one or more best beams according to the report previously received from the UE to transmit CSI-RS to the UE.
CSI-RSs are generally transmitted to enable the UE to calculate CSI from the antenna ports of the BS. Depending on the implementation, each CSI-RS port may correspond to one digital antenna port, or, if additional virtualization is performed, each CSI-RS port may correspond to more than one (e.g., four) digital antenna ports. The portion of the antenna array corresponding to more than one (e.g., four) digital antenna ports will define a subarray (i.e., a smaller portion) of the antenna array, and the essence of the above virtualization process will be to obtain for the entire antenna array an equivalent set of subarrays to reduce the number of antenna array ports, which will be described in detail below. In other words, given this additional virtualization, a virtualized representation of the antenna elements of the base station antenna array in the form of CSI-RS antenna ports is ultimately enabled. It should be noted that when communicating with the BS, the UE is not aware of the actual structure of the BS antenna array - this communication, in fact, is carried out at the level of the CSI-RS antenna ports of the BS, i.e. each CSI-RS antenna port is treated at the UE as a single emitting element, regardless of the number of antenna elements in the physical antenna array it covers.
Upon receipt from the BS of a CSI request (which may also be referred to as a 'a request to calculate CSI'), which may be transmitted by the BS on a periodic or aperiodic basis, and whose transmission may be via DCI, the UE performs calculations to obtain CSI using CSI-RS measurements that are being performed or already performed.
The calculation of the CSI at the UE comprises the calculation of a number of parameters that are included in the generated CSI. In particular, the UE selects a preferred number of MIMO layers corresponding to the number of simultaneous data streams transmitted from the BS that the UE intends to receive. This number of MIMO layers is reflected by the Rank Indicator (RI) parameter in the CSI. The UE also generates a precoding matrix from precoding vectors (e.g., vectors of a mathematical structure such as Discrete Fourier Transform (DFT), but not limited to such structure) that are selected from a predetermined codebook. The generated precoding matrix is reflected by the PMI parameter as part of the CSI. In addition, the UE determines the Channel Quality Indicator (CQI), which is included in the CSI as well.
The generated CSI, thus including RI, PMI, CQI, is transmitted from the UE to the BS as channel feedback information in response to said CSI request. Upon receiving the CSI, the BS, in particular, uses the CQI to select a modulation and error correction coding scheme (MCS) and applies the resulting precoding matrix to perform digital beamforming of the DL transmission (e.g., PDSCH) to the UE.
Aspects related, in particular, to the implementation of the codebook, the specifics of the representation of RI, PMI, CQI and other parameters as part of the CSI, are disclosed in the specification TS 38.214, v.17.4.0, and are also reflected in the patent RU 2811989, both of which are incorporated herein by reference in their entirety. In particular, type I codebook (see Table 5.2.2.2.1-2 from said specification) can be used as the codebook. It should be noted that RU 2811989 also discloses promising technologies for implementing precoding in the DL direction.
As discussed above, the BS broadcasts synchronization signals on all or part of the beams, and the BS uses a corresponding specified transmit beam to transmit each synchronization signal. The UE measures the received power (e.g., L1-RSRP) of each synchronization signal, selects a predetermined number M of synchronization signals with the largest RSRP, i.e. M best synchronization signals, and generates a report (e.g., in the form of an ordered or unordered list of selected synchronization signals) indicating the indices of the selected synchronization signals or their ordinal numbers in the list and the corresponding measurements of the received power of the corresponding selected synchronization signals. Received power measurements in the list can be indicated by absolute values (for example, L1-RSRP values) or relative values relative to the listed synchronization signal whose received power measurement is the highest.
M is a natural number that is typically preconfigured by the BS for the UE and accordingly signaled in advance by the BS to the UE, for example, through Radio Resource Control (RRC) protocol signaling. Essentially, through parameter M, the BS indicates to the UE what required number of its best synchronization signals the UE should report to the BS. In particular, M can take the values 1, 2, 4, but is not limited to these values.
The indices of the selected synchronization signals (e.g., SSB-RI) are reported by bit values of a given length. The following describes a non-restrictive approach by which appropriate RSRPs for SSB-RI may be reported. A quantization-based implementation may be used for the RSRP report. Namely, a set of ranges of absolute values of received power in the corresponding units of measurement is preset, and a unique index value is assigned to each range. This configuration is summarized in illustrative Table 1 below.
Table 1: Absolute L1-RSRP (best SS/PBCH) reporting
In Table 1, the right column indicates the unit of measurements of Synchronization Signal Received Power (SS-RSRP), namely dBm; the two middle columns list the ranges of absolute values of the L3 and L1 synchronization signal received powers, respectively in dBm; the left column lists index values, each of which uniquely defines a corresponding range of absolute power values. To illustrate, if the measured RSRP value for some of the best synchronization signals is -44.6 dBm, then, according to Table 1 , the report indicates the index RSRP_112 corresponding to the range [-45;-44].
In addition, a differential approach can be used, which is also based on a quantized representation. From the M best synchronization signals, the synchronization signal to which the largest RSRP corresponds is determined, and together with the index of this synchronization signal, the corresponding index value from the table of absolute received power values (for example, RSRP_i according to Table 1 above) is reported, indicating the range of absolute received power values in which this largest RSRP falls, and for each of the remaining (M - 1) synchronization signal indexes (SSB-RI), the corresponding index value DIFFRSRP_j, j = {0, 1,..., 15} for the corresponding range of relative received power values is indicated according to Table 2 that specifies the range of received power values relative to the largest RSRP. Such a table is illustrated below by Table 2.
[Table 2]
In Table 2 , the middle column lists the difference ranges of the corresponding RSRP values with respect to the largest RSRP, and the unit of these difference, relative ΔRSRP values, as indicated by the right column of Table 2, is dB; the left column lists index values, each of which uniquely defines a corresponding range of relative power values.
In a typical implementation of the present approach, the M synchronization signals are ordered in the list reported to the BS in descending order of the corresponding measured RSRP. That is, first, the synchronization signal with the largest RSRP and the index value RSRP_i of the corresponding range of absolute received power values are indicated, and then, indicated in descending order of the corresponding difference RSRP values are the remaining (M - 1) synchronization signals with index values DIFFRSRP_j of the corresponding relative received power ranges (according to Table 2) or index values RSRP_i of absolute received power values (according to Table 1). Arranging this order of information reported to the BS in the RSRP report, which may be in the form of a list, allows the BS to subsequently indicate the synchronization signal selected by the BS by means of a corresponding bit value in the DCI field signaling the ordinal number of the selected synchronization signal according to the order of the synchronization signals in the list.
The UE then performs UL transmission of the generated report to the BS via physical layer (L1) channels. This report can be further referred to in the text as RSRP report, and the synchronization signal received power can be namely L1-RSRP.
Applicable aspects of RSRP report generation and transmission are reflected in the TS 38.133 specification; namely, Tables 1, 2 given above for illustrative purposes, essentially correspond to similar tables given in TS 38.133 (see Section 10.1.6). This specification is incorporated herein by reference in its entirety.
Next let us proceed to the description of Fig. 4 illustrating a non-restrictive representation of the applicable type 1 codebook and other beamforming-related features. The upper left corner of Fig. 4 illustrates an example of a part or all of a two-dimensional base station antenna array in which the antenna elements (designated as × in this figure) are virtualized into = 2 antenna ports horizontally and = 2 antenna ports vertically. As can be seen from the illustration, each antenna port in this case corresponds to a subset of three adjacent antenna elements. The ability of each port to emit a signal with one of two different, orthogonal polarizations (P = 2) is also taken into account. These orthogonal polarizations, as shown in the center and top of Fig. 4, can be linear (vertical and horizontal) polarizations, as well as circular (right and left) polarizations. As the result, the antenna array under consideration supports ××P=8 digital antenna ports. Essentially, corresponds to a dimension in one (in this non-limiting example, horizontal) spatial direction, corresponds to a dimension in another (in this non-limiting example, vertical) spatial direction, and P corresponds to a dimension in polarization. Naturally, the same considerations can be applied without limitations to antenna arrays with other required dimensions (, ).
The lower right corner of Fig. 4 illustrates the representation of a codebook with reference to the antenna array discussed above with reference to the illustration in the upper left corner of Fig. 4. Each of the possible spatial beams in which the BS can carry out directional data transmission is represented in the codebook by a precoding vector. Essentially, the codebook is illustrated in Fig. 4 with a two-dimensional (horizontal and vertical) grid of beams. Each beam, and hence its corresponding precoding vector, is shown as a circle on this grid. Light gray circles conventionally indicate mutually orthogonal precoding vectors directly corresponding to × = 4 (i.e., two horizontally, two vertically) digital antenna ports of the shown antenna array. It should be understood that one digital port can be transmitted from several physical antennas.
In addition, through the use of oversampling coefficients (, ) a consistent linear phase shift is ensured for each precoding vector in the horizontal and vertical directions, respectively; as a consequence, the overall density of the beam structure under consideration increases significantly. As a result, the dimension of the codebook is × in horizontal direction and × in vertical direction, i.e. the total number of precoding vectors in the codebook is (×)×(×). Accordingly, the precoding vectors in the codebook are indexed horizontally by the index , = 0,...,( ×)-1, and vertically by the index , = 0,...,( ×)-1. In the case of considered Fig. 4 = = 4. The exact manner in which the precoding vectors (i.e., codebook vectors) are calculated will be described below. It should be noted that the scheme in Fig. 4 should be considered without regard to polarization, that is, such that each of the precoding vectors is used with one polarization.
