METHODS AND APPARATUSES FOR CODEBOOK RESTRICTION FOR TYPE-II FEEDBACK REPORTING AND HIGHER LAYER CONFIGURATION AND REPORTING FOR LINEAR

COMBINATION CODEBOOK IN A WIRELESS COMMUNICATIONS NETWORK

TECHNICAL FIELD

The present disclosure relates to the field of wireless communications, and in particular, to methods and apparatuses for efficient feedback reporting for at least a New Radio- (NR-) based wireless communication network system, which feedback includes Channel State Information (CSI), and higher layer configuration and reporting for linear combination codebook.

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 (PM I) and rank identifier (RI) to the gNB.

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) W1W2 codebook. The first codebook, or the so-called first stage precoder, W1, is used to select a number of beam vectors from a Discrete Fourier Transform-based (DFT-based) matrix which is also called the spatial codebook. The second codebook, or the so-called second stage precoder W2, is used to combine the selected beams. For Type-I and Type-II CSI reporting, W2 contains phase-only combining coefficients and complex combing coefficients, respectively. Moreover, for Type-II CSI reporting, W2 is calculated on a subband basis such that the number of columns of W2 depends on the number of configured subbands. Here, a subband refers to a group of adjacent physical resource blocks (PRBs). Although Type-II provides a significant higher resolution than Type-I CSI feedback, one major drawback is the increased 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-II 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.

As will be described in according with some embodiments herein, a problem of how to compress and efficiently quantize the combining coefficients of W2 is addressed.

But before going into the detailed description of the solution(s) of the present embodiments, an informative description is provided in order to better understand the problems of the prior art followed by a described how said problems are solved according to the embodiments of the present disclosure.

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

Assuming a rank-L (L may be up to two) transmission and a dual-polarized antenna array at the gNB with configuration (N1, N2, 2), the Rel.-15 double-stage precoder for the s-th subband for a layer is given by

where the precoder matrix W has 2 N1N2 rows corresponding to the number of antenna ports, and S columns for the reporting subbands/PRBs. The matrix W1 ∈ is the wideband first-stage precoder containing 2 U spatial beams for

both polarizations, which are identical for all S subbands, and WA 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.

According to [1], the reporting and quantization of the wideband amplitude matrix WA and subband combining coefficients in are quantized and reported as

follows:

- The wideband amplitude corresponding to the strongest beam which has an amplitude value of 1 is not reported. The wideband amplitude values

associated with the remaining 2U - 1 beams are reported by quantizing each amplitude value with 3 bits.

- The subband amplitudes and phase values of the coefficients associated with the first leading beam are not reported (they are assumed to be equal to 1 and 0).

- For each subband, the amplitudes of the B coefficients associated with the first B - 1 leading beams (other than the first leading beam) are quantized with 1 bit (quantization levels [sqrt(0.5), 1]). The amplitude values of the remaining 2 U - B beams are not reported (they are assumed to be equal to 1).

- For each subband, the phase values of the B - 1 coefficients associated with the first B - 1 leading beams (other than the first leading beam) are quantized with 3 bits. The phase values of the remaining 2U - B beams are quantized with 2 bits.

- The number of leading beams for which the subband amplitude is reported is given by B = 4, 4 or 6 when the total number of configured spatial beams U = 2, 3, or 4, respectively.

BRIEF SUMMARY AND SOME DETAILED DESCRIPTION

In view of the drawbacks disclosed earlier, there is provided a communication device or a radio device or a user equipment (UE) and a method therein for providing a channel state information (CSI) feedback in a wireless communication system including at least the UE and a gNB or a radio network node. The UE comprising a processor and a memory, said memory containing instructions executable by said processor whereby said UE is operative by means of e.g. a transceiver to receive from a transmitter (e.g. the gNB or any suitable network node and/or radio communication device) a radio signal via a MIMO channel, where the radio signal contains DL reference signals according to a DL reference signal configuration. The UE is further operative, by means of e.g. the processor to:

- estimate the MIMO channel between the gNB and the UE based on the received DL reference signals for the configured resource blocks,

- calculate, based on a performance metric, a precoder matrix, for a number of antenna ports of the gNB and configured subbands, the precoder matrix

being based on two codebooks and a set of combination coefficients for complex scaling/combining one or more of vectors selected from a first codebook and a second codebook, wherein:

o the first codebook contains one or more transmit-side spatial beam components of the precoder, and

o the second codebook contains one or more delay components of the precoder, and

the UE is operative to report a CSI feedback and/or a PMI and/or a PMI/RI, used to indicate the precoder matrix for the configured antenna ports and resource blocks.

In accordance with some exemplary embodiments, the first codebook comprises a first DFT- or oversampled DFT-codebook-matrix of size N1N2 x 01, 1N101,2N2 containing the spatial beam components (N1N2 x 1 vectors) of the precoder matrix. Here, N1 and N2 refer to the number of antenna ports of the same polarization in the first and second dimension of the antenna array, respectively.

In general, for a two-dimensional (2D) antenna array, N1 and N2 are both greater than 1, whereas for a linear (or one-dimensional (1 D)) either N1 or N2 is one. The total number of antenna ports for dual-polarized antenna array that may be considered for better understanding is 2 N1N2. Furthermore, 01,1 e {1,2,3, .. } and 01,2 ∈ {1,2,3, . . } refer to the oversampling factors of the codebook matrix with respect to the first and second dimension, respectively. The second codebook comprises a second DFT, or discrete cosine transform (DCT-), or oversampled DFT-, or oversampled DCT-codebook matrix of size N3 x N3O2 containing the delay components (represented by N3 x 1 DFT-/DCT-vectors) of the precoder matrix, where O2 refers to the oversampling factor O2 = 1,2, .... of the second codebook matrix. Each DFT/DCT vector of the second codebook is associated with a delay (in the transformed domain), as each DFT/DCT vector may model a linear phase increase over the N3 subbands. Therefore, herein we may refer to DFT/DCT vectors of the second codebook in the following as delay vectors or simply delays.

In accordance with some exemplary embodiments, the precoder matrix F(l) of the l-th transmission layer is represented by a three-stage structure
where

- contains U(l) selected beam components/beam vectors from the first codebook of the /-th layer for the 2N1N2 antenna ports,

- contains selected delay vectors from the second codebook of the u- th

beam for the configured N3 subbands, where the number of delay vectors per
beam may be identical or different over the beams, and

- F® contains a number of complex-combining coefficients used to combine the selected U(l) beam vectors and delay vectors per layer.

The precoder matrix of the l-th transmission for the

configured 2N1N2 antenna ports and N3 subbands may also be represented in a double sum notation for the first polarization of the antenna ports as

and for the second polarization of the antenna ports as

where (u = 0, ..., U(l) - 1) represents the u-th spatial beam vector (contained in matrix selected from the first codebook, is the
delay vector (contained in matrix associated with the u- th beam and p-th

polarization selected from the second codebook, is the complex combining

coefficient (contained in matrix
associated with the u- th beam, d-th delay and p-th polarization, and α(l) is a normalizing scalar.

