Three-port uplink precoding

Abstract

The disclosure inter alia relates to a user equipment. The user equipment may comprise means for obtaining a precoding matrix for precoding an uplink data stream to be transmitted to a network node by the user equipment using three antenna ports. The uplink data stream may comprise at most three uplink layers, wherein each of the at most three uplink layers is to be transmitted to the network node using the three antenna ports. The precoding matrix may be obtainable based on performing at least the following: obtaining an oversampled 3×3N discrete Fourier transform, DFT, matrix with an oversampling factor N, wherein N is an arbitrary natural number, wherein the oversampled 3×3N DFT matrix comprises 3N column vectors forming N groups of column vectors, with each group n of the N groups of column vectors comprising the n th , (N + n) th , and (2N + n) th column vector of the oversampled 3×3N DFT matrix, with n ∈ {1,..., N}; determining a 3×3 matrix consisting of three column vectors comprised by a respective group of the N groups of column vectors; determining the precoding matrix based on the 3×3 matrix. The user equipment may further comprise means for generating, based on the uplink data stream and the precoding matrix, a precoded uplink data stream. The user equipment may further comprise means for transmitting the precoded uplink data stream to the network node using the three antenna ports.

Description

[0001] Three-Port Uplink Precoding TECHNOLOGICAL FIELD Various example embodiments relate to wireless communication networks, in particular to precoding an uplink data stream in such networks. BACKGROUND Multiple-input and multiple-output (MIMO) is a technique for multiplying the capacity of a radio link using multiple transmission and / or receiving antennas or antenna ports which is used in various wireless communication networks. Thereby, an antenna port, or simply port, may be understood as a logical concept representing a set of transmission and / or receiving resources which are perceived by a receiver as having the same radio channel properties. In MIMO, uplink (UL) data may be transmitted via the physical uplink shared channel (PUSCH) using one or more layers. Thereby, each of the one or more layers corresponds to an individual data stream. Multiple layers may thus be used to simultaneously transmit multiple data streams. In order to enable usage of MIMO, various precoding techniques may be used. Examples of wireless communication networks comprise cellular networks such as networks operating according to Long Term Evolution (LTE) or 5G radio access technology.5G radio access technology may also be referred to as New Radio (NR) access technology. The 3rd Generation Partnership Project, 3GPP, develops standards for LTE as well as 5G / NR. One of the topics discussed within 3GPP is how to improve various techniques related to MIMO and in particular to precoding an uplink data stream. SUMMARY OF SOME EXEMPLARY EMBODIMENTS Current 5G / NR radio access technology supports one-port (1-port), two-port (2-port), four-port (4-port) and eight- port (8-port) physical uplink shared channel (PUSCH) transmission. Presently commercially available user equipment (UE) devices, however, are typically equipped with only one or two transmission (Tx) antennas / antenna ports. As a result, within the current 5G / NR radio access technology, UEs presently commercially available only support one-port (1-port) or two-port (2-port) PUSCH transmission. Future UEs, on the other hand, might be equipped with three or more transmission antennas / antenna ports. In view of the above, certain embodiments of the disclosure may have the effect of enabling three-port uplink transmission, e.g. in 5G / NR. In particular, certain embodiments of the disclosure may allow for transmitting each of one or more UL layers using three (or more) antennas / antenna ports of a UE. In particular for transmitting an UL data stream using more than one antenna / antenna port, the UL data stream may be precoded. To this end, a precoding matrix may be used. A precoding matrix which allows to transmit each of one or more UL layers using all available antennas / antenna ports