For purposes of illustration, in the beam grid of Fig. 4, the darkest circle conventionally shows a specific beam (i.e., a specific transmission direction) selected from the codebook. Top and center in Fig. 4 shows standard, usually 4 phases, the values of which can be taken by the phasing coefficient. Physically, the phasing coefficient can form vertical, horizontal, left circular, and right circular polarizations.
Bottom left in Fig. 4 shows the general processing scheme implemented at the BS when forming transmission beam pattern. According to this scheme, the BS performs baseband processing to obtain virtual ports and corresponding transmitted spatial streams (MIMO layers). After this, digital beamforming is performed at the BS, the result of which are the digital ports of the antenna array formed with the required configuration and the corresponding CSI-RSs to be transmitted to the UE. The BS then performs digital-to-analog conversion on the signal obtained from the digital beamforming step. Finally, the analog signal undergoes analog beamforming and is emitted by the physical antennas towards the UE. Upon receiving such a signal, the UE can calculate the channel per each digital port of the BS antenna array, and in fact, the UE, using the codebook, finds and signals to the BS the best vector, which allows the signal transmitted from the digital ports of the BS to said UE to be phased in the most optimal way.
The codebook illustrated in Fig. 4 essentially corresponds to the simplest type 1 codebook, but the present invention should not be limited to this type of codebook because the present disclosure also applies to other types of codebook, such as type 2 codebook. Possible codebook configurations supported in 6G can be determined from Table 3 below:
[Table 3]
The first column in Table 3 above specifies the total number of CSI-RS antenna ports, . As shown in the table, the maximum number of digital antenna ports supported in 6G is 256. For comparison, the maximum number of digital antenna ports supported in 5G NR is only 32. Codebook configurations for 5G NR can be determined from the lines in above Table 3 for any ≤32. The second column of the Table specifies possible configurations of digital antenna ports, i.e. how this total number of digital antenna ports can be arranged in the two-dimensional antenna array. As the non-limiting example, if the number of digital antenna ports (CSI-RS ports) is 16, they can be arranged as 4x2 or 8x1 subarray grids without regard to polarization; the actual product is two times less, because different polarizations are used additionally. The third column specifies the applicable oversampling factors to provide denser coverage and more flexible configuration. The fourth column, as the non-limiting example for the case of RI=1, indicates the total number of PMI matrices in the codebook. According to the fourth column of Table 3, the pattern is observed that the number of PMI matrices generally increases with the total number of digitalantenna ports . This pattern is the obvious demonstration of the significantly higher computational load on the UE when CSI is calculated, because the codebook size in 6G becomes significantly larger to support more digital antenna ports (6G includes support for configurations with up to 256 CSI-RS antenna ports), and the transmit/receive beam becomes even narrower. In other words, in order for the codebook to completely cover the entire space around the BS, the number of PMI matrices increases significantly.
The following is the description of how the precoding matrix for the codebook is calculated at the UE side conventionally (i.e., without the number of antenna array ports being reduced). Precoding matrix is calculated according to the following equation 1.
[Equation 1]
where - the number of MIMO layers,
- the number of CSI-RS antenna ports,
- the precoding vector specified by indices and ,
- the polarization-phasing coefficient, defined as , i.e. =0,1,2,3.
The matrix in equation1 is the precoding matrix ordered in a predefined way. From equation1 it is clear that the entire precoding matrix is multiplied by the normalization factor , where is the number of CSI-RS antenna ports, which essentially corresponds to a uniform distribution of the BS transmit power to all MIMO layers. That is, the use of each new MIMO layer proportionally reduces the power allocation per MIMO layer.
Each column vector of the precoding matrix specifies a specific precoding vector for the corresponding MIMO layer. Thus, the number of column vectors of the precoding matrix corresponds to the required number of MIMO layers, each of which may represent a transmission from the BS to the UE of a corresponding signal. For example, if the number of transmitted signals from the BS to the UE is 3, then (the number of column vectors in the precoding matrix) will also be 3. The number of elements of each column vector (vertically) corresponds to the number of CSI-RS antenna ports. In this case, the first half of each column vector corresponds to the first polarization, and the second half of each column vector, where the polarization-phasing coefficient is applied additionally, corresponds to the second polarization. In other words, the column vectors are strictly ordered in the precoding matrix in such a way that they are first specified for an antenna of one polarization from the entire antenna array, and then for an antenna of a different polarization. In the codebook, the precoding vectors are ordered similarly.
Each precoding vector is the Kronecker product of a column vector to a column vector , where equation 2 and equation 3 are as below.
[Equation 2]
[Equation 3]
i.e. (math. expression 4)
In equations 2 and 3: - imaginary unit, denotes transposition. The precoding vector actually specifies the plane wave wavefront characterized by the indices and , i.e. by changing the index values , it is possible to actually control the direction of the precoding vector. The number of elements in the vector is equal to the number of antenna ports along one spatial dimension (in this case - horizontal), i.e. , and the number of elements in the vector is equal to the number of antenna ports along the other spatial dimension (in this case - vertical), i.e. ; wherein should be greater than or equal to , which determines the choice of the specific spatial dimension as the mentioned one and the other dimensions (see Fig. 4 for the illustration). Accordingly, the number of elements in any precoding vector will be ×. Regarding the possible values of the parameters , , , , see Table 3 above.
The following are non-limiting examples of precoding matrices that can be constructed based on type 1 codebook, sequentially for a selectable number of MIMO layers from being equal to the number from 1 to 8 in this example. For the precoding matrices can be constructed by analogy.
- for one MIMO layer : (equation 5),
- for two MIMO layers : (equation 6),
- for three MIMO layers : (equation 7),
- for four MIMO layers : (equation 8)
- for five MIMO layers : (equation 9)
- for six MIMO layers : (equation 10)
- for seven MIMO layers : (equation 11)
- for eight MIMO layers : (equation 12)
From the above equations 5-12 the general principle underlying the construction of the precoding matrix becomes clear: namely, first, the polarization dimension is used to the maximum, and only then a new precoding vector from the codebook is used (i.e., the DFT dimension). For example, the precoding matrix for two MIMO layers (= 2) uses one precoding vector with two different polarizations, which is respectively reflected by the phasing coefficients and -. This essentially means that both MIMO layers will be transmitted from the BS to the UE in the same spatial beam, but with different, orthogonal polarizations. The same principle is observable for and applicable to other values as well. The sequence of polarization priority engagement is shown above with circled arrows, wherein orthogonal polarizations are shown as vertical and horizontal only as the non-limiting example.
As stated earlier, the precoding matrix thus generated, reported by the UE to the BS through the PMI of the CSI, is applied at the BS to perform appropriate beamforming for data transmission. This aspect is shown in Fig. 4, which schematically shows the application of digital signal spatial processing in the BS transmitter. Illustrated by the contours in the central part of Fig. 4 below are possible beams in which data streams from the BS can be transmitted; and the illustration also shows the generated beam (in dark gray) that corresponds to one of the precoding vectors in the reported precoding matrix. For example, such a spatial transmit/receive beam could be the beam for case =2 discussed above.
Next, it will be described how the UE, having the codebook, can search for the optimal precoding matrix and the optimal number of layers, indicated respectively by the PMI and RI parameters included in the CSI calculated at the UE side, without reducing the number of antenna array ports (general case), based on the reception of the CSI-RS from the BS. The UE receives CSI-RSs from the BS and, if there is the CSI request from the BS, performs channel estimation based on each of the received CSI-RS to obtain a channel matrix having the dimension for each frequency subband, where is the number of UE receiving antennas, which is usually 2 or 4, but, in rare cases, can be 8; and is the number of CSI-RS antenna ports. Therefore, for the entire channel, the UE typically determines several channel matrices , each having a relatively large dimension defined by the product and . Thus, given that to calculate CSI the UE usually needs to perform many of such products with large-dimensional matrices, the authors of the present invention proposed to reduce the computational complexity of the CSI calculation at the UE by reducing the dimension of the channel matrix up to reduced dimension of the (equivalent) channel matrix using the matrix for reducing the number of antenna array ports, which will be described in detail below with reference to Figs. 2 and 3.
In general, how well UE performs the precoding matrix search indicated by the PMI and RI can be assessed by indirect characteristics (e.g., performance requirements). Based on this, the PMI/RI search problem can be reduced to the following optimization problem:
where
- the full precoding matrix,
- the non-limiting example of the objective (cost) function,
- the full-dimensional channel matrix measured at the UE on the basis of CSI-RSs,
- the precoding matrix that changes depending on the value of the RI specified by the index , and on the value of the PMI (codebook) specified by the index ,
- noise and interference power (covariance matrix),
- the identity matrix, and
- the determinant of the matrix.
Thus, in general (i.e., without reducing the dimension of the channel matrix), the UE measures the channel matrix , applies the precoding matrix to it and obtains the equivalent channel using the product of the specified terms. In other words, the UE is actually emulating what a specific channel will look like after applying the precoding matrix to it. The UE's task at it is to iterate over all codebook indices and and all ranks, find the optimal value optimizing the above-mentioned function , and select the optimal precoding matrix and the most optimal rank specified by the PMI and RI, respectively. Application of equations13-14 given above as the non-limiting example in particular allows to maximize the objective function, which, in this example, is the throughput function for MIMO systems.