For brevity, in the following embodiments the delay vectors and are

exemplified as identical across two polarizations, such that
However, the embodiments herein are not restricted to this example, which means that the embodiments may also be applicable when delay vectors are not identical over both polarizations.

Configuration of the second codebook (N3, 02)

In accordance with exemplary embodiments, the UE may be configured to receive from the gNB the higher layer (such as Radio Resource Control (RRC) layer or medium access control-control element (MAC-CE)) or physical layer (Layer 1 or L1) parameter oversampling denoted N3 for the configuration of the second codebook. The specific value of the number of subbands N3 may depend on the maximum expected delay spread of the radio channel and the computational complexity spent at the UE for calculating the combining coefficients of the precoder matrix. Therefore, the specific value of N3 may depend on parameters related to or associated with the radio channel (such as the channel delay spread) and different design aspects of the precoder. In one example, the value of N3 may be identical to the number of configured channel Quality Indicator (CQI) subbands (low computational complexity approach). In another example, the value of N3 may be identical to the number of configured PRBs (high computational complexity approach), although not necessary for the functioning of the embodiments herein.

In accordance with some exemplary embodiments, the value of N3 may be defined by/as the total number of subbands with subband size NPRB, wherein PRB stands for physical resource block, where NPRB denotes the number of PRBs per subband. The value of NPRB may depend on the parameters of a orthogonal frequency division multiplexing (OFDM) transmission signal such as a configured subcarrier spacing (SCS) and a channel delay spread of the channel. Two exemplary values for NPRB are 4 and 2 for 15 KHz and 30 KHz SCSs, respectively.

In accordance with some exemplary embodiments, the UE may be configured or operative to receive from the gNB a higher layer (RRC or MAC-CE) or physical layer (L1) parameter oversampling factor O2 for the configuration of the second codebook. The oversampling factor defines the grid size of the delay components of the precoder. A large oversampling factor may result in a very fine grid for the delay components of the precoder and enhanced performance, but it also increases the codebook size and the computational complexity for selecting the delay components of the precoder.

In accordance with some exemplary embodiments, the UE is configured or is operative to select the oversampling factor used for the configuration of the second codebook and signal to the gNB by higher layer (RRC or MAC-CE) or physical layer (L1) the oversampling factor O2.

In accordance with some exemplary embodiments, the UE is configured or is operative to use an a priori known (default) oversampling factor(s) O2 for the configuration of the second codebook. In such a case, the oversampling factor may depend on the total number of configured PRBs (e.g. the total system bandwidth), where a higher oversampling factor (e.g., O2 = 8 or O2 = 16) may be applied when the total number of PRBs is larger than a specific pre-determined value and a lower oversampling factor (e.g., O2 = 4, O2 = 2 or O1 = 1) otherwise.

In accordance with some exemplary embodiments, the UE may be configured or may be operative to signal its capability with respect to the oversampling factor of the second codebook. For example, a UE with a limited computational power may not support oversampling of the second codebook, and may signal 02 = 1. Hence, signaling UE capabilities may be advantageous in case the UE has limited computational power or capacity or CPU power.

In accordance with some exemplary embodiments, the UE may be configured or may be operative to signal its capability with respect to the total number of subbands N3 for configuration of the second codebook. For example, a UE with a limited computational power may not support high values forN3, and may indicate it by signaling a parameter (e.g, R=1) to the gNB. In the other case, a UE with a larger computational power may support high values forN3, and may indicate it by signaling a parameter (e.g, R=2) to the gNB. Hence, signaling UE capabilities may be advantageous in case the UE has limited computational power or capacity or CPU power.

Hence, the method performed by the UE includes signaling capability of the UE with respect to the total number of subbands N3 for configuration of the second codebook.

Beam configuration and Reporting of selected beam indices

In accordance with some exemplary embodiments, the UE is configured to or is operative to receive from the gNB a higher layer (RRC or MAC-CE) or physical layer (L1) parameter U(l), representing the number of spatial beams for the l-th transmission layer. The number of spatial beams U(l) and the selected spatial beam vectors from the first codebook are typically different for each transmission layer. However, the reporting of different spatial beam vectors for each transmission layer may result in a high feedback overhead. In order to reduce the feedback overhead in accordance with embodiments herein, the UE may be configured to or may be operative to select identical beam vectors from the first codebook for a subset of the transmission layers which is advantageous. For example, the UE may be configured to or be operative to select identical spatial beam vectors for the first and second transmission layers and different (but possibly identical) spatial beam vectors for the third and fourth transmission layers.

Delay configuration and Reporting of selected delay vectors

The configured t/® beam vectors and the delay vectors per beam of the

precoder matrix are aligned with the multipath components of the MIMO propagation channel. The multipath components of the radio channel generally occur in the form of multipath clusters, where a multipath cluster may be understood as a group of multipath components with similar channel propagation parameters such as angle-of-arrival, angle-of-departure and delay [3]. Depending on the cluster distribution in the spatial and delay domains of the radio channel, each beam vector of the precoder matrix may be associated with a single cluster or few clusters, where each cluster may have a different delay. Some of the beam vectors of the precoder matrix shall therefore be associated with a small number of delays/delay vectors and some of the beam vectors shall be associated with a large number of delays/delay vectors.

In accordance with some exemplary embodiments, the UE may be configured with a different number of delays per beam vector, or with subsets of beam vectors

having an identical number of delays and with a different number of delays per subset. The number of configured delays may increase (decrease) with a beam or subgroup beam index. The selected delay vectors by the UE may be non-identical,

partially identical, or fully identical over the beam indices and/or layer indices. Hence, the embodiments herein are not restricted to any specific delay vectors.

There is also provided a method performed by the UE as previously described. The method includes:

- estimating the MIMO channel (as previously described) between the gNB and the UE based on the received DL reference signals for the configured resource blocks,

- calculating, based on a performance metric, a precoder matrix, for a number of antenna ports of the gNB and configured subbands, the precoder matrix being based on two codebooks and a set of combination coefficients for complex scaling/combining one or more of vectors selected from a first codebook and a second codebook, wherein:

o the first codebook contains one or more transmit-side spatial beam components of the precoder, and

o the second codebook contains one or more delay components of the precoder, and

the UE reporting, to the gNB, a CSI feedback and/or a PMI and/or a PMI/RI, used to indicate the precoder matrix for the configured antenna ports and resource blocks.

According to an exemplary embodiment, the method further comprises receiving from the gNB the higher layer (such as Radio Resource Control (RRC) layer or medium access control-control element (MAC-CE)) or physical layer (Layer 1 or L1) parameter oversampling denoted N3 for the configuration of the second codebook.

