Apparatus, method and computer program for spatial basis vector indication

Abstract

There is provided an apparatus comprising selecting a first beam from a grid of beams comprising N1O1 × N2O2 two-dimensional discrete Fourier transform beams, determining at least one additional beam, wherein the at least one additional beam is orthogonal to the first beam in at least one of the horizontal or vertical direction, determining at least one of two beam groups to which the at least one additional beam belongs, one of the two beam groups being a horizontal orthogonal beam group associated with the first beam, and another group of the beam groups being a vertical orthogonal beam group associated with the first beam and providing channel state information to a network device, the channel state information comprising at least one indication indicative of the first beam, the at least one of the beam groups and the at least one additional beam.

Description

TITLE Apparatus, Method and Computer Program TECHNICAL FIELD

[0001] Various embodiments of this disclosure relate generally to methods, ap-paratus and computer programs, and in particular, but not exclusively, to spatial basisvector indication for type-I codebook.BACKGROUND

[0002] A communication system can be seen as a facility that enables communi-cation sessions between two or more communication devices, or provides communica-tion devices access to a network. A mobile or wireless communication network is oneexample of a communication network. A communication device may be provided witha service by an application server.

[0003] A mobile or wireless communication network may operate in accordancewith standard(s), such as those provided by 3GPP (Third Generation Partnership Pro-ject) or ETSI (European Telecommunications Standards Institute). Examples of mobile or wireless communication network that operate in accordance with 3GPP standards are generally referred to as 4G (4th Generation) networks, 5G (5th Generation) network, 5G-Advanced networks and 6G networks. SUMMARY

[0004] Some embodiments of this disclosure will be described with respect to cer-tain aspects. These aspects are not intended to indicate key or essential features of the various example embodiments of this disclosure, nor are they intended to be used to limit the scope of thereof. Other features, aspects, and elements will be readily apparent to a person skilled in the art in view of this disclosure. For example, it should be appre- ciated that further aspects may be provided by the combination of any two or more of the various aspects described herein.

[0005] In a first aspect there is provided a method comprising selecting a first beamfrom a grid of beams comprising× N^O^ two-dimensional discrete Fourier trans-form beams, determining at least one additional beam, wherein the at least one addi- tional beam is orthogonal to the first beam in at least one of the horizontal or vertical direction, determining at least one of two beam groups to which the at least one addi- tional beam belongs, one of the two beam groups being a horizontal orthogonal beamgroup associated with the first beam, and another group of the beam groups being avertical orthogonal beam group associated with the first beam and providing channelstate information to a network device, the channel state information comprising at least one indication indicative of the first beam, the at least one of the beam groups and the at least one additional beam.

[0006] The horizontal orthogonal beam group may comprise (^^ − 1)^^^^ beamsthat are orthogonal to the first beam in at least the vertical dimension, and ^^ − 1 beamsthat are orthogonal to the first beam only in the horizontal dimension, whereinand ^^are the oversampling factors in the horizontal and vertical dimension, respectively.

[0007] The vertical orthogonal beam group may comprise (^^ − 1)^^^^ beamsthat are orthogonal to the first beam in at least the horizontal dimension, and ^^ − 1beams that are orthogonal to the first beam only in the vertical dimension, whereinand ^^are the oversampling factors in the horizontal and vertical dimension, respec- tively.

[0008] The indication indicative of the at least additional spatial domain basis maycomprise log(^^^^^^) bits for the vertical group, and log(^^^^^^) bits for the horizontalgroup.

[0009] The channel state information may be associated with a type I codebook ofchannel state information.

[0010] The indication indicative of the beam group may comprise a one-bit indica-tor.

[0011] The first beam and the at least one additional beam may be vectors usedto form the precoding matrix corresponding to the reported precoding matrix indicator applicable to a vector of physical downlink shared channel symbols to calculate a chan- nel quality indicator.

[0012] In a second aspect there is provided a method comprising receiving channelstate information from the terminal device, the channel state information comprising atleast one indication indicative of a first beam selected from a grid of beams comprisingN^O^ × N^O^ two-dimensional discrete Fourier transform beams, at least one additionalbeam and at least one of two beam groups to which the at least one additional beam belongs, wherein the at least one additional beam is orthogonal to the first beam in at least one of the horizontal or vertical direction, one of the two beam groups being ahorizontal orthogonal beam group associated with the first beam, and another being avertical orthogonal beam group associated with the first beam and based on thechannel state information, determining a precoder for downlink transmission to the user equipment.

[0013] The horizontal orthogonal beam group may comprise (^^ − 1)^^^^ beamsthat are orthogonal to the first beam in at least the vertical dimension, and ^^ − 1 beamsthat are orthogonal to the first beam only in the horizontal dimension, whereinand ^^are the oversampling factors in the horizontal and vertical dimension, respectively.

[0014] The vertical orthogonal beam group may comprise (^^ − 1)^^^^ beamsthat are orthogonal to the first beam in at least the horizontal dimension, and ^^ − 1beams that are orthogonal to the first beam only in the vertical dimension, whereinand ^^are the oversampling factors in the horizontal and vertical dimension, respec- tively.

[0015] The indication indicative of the at least additional spatial domain basis maycomprise log(^^^^^^) bits for the vertical group, and log(^^^^^^) bits for the horizontalgroup.

[0016] The channel state information may be associated with a type I codebook ofchannel state information.

[0017] The indication indicative of the beam group may comprise a one-bit indica-tor.

[0018] The first beam and the at least one additional beam may be vectors usedto form the precoding matrix corresponding to the reported precoding matrix indicator applicable to a vector of physical downlink shared channel symbols to calculate a chan- nel quality indicator.

[0019] In a third aspect there is provided a method comprising means for perform-ing the method according to the first or second aspect.

[0020] In a fourth aspect there is provided an apparatus comprising at least oneprocessor, and at least one memory storing instructions which, when executed by the at least one processor, cause the apparatus at least to perform a method according to the first or second aspect.

