Codebook design for extremely large antenna arrays

Abstract

The present invention discloses a method of communication in a cellular network wherein the method comprises receiving a configuration of at least one of a set of first linear vectors, a set of first non-linear vectors, a set of second linear vectors and a set of second non-linear vectors from the base station (BS), determining a set of first basis vectors based on at least one first linear vector and at least one first non-linear vector, determining a set of second basis vectors based on at least one second linear vector and at least one second non-linear vector, determining a set of third basis vectors based on at least one of the first basis vectors and at least one of the second basis vectors, determining a set of complex weights, reporting the set of third basis vectors to at least one BS and reporting the set of complex weights to at least one BS.

Description

CODEBOOK DESIGN FOR EXTREMELY LARGE ANTENNA ARRAYS FIELD OF INVENTION

[0001] The present invention generally relates to Codebook design for extremely large antenna arrays. More specifically, the present invention is related to methods for determining precoder structure for very large number of CSI-RS (Channel State Information Reference Signal) transmission ports. BACKGROUND OF THE INVENTION

[0002] The subject matter discussed in the background section should not be assumed to be prior art merely as a result of its mention in the background section. Similarly, a problem mentioned in the background section or associated with the subject matter of the background section should not be assumed to have been previously recognized in the prior art. The subject matter in the background section merely represents different approaches, which in and of themselves may also correspond to implementations of the claimed technology.

[0003] In a wireless technology, the downlink (DL) channel state information (CSI) is required at the base station (BS) to make an effective transmission to a user equipment (UE). In 5G new radio (NR) technology, a framework is adopted by the specification such that the DL CSI is acquired by the BS from the UE through a feedback channel in the uplink (UL). Based on the received CSI, the BS schedules resources for a UE appropriately. In 5G NR, the CSI consists of information such as precoding matrix indicator (PMI), Rank Indicator (RI), Layer Indicator (LI), channel quality indicator (CQI) etc. The PMI field in the CSI indicates to the BS an appropriate precoder matrix that could be used for transmission of data in the PDSCH. The UE selects a precoder BS based on the estimated channel using the CSI- reference signal (RS) for reporting to the BS such that the precoder enhances the effective channel gain. The best precoder selected by the UE is derived from a codebook that is configured by the BS.

[0004] Codebook design in 5G is a critical part of optimizing beamforming techniques, allowing the network to dynamically direct radio waves efficiently to improve connectivity, capacity, and coverage. The codebook is essentially a set of predefined beamforming patterns that guide how antennas in the base station or user equipment should transmit and receive signals. Efficient codebook design is necessary to meet the high demands of 5G, especially in scenarios with massive MIMO antennas and high-frequency bands.

[0005] In NR, a codebook comprises of a set of precoder matrices and they are derived based on oversampled DFT vectors. In this specification, the terms DFT vectors and beams are used interchangeably. 3GPP has introduced multiple precoder structures in Release 15 i.e., Type-1 Single-panel codebook, Type-1 Multi-panel codebook, Type-2 codebook and Type-2 Port selection codebook. Type-1 Single-panel codebook has a simpler structure and smaller performance gain compared to Type-2 codebook which has a more complex structure and gives higher performance gain. Type-2 CSI provides channel information with significantly higher granularity compared to Type-1 CSI. This higher granularity of the PMI feedback comes at a cost of a significantly higher feedback overhead.

[0006] Construction of a Release 15 Type-2 precoder depends on several variables such as number of CSI-RS ports, number of beams, over-sampling factors etc. All these parameters are configured to the UE by the BS via RRC signalling. The number of CSI-RS ports is derived by the UE based on the formula2^^1^^2, where BS configures^^1and^^2to the UE using the higher layer parameter n1-n2-codebookSubsetRestriction. UE obtains the over-samplingfactors (^^1, ^^2) based on the configured ^^1 and ^^2 values from the Table 5.2.2.2.1-2 specifiedin TS 38.214 document. Based on these ^^1, ^^2, ^^1and ^^2values, the UE forms a beam-grid that consists of ^^1^^2^^1^^2beams. Each beam in the beam-grid is represented by an over- sampled 2D-DFT vector.

[0007] Fig. 1 of the present invention illustrates an embodiment of beam grid as per theprior art. It shows a beam-grid for (^^1, ^^2) = (2,2) and (^^1, ^^2) = (4,4). As shown in thefigure, the total number of beams present in the beam-grid is ^^1 ∗ ^^2 ∗ ^^1 ∗ ^^2. Each beam inthe beam-grid is represented asand ^^ ∈ {0, .. , ^^1^^1 − 1} and ^^ ∈ {0, .. , ^^2^^2 − 1}.

[0008] For the purposes of the present specification ^^^^,^^is represented as the transpose of Kronecker product of two vectors ^^^^and ^^^^i.e.,^^^^,^^ = (^^^^ ⊗ ^^^^)^^…………………………………………………………………….(2) where,andTwo beams ^^^^1,^^1 and ^^^^2,^^2 are considered as a set of orthogonal beams if (^^2 − ^^1) is aninteger multiple of ^^1&(^^2is an integer multiple of ^^2. A beam set is defined as a set of beams in which each beam in the beam set is orthogonal to any other beam in the beam set. A beam-grid of ^^1^^2^^1^^2beams comprises of ^^1^^2beam-sets and each beam-set comprises of ^^1^^2beams.

[0009] A R15 Type-2 precoder is constructed as a weighted linear combination of L number of orthogonal beams where the value of L is configured to the UE with the higher layerparameter numberOfBeams, where ^^ = 2 when ^^^^^^^^−^^^^ = 4 and ^^ ∈ {2, 3, 4} when ^^^^^^^^−^^^^ >4. The mathematical representation of the Type-2 precoder represented as a linear combination of L beams is shown below:……………………………..(3) Where ^̅^ represents a beamand ^^^^represents a complex coefficient corresponding beam ^̅^^^. The R15 specification facilitates the UE to signal Type-2 precoder per each sub-band of the reporting bandwidth. This is achieved by reporting different complex coefficients for each sub-band in spite of using the same set of L beams for each sub-band.

[0010] The R15 Type-2 precoder can be represented in matrix form as below:^^ = ^^1^^2 ………………………………………………………………………………..(4)Where ^^1, also referred to as spatial domain (SD) basis, captures the long-term variations in the channel and ^^2captures the short-term variations in the channel. In Rel-15 Type-II precoder, the SD basis is the same for all sub-bands and all layers. ^^1matrix contains the beams and ^^2matrix contains the complex coefficients that are used for construction of the Type-2 precoder respectively.Hence, the R15 Type-2 precoder for N sub-bands and layer l is represented as below in matrix form:

[0011] Even though Type-2 CSI provides more channel information, this comes with a price of higher reporting overhead since more information bits are required for feedback. Hence, in Release 16 of NR, enhancements have been made to the R15 Type-2 codebook to reduce the CSI feedback overhead. This reduction in feedback overhead was achieved in R16 Type-2 CSI by applying frequency domain compression. The correlation among the coefficients in ^^2can be exploited and used for compression. In R16 Type-2 CSI, DFT vectors are used for the compression of ^^2coefficients. The UE compresses the elements in ^^2matrix using M DFT vectors and reports back to the BS the vectors used for compression and the complex coefficients for each of the DFT vectors. The value of M is configured by the BS to the UE based on the channel conditions.