According to another exemplary embodiment, the method further comprises receiving from the gNB a higher layer (RRC or MAC-CE) or physical layer (L1) parameter oversampling factor O2 for the configuration of the second codebook.

Beam configuration and Reporting of selected beam indices

In accordance with some exemplary embodiments, the method may further comprises receiving from the gNB a higher layer (RRC or MAC-CE) or physical layer (L1) parameter U(l), representing the number of spatial beams for the l-th transmission layer. The number of spatial beams U(l) and the selected spatial beam vectors from the first codebook are typically different for each transmission layer. However, the reporting of different spatial beam vectors for each transmission layer may result in a high feedback overhead. In order to reduce the feedback overhead in accordance with embodiments herein, the method comprises selecting identical beam vectors from the first codebook for a subset of the transmission layers which is advantageous. For example, for the UE, the method may be configured to select identical spatial beam vectors for the first and second transmission layers and different (but possibly identical) spatial beam vectors for the third and fourth transmission layers.

Delay configuration and Reporting of selected delay vectors

The configured U(l) beam vectors and the delay vectors per beam of the

precoder matrix are aligned with the multipath components of the MIMO propagation channel. The multipath components of the radio channel generally occur in the form of multipath clusters, where a multipath cluster may be understood as a group of multipath components with similar channel propagation parameters such as angle-of-arrival, angle-of-departure and delay [3]. Depending on the cluster distribution in the spatial and delay domains of the radio channel, each beam vector of the precoder matrix may be associated with a single cluster or few clusters, where each cluster may have a different delay. Some of the beam vectors of the precoder matrix shall therefore be associated with a small number of delays/delay vectors and some of the beam vectors shall be associated with a large number of delays/delay vectors.

In accordance with some exemplary embodiments, the method performed by the UE may include that the UE be configured with a different number of delays
per beam vector, or with subsets of beam vectors having an identical number of delays and with a different number of delays per subset. The number of configured delays may increase (decrease) with a beam or subgroup beam index. The

selected delay vectors by the UE may be non-identical, partially identical, or fully identical over the beam indices and/or layer indices. Hence, the embodiments herein are not restricted to any specific delay vectors.

There is also provided a computer program comprising instructions which when executed on at least one processor of the UE according to the method related or associated with the UE described above, cause the at least said one processor to carry out the method according to anyone of the method subject-matter disclosed earlier. A carrier is also provided containing the computer program wherein the carrier is one of a computer readable storage medium; an electronic signal, optical signal or a radio signal.

There is also provided a method performed by the gNB or a radio network node or a radio base station and a radio network node or a gNB. The gNB is configured to perform at least the steps disclosed earlier. The method performed by the gNB includes in method terms, what has been defined as “configured to. As an example, the method in the gNB may include receiving from the UE a CSI feedback and/or a PM I and/or a PMI/RI, used to indicate the precoder matrix for the configured antenna ports and resource blocks.

According to an exemplary embodiment, the method, by the gNb may include transmitting to the UE a higher layer (such as Radio Resource Control (RRC) layer or medium access control-control element (MAC-CE)) or physical layer (Layer 1 or L1) parameter oversampling denoted N3 for the configuration of the second codebook.

According to another exemplary embodiment, the method further comprises transmitting to the UE a higher layer (RRC or MAC-CE) or physical layer (L1) parameter oversampling factor O2 for the configuration of the second codebook.

Beam configuration and Reporting of selected beam indices

In accordance with some exemplary embodiments, the method may further comprises transmitting to the UE a higher layer (RRC or MAC-CE) or physical layer (L1) parameter U(l), representing the number of spatial beams for the l-th

transmission layer. The number of spatial beams U(l) and the selected spatial beam vectors from the first codebook are typically different for each transmission layer. However, the reporting of different spatial beam vectors for each transmission layer may result in a high feedback overhead. In order to reduce the feedback overhead in accordance with embodiments herein, the method comprises selecting identical beam vectors from the first codebook for a subset of the transmission layers which is advantageous. For example, for the UE, the method may be configured to select identical spatial beam vectors for the first and second transmission layers and different (but possibly identical) spatial beam vectors for the third and fourth transmission layers.

Delay configuration and Reporting of selected delay vectors

The configured U(l) beam vectors and the delay vectors per beam of the

precoder matrix are aligned with the multipath components of the MIMO propagation channel. The multipath components of the radio channel generally occur in the form of multipath clusters, where a multipath cluster may be understood as a group of multipath components with similar channel propagation parameters such as angle-of-arrival, angle-of-departure and delay [3]. Depending on the cluster distribution in the spatial and delay domains of the radio channel, each beam vector of the precoder matrix may be associated with a single cluster or few clusters, where each cluster may have a different delay. Some of the beam vectors of the precoder matrix shall therefore be associated with a small number of delays/delay vectors and some of the beam vectors shall be associated with a large number of delays/delay vectors.

In accordance with some exemplary embodiments, the method performed by the gNB may include configuring the UE with a different number of delays per
beam vector, or with subsets of beam vectors having an identical number of delays and with a different number of delays per subset. The number of configured delays may increase (decrease) with a beam or subgroup beam index. The selected delay vectors by the UE may be non-identical, partially identical, or fully identical over the beam indices and/or layer indices. Hence, the embodiments herein are not restricted to any specific delay vectors.

According to another aspect of embodiments herein, there is also provided a radio base station or gNB, the radio base station comprising a processor and a memory, said memory containing instructions executable by said processor whereby said gNB is operative to perform any one of the subject-matter of method steps described above.

There is also provided a computer program comprising instructions which when executed on at least one processor of the gNB according to the method related or associated with the gNB described above, cause the at least said one processor to carry out the method according to anyone of the method subject-matter disclosed earlier. A carrier is also provided containing the computer program wherein the carrier is one of a computer readable storage medium; an electronic signal, optical signal or a radio signal.

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:

Figures 1-4 depict several examples of delay configurations for the precoder matrix of a layer with different computational complexities and feedback overheads for selecting and reporting the delay vectors per beam are provided.

Figures 5-12 depicts examples of the number of feedback bits for amplitude reporting according to some exemplary embodiments herein Figure 13 is an exemplary block diagram depicting a radio base station or gNB or network node according to exemplary embodiments herein.

Figure 14 is a block diagram depicting a UE or communication device or radio device according to exemplary embodiments herein.

Figure 15 is an Illustration of Codebook subset restriction on spatial beams and delays. Delay 3 associated with spatial beam 2 might cause high interference to adjacent cell UEs.

Figure 16 shows the case of selecting X = 2 beam groups out of O1,1O1,2 =

4 beam groups when N1 = N2 = 4 and 01,1 = 01,2 = 2. Each beam group contains N1N2 = 16 vectors.

