WO2022066747A1

WO2022066747A1 - Device and method for performing csi reporting for type ii port selection codebook

Info

Publication number: WO2022066747A1
Application number: PCT/US2021/051524
Authority: WO
Inventors: Nadisanka Rupasinghe; Yuki Matsumura
Original assignee: Ntt Docomo, Inc.; Docomo Innovations, Inc.
Priority date: 2020-09-22
Filing date: 2021-09-22
Publication date: 2022-03-31

Abstract

A terminal is disclosed that includes a receiver that receives beamforming information relating to one or more beamformed Channel State Information - Reference Signals (CSI-RSs), the beamforming information corresponding to Spatial Domain (SD) beam selection and Frequency Domain (FD) bases selection. The terminal also includes a processor that: considers a first port selection sampling size for the SD beam selection, considers a second port selection sampling size for the FD bases selection, selects a plurality of SD ports out of a plurality of beamformed CSI-RS ports, selects a plurality of FD ports out of the plurality of beamformed CSI-RS ports, and jointly reports SD beams and FD bases using an SD-FD basis group.

Description

DEVICE AND METHOD FOR PERFORMING CSI REPORTING FOR TYPE II PORT SELECTION CODEBOOK

TECHNICAL FIELD

[0001] One or more embodiments disclosed herein relate to a device and a method for performing CSI reporting for Type II port selection Codebook.

BACKGROUND

[0002] New Radio (NR) supports Type II channel state information (CSI) feedback for rank 1 and rank 2 (Release 15 of NR). In the Type II CSI feedback, an amplitude scaling mode is configured.

[0003] In the amplitude scaling mode, a user equipment (UE) may be configured to report a wideband (WB) amplitude with a subband (SB) amplitudes and SB phase information. In the conventional scheme, considerable fraction of the total overhead may be occupied by overhead for the SB amplitude and phase reporting. The equation below shows the SB precoder generation in NR Release 15 Type II CSI for single layer transmission.

[0004] W = W_spaceW_coeff (1)

[0005] Here, the matrix W (N_t X N_SB) captures precoding vectors for N_SB sub- bands. N_t denotes a number of available TXRU ports. W_space (N_t x 2L) consists of a 2L wideband spatial 2D-Discrete Fourier Transform (DFT) beams. The matrix captures the SB combination coefficients as represented in (1) by W_coeff. The SB amplitude and phase information needs to be reported are in W_coeff. Those SB amplitude and phase information needs to be reported are in W_coeff. As discussed, reporting this information will occupy large portion of the feedback overhead and hence it is necessary somehow compress this information.

[0006] One way to achieve this is through the frequency domain compression. Let us look at how frequency domain compression can be incorporated here. Let U = {set of selected 2D — DFT spatial beams}. Now, the u^th row of W_coeff which

captures the complex combination coefficient associated with u^th(∈ U) spatial beam can be given as,

[0007] (2)

[0008] where

i ∈ {1, ••• ,N_SB} is the combination coefficient for i^th sub-band of u^th spatial beam. Note here that, (2) captures frequency domain channel representation of the u^th spatial beam. Since the beam focuses the energy to a particular direction, intuitively it can be understood that there will be few scatterers within the channel. As a result, if we consider the frequency domain representation of the channel corresponding to u^th spatial beam, there will be few significant taps in the channel impulse response. If these significant taps can be identified properly and fed back to the gNB, frequency domain channel can be almost accurately regenerated at the gNB. This way the frequency domain compression can reduce feedback overhead associated with W_coeff by reporting the information of significant channel taps. Number of significant taps to report may differ based on the approach considered for detecting significant taps in the channel impulse response.

[0009] Further, the NR supports Type II CSI reporting for precoding downlink transmissions on a Physical Downlink Shared Channel (PDSCH). In this regard, Type II solutions focus on providing detailed CSI for the purposes of Multi-User Multiple- Input Multiple-Output (MIMO). In NR Release 15, these solutions support a maximum Rank of 2 corresponding to a maximum of 2 layers per UE (i.e., hereinafter also referred to as terminal or device). In NR Release 15, 2x2 MIMO offers two spatial streams of wirelessly transmitting and receiving data on the same channel or frequency. For this implementation, a maximum number of layers per cell is higher compared to previous releases to allow multiple UE to use 2x2 MIMO simultaneously while sharing a common Resource Block allocation. Type II reports are based upon selecting a set of beams and then specifying relative amplitudes and phases to generate a weighted combination of beams for each layer of transmission. As such, Type II Port Selection solution relies on a Base Station having some advance information to allow beamforming of the CSI Reference Signal (RS) transmissions. This advance information can originate from uplink measurements if channel reciprocity is available. Otherwise it can originate from Beam Management reports or it can use wideband reports from different Precoding Matrix Indicator (PMI) reporting solutions (i.e., a hybrid solution is when a combination of PMI reporting solutions is used).

[0010] In NR, the majority of parameters associated with PMI reporting are configured using a CodebookConfig parameter structure. This parameter structure uses the combination of codebookType and subtype to identify any relevant PMI reporting solutions. Each PMI reporting solution and the corresponding relevant parameter sets for the Type II Port Selection solution.

CITATION LIST

NON-PATENT REFERENCE

[0011]

[Non-Patent Reference 1] 3GPP RP 193133, “New WID: Further enhancements on MIMO for NR”, Dec., 2019.

[Non-Patent Reference 2] 3GPP TS 38.214, “NR; Physical layer procedures for data (Release 16)”.