[0012] As per equation (5), the Type-2 precoder is reported for N sub-bands and the precoder is constructed as a weighted linear combination of L beams, where the value of L isconfigured to the UE by the higher layer parameter paramCombination-r16 such that ^^ ∈{2,4,6}. In this case, the number of coefficients in ^^2matrix is 2L*N. By exploiting the correlation among the coefficients across sub-bands, ^^2can be compressed and it can be represented as:In the above equation, ^^^^, also referred to as frequency domain (FD) basis, consists of M DFT vectors used for the compression of ^^2matrix and ^̃^2consists of the compressed complex coefficients. The M DFT vectors are selected from a N-Point DFT matrix, where N represents number of sub-bands for which the precoder is being reported for. Hence, the R16 Type 2 codebook can be represented as:^^ = ^^1^̃^2^^^^^^………………………………………………….(7)

[0013] In R16, support for transmissions to a single device from multiple transmission reception points (TRPs) is introduced. Two types of M-TRP transmissions were introduced in NR viz., Non-coherent joint transmission (NCJT) introduced in R16 and coherent joint transmission (CJT) introduced in R18. One main difference between NCJT and CJT is that, in NCJT different layers are transmitted to the UE from different TRPs. Since the layers that are transmitted from different TRPs are different, there is no need for the BS to get the channel feedback for the channel combined across all the coordinating TRPs. Hence, in NCJT, a precoder is selected and reported to the BS such that the precoder for one TRP is selected independently of the channel of other coordinating TRPs.

[0014] The disadvantage of NCJT transmission is due to separate layers being transmitted from different TRPs. Hence in NCJT, the entire channel gain is not exploited as the precoders are selected independently of the coordinating TRPs. The main challenge in exploiting the entire channel gain is to introduce a new CSI feedback framework that combines the channel across TRPs in a coherent fashion. In R18 of NR, a CJT CSI feedback framework was introduced in which the precoder is selected based on the channel combined across all the coordinating TRPs. For the Rel-18 Type-2 codebook for CJT mTRP, two modes of PMI reporting are supported.

[0015] Mode 1 allows independent SD basis selection and independent FD basis selection. The precoder is represented as shown below:Mode 2 allows only independent SD basis selection whereas FD basis is selected commonly across all the TRPs. The precoder is represented as shown below:Therefore, there remains a need for better CSI feedback framework for exploitation of channel gain.SUMMARY OF THE INVENTION

[0016] This summary is provided to introduce aspects related to a method for signaling by determining precoder structure for very large number of CSI-RS (Channel State Information Reference Signal) transmission ports and the aspects are further described below in the detailed description. This summary is not intended to identify essential features of the claimed subject matter nor is it intended for use in determining or limiting the scope of the claimed subject matter.

[0017] In an embodiment of the present disclosure, a method for wireless communications at a user equipment (UE) is disclosed which comprises receiving, by the UE, a configuration of at least one of a set of first linear vectors, a set of first non-linear vectors, a set of second linear vectors and a set of second non-linear vectors from the base station (BS); determining, by the UE, a set of first basis vectors based on at least one first linear vector and at least one first non-linear vector; determining, by the UE, a set of second basis vectors based on at least one second linear vector and at least one second non-linear vector; determining, by the UE, a set of third basis vectors based on at least one of the first basis vectors and at least one of the second basis vectors; determining, by the UE, a set of complex weights; reporting, by the UE, the set of third basis vectors to at least one BS; and reporting, by the UE, the set of complex weights to at least one BS.

[0018] In another embodiment of the present disclosure, each complex weight corresponds to third basis vector in the reported set of third basis vectors.

[0019] In yet another embodiment, the set of third basis vectors is reported using the associated indices of the first linear vector, the first non-linear vector, the second linear vector and the second non-linear vector.

[0020] In another embodimentthe third basis vector (^̃^^^) is obtained by the UE as a Kronecker product of one of at least one first basis vector and at least one second basis vector or at least one second basis vector and at least one first basis vector.

[0021] In another embodiment, the first basis vector is obtained by the UE as the element-wise multiplication of at least one first linear vector and at least one first non-linear vector.

[0022] In another embodiment, the first linear vector is obtained by the UE based on at least one of number of antenna elements in the first dimension of an antenna panel (^^1) and an oversampling factor (^^1).

[0023] In another embodiment, the first linear vector is a DFT based vector.

[0024] In another embodiment, the first non-linear vector is obtained by the UE based on at least one of number of antenna elements in the first dimension of an antenna panel (^^1), an oversampling factor (^^1), a function of the antenna spacing in the first dimension of the antenna panel and an additional parameter ^^1.

[0025] In another embodiment, a set of ^^1values are configured to the UE by the BS.

[0026] In another embodiment, a set of ^^1values is obtained by the UE as ^^1uniformly sampled values within a range ^^1,^^^^^^and ^^1,^^^^^^.

[0027] In another embodiment, at least one of ^^1,^^^^^^, ^^1,^^^^^^and ^^1are configured to the UE by the BS.

[0028] In another embodiment, ^^1,^^^^^^and ^^1,^^^^^^are obtained by the UE as a function of at least one of ^^1, ^^1,1, ^^2,1and ^^1.

[0029] In another embodiment, at least one of ^^1,1, ^^2,1and ^^1are configured to the UE by the BS.

[0030] In another embodiment, ^^1,1and ^^2,1are obtained by the UE based on the antenna spacing in the first dimension of the antenna panel.

[0031] In another embodiment, the second basis vector is obtained by the UE as the element-wise multiplication of at least one second linear vector and at least one second non- linear vector.

[0032] In another embodiment, the second linear vector is obtained by the UE based on at least one of number of antenna elements in the second dimension of the antenna panel (^^2) and an oversampling factor (^^2).

[0033] In another embodiment, the second linear vector is a DFT based vector.

[0034] In another embodiment, the second non-linear vector is obtained by the UE based on at least one of number of antenna elements in the second dimension of the antenna panel (^^2), an oversampling factor (^^2), a function of the antenna spacing in the second dimension of the antenna panel and an additional parameter ^^2.

[0035] In another embodiment, a set of ^^2values are configured to the UE by the BS.

[0036] In another embodiment, a set of ^^2values is obtained by the UE as ^^2uniformly sampled values within a range ^^2,^^^^^^and ^^2,^^^^^^.

[0037] In another embodiment, at least one of ^^2,^^^^^^, ^^2,^^^^^^and ^^2are configured to the UE by the BS.

[0038] In another embodiment, ^^2,^^^^^^and ^^2,^^^^^^are obtained by the UE as a function of at least one of ^^2, ^^1,2, ^^2,2and ^^2.

[0039] In another embodiment, at least one of ^^1,2, ^^2,2and ^^2are configured to the UE by the BS.

[0040] In another embodiment, ^^1,2and ^^2,2are obtained by the UE based on the antenna spacing in the second dimension of the antenna panel.