[0021] In a fifth aspect there is provided a non-transitory computer readable me-dium comprising instructions wherein the instructions when executed by at least one processor of an apparatus cause the apparatus to perform the method according to thefirst or second aspect.

[0022] In a sixth aspect there is provided a computer program comprising in-structions which, when executed by an apparatus, cause the apparatus to perform atleast the method according to the first or second aspect.

[0023] Some embodiments of the invention are defined in the dependentclaims.

[0024] In the above, many different aspects have been described. As previouslynoted, it should be appreciated that further aspects may be provided by the combination of any two or more of the aspects described above (or otherwise in this disclosure).

[0025] Various other aspects are also described in the following detailed descrip-tion and in the claims. BRIEF DESCRIPTION OF THE FIGURES

[0026] Some embodiments will be described, by way of non-limiting and illustra-tive example only, with reference to the figures, in which:

[0027] Fig.1 shows an example of a communication network to which examplesdisclosed herein may be applied;

[0028] Fig. 2 shows an example grid of beams comprising× N^O^ two-di-mensional DFT beams;

[0029] Fig. 3 shows an example grid of beams comprising× N^O^ two-di-mensional DFT beams;

[0030] Fig.4 shows an example table of beam choices for four beams;

[0031] Fig.5 shows a flowchart of an example method;

[0032] Fig.6 shows a flowchart of an example method;

[0033] Fig. 7 shows an example grid of beams comprising× N^O^ two-di-mensional DFT beams;

[0034] Fig. 8 shows an example grid of beams comprising× N^O^ two-di-mensional DFT beams;

[0035] Fig. 9 shows fields of an example indication of beams;

[0036] Fig. 10 shows a flowchart of how the indication of beam group determineshow beam B, C, D are reported;

[0037] Fig.11 shows a signalling flow according to any example;

[0038] Fig. 12 shows an example of an apparatus.DETAILED DESCRIPTION

[0039] The following embodiments are provided by way of non-limiting and illus-trative example. Although the specification may refer to “an”, “one”, or “some” embodi- ment(s) in several locations of the text, this does not necessarily mean that eachreference is made to the same embodiment(s), or that a particular feature only applies to a single embodiment. Single features of different embodiments may also be com- bined to provide other embodiments. Further, when a particular feature, structure, or characteristic is described in connection of an embodiment, it intended such feature, structure, or characteristic may be applied in connection with other embodiments (whether or not explicitly described).

[0040] It shall be understood that although the terms “first,” “second” and the likemay be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another.

[0041] For the purposes of this disclosure, the phrases “at least one of A or B”,“at least one of A and B”, and “A and / or B” means (A), (B), or (A and B). For the pur- poses of this disclosure, the phrase “A, B, and / or C” means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C).

[0042] As used herein, the term “or” refers to a non-exclusive “or” unless otherwiseindicated (e.g., use of “or else” or “or in the alternative”).

[0043] As used herein, unless stated explicitly, performing a respective feature,step, or functionality “in response to A” does not indicate that the respective feature, step, or functionality is performed immediately after “A” occurs as one or more interven- ing features, steps, or functionalities may be performed (at least in part) between an occurrence of the respective feature, step, or function and “A”. Analogously, performing a respective feature, step, or functionality “based on A” does not indicate that the re- spective feature, step, or functionality is performed solely based on “A” as the respective feature, step, or functionality may be further based on one or more other features, steps, or functionalities in addition to “A”.

[0044] Embodiments described herein may be implemented in a communicationnetwork, such as any of the following radio access technologies (RATs): Worldwide Interoperability for Micro-wave Access (WiMAX), Global System for Mobile communi- cations (GSM, 2G), GSM EDGE radio access Network (GERAN), General Packet Ra-dio Service (GRPS), Universal Mobile Telecommunication System (UMTS, 3G) basedon basic wideband-code division multiple access (W-CDMA), high-speed packet ac- cess (HSPA), Long Term Evolution (LTE), LTE-Advanced, and enhanced LTE (eLTE), 5G (also called NR), or any future RAT such as 6G. Moreover, communication within the communication network may utilize any proper wireless communication technology, comprising but not limited to: Code Division Multiple Access (CDMA), Frequency Divi- sion Multiple Access (FDMA), Time Division Multiple Access (TDMA), FrequencyDivision Duplex (FDD), Time Division Duplex (TDD), Multiple-Input Multiple-Output (MIMO), Orthogonal Frequency Division Multiple (OFDM), and / or Discrete Fourier Transform spread OFDM (DFT-s-OFDM).

[0045] As used herein, the term “network device” or “network node” refers to anode in a communication network via which user equipment may access the network and / or which is configured to control radio communication and managing radio re- sources within a cell. The network node or network device may be referred to as a base station (BS), an access point (AP) or an access node. The network device may be, depending on the applied technology, for example, a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), an NR NB (also referred to as a gNB), a Remote Radio Unit (RRU), a radio head (RH), a remote radio head (RRH), a relay, an Integrated Access and Backhaul (IAB) node, a low power node, a non-terrestrial network (NTN) or non-ground network device, such as a satellite network device, a low earth orbit (LEO) sat-ellite and a geosynchronous earth orbit (GEO) satellite, or an aircraft network device.

[0046] Moreover, in connection of split radio access network (RAN), the networkdevice may refer to a centralised unit (CU) of a base station and / or a distributed unit (DU) of a base station. An interface between CU and DU may be referred to as an F1 interface in NR. In the split RAN architecture, node operations may be carried out, at least partly, in the central / centralized unit, CU, (e.g. server, host or node) operationally coupled to the DU, (e.g. a radio head / node). One CU may control one or more DUs, acting at least as transmit / receive (Tx / Rx) nodes. In some embodiments, the DUs may comprise e.g. a radio link control (RLC), medium access control (MAC) layer and a physical (PHY) layer, whereas the CU may comprise the layers above RLC layer, such as a packet data convergence protocol (PDCP) layer, a radio resource control (RRC) and an internet protocol (IP) layers. Other functional splits are possible too. In practice, any processing task may be performed in either the CU or the DU and the boundary where the responsibility is shifted between the CU and the DU may depend on the applied implementation.