Figure 17 shows the beam vectors restricted in one beam group containing N1N2 = 16 vectors using 4 amplitude levels depicted using 4 different colors.

Figure 18 Selecting H = 2 delay groups out of 4 N3 delay vectors when oversampling factor 02 = 4.

Figure 19 shows the delay vectors restricted in one delay group of size N3 = 8 using 4 amplitude levels depicted using 4 different colors.

Figure 20 depicts unequal distribution of amplitude values of non-linear amplitude set A for N=4.

Figure 21 shows equal distribution of amplitude values over entire range of 'O'to '1' of the linear amplitude set A for N=4.

Figure 22 depicts comparison of the distribution of the amplitude values from non-linear and linear amplitude sets for N=4.

DETAILED DESCRIPTION

In order to perform the previously described process or method steps related to the radio network node (e.g. a radio base station or gNB), some embodiments herein include a network node for receiving feedback from a UE as previously described. As shown in Figure 13, the network node or radio base station or gNB 800 comprises a processor 810 or processing circuit or a processing module or a processor or means 810; a receiver circuit or receiver module 840; a transmitter circuit or transmitter module 850; a memory module 820 a transceiver circuit or transceiver module 830 which may include the transmitter circuit 850 and the receiver circuit 840. The network node 800 further comprises an antenna system 860 which includes antenna circuitry for transmitting and receiving signals to/from at least the UE. The antenna system employs beamforming as previously described.

The network node 500 may belong to any radio access technology including 2G, 3G, 4G or LTE, LTE-A, 5G, WLAN, and WiMax etc. that support beamforming technology.

The processing module/circuit 810 includes a processor, microprocessor, an application specific integrated circuit (ASIC), field programmable gate array (FPGA), or the like, and may be referred to as the “processor 810.” The processor 810 controls the operation of the network node 800 and its components. Memory (circuit or module) 820 includes a random access memory (RAM), a read only memory (ROM), and/or another type of memory to store data and instructions that may be used by processor 810. In general, it will be understood that the network node 800 in one or more embodiments includes fixed or programmed circuitry that is configured to carry out the operations in any of the embodiments disclosed herein.

In at least one such example, the network node 800 includes a microprocessor, microcontroller, DSP, ASIC, FPGA, or other processing circuitry that is configured to execute computer program instructions from a computer program stored in a non-transitory computer-readable medium that is in, or is 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 connote storage of at least some persistence. The execution of the program instructions specially adapts or configures the processing circuitry to carry out the operations disclosed herein including anyone of method steps already described. Further, it will be appreciated that the network node 800 may comprise additional components not shown in Figure 13.

Details on the functions and operations performed by the network node have already been described and need not be repeated again.

In order to perform the previously described process or method steps related to the UE or communication device or radio device, some embodiments herein include a UE for providing efficient feedback reporting for at least a New Radio-(NR) based wireless communication network system, which feedback includes Channel State Information (CSI).

As shown in Figure 14, the UE 900 comprises a processor910 or processing circuit or a processing module or a processor or means 910; a receiver circuit or receiver module 940; a transmitter circuit or transmitter module 950; a memory module 920 a transceiver circuit or transceiver module 930 which may include the transmitter circuit 950 and the receiver circuit 840. The UE 900 further comprises an antenna system 960 which includes antenna circuitry for transmitting and receiving signals to/from at least the UE. The antenna system employs beamforming as previously described.

The network node 500 may belong to any radio access technology including 2G, 3G, 4G or LTE, LTE-A, 5G, WLAN, and WiMax etc. that support beamforming technology.

The processing module/circuit 910 includes a processor, microprocessor, an application specific integrated circuit (ASIC), field programmable gate array (FPGA), or the like, and may be referred to as the “processor 910.” The processor 910 controls the operation of the network node 900 and its components. Memory (circuit or module) 920 includes a random access memory (RAM), a read only memory (ROM), and/or another type of memory to store data and instructions that may be used by processor 910. In general, it will be understood that the UE 900 in one or more embodiments includes fixed or programmed circuitry that is configured to carry out the operations in any of the embodiments disclosed herein.

In at least one such example, the UE 900 includes a microprocessor, microcontroller, DSP, ASIC, FPGA, or other processing circuitry that is configured to execute computer program instructions from a computer program stored in a non-transitory computer-readable medium that is in, or is 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 connote storage of at least some persistence. The execution of the program instructions specially adapts or configures the processing circuitry to carry out the operations disclosed herein including anyone of method steps already described. Further, it will be appreciated that the UE 900 may comprise additional components not shown in Figure 14.

Details on the functions and operations performed by the UE have already been described and need not be repeated again.

In the following, several examples of delay configurations for the precoder matrix of a layer with different computational complexities and feedback overheads for selecting and reporting the delay vectors per beam are provided. Figures 1-4 show different example of delay configurations. It is worth noting that these figures depicts only some examples and the embodiments are not restricted to these in any way. In the following “configured to” and “operative to” or “adapted to” may be used interchangeably.

In one example, the UE is configured with for the first beam leading beam) and

for the ( U - 1)-th beam and the number of delays/delay vectors may

increase with the beam index.

In one example, the UE is configured with for the first beam (leading beam)

and for the ( U - 1)-th beam and the number of delays/delay vectors may

increase with the beam index.

In another example, the UE is configured with for the first beam (leading

beam) and for the ( U - 1)-th beam and the number of delays/delay

vectors may increase with the beam index.

In another example, the UE is configured with delays/delay vectors for

the first beam (leading beam) and delays/delay vectors for the ( U - 1)-

th beam and the number of delays/delay vectors may increase with the beam index.

In another example, the UE is configured with a single delay/delay vector for the first beam (leading beam), N1 delays/delay vectors for the second beam and N2 delays/delay vectors for the (U-1)-th beam and the number of delays/delay vectors may increase with the beam index.

In another example, the UE is configured with an identical number of delays/delay vectors for all beams.

In another example, the UE is configured with a single delay/delay vector for the first beam (leading beam) and delays/delay vectors for the

remaining beams.

(a) Reporting of delay vectors

In accordance with embodiments, the UE may report for each beam or for each beam group a delay indicator for the delay vectors selected from the second

codebook to the gNB. The delay indicator may refer to a set of indices where each index is associated with a delay vector from the second codebook.

In accordance with embodiments, to reduce the feedback overhead for reporting the multiple delay indicators, the UE is configured to select for each beam the delay vectors from a “common” set of non-identical delay vectors and to report only a single delay indicator. The number of delay vectors in the common set is not greater than ∀u. The UE may therefore report only a single delay

indicator instead of multiple delay indicators where the single delay indicator refers to the indices of the delay vectors from the common set. The delay vectors associated with the u- th beam are identical with a subset of the delay vectors associated with the (u+1)- th (or (u-1)- th) beam, such that ∀u' ≥
u (or ∀u' ≤ u). For example, the delay vectors associated with the i-th beam may be identical with a subset of the delay vectors associated with the (i+n)-th beam (n > 1). The UE then reports only the indices associated with the delay

vectors of the ( U - 1)-th beam to the gNB.