[0041] In an embodiment of the present invention, a method for wireless communications at a user equipment (UE), is disclosed and comprises receiving, by the UE, a configuration of first basis vectors from a base station (BS); determining, by the UE, a first set of first basis vectors corresponding to at least one sub-panel; determining, by the UE, at least one of a first set of complex weights corresponding to at least one sub-panel and a set of third sets of transformed complex weights; reporting, by the UE, the determined first set of first basis vectors to at least one BS; and reporting, by the UE, at least one of determined first set of complex weights and a set of third sets of transformed complex weights to the base station.

[0042] In another embodiment, a complex weight in the first set of complex weight corresponds to at least one sub-panel.

[0043] In another embodiment, the first set of first basis vectors is reported by signalling at least one of a first set of indices and a second set of indices.

[0044] In another embodiment, the number of sub-panels is dependent upon total number of transmission ports and number of transmission ports within a sub-panel.

[0045] In another embodiment, the sub-panel is associated with a sub-panel index.

[0046] In another embodiment, the association between at least one sub-panel and at least one transmission port is configured to the UE by the BS.

[0047] In another embodiment, a complex weight in the first set of complex weights corresponds to at least one of the first basis vector in the first set of first basis vectors and a sub-panel index.

[0048] In another embodiment, determining a first set of first basis vectors corresponding to a sub-panel comprises determining, by the UE, a set of common first basis vectors based on the first set of indices; determining, by the UE, a subset of second set of indices corresponding to the sub-panel; determining, by the UE, a set of separate first basis vectors corresponding to the sub-panel based on the subset of second set of indices; and determining, by the UE, the first set of first basis vectors corresponding to the sub-panel as the union of the set of common first basis vectors and the set of separate first basis vectors.

[0049] In another embodiment, determining a first set of first basis vectors corresponding to a sub-panel comprises determining, by the UE, the first set of first basis vectors corresponding to the reference sub-panel based on the first set of indices; determining, by the UE, a first set of beam pair indices by generating a beam pair index (^^1,^^^^^^,^^2,^^^^^^) for each element in the first set of indices; determining, by the UE, a subset of second set of indices corresponding to the sub-panel; determining, by the UE, a second set of beam pair indices by generating a beam pair index (^^ ^^^^^^^^^^^^ ^^^^^^^^^^^^ 1,^^,^^2,^^) for each element in the determined subset of second set of indices; determining, by the UE, a third set of beam pair indices corresponding to the sub-panel based on the first set of beam pair indices and the second set of beam pair indices; determining, by the UE, a third set of indices based on the determined third set of beam pair indices; and determining, by the UE, the first set of first basis vectors corresponding to the sub-panel based on the third set of indices corresponding to the sub-panel.

[0050] In another embodiment, the third set of beam pair indices corresponding to a sub-panel are determined by the UE as the sum of the first set of beam pair indices and the second set of beam pair indices.

[0051] In another embodiment, each element in the second set of indices is obtained by the UE based on a set of offset pairs (^^ ^^^^^^^^^^^^ ^^^^^^^^^^^^ 1 ,^^2) configured to the UE by the BS.

[0052] In another embodiment, determining the set of third sets of transformed complex weights comprises configuring, by the BS to the UE, a set of second basis vectors for transforming the first set of complex weights; determining, by the UE, a set of second sets of complex weights wherein the second set of complex weights corresponds to a first basis vector in the first set of first basis vectors; determining, by the UE, a subset of second basis vectors; determining, by the UE, a set of third sets of transformed complex weights wherein the third set of transformed complex weights are determined based on a second set of complex weights and the subset of second basis vectors; and reporting, by the UE to the BS, the set of third sets of transformed complex weights and the subset of second basis vectors.

[0053] In an embodiment of the present invention, a method for wireless communications at a user equipment (UE), is disclosed which comprises determining, by the UE, plurality of cluster of basis vectors wherein the cluster is a set of basis vectors; determining, by the UE, a set of complex weights; and reporting, by the UE to the BS, the plurality of cluster of basis vectors and a set of complex weights.

[0054] In another embodiment, the basis vector in the cluster is obtained by the UEusing at least one of a reference basis vector and the size of the cluster.

[0055] In another embodiment, reporting the plurality of cluster of basis vectors comprises reporting the index of the reference basis vector corresponding to the cluster and the size of the cluster corresponding to the cluster.

[0056] In another embodiment, the complex weight in the set of complex weights corresponds to at least one cluster of first basis vectors and a layer index of the precoder.

[0057] In another embodiment, number of beams in a cluster ^^ is defined by the size of the cluster ^^^^.

[0058] In another embodiment,is the product of ^^^^,1and ^^^^,2wherein ^^^^,1is obtained by the UE from a configured set of ^^^^,1values and ^^^^,2is obtained by the UE from a configured set of ^^^^,2values.

[0059] In another embodiment, ^^^^,1and ^^^^,2are the sizes of the cluster ^^ in the firstdimension of the antenna panel and the second dimension of the antenna panel, respectively.

[0060] Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The accompanying drawings constitute a part of the description and are used to provide a further understanding of the present invention.

[0062] Fig.1 illustrates an embodiment of beam grid as per the prior art.

[0063] Fig.2 illustrates an example of a wireless network according to an embodiment of the present invention;

[0064] Fig. 3 illustrates an antenna panel sub-panel according to an embodiment of the present invention;

[0065] Fig.4 illustrates a flow chart describing the method for determination of a precoder in accordance with an embodiment of the present invention;

[0066] Fig. 5 illustrates a flow chart for describing a method to signal the ^^1^^matrix in accordance with an embodiment of the present invention;

[0067] Fig.6 illustrates a flow chart for describing a method for offset based signalling in accordance with an embodiment of the present invention;

[0068] Fig.7 illustrates a flow chart for describing a method of signalling in accordance with an embodiment of the present invention;

[0069] Fig.8 illustrates a flow chart for describing a method of determination of a precoder in accordance with an embodiment of the present invention;

[0070] Fig. 9 illustrates a linear antenna array setup at a BS communicating to a UE in accordance with an embodiment of the present invention;

[0071] Fig. 10 illustrates a flow chart for describing a method wherein the current NR codebooks are extended in accordance with an embodiment of the present invention;

[0072] A more complete understanding of the present invention and its embodiments thereof may be acquired by referring to the following description and the accompanying drawings. DETAILED DESCRIPTION OF THE INVENTION

[0073] Exemplary embodiments now will be described with reference to the accompanying drawings. The disclosure may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. The terminology used in the detailed description of the particular exemplary embodiments illustrated in the accompanying drawings is not intended to be limiting. In the drawings, like numbers refer to like elements.

[0074] It is to be noted, however, that the reference numerals used herein illustrate only typical embodiments of the present subject matter, and are therefore, not to be considered for limiting its scope, for the subject matter may admit to other equally effective embodiments.

[0075] The specification may refer to “an”, “another”, “one” or “some” embodiment(s) in several locations.

[0076] This does not necessarily imply that each such reference is to the same embodiment(s), or that the feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments.

[0077] As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms “includes”, “comprises”, “including” and / or “comprising” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. Furthermore, “connected” or “coupled” as used herein may include operatively connected or coupled. As used herein, the term “and / or” includes any and all combinations and arrangements of one or more of the associated listed items.