The above description of the general case of precoding matrix search performed at the UE is not optimal for 6G technology, since for each matrix the UE needs to perform a computationally complex operation, namely, calculate the product to obtain the equivalent channel to approximate how the channel will look like when the matrix is applied. Moreover, since the size of the channel matrix becomes very large in 6G technology, up to 8*256, and the dimension of the matrix itself is quite large, calculation of the equivalent channel becomes complex for the UE. In addition, as demonstrated by the pattern described above with reference to Table 3, due to the large number of antenna ports, the number of PMI matrices in the codebook increases, i.e. the space in which the UE needs to optimize according to the above equations 13-14 becomes large as well. In other words, the traditional scheme of searching for PMI and RI at the UE, described above is not optimal to use in the next generation communication technology (e.g. 6G with the support of xMIMO), because there is a problem of computational complexity of finding the optimal precoding matrix at the UE side. These technical problems are solved by the present invention as will be described in detail below.
Fig. 2 shows schematically how the interaction between the BS and the UE occurs according to the present invention. What is shown on the left in Fig. 2 under the abbreviation 'BS' corresponds to the BS-implemented method for receiving CSI calculated over a reduced number of antenna array ports, and what is shown on the right in Fig. 2 under the abbreviation 'UE' corresponds to UE-implemented method for generating and transmitting said CSI. The interaction of the BS and the UE begins at step S100 of transmitting by the BS at least one synchronization signal (e.g. SS/PBCH), each of the at least one synchronization signal having an associated set of preconfigured codebook parameter values applied at the UE to determine the matrix for reducing the number of antenna array ports, obtain an equivalent channel with the reduced number of ports based on said matrix, and calculate CSI over such an equivalent channel. At step S101, said at least one synchronization signal is received by the UE.
Each specific synchronization signal transmitted by the BS in step S100 has its own set of preconfigured codebook parameter values associated with it. Said set of preconfigured codebook parameter values comprises, for the corresponding synchronization signal, its values of the following parameters: the number of antenna array ports in the first dimension and the number of antenna array ports in the second dimension; precoding vectors oversampling factor for the first dimension and precoding vectors oversampling factor for the second dimension; and indices and of the precoding vectors defining the transmit beam of the corresponding synchronization signal.
In step S102, the UE measures the received power of each synchronization signal of the at least one synchronization signal it receives. As stated above, the synchronization signal can be namely SS/PBCH, and the measured received power can be L1-RSRP. Then, in step S103, the UE selects from the received and measured signals, respectively, the M (M is a configurable parameter) synchronization signals for which the obtained measurements of received power are the highest. The division into steps S102 and S103, illustrated in Fig. 2 is the logical division based on the different functions performed. This division is made only for the purpose of a more consistent and detailed description of the present invention. However, such a division into steps should not be interpreted as any limitation of the present invention, since similar functions in an actual implementation may be performed in fewer (including as a single step) or more (than 2) steps. As the result of measuring each synchronization signal and selecting the M best synchronization signals, indices of the M best synchronization signals to be reported to the BS along with the corresponding L1-RSRP values are obtained. This reporting can be carried out as described above with reference to Tables 1 and 2, indicating the indexes of the M best synchronization signals and the index values of the absolute and/or relative values of the measured received power, reported, for example, in the form of the list ordered from the selected synchronization signal with the highest received power to the selected synchronization signal with the lowest received power, or unordered list in which each selected synchronization signal is reported with its corresponding absolute L1-RSRP value. This information may be signaled from the UE to the BS in MAC Control Element (MAC CE). The MAC CE message including SSB-RI/L1-RSRP (instead of an L1 message in 5G NR) provides reliable reception of SSB-RI at the BS, subject to an agreed understanding of the SSB-RIs between the BS and the UE, which can be achieved by pre-configuring them to use a specific sets of synchronization signals with strictly defined SSB-RIs.
The non-limiting example of the structure of the list ordered on the basis of synchronization signals received power is illustrated with the following Table 4.
[Table 4]
In this example, the value of M (i.e., the number of synchronization signals selected at the UE side out of the total number of SS/PBCHs transmitted by the BS) was preconfigured to be 4. In this example, as the result of measurements of the received power of synchronization signals SS/PBCHs, carried out at the UE, the UE has determined that the best synchronization signals are the synchronization signals with indexes {k0, k1, k3, k4}. Moreover, since the maximum received power measurement at the UE was obtained for the synchronization signal k1, this synchronization signal is indicated first in the list (i.e. with the ordinal number m = 0 of the list entry) and with the index value of the absolute L1-RSRP power determined according to Table 1. The second in the list (m =1) is the synchronization signal k3, which is the second best synchronization signal because the RSRP of this signal k3 is less than the RSRP of signal k1, but greater than the RSRP of every other measured signal. The power of the second and subsequent signals in the list is indicated relative to the absolute power of the signal k1 with the index values as determined according to Table 2. The third (m=2) in the list is the synchronization signal k4, which is the third best synchronization signal because the RSRP of this signal k4 is less than the RSRP of signal k3, but greater than the RSRP of every other measured signal. The fourth (m=3) in the list is the synchronization signal k0, which is the fourth best synchronization signal because the RSRP of this signal k0 is less than the RSRP of signal k4, but greater than the RSRP of every other measured signal. The signal with index k2 was not included in the list, because its RSRP turned out to be less than the RSRP of signals with indices k1, k3, k4 and k0.
The example list structure described above with reference to Table 4 should not be interpreted as any limitation of the present invention. When using the ordered list according to this example, the particular synchronization signal selected in step S106 by the BS is transmitted subsequently in step S107 to the UE by the bit value in DCI field reflecting, among other things, the ordinal number m of the entry of the selected synchronization signal according to the list, which will be described in detail below.
The non-limiting example of the unordered synchronization signal list structure is illustrated in the following Table 5.
[Table 5]
The example of the alternative list structure used according to Table 5 differs from the example list structure described above with reference to Table 4 in that the entries in the list according to Table 5 do not need to be ordered according to received power values, but instead the index of each of the selected signals is reported together with the index value of the corresponding absolute L1-RSRP power. Moreover, in comparison with the list structure illustrated in Table 4, the list structure illustrated in Table 5 provides more accurate information about the power of the received synchronization reference signal, because absolute values allow a wider L1-RSRP range to be quantized. At the same time, the list structure illustrated in Table 4 reduces the number of used bits required to transmit the relative L1-RSRP power. The example of the alternative list structure described above with reference to Table 5 should not be interpreted as any limitation of the present invention as well.
Returning to the BS and UE interaction illustrated with reference to Fig. 2, the UE transmits in step S104 to the BS the list comprising the indices of the selected synchronization signals and the received powers corresponding to the selected synchronization signals. In step S105, the selected synchronization signals and their received powers at the UE are received by the BS. Next, at step S106, the BS performs beam selection procedure selecting one of the M synchronization signals (and the corresponding beam) previously selected by the UE. Here let us note additionally that the beam that the BS uses to transmit the synchronization signal may not exactly match the beam that the UE uses to reduce the number of ports. In other words, beam selection occurs at the BS, but on the UE side its approximation, for example, in the direction of maximum gain can be used. The beam selection procedure performed at the BS may be carried out in any manner known in the art, including a method based on machine learning, and based on any criteria and data that the base station may be aware of. As the non-limiting example, in the single-user data transmission mode (SU-MIMO), the BS may select the strongest beam, and in multi-user data transmission mode (MU-MIMO), the BS may select a beam that will provide maximum transmit power between the BS and the UE, while causing minimal interference to other users. One of ordinary skill in the art will understand how these methods can be practiced.
Once the beam selection procedure is done, the BS transmits at step S107 to the UE at least one CSI-RS and the request to calculate the CSI at the UE side on the at least one CSI-RS received by the UE. The CSI calculation request may be signaled in the DCI. In this case, the index of the synchronization signal selected by the BS (and the corresponding beam) is additionally signaled by the bit value in the DCI field. In the non-limiting example, the CSI calculation request field in the DCI may include a reference to or direct indication of a specific SSB-RI from the indexes previously received in step S105 from the UE. Non-limiting examples of allocating specific bit values to perform such signaling are given in Table 6 below.
[Table 6]
The non-limiting examples of allocating particular bit values given in Table 6 should not be interpreted as any limitation of the present invention, since the bit values can be redefined differently, the number of options supported and signaled SSB-RIs can be expanded by using the bit values with a large number of bits (for example, bit values of three bits), etc.
At step S108 the UE receives from the BS the at least one CSI-RS and the CSI request signaled in the DCI according to the exemplary scheme shown above in Table 6. If the bit value in the DCI field of the received CSI request indicates that the UE should calculate the CSI and thereby use a particular synchronization signal to reduce the number of antenna array ports, the UE proceeds to step S109, where the UE determines, as shown in Fig. 3 in more detail, from the synchronization signal signaled by the index and the associated set of preconfigured codebook parameter values, the matrix to be used by the UE to reduce the number of BS antenna array ports in CSI calculation.