In accordance with embodiments, the UE may be configured to report the indices of the selected delay vectors from the common set in a sorted way such that the gNB may associate the selected delay vectors from the common set to each beam. The information on the sorting is either known or reported to the gNB. In one example, the UE may sort the delay indices with respect to the power/amplitude of the associated combining coefficients over the beams in a decreasing order. The

first index in the report may then correspond to the strongest delay (i.e., the delay associated with the combining coefficients having the highest power/amplitude).

Examples of some delay configurations and reporting of the single delay indicator are shown in Fig. 1 to Fig. 4.

In accordance with embodiments, the UE may be configured not to report the single delay indicator or multiple delay indicators to the gNB. In such a case, the UE and gNB know a priori the set of delay vectors from the second codebook.

In accordance with embodiments, the UE is configured to report the delay indicator for the selected delay vectors from the second codebook. The DFT/DCT delay vectors in the codebook may be grouped into O2 orthogonal subgroups/submatrices, where each DFT/DCT delay vector in a subgroup may be associated with an index. For example, when there O2N3 delay vectors in the second codebook, there are O2 subgroups/submatrices, where the first delay vector in a subgroup/submatrix may be associated with a first index (“0”), second delay vector is associated with a second index (“1”), and the last delay vector is associated with the index (“N3 - 1”). In order to reduce the computational complexity for selecting T delay DFT/DCT vectors, the UE may be configured to select T delay vectors out of a subgroup of O2 subgroups/submatrices from the second codebook. When reporting the indices of the T selected DFT/DCT delay vectors, the UE may then report the group index (0,1, ... , O2 - 1) and the associated indices for the selected T delay vectors within the selected subgroup. Therefore, for reporting the selected delay vectors and subgroup index,
feedback bits are required.

In accordance with embodiments, when the number of delay vectors to be reported is large compared to the subgroup size (N3), it is beneficial to associate each delay vector in a subgroup directly with a single bit of an N3-length bitmap and to report the bitmap instead of reporting the indices of the delay vectors. The number of feedback bits then accounts to N3 bits for reporting the bitmap and log2(O2 ) bits for the subgroup indication.

In accordance with embodiments, the UE is configured to report the group index (0,1, ... , O2 - 1), e.g., by higher layer (RRC) and not to report the indices of the T selected DFT/DCT delay vectors.

In accordance with embodiments, the UE is configured to the report the indices of the T selected DFT/DCT delay vectors, e.g., by higher layer (RRC) and not to report the group index.

In accordance with some exemplary embodiments, in addition to the report of the delay indicator (if reported), the UE may indicate the selected delay vectors associated with the non-zero combining coefficients per beam, or K selected combining coefficients (corresponding to the coefficients with the highest amplitude/power) for the 2U beams in the report. In such a case, the delay vectors of each beam are associated with a bitmap, where is the number

of configured delay vectors of the u-th beam. Each bit in the bitmap is associated with a single delay of the ∀u common delay vectors. For example, the

first bit may be associated with the first common delay vector, the second bit with the second common delay vector and so on. The UE report then contains for the c/-th beam a
bitmap for indicating the selected delay vectors associated with the non-zero combining coefficients or the K selected combining coefficients. When a delay/delay vector is common to all beams and is associated with only zero-valued combining coefficients, the corresponding combining coefficients are not reported and not indicated by the bitmap. The corresponding index is removed from the delay indicator reported to the gNB. Similarly, when a beam vector is only associated with zero-valued combining coefficients, the corresponding combining coefficients are not reported and not indicated by the bitmap. For example, when the u-th beam is only associated with zero-valued combining coefficients, the
bitmap associated with the u-th beam and the corresponding combining

coefficients are not reported.

(b) Configuration of parameters

In accordance with embodiments, the UE is configured to receive from the gNB the higher layer (RRC or MAC-CE) or physical layer parameters for the U beams

and L transmission layers, where the number of delay vectors may be different,

identical or partially identical over the beams. When the number of delays may increase (decrease) with the beam or subgroup beam index in a known manner, it is sufficient to signal only a subset of the parameters or none of the parameters

for the delay configuration of the precoder matrix.

For example, when the UE is configured with for the first beam (leading

beam) and for the ( U - 1)-th beam, the gNB may not signal the

parameters

For example, when the UE is configured with for the first beam (leading

beam) and for the ( U - l)-th beam, the gNB may signal the single

parameter for the delay configuration of the precoder matrix.

For example, when the UE is configured with for the first beam (leading

beam) and for the (U - 1)-th beam, the gNB may signal the two

parameters and for the delay configuration of the precoder matrix.

For example, when the UE is configured with a single delay for the first beam (leading beam), N1 delays for the second beam and N2 delays for the (U- 1)-th beam, the gNB may signal the two parameters and for the delay

configuration of the precoder matrix.

For example, when the UE is configured with an identical number of delays D(l) for all or a subset of beams, the gNB may signal the single parameter D(l) for the delay configuration of the precoder matrix.

In accordance with embodiments, the UE is configured to select and to report the parameters for the U beams and L transmission layers to the gNB. When the

number of delays may increase (decrease) with the beam or subgroup beam index in a known manner, it is sufficient to report only a subset of the parameters or
none of the parameters for the delay configuration of the precoder matrix.

In accordance with embodiments, the UE is configured to use a priori known parameters for the delay configuration of the precoder matrix.

(c) Non-reporting of the first delay vector associated with the leading beam

In accordance with embodiments, the UE is configured with at least one delay vector for the leading beam where the first delay vector for the leading beam is identical to the first delay vector from the selected subgroup/submatrix out of the O2 subgroups/submatrices from the second codebook. The leading beam is associated with the strongest combining coefficient (which corresponds to the coefficient having the largest power/amplitude over all combining coefficients).

In accordance with embodiments, the UE is configured not to report the index associated with the first delay vector of the leading beam. This means, the UE is configured to remove the index associated with the first delay vector of the leading beam from the delay indicator, i.e. , the index associated with the first delay vector associated with the leading beam is not reported.

In accordance with embodiments, the UE is configured to normalize the selected delays vectors with respect to a single reference delay vector. This means, the corresponding delays in the time/delay domain of the delay vectors are subtracted from a single reference delay. The reference delay vector may be identical with the first delay vector of the leading beam. The reference delay vector is known at the gNB and hence the associated delay index is not reported to the gNB.