SUMMARY

[0012] In general, in one aspect, embodiments disclosed herein relate to a terminal that includes a receiver that receives beamforming information relating to one or more beamformed Channel State Information - Reference Signals (CSI-RSs), the beamforming information corresponding to Spatial Domain (SD) beam selection and Frequency Domain (FD) bases selection; and a processor that: considers a first port selection sampling size for the SD beam selection, considers a second port selection sampling size for the FD bases selection, selects a plurality of SD ports out of a plurality of beamformed CSI-RS ports, selects a plurality of FD ports out of the plurality of beamformed CSI-RS ports, and jointly reports SD beams and FD bases using an SD- FD basis group.

[0013] In general, in one aspect, embodiments disclosed herein relate to terminal that includes a receiver that receives beamforming information relating to one or more beamformed Channel State Information - Reference Signals (CSI-RS s), the beamforming information corresponding to Spatial Domain (SD) beam selection and Frequency Domain (FD) bases selection; and a processor that: considers a first port selection sampling size for the SD beam selection, considers a second port selection sampling size for the FD bases selection, selects a plurality of SD ports from the first port selection sampling size out of beamformed CSI-RS ports, selects a plurality of FD ports out of the second port selection sampling size out of the beamformed CSI-RS ports, and jointly reports SD beams and FD bases.

[0014] In general, in one aspect, embodiments disclosed herein relate to a terminal that includes a receiver that receives beamforming information relating to one or more beamformed Channel State Information - Reference Signals (CSI-RS), the beamforming information corresponding to Spatial Domain (SD) beam selection and Frequency Domain (FD) bases selection; and a processor that: considers a first port selection sampling size for the SD beam selection, considers a second port selection sampling size for the FD bases selection, selects a plurality of SD ports from the first port selection sampling size out of beamformed CSI-RS ports, selects a plurality of FD ports out of the second port selection sampling size out of the beamformed CSI-RS ports, and reports non-zero LC coefficients for FD bases associated to a particular SD beam.

[0015] In general, in one aspect, embodiments disclosed herein relate to method for performing Channel State Information (CSI) reporting for type II port selection codebook that includes obtaining beamforming information relating to one or more beamformed CSI-Reference Signals (CSI-RS s), the beamforming information corresponding to SD beam selection and FD bases selection; considering a first port selection sampling size for the SD beam selection; considering a second port selection sampling size for the FD bases selection; selecting a plurality of SD ports from the first port selection sampling size out of beamformed CSI-RS ports; selecting a plurality of FD ports out of the second port selection sampling size out of the beamformed CSI-RS ports; and jointly reporting SD beams and FD bases using a SD-FD basis group.

[0016] In general, in one aspect, embodiments disclosed herein relate to a method for performing CSI reporting for type II port selection codebook. The method includes obtaining beamforming information relating to one or more beamformed Channel State Information - Reference Signals (CSI-RSs), the beamforming information corresponding to Spatial Domain (SD) beam selection and Frequency Domain (FD) bases selection. The method also includes considering a first port selection sampling size for the SD beam selection; considering a second port selection sampling size for the FD bases selection; selecting a plurality of SD ports from the first port selection sampling size out of beamformed CSI-RS ports; and selecting a plurality of FD ports out of the second port selection sampling size out of the beamformed CSI-RS ports. The method also includes jointly reporting SD beams and FD bases.

[0017] In general, in one aspect, embodiments disclosed herein relate to a method for performing CSI reporting for type II port selection codebook. The method includes obtaining beamforming information relating to one or more beamformed Channel State Information - Reference Signals (CSI-RSs), the beamforming information corresponding to Spatial Domain (SD) beam selection and Frequency Domain (FD) bases selection. The method also includes considering a first port selection sampling size for the SD beam selection; considering a second port selection sampling size for the FD bases selection; selecting a plurality of SD ports from the first port selection sampling size out of beamformed CSI-RS ports; and selecting a plurality of FD ports out of the second port selection sampling size out of the beamformed CSI-RS ports. The method also includes reporting non-zero LC coefficients for FD bases associated to a particular SD beam.

[0018] Advantageously, enhancements on CSI measurement and reporting are being discussed in the development of Release 17 of NR. One of such enhancements includes evaluating and, if needed, specifying CSI reporting for Downlink (DL) multi- Transmission Reception Points (TRP) and/or multi-panel transmission to enable more dynamic channel/interference hypotheses for non-coherent joint transmission (NCJT), targeting both Frequency Range 1 (FR1) (i.e., 410 MHz to 7,125 MHz, sub-6 GHz) and Frequency Range 2 (FR2) (i.e., 24,250 MHz to 52,600 MHz, mmWaves). Another of such enhancements includes evaluating and, if needed, specifying Type II port selection codebook enhancements (based on Rel.15/16 Type II port selection) where information related to angle(s) and delay(s) are estimated at a gNB based on Sound Reference Signal (SRS) by utilizing DL/Uplink (UL) reciprocity of angle and delay. The remaining DL CSI is reported by the UE, mainly targeting Frequency Division Duplex (FDD) FR1 to achieve better trade-off among UE complexities, performance, and reporting overhead.

[0019] In view of the above enhancements, the present invention describes that Type II port selection codebook can be further enhanced taking into consideration angle-delay reciprocity of propagation channel and using UL SRS transmission.

[0020] Other aspects of the disclosure will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 shows a diagram showing a configuration of a wireless communication system according to one or more embodiments of the present invention.

[0022] FIG. 2 shows a diagram showing a configuration of a wireless communication system according to one or more embodiments of the present invention.

[0023] FIG. 3 A shows an example in accordance with one or more embodiments.

[0024] FIG. 3B shows an example in accordance with one or more embodiments.

[0025] FIG. 4 a diagram showing a configuration of a wireless communication system according to one or more embodiments of the present invention.

[0026] FIG. 5 shows a CSI reporting example in accordance with one or more embodiments. [0027] FIG. 6 shows a CSI reporting example in accordance with one or more embodiments.

[0028] FIG. 7 shows a CSI reporting example in accordance with one or more embodiments.