[0078] The phrases “in one embodiment,” “according to one embodiment,” “in some embodiments,” and the like generally mean that the particular feature, structure, or characteristic following the phrase may be included in at least one embodiment of the present disclosure, and may be included in more than one embodiment of the present disclosure (importantly, such phrases do not necessarily refer to the same embodiment).

[0079] The word “example” or “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any implementation described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other implementations.

[0080] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure pertains. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0081] Although various arrow types and line types may be employed in the flowchart and / or block diagrams, they are understood not to limit the scope of the corresponding embodiments. Indeed, some arrows or other connectors may be used to indicate only the logical flow of the depicted embodiment. For instance, an arrow may indicate a waiting or monitoring period of unspecified duration between enumerated steps of the depicted embodiment. It will also be noted that each block of the block diagrams and / or flowchart diagrams, and combinations of blocks in the block diagrams and / or flowchart diagrams, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and code.

[0082] As used herein, the terms “user equipment” (UE) and “base station” are not intended to be specific or otherwise limited to any particular radio access technology (RAT), unless otherwise noted. In general, a UE may be any wireless communication device (e.g., a mobile phone, router, tablet computer, laptop computer, tracking device, wearable (e.g., smartwatch, glasses, augmented reality (AR) / virtual reality (VR) headset, etc.), vehicle (e.g., automobile, motorcycle, bicycle, etc.), Internet of Things (IoT) device, etc.) used by a user to communicate over a wireless communications network. A UE may be mobile or may (e.g., at certain times) be stationary, and may communicate with a radio access network (RAN). Generally, UEs can communicate with a core network via a RAN, and through the core networkthe UEs can be connected with external networks such as the Internet and with other UEs. Of course, other mechanisms of connecting to the core network and / or the Internet are also possible for the UEs, such as over wired access networks, wireless local area network (WLAN) networks (e.g., based on IEEE 802.11, etc.) and so on.

[0083] A base station may operate according to one of several RATs in communication with UEs depending on the network in which it is deployed, and maybe alternatively referred to as an access point (AP), a network node, a NodeB, an evolved NodeB (eNB), a New Radio (NR) Node B (also referred to as a gNB or gNodeB), etc.

[0084] The detailed description includes specific details for the purpose of providing a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.

[0085] Fig. 2 illustrates an example of a wireless network 200, in accordance with the present disclosure. The wireless network 200 may be or may include elements of a 5G (e.g., NR) network. The wireless network 200 may include one or more network nodes 210 (shown as a network node 210a, a network node 210b), a user equipment (UE) 220 or multiple UEs 220 (shown as a UE 220a, a UE 220b, a UE 220c), and / or other entities. A network node 210 is a network node that communicates with UEs 220. As shown, a network node 210 may include one or more network nodes. In the example shown in Fig. 2, the network node 210a may be a macro network node for a macro cell 202a. A network controller 230 may couple to or communicate with a set of network nodes 210 and may provide coordination and control for these network nodes 210. The network controller 230 may communicate with the network nodes 210 via a backhaul communication link or a midhaul communication link. The network nodes 210 may communicate with one another directly or indirectly via a wireless or wireline backhaul communication link. In some aspects, the network controller 230 may be a CU or a core network device, or may include a CU or a core network device. In some aspects, a network node 210 (e.g., a radio unit) may include a communication manager 240. The communication manager 240 may output capability information regarding a number of beamforming codebooks supported by the radio unit; obtain configuration information that configures one or more beamforming codebooks for an antenna array of the radio unit; and communicate using the one or more beamforming codebooks.

[0086] A CSI report consists of multiple fields such as CQI (Channel Quality Indicator), PMI (Precoding Matrix Indicator), RI (Rank Indicator), LI (Layer Indicator), etc. Each of thesefields report a different metric related to the channel and contains essential information about the quality of the communication channel between the UE and the base station, which is used for optimizing the transmission of data.

[0087] The current specification deals with Precoding Matrix Indicator and accordingly, the signalling aspect related to the PMI field in the CSI reporting framework is discussed throughout the specification.

[0088] As per Release 15 specification, when ^^ ≤ 2, where ^^ is the associated RI value,each Type-II PMI corresponds to the codebook indices ^^1and ^^2where: ^^[^^1,1^^1,2^^1,3,1^^1,4,1] 1= { ^^ = 1[^^1,1^^1,2^^1,3,1^^1,4,1^^1,3,2^^1,4,2]^^ = 2………………..(10) Where subbandAmplitude is configured by the BS to the UE via RRC signalling. The L DFT vectors used for obtaining the precoder are identified by the indices ^^1,1and ^^1,2, which in-turn are translated to ^^1and ^^2indicating the corresponding ^^ and ^^ values respectively. Thestrongest coefficient on layer l, l = 1,..,v is identified by ^^1,3,^^ ∈ {0,1, .. ,2^^ − 1}. The amplitudecoefficients for layer l are identified by ^^1,4,^^and ^^2,2,^^whereas the phase coefficients for layer l are identified by ^^2,1,^^.

[0089] As per Rel-16 NR specification, the PMI value corresponds to the codebook indices ^^1and ^^2where:…………………….(11)

[0090] The LDFT vectors used for obtaining the precoder are identified by the indices ^^1,1and ^^1,2, which in-turn are translated to ^^1and ^^2indicating the corresponding ^^ and ^^ values respectively. The number of precoding matrices to be reported (^^3) is calculated based on higher layer parameter numberOfPMI-SubbandsPerCQI-Subband (^^), the number of configured sub-bands in csi-ReportingBand, and sub-band size configured by subbandSize.The number of DFT vectors used for compression (^^^^) is calculated as ^^^^ =where ^^^^is indicated by higher layer parameter paramCombination-r16.

[0091] The precoding matrices indicated by the PMI are determined from ^^ + ^^^^ vectors.Out of these ^^ + ^^^^ vectors, ^^ vectors represent the 2D-DFT beams in the beam-grid and theremaining ^^^^vectors are used for compressing the coefficients in ^^2matrix. The UE shall report the RI value ^^ according to the configured higher layer parameter typeII-RI-Restriction- r16.

[0092] ^^2,3,^^indicates the wideband amplitudes for layer ^^ and two polarizations. The DFT vectors that are used for FD-compression are picked from a ^^3point DFT matrix. The combination of ^^^^DFT vectors out of the ^^3DFT vectors is indicated by ^^1,6,^^and ^^1,5for layer ^^. ^^1,7,^^indicates the locations of non-zero coefficients in ^̃^2matrix for layer ^^. ^^2,4,^^and ^^2,5,^^indicates the amplitudes and phases of all the non-zero coefficients in ^̃^2matrix. ^^1,8,^^indicates the strongest coefficient among all the non-zero coefficients in ^̃^2matrix for layer ^^.