Codebook subset restriction

In accordance with some exemplary embodiments, the UE is configured to select the delays/delay vectors per beam and layer from a subset of the delay vectors from the second codebook. The number of delay vectors and the specific delay vectors in the subset are associated with the delay values of the MIMO channel impulse response(s) (CIR(s)) between the UE and gNB. For example, when the average delay spread of the MIMO channel is small (which is typically observed in Line-of-sight (LOS) channel(s)), the energy of the channel impulse response is concentrated in a single main peak and only a few dominant delays are associated with the main peak. In such a case, the UE selects only few delay vectors from a second codebook, where the corresponding delays of the selected delay vectors are associated with the dominant channel delays of the MIMO CIR. In contrast, when the average delay spread of the channel impulse response is large (as observed in Non-Line-of-sight (NLOS) channel(s)), the energy of the channel impulse response is concentrated in a one or more peaks and a larger number of dominant channel delays is associated with the peak(s) of the CIR. Then, the UE selects a larger number of delay vectors from the second codebook. Therefore, for typical MIMO channel settings, the selected delay vectors by the UE are mainly associated with a subset of the delay vectors from the second codebook. Therefore, the size of the second codebook may be reduced, and thus the computational complexity for selecting the delay vectors by the UE.

In one example, the UE is configured to select the delay vectors from a subset of the second codebook where the subset is defined by the first Z1 vectors and the last Z2 vectors of a DFT matrix.

In one example, the UE is configured to select the delay vectors from multiple subsets of the second codebook. The DFT/DCT delay vectors in the codebook may be grouped into O2 orthogonal subgroups/submatrices, where each DFT/DCT delay vector in a subgroup may be associated with an index. For example, when there O2N3 delay vectors in the second codebook, there are O2 subgroups/submatrices, where the first delay vector in a subgroup/submatrix may be associated with a first index (“0”), second delay vector is associated with a second index (“1”), and the last delay vector is associated with the index (“N3 - 1”). For each orthogonal subgroup, the UE is configured to select the delay vectors from a subset of orthogonal DFT vectors from the subgroup. In one instance, the subset associated with a subgroup may be defined by the first Z delay vectors of the subgroup. In another instance, the subset associated with a subgroup may be defined by the first Z1 delay vectors and the last delay Z2 vectors of the orthogonal delay vectors of the subgroup. In another instance, the subset associated with a subgroup may also be defined by the i1:i2 orthogonal delay vectors in the subgroup. In another instance, the subset associated with a subgroup may also be defined by the orthogonal delay vectors and the i3: i4 orthogonal delay vectors in the subgroup.

In accordance with embodiments, the UE is either configured by the gNB with a subset of delay vectors from the second codebook by higher layer (such as Radio Resource Control (RRC) layer or MAC-CE) or physical layer, or with a priori known (default) subset(s) of delay vectors from the second codebook, or to report the selected subset(s) of delay vectors to the gNB.

In accordance with embodiments, the UE is configured by the gNB with the higher layer (such as Radio Resource Control (RRC) layer or MAC-CE) or physical layer parameter(s) Z or Z1 and Z2 that indicate the subset of delay vectors (from a subgroup of 02 orthogonal subgroups/submatrices) from the second codebook, or with a priori known (default) parameter(s) Z or Z1 and Z2 that indicate the subset of delay vectors (from a subgroup of O2 orthogonal subgroups/submatrices) from the second codebook, or to report parameter(s) Z or Z1 and Z2 that indicate the selected subset of delay vectors (from a subgroup of O2 orthogonal subgroups/submatrices) from the second codebook.

In accordance with some exemplary embodiments, the UE is configured to report a bitmap to indicate the selected delay vectors of the subset from the second codebook. The length of the bitmap is given by the size of the subset. A “1” in the bitmap may indicate that the corresponding delay vector of the subset is selected, and a “0” in the bitmap may indicate that the corresponding delay vector is not selected.

In accordance with embodiments, the UE may be configured to select the delay vectors for one layer or a for set of layers from one subgroup out of the O2 orthogonal subgroups/submatrices from the second codebook and for others layers from a different subgroup out of the O2 orthogonal subgroups/submatrices from the second codebook.

In accordance with embodiments, to reduce the interferences between different transmission layers, the UE may be configured to select a first set of delay vectors for one layer or for a set of layers from one subgroup out of the O2 orthogonal subgroups/submatrices from the second codebook and for other layers a second set of delay vectors from the same subgroup, where the first and second set of delay vectors are orthogonal to each other.

In accordance with embodiments, to reduce the interferences between different transmission layers, the UE is configured to select a first set of delay vectors for a first set of layer(s) from one subgroup out of the O2 orthogonal subgroups/submatrices from the second codebook and for a different second set of layer(s) a second set of delay vectors from the same subgroup, where the first and second set of delay vectors are partially orthogonal to each other. In one example, the UE is configured to select N delay vectors for the first set of layer(s) and M delay vectors for the second set of layer(s) and out of two sets of selected delay vectors at least G delay vectors are orthogonal to each other. In another example, the UE is configured to select an identical number of delay vectors for both sets of layers and at least G delay vectors are orthogonal to each other. The parameter G may be configured by the gNB, or reported by the UE, or fixed and known at the UE.

CLAIMS

1. A method performed by a User Equipment, UE, the method comprising:

- receiving from a network node, a radio signal via a Multiple Input Multiple Output, MIMO, channel, wherein the radio signal contains at least one DownLink, DL, reference signal according to a DL reference signal configuration;

- estimating said MIMO channel based on said received at least one DL reference signal for configured resource blocks;

- calculating a precoding matrix for a number of antenna ports of the network node and configured subbands; the precoding matrix being based on a first codebook and on a second codebook and a set of combination coefficients for complex scaling/combining one or more of vectors selected from the first codebook and the second codebook, wherein the first codebook contains one or more transmit-side spatial beam components/vectors of the precoding matrix and the second codebook contains one or more delay components/vectors of the precoding matrix;

- receiving from said network node a higher layer configuration comprising indicating a subset of beam vectors from the first codebook and a maximum allowable average amplitude value per beam vector for restricting the average amplitude, or power, of the combining coefficients associated with the beam vector; and

- reporting, to the network node, a Channel State Information, CSI, feedback and/or a Precoder matrix Indicator, PMI and/or a PM I/Rank Indicator, PMI/RI, used to indicate the precoding matrix for the configured antenna ports and subbands, wherein the report contains a bitmap for indicating at least selected delay vectors and spatial beam vectors

associated with the non-zero combining coefficients of said set of combination coefficients.

