Method and apparatus for reducing feedback overhead

Abstract

Embodiments herein relate to a method performed by a radio network node (700) for reducing feedback overhead, a radio network node (700), a method performed by a UE (500), and a UE (500). The method performed by the UE (500) comprises at least: (401) decomposing each term corresponding to the (i, j)th combined coefficient of a precoder matrix into at least two coefficients; (402) quantizing each of the at least two coefficients individually with at least one bit; and (403) reporting information related to at least one phase value or at least one amplitude value or at least one phase value and amplitude value of the quantized coefficient.

Description

Technical Field

[0001] The present disclosure relates to the field of wireless communications, and in particular, to methods and apparatus for reducing feedback overhead (eg, CSI feedback) by using efficient amplitude and phase quantization and reporting of coefficients in communication networks. Background Art

[0002] Beamforming is a very important part of the 3rd Generation Partnership Project (3GPP) Release (Rel.) 15 that defines the New Radio (NR) access technology, which enables the radio base station (also denoted herein as gNB) and the user equipment (UE) to establish and adapt the communication link using spatially precoded pilot signals. Important information in 5G to improve the communication link and efficiently adapt the beamforming technology is the feedback on the channel state information or CSI feedback report reported by the gNB and / or UE.

[0003] In Rel.-15 Type II CSI reporting, it is assumed that two-stage precoding is performed on a per-subband basis in the frequency domain, i.e., a single precoder is calculated for a group of adjacent physical resource blocks (PRBs) called a 'subband'. The Rel.-15 Type II two-stage precoder comprises two components: a first-stage precoder denoted as F1, which is the same for all subbands and which contains selected entries / beams selected from a discrete Fourier transform-based codebook (DFT-based codebook); and a second-stage precoder denoted as F2, which contains subband-dependent beam combining coefficients for all subbands.

[0004] The feedback overhead for reporting beam-combining coefficients increases roughly linearly with the number of subbands and becomes quite large for a large number of subbands. In order to overcome the high feedback overhead of Rel.-15 Type II CSI reporting, it was decided in the 3GPP Radio Access Network (RAN) standardization meeting 3GPP RAN#81 [1] to study feedback compression schemes for the second stage precoder F2. In several papers [2] to [7], it has been demonstrated that the number of beam-combining coefficients in F2 can be greatly reduced when F2 is transformed into the delay domain using a small set of DFT or discrete cosine transform (DCT) basis vectors.

[0005] Rel.-15 dual-level precoding and CSI reporting:

[0006] Assuming rank R transmission and a dual-polarized antenna array with configuration (N1, N2, 2) at the gNB, the Rel.-15 two-stage precoder disclosed in [8] for the s-th subband and r-th transmission layer is given by

[0007]

[0008]

[0009] The precoder matrix F (r) (s) has 2N1N2 rows corresponding to the number of ports, and S columns for reported subbands / PRBs. is a wideband first-stage precoder with 2L spatial beams for two polarizations that are the same for all S subbands, and F A is a diagonal matrix containing 2L broadband amplitudes associated with the 2L spatial beams, and is a second-stage precoder containing 2L subband (subband amplitude and phase) complex frequency-domain combining coefficients associated with the 2L spatial beams for the sth subband.

[0010] According to [8], the broadband amplitude matrix F A and The reporting and quantization of the subband combining coefficients in are quantized and reported as follows:

[0011] Matrix F A Quantification and reporting of broadband amplitude

[0012] - The wideband amplitude corresponding to the strongest beam having an amplitude value of 1 is not reported. The wideband amplitude values ​​associated with the remaining 2L-1 beams are reported by quantizing each amplitude value with 3 bits.

[0013] Subband Precoder Quantification and reporting of amplitude and phase values:

[0014] - The amplitude and phase values ​​of the coefficients associated with the first pilot beam are not reported (they are assumed to be equal to 1 and 0).

[0015] - For each subband, the amplitudes of the B coefficients associated with the first B-1 pilot beams (other than the first pilot beam) are represented by 1 bit - Quantification.

[0016] - The amplitude values ​​of the remaining 2L-B beams are not reported (they are assumed to be equal to 1).

[0017] - For each subband, the phase values ​​of the B-1 coefficients associated with the first B-1 pilot beams (other than the first pilot beam) are quantized with 3 bits.

[0018] - The phase values ​​of the remaining 2L-B beams are quantized with 2 bits.

[0019] The number of leading beams for which subband amplitudes are reported is given by B=4, 4 or 6 when the total number of configured spatial beams L=2, 3 or 4, respectively.

[0020] Spatial Delay Precoder:

[0021] For the matrix F (r)All S sub - band collecting precoders F (r) (s), we obtain [2, 3, 7]

[0022]

[0023] Next, the second - stage precoder can be written as:

[0024] whose u - th row contains the complex combination coefficients associated with the u - th beam on the S sub - bands,

[0025]

[0026] By considering the transformation on the sub - band precoder the total precoder can be written as

[0027]

[0028] where the matrix contains the complex combination coefficients, and the matrix is composed of many elementary vectors used to perform compression in the frequency domain. Generally, when V < S, there is compression in the combination coefficients in (3). Each complex coefficient in is associated with a specific delay (in the transformed domain) because each DFT / DCT elementary vector can be modeled as a linear - phase increase on the sub - bands.

[0029] At the transmission layer, the number of spatial beams and the indices of the spatial beams can be different, the same, partially the same, or not all the same.

[0030] In addition, regarding the spatial beams, the delays on the beams can be partially the same or not all the same. Due to different spatial - beam configurations on the layer, the delay configurations can also vary on the layer. Therefore, multiple configurations of delays and delay configurations are possible. However, the spatial beams and delay configurations of the spatial - delay precoder should be aligned with the physical structure of the radio channel. The radio channel includes many clusters of scatterers associated with corresponding delays (see Figure 1 channel cluster #1, delay #1, ……, channel cluster #3, delay #2 in

[0031] In Figure 1In the example of FIG. 1 , each transmission spatial beam of the gNB (in the example, beam #1, beam #2, beam #3, and beam #4) is associated with a single or a few channel clusters with corresponding delays. Beam #1 is associated with cluster #1 and delay #1. Beam #2 and beam #3 are associated with direct line-of-sight (LOS) channel components and with cluster #3 and delay #3. Beam #4 is associated with cluster #2 and delay #2. As shown, the delays of cluster #1 and cluster #2 are different and longer than the delay of cluster #3 (which is closer to the UE).