This step S109 may be performed at the UE side according to the following non-limiting implementation. The bit value in the DCI field signals a particular synchronization signal by reflecting its index (e.g., SSB-RI). As mentioned above, each specific synchronization signal transmitted by the BS at step S100 has its own associated set of preconfigured codebook parameter values, containing specific values, corresponding to a given synchronization signal, of the following parameters: , , , , and . To determine the specific values of the specified parameters, the UE accesses a predefined function or mapping table of at least the index of the synchronization signal to the predefined values of the parameters , , , , and . Said function or mapping table may be preconfigured in the same manner for both the BS and the UE. The mapping itself can be performed according to any rule that is subject to determination by the network operator and/or equipment manufacturers and inclusion in the appropriate specification. For example, for a particular synchronization signal indicated by a particular SSB-RI, the particular values of the associated set of parameter values may be selected so as to, for example, match the width (parameters , ) and direction of the beam (parameters , , and ) used to transmit the synchronization signal, and an effective beam used to reduce the number of CSI-RS ports. Additionally or alternatively, the supported complexity of the UE's receiver may be taken into account to calculate the CSI. In this case, the parameters (, ) should be selected appropriately so that the UE is able to perform the CSI calculation. Other options are possible as well.
Once the associated set of preconfigured values of codebook parameters , , , , and is determined, the UE may, according to the present non-limiting implementation, find some equivalent in the form of the matrix for reducing the number of antenna array ports, which is essentially a (coarse) precoding matrix, with the help of which it would be possible to reduce the dimension of the channel matrix obtained by the UE as the result of channel measurements (between the BS and the given UE) performed by the UE based on the at least one CSI-RS received in step S108 from the BS. The channel matrix itself can be calculated by the UE in the present invention by any method known in the art, without any limitation, therefore, a detailed description of the calculation of the channel matrix is not given here.
The PR-PMI (Port Reduction - Precoding Matrix Indicator) unit shown in Fig. 3 may be responsible for implementing this step S109 in the UE. In the actual UE implementation, the PR-PMI unit may have a software and/or hardware implementation (e.g., as a processor or a part thereof). Obtainment of the matrix for reducing the number of antenna array ports in the PR-PMI unit can be performed according to the following equation 15.
[Equation 15]
The number of column vectors (i.e., horizontal dimension) of this matrix for reducing the number of antenna array ports corresponds to the number of virtual antenna array ports for CSI once the port number is reduced, i.e. this matrix dimension actually defines to what number the BS wishes/allows the UE to reduce the channel dimension; this parameter is a parameter configured by the network operator or equipment manufacturer. The number of elements in each column vector (i.e., vertical dimension) of the matrix for reducing the number of antenna array ports corresponds to the total number of antenna array ports (for example, 256, 128, 64 according to the possible configurations in Table 3, i.e., to the original number of antenna array ports before the reduction). Moreover, by analogy with the precoding matrix , the description of which is given above with reference to the equation1, the first half of each column vector of the matrix for reducing the number of antenna array ports corresponds to the first polarization, and the second half of each column vector corresponds to the second polarization. In other words, the column vectors are strictly ordered in the matrix for reducing the number of antenna array ports in such a way that they are first specified for an antenna of one polarization from the entire reduced antenna array, and then for an antenna of a different polarization.
Like in the precoding matrix , the elements of the matrix for reducing the number of antenna array ports are ordered in a manner similar to how the corresponding elements are arranged in the applicable codebook (e.g., in type 1 codebook). Upper half of the matrix for reducing the number of antenna array ports is applied to the first polarization, and the lower half of the matrix for reducing the number of antenna array ports is applied to the second polarization. Said two halves of the matrix for reducing the number of antenna array ports are identical, i.e. the reduction in the number of ports will apply equally to both the first polarization of the antenna array and the second (orthogonal) polarization of the antenna array.
Due to the fact that indexing and of codebook vectors (for example, DFT vectors) is used according to two dimensions (horizontal and vertical), the matrix for reducing the number of antenna array ports, which will be applied in the same way to each subarray from the set of subarrays generated by reducing the number of antenna array ports, will have the structure defined according to the following equation 16.
[Equation 16]
where
- the vector for reducing the number of antenna array ports along the first dimension (in this example - horizontally);
- Kronecker product; and
- the vector for reducing the number of antenna array ports along the second dimension (in this example - vertically).
There are several possible embodiments of determining the vectors and for reducing the number of antenna array ports along the first and second dimensions, respectively. According to the first embodiment, the vectors and placed into the math. expression 16 specified above are determined according to the following equations 17 and 18.
[Equation 17]
[Equation 18]
where
- the parameter specified directly (for example, in the form of the fraction), which actually defines the angle along the first dimension (in this example - horizontally) of the precoding vector, with the help of which each subarray from the set of subarrays generated by reducing the number of antenna array ports will be virtualized,
- the parameter specified directly (for example, in the form of the fraction), which actually defines the angle along the second dimension (in this example - vertically) of the precoding vector, with the help of which each subarray from said set of subarrays will be virtualized,
is the index of the antenna port in the subarray for the first dimension, and
is the index of the antenna port in the subarray for the second dimension.
In the above described embodiment of determination of and , it is assumed that the precoding vectors defining the transmit beam of the corresponding synchronization signal for the virtualized antenna array are determined in the associated set of preconfigured parameter values by the and parameters of the precoding vector direction angles along the two dimensions. In other words, in this embodiment, PR-PMI is specified by said parameters and , and the structure of the codebook and the partitioning of the antenna array into the equivalent set of subarrays is defined by the parameters , , , .
In the other embodiment, for determining and the less explicit characteristic of the precoding vector is used, since the angles of the precoding vector along the first and second dimensions are specified in this embodiment not directly, as in the embodiment described above, but indirectly through indices (parameters) and for two dimensions, which, being substituted into the following equations 19 and 20 approximate the direction of the precoding vector along the corresponding dimensions (horizontally and vertically).
[Equation 19]
[Equation 20]
where
- sampling of the directions of the precoding vectors, determined by the number of antenna array ports along the first dimension and the oversampling factor of the precoding vectors for the first dimension,
- sampling of the directions of the precoding vectors, determined by the number of antenna array ports along the second dimension and the oversampling factor of the precoding vectors for the second dimension,
and - indices of precoding vectors along the two dimensions, approximating the direction of the transmit/receive beam of the corresponding synchronization signal,
is the index of the antenna port in the subarray for the first dimension, and
is the index of the antenna port in the subarray for the second dimension.
In this other embodiment, PR-PMI is approximated by said indices and , and the structure of the codebook and the partitioning of the antenna array into the equivalent set of subarrays is defined by the parameters , , , .
It should be understood that in the technical solution disclosed herein, the beam that the BS uses to transmit the synchronization signal and the beam that is to be used by the UE for port reduction may be completely identical beams, defined directly, or substantially identical beams (i.e., beams having essentially identical directions), one of which is obtained by approximating the other. Several options are possible: 1. the beams are the same (i.e. they have the DFT type structure and are specified directly); 2. the beams match approximately, i.e. the DFT type mathematical structure may be used for port reduction, and a mathematical structure of a different type may be used for the synchronization signals (or the DFT type mathematical structure, but with different parameters that would be obvious to one of ordinary skill in the art based on the examples above). Thus, the approximation is related to option 2, since this option can provide an approximate match in the direction of the beams, or an approximate match in the direction of the beams and the angular width at a certain level (for example, at the 3 dB level). Considering the above, it should be clear that the described equations17-18, 19-20 are given above as the non-limiting implementation examples.
Once the matrix for reducing the number of antenna array ports is determined, the UE proceeds to step S110 illustrated in Figs. 2 and 3, on which the UE obtains an equivalent channel with a reduced number of ports by applying the matrix for reducing the number of antenna array ports to the channel matrix according to the following equation 21.
[Equation 21]
where
is the equivalent channel matrix with the reduced number of antenna ports, i.e. the dimension of < the dimension of .
Thereafter, step S111 is performed, on which the UE performs CSI calculation with the search for optimal RIs/PMIs from said equivalent channel matrix . This calculation is performed according to the following equations 22, 23 being the respectively modified versions of the above equations 13, 14, which use the equivalent channel and the matrix of reduced dimensions to make the operations performed by the UE at this step S111 simpler in terms of computational complexity, because the number of PMI candidates, among which the search for the optimal PMI is carried out, and the dimensions of the matrices involved in the calculations are reduced.
[Equation 22]
[Equation 23]
where
- the precoding matrix for the reduced number of antenna ports,
- the non-limiting example of MIMO-systems-throughput-related objective function to be maximized,
- the dimensionally-reduced equivalent of the channel matrix ,
- the dimensionally-reduced precoding matrix that changes depending on the value of the RI specified by the index and on the value of the PMI (codebook) specified by the index ,
- noise and interference power (covariance matrix),
- the identity matrix, and
- the determinant of the matrix.
The division into steps S109, S110 and S111 illustrated in Fig. 2 is the logical division based on the different functions performed. This division is made only for the purpose of a more consistent and detailed description of the present invention. However, such a division into steps should not be interpreted as any limitation of the present invention, since similar functions in an actual implementation may be performed in fewer (including as a single step) or more (>3) steps.
Then, in step S112 the UE performs UL transmission to the BS of the CSI calculated over said equivalent channel with the reduced number of antenna array ports in response to the CSI request received in step S108. In step S113 the BS receives said CSI from the UE and in step S114 it reconstructs the full (complete) precoding matrix by applying said matrix for reducing the number of antenna array ports previously applied at the UE for reducing the number of antenna array ports to the precoding matrix indicated by the PMI contained in the received CSI.The matrix for reducing the number of ports of the antenna array applied at the UE is either known to the BS in advance (preconfigured), or the BS can easily derive such a matrix in the same way as the UE derives it using the above equations15-20, based on the same set of preconfigured codebook parameter values associated with the synchronization signal indicated from the BS to the UE in step S107. Therefore, reconstruction of the full precoding matrix is performed according to the following equation 24.