[0047] The term “terminal device” refers to any end device that may be config-ured to perform wireless communication. By way of example, a terminal device may be referred to as a communication device, user equipment (UE), a Subscriber Station (SS), or a Mobile Station (MS). The terminal device may include a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones a tablet, a wearable terminal device, a personal digital assistant (PDA), portable computers, desktop computer, image capture terminal devices such as digital cameras, gamingterminal devices, music storage and playback appliances, vehicle-mounted wireless terminal devices, USB dongles, an Internet of Things (IoT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and / or other wireless devices operating in an industrial and / or an automated processing chain contexts), a consumer electronics device, a device operating on commercial and / or industrial wireless networks, and the like.

[0048] A term “resource”, as used herein, may refer to radio resources in timedomain, in frequency domain, in space domain, and / or in code domain. Some examplesof resources may include, e.g., a physical resource block (PRB), a radio frame, a sub-frame, a time slot, a subband, a frequency region, a sub-carrier, a beam, etc. The term “transmission” and / or “reception” may refer to wirelessly transmitting and / or receiving via a wireless propagation channel on radio resources.

[0049] Fig. 1 illustrates an example of a communication network to which exam-ples disclosed herein may be applied. The communication network or a cellular com- munication network may comprise a network node 110 configured to provide one or more cells, such as cell 100, and a network node 112 configured to provide one or moreother cells, such as cell 102. Each cell may, for example, be a macro cell, a micro cell,femto, or a pico cell. The cell may define a coverage area or a service area of the corresponding access node.

[0050] The network node (110, 112) may be configured to provide a user equip-ment (UE) 120 (one or more UEs) with wireless access to the communication network. The wireless access may comprise downlink (DL) communication from the network node (110, 112) to the UE 120 and uplink (UL) communication from the UE 120 to thenetwork node (110, 112). Examples of uplink channels may comprise physical uplinkcontrol channel (PUCCH) for transmitting control information and physical uplink shared channel (PUSCH) for transmitting data towards the network. Examples of downlink channels may comprise physical downlink control channel (PDCCH) for transmitting control information and physical downlink shared channel (PDSCH) for transmitting data towards the user equipment.

[0051] There may be a plurality of UEs (120, 122) in the system. Each of theplurality of UEs may be served by the same or by different network nodes (110, 112).UE may be configured with dual connectivity (DC), wherein the UE, for example UE120, may be connected to multiple network nodes (110, 112). The UEs (120, 122) maycommunicate with each other, in case device-to-device (D2D) communication interfaceis established between them via a so-called sidelink (SL). Such D2D communications may be referred to as machine-to-machine, peer-to-peer (P2P) communications, or ve- hicle-to-vehicle (V2V), for example.

[0052] In the case of multiple network nodes in the communication network, thenetwork nodes may be connected to each other via an interface. LTE specifications, forexample, refer to such an interface as an X2 interface. An interface between an LTEnode and a 5G node, or between two 5G nodes may be called an Xn interface.

[0053] The network nodes 110 and 112 may be further connected via anotherinterface to a core network 116 of the communication network. The LTE specifications specify the core network as an evolved packet core (EPC), and the core network may comprise a plurality of entities (e.g. a mobility management entity (MME) and a gateway node). The MME may handle mobility of terminal devices in a tracking area encom- passing a plurality of cells and handle signalling connections between the terminal de- vices and the core network. The gateway node may handle data routing in the core network and to / from the terminal devices. The 5G specifications specify the core net-work as a 5G core (5GC). The 5GC may, for example, comprise an access and mobilitymanagement function (AMF) and a user plane function / gateway (UPF) and other func- tions. The AMF may handle termination of non-access stratum (NAS) signalling, NAS ciphering & integrity protection, registration management, connection management, mobility management, access authentication and authorization, security context man-agement. The UPF node may, for example, support packet routing and forwarding,packet inspection and quality of service (QoS) handling.

[0054] As part of Rel19, Type-I codebook has been extended to support largertransmit antenna arrays with up to 128 CSI-RS ports.

[0055] For the Rel-19 Type-I SP codebook refinement for 48, 64, and 128 CSI-RS ports with RI=5-8, the following schemes are supported:^ The same O1=O2 value(s) as RI=1-4 are supported^ Scheme-A:o W1 structure:^ The 1st SD basis vector is freely selected and subsequent 2(RI=5-6) or 3 SD basis vectors (RI=7-8) are freely selected such that they are orthogonal in at least one dimension (horizontal or vertical). ^The v layers are mapped to the selected SD basis vectors follow-ing legacy Rel-15 Type-I for RI=5-8.^ W2 structure:o Following legacy Rel-15 Type-I RI=5-8^ Scheme-B (based on Scheme2 described in RAN1#116bis):o W1 structure:^ Independent selection of different ceil(v / 2) SD basis vectorsfor RI = v, where each SD basis vector is applied to two re- spective layers following legacy Rel-15 Type-I for RI=5-8, ex- cept that, if v is odd, the last SD basis vector is applied to the orphan layer. -FFS: mapping between the orphan layer and its selectedSD basis vector and, if needed, UE reporting of the se- lection -FFS: support of 4 selected SD basis vectors for RI=5-6^ The SD basis vectors are freely selected from a group ofN1N2 orthogonal SD DFT basis vectors via combinatorial in- dication, as well as a layer-common (q1,q2) oW2 structure:^ For the orphan layer, the inter-polarization co-phasing is se-lected from {1, j, -1, -j} ^For two layers sharing a same SD basis vector, the inter-po-larization co-phasing between two layers is selected from the following pairs {(1, -1), (j, -j)} to achieve inter-layer orthogo- nality.^ Only Scheme-A (RI=1-4+RI=5-8) and Scheme-B (RI=1-4+RI=5-8) are supportedin Rel-19