[0032] In order to capture most of the energy of the radio channel at the UE, the spatial DFT / DCT beams of the first stage precoder need to be pointed in the direction of the channel clusters. In a typical channel setting, the clusters are evenly distributed around the gNB and each transmit spatial beam is associated with a single or a few adjacent clusters. Furthermore, due to the even distribution of the channel clusters, each cluster is associated with a different delay. The number of clusters with which each spatial beam is associated depends mainly on the beamwidth (which is related to the aperture size of the antenna array at the gNB). The larger the beamwidth (i.e., the smaller the aperture size of the antenna array), the more channel clusters are associated with the spatial beam. Therefore, the delay configuration of each spatial beam (the number of delays per beam and the value of the delays) depends on the channel cluster with which the spatial beam is associated.

[0033] For the transformed precoder, each spatial beam is associated with a single delay or a set of small delays. The transmit beam is therefore "delayed" by a specific delay before transmission. The delays need to be chosen in such a way that all 2L beams are coherently combined at the UE. Note again that each delay is represented by an entry of a DFT / DCT vector that models a linear phase increase over the subband.

[0034] The selection of delays for the spatial beams is therefore identical to the selection of the DFT / DCT vectors. Due to the delay profile of the channel cluster, it will be appreciated that the delays associated with one spatial beam may be different from the delays associated with another spatial beam. Similarly, the delay configuration (number of delays and delay values) may be different for different beams. Different delay configurations are discussed in detail in applicant's documents [2], [3], [7]. Note that at the time of filing this application, document [7] had not yet been published, and therefore [7] should not be considered prior art to the subject matter and teachings of the claims of this application.

[0035] When different DFT / DCT vectors are used per spatial beam, a matrix containing all selected DFT / DCT vectors for all configured spatial beams can be used to form a common matrix for transform. The common transform matrix contains all selected DFT / DCT vectors for all beams. When the matrix is ​​used for transform, the combined coefficients associated with one beam contain only a few non-zero coefficients for the DFT / DCT vector with which it is associated, and are zero otherwise. Therefore, the matrix in (3) The complex combination coefficients in can contain a large number of values ​​close to zero.

[0036] 3GPP Draft; R-1812242, 3rd Generation Partnership Project (3GPP), Mobile Competence Center; 650, ROUTESDES LUCIOLES; F-06921 SOPHIA-ANTIPOLIS CEDEX; France, RAN WG1, Spokane, USA, November 2018, discloses discussion on CSI enhancement in Re-16.

[0037] 3GPP Draft; R-1812242, 3rd Generation Partnership Project (3GPP), Mobility Competence Center; 650, ROUTESDES LUCIOLES; F-06921 SOPHIA-ANTIPOLIS CEDEX; France, RAN WG1, Spokane, China, November 2018, Public Discussion on Type II CSI Overhead Reduction. Summary of the invention

[0038] The aim of the embodiments herein is to provide a method and apparatus in the form of a user equipment (UE) and a radio base station or network node or gNB, respectively, for reducing (CSI) feedback overhead by using efficient amplitude and phase quantization and reporting of coefficients in a communication network using beamforming and / or MIMO operation. In addition, the present embodiments address the problem of how to efficiently quantize and report the combined coefficients of the transform.

[0039] According to aspects of the embodiments herein, there is provided a method performed by a UE for reducing CSI-related feedback overhead in a communication network using MIMO operation:

[0040] - will correspond to the precoder matrix decomposing each term of the (i, j)th combining coefficient of into at least two coefficients, wherein r represents the rth transmission layer; the (i, j)th combining coefficient is associated with the i-th beam and the j-th delay, and wherein each combining coefficient is associated with amplitude and phase information;

[0041] - individually quantizing each of the at least two coefficients using at least one bit, and

[0042] - reporting information about at least one phase value or at least one amplitude value or at least one phase value and amplitude value of said quantized coefficients.

[0043] According to another aspect of the embodiments herein, there is provided an apparatus in the form of a UE for reducing feedback overhead in a communication network, the UE comprising a processor and a memory containing instructions executable by the processor, whereby the UE is operable to perform any one of the subject matters of method claims 1 to 22.

[0044] There is also provided a computer program comprising instructions which, when executed on at least one processor of a UE according to claim 23, cause at least the one processor to perform the method according to any one of claims 1 to 22.

[0045] A carrier embodying the computer program, wherein the carrier is one of a computer-readable storage medium, an electronic signal, an optical signal or a radio signal.

[0046] There is also provided a method performed by a radio network node gNB for reducing feedback overhead related to channel state information CSI in a communication network using multiple-input multiple-output MIMO operation, the method comprising: receiving from a UE a report comprising information related to at least one phase value or at least one amplitude value or at least one phase value and amplitude value of each quantized coefficient quantized by the UE with at least one bit;

[0047] which corresponds to the precoder matrix Each term of the (i, j)th combining coefficient is decomposed by the UE into at least two coefficients, where r represents the rth transmission layer; the (i, j)th combining coefficient is associated with the i-th beam and the j-th delay, and each combining coefficient is associated with amplitude and phase information.

[0048] According to another aspect of the embodiments herein, there is also provided a radio network node or gNB for reducing feedback overhead in a communication network, the radio network node comprising a processor and a memory, the memory containing instructions executable by the processor, whereby the radio network node is operable to perform the subject matter of any one of claims 24-33.

[0049] There is also provided a computer program comprising instructions which, when executed on at least one processor of a radio network node according to claim 34, cause at least the one processor to perform a method according to any one of claims 24-33.

[0050] Also provided is a carrier embodying the computer program, wherein the carrier is one of a computer-readable storage medium, an electronic signal, an optical signal or a radio signal.

[0051] Several advantages of the embodiments herein are set forth in the detailed section of the disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Examples of embodiments and advantages of embodiments herein are described in more detail with reference to the accompanying drawings, in which:

[0053] Figure 1 Depicted is an example network scenario in which embodiments herein may be used.

[0054] Figure 2 The diagram is in the matrix Amplitude distribution of the combination coefficients in .

[0055] Figure 3 Figure 2 shows the coefficient b for Scheme 3 according to the embodiments herein. i,j Amplitude distribution.

[0056] Figure 4 A flowchart illustrating a method performed by a UE according to some exemplary embodiments herein.

[0057] Figure 5 is a block diagram depicting a UE according to exemplary embodiments herein.

[0058] Figure 6 is a block diagram depicting a radio network node according to exemplary embodiments herein. DETAILED DESCRIPTION

[0059] In the following, a detailed description of exemplary embodiments in several contexts is presented in conjunction with the drawings to enable easier understanding of the solutions described herein.