[0093] In 3GPP Release 18 (R18), CJT (Coordinated Joint Transmission) is an advanced transmission technique supported for improving coverage and capacity in 5G networks, especially in dense urban environments or areas with high interference. CJT allows a set of Transmission Reception Points (TRPs) to jointly transmit data to the User Equipment (UE), coordinating their transmission in a way that optimizes signal strength, reduces interference, and improves overall network performance. The UE is configured with ^^^^^^^^CSI-RS resources in a resource set for channel measurement such that each CSI-RS resource corresponds to aTRP and ^^^^^^^^ corresponds to maximum number of coordinating TRPs. The values of ^^1, ^^2^^2 are the same for all ^^^^^^^^ CSI-RS resources. As shown in equations (8) and (9), theUE selects N TRPs among the configured ^^^^^^^^TRPs and reports to the BS using a bitmap.

[0094] A set of ^^^^ ∈ {1,2,4} combinations of values of {^^1, .. , ^^^^^^^^^^} is configured by thehigher layer parameter paramCombination-CJT-L-r18, where the value of ^^^^is configured byhigher layer parameter numberOfSDCombinations. The value of ^^^^corresponding to CSI-RSresource n, for ^^ = 1, .. , ^^^^^^^^, indicates the number of beams present in the spatial basiscorresponding to CSI-RS resource n. The PMI value for the N selected CSI-RS resources corresponds to the codebook indices ofand ^^2where:

[0095] The precoding matrices indicated by the PMI are determined from ∑^^ ^^=1 ^^+ ^^vectors, where {^^ , .. ,are the indices of the N selected CSI-RS resources inthe corresponding values from the selected combinationvectors are signalled by the indicesand ^^1,2. For mode 2, ^^^^vectors corresponding to the FD basis are common for all the N selected CSI-RS resources and are indicated by ^^1,5and ^^1,6,^^similar to R16 PMI reporting. For mode 1, an FD basis corresponding to the first CSI-RS resource among the N selected CSI-RS resources is reported by indices ^^ and. The FD basis corresponding to the remaining (N-1) CSI-RS is determined based on the offset ^^^^reported for the ^^-th selected CSI-RS resource and the FD basis of the first selected CSI-RS resources. The offsets ^^^^are reported by the index ^^1,9.

[0096] The current NR specification supports a CSI reporting framework for up to 32 Tx ports. The present specification describes the PMI reporting framework for a very large number of Tx ports beyond 32 Tx ports. One of the major problems is that the currently used DFT- based precoders are not the most efficient precoders and it needs to be addressed while designing a precoder structure for very large number of Tx ports. The inefficiency is mainly because of the linear nature of the DFT-based precoders. The DFT-based precoders are used as the basic building blocks of the existing precoders as described in the previous sections. Since, the existing precoder is defined for smaller number (32) of Tx ports (CSI-RS Ports as per NR), using the DFT based precoders are considered to be an optimal solution.

[0097] Increasing the number of transmit antennas to an extremely large number results in non-linearity between the phases of the received signals from two consecutive transmit antennas i.e., the phase change between the received signals of any two consecutive transmit antennas is not constant for any given path. Hence, straight-forward extension of the current precoder is not an optimal solution. In this specification, different methods of signalling a precoder to the BS are proposed.

[0098] The aim of the present specification is to deal with the non-linearity in the phase of the channel across multiple Tx antennas. One way of solving the problem of non-linearity is by dividing the non-linearity into several small linear parts. Same principle is applied in the following method. Accordingly, an antenna panel is divided into multiple sub-panels and a PMI is reported to the BS for each of the sub-panels.

[0099] Fig.3 illustrates an antenna panel sub-panel which refers to a smaller grouping or subset of antenna elements within a larger panel that works together as a functional unit. If the number of Tx ports is ^^^^^^^^^^^^(^^^^^^^^^^^^ / 2 for each polarizaiton), they are divided into multiple sub-panels where the number of Tx ports within a sub-panel is ^^^^^^^^−^^^^^^^^^^. The number of sub- panels present in the antenna panel are ^^^^^^^^−^^^^^^^^^^= ^^^^^^^^−^^^^^^^^^^. If all the Tx ports are indexedas {0,1, .. , ^^^^^^^^^^^^ − 1} such that port indices {0,1, .. , ^^^^^^^^^^^^ / 2 − 1} belongs to one polarizationand− 1} belongs to another polarization, and the sub-panels areindexed as {0,1, .. , ^^^^^^^^−^^^^^^^^^^ − 1}, then the association between the Tx port with index ^^ andthe sub-panel with index ^^ is configured to the UE by the BS via higher layer signalling. This association can also be derived by the UE based on the size of the sub-panel configured to the UE by the BS via higher layer signalling.

[0100] The UE reports a PMI corresponding to each of the sub-panel. The PMI for any sub-panel can be any one of Type-1 Single-panel codebook, Type-2 codebook or Enhanced Type-2 codebook. Hence, the PMI structure can be represented as below:………………….(13) where ^^^^is the PMI corresponding to sub-panel with index ^^.

[0101] Fig.4 illustrates a flow chart describing the method for determination of a precoder in accordance with the disclosures of the present invention. At step 401, the base station configures a set of first basis vectors. At step 402, the base station configures the association between at least one set of antenna elements and at least one sub-panel. At step 403, the UE determines a first set of first basis vectors corresponding to each sub-panel. At step 404, the UE determines a first set of complex weights corresponding to each sub-panel. At step 405, the UE reports the determined first set of basis vectors and the complex weights corresponding to at least one sub-panel to the base station. At step 406, the base station determines the overall precoder based on the received first set of basis vectors and set of complex weights corresponding to at least one sub-panel.

[0102] As mentioned above, ^^^^can be from any one of Type-1, Type-2 and EnhancedType-2 codebook. In case of Type-2 codebook, ^^^^ can be represented as ^^^^ = ^^1^^^^2^^ similarto as mentioned in equation (4), whereas in case of enhanced Type-2 codebook, ^^^^can berepresented as ^^^^ = ^^1^^^̃^2^^^^^^^^^^ similar to as mentioned in equation (7). ^^1^^and ^^2^^represents the SD basis and beam coefficients respectively for sub-panel ^^ and ^^1^^, ^̃^2^^and ^^^^^^^^ represents the SD basis, the compressed beam coefficients and FD basis respectively for sub-panel ^^.

[0103] Fig.5 illustrates a flow chart for describing a method to signal the ^^1^^matrix. At step 501, UE determines a set of common first basis vectors corresponding to all sub-panels. At step 502, UE determines a set of different first basis vectors corresponding to each sub- panel. At step 503, UE determines the first set of first basis vectors as the union of the set of common first basis vectors and the set of different first basis vectors corresponding to each sub-panel.

[0104] Since all the sub-panels are present in the same antenna panel, the channel characteristics across the sub-panels may be similar. This may result in picking the same sub- set of beams for all the sub-panels present in the antenna panel. One method of reporting a ^^1matrix is by reporting a common spatial basis (^^1,^^^^^^^^^^^^) and a different spatial basis (^^1,^^^^^^^^^^^^^^^^,^^) for the sub-panel with index ^^. The common spatial basis is reported commonly for all the sub-panels and the different spatial basis is reported separately for each of the sub- panel. Hence, the ^^1matrix for sub-panel ^^ can be represented as:……………………………….(14) The number of beams present inand ^^1,^^^^^^^^^^^^^^^^,^^are ^^^^^^^^^^^^^^and ^^^^^^^^^^^^^^^^^^respectively. Both ^^^^^^^^^^^^^^and ^^^^^^^^^^^^^^^^^^are configured to the UE by the BS via higher layer signalling.