[Equation 24]
Once the full precoding matrix is reconstructed the BS performs in step S115 a subsequent transmission to the UE of any data and/or signals while beamforming the transmission based on said full precoding matrix. At step S116 the UE respectively receives the transmission of data and/or signals from the BS. Therefore, the present invention reduces the CSI-calculation-related computational load on the UE, but does not subsequently negatively impact the efficiency and quality of communication between the BS and the UE.
Next, let us turn to Fig. 5 schematically illustrating the non-limiting example of the beam radiation pattern applied by the BS when transmitting in this example eight synchronization signals, each of which is transmitted by its transmit/receive beam 0-7, which corresponds to the pre-configuration provided in advance in the same way for both the BS and the UE. The number of synchronization signals, as well as the shown radiation pattern (i.e., the configuration and the number of transmit/receive beams) of the synchronization signals are configurable parameters, i.e. in an actual implementation, the number of synchronization signals and the radiation pattern may differ from those shown in Fig. 5.
For each synchronization signal transmitted by the corresponding transmit/receive beam 0-7, a unique set of values of codebook parameters , , , , and is configured in advance, which is applied at the UE to determine the matrix for reducing the number of antenna array ports, obtain the equivalent channel with the reduced number of ports based on said matrix, and calculate CSI over the equivalent channel. The non-limiting example of the configuration of these parameters is shown in the following Table 7.
[Table 7]
The preconfigured set of values of codebook parameters , , , , and for each synchronization signal (e.g. SS/PBCH) emitted by the BS becomes known due to said pre-configuration of both the BS and all UEs supporting a particular communication standard, which will be served by the BS in the mobile communications network of the corresponding communication standard. Therefore, if the UE receives, at step S101, the synchronization signal 0 transmitted from the BS with the corresponding transmit beam 0, the UE will be able to determine, due to said pre-configuration, the following set of codebook parameter values: , , , , and as said preconfigured set of parameter values, and perform, in the steps S109, S110, S111 described above, CSI calculation over the equivalent channel using that particular set of values. In the other example, if the UE receives, at step S101, the synchronization signal 1 transmitted from the BS with the corresponding transmit beam 1, the UE will be able to determine, due to said pre-configuration, the following set of codebook parameter values: , , , , and as said preconfigured set of parameter values, etc.
It should be understood that the specific values of the parameters in the set in an actual implementation of the present invention may differ from the values shown in Table 7. In addition, it should be clear that there may be more than two levels of the hierarchy of transmit/receive beams, i.e. the configurations of subarrays of antenna array: see, e.g., Fig. 6 illustrating the other non-limiting example of the radiation pattern used by the BS to transmit sixteen synchronization signals, each of which is transmitted by its own transmit/receive beams 1-16, these beams being distributed in this example into four levels of the hierarchy of transmit/receive beams.
Forming patterns of beams (beamforming) of synchronization signals shown in Fig. 5 or 6 is carried out as determined by the BS. In one non-limiting example, the specific radiation pattern(s) depends on the particular implementation of the BS. In another non-limiting example, the specific radiation pattern(s) depends on the specific location of the BS in the area. In yet another non-limiting example, a particular radiation pattern(s) may be dynamically adjusted depending on current network operating conditions (e.g., but not limited to, the number of active users, etc.).
General approaches to forming radiation patterns of synchronization signals on the BS side may be as follows. Several hierarchy levels (two in the example of Fig. 5a and four in the example of Fig. 6) can be formed to serve both UEs that may be located close to the BS, and UEs that may be located at a greater distance from the BS. To serve nearby UEs, the BS typically configures beam(s) that, in terms of vertical angle (i.e., elevation angle), is(are) emitted with a large absolute deviation from the horizon, and in terms of azimuthal angle, is(are) wide in the azimuthal plane and is emitted with a lower gain, because it makes no sense to form such a beam(s) with a narrow radiation pattern and high gain. In the example of Fig. 5a, the beam that serves nearby UEs is beam 0, and in the example of Fig. 6 with a larger number of hierarchies, which can be applicable for larger cells, the beams that serve nearby UEs are beams 1, 2, 3.
Accordingly, to serve UEs that are further away from the BS, the reverse logic is typically applied, namely, to serve UEs that are farther away, the BS typically configures beam(s) that, in terms of vertical angle (i.e., elevation angle) is(are) emitted in directions that have a smaller absolute deviation from the horizon, and in terms of azimuthal angle, is(are) narrower in the azimuthal plane and emitted with a higher gain, because it makes sense to design such beam(s) with the narrow beam pattern and high gain (i.e., with higher energy concentration) given the greater distance to the possible location of the UEs. It should be clear that the total number of individual beams increases as the gain increases, because a beam with a higher gain becomes narrower in the azimuthal plane and more beams are required to cover the entire area served by the BS. In the example of Fig. 5a, the beams that serve UEs located further away are beams 1-7, and in the example of Fig. 6 with larger number of hierarchies, the beams that serve further-away UEs are beams 4-16.
Non-limiting examples of configurations of subarrays of antenna array, which are listed above in Table 7, configure the radiation pattern of eight beams 0-7 for transmitting eight synchronization signals shown in Fig. 5a. Each precoding vector for each synchronization signal has a strictly defined directionality horizontally and vertically, which is clearly demonstrated by the illustrations of Fig. 5. As noted above, the BS can control this direction by changing the values of the indices (parameters) and , which are contained for particular synchronization signals in the corresponding configurations as illustrated on the basis of the example related to Table 7 given above. Knowing the association of indices and with the corresponding synchronization signal (e.g. with SSB-RI of this signal), some equivalent, in terms of precoding vectors, of the direction of the beam with which the BS transmits the corresponding synchronization signal can be determined. In this specific example of Fig. 5a, which should not be interpreted as limiting the present invention, there are eight precoding vectors defining transmit/receive beams 0-7 in total.
Let us consider beam 0 of Fig. 5a corresponding to the configuration 1 shown in the second row of Table 7 above. This beam is wide in the azimuthal plane and narrow in the vertical plane as illustrated by Fig. 5b. The equivalent radiation pattern of the given beam 0 can be obtained using the subarray, which will be characterized by:
- the value along the first dimension (in this example, in the vertical plane), so that beam 0 is narrow in the corresponding plane, and the value along the second dimension (in this example, in the azimuthal plane), so that beam 0 is wide in the corresponding plane; the values of these parameters are defined in the second column and the second row of Table 7,
- oversampling along the first dimension and oversampling along the second dimension; the values of these parameters are defined in the third column in the second row of Table 7; thus, the first dimension is oversampled by the factor of 16 to allow granular (fine) tuning of the beam in the vertical plane, and
- the index of the precoding vector along the first dimension and the index of of the precoding vector along the second dimension, which determine the actual direction of beam 0; the values of these parameters are defined in the fourth column in the second row of Table 7.
Knowing the specific values of the above parameters associated with synchronization signal 0 transmitted by beam 0, the UE will be able, if necessary (if the L1-RSRP measurement of this synchronization signal appeared to be one of the largest or largest one, or if the BS indicated at step S107 this synchronization signal 0 transmitted by beam 0), to obtain the equivalent radiation pattern that will match with the radiation pattern used to transmit this synchronization signal 0 by the BS by substituting this set of values into the equations15-20 described above and performing subsequent CSI calculation according to equations21-23.
The above description applies in a similar manner to each synchronization signal 1-7 transmitted by the respective beams 1-7 shown in Fig. 5, but unlike beam 0 shown in Fig. 5a, each of the beams 1-7 is characterized by the different direction in the azimuthal plane (i.e. all these beams have different values of the index , see columns 4-10 in the last row of Table 7 above), but the same direction in the vertical plane (i.e. all these beams have the same value '31' of the index , see columns 4-10 in the last row of Table 7 above). In addition, each of the beams 1-7 is narrow in the azimuthal plane, so unlike beam 0 shown in Fig. 5a, the value of each beam of beams 1-7 is '4',and not '1', see second column in the last row of Table 7 above. In this case, the width of each beam of beams 1-7 in the vertical plane is similar to the width of beam 0 in the vertical plane, so the value for both each beam of beams 1-7 and beam 0 is configured equal to '2', see rows 2-3 in the second column of Table 7.
Therefore, for each synchronization signal, the parameters , , , and can be configured, and index values can be reported, so that the UE knows and can determine some equivalent of the radiation pattern used to transmit the synchronization signal of each SSB-RI. This allows the UE to essentially emulate the radiation pattern for a specific synchronization signal and use it to reduce the dimensionality of the channel matrix according to equation21 described above.
Next, with additional reference to Figs. 7 and 8 let us describe the non-limiting example of the technical implementation of constructing a synchronization signal precoding matrix, and also illustrate various examples of partitioning an antenna array into multiple subarrays that can be achieved in the given technical implementation. The BS can apply a procedure according to which the antenna array is partitioned into subarrays, and certain directivity is formed in each of the subarrays with the use of precoding vectors . Phasing vector can then be used to phase the signals from the subarrays. Application of the phasing vector provides an omni- or quasi-omni radiation pattern that co-phases the virtual ports of the subarrays into a single port without substantially changing the radiation pattern previously provided by the precoding vectors. The application of the co-phasing vector is necessary due to the need to obtain single port from all subarrays of the antenna array to transmit the synchronization signal, since the synchronization signal is single-port. The non-limiting example of applicable here implementation of how the co-phasing vector should be applied when constructing a synchronization signal precoding vector is described in detail in C. -Y. Pai, Z. Liu, Y. -Q. Zhao, Z. -M. Huang and C. -Y. Chen, "Designing Two-Dimensional Complete Complementary Codes for Omnidirectional Transmission in Massive MIMO Systems," 2022 IEEE International Symposium on Information Theory (ISIT), Espoo, Finland, 2022, pp. 2285-2290, doi: 10.1109/ISIT50566.2022.9834723. But the present invention should not be limited to the method described in this article describing generation of the co-phasing vector , because other methods for generating such a vector may be known to those of ordinary skill in the art.
