Three-component codebook based CSI reporting

TECHNICAL FIELD

The present invention relates to the field of wireless communications, and in particular to methods, user equipments, network nodes and computer program products for providing channel state information, CSI, feedback from a user equipment in the form of one or more CSI reports in a wireless communication system.

BACKGROUND

In a wireless communications system, such as New Radio, also called 3GPP Fifth Generation wireless communications system or 5G for short, downlink (DL) and uplink (UL) signals convey data signals, control signals comprising DL control information (DCI) and/or uplink control information (UCI), and a number of reference signals (RSs) used for different purposes. A radio network node or a radio base station or a gNodeB (or gNB or gNB/TRP (Transmit Reception Point)) transmits data and DCI through the so-called physical downlink shared channel (PDSCH) and the physical downlink control channel (PDCCH), respectively.

A UE transmits data and UCI through the so-called physical uplink shared channel (PUSCH) and physical uplink control channel (PUCCH), respectively. Moreover, the DL or UL signal(s) of the gNB respectively the user equipment, UE or a radio device, may contain one or multiple types of RSs including a channel state information RS (CSI-RS), a demodulation RS (DM-RS), and a sounding RS (SRS). The CSI-RS (SRS) is transmitted over a DL (UL) system bandwidth part and used at the UE (gNB) for CSI acquisition. The DM-RS is transmitted only in a bandwidth part of the respective PDSCH/PUSCH and used by the UE/gNB for data demodulation.

One of many key feature of 5G is the use of multi-input multi-output (MIMO) transmission schemes to achieve high system throughput compared to previous generations of mobile systems. MIMO transmission generally demands the availability of accurate CSI used at the gNB for a signal precoding using a precoding matrix of the data and control information. The current third Generation Partnership Project Release 15 specification (3GPP Rel. 15) therefore provides a comprehensive framework for CSI reporting. The CSI is acquired in a first step at the UE based on received CSI-RS signals transmitted by the gNB. The UE determines in a second step based on the estimated channel matrix a precoding matrix from a predefined set of matrices called ‘codebook’. The selected precoding matrix is reported in a third step in the form of a precoding matrix identifier (PMI) and rank identifier (Rl) to the gNB.

3GPP Rel.-15 dual-stage precoding and CSI reporting

In the current Rel.-15 NR specification, there exist two types (Type-I and Type-ll) for CSI reporting, where both types rely on a dual-stage, i.e. , two components, W1 W2 codebook. The first component, or the so-called first stage precoder, W is used to select a number of beam vectors and, if configured, the rotation oversampling factors from a Discrete Fourier Transform -based (DFT-based) matrix which is also called the spatial codebook. The spatial codebook comprises an DFT- or oversampled DFT matrix of dimension N1N2 x N101N202, where and 02 denote the oversampling factors with respect to the first and second dimension of the codebook, respectively. The DFT vectors in the codebook are grouped into (q1, q2 ), 0 £ q1 £ 01 - 1, 0 £ q2 £ 02 - 1 subgroups, where each subgroup contains N1N2 DFT vectors, and the parameters q1 and q2 are denoted as the rotation oversampling factors. The second component, or the so-called second stage precoder, W2, is used to combine the selected beam vectors.

Assuming a rank-/? transmission and a dual-polarized antenna array at the gNB with configuration (N1, N2, 2), the Rel.-15 double-stage precoder disclosed in [1 ] for the s-th subband and r-th transmission layer is given by

where the precoder matrix W(r)(s) has 2 N1N2 rows corresponding to the number of antenna ports, and S columns for the reporting subbands/PRBs. The matrix W1 Î CPN N x2u is the wideband first-stage precoder containing 2U spatial beams for both polarizations, which are identical for all S subbands, and FA is a diagonal matrix containing 2U wideband amplitudes associated with the 2U spatial beams, and

is the second-stage precoder containing 2U subband, subband amplitude and phase,

complex frequency-domain combining-coefficients associated with the 2U spatial beams for the s-th subband.

For the 3GPP Rel.-15 dual-stage Type-ll CSI reporting, the second stage precoder, W2 is calculated on a subband basis such that the number of columns of
depends on the number of configured subbands.

Here, a subband refers to a group of adjacent physical resource blocks (PRBs). One major drawback of the Type-ll CSI feedback is the large feedback overhead for reporting the combining coefficients on a subband basis. The feedback overhead increases approximately linearly with the number of subbands, and becomes considerably large for large numbers of subbands. To overcome the high feedback overhead of the Rel.-15 Type-ll CSI reporting scheme, it has recently been decided in 3GPP RAN#81 [2] (3GPP radio access network (RAN) 3GPP RAN#81) to study feedback compression schemes for the second stage precoder W2. In several contributions [3]-[4], it has been demonstrated that the number of beam-combining coefficients in W2 may be drastically reduced when transforming W2 using a small set of DFT basis vectors into the delay domain. The corresponding three-stage precoder relies on a three-stage, i.e. , three components,
codebook. The first component, represented by matrix W1 is identical to the Rel.-15 NR component, independent of the layer (r), and contains a number of spatial domain (SD) basis vectors selected from a spatial codebook. The second component, represented by matrix
is layer-dependent and used to select a number of delay domain (DD) basis vectors from a Discrete Fourier Transform -based (DFT-based) matrix which is also called the delay codebook. The component, represented by matrix is third

layer-dependent and contains a number of combining coefficients that are used to combine the selected SD basis vectors and DD basis vectors from the spatial and delay codebooks, respectively.

Assuming a rank-R transmission the three-component precoder matrix or CSI matrix for a configured 2 N1N2 antenna/DL-RS ports and configured N3 subbands is represented for the first polarization of the antenna ports and r-th transmission layer as

and for the second polarization of the antenna ports and r-th transmission layer as

where
represents the u- th SD basis vector selected from the spatial codebook, is the d-th DD basis vector associated with the

r-th layer selected from the delay codebook, is the complex delay-domain

combining coefficient associated with the u- th SD basis vector, ci-th DD basis vector and p-th polarization, U represents the number of configured SD basis vectors, D represents the number of configured DD basis vectors, and α(ɩ'p) is a normalizing scalar.

A major advantage of the three-component CSI reporting scheme in equation (2) is that the feedback overhead for reporting the combining coefficient of the precoder matrix or CSI matrix is no longer dependent on the number of configured frequency domain subbands, i.e. , it is independent from the system bandwidth. Moreover, the feedback overhead and the performance of the precoder matrix or CSI matrix can be controlled by the gNB by configuring to the UE a maximum number of non-zero combining coefficients, K, per layer, or all layers, that can be contained in the third component,
and are reported by the UE. As only the amplitude and phase information of non-zero combining coefficients are reported, an indicator such as a bitmap is required that indicates which of the 2UD coefficients per layer are selected and reported by the UE. According to [5], the selected non-zero coefficients of the r-th layer are indicated by a bitmap, where each bit in the bitmap is associated with a polarization index (p Î {1,2}), an SD basis index (0 £ u £ U - 1) and DD basis index (0 £ d £ D - 1). A "1" in the bitmap indicates that the combining coefficient associated with the polarization index p, SD basis index u, and DD basis index d is non-zero, selected and reported by the UE. A “0” in the bitmap indicates that the combining

coefficient associated with the polarization index p, SD basis index u, and DD basis index d is zero, and hence not reported by the UE.