2. The method according to claim 1 wherein the precoding matrix,

of a Fth transmission layer is represented by a

double sum notation for a first polarization of the antenna ports,

and for a second polarization of the antenna ports,

wherein (u = 0, ..., U(l) — 1) representing U(l) selected beam

components or Discrete Fourier Transform, DFT-based beam vectors selected from the first codebook for antenna ports, where N1 and N2 refer to the number of antenna ports of a same polarization in a first and second dimension of an antenna array of the network node, respectively,

( d = 0, ... ,D(l) — 1) representing D(l) selected delay components

or Discrete Fourier Transform, DFT-based delay vectors for the u-th beam selected from the second codebook, wherein the number of DFT-based delay vectors D(l) is identical for all the beams, are the complex

combining coefficients associated with the U(l) selected beam vectors and D(l) selected delay vectors, and α(l) is a normalizing scalar.

3. The method according to claim 1 or claim 2 further comprising reporting K or less than K non-zero combining coefficients per layer, and K or less than K non-zero combining coefficients for all layers.

4. The method according to claim 3 wherein the parameter K is received from the network node via RRC, and the parameter is priori known by the UE.

5. The method according to claim 3 wherein the bitmap contains K or less than K number of “1”s per layer.

6. The method according to anyone of claims 1-5 wherein a bit value 1 in the bitmap indicates that the non-zero combining coefficient with associated vectors selected from the first and second codebooks is reported, and a bit value 0 indicates that the corresponding combining coefficient is not reported.

7. The method according to claim 1 wherein the maximum allowable average amplitude value wz for a z-th beam vector in the subset of beam vectors from the first codebook restricts the average amplitude, or power, of the associated combining coefficients of a l-th layer by

8. The method according to claim 1 or claim 7 comprising indicating beam vectors in the subset of beam vectors and the maximum allowable average amplitude value per beam vector by a bitmap B, wherein the bitmap B comprises two parts, a first bitmap part Bi and a second bitmap part Bå, wherein B = B1B2.

9. The method according to claim 8 wherein the first bitmap part B1 indicates G beam groups (g = 1, .., G), where each beam group comprises R beam vectors.

10. The method according to claim 8 wherein the second bitmap part B2 is defined by a RNB -length bit sequence r = 0, ... , R -

1,

where is a bit sequence of length NB

indicating the maximum allowed average amplitude value wgr for the r-th beam vector in the g-th beam group in the subset of beam vectors.

11. The method according to claim 10 wherein a mapping of bits to
a maximum allowable average amplitude for NB = 2 is given by:

12. The method according to claim 9 wherein each of the G beam groups indicated by the first bitmap group B1 comprises N1N2 orthogonal DFT beam vectors selected from the first codebook where the indices of the beam vectors of the g-th beam group are defined by the index set:

where for

denotes the beam group index indicated by the first bitmap part B1.

13. The method according to claim 2 comprising receiving from the network node, via higher layer signaling, a configuration, including the parameter U(l), indicating the number of spatial beam vectors, and the parameter D(l) indicating the number of delay vectors.

14. The method according to claim 13 wherein the parameter D(l) depends on a configured codebook size (N3) of the second codebook and is given by D(l) = pN3, where parameter p ≤ 1 controls the feedback overhead, and wherein the parameter p is received from the network node via higher layer signaling.

15. The method according to claim 3 and claim 13 wherein the parameter K is given by K = β2D(l)U(l) where the parameter β ≤ 1 controls the feedback overhead, and the parameter β is configured via higher layer signaling.

16. The method according to claim 1 wherein the report is transmitted in an uplink control information in a physical uplink control channel, and wherein the report comprises two parts including a first part and a second part and wherein the first part has a fixed payload size and contains at least a parameter indicating a number of non-zero combining coefficients for all layers.

17. The method according to claim 16 wherein the second part includes a first precoding matrix identifier and a second precoding matrix identifier, wherein the first precoding matrix identifier contains a number of selected spatial beam indices for a selected subgroup from the first codebook and selected subgroup of indices per layer.

18. The method according to claim 17 wherein the first precoding matrix identifier contains a number of delay identifiers indicating common delay vectors selected by the UE and the bitmap indicating indices of selected non-zero combining coefficients K1 per layer.

19. The method according to claim 16 comprising reporting the strongest coefficient indicator which indicates the position of the strongest combining coefficient associated with a stronger polarization per layer, and a polarization-specific common amplitude value which is associated with the combining coefficients of the weaker polarization per layer.

20. The method according to claim 17 wherein the second matrix identifier contains K1 — 1 phase values and K1 — 1 amplitude values per layer for all layers.

21. The method according to anyone of claim 1 or claim 2 comprising quantizing and reporting the combining coefficients per beam of the

precoding matrix, wherein each combining coefficient is a product of

three coefficients al,p,i, bl,p,i,j and dl,p,i,j and is given by:

where al,p,i is a real-valued coefficient representing a common amplitude across all combining coefficients associated with a /-th beam, p-th polarization and l-th layer, bl,p,i,j is a real-valued normalized combining- coefficient representing the amplitude associated with the /-th beam, y-th delay vector, p-th polarization and /-th layer, and n ∈

{0,1, ... , 2N — 1 }, N ∈ {1,2, 3, 4} is a coefficient to indicate the phase of

22. The method according to claim 1 or claim 2 comprising quantizing and reporting the combining coefficients per beam of the precoding matrix, wherein each combining coefficient is a product of three coefficients

ci,p,j , bl,p,i,j and dl,p,i,j,

where cl,p,j is a polarization-dependent real-valued coefficient representing a common amplitude across all combining coefficients associated with the j-th delay vector and l- th layer, bl,p,i,j is a real-valued normalized combining-coefficient representing the amplitude associated with the /-th beam, y-th delay vector, p-th polarization and l-th layer, and
n ∈ (0,1, ..., 2N — 1 }, N ∈ {1,2, 3, 4} is a coefficient to indicate

the phase of

23. The method according to claim 1 or claim 2 comprising quantizing and reporting the combining coefficients per beam of the precoding matrix,

wherein each combining coefficient is a product of three coefficients al,p,i bl,p,i,j and dl,p,i,j, and is given by:

where al,p,i is a polarization-specific real-valued coefficient representing a common amplitude across all combining coefficients associated with the p- th polarization and l-th layer, bl,p,i,j is a real-valued normalized combining- coefficient representing the amplitude associated with the i-th spatial beam vector, j-the delay vector, p-th polarization and Z-th layer, and
n ∈ {0,1, ..., 2W 1 l},N ∈ {0,1, 2, 3, 4} is a coefficient to indicate

the phase of

24. The method according to claim 21 or claim 23 wherein the quantization of the amplitudes al,p,i is identical for all combining coefficients of a layer.

25. The method according to anyone of claims 21-23 wherein the quantization of the amplitudes bl,p,i,j is identical for all combining coefficients of a layer.

26. The method according to claim 22 wherein the quantization of the amplitudes cl,p,j is identical for all combining coefficients of a layer.

27. The method according to claim 21 or claim 23 wherein the amplitudes al,p,i are partitioned, per layer, into at least two disjoint subsets, and each subset is assigned a single and different value for said quantization.