In general case, the synchronization signal precoding matrix may be determined and applied at the BS according to the following equation 25.
[Equation 25]
where
and are indices of precoding vectors along two dimensions, which define the direction of the transmit/receive beam of the corresponding synchronization signal,
are precoding vectors specified by the indices are precoding vectors specified by the indices and ,
is the phasing vector providing omni- or quasi-omni radiation pattern of the synchronization signal.
At the same time, depending on what beam the BS currently needs to form to transmit one or another synchronization signal (for example, beam 0 in Fig. 5a or any of the beams 1-7 in the same figure), the BS partitions its antenna array into subarrays in an appropriate manner. Similarly, upon receipt of the corresponding synchronization signal, the UE attempts to emulate such a partitioning to reduce the number of antenna array ports in calculation of CSI. Let us note here that said partitioning is logical and represents only one of the possible options. Other beamforming techniques may be used to transmit the synchronization signal. In this case, as stated above, the UE-side partitioning will be an approximation of beams used by the BS to transmit synchronization signals. Non-limiting examples of antenna array partitioning and virtualization are shown in Figs. 7 and 8.
Fig. 8a shows the way of partitioning/virtualizing the antenna array into two subarrays, each of which covers 16 antenna elements. Each of these two subarrays is large enough both horizontally and vertically so that applying a precoding vector to them will result in a sufficiently narrow beam both horizontally and vertically. With the help of such a partition, beams like the beams 1-7 in Fig. 5a or like the beams 9-16 in Fig. 6 can be obtained. The specific direction of the beam within the subarray can be adjusted by changing the values of the indices , . In other words, the wider the beam needs to be made, the fewer the number of antenna elements the BS includes in the corresponding subarray; and vice versa, the narrower the beam needs to be made, the BS includes a larger number of antenna elements in the corresponding subarray.
Fig. 8b shows the other non-limiting example of partitioning/virtualizing the antenna array into eight subarrays. Each subarray in this example has 1 antenna element horizontally, which will give a wide lobe in the azimuthal plane, i.e. the beam will not be given any specific direction in the azimuthal plane; such a beam will correspond to the beam 0 in Fig. 5a. Moreover, each subarray in this example has 4 antenna elements vertically, which provides a sufficiently large aperture to form a sufficiently narrow beam like the beam 1 in Fig. 5a. Other non-limiting examples of antenna array partitioning/virtualization are shown in Fig. 7 and Fig. 8c.
Fig. 9 illustrates a schematic diagram of the BS 300 according to the second aspect of the present invention, which is configured to perform the method according to the first aspect of the present invention due to that it comprises at least a transceiver antenna unit 305 configured to communicate with the UE and any other devices within the coverage area of the corresponding cell; and a processor 310 operably coupled to the transceiver antenna unit 305 and configured to perform the method of the first aspect of the present invention or any possible implementation of the first aspect of the present invention. The BS may be, but is not limited to, a Transmit-Receive Point (TRP), an Access Point (AP) or a NodeB, an eNodeB, a gNodeB (gNB).
The BS 300 is shown in Fig. 9 in a relatively simplified, schematic form, so this figure does not show all the components actually contained in the BS 300, but only those through which the present invention is implemented. As is known, the BS may comprise other components not shown in Fig. 9, such as a power supply, various interfaces, I/O means, interconnects, random access and read only memory storing instructions executable by the processor 310 to carry out the method of the first aspect of the present invention or any possible implementation of the first aspect of the present invention, and an operating system, etc. The transceiver antenna unit 305 may include a transceiver and an antenna coupled to each other. The antenna can be implemented as a massive or extremely massive MIMO antenna array with a large number of antenna ports, which supports hybrid analog and digital beamforming capabilities.
The processor 310 of the BS 300 may be a central processing unit, a special purpose processor, another processing unit such as a Graphics Processing Unit (GPU), or a combination thereof. The processor 310 may be implemented as an integrated circuit, such as Field Programmable Gate Array (FPGA), Application-Specific Integrated Circuit (ASIC), System-on-Chip (SoC), etc.
Fig. 10 illustrates a schematic diagram of the UE 400 according to sixth aspect of the present invention, which is configured to implement the method according to fourth or fifth aspect of the present invention due to that it comprises at least a transceiver antenna unit 405 configured to communicate with BS and any other devices within the coverage area of the corresponding cell, and the processor 410 operatively coupled to the transceiver antenna unit 405 and configured to perform the method of the fourth or fifth aspect of the present invention or any possible implementation of these aspects of the present invention. The UE may include, but is not limited to, a mobile phone, tablet, laptop, PC, wearable electronic device (e.g. glasses, watch), AR/VR headset, Internet of Things (IoT) device, in-vehicle equipment or any other electronic device that supports mobile communications. The UE may be referred to differently, e.g. as user terminal, terminal, user device, terminal device, subscriber device and so on.
The UE 400 is shown in Fig. 10 in a relatively simplified, schematic form, so the figure does not show all of the components actually contained in the UE 400, but only those that enable the present invention to be implemented. As is known, the UE may comprise other components not shown in Fig. 10, such as a power supply, a battery, various interfaces, I/O means, interconnects, random access and read only memory storing instructions executable by the processor 410 to carry out the method of the fourth or fifth aspects of the present invention or any possible implementation of these aspects of the present invention, as well as an operating system, etc. The transceiver antenna unit 405 may include a transceiver and an antenna coupled to each other. The antenna can be implemented as a massive or extremely massive MIMO antenna array with a large number of antenna ports, which supports hybrid analog and digital beamforming capabilities.
The processor 410 of the UE 400 may be a central processing unit, a special purpose processor, another processing unit such as GPU, or a combination thereof. The processor 410 may be implemented as an integrated circuit, such as an FPGA, ASIC, SoC, etc.
Fig. 11 illustrates a schematic diagram of the communication system 500 according to eighth aspect of the present invention. The communications system 500 includes one BS 300 that is installed to serve UEs 400 in three deployed cells 1, 2, 3. The BS may correspond to the BS 300 that is described in detail above with reference to Fig. 9, and each UE 400 may correspond to the UE 400 that is described in detail with reference to Fig. 10, therefore detailed descriptions of the BS 300 and UE 400 are not repeated here. The communication system 500 may simultaneously support two active Radio Access Technologies (RATs) of, e.g., 4G LTE, 5G NR, 6G.
Specific details shown in Fig. 11 should not be considered as a limitation of the present technology, since the system 500 may have a different architecture and be characterized/illustrated differently, for example, each cell of cell 1, cell 2, cell 3 may have its own BS 300, the number of UEs 400 in the cells may differ from what is shown, cells 1, 2, 3 may be a single larger cell, the shape and space covered by the cells may differ from those shown and so on. The number of cells can be more or less than 3.
The present invention may further be implemented as a storage medium storing processor-executable instructions that, when executed by a processor of a device equipped with a transceiver antenna unit, perform a method of any aspect of the disclosed invention or any possible implementation of the corresponding aspect. The storage medium may be any non-transitory computer readable medium, media, storage area, storage device, etc., such as, but not limited to, HDD, optical medium, semiconductor medium, SSD and so on.
The technical solutions disclosed herein are methods for communicating between BS and UE, namely for requesting CSI, calculating CSI with less computational complexity for the UE, and reporting the obtained CSI to the BS to enable subsequent efficient communication between the BS and the UE.
The present invention can be used in 3GPP compliant communication networks comprising BSs and UEs supporting xMIMO antenna technology for up to 256 digital ports / 3072 antenna elements. The proposed frequency range for use of the disclosed invention is the upper portion of the mid-frequency range (9-13 GHz). The solutions of the present disclosure may be implemented with analog/digital single-beam/multi-beam beamforming and TDD (unpaired spectrum) and/or FDD duplex modes. Other applications of the technology disclosed herein will become apparent to those of ordinary skill in the art upon reading this detailed application disclosure.
At least one aspect of the disclosed technical solution may be implemented by an AI model. An AI-related function can be performed through ROM, RAM, and processor(s) (CPU, GPU, NPU). The processor(s) controls the processing of input data according to a predefined operating rule or artificial intelligence (AI) model stored in ROM and RAM. The predefined operating rule or artificial intelligence model is provided through learning. Here, "provided through learning" means that by applying a learning algorithm to a set of training data, the predefined operating rule or AI model with a desired characteristic is created. As non-limiting examples, an AI model may be created to determine, from the synchronization signal signaled by the index and its associated set of preconfigured codebook parameter values, the matrix for reducing the number of antenna array ports; and/or AI model to obtain the equivalent channel with reduced number of ports or CSI based on the matrix for reducing the number of antenna array ports or based on the set of preconfigured codebook parameter values. In this case, the set of preconfigured codebook parameter values or any other data describing the possible interaction of the UE and BS in a particular communication network and/or the current operating conditions of the communication network can be used as training data for training such an AI model. The training may be performed on the device itself (i.e., online) that uses the AI model of the embodiment and/or may be implemented through a separate server/system (i.e., offline).