According to [6], the strongest combining coefficient per layer is normalized to 1 and not reported. In order to indicate which of the 2UD coefficients of a layer is the strongest combining coefficient, a strongest coefficient indicator (SCI) is reported per layer by the UE.

According to [6], the non-zero combining coefficients are
quantized as follows:

where the amplitude of the combining coefficient is given by two amplitudes, the

first and the second amplitudes denoted by respectively. Here, P

denotes the polarization reference amplitude defined for each polarization which is common for all amplitude values associated with a polarization p (p = 1,2). For the polarization index of the U SD components associated with the SCI, = 1 and not
reported. The polarization reference amplitude associated with the other polarization is quantized with a' bits. In addition, the amplitude and the phase

of each combining coefficient is quantized with a bits and b bits,

respectively.

Configuration and reporting of the three-component CSI scheme

For the configuration of the precoder matrix or CSI matrix, a CSI report configuration may be signaled via higher layer (e.g., RRC) from the gNB to the UE, wherein the higher layer CSI report configuration may contain the following information [7]:

- A parameter U indicating a number of SD basis vectors to be selected by UE from the spatial codebook for the calculation of W

- A parameter D, or variants thereof, indicating a number of DD basis vectors to be selected by UE per layer from the delay codebook for the calculation of
- A parameter K, or variants thereof, indicating a maximum number of non-zero coefficients contained in matrix per layer, or all layers, and used by the

UE to combine the selected SD basis vectors and DD basis vectors, and

- A parameter N3 indicating the number of frequency domain subbands of the CSI matrix and the dimension of the DD basis vectors in the delay codebook, and

- Additional parameter(s) for the configuration of the reporting of the DD basis vectors.

The CSI report may contain at least a rank indicator (Rl) indicating the selected number of layers of the CSI matrix, the number of selected number of non-zero combining coefficients across all layers, KNZ, and a PMI defining the three components of the CSI matrix, wherein the PMI contains at least the following information [7]:

- A spatial domain subset indicator (SD basis indicator) indicating the selected U SD basis vectors and, if configured, the selected oversampling rotation factors from the spatial codebook for the Rl layers of the CSI matrix,

- A delay domain subset indicator (DD basis indicator) indicating per layer the selected DD basis vectors,

- A strongest coefficient indicator (SCI) per layer indicating the SD basis index, or the SD and DD basis indices, associated with the strongest combining coefficient, which is not reported,

- Amplitude and phase information associated with the KNZ,r selected non-zero quantized delay domain combining coefficients per layer,

- A bitmap per layer indicating the SD basis indices and DD basis indices associated with the KNZ,r non-zero coefficients per layer,

- A polarization specific reference amplitude per layer, and

- Possible additional parameter(s) associated with the DD basis subset indication.

UCI omission for 3GPP Rel.-15 CSI reporting

UCI omission [1] for PUSCH-based resource allocation and CSI reporting was introduced in 3GPP Rel-15. It allows a UE to drop some parts of one or more CSI report(s) in the case that the PUSCH resource allocation is not sufficient to carry the entire content of the CSI report(s). UCI omission may happen when the base station did not accurately allocate the PUSCH resources when scheduling the CSI report(s).

For example, the base station may allocate resources for a rank-1 (Rl=1) CSI report, but the UE determines a rank-2 transmission and reports a rank-2 (Rl=2) CSI report of which size is larger than the size of the allocated PUSCH resources. In such a case, the UE has to drop a portion of the UCI content. In 3GPP Rel. 15 the dropping is achieved by decomposing the UCI payload associated with the CSI reports into smaller portions, the so-called priority levels, see Table 5.2.3-1 of [1], where priority level 0 has the highest priority, and NREP represents the total number of CSI reports configured to be carried on the PUSCH. Each priority level is associated with a part of a CSI report. The UE drops the CSI portions with lower priority such that the payload size of the CSI reports fits with the PUSCH resource allocation. Moreover, the CSI payload is portioned into two parts: CSI part 1 and CSI part 2. The CSI part 1 contains the Rl and an indicator that indicates the size of CSI part 2. The size of CSI part 1 is fixed, whereas the size of CSI part 2 varies depending on the determined Rl by the UE and some other factors. Since the gNB needs to know CSI part 1 in order to decode CSI part 2, UCI omission is only performed on CSI part 2.

The CSI part 2 is composed on 2 NREP + 1 CSI portions. Here, 2 NREP CSI portions, the so-called subband PMIs, contain the CSI content(s) associated with the even and odd subbands of the NREP CSI report(s). Moreover, each subband PMI is associated with a priority level, starting from index 1 to 2 NREP. In addition, the first CSI portion which is associated with priority level index 0 contains information for all 2 NREP subband PMIs, i.e. , for the entire CSI reporting band. The motivation behind the Rel. 15 subband-based CSI decomposition and omission method is that in case of omission of a first subband PMI of CSI report n, the gNB may use the CSI content of the reported second subband PMI of CSI report n to estimate the CSI of the omitted first subband PMI by using an interpolation scheme. In this way, a severe degradation of the performance can be avoided as neighbored subbands are typically highly correlated.

SUMMARY

For the known three-component CSI reporting scheme, the 3GPP Rel. 15 UCI omission procedure cannot be reused, since subband-based PMI does not exists and a decomposition of the CSI part 2 into a number of subband PMIs is not possible. Consequently, new UCI omission rules are required.

Note that the three-component CSI reporting scheme, the CSI payload of a CSI report can be controlled by the UE by the number of non-zero coefficients to be reported. In case of UCI omission, the UE may simply reduce the number of non-zero coefficients to be reported for one or more of the CSI reports based on the available PUSCH resources. However, a reduction of the number of non-zero combining coefficients would require a recalculation of the combining coefficients, SD and DD basis vectors of the CSI matrices for the one or more CSI reports, occupying additional UE resources. Such additional UE resources may not be available at the UE. Therefore, the UCI omission scheme should not be require a recalculation of CSI matrices for one or more CSI reports.

For the three-component CSI reporting scheme, the size of the payload of the CSI reports is mainly determined by the bitmaps and the amplitude and phase information of the reported non-zero combining coefficients of the CSI reports.

In this invention, different segmentation schemes for the bitmaps and the amplitude and phase information of the reported non-zero combining coefficients of the CSI reports for the three-component CSI reporting scheme are proposed.

In one solution of this invention, the UCI omission scheme is based on dropping a portion of the amplitude and phase information of the non-zero combining coefficients of a CSI report.

In another solution of this invention, the UCI omission scheme is based on dropping a portion of the amplitude and/or phase information of the non-zero combining coefficients and a portion of the bitmaps that are associated with the dropped combining coefficients.