[0056] Two schemes have been introduced for this codebook extension,Scheme-A and Scheme-B. The two schemes differ in the way the spatial domain (SD)basis vectors (or spatial domain beams) are selected from the two-dimensional (2D)discrete Fourier transform (DFT) beam grid and the co-phasing coefficients across po-larisations for the selected beams

[0057] For ranks 5 to 8, a new SD basis vector selection mechanism has beenagreed for Scheme-A, whereby the spatial beams after the first beam, also referred toas anchor or reference beam, are selected from an extended orthogonal set. The an-chor beam is freely selected from an oversampled grid of beams. The extension isbased on the Kronecker structure of the 2D DFT beams, such that two orthogonal beams need to be orthogonal at least in one of the two dimensions. In legacy orthogo- nal beam selections, orthogonality in both dimensions is required.

[0058] In both legacy Type-I and Type-II codebooks, when oversampling is appliedto the 2D DFT grid of beams, the beams are selected from one of the ^^^^maximalorthogonal sets of beams of size ^^^^ , where ^^ × ^^ is the port layout with ^^ Azimuthbeams and ^^elevation beams, and ^^are the oversampling factors in the twodimensions, respectively. Maximal orthogonal sets of beams are disjoint orthogonalsets, i.e., any given beam in the codebook belongs to only one maximal orthogonal set.

[0059] Fig.2 illustrates the maximal orthogonal group of anchor beam A.

[0060] The Kronecker structure of the spatial beam definition is shown in equation(1).Due to the Kronecker structure, for any given beam, there are more than ^^^^ − 1 or-thogonal beams in the extended codebook, as illustrated in Fig.3. It can be shown thatthe size of this extended orthogonal set is larger than ^^^^and is equal to extended orthogonal group size = (^^ − 1)^^^^− (^^ − 1)(^^ − 1)

[0061] One issue related to the new extended set of orthogonal candidates for theselection of SD basis vectors is how to report the selected beams in an efficient way,e.g., by using as few signalling bits as possible, with signalling that can be specified ina relatively easy manner. Optimising the signalling for the selected SD bases other than the anchor beam is not a trivial problem. Let us consider the indication of up to 4 se-lected SD basis, denoted as beam A, B, C, D, where A is the anchor beam. Note that 3SD bases are indicated for rank 5 and 6, and 4 SD bases are indicated for rank 7 and 8. The number of choices for the anchor beam is simply ^^^^^^^^as in legacy Rel15 Type-I, where ^^,^ ∈ {0,1, … , ^^^^}indicate the Azimuth and elevation indices of beam A, respectively.

[0062] The number of choices for the second beam, beam B, corresponds tothe size of the extended orthogonal set of beam A, i.e.,− 1)^^^^ +(^^ − 1)^^^^ −− 1)(^^ − 1). For the third beam, beam C, however, things be-come more complicated, because the number of candidate choices depends on the location of beam B with respect to beam A and the intersection between the extended orthogonal sets of beam A and B. We can identify 5 different cases, each with a differ- ent number of choices for beam C. For the fourth beam, beam D, the candidate set size depends on the relative position of the selected beam A, B and C and the inter- section between the extended orthogonal sets of beam A, B and C, which leads to 20different cases. The complexity of these combinations is illustrated in Error! Refer-ence source not found. Table shown in Fig.4. Using this approach to define a sig-nalling method for the SD basis set is clearly impractical, even more so because it leads to a variable number of bits needed, depending on the relative position of the selected SD bases. Note that the bitwidth of the SD basis indication needs to be fixed for a given parameter combination, such that the payload size is predictable without need for further indication of which cases of the Table of Fig.4 are applicable.

[0063] Fig. 5 shows a flowchart of a method. The method may be performed atan apparatus. The apparatus may comprise or be comprised in a UE.

[0064] At 501, the method comprises selecting a first beam from a grid of beamscomprising× N^O^ two-dimensional discrete Fourier transform (DFT) beams.

[0065] At 502, the method comprises determining at least one additional beam,wherein the at least one additional beam is orthogonal to the first beam in at least one of the horizontal or vertical direction.

[0066] At 503, the method comprises determining at least one of two beam groupsto which the at least one additional beam belongs, one of the two beam groups being a horizontal orthogonal beam group associated with the first beam and another group of the beam groups being a vertical orthogonal beam group associated with the first beam.

[0067] At 504, the method comprises providing channel state information to a net-work device, the channel state information comprising at least one indication indicative of the first beam, the at least one of the beam groups and the at least one additional beam.

[0068] Fig. 6 shows a flowchart of a method. The method may be performed atan apparatus. The apparatus may comprise or be comprised in a network node such as a RAN node (e.g., gNB).

[0069] At 601, the method comprises receiving channel state information fromthe terminal device, the channel state information comprising at least one indicationindicative of a first beam selected from a grid of beams comprising× N^O^ two-dimensional DFT beams, at least one additional beam and at least one of two beam groups to which the at least one additional beam belongs, wherein the at least one ad- ditional beam is orthogonal to the first beam in at least one of the horizontal or vertical direction, one of the two beam groups being a horizontal orthogonal beam group as- sociated with the first beam and another being a vertical orthogonal beam group asso- ciated with the first beam.

[0070] At 602, the method comprises based on the channel state information,determining a precoder for downlink transmission to the user equipment.

[0071] In an example embodiment, the first beam and the at least one addi-tional beam are vectors (e.g., SD basis vectors) used to form the precoding matrix corresponding to the reported precoding matrix indicator (PMI) applicable to a vector of physical downlink shared channel (PDSCH) symbols to calculate a channel qualityindicator. The term “beam” and SD basis vector are used interchangeably in the fol-lowing.