The AI model may be a decision tree-based algorithm or consist of multiple neural network layers. Each layer has a plurality of weights and performs the operation of the layer through a calculation based on the result of the calculation in the previous layer and the application of a plurality of weights and other parameter values. Examples of decision tree-based algorithms include random forest, ensemble trees, etc., and examples of neural networks include, but are not limited to, Convolutional Neural Network (CNN), Deep Neural Network (DNN), Recurrent Neural Network (RNN), Restricted Boltzmann Machine (RBM), Deep Belief Network (DBN), Bidirectional Recurrent Deep Neural Network (BRDNN), Generative Adversarial Network (GAN), Transformer Networks, Deep Q Network, Large Language Models and so on.
A learning algorithm is a method of training a predetermined target device or target function based on a corresponding set of training data that causes, enables, controls, or provides an output of the target device or target function. Examples of learning algorithms include, but are not limited to, supervised learning, unsupervised learning, semi-supervised learning or reinforcement learning, and so on.
One skilled in the art will appreciate that the various illustrative logical blocks (functional blocks or modules) and steps (operations) used in the embodiments of the disclosed technical solution may be implemented by electronic hardware, computer software, or a combination thereof. Whether functions are implemented using hardware or software depends on the specific application and the overall system design requirements. One skilled in the art may employ various methods for implementing the described functions for each particular application, but such implementation should not be considered beyond the scope of the embodiments disclosed herein.
It should also be noted that the order of steps of any disclosed method is not strict because some one or more steps may be rearranged in the actual order of execution and/or combined with another one or more steps, and/or divided into a larger number of sub-steps, as discussed above.
Throughout this application, reference to an element in the singular form does not preclude the presence of multiple of such elements in the actual implementation of the invention, and, conversely, reference to an element in the plural does not exclude the presence of only one such element in the actual implementation of the invention. Any specific value or range of values stated above should not be interpreted in a limiting sense, but rather such a specific value or range of values should be considered to represent the midpoint of a larger range, up to approximately 50 % or more % on either side of the specified value or from the boundaries of the specified smaller range.
While this disclosure has been shown and described with reference to specific embodiments and examples thereof, those skilled in the art will understand that various changes in form and content may be made without departing from the spirit and scope of this disclosure as defined by the appended claims and their equivalents. In other words, the foregoing detailed description is based on specific examples and possible implementations of the present invention, but this should not be interpreted to mean that only the explicitly disclosed implementations are feasible. It is intended that any change or substitution that could be made to this disclosure by one of ordinary skill in the art without creative and/or technical contribution shall be within the scope of protection (subject to equivalents) provided by the following claims.

Claims (15)

  1. A method performed by a base station (BS) for receiving Channel State Information (CSI) calculated over a reduced number of antenna array ports, the method comprising:
    transmitting at least one synchronization signal, wherein each of the at least one synchronization signal has an associated set of preconfigured codebook parameter values, which is applied by a terminal to determine a matrix for reducing the number of antenna array ports, obtain an equivalent channel with the reduced number of ports based on said matrix, and calculate CSI over the equivalent channel,
    receiving from the terminal an index of each of one or more synchronization signals selected by the terminal from the previously transmitted at least one synchronization signal, and received power of each of the one or more synchronization signals, the one or more synchronization signals being selected by the terminal as having high received power values,
    selecting from the one or more synchronization signals indicated by the indices received from the terminal, a synchronization signal to obtain a corresponding set of preconfigured codebook parameter values,
    transmitting to the terminal at least one CSI Reference Signal (CSI-RS) and a request to calculate CSI on the at least one CSI-RS received by the terminal, wherein a bit value in the Downlink Control Information (DCI) field additionally signals an index of the selected synchronization signal,
    receiving from the terminal CSI calculated by the terminal over the equivalent channel with the reduced number of antenna array ports, wherein the equivalent channel is obtained by accessing the set of preconfigured codebook parameter values, which is associated with the synchronization signal signaled by the index of the selected synchronization signal, and defines the matrix for reducing the number of antenna array ports, and applying said matrix to a channel matrix,
    reconstructing a full precoding matrix by applying said matrix for reducing the number of antenna array ports applied previously to reduce the number of antenna array ports to a precoding matrix indicated by a Precoding Matrix Indicator (PMI) contained in the received CSI, and
    transmitting data or signals to the terminal, the transmission being subjected to beamforming based on the reconstructed full precoding matrix.
  2. The method of claim 1, wherein the at least one synchronization signal is a Synchronization Signal / Physical Broadcast Channel (SS/PBCH) block, and
    wherein each synchronization signal transmitted by the BS includes a set of preconfigured codebook parameter values containing at least one value of a number of antenna array ports along a first dimension and a number of antenna array ports along a second dimension, an oversampling factor of precoding vectors for the first dimension and an oversampling factor of precoding vectors for the second dimension, orparameters of precoding vectors, which define or approximate a transmit beam of the corresponding synchronization signal.
  3. The method of claim 1, wherein the received power of the synchronization signal measured by the terminal is Layer 1 Reference Signal Received Power (L1-RSRP), and
    wherein receiving from the terminal the index of each of the one or more synchronization signals selected by the terminal is performed through Media Access Control (MAC) layer signaling,
    in case more than one synchronization signal is selected by the terminal, the indices of these selected synchronization signals are received as an ordered list or an unordered list,
    in the case of receiving the indices of the selected synchronization signals as the ordered list:
    the indices are ordered in the list according to the measured received power values of the respective synchronization signals, said list starting with an index of that synchronization signal of the synchronization signals selected by the UE for which the received power measurement obtained at the terminal is the highest,
    wherein the bit value in the DCI field signaling the index of the synchronization signal selected by the BS specifies the ordinal number of the selected synchronization signal index in said list; or
    in the case of receiving the indices of the selected synchronization signals as the unordered list:
    the index of each selected synchronization signal is reported along with the absolute value of the received power of the corresponding synchronization signal,
    wherein the bit value in the DCI field signaling the index of the synchronization signal selected by the BS specifies the index of the selected synchronization signal in the list.
  4. The method of claim 1, wherein absence of selected synchronization signal index signaling with a bit value in the DCI field or signaling a predetermined bit value in the DCI field causes the terminal to perform CSI calculation over the entire antenna array.
  5. A base station (BS) for receiving Channel State Information (CSI) calculated over a reduced number of antenna array ports, the BS comprising:
    a transceiver; and
    at least one processor configured to:
    transmit, via the transceiver, at least one synchronization signal, wherein each of the at least one synchronization signal has an associated set of preconfigured codebook parameter values, which is applied by a terminal to determine a matrix for reducing the number of antenna array ports, obtain an equivalent channel with the reduced number of ports based on said matrix, and calculate CSI over the equivalent channel,
    receive, from the terminal via the transceiver, an index of each of one or more synchronization signals selected by the terminal from the previously transmitted at least one synchronization signal, and received power of each of the one or more synchronization signals, the one or more synchronization signals being selected by the terminal as having high received power values,
    select from the one or more synchronization signals indicated by the indices received from the terminal, a synchronization signal to obtain a corresponding set of preconfigured codebook parameter values,
    transmit, to the terminal via the transceiver, at least one CSI Reference Signal (CSI-RS) and a request to calculate CSI on the at least one CSI-RS received by the terminal, wherein a bit value in the Downlink Control Information (DCI) field additionally signals an index of the selected synchronization signal,
    receive, from the terminal via the transceiver, CSI calculated by the terminal over the equivalent channel with the reduced number of antenna array ports, wherein the equivalent channel is obtained by accessing the set of preconfigured codebook parameter values, which is associated with the synchronization signal signaled by the index of the selected synchronization signal, and defines the matrix for reducing the number of antenna array ports, and applying said matrix to a channel matrix,
    reconstruct a full precoding matrix by applying said matrix for reducing the number of antenna array ports applied previously to reduce the number of antenna array ports to a precoding matrix indicated by a Precoding Matrix Indicator (PMI) contained in the received CSI, and
    transmit data or signals, to the terminal via the transceiver, the transmission being subjected to beamforming based on the reconstructed full precoding matrix.
  6. The BS of claim 5, wherein the at least one synchronization signal is a Synchronization Signal / Physical Broadcast Channel (SS/PBCH) block, and
    wherein each synchronization signal transmitted by the BS includes a set of preconfigured codebook parameter values containing at least one value of a number of antenna array ports along a first dimension and a number of antenna array ports along a second dimension, an oversampling factor of precoding vectors for the first dimension and an oversampling factor of precoding vectors for the second dimension, orparameters of precoding vectors, which define or approximate a transmit beam of the corresponding synchronization signal.
  7. The BS of claim 5, wherein the received power of the synchronization signal measured by the terminal is Layer 1 Reference Signal Received Power (L1-RSRP), and
    wherein receiving from the terminal the index of each of the one or more synchronization signals selected by the terminal is performed through Media Access Control (MAC) layer signaling,
    in case more than one synchronization signal is selected by the terminal, the indices of these selected synchronization signals are received as an ordered list or an unordered list,
    in the case of receiving the indices of the selected synchronization signals as the ordered list:
    the indices are ordered in the list according to the measured received power values of the respective synchronization signals, said list starting with an index of that synchronization signal of the synchronization signals selected by the UE for which the received power measurement obtained at the terminal is the highest,
    wherein the bit value in the DCI field signaling the index of the synchronization signal selected by the BS specifies the ordinal number of the selected synchronization signal index in said list; or
    in the case of receiving the indices of the selected synchronization signals as the unordered list:
    the index of each selected synchronization signal is reported along with the absolute value of the received power of the corresponding synchronization signal,
    wherein the bit value in the DCI field signaling the index of the synchronization signal selected by the BS specifies the index of the selected synchronization signal in the list.