The present invention proposes a method performed by a user equipment, UE, for providing channel state information, CSI, feedback in the form of one or more CSI reports in a wireless communication system, the method comprising:

- receiving, from a network node, gNB, higher layer configuration(s) of one or more downlink reference signals, and one or more CSI report configuration(s) associated with the downlink reference signal configuration(s), and a radio signal via a MIMO channel, the radio signal including the downlink reference signal(s) according to the one or more downlink reference signal configurations, - estimating, the downlink MIMO channel based on measurements on the received one or more downlink reference signals, the downlink reference signals provided over a configured number of frequency domain resources, time domain resources and one or more ports,

- determining, for each CSI report configuration, a precoding matrix based on an estimated channel matrix and two codebooks, the two codebooks including

- a spatial codebook comprising one or more spatial domain (SD) basis components of the precoder, and

- a delay codebook comprising one or more delay domain (DD) basis components of the precoder,

and one or more non-zero combining coefficients for complex combining of the one or more SD and DD basis vectors, and

- reporting to the network node, the one or more CSI reports for the one or more CSI report configurations.

Each CSI report contains the selected precoding matrix in the form of a precoding matrix identifier, PMI, and a rank identifier, Rl, indicating the transmission rank for the Rl layers of the precoding matrix, and each CSI report comprises two parts: CSI part 1 and CSI part 2, where CSI part 1 has a fixed payload size and comprises information indicating the size of the payload of CSI part 2. CSI part 2 comprises at least the amplitude and phase information of the selected non-zero combining coefficients and the bitmaps of all Rl layers indicating the non-zero combining coefficients of the CSI report, wherein the bitmap of each layer is segmented into D bit-sequences with respect to the DD basis indices of the selected DD basis vectors. Each bit-sequence comprises 2U x 1 bits which are associated with 2U spatial beams, wherein U denotes the number of selected SD basis vectors from the spatial codebook, and each DD basis index is associated with a delay vector from the delay codebook and, wherein the D bit-sequences are ordered with respect to one of two ordering scheme for the N3 DD basis indices, where N3 denotes the number of DD basis indices of the delay codebook, where the N3 DD basis indices are ordered as

0,1, N3 - 1, 2, N3 - 2, 3, N3 - 3, 4, N3 - 4,5, ...

according to a first ordering scheme, or where the N3 DD basis indices are ordered as 0 ,N3 - 1,1, N3 - 2,2, N3 - 3,3, N3 - 4,4, N3 - 5,5, ...

according to a second ordering scheme. The ordering of the amplitude and phase information of the combining coefficients follows the ordering of the bit-sequences of the bitmaps of all Rl layers. A portion, or the entirety, of CSI part 2 is available for omission from the CSI report.

According to one proposed aspect of the invention, CSI part 1 contains at least the information on the selected number of non-zero combining coefficients across all Rl layers and an indication of the transmission rank for the Rl layers of the selected precoding matrix.

It is also proposed that CSI part 2 contains at least the following information for the Rl layers of the selected precoding matrix:

- a spatial domain, SD, basis subset indicator, including, if configured, the rotation oversampling factors, indicating the selected SD basis vectors from the spatial codebook,

- one or more delay domain, DD, basis subset indicators indicating the selected DD basis vectors from the delay codebook,

- the phase and amplitude of the selected non-zero delay-domain combining coefficients,

- a strongest coefficient indicator, SCI, indicating the DD and SD vector associated with the strongest coefficient per layer,

- a polarization reference amplitude per layer,

- a bitmap for indicating the non-zero combining coefficients per layer, and

- possible additional parameter(s) associated with the DD basis subset indication.

Another aspect of the invention teaches that the CSI part 2 of the NREP CSI reports can be segmented into TNREP + 1 CSI subgroups, wherein always T CSI subgroups are associated with a single CSI report, and one CSI subgroup contains information associated with all NREP CSI reports, wherein each CSI subgroup is associated with a priority, priority level.

It is proposed that the CSI subgroup that contains information associated with all NREP CSI reports may have the highest priority, priority level 0, and the remaining TNREP CSI subgroups may be associated with the lower priority levels 1 to TNREP, and that the last CSI subgroup TNREP is associated with the lowest priority level TNREP.

It is also proposed that the CSI subgroups may have priorities according as follows:

Priority 0: Part 2 joint CSI subgroup for CSI report 1 to NREP Priority 1 : Part 2 CSI subgroup 1 for CSI report 1

Priority T: Part 2 CSI subgroup T for CSI report 1

Priority T + 1: Part 2 CSI subgroup 1 for CSI report 2

Priority 2 T: Part 2 CSI subgroup T for CSI report 2

Priority T(NREP - 1) + 1: Part 2 CSI subgroup 1 for CSI report NREP

Priority TNREP : Part 2 CSI subgroup T for CSI report NREP.

It is proposed that in case of omission, the UE may drop the CSI subgroups with lower priority until the payload size of the CSI reports fits with the resource allocation from the gNB. When omitting a CSI subgroup for a particular priority level, the UE may omit all the CSI content at that priority level.

The parameter T may indicate the number of CSI subgroups per CSI report and may be related to the granularity of the CSI content that is omitted from a CSI report, wherein a high value of T indicates a high granularity and a low value of T indicates a low granularity, and wherein each CSI report is associated only with two CSI subgroups when the parameter T is given by the value of 2.

One proposed aspect of the invention teaches that the first CSI subgroup, called as the joint CSI subgroup, is associated with priority level 0 contains CSI information of all NREP CSI reports, and wherein the joint CSI subgroup contains the information of at least one the following parameters:

- the selected SD basis subset indicator including, if configured, the rotation oversampling factors, and

the SCI(s) for the Rl layers.

It is also proposed that the CSI subgroup with highest priority of a CSI report contains at least the information of the following parameters:

- the selected DD basis subset indicator(s) for the Rl layers,

- the polarization reference amplitude value(s) for the Rl layers, and

- the bitmap(s) for indicating the KNZ non-zero combining coefficients for the Rl layers, and

- possible additional parameter(s) associated with the DD basis subset indication.

One proposed aspect of the invention teaches that the CSI subgroup with highest priority of a CSI report may contain at least the information of the following parameters:

- the selected DD basis subset indicator(s) for the Rl layers,

- the polarization reference amplitude value(s) for the Rl layers,

- the bitmap(s) for indicating the KNZ non-zero combining coefficients for the Rl layers, and

- the window parameter Minit.

It is also proposed that the corresponding ordered bitmaps for the Rl layers may be grouped together to a bitmap of size 2UD x Rl and segmented into D segments, wherein each segment has a size of 2U x Rl, wherein the d-th segment is associated with the 2U SD components of all Rl layers.

It is proposed that bits in a bit-segment associated with the same SD basis index of all layers may be grouped together and sorted with respect to an increasing layer index, and that Rl bits associated with a first SD basis index may be grouped together and followed by Rl bits associated with a second SD basis index, and so on.

Another aspect of the invention is that the ordering of the DD basis indices per layer according to the second ordering scheme maty be realized by the equation:

is the ƒ-th DD basis index out of D

DD basis indices for each layer, and wherein v is the total number of layers.

Yet another aspect of the invention is that the ordering of the bits in the bitmap may be realized by the equation:

where v is the total number of layers, U is the number of selected

SD basis vectors per polarization and D is the number of DD basis indices.

Another aspect of the invention is that the first segment of a CSI subgroup with highest priority may be associated with DD basis vector index 0.

Another aspect of the invention is that the UE may be configured for a CSI report to perform a cyclic shift operation on the selected combining coefficients and the selected DD basis vectors per layer with respect to the DD basis vector that is associated with the SCI so that the DD basis vector with index 0 is associated with the SCI.