[0105] Fig. 6 illustrates a flow chart for describing a method for offset based signalling. At step 601, the base station configures a set of offset pairs and a reference sub-panel index. At step 602, the UE determines a set of first basis vectors associated with the reference sub- panel. At step 603, UE determines a set of offset pairs corresponding to at least one sub-panel. At step 604, a set of first basis vectors corresponding to a sub-panel is formed by using the set of first basis vectors corresponding to the reference sub-panel and a set of offset pairs corresponding to the sub-panel.

[0106] As per this method, a reference SD basis (^^1,^^^^^^) is reported by the UE corresponding to a reference sub-panel. The UE reports the reference ^^1to the BS using the existing PMI reporting procedures in NR. reporting of the ^^1matrices corresponding to the sub-panels other than the reference sub-panel is done by using an offset based reporting. Forexample, if ^^1,^^^^^^ consists of beam indices {^^0,^^^^^^, ^^1,^^^^^^, .. , ^^^^−1,^^^^^^} identified using^^1,^^^^^^and ^^2,^^^^^^, a set of beam offsets indicated asare signalled to the UE corresponding to a sub-panel ^^ such that the ^^1matrix corresponding to sub-panel ^^ is computed as:…………………………………(15) derived usingThe set of possible values forare configured to the UE by the BS higher layer signalling. This method can be used to reduce feedback overhead by limiting the set of beam offsets.

[0107] Fig. 7 illustrates a flow chart for describing a method of signalling. At step 701, the base station configures a set of second basis vectors for compressing the complex weights across sub-panels. At step 702, UE determines a set of complex weights corresponding to a given SD basis vector across all sub-panels. At step 703, UE determines a subset of second basis vectors and a second set of complex weights corresponding to each first basis vector in the first set of first basis vectors. At step 704, UE reports the subset of second basis vectors andthe second set of complex weights corresponding to each first basis vector in the first set of first basis vectors.

[0108] As shown in equation (4), a Type-2 precoder can be represented as: ^^ = ^^1^^2represents the spatial domain basis and ^^2represents the coefficients corresponding to each beam present in ^^1matrix. If Type-2 precoder is signalled for each of the sub-panel,the precoder for sub-panel ^^ is

[0109] By substituting this in equation (13), we get:…………………….(16)

[0110] If the spatial domain basis is common for all the sub-panels, i.e., ^^1,^^ = ^^1,equation (16) can be written as:……………………………….(17) Where………………………………(18) If the ^^2matrix is re-written as:………………………………(19) It can be compressed by using DFT-vectors of length ^^^^^^^^−^^^^^^^^^^. After compressing, ^^2^^^^^^can written as: ^^^^^^^^2 = ^̂^2^^^^^^^^^^………………………………(20) Where ^^^^contains the vectors that are used for compression of ^^2^^^^^^matrix. The number of vectors that are used for the compression is configured to the UE by the BS via higher layersignalling. The UE reports ^^1, ^̂^2^^^^^^and ^^^^to the BS as a part of CSI feedback.

[0111] As more antennas, i.e., of the order of a few hundreds or thousands are packed in an antenna array, the fundamental characteristic of the channel changes around the antenna array. The far-field boundary of the antenna array, defined by the Rayleigh distance is pushed further away from the antenna array. This characteristic contributes to the breakdown of the conventional planar wave propagation model which renders a loss in energy capture from the wave propagation. The existing DFT codebook designed to receive signals in the far-field become inefficient in acting as basis vectors for determining the near-field precoder. Thus, the spherical wave propagation model needs to be taken into consideration.

[0112] Fig. 8 illustrates a flow chart for describing a method of determination of a precoder. At step 801, the UE receives a configuration of at least one of a set of first linear vectors, a set of first non-linear vectors, a set of second linear vectors and a set of second non- linear vectors from the BS. At step 802, the UE determines a set of first basis vectors based on at least one first linear vector and at least one first non-linear vector. At step 803, the UE determines a set of second basis vectors based on at least one second linear vector and at least one second non-linear vector. At step 804, the UE determines a set of third basis vectors based on at least one of the first basis vectors and at least one of the second basis vectors. At step 805, the UE determines a set of complex weights. At step 806, the UE reports the set of third basis vectors to at least one BS, wherein the set of third basis vectors is reported using the associated indices of the first linear vector, the first non-linear vector, the second linear vector and the second non-linear vector. At step 807, the UE reports the set of complex weights to at least one BS.

[0113] Unlike the Far-Field precoders which employ DFT vectors for beamforming, the Near-Field Precoders need to incorporate an additional non-linearity in terms of the antenna index. The precoder structure proposed in this section follows the existing NR precoder structures withmodified as ^^1.̃Hence, the updated precoder structure is shown herein. Precoder structure without sub-band compression is modified as: ^^ = ^^1̃^^2and with sub-band compression is modified as:The ^^1̃matrix can be written as a block diagonal matrix, ^^where ^̃^^^represents the basis vector for the construction of the non-linear precoder.

[0114] The basis vector, ^̃^^^is written as a combination of the basis vectors from both the dimensions of the antenna array as,Here ^̃^^^and are in turn defined as a dot product of linear and non-linear basis vectors. The first basis vector is derived as the element-wise multiplication of at least one first linear vector and at least one first non-linear vector This can be represented as:and ^̃^^́^ = ^̃^^́^,^^^^^^^^^^^^^^̃^^́^,^^^^^^−^^^^^^^^^^^^where ^̃^^^,^^^^^^^^^^^^and ^̃^^́^,^^^^^^^^^^^^corresponds to the existing DFT basis vectorsand ^^^^respectively mentioned in equations (1) and (2). The entries of ^̃^^^,^^^^^^−^^^^^^^^^^^^and ^̃^^́^,^^^^^^−^^^^^^^^^^^^are defined as a function of angle and distance. Thus, the the third basis vector (^̃^^^) is derived as a Kronecker product of at least one first basis vector and at least one second basis vector or vice-versa. Each complex weight corresponds to third basis vector in the reported set of third basis vectors and the first basis vector is obtained by the UE as the element-wise multiplication of at least one first linear vector and at least one first non-linear vector. 2^^^^ 2^^^^ Defining ^^^^= ^^^^and

[0115] Where ^^ = ^^1 ∗ ^^ + ^^ and ^́^ = ^^2 ∗ ^^ + ^^. Here, the segregation of the channeloccurs both in the angular and distance domains. The first linear vector is derived based on at least one of the number of antenna elements in the first dimension of the antenna panel (^^1) and an oversampling factor (^^1) and the first linear vector is a DFT based vector.