[0060] As previously described, in the 3GPP New Radio system, two types of codebooks, ie, Type 1 and Type 2 codebooks, have been standardized for CSI feedback supporting advanced MIMO operations.

[0061] The present embodiment addresses the problem of how to efficiently quantize and report transformed combining coefficients in order to reduce CSI feedback additions in communication networks using beamforming.

[0062] A. matrix Quantification and reporting of complex combination coefficients

[0063] The previously proposed and repeated formula in equation (3) is The overall precoder can be written as follows

[0064]

[0065] (3) Each complex coefficient in is associated with a specific delay (in the transformed domain) because each DFT / DCT basis vector can model a linear phase increase over that subband. Contains complex combining coefficients. The values ​​of N1 and N2 are design parameters and may be included in the configuration of the antenna array at the gNB, which may be, for example, dual-polarized, but the embodiments herein are not limited to dual-polarized antenna arrays.

[0066] According to an exemplary embodiment, The method for obtaining the amplitude and phase values ​​of the coefficients in is to directly quantize each amplitude and phase value using N1 and N2 bits respectively.

[0067] For example, suppose the matrix Contains UD coefficients, then UD(N1+N2) bits are required for reporting to the gNB However, as mentioned previously, each of the U beams is typically associated with only one set of delays and not all D delays. Therefore, the matrix can be viewed as a sparse matrix, where a large number of the coefficients are close to zero.

[0068] In the following description, the matrix in equation (3) The complex combining coefficients may contain the complex combining coefficients associated with all (2L) spatial beams (i.e., U=2L), or only a subset of the spatial beams (e.g., U<2L), and / or all (V) delays / basis vectors (i.e., D=V), or only a subset of the delays / basis vectors (i.e., D <V)。

[0069] 1. Selection and reporting of non-zero coefficients by using bitmaps

[0070] To save for reporting The method according to the exemplary embodiment is to only feed back the quantized version of the feedback overhead of The bitmap indicates the index of the reported coefficient. For example, the first bit in the bitmap may be associated with the first coefficient and the second bit with the matrix , etc. When a bit in the bitmap is set to '1', the corresponding coefficient (amplitude and / or phase) may be reported, and otherwise, not reported. In the manner described, the overhead for reporting combined coefficients may be greatly reduced; however, the number of feedback bits is not fixed and may vary for each reporting instance (see below for how the number of feedback bits may be fixed).

[0071] 2. Selection and reporting of the K strongest coefficients

[0072] To fix the number of feedback bits used to report the combining coefficients, the receiver can be configured as a feedback matrix The amplitude and / or phase values ​​of the K strongest coefficients of the gNB are given by When a bit in the bitmap is set to '1', the UE may be configured to report the associated coefficient b to the gNB. i,j The bitmap may therefore contain no more than K "1's".

[0073] To increase flexibility in selecting coefficients and improve system performance, a receiver (e.g., a UE or another gNB) may be configured to select the matrix K for each row / beam in u The strongest coefficients, where parameter K u It can be configured by gNB (transmitter). Note that for the matrix The set of rows / beams, K u The values ​​of can be the same. In this case, a single parameter R can be used to configure the multipole parameter K d .

[0074] Similarly, the receiver can be configured to select the matrix Each column / delay in K d The strongest coefficients, where parameter K d It can be configured by gNB. Note that for the matrix The set of columns / delays, K d The values ​​of can also be the same. In this case, a single parameter 0 is used to configure multiple parameters K d .

[0075] 3. For reporting Selection of submatrices

[0076] According to an exemplary embodiment, in order to reduce the time required for reporting The receiver can be configured to only report the coefficients in Amplitude and / or phase information of a subset of the coefficients in . The subset of coefficients in may contain the combined coefficients associated with the "strongest" beam and / or the "strongest" delay. In that case, it may be assumed that The rows and / or columns of are ordered in such a way that the combination coefficients satisfy the following:

[0077]

[0078] and / or

[0079]

[0080] In an example, the receiver may be configured to report the amplitude and / or phase information of the coefficients associated with the U' "strongest" beams. The receiver may then report the amplitude and / or phase information of the coefficients:

[0081] In another example, the receiver may be configured to report the amplitude and / or phase information of the coefficients associated with the D "strongest" delays. The receiver may report the amplitude and / or phase information of the coefficients:

[0082] In another example, the receiver may be configured to report the amplitude and / or phase information of the coefficients associated with the U' "strongest" beams and the D "strongest" delays. The receiver may report the amplitude and / or phase information of the coefficients:

[0083] In order to further significantly reduce the time required for reporting A quantized version of the feedback overhead is described in accordance with some embodiments herein for Three decomposition and quantification schemes:

[0084] 1. Solution 1

[0085] The first approach associates the matrix associated with the i-th beam and the j-th delay The (i,j)th combination coefficient is decomposed into two coefficients di and b i,j ,

[0086]

[0087] where b i,j is the complex-valued normalized combining coefficient associated with the i-th beam and the j-th delay, and a i is a real-valued coefficient representing the common amplitude of the combined coefficients of all delays associated with the i-th beam. Note that the value a i The calculation of is implementation specific.

[0088] 2. Solution 2

[0089] The second approach associates the matrix associated with the i-th beam and the j-th delay The (i,j)th combination coefficient is decomposed into two coefficients d j and b i,j ,

[0090]

[0091] where b i,jis the complex-valued normalized combining coefficient associated with the i-th beam and the j-th delay, and d j is a real-valued coefficient representing the common amplitude of the combining coefficients of all beams associated with the jth delay. Note that the value d j The calculation of is implementation specific.

[0092] 3. Solution 3

[0093] A third approach associates the matrix associated with the i-th beam and the j-th delay The (i,j)th combination coefficient is decomposed into three coefficients a j and b i,j ,

[0094]

[0095] where b i,j is the complex-valued normalized combining coefficient associated with the i-th beam and the j-th delay, d j is a real-valued coefficient representing the common amplitude of the combined coefficients of all beams associated with the jth delay, and a i is a real-valued coefficient representing the common amplitude of the combined coefficients of all delays associated with the i-th beam. Note that the value a i and d j The calculation of is implementation specific.

[0096] The receiver can be configured to represent the The combination coefficients in , or only a set of the combination coefficients. Note that the proposed schemes can also be combined for representing the combination coefficients. For example, the receiver can be configured to represent by scheme 1 or scheme 2 The first set of combination coefficients of is represented by Scheme 3 A second set of combination coefficients of .