[0072] It can be shown that, to ensure orthogonality between all the selected SDbasis vectors, the selected SD basis vectors must belong to at least one and the samebeam group, either the vertical or the horizontal orthogonal group of the anchor beam, or both. For example, if any one of beams B, C, D, etc. belongs to the vertical but not the horizontal orthogonal beam group of beam A, then also the remaining other selected beams must be in the same vertical orthogonal beam group. Note that, in the special case of all the selected beams belonging to the maximal orthogonal group of beam A, shown in Error! Reference source not found.3, all the selected beams belong to both vertical and horizontal orthogonal groups.

[0073] The proposed signalling of SD basis vectors from the extended orthogonalcandidate set is based on the property described above, which must be satisfied toensure orthogonality between the selected SD bases. That is, that all the selectedbeams must be orthogonal to one another in at least one dimension (e.g., in at leastone of the horizontal or vertical direction). It can be shown, for example by induction, that for a given anchor beam A, this condition can be met if all the selected beams belong to one of two groups, which we refer to as horizontal and vertical orthogonal groups of beam A, respectively.

[0074] By exploiting this property, a one-bit indicator, say ^^, to distinguish be-tween the two orthogonal groups of the anchor beam. In an example embodiment, theindication indicative of the beam group comprises a one-bit indicator.

[0075] The one-bit indicator may be introduced to indicate whether the reportedSD bases belong to the same horizontal or vertical orthogonal group as the anchor beam. Depending on the value of this one-bit indicator, each SD beam after the anchorbeam may be indicated with log ^^^^ + log ^^ bits or log+ log ^^^^ bits. Note thatthe number of bits needed to indicate an SD beam is the same in both cases, if theoversampling factors are the same in the two dimensions, i.e.,= ^^. Therefore, thisone-bit indicator can be included in Part 2, as the payload for the SD basis indicator is independent of which orthogonal group is indicated.

[0076] Fig. 7 shows an example of a vertical orthogonal beam group of anchorbeam A.

[0077] The vertical orthogonal beam group of beam A may comprise(^^ − 1)^^^^ beams that are orthogonal to A in at least the horizontal (Azimuth) di-mension and the ^^ − 1 beams that are orthogonal to A only in the vertical (elevation)dimension (whereinand ^^ are the oversampling factors in the horizontal and verti-cal dimension, respectively). The beams in the vertical orthogonal group may be iden-tified by a pair of indices, (^^, ^^), with ^^ ∈ {0,1, … , ^^ − 1} and ^^ ∈ {0,1, , … , ^^^^ − 1}.Note that the size of the vertical orthogonal group of beam A− 1)^^^^ + ^^ −1, which is smaller than ^^^^^^, i.e. the vertical orthogonal group of beam A is a sub-set of the beams that can be identified by (^^, ^^), with ^^ ∈ {0,1, … ,− 1} and ^^ ∈{0,1, , … , ^^^^ − 1}.

[0078] Fig. 8 shows an example of a horizontal orthogonal beam group of beamA.

[0079] The horizontal orthogonal beam group of beam A may comprise(^^ − 1)^^^^ beams that are orthogonal to A in at least the vertical (elevation) dimen-sion and the ^^ − 1 beams that are orthogonal to A only in the horizontal (Azimuth)dimension. The beams in the horizontal orthogonal group may be identified by a pair ofindices, (^^, ^^), with ^^ ∈ {0,1, … , ^^^^ − 1} and ^^ ∈ {0,1, , … , ^^ − 1}. Note that the sizeof the horizontal orthogonal group of beam A is (^^ − 1)^^^^ + ^^ − 1, which is smallerthan ^^^^^^, i.e. the horizontal orthogonal group of beam A is a subset of the beamsthat can be identified

[0080] Fig. 9 shows the fields of the proposed indication of the SD basis vectorselection, in the example of four reported SD basis, e.g., beam A, B, C and D whichapplies to reported ranks 7 or 8. The indication of beam group, which is a one-bit indi- cator, is used to determine how beam B, C and D are reported.

[0081] Fig. 10 shows a flowchart of how it is determined how beams B,C and Dare reported.

[0082] Each selected beam may be indicated by a separate pair of indices,(^^, ^^) as in the following example.For the anchor beamFor the remaining beams B, C, D:^ if ^^ = 0 (vertical orthogonal group of A), then ^^,^, ^^,^, ^^,^ ∈ {0,1, … , ^^},^^,^, ^^,^, ^^,^ ∈ {0,1, … , ^^^^}^ if ^^ = 1 (horizontal orthogonal group of A), then ^^,^, ^^,^, ^^,^ ∈ {0,1, … , ^^^^},^^,^, ^^,^, ^^,^ ∈ {0,1, … , ^^}

[0083] In another example, the value ^^ = 0 may indicate the horizontal groupand ^^ = 1 the vertical group.

[0084] As shown in Fig.10, the indication indicative of the at least additionalspatial domain basis comprises log(^^^^^^) bits for the vertical group, andlog(^^^^^^) bits for the horizontal group. The number of bits needed to indicate beamB, C and D is log(^^^^^^) for the vertical group, and log(^^^^^^) for the horizontalgroup, hence the two bitwidths are the same for ^^ = ^^.