[0029] FIG. 8 shows a CSI reporting example in accordance with one or more embodiments.

[0030] FIG. 9 shows a CSI reporting example in accordance with one or more embodiments.

[0031] FIG. 10 shows a block diagram of an assembly in accordance with one or more embodiments.

[0032] FIG. 11 shows a block diagram of an assembly in accordance with one or more embodiments.

DETAILED DESCRIPTION

[0033] Specific embodiments of the invention will now be described in detail with reference to the accompanying figures. Like elements in the various figures are denoted by like reference numerals for consistency.

[0034] In the following detailed description of embodiments of the invention, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to one of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.

[0035] Throughout the application, ordinal numbers (e.g., first, second, third, etc.) may be used as an adjective for an element (i.e., any noun in the application). The use of ordinal numbers is not to imply or create any particular ordering of the elements nor to limit any element to being a single element unless expressly disclosed, such as by the use of the terms “before”, “after”, “single”, and other such terminology. Rather, the use of ordinal numbers is to distinguish between the elements. By way of an example, a first element is distinct from a second element, and the first element may encompass more than one element and succeed (or precede) the second element in an ordering of elements.

[0036] A wireless communication system 100 according to one or more embodiments of the present invention will be described below with reference to FIG. 1.

[0037] As shown in FIG. 1, the wireless communication system 100 includes a User Equipment (UE) 10, a Base Station (BS) 20, and a core network 30. The wireless communication system 100 may be a New Radio (NR) system or a Long Term Evolution (LTE)/LTE- Advanced (LTE-A) system.

[0038] The BS 20 communicates with the UE 10 via multiple antenna ports using a multiple-input and multiple-output (MIMO) technology. The BS 20 may be a gNodeB (gNB) or an Evolved NodeB (eNB). The BS 20 receives downlink packets from a network equipment such as upper nodes or servers connected on the core network 30 via the access gateway apparatus, and transmits the downlink packets to the UE 10 via the multiple antenna ports. The BS 20 receives uplink packets from the UE 10 and transmits the uplink packets to the network equipment via the multiple antenna ports.

[0039] The BS 20 includes antennas for MIMO to transmit radio signals between the UE 10, a communication interface to communicate with an adjacent BS 20 (for example, X2 interface), a communication interface to communicate with the core network (for example, SI interface), and a CPU (Central Processing Unit) such as a processor or a circuit to process transmitted and received signals with the UE 10. Functions and processing of the BS 20 described below may be implemented by the processor processing or executing data and programs stored in a memory. However, the BS 20 is not limited to the hardware configuration set forth above and may include any appropriate hardware configurations. Generally, a plurality of the BSs 20 may be disposed so as to cover a broader service area of the wireless communication system 1.

[0040] The UE 10 communicates with the BS 20 using the MIMO technology. The UE 10 transmits and receives radio signals such as data signals and control signals between the BS 20 and the UE 10. The UE 10 may be a mobile station, a smartphone, a cellular phone, a tablet, a radio terminal, a mobile router, or information processing apparatus having a radio communication function such as a wearable device.

[0041] The UE 10 includes a CPU such as a processor, a RAM (Random Access Memory), a flash memory, and a radio communication device to transmit/receive radio signals to/from the BS 20 and the UE 10. For example, functions and processing of the UE 10 described below may be implemented by the CPU processing or executing data and programs stored in a memory. The UE 10 is not limited to the hardware configuration set forth above and may be configured with, e.g., a circuit to achieve the processing described below.

[0042] The wireless communication 1 supports Type II CSI feedback. As shown in FIG. 1, at step SI, the BS 20 transmits CSI-Reference Signals (RSs). When the UE 10 receives the CSI-RSs from the BS 20, the UE 10 performs measurements of the received CSI-RSs. Then, at step S2, the UE 10 performs CSI reporting to notify the BS 20 of the CSI as CSI feedback. For example, the CSI includes at least one of rank indicator (RI), precoding matrix indicator (PMI), channel quality information (CQI), CSI-RS resource indicator (CRI), a wideband (WB) amplitude, and a subband (SB) amplitude. In one or more embodiments of the present invention, the CSI reporting that reports the SB amplitude may be referred to as SB amplitude reporting. For example, rather than reporting the SB amplitude every time when the CSI reporting takes place, the periodicity of reporting the SB amplitude may be dynamically adjusted using higher layer signaling from the BS 20. The SB amplitude reporting may be performed for K leading coefficients. For example, if K is small, the number of coefficients reporting SB amplitudes is small.

[0043] If the SB amplitudes are small compared to an amplitude of the strongest coefficient, achievable gains with SB amplitude reporting may be marginal. That may occur when a user channel is highly sparse in an environment with very few scatterers, for example. [0044] Furthermore, in one or more embodiments, while Type II CSI feedback may allow layer handling up to layers with RI of 1 and 2, by altering the scheme, Type II CSI feedback may also be implemented in ranks greater than 2. As such, by extending Type II CSI feedback scheme for rank > 2, spectral efficiency can be further enhanced. Extending the Type II CSI feedback scheme to ranks greater than 2 may reduce the overhead generally associated with the scheme.

[0045] To this point and as indicated above, Type II CSI precoding vector generation for N₃ precoding matrix indicator (PMI) sub-bands (SBs) considering RI = v, layer I G {1,2, ••• v] transmission may be evaluated. For example,

[0046] W_t(N_t X N₃) = W_uW_coeffJ (3)

[0047] In the above equation, W_{1 l} (N_t X 2L) is a matrix consisting of L SD 2D- DFT basis for layer I, L is a Beam number, N_tis a Number of ports, and W_{coeff z}

(2L X A₃) is an SB complex combination coefficient matrix for layer I.

[0048] In the above equations, SD 2D-DFT basis subset may be given as ••• b_{l L}] where b_{t i} is an /-th (G {1, ••• , L}) 2D DFT basis vector corresponding to an /-th layer.