[0097] 4. Coefficient a i 、b i,j and d j Quantification

[0098] In the Each term is decomposed into coefficient a i and b i,j or j and b i,j or a i d j and b i,j After that, the coefficients are quantized separately according to the embodiment. The main advantage of the above decomposition scheme is that b i,j The amplitude value can be compared The amplitude values ​​of the combined coefficients in are quantized with significantly lower number of bits. Therefore, when one of the proposed decomposition schemes is applied, the number of bits used to report The feedback overhead of the amplitude value of the term in .

[0099] For example, the receiver can be configured to use N a (and / or N d ) digits equally quantize the real-valued coefficients a i (and / or j ). For amplitude and phase, each complex-valued coefficient b i,j Available N b,1 and N b,2 quantized by one digit, where N b,1 Can be lower than N b,2 .

[0100] Feedback cost savings for solution 1:

[0101] For solution 1, assume that there is a matrix There are UD combination coefficients in it, and a total of UN a +UD(N b,1 +N b,2 ) The first digit is used to report the coefficient a i and b i,j In contrast, when each amplitude is expressed as N a The units digit and each phase are represented by N a One-bit direct quantization matrix 2UDN is required for a The units digit is used for reporting The coefficient of b,2 =N a The units are equally quantized b i,j The phase value of the feedback saved by scheme 1 can be calculated by U(D(N a -N b,1 )-N a ) bits are given. For U=8、D=4、N a =4 and N b,1 = 2 beam (U), delay (D) and quantization bit (N a ) is a typical value of the number of Compared to direct quantization of the terms in , a total of 32 bits can be saved for amplitude and phase reporting.

[0102] Feedback cost savings for solution 2:

[0103] For scenario 2, again assume that there is a matrix There are UD combination coefficients in the d +UD(N b,1 +N b,2 ) The first digit is used to report the coefficient d j and bi,j The amplitude and phase information of b,2 =N d The units are equally quantized b i,j The phase value of the feedback saved by Scheme 2 is D(U(N d -N b,1 )-N d ) bits are given. For U=8、D=4、N d =4 and N b,1 = 2 beam (U), delay (D) and quantization bit (N d ) is a typical value of the number of Compared to direct quantization of the terms in , a total of 48 bits can be saved for amplitude and phase reporting.

[0104] Feedback cost savings for solution 3:

[0105] For scenario 3, again assume that there is a matrix There are UD combination coefficients in it, and a total of UN a +DN d +UD(N b,1 +N b,2 ) The first digit is used to report the coefficient a i d j and b i,j The amplitude and phase information of a =N d The units digits quantize the real-valued coefficients a equally i and d j And use N b,2 =N a Quantization of the units i,j The phase value of the feedback saved by Scheme 3 is given by UD(N a -N b,1 )-(U+D)N a The ones digit is given. For U = 8, D = 4, N a =4 and N b1 = 1 beam (U), delay (D) and quantization bit (N a ) is a typical value of the number of Compared to direct quantization of the terms in , a total of 48 bits can be saved for reporting amplitude and phase information.

[0106] 5. By using the bitmap for the non-zero coefficients b i，j Selection and reporting

[0107] To reduce the number of reports The UE can be configured to report the quantized non-zero coefficients b i,j To indicate the quantized non-zero coefficient bi,j In addition to the amplitude and / or phase information, the receiver can also be configured to report a bitmap, where each bit in the bitmap corresponds to the coefficient b i,j For example, the first bit can be associated with the coefficient b 1,1 The second digit can be associated with the coefficient b 1,2 When a bit in the bitmap is set to one, the UE may report the associated coefficient b to the gNB. i,j The bitmap may thus contain P "1's", where P corresponds to non-zero coefficients b i,j The number of.

[0108] 6.K strongest coefficients b i,j Selection and reporting

[0109] To reduce the number of reports To reduce the overhead of the coefficients in and to fix the number of feedback bits used for CSI reporting, the UE can be configured to report the matrix only phase values, only amplitude values, or both amplitude and phase values ​​of the K strongest coefficients, where the value of parameter K is configurable by the gNB.

[0110] The K strongest coefficients can be obtained from To indicate the index of the K strongest coefficients, in addition to the K amplitude and / or phase information, the receiver can be configured to report a bitmap, where each bit in the bitmap corresponds to the coefficient b. i,j For example, the first bit can be associated with the coefficient b 1,1 The second digit is related to the coefficient b 1,2 When a bit in the bitmap is set to one, the UE may report the associated coefficient b to the gNB. i,j The phase and / or amplitude values ​​of the bitmap may thus contain K "1s". In the quantized matrix When the number of non-zero amplitude values ​​of is less than K, the UE may only report the quantized matrix The bitmap may then contain less than K "1's".

[0111] The amount of feedback required to report amplitude and phase information is determined by The amplitude and phase information of the UN a +DN d +K(N b,1 +N b,2 ) bits and UD bits for the bitmap (for Scheme 3). Therefore, Compared with the case where the amplitude and phase information of all coefficients in the b,1 +N b,2)-UD units digit.

[0112] To increase the flexibility of the selection coefficients and improve system performance, the receiver can be configured to select the matrix K for each row / beam in u The strongest coefficients, where parameter K u It can be configured by gNB. Note that for the matrix The set of rows / beams, K u The values ​​of can be the same. In this case, a single parameter R can be used to configure the multipole parameter K d .

[0113] Similarly, the receiver can be configured to select the matrix Each column / delay in K d The strongest coefficients, where parameter K d It can be configured by gNB. Note that for the matrix The set of columns / delays, K d The values ​​of can also be the same. In this case, a single parameter 0 is used to configure multiple parameters K d .

[0114] 7. Reporting of only phase information and 1-bit amplitude quantization of matrix B without bitmap indication

[0115] Figure 2 and Figure 3 The matrix is ​​shown when the proposed third decomposition scheme is applied according to the previously described embodiment. The amplitude distribution and coefficient b of the combination coefficient in i,j Amplitude distribution.

[0116] As shown, when the proposed third decomposition scheme is applied, with the matrix In contrast, the coefficient b i,j can be efficiently represented by only two quantization levels. i,j The amplitude information of can therefore be quantized using only one bit for the amplitude value. The receiver can therefore be configured with N b,1 =1, and each amplitude value can be represented by two quantization levels "a" and "b", where for example "a" and / or "b" are given by "a=0" and "b=1". The bits in the bitmap then directly correspond to the coefficients b i,j The amplitude value of the two quantization levels, and does not require b i,j The amplitude value is additionally reported. b,1 = 1, the amount of feedback used to report phase values ​​is also greatly reduced, because there is no need to report phase values ​​associated with zero amplitude coefficients. The same quantization level can also be used in scheme 1 and scheme 2 to quantize coefficients b i,j .