[0085] Table 1 illustrates how the proposed signalling of the SD basis vectorssimplifies the complexity of cases listed in the Table shown in Fig.4. Note that the in-dication of beam group of Fig.9 determines which of the two cases is applicable forthe choices of beams B, C and D in Table 1. Beam A Beam B Beam C Beam D Case Choices Choices Choices Choices 1^^^^^^ ^^^^^^ ^^^^^^^^^^^^^^2 ^^^^^^ ^^^^^^ ^^^^^^Table 1

[0086] The channel state information (CSI) may be provided to the network in aCSI report. In some cases,= ^^, as agreed, for example, in Rel19 for the sup-ported port layouts. That is, the oversampling factors are the same for the two dimen-sions (^^ = ^^), for all the supported combinations of ^^, ^^. In this case, the numberof bits required to signal beam B, C and D is the same in both cases, hence the beam group indicator can be reported in Part 2 CSI together with the indicators for beam A, B, C and D because the payload size is determined only by the values of ^^, ^^and =^^. In an example embodiment, the one-bit indicator ^^ is mapped to uplink con-trol information (UCI) Part 2 of a CSI report, together with the other PMI parameters.≠ ^^ for some combinations of ^^, ^^, because the payload size of the beam indi-cation varies depending on the value of ^^, this one-bit indicator may be reported in UCIPart 1.

[0087] The channel state information report may be associated with a Type-Icodebook of channel state information. A method as described with reference to Fig. 4may comprise receiving a set of channel state information reference signal resources from a network device and determining the first beam and the at least one additional beam based on the measurement of the reference signal resources.

[0088] Fig. 11 shows a signalling diagram of a Type-I CSI report including thebeam indication mechanism described with reference to Figs.4 to 10 above.

[0089] At step 1, the UE provides a UE capability indication of supporting Type-1 codebook with Scheme-A.

[0090] At step 2, the gNB configures / triggers / activates Type-1 CSI reporting.

[0091] At step 3, the gNB transmits CSI-RS resources.

[0092] At step 4, the UE calculates CSI, including SD basis vector (or beam)selection for Type-1 PMI, and selects a first SD basis (or beam), at least one additional SD basis (or beam) and determines one of at least two beam groups the SD bases belong to.

[0093] At step 5, the UE reports CSI containing separate SD basis (or beam)indicators and an indicator of which beam group the SD bases (or beams) belong to.

[0094] At step 6, the gNB reconstructs precoding matrices and calculates theprecoder for PDSCH transmission.

[0095] Fig. 12 shows, by way of example, a block diagram of an apparatus 10.The apparatus 10 comprises, for example, at least one processor 12 and at least onememory 14 storing instructions 15 that, when executed by the at least one processor,cause the apparatus 10 at least to perform the method or methods (or portion(s) thereof)as disclosed herein, and any of the embodiments (or respective portion(s) thereof). In an example, the at least one memory and the instructions (e.g. a computer program code, software), are configured, with the at least one processor, to cause the apparatus10 to perform the method or methods (or portion(s) thereof) as disclosed herein, andany of the embodiments (or respective portion(s) thereof).

[0096] A processor 12 may comprise circuitry, or be constituted as circuitry orcircuitries, the circuitry or circuitries being configured to perform phases of methods in accordance with embodiments described herein.

[0097] As used herein, the term “circuitry” may refer to one or more or all of thefollowing: (a) hardware-only circuit implementations, such as implementations in only analog and / or digital circuitry, and (b) combinations of hardware circuits and software, such as, as applicable: (i) a combination of analog and / or digital hardware circuit(s) with software / firmware and (ii) any portions of hardware processor(s) with software (includ- ing digital signal processor(s)), software, and memory(ies) that work together to causean apparatus, such as a user equipment, to perform various functions) and (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a micropro- cessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation. This definition of circuitry applies to all uses of this term herein, including in any claims. As a further example, as used herein, the term circuitry also covers an implementation of merely a hardware circuit or proces- sor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or pro- cessor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[0098] The memory 14 may be implemented using any suitable data storagetechnology. The memory may comprise a database for storing data. The memory 14may, for example, be at least in part external to apparatus 10 but accessible to appa-ratus 10.

[0099] The instructions 15 may be comprised in a computer readable medium ora non-transitory computer readable medium. A term non-transitory, as used herein, is a limitation of the medium itself (i.e. tangible, not a signal) as opposed to a limitation on data storage persistency (e.g. random access memory, RAM, vs. read only memory, ROM).

[0100] For example, the apparatus 10 is a terminal device, such as a UE. Asanother example, the apparatus is comprised in such a terminal device, e.g. as a chip-set configured to control the terminal device. The apparatus 10 may be caused or con-figured or comprise means to perform at least the method of Fig. 4 and / or any one ormore of the embodiments described herein.

[0101] As another example, the apparatus 10 is a network entity. In anotherembodiment, the apparatus is comprised in such a network entity, e.g. as a chipsetconfigured to control the network entity. The apparatus 10 may be caused or configuredor comprise means to perform at least the method of Fig. 5 and / or any one or more ofthe embodiments described herein.

[0102] The apparatus may comprise one or more entities of any of protocollayers, such as a MAC entity, an RRC entity, an RLC entity, a PDCP entity or a PHY entity. In some embodiments, the entity is configured to perform at least the method ofFigs. 5, and / or any one or more of the embodiments described.

[0103] The apparatus 10 comprises a radio interface 16. The radio interface16 may provide the apparatus 10 with communication capabilities. The radio interface16 may comprise a receiver configured to receive information in accordance with atleast one cellular or non-cellular standard. The radio interface 16 may comprise a trans- mitter configured to transmit information in accordance with at least one cellular or non- cellular standard. The receiver may comprise more than one receiver. The transmittermay comprise more than one transmitter. The radio interface 16 may comprise a trans-ceiver configured to receive and transmit information in accordance with at least onecellular or non-cellular standard. The transceiver may comprise more than one trans-ceiver.

[0104] The apparatus 10 may comprise a user interface 18 comprising, forexample, at least one of a keypad, a microphone, a touch display, a display, a speaker, etc. The user interface 18 may be used to control the apparatus by the user. The user interface 18 may be external to the apparatus 10. For example, the apparatus 10 may be connected to another device, such as a computer, either via wireless or wired con- nection, and the apparatus 10 is controlled by the user via the computer.