This means that the CSI subgroup with the highest priority per CSI report may contain information of a first fraction of the amplitude and phase values of the selected non- zero delay-domain combining coefficients, and the remaining T - 1 CSI subgroups with lower priority may contain the remaining fraction of amplitude and phase values of the CSI report.

It is also proposed that each CSI subgroup with the highest priority and associated with a single CSI report may contain at least a fraction of the bitmaps for the Rl layers and the phase and amplitude information of a fraction of the KNZ non-zero combining coefficients.

This means that the CSI subgroup with highest priority may contain:

- the v2LD - KNZ/2] highest priority elements of the bitmap of RI = v layers,

the KNZ/2] - u highest priority amplitude values, and

the KNZ/2] - u highest priority phase values.

It is also proposed that each CSI subgroup associated with a single CSI report may contain the amplitude and phase information of the combining coefficients associated with a portion of the bitmaps of the Rl layers.

It is proposed that each CSI subgroup with the highest priority associated with a single CSI report may contain at least the fraction of the bitmaps and the information of the combining coefficients associated with the DD basis vector index of the SCI for the Rl layers.

It is also possible that each CSI subgroup that has the highest priority and is associated with a single CSI report may contain at least the bitmaps associated with one or more DD basis vector indices, for the Rl layers of the precoding matrix indicated in the CSI report, and the CSI subgroup may contain the corresponding amplitude and/or phase information of the combining coefficients associated with the bitmaps.

It is proposed that each CSI subgroup, that contains information of a fraction of the combining coefficients, may contain phase and amplitude values, associated with a maximum of combining coefficients of a CSI report, and that the remaining

CSI subgroups with lower priority may contain the remaining phase and amplitude values, of the CSI report.

It is then proposed that the CSI subgroup that has the highest priority per CSI report may contain KNZ/2]] - v highest priority amplitude values and KNZ/2] - v highest priority phase values, and that the CSI subgroup that has the lowest priority may contain KNZ/2] lowest priority amplitude values and KNZ/2] lowest priority phase values.

Another aspect of the invention proses that the phase and amplitude values of the combining coefficients may be segmented into two CSI subgroups when T = 2 and x = 2, where the first CSI subgroup contains the phase and amplitude values associated with combining coefficients and the second CSI subgroup contains

the phase and amplitude associated with the remaining combining
coefficients of a CSI report.

It is proposed that the amplitude and phase information of the combining coefficients in a CSI subgroup may be ordered such that the amplitude information of X combining coefficients (Xa bits) is followed by the phase information of X combining coefficients (Xb bits)

It is then proposed that for the CSI subgroup with highest priority per CSI report, the highest priority bits associated with the amplitude values may be

followed by the
highest priority bits associated with the phase values, and wherein v is the total number of transmission layers.

It is also possible that for the CSI subgroup with lower priority per CSI report, the KNZ/2 x a highest priority bits associated with the amplitude values are followed by the KNZ/2 X b highest priority bits associated with the phase values, and wherein v is the total number of transmission layers.

The bit-width of the CSI subgroup may be associated with a single CSI report and highest priority may be fixed and given by A + B, where A is the combined bit-width of all components that are contained in the CSI subgroup apart from the number of non- zero combining coefficients, and B is the bit-width associated with the amplitude (a) and phase information ( b ) of a fraction of the combining coefficients

The present invention also relates to a method performed by a network node, gNB, for receiving channel state information, CSI, feedback in the form of one or more CSI reports in a wireless communication system, the method comprising:

- sending, to a user equipment, UE, higher layer configuration(s) of one or more downlink reference signals, and one or more CSI report configuration(s) associated with the downlink reference signal configuration(s), and a radio signal via a MIMO channel, the radio signal including the downlink reference signal(s) according to the one or more downlink reference signal configuration(s),

- receiving, from the UE one or more CSI reports for one or more CSI report configurations,

wherein the one or more CSI reports are generated by the UE by:

- estimating, the downlink MIMO channel based on measurements on the received one or more downlink reference signals, the downlink reference signals provided over a configured number of frequency domain resources, time domain resources and one or more ports,

- determining, for each CSI report, a precoding matrix based on the estimated channel and two codebooks, the two codebooks including

- a spatial codebook comprising one or more spatial domain (SD) basis components of the precoder, and

- a delay codebook comprising one or more delay domain (DD) basis components of the precoder,

and one or more non-zero combining coefficients for complex combining of the one or more SD and DD basis vectors,

wherein each CSI report contains the selected precoding matrix in the form of a precoding matrix identifier, PMI, and a rank identifier, Rl, indicating the transmission rank for the Rl layers of the precoding matrix, and wherein each CSI report comprises two parts: CSI part 1 and CSI part 2, wherein CSI part 1 has a fixed payload size and comprises information indicating the size of the payload of CSI part 2, wherein CSI part 2 comprises at least the amplitude and phase information of the selected non-zero combining coefficients of the CSI report, wherein the bitmap of each layer is segmented into D bit-sequences with respect to the DD basis indices of the selected DD basis vectors, wherein each bit-sequence comprises 2U x 1 bits which are associated with 2U spatial beams, wherein U denotes the number of selected SD basis vectors from the spatial codebook, and each DD basis index is associated with a delay vector from the delay codebook and, wherein the D bit-sequences are ordered with respect to one of two ordering scheme for theN3 DD basis indices, whereN3 denotes the number of DD basis indices of the delay codebook, where the N3 DD basis indices are ordered as

0,1, N3 - 1, 2, N3 - 2, 3, N3 - 3, 4, N3 - 4,5, ...

according to a first ordering scheme, or where the N3 DD basis indices are ordered as 0 ,N3 - 1,1, N3 - 2,2, N3 - 3,3, N3 - 4,4, N3 - 5,5, ...

according to a second ordering scheme, and wherein the ordering of the amplitude and phase information of the combining coefficients follows the ordering of the bit-sequences of the bitmaps of all Rl layers, and wherein a portion, or the entirety, of CSI part 2 is available for omission from the CSI report.

The invention also relates to a user equipment, UE, comprising a processor and a memory, the memory containing computer program code executable by the processor whereby the UE is operative to perform any one of the subject matter of the inventive method performed by a user equipment.

The invention also relates to a network node comprising a processor and a memory, the memory containing computer program code executable by the processor whereby the network node is operative to perform any one of the subject matter of the inventive method performed by a network node.

The invention also relates to a computer program product comprising computer program code, which, when executed by a processor, enables the processor to perform any one of the subject matter of inventive method relating to a user equipment.

The invention also relates to a computer program product comprising computer program code, which, when executed by a processor, enables the processor to perform any one of the subject matter of inventive method relating to a network node.