[0117] Note that the above also applies to Scheme 1 and Scheme 2, i.e., the receiver can be configured with N b,1 =1, each amplitude value can be represented by two quantization levels "a" and "b", where, for example, "a" and / or "b" are given by "a=0" and "b=1".

[0118] 8. For b i ， j Different quantization levels of the phase value

[0119] In order to further reduce the reported coefficient b i,j The receiver can be configured to use the phase information overhead of coefficient b i,j Different quantization levels are applied to the phase values ​​of N′. b,2 The bits are used for the phase values ​​associated with the non-zero coefficients and the U' strongest beams, and N" b,2 bits are used for the phase values ​​associated with the non-zero coefficients and the remaining beams, where N′ b,2 >N″ b,2 .

[0120] B. Report of the index associated with the selected DFT / DCT vector:

[0121] In addition to the matrix In addition to the reporting of the quantized coefficients of the matrix, the following also describes the method for efficiently reporting and matrices according to the exemplary embodiments of the present invention. A method for indexing a DFT / DCT vector associated with a complex combination of coefficients of a DFT / DCT basis vector. The DFT / DCT vector is selected from a set of predetermined DFT / DCT basis vectors, where each DFT / DCT basis vector is associated with an index. For example, when there are S DFT / DCT basis vectors, the first DFT / DCT basis vector is associated with a first index ("1"), the second DFT / DCT basis vector is associated with a second index ("1"), and the last DFT / DCT basis vector is associated with an index ("S"). When D selected DFT / DCT basis vectors are reported, D[log2(S)] feedback bits are required.

[0122] Instead of directly reporting the indices of the DFT / DCT basis vectors, the receiver may be configured to report a bitmap, where each bit in the bitmap is associated with an index "d" from a set of basis vectors.

[0123] For example, the first bit may be associated with index 1, the second bit may be associated with index 2, etc. A "1" in the bitmap at position "d" then indicates selection of the DFT / DCT vector associated with index "d".

[0124] As an example, when the number of subbands S=13 and D=6, the amount of feedback needed to report the index of the selected DFT / DCT vector is given by D[log2(S)]=24, where in contrast, only S=13 bits are needed when using a bitmap.

[0125] According to an embodiment, when the reported bitmap includes a "1" at position "1", then the amplitude and phase values ​​of the pilot beam must be considered as follows:

[0126] A "1" at position 1 of the bitmap indicates that the amplitude and phase of the combining coefficients of the preamble beam associated with index "1" are given by 1 and 0, respectively, and are not reported. The amplitude and phase values ​​of the remaining combining coefficients of the preamble beams associated with other indices are given by 0 and 0, respectively, and are not reported. The amplitude and phase associated with the preamble beam are known at the gNB.

[0127] As described at the outset, the proposed solution is suitable for the 3GPP Rel-15 framework. The following proposes modifications (1) to (7) to the Rel. 15 framework according to some embodiments herein, which are proposed herein by the inventors.

[0128] (1) Response to gNB report b i,j The number of leading beams (B) of amplitude values ​​for the proposed CSI report using DFT / DCT transform is given by B=2L or 2L-1, instead of B=4, 4 and 6 for L=2, 3 and 4 as in the current Rel.15, where L is the number of configured spatial beams.

[0129] (2) b associated with the first leading beam i,j All quantized amplitude and phase values ​​are not reported to the gNB.

[0130] (3) When N a =3, used to quantify a i The amplitude set of is given by

[0131]

[0132] (4) When N d =3, used to quantify d j The amplitude set is given as unity

[0133]

[0134] (5) When N d =2, used to quantify d j The amplitude set of is given by

[0135]

[0136] (6) for b i,j The quantized amplitude set of is given as {0,1}.

[0137] (7) used to quantify b i,j The phase set is given by the 8PSK or 16PSK constellation.

[0138] It should be mentioned that, unlike equation (3) above, we can introduce the U×S matrix in the following The new transform / decomposition of , which can be combined with the three decomposition / quantization schemes mentioned above. Compared with equation (3), the following transform / decomposition further reduces the overhead of reporting the combined coefficients when combined with the three decomposition / quantization schemes mentioned above. Decomposed into three matrices,

[0139]

[0140] in

[0141] -A (r) It contains the matrix A real-valued U×U diagonal matrix of U “broadband” amplitude coefficients for the individual rows / beams of

[0142] - is a complex-valued U×S matrix containing US “subband” combining coefficients for U beams and S subbands, and

[0143] -B (r) is a real-valued S×S diagonal matrix with S values ​​on its diagonal.

[0144] Matrix A (r) Contains matrix The value of the "average" amplitude of the row / beam of the combination coefficients. (r) is the matrix that forces the association with the leading beam The S combination coefficients in the rows of A are normalized to "1". Note that the leading beam is consistent with the matrix A. (r) By now considering the subband coefficient matrix The frequency domain combination coefficients can be transformed Written as:

[0145]

[0146] in in Contains the matrix The V basic vectors in are associated with 2L×V complex combination coefficients (see equation (3)), and C (r) is a V×V diagonal matrix containing the “common” amplitude values ​​of the V basis vectors.

[0147] Quantification and reporting were as described previously.

[0148] For B (r) For reporting, the receiver (or, for example, UE) may be configured to use each coefficient N B The units digit reports or does not report the diagonal matrix B (r) When the receiver is configured not to report S coefficients, the transmitter (e.g., gNB) assumes that when reconstructing the precoder matrix, the matrix B (r) is given by the identity matrix. Note that the matrix B (r) The coefficients in can be represented by only two quantization levels "a" and "b", where, for example, "a" and / or "b" are represented by and "b=1" are given.

[0149] It should be mentioned that all parameters and represented values ​​may take any suitable values, and some or all are design parameters that, when used, achieve the technical effects and advantages of the embodiments described in this disclosure.

[0150] See also Figure 4 , illustrating a flow chart of a method performed by a UE 500 for reducing CSI-related feedback overhead in a communication network using MIMO operation, the method comprising:

[0151] -(401) will correspond to the precoder matrix Each term of the (i, j)th combining coefficient of is decomposed into at least two coefficients, where r represents the rth transmission layer; the (i, j)th combining coefficient is associated with the i-th beam and the j-th delay, and each combining coefficient is associated with amplitude and phase information;

[0152] -(402) individually quantizing each of the at least two coefficients using at least one bit, and

[0153] -(403) reporting information related to at least one phase value or at least one amplitude value or at least one phase value and amplitude value of the quantized coefficient.

[0154] A method performed by a UE according to some embodiments herein is presented in the subject matter of claims 1 to 22 .