[0105] In an embodiment, at least some of the processes described herein maybe carried out by an apparatus comprising means for carrying out at least some of the described processes. Means for performing method steps as disclosed herein may in- clude software and / or hardware components of the apparatus 10. For example, the at least one processor 12, the memory 14, and the computer program code form means for carrying out the method or methods (or portion(s) thereof) as disclosed herein, and any of the embodiments (or respective portion(s) thereof). As used herein the term “means” is to be construed in singular form, i.e. referring to a single element, or in plural form, i.e. referring to a combination of single elements. Therefore, terminology “means for [performing A, B, C]”, is to be interpreted to cover an apparatus in which there is only one means for performing A, B and C, or where there are separate means for performing A, B and C, or partially or fully overlapping means for performing A, B, C. Further, terminology “means for performing A, means for performing B, means for per- forming C” is to be interpreted to cover an apparatus in which there is only one means for performing A, B and C, or where there are separate means for performing A, B and C, or partially or fully overlapping means for performing A, B, C.

[0106] There may be provided an apparatus comprising at least one processor,and at least one memory storing instructions which, when executed by the at least oneprocessor, cause the apparatus at least to perform selecting a first beam from a grid ofbeams comprising N^O^ × N^O^ two-dimensional discrete Fourier transform beams,determining at least one additional beam, wherein the at least one additional beam is orthogonal to the first beam in at least one of the horizontal or vertical direction, deter- mining at least one of two beam groups to which the at least one additional beam be- longs, one of the two beam groups being a horizontal orthogonal beam group associ- ated with the first beam, and another group of the beam groups being a vertical orthog-onal beam group associated with the first beam and providing channel state informationto a network device, the channel state information comprising at least one indication indicative of the first beam, the at least one of the beam groups and the at least one additional beam.

[0107] The horizontal orthogonal beam group may comprise (^^ − 1)^^^^ beamsthat are orthogonal to the first beam in at least the vertical dimension, and ^^ − 1 beamsthat are orthogonal to the first beam only in the horizontal dimension, whereinand ^^are the oversampling factors in the horizontal and vertical dimension, respectively.

[0108] The vertical orthogonal beam group may comprise (^^ − 1)^^^^ beamsthat are orthogonal to the first beam in at least the horizontal dimension, and ^^ − 1beams that are orthogonal to the first beam only in the vertical dimension, whereinand ^^are the oversampling factors in the horizontal and vertical dimension, respec- tively.

[0109] The indication indicative of the at least additional spatial domain basis maycomprise log(^^^^^^) bits for the vertical group, and log(^^^^^^) bits for the horizontalgroup.

[0110] The channel state information may be associated with a type I codebook ofchannel state information.

[0111] The indication indicative of the beam group may comprise a one-bit indica-tor.

[0112] The first beam and the at least one additional beam may be vectors usedto form the precoding matrix corresponding to the reported precoding matrix indicator applicable to a vector of physical downlink shared channel symbols to calculate a chan- nel quality indicator.

[0113] There may be provided an apparatus comprising at least one processor,and at least one memory storing instructions which, when executed by the at least oneprocessor, cause the apparatus at least to perform receiving channel state informationfrom the terminal device, the channel state information comprising at least one indica-tion indicative of a first beam selected from a grid of beams comprising × N^O^two-dimensional discrete Fourier transform beams, at least one additional beam and at least one of two beam groups to which the at least one additional beam belongs, wherein the at least one additional beam is orthogonal to the first beam in at least one of the horizontal or vertical direction, one of the two beam groups being a horizontal orthogonal beam group associated with the first beam, and another being a vertical orthogonal beam group associated with the first beam and based on the channel state information, determining a precoder for downlink transmission to the user equipment.

[0114] The horizontal orthogonal beam group may comprise (^^ − 1)^^^^ beamsthat are orthogonal to the first beam in at least the vertical dimension, and ^^ − 1 beamsthat are orthogonal to the first beam only in the horizontal dimension, whereinand ^^are the oversampling factors in the horizontal and vertical dimension, respectively.

[0115] The vertical orthogonal beam group may comprise (^^ − 1)^^^^ beamsthat are orthogonal to the first beam in at least the horizontal dimension, and ^^ − 1beams that are orthogonal to the first beam only in the vertical dimension, whereinand ^^are the oversampling factors in the horizontal and vertical dimension, respec- tively.

[0116] The indication indicative of the at least additional spatial domain basis maycomprise log(^^^^^^) bits for the vertical group, and log(^^^^^^) bits for the horizontalgroup.

[0117] The channel state information may be associated with a type I codebook ofchannel state information.

[0118] The indication indicative of the beam group may comprise a one-bit indica-tor.

[0119] The first beam and the at least one additional beam may be vectors usedto form the precoding matrix corresponding to the reported precoding matrix indicator applicable to a vector of physical downlink shared channel symbols to calculate a chan- nel quality indicator.

[0120] There is provided a computer program comprising instructions which, whenexecuted by an apparatus, cause the apparatus to perform at least the following: se-lecting a first beam from a grid of beams comprising× N^O^ two-dimensional dis-crete Fourier transform beams, determining at least one additional beam, wherein the at least one additional beam is orthogonal to the first beam in at least one of the hori- zontal or vertical direction, determining at least one of two beam groups to which the at least one additional beam belongs, one of the two beam groups being a horizontalorthogonal beam group associated with the first beam, and another group of the beam groups being a vertical orthogonal beam group associated with the first beam and providing channel state information to a network device, the channel state information comprising at least one indication indicative of the first beam, the at least one of the beam groups and the at least one additional beam.