The invention provides a method through which new UCI omission rules are implemented enabling a UE using the known three-component CSI reporting scheme to make use of an omission procedure without requiring a recalculation of the combining coefficients, SD and DD basis vectors of the CSI matrices for the one or more CSI reports.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of embodiments and advantages of the embodiments herein are described in more detail with reference to attached drawings in which:

Figure 1 is a schematic and simplified illustration of a user equipment in communication with a radio base station,

Figure 2 is an illustration of scheme 1 showing an example CSI part 2 decomposition into a number of CSI subgroups. NREP CSI subgroups with priority level (t - 1 )NREP to tNREP - 1 (1 £ t £ T) are always associated with NREP CSI reports,

Figure 3 is an illustration of scheme 1 showing a Decomposition of CSI part 2 into a number of CSI subgroups. T CSI subgroups with priority level (n - 1 )T to nT - 1 (1 £ n £ NREP ) are always associated with a single CSI report,

Figure 4 is an illustration of scheme 2 showing an example of decomposition of CSI part 2 into a number of CSI subgroups. The first CSI subgroup with the highest priority contains information of CSI report 1 to NREP. T CSI subgroups with priority level (n - 1 )T + 1 to nT (1 £ n £ NREP ) are always associated with a single CSI report,

Figure 5 is an illustration of scheme 2 showing an example of decomposition of CSI part 2 into a number of CSI subgroups. The first CSI subgroup with the highest priority contains information of CSI report 1 to NREP. NREP CSI subgroups with priority level (t - T)NREP + 1 to tNREP (1 £ t £ T) are always associated with NREP CSI reports,

Figure 6 is an illustration of an example of CSI content contained in the first joint CSI subgroup with priority level 0 and CSI content of the CSI subgroup that has highest priority and is associated with a single CSI report n,

Figure 7 is an illustration of Example of CSI content contained in first joint CSI subgroup with priority level 0 and CSI content of the T CSI subgroups associated with CSI report n,

Figure 8 is an illustration of CSI content of T = 2 CSI subgroups with respect to the third method for decomposition scheme 1 ,

Figure 9 is an illustration of CSI content of first and second CSI subgroup associated for CSI report t, with segmentation into D segments, where D denotes the number of configured delay vectors per layer of the CSI matrix of CSI report t.

Figure 10 is an illustration of further segmentation of segment k into sub-segments, each sub-segment is associated with all SD components and a DD basis index of a single layer,

Figure 11 is an illustration of segmentation of segment k into kr,2U sub-segments, each sub-segment is associated with all SD components and a DD basis index of a single layer,

Figure 12 is an illustration of segmentation of a bitmap contained in a CSI subgroup into Rl segments, each of 2UD bits,

Figure 13 is an illustration of segmentation of bitmap of size 2UD x 1 into sub- segments, each of size 2U x 1,

Figure 14 is an illustration of segmentation of bitmap of size 2UD x 1 into sub- segments, each of size 2D x 1,

Figure 15 is an illustration of segmentation of bitmap of size 2UD x 1 into sub- segments, each of size D x 1,

Figure 16 is an illustration of segmentation of bitmap into D segments, each of size 2U x RI bits,

Figure 17 is an illustration of segmentation of 2U x RI bits segment into sub-segments of 2RI bits each,

Figure 18 is an illustration of segmentation of 2U x RI bits segment into sub-segments of RI bits each,

Figure 19 is an illustration of segmentation of 2U x RI bits into sub-segments of 2U bits each,

Figure 20 is an illustration of amplitude information followed by the phase information of each combining coefficient,

Figure 21 is an illustration of amplitude information of all X combining coefficients followed by the phase information of all X combining coefficients,

Figure 22 is an illustration of phase information of all X combining coefficients followed by the amplitude information of all X combining coefficients,

Figure 23 is a schematic illustration of a first scheme for ordering of DD basis indices,

Figure 24 is a schematic illustration of a second scheme for ordering of DD basis indices,

Figure 25 is an illustration of mapping of the spatial beam indices to the indices gl,u and gl,U+u

Figure 26 is an illustration of a direct mapping of the bitmap associated with a spatial beam index and a segment Ad onto the index

Figure 27 is an illustration of the mapping of the bit associated with a spatial beam index
onto the index
when the strongest coefficient is associated with the first polarization for U = 4,

Figure 28 is an illustration of the mapping of the bit associated with a spatial beam index
onto the index
when the strongest coefficient is associated with the first polarization for U = 4, Figure 29 is an illustration of the mapping of the bit associated with a spatial beam index onto the index
when the
strongest coefficient is associated with the second polarization for U = 4, Figure 30 is an illustration of the mapping of the bit associated with a spatial beam index
onto the index
when the strongest coefficient is associated with the first polarization for U = 4, Figure 31 is an illustration of the mapping of the bitmap associated with a spatial beam index onto the index

Figure 32 is an illustration of the mapping of the bitmap associated with a spatial beam index
onto the index

Figure 33 is a schematic and simplified illustration of a user equipment and a computer program product.

DETAILED DESCRIPTION

In the following is presented a detailed description of the exemplary embodiments in conjunction with the drawings, in several scenarios, to enable easier understanding of the solution(s) described herein.

As previously described, in 3GPP new radio system, a UCI omission procedure has been standardized in Rel. 15, which omission procedure cannot be reused, since subband-based PMI does not exist and a decomposition of the CSI part 2 into a number of subband PMIs is not possible. Consequently, new UCI omission rules are required

Figure 1 is a simplified illustration of a method performed by a user equipment, UE, and a radio base station, gNB, for providing channel state information, CSI, feedback in the form of one or more CSI reports in a wireless communication system A, the method comprising:

- receiving, from a network node, gNB, higher layer configuration(s) of one or more downlink reference signals, and one or more CSI report configuration(s) associated with the downlink reference signal configuration(s), and a radio

signal via a MIMO channel, the radio signal including the downlink reference signal(s) according to the one or more downlink reference signal configurations,

- estimating, the downlink MIMO channel based on measurements on the received one or more downlink reference signals, the downlink reference signals provided over a configured number of frequency domain resources, time domain resources and one or more ports,

- determining, for each CSI report configuration, a precoding matrix based on an estimated channel matrix and two codebooks, the two codebooks including

- a spatial codebook comprising one or more spatial domain (SD) basis components of the precoder, and

- a delay codebook comprising one or more delay domain (DD) basis components of the precoder,

and one or more non-zero combining coefficients for complex combining of the one or more SD and DD basis vectors, and

- reporting to the network node, the one or more CSI reports for the one or more CSI report configurations.

Each CSI report contains the selected precoding matrix in the form of a precoding matrix identifier, PMI, and a rank identifier, Rl, indicating the transmission rank for the Rl layers of the precoding matrix, and each CSI report comprises two parts: CSI part

1 and CSI part 2, where CSI part 1 has a fixed payload size and comprises information indicating the size of the payload of CSI part 2. CSI part 2 comprises at least the amplitude and phase information of the selected non-zero combining coefficients of the CSI report, and a portion, or the entirety, of CSI part 2 is available for omission from the CSI report.

In accordance to an embodiment, the UE is configured with NREP CSI reports to be carried on the PUSCH, wherein each CSI report may comprise two parts: CSI part 1 and CSI part 2, where CSI part 1 has a fixed payload size and is used to indicate the size of the payload of CSI part 2. The CSI part 1 may contain at least the information on the number of the combining coefficients across all layers and an indication of the transmission rank (Rl) for the Rl layers of the selected precoding matrix. The CSI part

2 of a CSI report may contain at least the following information for the Rl layers of the selected CSI matrix for the configured antenna ports and subbands:

- a selected SD basis subset indicator including, if configured, the rotation oversampling factors,

- a selected DD basis subset indicator per layer,

- the phase and amplitude of the selected non-zero delay-domain combining coefficients per layer,

- a strongest coefficient indicator (SCI) per layer,

- a polarization reference amplitude per layer,

- a bitmap for indicating the non-zero combining coefficients per layer, and

- possible additional parameter(s) associated with the DD basis subset indication.