may be referred to as a fully coherent precoding matrix. Similarly, a user equipment capable of transmitting each of one or more UL layers using all available antennas / antenna ports may be referred to as a fully coherent user equipment. Certain embodiments of the disclosure may therefore enable fully coherent three-port uplink transmission. Further, certain embodiments of the disclosure may have the effect of providing and / or using one or more precoding matrices being unitary, comprising pairwise orthogonal vectors and / or comprising one or more vectors having constant magnitude / modulus, e.g. having unit length. According to a first exemplary aspect, there is disclosed a user equipment. The user equipment may comprise means for obtaining a precoding matrix for precoding an uplink data stream to be transmitted to a network node by the user equipment using three antenna ports. The uplink data stream may comprise at most three uplink layers, wherein each of the at most three uplink layers is to be transmitted to the network node using the three antenna ports. The precoding matrix may be obtainable based on performing at least the following: obtaining an oversampled 3×3^^ discrete Fourier transform, DFT, matrix with an oversampling factor ^^, wherein ^^ is an arbitrary natural number, wherein the oversampled 3×3^^ DFT matrix comprises 3^^ column vectors forming ^^ groups of column vectors,with each group ^^ of the ^^ groups of column vectors comprising the ^^^^ℎ, (^^ + and (2^^ + ^^)^^ℎ columnvector of the oversampled 3×3^^ DFT matrix, with ^^ ∈ {1, … , ^^}; determining a 3×3 matrix consisting of threecolumn vectors comprised by a respective group of the ^^ groups of column vectors; determining the precoding matrix based on the 3×3 matrix. The user equipment may further comprise means for generating, based on the uplink data stream and the precoding matrix, a precoded uplink data stream. The user equipment may further comprise means for transmitting the precoded uplink data stream to the network node using the three antenna ports. According to a second exemplary aspect, there is disclosed a user equipment. The user equipment may comprise means for obtaining a precoding matrix for precoding an uplink data stream to be transmitted to a network node by the user equipment using three antenna ports. The uplink data stream may comprise at most three uplink layers, wherein each of the at most three uplink layers is to be transmitted to the network node using the three antenna ports. The precoding matrix may comprise or may correspond to at least one of the following matrices: 1 1 1 1 1 −0.5 − 0.866^^1 −0.5 + 0.866^^1 [1] ;[] ;[] ;[0.5 − 0.866^^ ] ; 0.5 + 0.866^^ ] ;√3−0.5 + 0.866^^ −0.5 − 0.866^^ −0.5 − 0.866^^ −0.5 + −0.5 + ] ;−0.5 − ; 1 0.5 − 0.866^^ 0.5 + ] ;−1 −0.5 − 0.866^^ −0.5 + 1 The user equipment may further comprise means for generating, based on the uplink data stream and the precoding matrix, a precoded uplink data stream. The user equipment may further comprise means for transmitting the precoded uplink data stream to the network node using the three antenna ports. According to a third exemplary aspect, there is disclosed a network node. The network node may comprise means for receiving a precoded uplink data stream. The precoded uplink data stream may have been transmitted to the network node by a user equipment using three antenna ports. The precoded uplink data stream may have been generated by the user equipment based on an uplink data stream and a precoding matrix. The uplink data stream may comprise at most three uplink layers, wherein each of the at most three uplink layers may have been transmitted to the network node by the user equipment using the three antenna ports. The precoding matrix may be obtainable based on performing at least the following: obtaining an oversampled 3×3^^ discrete Fourier transform, DFT, matrix with an oversampling factor ^^, wherein ^^ is an arbitrary natural number, wherein the oversampled 3×3^^ DFT matrix comprises 3^^ column vectors forming ^^ groups of column vectors, with each group ^^ of the ^^ groups ofcolumn vectors comprising the ^^^^ℎ, (^^ + column vector of the oversampled 3×3^^ DFTmatrix, with ^^ ∈ {1, … , ^^}; determining