[0116] Fig.9 illustrates a linear antenna array setup at a BS communicating to a UE. From Fig.8, the distance to each antenna element ^^(^^)is formulated as a square root of the following parameters,where ^^ is the angle of arrival / departure from / to the BS, d is the distance between the reference antenna element of the BS, for example, the first element from one end of the antenna array and the UE, n, ∆ are the antenna index and the inter-element spacing respectively. Using second order Taylor Series approximation, the term ^^(^^)can be expanded as,Now the weight corresponding to the ^^1^^ℎelement of the precoder vector in one of the dimensions ^̃^^^,^^1can be derived from the expression for ^^(^^)as a complex exponential as,After defining a quantization for ^^^^^^^^ with the resolutionwe can define^^ Similarly, after defining a quantization for ^^^^^^^^ with the resolution of ^^2^^2. Δ, we can define^́^∆2

[0117] Introducing additional parameters, ^^1=, we can define:The parameter ^^^^^^^^assumes a value within a range specified by ^^^^^^^^,^^^^^^to ^^^^^^^^,^^^^^^. The UE derives the value of ^^1,^^^^^^and ^^1,^^^^^^as a function of at least one of ^^1, ^^1,1, ^^2,1and ^^1. The values of ^^1,1, ^^2,1and ^^1are configured to the UE by the base station. The value of ^^^^^^^^,^^^^^^is proportional to inverse of the square of the antenna number in a dimension,The proportionality constant is given as,Similarly, for ^^^^^^^^,^^^^^^the relation is inversely proportional to the antenna number,With a proportionality constant,These ranges are defined as,where ^^^^^^^^is a scaling factor for the Rayleigh distance for that dimension, ^^1,^^^^^^and ^^2,^^^^^^are scaling factors in terms of wavelength for the inter-element spacing and individual antenna length plus inter-element spacing for that dimension. The parameter ^^^^^^^^represents the antenna number for a specific dimension. The parameter ^^ is sampled uniformly as follows:In the above expression, ^^^^^^^^defines the number of samples to be taken in the respective dimension. UE derives ^^1values as ^^1uniformly sampled values within the range ^^1,^^^^^^and

[0118] Fig. 10 illustrates a method wherein the current NR codebooks are extended and made as near-field codebook based on energy spreading effect. At step 1001, the UE reports multiple clusters of basis vectors and a set of complex weights to the base station. At step 1002, the UE reports an index of a reference basis vector and the size of the cluster corresponding to each cluster. At step 1003, the UE derives the indices of all the basis vectors within a cluster based on the index of the reference basis vector corresponding to the cluster and the size of the cluster. At step 1004, the base station determines the precoder based on the received clusters of basis vectors and the received set of complex weights.

[0119] In this method, the current NR codebooks will be extended and made as near-field codebook based on energy spreading effect. Based on this extension, the precoder structure for the near-field is given as one of the below: ^^ = ^^1^^^^^^^^2Or ^^ = ^^1^^^^^^^̃^2^^^^^^The equation specified above is similar to Rel-15 Type-II precoder and Rel-16 Type-II precoder structure specified in equations (4) and (7). In this method, the SD basis matrix i.e., ^^1^^^^^^is given as:Where ^^^^is the ^^^^ℎbeam cluster containingbeams.is defined as the product of two components ^^^^,1and ^^^^,2i.e., ^^^^ = ^^^^,1 ∗ ^^^^,2^^^^,1represents the ^^^^ℎcluster size indimension of the panel and ^^2represents the ^^^^ℎcluster size in ^^2dimension of the panel. The matrix ^^^^is given as:Any ^^^^ consists of a reference beam ^^^^^^,^^^^ and (^^^^ − 1) other beams as a part of the cluster.The reference beam (^^^^^^,^^^^) is signalled to the BS by the UE is the CSI report. The values of ^^^^,1and ^^^^,2are either configured to the UE by the BS or indicated by the UE to the BS. The total number of beams present inwill be ^̅^ where: ^^−1 ^̅^ = ∑ ^^^^^^=0 If the coefficients in ^^2are reported for each of the beams independently, the number of reported coefficients will be 2^̅^ per wideband or per sub-band. If the coefficients in ^^2are reported for each of the clusters independently where the coefficients for all the beams within a cluster is same, the number of reported coefficients will be 2^^ per wideband or per sub-band.

[0120] The figures of the disclosure are provided to illustrate some examples of the invention described. The figures are not to limit the scope of the depicted embodiments of theappended claims. Aspects of the disclosure are described herein with reference to the invention to example embodiments for illustration. It should be understood that specific details, relationships, and method are set forth to provide a full understanding of the example embodiments. One of ordinary skill in the art recognize the example embodiments can be practiced without one or more specific details and / or with other methods.

[0121] Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products.

[0122] While this specification contains many specific implementation details, these should not be construed as limitations on the scope of any disclosures or of what may be claimed, but rather as descriptions of features specific to particular embodiments of particular disclosures. Certain features that are described herein in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable sub combination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a sub combination or variation of a sub combination.

[0123] Thus, particular embodiments of the subject matter have been described. Other embodiments are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results. In addition, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In certain implementations, multitasking and parallel processing may be advantageous.

[0124] It is to be understood that the disclosure is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to beincluded within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation, unless described otherwise.

Claims

WE CLAIM:

1. A method for wireless communications at a user equipment (UE), comprising: receiving, by the UE, a configuration of at least one of a set of first linear vectors, a set of first non-linear vectors, a set of second linear vectors and a set of second non-linear vectors from the base station (BS); determining, by the UE, a set of first basis vectors based on at least one first linear vector and at least one first non-linear vector; determining, by the UE, a set of second basis vectors based on at least one second linear vector and at least one second non-linear vector; determining, by the UE, a set of third basis vectors based on at least one of the first basis vectors and at least one of the second basis vectors; determining, by the UE, a set of complex weights; reporting, by the UE, the set of third basis vectors to at least one BS; and reporting, by the UE, the set of complex weights to at least one BS.

2. The method as claimed in claim 1, wherein each complex weight corresponds to third basis vector in the reported set of third basis vectors.

3. The method as claimed in claim 1, wherein the set of third basis vectors is reported using the associated indices of the first linear vector, the first non-linear vector, the second linear vector and the second non-linear vector.

4. The method as claimed in claim 1, wherein the third basis vector ( ^̃^^^) is obtained by theUE as a Kronecker product of one of at least one first basis vector and at least one second basis vector or at least one second basis vector and at least one first basis vector.

5. The method as claimed in claim 1, wherein the first basis vector is obtained by the UE as the element-wise multiplication of at least one first linear vector and at least one first non- linear vector.

6. The method as claimed in claim 1, wherein the first linear vector is obtained by the UE based on at least one of number of antenna elements in the first dimension of an antenna panel (^^1) and an oversampling factor (^^1).

7. The method as claimed in claim 1, wherein the first linear vector is a DFT based vector.

8. The method as claimed in claim 1, wherein the first non-linear vector is obtained by the UE based on at least one of number of antenna elements in the first dimension of an antenna panel (^^1), an oversampling factor (^^1), a function of the antenna spacing in the first dimension of the antenna panel and an additional parameter ^^1.

9. The method as claimed in claim 8, wherein a set of ^^1values is configured to the UE by the BS.

10. The method as claimed in claim 8, wherein a set of ^^1values is obtained by the UE as ^^1uniformly sampled values within a range ^^1,^^^^^^and ^^1,^^^^^^.

11. The method as claimed in claim 10, wherein at least one of ^^1,^^^^^^, ^^1,^^^^^^and ^^1are configured to the UE by the BS.