Decomposition for CSI part 2 - Scheme 1

In accordance with embodiments, in the first decomposition scheme (Scheme 1), the CSI part 2 of the NREP CSI reports may be segmented into TNREP CSI subgroups, wherein always T CSI subgroups are associated with a single CSI report. Moreover, each CSI subgroup is associated with a priority level, wherein the first subgroup has the highest priority level 0. The remaining TNREP - 1 CSI subgroups are associated with the lower priority levels 1 to TNREP - 1. The last CSI subgroup TNREP - 1 may be associated with the lowest priority level TNREP - 1.

Figure 2 illustrates a first example of Scheme 1, where always NREP CSI subgroups with priority level (t - 1)NREP to tNREP - 1 (1 £ t £ T) and associated with NREP CSI reports are grouped together.

Figure 3 illustrates a second example of Scheme 1, where always T CSI subgroups with priority level (n - 1 )T to nT - 1 (1 £ n £ NREP ) and associated with a single CSI report are grouped together

The parameter T indicates the number of CSI subgroups per CSI report and is related to the granularity of the CSI content that is omitted from a CSI report. A high value of T indicates a high granularity and a low value of T indicates a low granularity. When the parameter T is given by the value of 2, each CSI report is associated only with two CSI subgroups.

The parameter T indicating the number of CSI subgroups per CSI report may also depend on the CSI report. In one example, the parameter T may be dependent on the rank indicated in the CSI report. For instance, T = 2, if the rank indicated in the CSI report is larger than one, Rl>1 , and T = 1 if the rank indicated in the CSI report is one, Rl=1. In another example, the parameter T may be dependent on the number of non-zero coefficients KNZ indicated in the CSI report. For instance, T = 2, if the number of non-zero coefficients indicated in the CSI report is larger than a specific threshold value, i.e. , KNZ > KNZ, and T = 1 otherwise.

In contrast to Rel. 15 CSI decomposition, where the first CSI subgroup contains information of all NREP CSI reports, each subgroup in the proposed decomposition contains the information associated only with a single CSI report.

In case of UCI omission, the UE drops the CSI subgroups with lower priority until the payload size of the CSI reports fits with the PUSCFI resource allocation. When omitting a CSI subgroup for a particular priority level, the UE omits all the CSI content at that priority level.

Decomposition for CSI part 2 - Scheme 2

A drawback of the above CSI decomposition scheme 1, shown in Fig. 2 and Fig. 3, is that when all CSI subgroups associated with a single CSI report are dropped, the complete CSI report is dropped. To avoid the complete dropping of the CSI content of a CSI report, the following embodiment proposes a CSI decomposition that allows the gNB to recalculate partly the CSI matrices for all NREP CSI subgroups even all CSI subgroups are dropped by the UE, except the first CSI subgroup with the highest priority, priority level 0.

In accordance with embodiments, the CSI part 2 of the NREP CSI reports may be segmented into TNREP + 1 CSI subgroups, wherein always T CSI subgroups are associated with a CSI report. The CSI first subgroup contains information associated with all NREP CSI reports.

Each CSI subgroup is associated with a priority level, wherein the first subgroup has the highest priority level 0. The remaining TNREP CSI subgroups are associated with the lower priority levels 1 to TNREP, where the last CSI subgroup TNREP may be associated with the lowest priority level TNREP.

The parameter T indicates the number of CSI subgroups per CSI report and is related to the granularity of the CSI content that is omitted from a CSI report. A high value of T indicates a high granularity and a low value of T indicates a low granularity. When the parameter T is given by the value of 2, each CSI report is associated only with two CSI subgroups.

The parameter T indicating the number of CSI subgroups per CSI report may also depend on the CSI report. In one example, the parameter T may be dependent on the rank indicated in the CSI report. For instance, T = 2, if the rank indicated in the CSI report is larger than one, Rl>1 , and T = 1 if the rank indicated in the CSI report is one, Rl=1 . In another example, the parameter T may be dependent on the number of non-zero coefficients KNZ indicated in the CSI report. For instance, T = 2, if the number of non-zero coefficients indicated in the CSI report is larger than a specific threshold value, i.e. , KNZ £ KNZ, and T = 1 otherwise.

In case of UCI omission, the UE drops the CSI subgroups with lower priority until the payload size of the CSI reports fits with the PUSCFI resource allocation. When omitting a CSI subgroup for a particular priority level, the UE omits all the CSI content at that priority level.

Figure 4 illustrates a first example of Scheme 2, where always T CSI subgroups with priority level (n - 1 )T + 1 to nT (1 £ n £ NREP ) and associated with a single CSI report are grouped together.

Figure 5 illustrates a second example of Scheme 2, where always NREP CSI subgroups with priority level (t - 1)NREP + 1 to tNREP (1 £ t £ T) and associated with NREP CSI reports are grouped together.

Content of a CSI subgroup

In accordance with embodiments, when the first CSI subgroup, associated with priority level 0, contains CSI information of all NREP CSI reports, the joint CSI subgroup may contain the information of at least one of the following parameters:

- the selected SD basis subset indicator including, if configured, the rotation oversampling factors,

the selected DD basis subset indicator(s) for the Rl layers,

- the SCI(s) for the Rl layers,

- the polarization reference amplitude value(s) for the Rl layers,

- the bitmap(s) for indicating the KNZ non-zero combining coefficients for the Rl layers, and

- possible additional parameter(s) associated with the DD basis subset indication.

For the segmentation of the phase and amplitude values of the NREP CSI reports for Scheme 2, two partitioning approaches are proposed in the following.

In the first approach, a first portion of the phase and amplitude values of the selected non-zero delay-domain combining coefficients of the NREP CSI reports is contained in the first joint CSI subgroup that has the highest priority. An example of the CSI content of the first joint CSI subgroup and of the CSI subgroup that has the highest priority and is associated with a single CSI report with respect to the first approach is shown in Figure 6.

In the second approach, the first CSI subgroup that has the highest priority does not contain any phase and amplitude values of the selected non-zero delay-domain combining coefficients for the NREP CSI reports, and only the remaining CSI subgroups contain the information of the non-zero combining coefficients. An example of the CSI content of the first joint CSI subgroup and of the CSI subgroups associated with a single CSI report with respect to the second approach is shown in Figure 7.