[0155] In order to perform the previously described procedures or method steps related to the UE, the embodiments herein include a UE for reducing feedback overhead in a communication network. Figure 5, UE 500 includes a processor 510 or processing circuit or processing module or processor or means 510; a receiver circuit or receiver module 540; a transmitter circuit or transmitter module 550; a memory module 520; a transceiver circuit or transceiver module 530, which may include the transmitter circuit 550 and the receiver circuit 540. UE 500 further includes an antenna system 560, which includes antenna circuitry for transmitting signals to and receiving signals from at least a radio network node or gNB. The antenna system may use beamforming, as previously described.

[0156] UE 500 may operate in any radio access technology that supports beamforming technology, including 2G, 3G, 4G or LTE, LTE-A, 5G, WLAN, and WiMax, among others.

[0157] The processing module or / circuitry 510 includes a processor, a microprocessor, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), etc., and may be referred to as a "processor 510". The processor 510 controls the operation of the network node 500 and its components. The memory (circuitry or module) 520 includes a random access memory (RAM), a read-only memory (ROM), and / or another type of memory to store data and instructions that can be used by the processor 510. In general, it should be understood that the UE 500 in one or more embodiments includes a fixed or programmed circuit system that is configured to perform operations in any of the embodiments disclosed herein.

[0158] In at least one such example, UE 500 includes a microprocessor, microcontroller, DSP, ASIC, FPGA, or other processing circuitry configured to execute instructions from a computer program stored in a non-transitory computer-readable medium in or accessible to the processing circuitry. Here, "non-transitory" does not necessarily mean permanent or unchanging storage, and may include storage in working or volatile memory, but the term does mean at least some persistent storage. Execution of the program instructions specifically adapts or configures the processing circuitry to perform the operations disclosed herein, including any of method claims 1 to 22. Additionally, it should be appreciated that UE 500 may include Figure 5 Additional components not shown.

[0159] As previously mentioned, UE 500 is operative to: Each term of the (i, j)th combining coefficient of is decomposed into at least two coefficients, where r represents the rth transmission layer; the (i, j)th combining coefficient is associated with the i-th beam and the j-th delay, and each combining coefficient is associated with amplitude and phase information; each of the at least two coefficients is quantized separately with at least one bit; and information related to at least one phase value or at least one amplitude value or at least one phase value and amplitude value of the quantized coefficient is reported.

[0160] The UE is configured to use a first scheme to associate the matrix associated with the i-th beam and the j-th delay The (i, j)th combination coefficient is decomposed into two coefficients a i and b i,j ,

[0161]

[0162] where b i,j is the complex-valued normalized combining coefficient associated with the i-th beam and the j-th delay, and a i is a real-valued coefficient representing the common amplitude of the combining coefficients of all delays associated with the i-th beam.

[0163] The UE (500) is configured to associate the matrix associated with the i-th beam and the j-th delay using the second scheme The (i,j)th combination coefficient is decomposed into two coefficients d j and b i,j ,

[0164]

[0165] where b i,j is the complex-valued normalized combining coefficient associated with the i-th beam and the j-th delay, and d j is a real-valued coefficient representing the common amplitude of the combining coefficients of all beams associated with the jth delay.

[0166] The UE (500) is configured to associate the matrix associated with the i-th beam and the j-th delay using the third scheme The (i,j)th combination coefficient is decomposed into three coefficients a j d j and b i,j ,

[0167]

[0168] where b i,j is the complex-valued normalized combining coefficient associated with the i-th beam and the j-th delay, d jis a real-valued coefficient representing the common amplitude of the combining coefficients of all beams associated with the jth delay, and a i is a real-valued coefficient representing the common amplitude of the combining coefficients of all delays associated with the i-th beam.

[0169] The UE (500) is configured to indicate through the first scheme, the second scheme or the third scheme The combination coefficients or only one set of the combination coefficients in .

[0170] Additional details regarding functionality or actions performed by the UE have been disclosed (see method steps performed by the UE).

[0171] There is also provided a computer program comprising instructions which, when executed on at least one processor 510 of a UE 500 according to claim 23, cause the processor 510 to perform the method according to any one of claims 1 to 22.

[0172] A method performed by a radio base station or a radio network node or a gNB 700 according to some exemplary embodiments is also provided.

[0173] A method for reducing CSI-related feedback overhead in a communication network using MIMO operation includes:

[0174] (601) receiving a report from UE 500 including information about at least one phase value or at least one amplitude value or at least one phase value and amplitude value of each quantized coefficient quantized by UE 500 with at least one bit; wherein the corresponding precoder matrix Each term of the (i, j)th combining coefficient is decomposed by the UE (500) into at least two coefficients, where r represents the rth transmission layer; the (i, j)th combining coefficient is associated with the i-th beam and the j-th delay, and each combining coefficient is associated with amplitude and phase information.

[0175] The method includes configuring the UE to feedback the matrix The amplitude and / or phase values ​​of the K strongest coefficients, where the value of K can be configured by the radio network node (700) or the gNB.

[0176] The method includes configuring the UE to Each row / beam in selects K u The strongest coefficients, where parameter K u Can be configured by the radio base station or gNB.

[0177] The method includes configuring the UE to Each column / delay in selects K dThe strongest coefficients, where parameter K d Can be configured by a radio base station (700) or gNB.

[0178] The method comprises configuring the UE to A subset of the coefficients in reports only the amplitude and / or phase information.

[0179] The method includes configuring the UE to indicate by the first solution of claim 2, the second solution of claim 3 or the third solution of claim 4 or just one set of said combination coefficients.

[0180] The method includes configuring the UE to use N a (and / or N d ) digits equally quantize the real-valued coefficients a i (and / or j ), where a i is a real-valued coefficient representing the common amplitude of the combining coefficients for all delays associated with the i-th beam.

[0181] The method comprises configuring the UE to report the quantized non-zero coefficients b i,j The phase-only value, amplitude-only value, or amplitude-and-phase value of the

[0182] The method includes configuring the UE to report a bitmap, wherein each bit in the bitmap is associated with an index "d" from a set of DFT / DCT basis vectors.

[0183] Additional functions performed by the radio network node 700 have already been disclosed and need not be repeated.

[0184] In order to perform the previously described procedures or method steps in relation to a radio network node, some embodiments herein include a radio network node 700 for reducing feedback overhead in a communication network.