  8. The BS of claim 5, wherein absence of selected synchronization signal index signaling with a bit value in the DCI field or signaling a predetermined bit value in the DCI field causes the terminal to perform CSI calculation over the entire antenna array.
  9. A method performed by a terminal for transmitting Channel State Information (CSI) calculated over a reduced number of antenna array ports, the method comprising:
    receiving at least one synchronization signal, wherein each of the at least one synchronization signal has an associated set of preconfigured codebook parameter values, which is applied by the terminal to determine a matrix for reducing the number of antenna array ports, obtain an equivalent channel with the reduced number of ports based on said matrix, and calculate CSI over the equivalent channel,
    measuring received power of each of the at least one synchronization signal,
    selecting from the at least one synchronization signal, respectively, one or more synchronization signals for which the obtained received power measurements are the highest,
    transmitting to a Base Station (BS) an index of each of the one or more selected synchronization signals and the received power of each of the one or more selected synchronization signals,
    receiving from the BS at least one CSI Reference Signal (CSI-RS) and a request to calculate CSI on the at least one CSI-RS received by the terminal, wherein a bit value in the Downlink Control Information (DCI) field additionally signals an index of the synchronization signal selected by the BS from the synchronization signals whose indices were previously transmitted by the terminal to the BS,
    determining on the synchronization signal signaled by the index and the associated set of preconfigured codebook parameter values the matrix for reducing the number of antenna array ports,
    obtaining the equivalent channel with the reduced number of ports by applying the matrix for reducing the number of antenna array ports to a channel matrix,
    calculating the CSI over said equivalent channel,
    in response to the request to calculate CSI, transmitting to the BS the CSI calculated over the equivalent channel with the reduced number of antenna array ports, and
    receiving data or signals transmission from the BS, wherein for the transmission the beam pattern is formed on the basis of a full precoding matrix reconstructed at the BS on the basis of the transmitted CSI calculated over the equivalent channel with the reduced number of antenna array ports.
  10. The method of claim 9, wherein the at least one synchronization signal is a Synchronization Signal / Physical Broadcast Channel (SS/PBCH) blockand wherein each synchronization signal received from the BS includes a set of preconfigured codebook parameter values containing at least one value of a number of antenna array ports along a first dimension and a number of antenna array ports along a second dimension, an oversampling factor of precoding vectors for the first dimension and an oversampling factor of precoding vectors for the second dimension, or parameters of precoding vectors, which define or approximate a receive beam of the corresponding synchronization signal.
  11. The method of claim 9, wherein the measured received power of the synchronization signal is Layer 1 Reference Signal Received Power (L1-RSRP),
    wherein transmitting to the BS the index of each of the one or more selected synchronization signals is performed through Media Access Control (MAC) layer signaling,
    in case of more than one synchronization signal is selected, the indices of these selected synchronization signals are transmitted as an ordered list or an unordered list,
    in the case of transmitting the indices of the selected synchronization signals as the ordered list:
    the indices are ordered in the list according to the measured received power values of the respective synchronization signals, said list starting with an index of that synchronization signal of the selected synchronization signals for which the obtained received power measurement is the highest,
    wherein the bit value in the DCI field signaling the index of the synchronization signal selected by the BS specifies the ordinal number of the selected synchronization signal index in said list; or
    in the case of transmitting the indices of the selected synchronization signals as the unordered list:
    the index of each selected synchronization signal is reported along with the absolute value of the received power of the corresponding synchronization signal,
    wherein the bit value in the DCI field signaling the index of the synchronization signal selected by the BS specifies the index of the selected synchronization signal in said list.
  12. The method of claim 9, wherein absence of selected synchronization signal index signaling with a bit value in the DCI field or signaling a predetermined bit value in the DCI field causes the terminal to perform CSI calculation over the entire antenna array.
  13. A terminal for transmitting Channel State Information (CSI) calculated over a reduced number of antenna array ports, the terminal comprising:
    a transceiver; and
    at least one processor configured to:
    receive, via the transceiver, at least one synchronization signal, wherein each of the at least one synchronization signal has an associated set of preconfigured codebook parameter values, which is applied by the terminal to determine a matrix for reducing the number of antenna array ports, obtain an equivalent channel with the reduced number of ports based on said matrix, and calculate CSI over the equivalent channel,
    measure received power of each of the at least one synchronization signal,
    select from the at least one synchronization signal, respectively, one or more synchronization signals for which the obtained received power measurements are the highest,
    transmit, to a Base Station (BS) via the transceiver, an index of each of the one or more selected synchronization signals and the received power of each of the one or more selected synchronization signals,
    receive, from the BS via the transceiver, at least one CSI Reference Signal (CSI-RS) and a request to calculate CSI on the at least one CSI-RS received by the terminal, wherein a bit value in the Downlink Control Information (DCI) field additionally signals an index of the synchronization signal selected by the BS from the synchronization signals whose indices were previously transmitted by the terminal to the BS,
    determine on the synchronization signal signaled by the index and the associated set of preconfigured codebook parameter values the matrix for reducing the number of antenna array ports,
    obtain the equivalent channel with the reduced number of ports by applying the matrix for reducing the number of antenna array ports to a channel matrix,
    calculate the CSI over said equivalent channel,
    in response to the request to calculate CSI, transmit, to the BS via the transceiver, the CSI calculated over the equivalent channel with the reduced number of antenna array ports, and
    receive data or signals transmission, from the BS via the transceiver, wherein for the transmission the beam pattern is formed on the basis of a full precoding matrix reconstructed at the BS on the basis of the transmitted CSI calculated over the equivalent channel with the reduced number of antenna array ports.
  14. The terminal of claim 13, wherein the at least one synchronization signal is a Synchronization Signal / Physical Broadcast Channel (SS/PBCH) blockand wherein each synchronization signal received from the BS includes a set of preconfigured codebook parameter values containing at least one value of a number of antenna array ports along a first dimension and a number of antenna array ports along a second dimension, an oversampling factor of precoding vectors for the first dimension and an oversampling factor of precoding vectors for the second dimension, or parameters of precoding vectors, which define or approximate a receive beam of the corresponding synchronization signal.
  15. The terminal of claim 13, wherein the measured received power of the synchronization signal is Layer 1 Reference Signal Received Power (L1-RSRP),
    wherein transmitting to the BS the index of each of the one or more selected synchronization signals is performed through Media Access Control (MAC) layer signaling,
    in case of more than one synchronization signal is selected, the indices of these selected synchronization signals are transmitted as an ordered list or an unordered list,
    in the case of transmitting the indices of the selected synchronization signals as the ordered list:
    the indices are ordered in the list according to the measured received power values of the respective synchronization signals, said list starting with an index of that synchronization signal of the selected synchronization signals for which the obtained received power measurement is the highest,
    wherein the bit value in the DCI field signaling the index of the synchronization signal selected by the BS specifies the ordinal number of the selected synchronization signal index in said list; or
    in the case of transmitting the indices of the selected synchronization signals as the unordered list:
    the index of each selected synchronization signal is reported along with the absolute value of the received power of the corresponding synchronization signal,
    wherein the bit value in the DCI field signaling the index of the synchronization signal selected by the BS specifies the index of the selected synchronization signal in said list,
    wherein absence of selected synchronization signal index signaling with a bit value in the DCI field or signaling a predetermined bit value in the DCI field causes the terminal to perform CSI calculation over the entire antenna array.
PCT/KR2025/002940 2024-03-06 2025-03-05 Method for reporting channel state information with reduced number of ports and device implementing said method Pending WO2025188074A1 (en)

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20190182786A1 (en) * 2016-08-10 2019-06-13 Huawei Technologies Co., Ltd. Communication link acquisition and tracking in millimeter wave bands
US20210307098A1 (en) * 2018-07-31 2021-09-30 Lg Electronics Inc. Method and device for transmitting synchronization signal by means of sidelink terminal in wireless communication system
US20210368455A1 (en) * 2019-11-28 2021-11-25 Southeast University Large-scale mimo wireless transmission method for millimeter wave/terahertz networks
CN114745032A (en) * 2022-04-06 2022-07-12 东南大学 Non-cellular large-scale MIMO intelligent distributed beam selection method
CN115378767B (en) * 2021-05-21 2024-01-09 维沃移动通信有限公司 Delayed Doppler domain channel information feedback method, device and electronic equipment

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20190182786A1 (en) * 2016-08-10 2019-06-13 Huawei Technologies Co., Ltd. Communication link acquisition and tracking in millimeter wave bands
US20210307098A1 (en) * 2018-07-31 2021-09-30 Lg Electronics Inc. Method and device for transmitting synchronization signal by means of sidelink terminal in wireless communication system
US20210368455A1 (en) * 2019-11-28 2021-11-25 Southeast University Large-scale mimo wireless transmission method for millimeter wave/terahertz networks
CN115378767B (en) * 2021-05-21 2024-01-09 维沃移动通信有限公司 Delayed Doppler domain channel information feedback method, device and electronic equipment
CN114745032A (en) * 2022-04-06 2022-07-12 东南大学 Non-cellular large-scale MIMO intelligent distributed beam selection method

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