CLAIMS

1. A method performed by a user equipment, UE, for providing channel state information, CSI, feedback in the form of one or more CSI reports in a wireless communication system, the method comprising:

- receiving, from a network node, gNB, higher layer configuration(s) of one or more downlink reference signals, and one or more CSI report configuration(s) associated with the downlink reference signal configuration(s), and a radio signal via a MIMO channel, the radio signal including the downlink reference signal(s) according to the one or more downlink reference signal configuration(s),

- estimating, the downlink MIMO channel based on measurements on the received one or more downlink reference signals, the downlink reference signals provided over a configured number of frequency domain resources, time domain resources and one or more ports,

- determining, for each CSI report, a precoding matrix based on the estimated channel and two codebooks, the two codebooks including

- a spatial codebook comprising one or more spatial domain (SD) basis components of the precoder, and

- a delay codebook comprising one or more delay domain (DD) basis components of the precoder,

and one or more non-zero combining coefficients for complex combining of the one or more SD and DD basis vectors, and

- reporting, to the network node, the one or more CSI reports for the one or more CSI report configurations,

wherein each CSI report contains the selected precoding matrix in the form of a precoding matrix identifier, PM I, and a rank identifier, Rl, indicating the transmission rank for the Rl layers of the precoding matrix, and wherein each CSI report comprises two parts: CSI part 1 and CSI part 2, wherein CSI part 1 has a fixed payload size and comprises information indicating the size of the payload of CSI part 2, wherein CSI part 2 comprises at least the amplitude and phase information of the selected non-zero combining coefficients and the bitmaps of all Rl layers indicating the non-zero combining coefficients of the CSI report, wherein the bitmap of each layer is segmented into D bit-sequences with respect to the DD basis indices of the selected DD basis

vectors, wherein each bit-sequence comprises 2U x 1 bits which are associated with 2U spatial beams, wherein U denotes the number of selected SD basis vectors from the spatial codebook, and each DD basis index is associated with a delay vector from the delay codebook and, wherein the D bit-sequences are ordered with respect to one of two ordering scheme for theN3 DD basis indices, whereN3 denotes the number of DD basis indices of the delay codebook, where the N3 DD basis indices are ordered as

0,1, N3 - 1, 2, N3 - 2, 3, N3 - 3, 4, N3 - 4,5, ...

according to a first ordering scheme, or where the N3 DD basis indices are ordered as 0 ,N3 - 1,1, N3 - 2,2, N3 - 3,3, N3 - 4,4, N3 - 5,5, ...

according to a second ordering scheme, and wherein the ordering of the amplitude and phase information of the combining coefficients follows the ordering of the bit-sequences of the bitmaps of all Rl layers, and wherein a portion, or the entirety, of CSI part 2 is available for omission from the CSI report.

2. The method of claim 1 , wherein CSI part 1 contains at least the information on the selected number of non-zero combining coefficients across all Rl layers and an indication of the transmission rank for the Rl layers of the selected precoding matrix.

3. The method of claim 1 , wherein CSI part 2 contains at least the following information for the Rl layers of the selected precoding matrix:

- a spatial domain, SD, basis subset indicator, including, if configured, the rotation oversampling factors, indicating the selected SD basis vectors from the spatial codebook,

- one or more delay domain, DD, basis subset indicators indicating the selected DD basis vectors from the delay codebook,

- the phase and amplitude of the selected non-zero delay-domain combining coefficients,

- a strongest coefficient indicator, SCI, indicating the DD and SD vector associated with the strongest coefficient per layer,

- a polarization reference amplitude per layer,

- a bitmap for indicating the non-zero combining coefficients per layer, and

- possible additional parameter(s) associated with the DD basis subset

indication.

4. The method of claim 1 or claim 3, wherein CSI part 2 of the NREP CSI reports is segmented into TNREP + 1 CSI subgroups, wherein always T CSI subgroups are associated with a single CSI report, and one CSI subgroup contains information associated with all NREP CSI reports, and wherein each CSI subgroup is associated with a priority (priority level).

5. The method of claim 4, wherein the CSI subgroup that contains information associated with all NREP CSI reports has the highest priority (priority level 0), and the remaining TNREP CSI subgroups are associated with the lower priority levels 1 to TNrep, and wherein the last CSI subgroup TNREP is associated with the lowest priority level TNrep.

6. The method of claim 4 or claim 5, wherein the CSI subgroups have priorities according as follows:

Priority 0: Part 2 joint CSI subgroup for CSI report 1 to NREP Priority 1 : Part 2 CSI subgroup 1 for CSI report 1

Priority T: Part 2 CSI subgroup T for CSI report 1

Priority T + 1: Part 2 CSI subgroup 1 for CSI report 2

Priority 2 T: Part 2 CSI subgroup T for CSI report 2

Priority T(NREP - 1) + 1: Part 2 CSI subgroup 1 for CSI report NREP

Priority TNREP : Part 2 CSI subgroup T for CSI report NREP.

7. The method of any one of claims 4 to 6, wherein, in case of omission, the UE drops the CSI subgroups with lower priority until the payload size of the CSI reports fits with the resource allocation from the gNB.

8. The method of claim 7, wherein, when omitting a CSI subgroup for a particular priority level, the UE omits all the CSI content at that priority level.

9. The method of any one of claims 4 to 6, wherein the parameter T indicates the number of CSI subgroups per CSI report and is related to the granularity of the CSI content that is omitted from a CSI report, wherein a high value of T indicates a high granularity and a low value of T indicates a low granularity, and wherein each CSI report is associated only with two CSI subgroups when the parameter T is given by the value of 2.

10. The method of any one of claims 4 to 6, wherein the joint CSI subgroup associated with priority level 0 contains CSI information of all NREP CSI reports, and wherein the joint CSI subgroup contains the information of at least one of the following parameters:

- the selected SD basis subset indicator including, if configured, the rotation oversampling factors, and

- the SCI(s) for the Rl layers.

11. The method of any one of claims 4 to 6, wherein the CSI subgroup with highest priority of a CSI report contains at least the information of the following parameters:

- the selected DD basis subset indicator(s) for the Rl layers,

- the polarization reference amplitude value(s) for the Rl layers,

- the bitmap(s) for indicating the KNZ non-zero combining coefficients for the Rl layers, and

- possible additional parameter(s) associated with the DD basis subset indication.

12. The method of any one of claims 4 to 6, wherein the CSI subgroup with highest priority of a CSI report contains at least the information of the following parameters:

- the selected DD basis subset indicator(s) for the Rl layers,

- the polarization reference amplitude value(s) for the Rl layers,

- the bitmap(s) for indicating the KNZ non-zero combining coefficients for the Rl layers, and

- the window parameter Minit.

13. The method of any preceding claim, wherein the corresponding ordered bitmaps for the Rl layers are grouped together to a bitmap of size 2UD x RI and segmented into D segments, wherein each segment has a size of 2U x RI, wherein the d-th segment is associated with the 2U SD components of all RI layers.

14. The method according to claim 13, wherein the bits in a bit-segment associated with the same SD basis index of all layers are grouped together and sorted with respect to an increasing layer index, and wherein RI bits associated with a first SD basis index are grouped together and followed by RI bits associated with a second SD basis index, and so on.

15. The method of claim 1 , wherein the ordering of the DD basis indices per layer according to the second ordering scheme is realized by the equation:

basis index out of D

DD basis indices for each layer, and wherein v is the total number of layers.

16. The method of any preceding claim, wherein the ordering of the bits in the bitmap is realized by the equation:

where v is the total number of layers, U is the number of selected

SD basis vectors per polarization and D is the number of DD basis indices.

17. The method of any preceding claim, wherein the first segment of a CSI subgroup with highest priority may be associated with DD basis vector index 0.

18. The method of any preceding claim, wherein the UE is configured for a CSI report to perform a cyclic shift operation on the selected combining coefficients and the selected DD basis vectors per layer with respect to the DD basis vector that is

associated with the SCI so that the DD basis vector with index 0 is associated with the SCI.