[0185] like Figure 6 , the radio network node 700 includes a processor 710 or processing circuit or processing module or processor or means 710; a receiver circuit or receiver module 740; a transmitter circuit or transmitter module 770; a memory module 720; a transceiver circuit or transceiver module 730, which may include the transmitter circuit 770 and the receiver circuit 740. The radio network node 700 further includes an antenna system 760, which includes antenna circuitry for transmitting and receiving signals to and from at least the network node and other UEs, etc. The antenna system uses beamforming, as previously described.

[0186] The radio network node 700 may operate in any radio access technology that supports beamforming technology, including 2G, 3G, 4G or LTE, LTE-A, 5G, WLAN, and WiMax, among others.

[0187] The processing module or / circuitry 710 includes a processor, a microprocessor, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), etc., and may be referred to as a "processor 710". The processor 710 controls the operation of the UE 700 and its components. The memory (circuitry or module) 720 includes a random access memory (RAM), a read-only memory (ROM), and / or another type of memory to store data and instructions that can be used by the processor 710. In general, it should be understood that the radio network node 700 in one or more embodiments includes a fixed or programmed circuit system that is configured to perform operations in any of the embodiments disclosed herein.

[0188] In at least one of the described examples, the radio network node 700 includes a microprocessor, microcontroller, DSP, ASIC, FPGA or other processing circuitry configured to execute instructions from a computer program stored in a non-transitory computer-readable medium in or accessible to the processing circuitry. Here, "non-transitory" does not necessarily mean permanent or unchanging storage, and may include storage in working or volatile memory, but the term does mean at least some persistent storage. Execution of the program instructions specifically adapts or configures the processing circuitry to perform the operations disclosed herein, including at least the features of independent method claim 24. In addition, it should be appreciated that the radio network node 700 may include Figure 6 Additional components not shown.

[0189] In order to reduce feedback overhead related to channel state information (CSI) in a communication network using multiple-input multiple-output (MIMO) operation, the gNB is operable to perform any of the subject matters of method claims 24 to 33.

[0190] The additional functions performed by the radio network node 700 have already been disclosed and need not be repeated again.

[0191] There is also provided a computer program comprising instructions which, when executed on at least one processor 710 of a radio network node 700 according to claim 34, cause at least the one processor 710 to perform the method according to at least claims 24 to 33.

[0192] There is also provided a carrier containing the computer program, wherein the carrier is one of a computer-readable storage medium, an electronic signal, an optical signal or a radio signal.

[0193] As is apparent from the detailed description presented above, several advantages are achieved by the disclosed embodiments.

[0194] Throughout this disclosure, the words "comprise" or "comprising" have been used in a non-limiting sense, i.e., meaning "consisting at least of..." Although specific terms may be used herein, they are used only in a generic and descriptive sense and not for purposes of limitation. The embodiments herein may be applied to any wireless system in which beamforming technology may be used, including GSM, 3G or WCDMA, LTE or 4G, LTE-A (or Advanced LTE), 5G, WiMAX, WiFi, satellite communications, TV broadcasting, etc.

[0195] References

[0196] [1] Samsung, “Revised WID: Enhancements for MIMO for NR,” RP-182067, 3GPP RAN #81, Gold Coast, Australia, September 10-13, 2018.

[0197] [2] Fraunhofer IIS, Fraunhofer HHI, “Enhancements to the Type II CSI Reporting Scheme,” R1-1806124, Busan, South Korea, May 21–25, 2018.

[0198] [3] Fraunhofer IIS, Fraunhofer HHI, “Enhancements to Type II CSI Reports,” R1-1811088, Chengdu, China, October 8–12, 2018.

[0199] [4] Fraunhofer IIS, Fraunhofer HHI, “Spatial Delay-Paired Subband Precoding for Millimeter-Wave Channels,” R1-1800597, Vancouver, Canada, January 22–26, 2018.

[0200] [5] Ericsson, “CSI Enhancements for MU-MIMO Support,” R1-1811193, Chengdu, China, October 8-12, 2018.

[0201] [6] Huawei, HiSilicon, “Discussion on CSI Enhancement for MU-MIMO,” R1-1810103, Chengdu, China, October 8-12, 2018.

[0202] [7] Fraunhofer IIS, Fraunhofer HHI, “Enhancements to the Type II CSI Reporting Scheme,” R1-1813130, Spokane, USA, November 12–16, 2018.

[0203] [8] 3GPP TS 38.214 V15.3.0, “3GPP; TSG RAN; NR; Physical layer procedures for data (Release 15)”, September 2018.

[0204] [9] Nokia, Nokia Shanghai Bell, “CSI feedback overhead reduction for MU-MIMO enhancements,” R1-1813488, November 12-16, 2018.

Claims

1. A method for reducing feedback overhead related to channel state information (CSI) in a communication network using multiple-input multiple-output (MIMO) operation, performed by a user equipment (UE) (500), the method comprising: -(401) will correspond to the precoder matrix F (r) The precoder matrix Each term of the (i, j)th combining coefficient of is decomposed into at least two coefficients, where r represents the rth transmission layer; the (i, j)th combining coefficient is associated with the i-th beam and the j-th delay, and each combining coefficient is associated with amplitude and phase information Where the precoder matrix F (r) is the wideband first-stage precoder matrix The matrix and matrix The product of the wideband first-stage precoder matrix Containing 2L spatial beams that are the same for all subbands, the matrix comprising a plurality of basis vectors for performing compression in the frequency domain; The matrix The decomposed (i,j)th combination coefficient is given as: where b i,j is the complex-valued normalized combining coefficient associated with the i-th beam and the j-th delay, and a i is a real-valued coefficient representing the common amplitude of the combined coefficients of all delays associated with the i-th beam; -(402) individually quantizing each of the at least two coefficients using at least one bit, and -(403) reporting information related to at least one phase value or at least one amplitude value or at least one phase value and amplitude value of the quantized coefficient.

2. The method according to claim 1, comprising using N a The real-valued coefficients a are equally quantized (402) by the units. i , where each complex-valued coefficient b i,j With N for the amplitude and phase respectively b,1 and N b,2 quantized by one digit, where N b,1 Can be lower than N b,2 .

3. The method according to claim 1, comprising using N a Units and each phase uses N a quantize the matrix (402) The above items and 2UDN a The units digit is used for reporting The coefficients of where UD is a matrix The number of combination coefficients in .

4. The method according to claim 1, comprising reporting a matrix only the phase value, only the amplitude value or the amplitude and phase values ​​of the K strongest coefficients, wherein the value of parameter K is configurable by the radio network node or gNB.

5. The method according to claim 4, comprising: Each row / beam in selects K u The strongest coefficients, where parameter K u Can be configured by the radio network node or gNB.