a 3×3 matrix consisting of three column vectors comprised by a respectivegroup of the ^^ groups of column vectors; determining the precoding matrix based on the 3×3 matrix. The network node may further comprise means for determining, based on the received precoded uplink data stream, the uplink data stream. According to a fourth exemplary aspect, there is disclosed a network node. The network node may comprise means for receiving a precoded uplink data stream. The precoded uplink data stream may have been transmitted to the network node by a user equipment using three antenna ports. The precoded uplink data stream may have been generated by the user equipment based on an uplink data stream and a precoding matrix. The uplink data stream may comprise at most three uplink layers, wherein each of the at most three uplink layers may have been transmitted to the network node by the user equipment using the three antenna ports. The precoding matrix may comprise or may correspond to at least one of the following matrices: 1 1 11 1 05 08 6^^1 −0.5 + 0.866^^1 0.5 − 0.866^^1 1 −. − . 61 [1] ;[] ;[] ;[] ; 0.5 + 0.866^^ ] ;3 √−0.5 + 0.866^^ −0.5 − 0.866^^ −0.5 − 0.866^^ −0.5 +- ; The network node may further comprise means for determining, based on the received precoded uplink data stream, the uplink data stream. According to a fifth exemplary aspect, there is disclosed a user equipment. The user equipment may comprise means for obtaining a precoding matrix for precoding an uplink data stream to be transmitted to a network node by the user equipment using three antenna ports. The uplink data stream may comprise at most three uplink layers, wherein each of the at most three uplink layers is to be transmitted to the network node using the three antenna ports. The precoding matrix may be obtainable based on performing at least the following: obtaining a 3^^×3^^ discrete Fourier transform, DFT, matrix with a matrix order parameter ^^, wherein ^^ is an arbitrary natural number, wherein the3^^×3^^ DFT matrix comprises 3^^ rows forming 3^^ − 2 sub-matrices, with each of the 3^^ − 2 sub-matricesconsisting of three consecutive rows of the 3^^×3^^ DFT matrix, wherein each of the 3^^ − 2 sub-matrices comprises3^^ column vectors forming ^^ groups of column vectors, with each group ^^ of the ^^ groups of column vectorscomprising the ^^^^ℎ, (^^ + ^^)^^ℎ, and (2^^ + ^^)^^ℎ column vector of the respective sub-matrix, with ^^ ∈ {1, … , ^^};determining a 3×3 matrix based on a sub-matrix of the 3^^ − 2 sub-matrices, the 3×3 matrix consisting of threecolumn vectors comprised by a respective group of the ^^ groups of column vectors comprised by the sub-matrix; determining the precoding matrix based on the 3×3 matrix. The user equipment may further comprise means for generating, based on the uplink data stream and the precoding matrix, a precoded uplink data stream. The user equipment may further comprise means for transmitting the precoded uplink data stream to the network node using the three antenna ports. According to a sixth exemplary aspect, there is disclosed a user equipment. The user equipment may comprise means for obtaining a precoding matrix for precoding an uplink data stream to be transmitted to a network node by the user equipment using three antenna ports. The uplink data stream may comprise at most three uplink layers, wherein each of the at most three uplink layers is to be transmitted to the network node using the three antenna ports. The precoding matrix may comprise or may correspond to at least one of the following matrices: The user equipment may further comprise means for generating, based on the uplink data stream and the precoding matrix, a precoded uplink data stream. The user equipment may further comprise means for transmitting the precoded uplink data stream to the network node using the three antenna ports. According to a seventh exemplary aspect, there is disclosed a network node. The network node may comprise means for receiving a precoded uplink data stream. The precoded uplink data stream may have been transmitted to the network node by a user equipment using three antenna ports. The precoded uplink data stream may have been generated by the user equipment