19. The method of any one of claims 4 to 6 or 11 to 18, wherein the CSI subgroup with the highest priority per CSI report contains information of a first fraction of the amplitude and phase values of the selected non-zero delay-domain combining coefficients, and the remaining T - 1 CSI subgroups with lower priority contain the remaining fraction of amplitude and phase values of the CSI report.

20. The method of any one of claims 4 to 6 or claims 11 to 19, wherein each CSI subgroup with the highest priority and associated with a single CSI report contain at least a fraction of the bitmaps for the Rl layers and the phase and amplitude information of a fraction of the KNZ non-zero combining coefficients.

21. The method according to claim 20, wherein the CSI subgroup with highest priority contains:

- the v2LD - [KNZ/2] highest priority elements of the bitmap of Rl = v layers,

- the KNZ/2] - v highest priority amplitude values, and

- the [KNZ/2] - v highest priority phase values.

22. The method of any one of claims 4 to 6 or claims 11 to 21 , wherein each CSI subgroup associated with a single CSI report contains the amplitude and phase information of the combining coefficients associated with a portion of the bitmaps of the Rl layers.

23. The method of any one of claims 4 to 6 or claims 11 to 22, wherein each CSI subgroup with the highest priority associated with a single CSI report contains at least the fraction of the bitmaps and the information of the combining coefficients associated with the DD basis vector index of the SCI for the Rl layers.

24. The method of any one of claims 4 to 6 or claims 10 to 23, wherein each CSI subgroup that has the highest priority and is associated with a single CSI report

contains at least the bitmaps associated with one or more DD basis vector indices, for the Rl layers of the precoding matrix indicated in the CSI report, and the CSI subgroup contains the corresponding amplitude and/or phase information of the combining coefficients associated with the bitmaps.

25. The method of any one of claims 20 to 24, wherein each CSI subgroup, that contains information of a fraction of the combining coefficients, contains phase and amplitude values associated with a maximum of combining coefficients of

a CSI report, and wherein the remaining CSI subgroups with lower priority contain the remaining phase and amplitude values, of the CSI report.

26. The method of claim 25, wherein the CSI subgroup that has the highest priority per CSI report contains [KNZ/ 2] - v highest priority amplitude values and [KNZ/ 2] - v highest priority phase values, and the CSI subgroup that has the lowest priority contains KNZ/2] lowest priority amplitude values and KNZ/2] lowest priority phase values.

27. The method of claim 25, wherein the phase and amplitude values of the combining coefficients are segmented into two CSI subgroups when T = 2 and x = 2, where the first CSI subgroup contains the phase and amplitude values associated with combining coefficients and the second CSI subgroup contains the phase and amplitude associated with the remaining combining coefficients of a CSI

report.

28. The method of any one of claims 20 to 27, wherein the amplitude and phase information of the combining coefficients in a CSI subgroup are ordered such that the amplitude information of X combining coefficients (Xa bits) is followed by the phase information of X combining coefficients (Xb bits)

29. The method of claim 28, wherein for the CSI subgroup with highest priority per CSI report, the highest priority bits associated with the amplitude values

are followed by the ([KNZ/ 2] - v) x b highest priority bits associated with the phase values, and wherein v is the total number of transmission layers.

30. The method of claim 28, wherein for the CSI subgroup with lower priority per CSI report, the ([KNZ/ 2 - xv a) highest priority bits associated with the amplitude values are followed by the ([KNZ/ 2] -- xvv b)) highest priority bits associated with the phase values, and wherein v is the total number of transmission layers.

31. The method of any one of claims 4 to 6 or claims 10 to 30 , wherein the bit-width of the CSI subgroup associated with a single CSI report and highest priority is fixed and given by A + B, where A is the combined bit-width of all components that are contained in the CSI subgroup apart from the number of non-zero combining coefficients, and B is the bit-width associated with the amplitude (a) and phase information ( b ) of a fraction of the combining coefficients

32. A method performed by a network node, gNB, for receiving channel state information, CSI, feedback in the form of one or more CSI reports in a wireless communication system, the method comprising:

- sending, to a user equipment, UE, higher layer configuration(s) of one or more downlink reference signals, and one or more CSI report configuration(s) associated with the downlink reference signal configuration(s), and a radio signal via a MIMO channel, the radio signal including the downlink reference signal(s) according to the one or more downlink reference signal configuration(s),

- receiving, from the UE one or more CSI reports for one or more CSI report configurations,

wherein the one or more CSI reports are generated by the UE by:

- estimating, the downlink MIMO channel based on measurements on the received one or more downlink reference signals, the downlink reference signals provided over a configured number of frequency domain resources, time domain resources and one or more ports,

- determining, for each CSI report, a precoding matrix based on the estimated channel and two codebooks, the two codebooks including

- a spatial codebook comprising one or more spatial domain (SD) basis components of the precoder, and

- a delay codebook comprising one or more delay domain (DD) basis components of the precoder,

and one or more non-zero combining coefficients for complex combining of the one or more SD and DD basis vectors,

wherein each CSI report contains the selected precoding matrix in the form of a precoding matrix identifier, PMI, and a rank identifier, Rl, indicating the transmission rank for the Rl layers of the precoding matrix, and wherein each CSI report comprises two parts: CSI part 1 and CSI part 2, wherein CSI part 1 has a fixed payload size and comprises information indicating the size of the payload of CSI part 2, wherein CSI part 2 comprises at least the amplitude and phase information of the selected non-zero combining coefficients of the CSI report, wherein the bitmap of each layer is segmented into D bit-sequences with respect to the DD basis indices of the selected DD basis vectors, wherein each bit-sequence comprises 2U x 1 bits which are associated with 2U spatial beams, wherein U denotes the number of selected SD basis vectors from the spatial codebook, and each DD basis index is associated with a delay vector from the delay codebook and, wherein the D bit-sequences are ordered with respect to one of two ordering scheme for theN3 DD basis indices, whereN3 denotes the number of DD basis indices of the delay codebook, where the N3 DD basis indices are ordered as

0,1, N3 - 1, 2, N3 - 2, 3, N3 - 3, 4, N3 - 4,5, ...

according to a first ordering scheme, or where the N3 DD basis indices are ordered as 0 ,N3 - 1,1, N3 - 2,2, N3 - 3,3, N3 - 4,4, N3 - 5,5, ...

according to a second ordering scheme, and wherein the ordering of the amplitude and phase information of the combining coefficients follows the ordering of the bit-sequences of the bitmaps of all Rl layers, and wherein a portion, or the entirety, of CSI part 2 is available for omission from the CSI report.

33. A user equipment, UE, comprising a processor and a memory, the memory containing computer program code executable by the processor whereby the UE is operative to perform any one of the subject matter of claims 1 to 31 .

34. A network node comprising a processor and a memory, the memory containing computer program code executable by the processor whereby the network node is operative to perform any one of the subject matter of claim 33.

35. A computer program product comprising computer program code, which, when executed by a processor, enables the processor to perform any one of the subject matter of claims 1 to 31.

36. A computer program product comprising computer program code, which, when executed by a processor, enables the processor to perform any one of the subject matter of claim 33.