[0049] In one or more embodiments, frequency domain (FD) compression must be accounted for as information within W_{coeff b} which may be compressed. As such, corresponding overhead may be further reduced. For example, Type II CSI precoding vectors of layer / for N₃ SBs considering FD compression can be given by expanding W_{coeff, l} from rule (3).

[0051] In the above equation, W_{freq l} (N₃ X M) is a matrix consisting of M FD DFT basis vectors for layer I

X M) is a matrix consisting of complex combination coefficients for layer I. Furthermore, frequency domain DFT basis subset may be given as [f_{l 1},

basis vector

TV corresponding to the /-th layer. Additionally, M is calculated as, M = p x - - where R ∈ {1,2}. Given L and p, number of SD and FD basis subsets for layer I can be identified.

[0052] In one or more embodiments, in order to achieve a proper balance between performance and overhead, it is important to identify SD and FD bases across layers appropriately.

[0053] A wireless communication system 200 according to one or more embodiments of the present invention will be described below with reference to FIG. 2.

[0054] As shown in FIG. 2, the wireless communication system 200 includes the BS 20 that communicates with the UE 10 via multiple antenna ports using the MIMO technology. A Type II port selection codebook does not require the UE 10 to derive spatial domain (SD) beams considering 2D-DFT basis as in regular Type II codebook. In this case, the BS 20 may be a gNB that transmits a number K of beamformed (BF) CSI-RS ports as a considering set of SD beams. The UE 10 has to identify a number L (< A) of best CSI-RS ports (i.e., beams) and to report their corresponding indices within

[0055] SB-wise precoding vector generation with NR Release 16 Type II port selection codebook for layer I ∈ {1, 2, 3, 4} by further modifying (3) and (4) can be given as:

[0057] In this case, Q(N_t x K) may represent a number K of SD beams used for

CSI-RS beamforming, W^K x 2L) may represent a block diagonal matrix,

(2L X M) may represent a linear combination (LC) coefficient matrix, and Vfy _z (N ₃ X M) may be used for DFT basis vectors (i.e., FD bases).

[0058] A number of CSI-RS ports P_CSI-RS may include the number K being configured by higher layer signaling. In this case, P_CSI-RS ∈ {4, 8, 12, 16, 24, 32}.

consists of column vectors of an identity matrix. As such, the vectors correspond to any selected beams. To this point, a number of ports is selected, and these ports may include the number L being configured by higher layer signaling. In this case, L ∈ {2, 3, 4} when PCSI-RS > 4.

[0059] The SD beams within Q is selected transparent to the UE 10. Specifically, the SD beams can be determined based on sounding reference signals (SRS) or Uplink (UL) Demodulation Reference Signal (DMRS) transmission. In this case, even though UL dominant sub-space is not the same as that of downlink (DL), port selection in the DL allows the UE 10 to approximately select ports covering the DL dominant sub- space.

[0060] FIG. 3 A and FIG. 3B show reporting of W₁ based on selected beams. In some embodiments, a parameter d may be configured by the BS 20 determines a sampling granularity for port groups. In this case, a CSI report in NR may be made up of two granularities (e.g., categories). In some embodiments, d may be configured as d ∈ {1, 2, 3, 4} and d < L. In such case, the UE 10 may report i_1;1 as part of PMI to select L beams following:

[0062] For example, as shown in FIG. 3A and FIG. 3B, (6) may be used to determine available port-pairs for selection out of the beams for polarization. In FIG.

3 A, letting K = 8 and L = 2, the calculation may result in one case where d = 2 such that

In this regard, the available port-pairs for selection may be equal to {Bl, B2{ and {B3, B4{. In FIG. 3B, letting K = 8 and L = 2, the calculation may result in another case where d = 1 such that i_{1 1} = {0, 1, 2, 3}. In this regard, the available port- pairs for selection may be equal to {Bl, B2{, {B2, B3{, {B3, B4{, and {B4, Bl}.

[0063]

set as follow:

[0064] Wi = where E =

[0065] J In this case, , where ’

’

represents a vector with all zeros except 1 at I^th location.

[0066] In view of the aforementioned calculations, a Type II port selection codebook can be further enhanced by taking into consideration the port selection of both SD beams and frequency domain (FD) basis vectors

of (5). As such, in some embodiments, a general structure for SB-wise precoder generation for port selection codebook can be given by:

[0068] In this case, Q(N_t x K) may represent a number K of beamformed CSI- RS ports for SD beam selection such that b_L is i ∈ {1, 2, ... K} for an z-th SD basis vector, S(N_t x K') may represent a number K’ of beamformed CSI-RS ports for FD basis selection such that fj is j ∈ {1, 2, ... K'} for an /-th FD basis vector, W^K x 2L) may represent a block diagonal matrix where each matrix block consists of L columns of an (K X K) identity matrix. W_{f z}(K' X M) may represent a matrix consisting of columns of an (K' X K') identity matrix, and (2L X M) may represent a linear

combination (LC) coefficient matrix. Further, in this case, Q and 5 may be, for example, Q = [b₁ b₂ ... b_K] and S' = [f₁ f₂ ... f_K].

[0069] In (7), beamforming is done both in SD and FD, and FD bases for beamforming can be determined considering delay reciprocity. The BS 20 transmits (K x K’) beamformed CSI-RS ports. The selection of K SD beams and K’ FD bases is transparent to the UE. In this case, the UE selects a number 2L of SD beams (for two polarizations) and a number M of FD bases and report them back to the BS 20 as part of the PMI. Here, the

and the

may capture selected SD and FD bases. In addition, the W_z is reported along with the LC coefficients by the UE 10.