12. The method as claimed in claim 10, wherein ^^1,^^^^^^and ^^1,^^^^^^are obtained by the UE as a function of at least one of ^^1, ^^1,1, ^^2,1and ^^1.

13. The method as claimed in claim 12, wherein at least one of ^^1,1, ^^2,1and ^^1are configured to the UE by the BS.

14. The method as claimed in claim 12, wherein ^^1,1and ^^2,1are obtained by the UE basedon the antenna spacing in the first dimension of the antenna panel.

15. The method as claimed in claim 1, wherein the second basis vector is obtained by the UE as the element-wise multiplication of at least one second linear vector and at least one second non-linear vector.

16. The method as claimed in claim 1, wherein the second linear vector is obtained by the UE based on at least one of number of antenna elements in the second dimension of the antenna panel (^^2) and an oversampling factor (^^2).

17. The method as claimed in claim 1, wherein the second linear vector is a DFT based vector.

18. The method as claimed in claim 1, wherein the second non-linear vector is obtained by the UE based on at least one of number of antenna elements in the second dimension of the antenna panel (^^2), an oversampling factor (^^2), a function of the antenna spacing in the second dimension of the antenna panel and an additional parameter ^^2.

19. The method as claimed in claim 18, wherein a set of ^^2values is configured to the UE by the BS.

20. The method as claimed in claim 18, wherein a set of ^^2values is obtained by the UE as ^^2uniformly sampled values within a range ^^2,^^^^^^and ^^2,^^^^^^.

21. The method as claimed in claim 20, wherein at least one of ^^2,^^^^^^, ^^2,^^^^^^and ^^2are configured to the UE by the BS.

22. The method as claimed in claim 20, wherein ^^2,^^^^^^and ^^2,^^^^^^are obtained by the UE as a function of at least one of ^^2, ^^1,2, ^^2,2and ^^2.

23. The method as claimed in claim 22, wherein at least one of ^^1,2, ^^2,2and ^^2are configured to the UE by the BS.

24. The method as claimed in claim 22, wherein ^^1,2and ^^2,2are obtained by the UE basedon the antenna spacing in the second dimension of the antenna panel.

25. A method for wireless communications at a user equipment (UE), comprising: receiving, by the UE, a configuration of first basis vectors from a base station (BS); determining, by the UE, a first set of first basis vectors corresponding to at least one sub- panel; determining, by the UE, at least one of a first set of complex weights corresponding to at least one sub-panel and a set of third sets of transformed complex weights;reporting, by the UE, the determined first set of first basis vectors to at least one BS; andreporting, by the UE, at least one of determined first set of complex weights and a set of third sets of transformed complex weights to the base station.

26. The method as claimed in claim 25, wherein a complex weight in the first set of complex weight corresponds to at least one sub-panel.

27. The method as claimed in claim 25, wherein the first set of first basis vectors is reportedby signalling at least one of a first set of indices and a second set of indices.

28. The method as claimed in claim 25, wherein the number of sub-panels is dependent upon total number of transmission ports and number of transmission ports within a sub-panel.

29. The method as claimed in claim 25, wherein the sub-panel is associated with a sub-panel index.

30. The method as claimed in claim 25, wherein the association between at least one sub- panel and at least one transmission port is configured to the UE by the BS.

31. The method as claimed in claim 25, wherein a complex weight in the first set of complex weights corresponds to at least one of the first basis vector in the first set of first basis vectors and a sub-panel index.

32. The method as claimed in claim 27, wherein determining a first set of first basis vectors corresponding to a sub-panel comprises:determining, by the UE, a set of common first basis vectors based on the first set of indices;determining, by the UE, a subset of second set of indices corresponding to the sub-panel; determining, by the UE, a set of separate first basis vectors corresponding to the sub-panel based on the subset of second set of indices; and determining, by the UE, the first set of first basis vectors corresponding to the sub-panel as the union of the set of common first basis vectors and the set of separate first basis vectors.

33. The method as claimed in claim 27, wherein determining a first set of first basis vectors corresponding to a sub-panel comprises: determining, by the UE, the first set of first basis vectors corresponding to the reference sub- panel based on the first set of indices;determining, by the UE, a first set of beam pair indices by generating a beam pair index(^^1,^^^^^^,^^2,^^^^^^) for each element in the first set of indices; determining, by the UE, a subset of second set of indices corresponding to the sub-panel;determining, by the UE, a second set of beam pair indices by generating a beam pair index(^^ ^^^^^^^^^^^^ 1,^^ , ^^^^^^^^^^^^^^ 2,^^ ) for each element in the determined subset of second set of indices;determining, by the UE, a third set of beam pair indices corresponding to the sub-panel basedon the first set of beam pair indices and the second set of beam pair indices;determining, by the UE, a third set of indices based on the determined third set of beam pair indices; and determining, by the UE, the first set of first basis vectors corresponding to the sub-panel based on the third set of indices corresponding to the sub-panel.

34. The method as claimed in claim 33, wherein the third set of beam pair indices corresponding to a sub-panel are determined by the UE as the sum of the first set of beam pair indices and the second set of beam pair indices.

35. The method as claimed in claim 33, wherein each element in the second set of indices is obtained by the UE based on a set of offset pairs (^^ ^^^^^^^^^^^^ 1, ^^^^^^^^^^^^^^ 2 ) configured to the UE by the BS.

36. The method as claimed in claim 25, wherein determining the set of third sets of transformed complex weights comprises: configuring, by the BS to the UE, a set of second basis vectors for transforming the first set of complex weights;determining, by the UE, a set of second sets of complex weights wherein the second set ofcomplex weights corresponds to a first basis vector in the first set of first basis vectors;determining, by the UE, a subset of second basis vectors;determining, by the UE, a set of third sets of transformed complex weights wherein the third set of transformed complex weights are determined based on a second set of complex weights and the subset of second basis vectors; and reporting, by the UE to the BS, the set of third sets of transformed complex weights and the subset of second basis vectors.

37. A method for wireless communications at a user equipment (UE), comprising: determining, by the UE, plurality of cluster of basis vectors wherein the cluster is a set of basis vectors; determining, by the UE, a set of complex weights; and reporting, by the UE to the BS, the plurality of cluster of basis vectors and a set of complex weights.

38. The method as claimed in claim 37, wherein the basis vector in the cluster is obtained by the UE using at least one of a reference basis vector and the size of the cluster.

39. The method as claimed in claim 37, wherein reporting the plurality of cluster of basis vectors comprises reporting the index of the reference basis vector corresponding to the cluster and the size of the cluster corresponding to the cluster.

40. The method as claimed in claim 37, wherein the complex weight in the set of complex weights corresponds to at least one cluster of first basis vectors and a layer index of the precoder.

41. The method as claimed in claim 37, wherein number of beams in a cluster ^^ is defined by the size of the cluster ^^^^.

42. The method as claimed in claim 41, whereinis the product of ^^^^,1and ^^^^,2wherein ^^^^,1is obtained by the UE from a configured set of ^^^^,1values and ^^^^,2is obtained by the UE from a configured set of ^^^^,2values.

43. The method as claimed in claim 42, wherein ^^^^,1and ^^^^,2are the sizes of the cluster ^^ in the first dimension of the antenna panel and the second dimension of the antenna panel, respectively.

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