[0121] There is provided a computer program comprising instructions which, whenexecuted by an apparatus, cause the apparatus to perform at least the following: re-ceiving channel state information from the terminal device, the channel state infor-mation comprising at least one indication indicative of a first beam selected from a gridof beams comprising× N^O^ two-dimensional discrete Fourier transform beams,at least one additional beam and at least one of two beam groups to which the at least one additional beam belongs, wherein the at least one additional beam is orthogonal tothe first beam in at least one of the horizontal or vertical direction, one of the two beamgroups being a horizontal orthogonal beam group associated with the first beam, and another being a vertical orthogonal beam group associated with the first beam and based on the channel state information, determining a precoder for downlink transmis- sion to the user equipment.

[0122] Even though this disclosure has been described above with reference tonon-limiting and illustrative examples according to the accompanying figures, it is clearthat the scope of this disclosure is not restricted thereto – but can be modified in manydifferent ways. As technology advances, it will become apparent to a person skilled in art as to how the disclosure can be further implemented and / or modified in various ways. Further, it is clear to a person skilled in the art that the embodiments described herein may, but are not required to, be combined in various ways with other embodi- ments described herein.

Claims

CLAIMS1. An apparatus comprising means for:selecting a first beam from a grid of beams comprising× N^O^ two-dimensional discrete Fourier transform beams; determining at least one additional beam, wherein the at least one addi- tional beam is orthogonal to the first beam in at least one of the horizontal or vertical direction; determining at least one of two beam groups to which the at least one additional beam belongs, one of the two beam groups being a horizontal orthogonal beam group associated with the first beam, and another group of the beam groups be- ing a vertical orthogonal beam group associated with the first beam; and providing channel state information to a network device, the channel state information comprising at least one indication indicative of the first beam, the at least one of the beam groups and the at least one additional beam.

2. The apparatus according to claim 1, wherein the horizontal orthogonalbeam group comprises (^^ − 1)^^^^ beams that are orthogonal to the first beam in atleast the vertical dimension, and ^^ − 1 beams that are orthogonal to the first beamonly in the horizontal dimension; the vertical orthogonal beam group comprises− 1)^^^^ beams thatare orthogonal to the first beam in at least the horizontal dimension, and ^^ − 1beams that are orthogonal to the first beam only in the vertical dimension; whereinand ^^are the oversampling factors in the horizontal and vertical dimension, respectively.

3. The apparatus according to claim 2, wherein the indication indicative ofthe at least additional spatial domain basis comprises log(^^^^^^) bits for the verticalgroup, and log(^^^^^^) bits for the horizontal group.

4. The apparatus according to any of claims 1 to 3, wherein the channelstate information is associated with a type I codebook of channel state information.

5. The apparatus according to any of claims 1 to 4, wherein the indicationindicative of the beam group comprises a one-bit indicator.

6. The apparatus according to any of claims 1 to 5, wherein the first beamand the at least one additional beam are vectors used to form the precoding matrix corresponding to the reported precoding matrix indicator applicable to a vector of physical downlink shared channel symbols to calculate a channel quality indicator.

7. An apparatus comprising means for:receiving channel state information from the terminal device, the channelstate information comprising at least one indication indicative of a first beam selectedfrom a grid of beams comprising× N^O^ two-dimensional discrete Fourier trans-form beams, at least one additional beam and at least one of two beam groups to which the at least one additional beam belongs, wherein the at least one additional beam is orthogonal to the first beam in at least one of the horizontal or vertical direc- tion, one of the two beam groups being a horizontal orthogonal beam group associated with the first beam, and another being a vertical orthogonal beam group associated with the first beam; and based on the channel state information, determining a precoder for downlink transmission to the user equipment.

8. The apparatus according to claim 7, wherein the horizontal orthogonalbeam group comprises (^^ − 1)^^^^ beams that are orthogonal to the first beam in atleast the vertical dimension, and ^^ − 1 beams that are orthogonal to the first beamonly in the horizontal dimension; the vertical orthogonal beam group comprises− 1)^^^^ beams thatare orthogonal to the first beam in at least the horizontal dimension, and ^^ − 1beams that are orthogonal to the first beam only in the vertical dimension; whereinand ^^are the oversampling factors in the horizontal and vertical dimension, respectively.

9. The apparatus according to claim 8, wherein the indication indicative ofthe at least additional spatial domain basis comprises log(^^^^^^) bits for the verticalgroup, and log(^^^^^^) bits for the horizontal group.

10. The apparatus according to any of claims 7 to 9, wherein the channelstate information is associated with a type I codebook of channel state information.

11. The apparatus according to any of claims 7 to 10, wherein the indicationindicative of the beam group comprises a one-bit indicator.

12. The apparatus according to any of claims 7 to 11, wherein the first beamand the at least one additional beam are vectors used to form the precoding matrix corresponding to the reported precoding matrix indicator applicable to a vector of physical downlink shared channel symbols to calculate a channel quality indicator.

13. A method comprising:selecting a first beam from a grid of beams comprising× N^O^ two-dimensional discrete Fourier transform beams; determining at least one additional beam, wherein the at least one addi- tional beam is orthogonal to the first beam in at least one of the horizontal or vertical direction; determining at least one of two beam groups to which the at least one additional beam belongs, one of the two beam groups being a horizontal orthogonal beam group associated with the first beam and another group of the beam groups be- ing a vertical orthogonal beam group associated with the first beam; and providing channel state information to a network device, the channel state information comprising at least one indication indicative of the first beam, the at least one of the beam groups and the at least one additional beam.

14. A method comprising:receiving channel state information from the terminal device, the channelstate information comprising at least one indication indicative of a first beam selectedfrom a grid of beams comprising× N^O^ two-dimensional discrete Fourier trans-form beams, at least one additional beam and at least one of two beam groups to which the at least one additional beam belongs, wherein the at least one additional beam is orthogonal to the first beam in at least one of the horizontal or vertical direc- tion,one of the two beam groups being a horizontal orthogonal beam group associated with the first beam and another being a vertical orthogonal beam group as- sociated with the first beam; and based on the channel state information, determining a precoder for downlink transmission to the user equipment.

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