[0070] Based on the above, as shown in FIG. 4, (7) may be implemented in a communication system 400 including the UE 10 and the BS 20. In communication system 400, (1) UL SRS transmission is transmitted from the UE 10 to the BS 10. In response, the BS 20 may exchange (3) beamformed CSI-RS to the UE 10, which causes the UE 10 to report at least UL CSI including values related to W_1, , and W_{f l}. The

reporting provided by the UE 10 may be transmitted in (4) UL CSI reporting. To this point, by using reported SD beams, FD bases, and LC coefficients, the BS 20 determines the DL precoders as captured in equation (5).

[0071] Consistent with the above, FIG. 5 shows an example of UL CSI reporting. Specifically, FIG. 5 illustrates an example for performing joint reporting of selected SD beams and FD bases according to one or more embodiments. In this case joint reporting starts by considering a port selection sampling size for SD beam selection d and a port selection sampling size for FD bases selection d' . Then, selected SD ports out of a number K of beamformed CSI-RS ports and selected FD ports out of a number K' of beamformed CSI-RS ports can be reported jointly by selecting a SD-FD basis group. In the example of FIG. 5, the considerations include K = 8 and K' = 10, assuming single polarization, L = 4, d = 2, M = 2 and d' = 2.

[0072] In view of the above, when d = 2, possible SD beam groups for selection are {b₄, b₂, b₃, b₄}, {b₃, b₄, b₅, b₆}, {b₅, b₆, b₇, b₈}, and {b₇, b₈, b₁, b₂}. Further, when d' = 2, possible FD bases groups for selection are

L and

{f9,f10 For example, for reporting the SD-FD basis group including SD beams b₃, b₄, b₅, b₆ and FD bases f₇, f₈, the UE 10 reports locational parameters {x, y], where x and y indicate (implicitly or explicitly) a starting FD basis f₇ and SD beam b₃ , respectively of the SD-FD basis group. Further, in this case, the FD bases selection “Beam common” such that all SD beams may use a same FD bases.

[0073] In FIG. 5, an SD-FD grid 500 is shown including SD-FD basis groups 510, 520, 530, and 540 corresponding to the aforementioned SD beam groups for selection mapped in relation to the FD bases groups for selection. The SD-FD grid 500 captures all possible SD beams and FD bases.

[0074] In one or more embodiments, joint reporting of selected SD beams and FD bases includes configuration/selection of dimensional parameters L and M for SD- FD basis group. In the SD-FD grid 500, configuration of L and M may be performed using higher layer signaling or DCI. Possible values for a dimensional parameter L may be predefined. In this case, the NW may select the dimensional parameter L out of those using higher layer signaling or x-bit(s) in DCI. For example, when L ∈ {2, 4, 6, 8, 10, 12}, then using 3-bits in DCI the NW may select the dimensional parameter L value. In one case, possible values for a dimensional parameter M may be predefined. In this regard, the NW selects the dimensional parameter M out of those using higher layer signaling or x-bit(s) in DCI. For example, when M G {2, 4, 6, 8, 10, 12}, then using 3-bits in DCI NW selects M value. In another case, the NW configures, using higher layer signaling or DCI, values for both dimensional parameters L and M. For example, when using RRC/MAC-CE or DCI, the NW may configure L = 4 and M = 2.

[0075] The UE 10 may freely selects dimensional parameters L and M and the UE 10 may report these values to the BS 20 as part of the CSI. In this case, the NW configures either implicitly or explicitly, using higher layer signaling or DCI, upper or lower limit for the dimensional parameters L and M . For example, when using RRC/MAC-CE or DCI, the NW configures d < L and d' < M. Afterwards, the UE 10 can freely select the dimensional parameters L and M respecting the aforementioned restriction imposed by the NW. In this case, for different layers I G {1, 2, 3, 4}, different SD beams and FD bases may be selected considering beamformed CSI-RS transmission.

[0076] In one or more embodiments, a port selection sampling size for SD beam selection d and a port selection sampling size for FD bases selection d' are configured using higher layer signaling or DCI. In a one case, possible values for the port selection sampling size d may be predefined. In this case, the NW may select the port selection sampling size out of those using higher layer signaling or x-bit(s) in DCI. For example, when d ∈ {2, 4, 6, 8, 10, 12} as defined by d < L, the NW may use 3-bits in DCI to select the port selection sampling size d. In this regard, possible values for d' may be predefined. In this case, the NW may select a port selection sampling size out of those using higher layer signaling or x-bit(s) in DCI. For example, when d' ∈ {2, 4, 6, 8, 10, 12} as defined by d' < M, the NW may use 3-bits in DCI to select the d' value. In another case, only d needs to be configured and possible values for d may be predefined. The NW may select one out of those using higher layer signaling or x- bit(s) in DCI. For example, when d ∈ {1,2, 3, 4, 5, 6} as defined by d < L, the BS 20 may use 3-bits in DCI to selects the d value.

[0077] In one or more embodiments, when the port selection sampling size for SD beam selection d and the port selection sampling size for FD bases selection d' are not configured, the UE 10 may select SD-FD the basis group anywhere in the grid described in reference to FIG. 5. In this regard, when reporting selected SD-FD basis group, the UE 10 may report locational parameters {x, y} explicitly. Dimensional parameters L and M may be configured/selected following any of the embodiments described above. In this regard, the UE 10 may assume a pre-determined value for d and d' if they are not configured. For example, the UE 10 may assume that the d =1 and d’=l (without precluding other values) if these values are not configured.

[0078] In one or more embodiments, the UE 10 reports locational parameters {x, y} associated with starting FD basis {x} and starting SD beam {y}, respectively. Based on the configured values for d and K, a set of feasible values to select for x may be determined as discussed in Release 15 and Release 16 port selection codebook of the 3 GPP standard. The UE 10 may report one value out of selected. For example, based on d and K when x ∈ {0, 1], the UE may report x using 1 -bit. In some embodiments, based on the configured d' and K' , a set of feasible values to select for y may be determined as discussed in Release 15 and Release 16 of the 3GPP standard. The UE 10 may report one value out of selected. For example, based on d' and K' when y ∈ {0, 1], the UE may report y using 1-bit.