28. The method according to claim 27 wherein each subset contains the amplitudes al,p,i with respect to a single polarization.

29. The method according to claim 22 wherein the amplitudes cl,p,j· are partitioned, per layer, into at least two disjoint subsets, and each subset is assigned a single and different value for said quantization.

30. The method according to claim 29 wherein each subset contains the amplitudes cl,p,j with respect to a single polarization.

31. The method according to claim 27 wherein the amplitudes al,p,iof the first set contains the strongest amplitude and is quantized with 0 bits and not reported, and the amplitudes al,p,i of the second set are quantized with N=1 or 2 or 3 or 4 bits and reported.

32. The method according to claim 29 wherein the amplitudes cl,p,j of the first set contains the strongest amplitude and is quantized with 0 bits and not reported, and the amplitudes Cl,p,j of the second set are quantized with N=1 or 2 or 3 or 4 bits and reported.

33. The method according to claim 21 or claim 23 wherein al,p,i is quantized with 2, 3 or 4 bits, and the amplitude set is given by
and for x = 4, F = 1 and N = 4, the

amplitude set is given by

34. The method according to anyone of claims 21-23 comprising partitioning the amplitudes bl,p,i,j, per layer, into at least two disjoint subsets per layer and each subset is assigned a single value for quantization of the amplitudes bl,p,i,j.

35. The method according to claim 34 wherein the first set of said distinct subsets contains the amplitudes bl,p,i,j, corresponding to a number less or equal of K selected non-zero combining coefficients, indicated by the bitmap, and the second set contains the remaining amplitude coefficients.

36. The method according to claim 35 wherein the amplitudes of the first set are quantized with N=2, or 3 bits and reported, and the amplitudes of the second set are quantized with 0 bits and not reported.

37. The method according to anyone of claims 21-23 wherein quantization of phases dl,p,i,j is identical for all combining coefficients using a single value for a l-th layer, wherein the single value is known to the UE and is identical for all layers.

38. The method according to anyone of claims 21-23 comprising partitioning the phases dl,p,i,j into at least two disjoint subsets, per layer, and each subset is assigned a single value for phase quantization.

39. The method according to claim 38 wherein the first set contains the phases corresponding to a number less or equal of K selected non-zero combining coefficients, indicated by the bitmap, and the second set contains the remaining phases, and wherein the phases of the first set are quantized with N=2 or 3 or 4 bits and reported, and the phases of the second set are quantized with 0 bits and not reported.

40. The method according to claim 34 and 39 wherein the bitmap is used to indicate reported phases from the first set and second set and wherein the same bitmap is used for indicating the amplitudes bl,p,i,j of the first set and the second set.

41. The method according to anyone of claims 21-23 comprising quantizing the amplitudes bl,p,i,j or a subset of the amplitudes with N bits, wherein the amplitude set is given by and is represented

by log2(F + 1) = N bits, where F = 2N - 1, N=3 and x ∈ {1,2,3, ... } is a parameter that controls the amplitude level size.

42. The method according to claim 21 or claim 23 comprising normalizing the amplitudes al,p,iand reporting the amplitudes al,p,i except for the strongest amplitude.

43. The method according to claim 22 comprising normalizing the amplitudes Cl,p,j and reporting the amplitudes cl,p,j except for the strongest amplitude.

44. A method performed by a network node the method comprising:

- transmitting to a User Equipment, UE, a radio signal via a Multiple Input Multiple Output, MIMO, channel, wherein the radio signal contains at least one DownLink, DL, reference signal according to a DL reference signal configuration;

- receiving from the UE a report including a Channel State Information, CSI, feedback and/or a Precoder Matrix Indicator, PMI and/or a PM I/Rank Indicator, PMI/RI, used to indicate a precoding matrix for configured antenna ports and configured subbands, the precoding matrix being based on a first codebook and on a second codebook and a set of combination coefficients for complex scaling/combining one or more of vectors selected from the first codebook and the second codebook, wherein the first codebook contains one or more transmit-side spatial beam components/vectors of the precoding matrix and the second codebook contains one or more delay components/vectors of the precoding matrix;

- configuring the UE with a higher layer configuration comprising a subset of beam vectors from the first codebook and a maximum allowable average amplitude value per beam vector for restricting the average amplitude, or power, of the combining coefficients associated with the beam vector;

and wherein the report contains a bitmap for indicating at least selected delay vectors and spatial beam vectors associated with the non-zero combining coefficients of said set of combination coefficients.

45. The method according to claim 44 wherein the precoding matrix,

of a l-th transmission layer is represented by a

double sum notation for a first polarization of the antenna ports,

and for a second polarization of the antenna ports,

wherein representing t/® selected beam

components or Discrete Fourier Transform, DFT-based beam vectors selected from the first codebook for N1N2 antenna ports, where N1 and N2 refer to the number of antenna ports of a same polarization in a first and second dimension of an antenna array of the network node, respectively, representing D(l) selected delay components

or Discrete Fourier Transform, DFT-based delay vectors for the u-th beam selected from the second codebook, wherein the number of DFT-based delay vectors D® is identical for all the beams, are the complex

combining coefficients associated with the U(l) selected beam vectors and D(l) selected delay vectors, and α(l) is a normalizing scalar

46. The method according to claim 44 or claim 45 comprising receiving K or less than K non-zero combining coefficients per layer, and K or less than K non-zero combining coefficients for all layers.

47. The method according to claim 46 wherein the parameter K is transmitted to the UE via RRC or physical layer.

48. The method according to claim 44 or claim 45 comprising configuring the UE with the parameter U(l), indicating the number of spatial beam vectors, and with the parameter D® indicating the number of delay vectors via higher layer signaling.

49. The method according to claim 48 wherein the parameter D(l) depends on a configured codebook size (N3) and is given by D(l) = pN3, where parameter p £ 1 controls the feedback overhead, and wherein the parameter p is transmitted to the UE via higher layer signaling.

50. The method according to claim 47 and claim 48 wherein the parameter K is given by K = β2D(l)U(l) where the parameter β £ 1 controls the feedback overhead, and the parameter b is transmitted to the UE via higher layer signaling.

51. The method according to claim 44 comprising receiving the report in an uplink control information in a physical uplink control channel, and wherein the report comprises two parts including a first part and a second part and wherein the first part has a fixed payload size and contains at least a parameter indicating values of non-zero combining coefficients per layer.

52. A User Equipment, UE, (900) comprising a processor (910) and a memory (920), said memory (920) containing instructions executable by said processor (920) whereby said UE (900) is operative to perform any one of the subject-matter of method claims 1-43.

53. A network node (800) comprising a processor (810) and a memory (820), said memory (820) containing instructions executable by said processor (810) whereby said network node (800) is operative to perform any one of the subject-matter of method claims 44-51.