6. The method according to claim 4, comprising: Each column / delay in selects K d The strongest coefficients, where parameter K d Can be configured by the radio network node or gNB.

7. The method according to claim 1, comprising that the UE (500) can be configured by a radio base station or a gNB, wherein N b,1 =1, and each amplitude value is represented by two quantization levels "a" and "b", where, for example, "a" and / or "b" are given by "a=0" and "b=1".

8. The method according to claim 1, comprising: i,j Different quantization levels are applied to the phase values.

9. The method according to claim 8, comprising: b ' ,2 bits are used for the phase values ​​associated with non-zero coefficients and the U' strongest beams, and N b ″ ,2 bits are used for the phase values ​​associated with the non-zero coefficients and the remaining beams, where N b ' ,2 >N b ″ ,2 .

10. The method of claim 1, further comprising reporting and matrix The index of the complex combination of coefficients associated with the discrete Fourier transform / discrete cosine transform DFT / DCT vector.

11. The method of claim 10, comprising selecting the DFT / DCT vector from a set of predetermined DFT / DCT basis vectors, wherein each DFT / DCT basis vector is associated with an index.

12. The method of claim 11, comprising reporting a bitmap, wherein each bit in the bitmap is associated with a matrix The complex combined coefficients are associated with the index "d" of the set of discrete Fourier transform / discrete cosine transform DFT / DCT basis vectors.

13. The method of claim 12, comprising when the bitmap consists of a "1" at position "1", then considering the amplitude and phase values ​​of the pilot beam as follows: - a "1" at position 1 of the bitmap indicates that the amplitude and phase of the combining coefficient of the pilot beam associated with index "1" are given by 1 and 0, respectively, and are not reported; and - The amplitude and phase values ​​of the remaining combining coefficients of the pilot beam associated with other indices are given by 0 and 0, respectively, and are not reported.

14. The method according to claim 1, wherein the radio base station or gNB should report b i,j The number B of leading beams of said amplitude values ​​is given by B=2L or 2L-1 for reporting using DFT / DCT transform, where L is the number of configured spatial beams.

15. The method according to claim 1, comprising not reporting to the radio base station or gNB the b associated with the first pilot beam. i,j The quantized amplitude and phase values.

16. The method according to claim 3, wherein when N a =3, used to quantify a i The amplitude set of is given by 17. The method according to any one of claims 1 to 16, wherein the i,j The quantized amplitude set of is given as {0,1}.

18. The method according to any one of claims 1 to 16, wherein the i,j The amplitude set of is given by the 8PSK phase shift keying constellation or the 16PSK constellation.

19. The method of claim 1, comprising reporting a bitmap, wherein each bit in the bitmap corresponds to the coefficient b i,j associated with; and when the bit is set to 1, the report is related to the coefficient b i,j Associated phase and amplitude values.

20. The method of claim 19, wherein the bitmap includes no more than K "1's".

21. The method according to claim 1 or 20, comprising: When the number of non-zero amplitude values ​​is less than K, report the quantization matrix The amplitude and phase information of the non-zero coefficients.

22. The method of claim 1, comprising reporting non-zero coefficients b associated with the quantization i,j information related to only the phase value, only the amplitude value, or only the amplitude and phase values.

23. A user equipment (500) for reducing feedback overhead related to channel state information (CSI) in a communication network using multiple-input multiple-output (MIMO) operation, the UE (500) comprising a processor (510) and a memory (520) containing instructions executable by the processor (510), whereby the UE (500) is operable to perform any of the subject matters of method claims 1 to 22.

24. A method performed by a radio network node (700) or gNB for reducing feedback overhead related to channel state information (CSI) in a communication network using multiple-input multiple-output (MIMO) operation, the method comprising: (601) receiving from a UE (500) a report comprising information about at least one phase value or at least one amplitude value or at least one phase value and amplitude value of each quantized coefficient quantized by the UE (500) with at least one bit; which corresponds to the precoder matrix F (r) The precoder matrix Each term of the (i, j)th combining coefficient of is decomposed by the UE (500) into at least two coefficients, wherein r represents the rth transmission layer; the (i, j)th combining coefficient is associated with the i-th beam and the j-th delay, and wherein each combining coefficient is associated with amplitude and phase information; Where the precoder matrix F (r) is the wideband first-stage precoder matrix The matrix and matrix The product of the wideband first-stage precoder matrix Containing 2L spatial beams that are the same for all subbands, the matrix comprising a plurality of basis vectors for performing compression in the frequency domain; The matrix The decomposed (i,j)th combination coefficient is given as: where b i,j is the complex-valued normalized combining coefficient associated with the i-th beam and the j-th delay, and a i is a real-valued coefficient representing the common amplitude of the combining coefficients of all delays associated with the i-th beam.

25. The method according to claim 24, comprising configuring the UE (500) to feedback a matrix The amplitude and / or phase values ​​of the K strongest coefficients, where the value of K can be configured by the radio network node (700) or the gNB.

26. A method according to claim 24 or claim 25, comprising configuring the UE to Each row / beam in selects K u The strongest coefficients, where parameter K u Can be configured by the radio base station (700) or gNB.

27. The method according to any one of claims 24 to 26, comprising configuring the UE (500) to Each column / delay in selects K d The strongest coefficients, where parameter K d Can be configured by the radio base station (700) or gNB.

28. The method according to claim 24, comprising configuring the UE (500) to A subset of the coefficients in reports only the amplitude and / or phase information.

29. The method of claim 24, comprising configuring the UE (500) to use N a The units digits quantize the real-valued coefficients a equally i , where a i is a real-valued coefficient representing the common amplitude of the combining coefficients for all delays associated with the i-th beam.

30. The method of claim 24, comprising configuring the UE (500) to report the quantized non-zero coefficients b i,j only the phase value, only the amplitude value, or the amplitude and phase values.

31. The method according to any one of claims 24 to 30, comprising configuring the UE (500) to report a bitmap, wherein each bit in the bitmap is associated with an index "d" from a set of DFT / DCT basis vectors.

32. The method of claim 24, comprising receiving a bitmap from a UE, wherein each bit in the bitmap corresponds to the coefficient b i,j associated with; and when the bit is set to 1, the report is related to the coefficient b i,j Associated phase and amplitude values.

33. A method according to claim 32, wherein the bitmap includes no more than K "1's".

34. A radio network node (700) or gNB for reducing feedback overhead related to channel state information (CSI) in a communication network using multiple-input multiple-output (MIMO) operation, the gNB (700) comprising a processor (710) and a memory (720) containing instructions executable by the processor (710), whereby the gNB (500) is operable to perform any of the subject matter of method claims 24 to 33.

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