[0079] In one or more embodiments, the UE 10 directly reports FD basis and SD beam associated with x and y. For example in FIG. 5, the UE 10 may report FD basis f₇ and SD beam b₃ directly.

[0080] In one or more embodiments, for x, the values may be predefined or pre- determined, or configured through higher layers. Based on the value of x, the UE 10 may identify an associated predetermined value and the UE 10 may report this value to the BS 20. Similarly, for y, the values may be predefined or pre-determined, or configured through higher layers. Based on the value of y, the UE 10 may identify an associated predetermined value and the UE 10 may report this value to the BS 20.

[0081] FIG. 6 shows an example of UL CSI reporting. Specifically, FIG. 6 illustrates an example for performing joint reporting of selected SD beams and FD bases according to one or more embodiments. In this case, the UE 10 selects FD bases for each SD beam separately. As such, the FD bases selection is “Beam specific”. The reported SD-FD basis group by the UE 10 may capture an union of the FD bases associated with all the SD beams. In this example, considerations include K = 8 and K' = 10, assuming single polarization, L = 4, and M = 2. As shown in FIG. 6, the SD-FD basis group 630 is reported by the UE 10 is bounded by dimensional parameters L and |M|. In this regard, the considered SD-FD basis group which consists of SD beams b₂, b₃, b₄, and b₅. In FIG. 6, FD bases associated with each SD beam are mapped to blocks shaded following patterns 610, 620, 630, and 640 of an SD-FD grid 600. In the SD-FD grid 600, b₂ is mapped to f₄ and f₆, and shaded with pattern 610, b₃ is mapped to f₅ and f₆, and shaded with pattern 620, b₄ is mapped to f₃ and f₇, and shaded with pattern 630, and b₅ is mapped to f₇ and f₈, and shaded with pattern 640. The reported SD-FD basis group consists of FD bases set M = {f₃, f₄, f₅, f₆, f₇, f_s], In FIG. 6, for reporting the starting point of the SD-FD basis group, the UE 10 reports locational parameters {x, y] in which x and y indicate starting FD basis f₃ and SD beam b₂, respectively.

[0082] FIG. 7 shows an example of UL CSI reporting. Specifically, FIG. 7 illustrates an example for performing joint reporting of selected SD beams and FD bases according to one or more embodiments. In FIG. 7, the SD-FD grid 600 is reduced to include only the SD-FD basis group (delimited by the dotted line). To report SD beam specific FD bases from the SD-FD grid 600, the UE 10 uses a smaller size 2D bitmap of size L X |M|. In this example, the reporting overhead of this 2D bitmap may be reduced using compression techniques such as combinatorial signaling or Huffman coding. The 2D bitmap in FIG. 7 is based on the selected SD-FD basis group in FIG. 6. As FD bases are SD beam specific, the 2D bitmap in FIG. 7 selects FD bases associated with each SD beam uniquely from the selected SD-FD basis group. In some embodiments, when reporting LC coefficients in W_{i ;} a matrix of size L X |M| (considering a single polarization) may be considered. In this case, the UE 10 may report non-zero LC coefficients only for FD basis vectors associated with a particular SD beam in the reduced bitmap. For instance, in the previous example, a first row of W_z consists of 2 non-zero LC coefficients at 2^nd and 4^th locations.

[0083] In one or more embodiments, port selection sampling size for SD beam selection d may be configured by the NW. In some embodiments, SD beam group selection adheres to a configured d. For example, when d = 2, possible SD beam groups for selection are {b₁, b₂, b₃, b₄}, {b₃, b₄, b₅, b₆}, {b₅, b₆, b₇, b₈}, and

{b₇, b₈, b_n b₂}. In this case, port selection sampling size for FD bases selection d' may be configured by the NW. In some embodiments, FD bases selection within SD-FD basis group adheres to a configured d' .

[0084] In one or more embodiments, configuration/selection of L for SD-FD basis group may include configuring the number L using higher layer signaling or DCI. In one case, possible values for L may be predefined and the NW may select one of the values using higher layer signaling or x-bit(s) in DCI. For example, when L ∈ {2, 4, 6, 8, 10, 12], the NW selects the L value using 3-bits in DCI. In another case, the UE 10 freely selects L and reports the L value to the BS 20 as part of the CSI.

[0085] In one or more embodiments, in one case, configuration/selection of |M| for SD-FD basis group includes configuring the number |M| uses higher layer signaling or DCI. In another case, the UE 10 freely selects |M| and reports this value to the BS 20 as part of the CSI.

[0086] FIG. 8 shows an example of UL CSI reporting. Specifically, FIG. 8 illustrates a number of SD beams to select L and a port selection sampling size for SD beam selection d as configured by the NW. In this case, SD beam reporting may follow Release 16 of the 3GG standard to control SD beam selection approach. In the example of FIG. 8, selected FD bases reporting, starting position of FD bases group and the length M are considered for reporting f3,f₄,f₃,f₆ as defined by M = 4 and a starting position of f₃. In this example, M may be configured using higher layer using DCI. Then, reporting only starting position of FD bases group is sufficient. In some embodiments, M may be freely selected by the UE 10 and reported by the UE 10 to the NW as part of CSI.

[0087] FIG. 9 shows an example of UL CSI reporting. Specifically, FIG. 9 illustrates amplitude and phase quantized LC coefficients associated with selected SD- FD pairs, as reported to the NW by UE 20. In this case, a bitmap may be reported to inform the NW about the locations of non-zero LC coefficients. Afterwards, quantized versions of associated non-zero LC coefficients may be reported. For example, considering L = 2 and M = 2, along with rank = 1 and dual polarization, there are 2LM LC coefficients. In this case, out of the 2LM LC coefficients, only 4 are being reported. Then, the bitmap and the associated LC coefficients can be given following the format c^, as shown in FIG. 9, where LC coefficient associated with a b-th SD beam and a / -th FD basis in a /-th layer. In one or more embodiments, without reporting the bitmap in FIG. 9, the UE 10 may directly report quantized LC coefficients. This is mostly appropriate when each SD is associated with a single FD basis vector. Further, different quantization schemes may be considered for LC coefficient quantization. In one regard, same amplitude and phase quantization may be considered in the maimer that Type II port selection codebook is described by Release 16 of the 3 GPP standard. In another regard, different quantization schemes may be considered for LC coefficient quantization such that 16-PSK or higher may be considered for phase quantization.

[0088] The BS 20 according to one or more embodiments of the present invention will be described below with reference to the FIG. 10.

[0089] As shown in FIG. 10, the BS 20 may include an antenna 201 for 3D MIMO, an amplifier 202, a transmitter/receiver circuit 203 (hereinafter referred as including a CSI-RS scheduler), a baseband signal processor 204 (hereinafter referred as including a CS-RS generator), a call processor 205, and a transmission path interface

206. The transmitter/receiver 202 includes a transmitter and a receiver.

[0090] The antenna 201 may comprise a multi-dimensional antenna that includes multiple antenna elements such as a 2D antenna (planar antenna) or a 3D antenna such as antennas arranged in a cylindrical shape or antennas arranged in a cube. The antenna 201 includes antenna ports having one or more antenna elements. The beam transmitted from each of the antenna ports is controlled to perform 3D MIMO communication with the UE 10.

[0091] The antenna 201 allows the number of antenna elements to be easily increased compared with linear array antenna. MIMO transmission using a large number of antenna elements is expected to further improve system performance. For example, with the 3D beamforming, high beamforming gain is also expected according to an increase in the number of antennas. Furthermore, MIMO transmission is also advantageous in terms of interference reduction, for example, by null point control of beams, and effects such as interference rejection among users in multi-user MIMO can be expected.

[0092] The amplifier 202 generates input signals to the antenna 201 and performs reception processing of output signals from the antenna 201.

[0093] The transmitter included in the transmitter/receiver circuit 203 transmits data signals (e.g., reference signals and precoded data signals) via the antenna 201 to the UE 10. The transmitter transmits CSI-RS resource information that indicates a state of the determined CSI-RS resources (e.g., subframe configuration ID and mapping information) to the UE 20 via higher layer signaling or lower layer signaling. The transmitter transmits the CSI-RS allocated to the determined CSI-RS resources to the UE 10.

[0094] The receiver included in the transmitter/receiver circuit 203 receives data signals (i.e., reference signals and the CSI feedback information) via the antenna 201 from the UE 10. [0095] The CSI-RS scheduler 203 determines CSI-RS resources allocated to the CSI-RS. For example, the CSI-RS scheduler 203 determines a CSI-RS subframe that includes the CSI-RS in subframes. The CSI-RS scheduler 203 determines at least an RE that is mapped to the CSI-RS.

[0096] The CSI-RS generator 204 generates CSI-RS for estimating the downlink channel states. The CSI-RS generator 204 may generate reference signals defined by the LTE standard, dedicated reference signal (DRS) and Cell-specific Reference Signal (CRS), synchronized signals such as Primary synchronization signal (PSS) and Secondary synchronization signal (SSS), and newly defined signals in addition to CSI- RS.

[0097] The call processor 205 determines a precoder applied to the downlink data signals and the downlink reference signals. The precoder is called a precoding vector or more generally a precoding matrix. The call processor 205 determines the precoding vector (precoding matrix) of the downlink based on the CSI indicating the estimated downlink channel states and the decoded CSI feedback information inputted.

[0098] The transmission path interface 206 multiplexes CSI-RS on REs based on the determined CSI-RS resources by the CSI-RS scheduler 203.

[0099] The transmitted reference signals may be Cell-specific or UE-specific. For example, the reference signals may be multiplexed on the signal such as PDSCH, and the reference signal may be precoded. Here, by notifying a transmission rank of reference signals to the UE 10, estimation for the channel states may be realized at the suitable rank according to the channel states.

[00100] The BS 20 further, in one or more embodiments, comprising hardware configured for reducing feedback overhead associated with bitmap reporting between a user equipment and a base station. For example, the BS 20 may include the capabilities described above for reducing feedback overhead when communicating with the UE 10.

[00101] The UE 10 according to one or more embodiments of the present invention will be described below with reference to the FIG. 11. [00102] As shown in FIG. 11, the UE 10 may comprise a UE antenna 101 used for communicating with the BS 20, an amplifier 102, a transmitter/receiver circuit 103, a controller 104, the controller including a CSI feedback controller and a codeword generator, and a CSI-RS controller. The transmitter/receiver circuit 103 includes a transmitter and a receiver 1031.

[00103] The transmitter included in the transmitter/receiver circuit 103 transmits data signals (for example, reference signals and the CSI feedback information) via the UE antenna 101 to the BS 20.

[00104] The receiver included in the transmitter/receiver circuit 103 receives data signals (for example, reference signals such as CSI-RS) via the UE antenna 101 from the BS 20.

[00105] The amplifier 102 separates a PDCCH signal from a signal received from the BS 20.

[00106] The controller 104 estimates downlink channel states based on the CSI- RS transmitted from the BS 20, and then outputs a CSI feedback controller.

[00107] The CSI feedback controller generates the CSI feedback information based on the estimated downlink channel states using the reference signals for estimating downlink channel states. The CSI feedback controller outputs the generated CSI feedback information to the transmitter, and then the transmitter transmits the CSI feedback information to the BS 20. The CSI feedback information may include at least one of Rank Indicator (RI), PMI, CQI, BI and the like.

[00108] The CSI-RS controller determines whether the specific user equipment is the user equipment itself based on the CSI-RS resource information when CSI-RS is transmitted from the BS 20. When the CSI-RS controller 16 determines that the specific user equipment is the user equipment itself, the transmitter that CSI feedback based on the CSI-RS to the BS 20.

[00109] The UE 10 further, in one or more embodiments, comprising hardware configured for reducing feedback overhead associated with bitmap reporting between a user equipment and a base station. For example, the UE 10 may include the capabilities described above for reducing feedback overhead when communicating with the BS 20.

[00110] The above examples and modified examples may be combined with each other, and various features of these examples can be combined with each other in various combinations. The invention is not limited to the specific combinations disclosed herein.

[00111] Although the disclosure has been described with respect to only a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that various other embodiments may be devised without departing from the scope of the present invention. Accordingly, the scope of the invention should be limited only by the attached claims.

Claims

CLAIMS What is claimed is:

1. A terminal comprising : a receiver that receives beamforming information relating to one or more beamformed Channel State Information - Reference Signals (CSI-RSs), the beamforming information corresponding to Spatial Domain (SD) beam selection and Frequency Domain (FD) bases selection; and a processor that: considers a first port selection sampling size for the SD beam selection, considers a second port selection sampling size for the FD bases selection, selects a plurality of SD ports out of a plurality of beamformed CSI-RS ports, selects a plurality of FD ports out of the plurality of beamformed CSI-RS ports, and jointly reports SD beams and FD bases using an SD-FD basis group.

2. The terminal according to claim 1, wherein the processor further: configures a plurality of dimensional parameters associated to the SD-FD basis group.

3. The terminal according to claim 1, wherein the processor further: configures the first port selection size and configures the second port selection size, and wherein the first port selection size and the second port selection size are obtained using higher layer signaling.

4. The terminal according to claim 1, wherein the processor further: reports a first dimensional parameter associated with a starting FD basis of the SD-FD basis group, and

24 reports a second dimensional parameter associated with a starting SD beam of the SD-FD basis group. terminal according to claim 1, wherein the SD-FD basis group captures a union of FD bases associated with all SD beams when the FD selection is SD beam specific. terminal according to claim 5, wherein the processor further: considers separate bitmap(s) to select FD bases associated with each SD beam. terminal according to claim 5, wherein the processor further: reports selected FD bases for each SD beam within the selected SD-FD basis group using information relating to a linear combination coefficient matrix. terminal according to claim 1, wherein the SD-FD basis group is different for different layers. terminal according to claim 1, wherein the SD-FD basis group is the same for different layers. terminal according to claim 1, wherein the processor further: quantizes and reports LC coefficients for a Type II port selection codebook. rminal, comprising: a receiver that receives beamforming information relating to one or more beamformed Channel State Information - Reference Signals (CSI-RSs), the beamforming information corresponding to Spatial Domain (SD) beam selection and Frequency Domain (FD) bases selection; and a processor that: considers a first port selection sampling size for the SD beam selection, considers a second port selection sampling size for the FD bases selection, selects a plurality of SD ports from the first port selection sampling size out of beamformed CSI-RS ports, selects a plurality of FD ports out of the second port selection sampling size out of the beamformed CSI-RS ports, and jointly reports SD beams and FD bases. A terminal, comprising: a receiver that receives beamforming information relating to one or more beamformed Channel State Information - Reference Signals (CSI-RS), the beamforming information corresponding to Spatial Domain (SD) beam selection and Frequency Domain (FD) bases selection; and a processor that: considers a first port selection sampling size for the SD beam selection, considers a second port selection sampling size for the FD bases selection, selects a plurality of SD ports from the first port selection sampling size out of beamformed CSI-RS ports, selects a plurality of FD ports out of the second port selection sampling size out of the beamformed CSI-RS ports, and reports non-zero LC coefficients for FD bases associated to a particular SD beam. A method for performing Channel State Information (CSI) reporting for type II port selection codebook, the method comprising: obtaining beamforming information relating to one or more beamformed CSI- Reference Signals (CSI-RS s), the beamforming information corresponding to SD beam selection and FD bases selection; considering a first port selection sampling size for the SD beam selection; considering a second port selection sampling size for the FD bases selection; selecting a plurality of SD ports from the first port selection sampling size out of beamformed CSI-RS ports; selecting a plurality of FD ports out of the second port selection sampling size out of the beamformed CSI-RS ports; and jointly reporting SD beams and FD bases using a SD-FD basis group. method according to claim 12, further comprising: configuring a plurality of dimensional parameters associated to the SD-FD basis group. method according to claim 12, further comprising: configuring the first port selection size; configuring the second port selection size; and wherein the first port selection size and the second port selection size are obtained using higher layer signaling. method according to claim 12, further comprising: reporting a first dimensional parameter associated with a starting FD basis of the SD-FD basis group, and reporting a second dimensional parameter associated with a starting SD beam of the SD-FD basis group. method according to claim 12, further comprising: wherein the SD-FD basis group captures a union of FD bases associated with all SD beams when the FD selection is SD beam specific. method according to claim 16, further comprising: considering separate bitmap(s) to select FD bases associated with each SD beam. method according to claim 16, further comprising: reporting selected FD bases for each SD beam within the selected SD-FD basis group using information relating to a linear combination coefficient matrix. method according to claim 12, further comprising: wherein the SD-FD basis group is different for different layers. method according to claim 12, further comprising: wherein the SD-FD basis group is the same for different layers. method according to claim 12, further comprising: quantizing and reporting LC coefficients for a Type II port selection codebook.