based on an uplink data stream and a precoding matrix. The uplink data stream may comprise at most three uplink layers, wherein each of the at most three uplink layers may have been transmitted to the network node by the user equipment using the three antenna ports. The precoding matrix may be obtainable based on performing at least the following: obtaining a 3^^×3^^ discrete Fourier transform, DFT, matrix with a matrix order parameter ^^, wherein ^^ is an arbitrary natural number, wherein the 3^^×3^^ DFT matrix comprises 3^^rows forming 3^^ − 2 sub-matrices, with each of the 3^^ − 2 sub-matrices consisting of three consecutive rows ofthe 3^^×3^^ DFT matrix, wherein each of the 3^^ − 2 sub-matrices comprises 3^^ column vectors forming ^^ groupsof column vectors, with each group ^^ of the ^^ groups of column vectors comprising the ^^^^ℎ, and(2^^ + ^^)^^ℎ column vector of the respective sub-matrix, with ^^ ∈ {1, … , ^^}; determining a 3×3 matrix based on asub-matrix of the 3^^ − 2 sub-matrices, the 3×3 matrix consisting of three column vectors comprised by a respectivegroup of the ^^ groups of column vectors comprised by the sub-matrix; determining the precoding matrix based on the 3×3 matrix. The network node may further comprise means for determining, based on the received precoded uplink data stream, the uplink data stream. According to an eighth exemplary aspect, there is disclosed a network node. The network node may comprise means for receiving a precoded uplink data stream. The precoded uplink data stream may have been transmitted to the network node by a user equipment using three antenna ports. The precoded uplink data stream may have been generated by the user equipment based on an uplink data stream and a precoding matrix. The uplink data stream may comprise at most three uplink layers, wherein each of the at most three uplink layers may have been transmitted to the network node by the user equipment using the three antenna ports. The precoding matrix may comprise or may correspond to at least one of the following matrices: 1 1 1 1 1 1 1 2^^^^ 1 −2^^^^ 1 −2^^^^ 1 1 1 2^^^^ [1] ;[ −^^6] ;[ −^^6] ;[ ^^ 6] ;[ −1] ;[ ^^ 6] ;−2^^^^ 2^^^^ 2^^^^ −2^^^^ √31 √3 √3 √3 √3 6 6 1 √3 −^^ −^^ 6 −^^ −^^ 6 2^^^^ −2^^^^ −2^^^^ 2^^^^ 6 61 1 1 −^^6−2^^^^ 1 −^^ ^^ −1 ^^62^^^^ 1 2^^^ 1 1^ −2^^^^] ; ] ; ] ; ] ; ] ; ] ;[ [ [ [ [ [1 16 6 6 6 −^^ −^^ −^^ −^^3 3 3 3 3 3 √ √ √ √ √ √1 −1 1 1 −1 −1 −2^^^^ 2^^^^ 2^^^^ −2^^^^ 6 6 61 16−^^ −^^ −^^ −^^ 1 1 1 1 1 1 ]; ] ; ] ; ] ; ] ; ] ;[ [ [ [ [ [1 −11 1 −1 −1 3 3 3 3 3 3 √ √ 2^^^^ √ −2^^^^ √ −2^^^^ √ √ 2^^^^1 1 66 6 6−^^ −^^ −^^ −^^ 1 1 −1 −11 −12^^^^ −2^^^^ −2^^^^ 2^^^^ 1 1 1 1 1 1 6 6 6] ; ] ; ] ; ] ; ] ; ] ;[ [6[ [ [ [1 −^^ −^^ −^^ 1 −^^ −2^^^^ 2^^^^ 2^^^^ −2^^^^3 3 3 3 3 3 √ √ √ √ √ √1 −16 6 6 6 −^^ −^^ ^^ ^^ 1 1 1 11 12^^^^ −2^^^^ 2^^^^ −2^^^^ 1 1 1 6 6 6] ; ] ; ] ;[ [ [61 −^^ 1 −^^ −^^ −^^ −2^^^^ 2^^^^ −2^^^^ 2^^^^3 3 3 √ √ √1 16 6 6 6 −^^ −^^ −^^ −^^ 1 1 1 11 1−2^^^^ −2^^^^ 2^^^^ 2^^^^ 1 1 1 6 6 6] ; ] ; ] ;[ [ [6^^ −1 ^^ ^^ −1 ^^ 2^^^^ 2^^^^ −2^^^^ −2^^^^3 3 3 √ √ √1 16 6 6 6 −^^ −^^ −^^ −^^ The network node may further comprise means for determining, based on the received precoded uplink data stream, the uplink data stream. According to each of the exemplary aspects, a respective method is also disclosed. Thus, according to the first exemplary aspect, there is disclosed a method performed by a user equipment. The method may comprise obtaining a precoding matrix for precoding an uplink data stream to be transmitted to a network node by the user equipment using three antenna ports. The uplink data stream may comprise at most three uplink layers, wherein each of the at most three uplink layers is to be transmitted to the network node using the three antenna ports. The precoding matrix may be obtainable based on performing at least the following: obtaining an oversampled 3×3^^ discrete Fourier transform, DFT, matrix with an oversampling factor ^^, wherein ^^ is an arbitrary natural number, wherein the oversampled 3×3^^ DFT matrix comprises 3^^ column vectors forming ^^groups of column vectors, with each group ^^ of the ^^ groups of column vectors comprising the ^^^^ℎ, (^^ + ^^)^^ℎ, andcolumn vector of the oversampled 3×3^^ DFT matrix, with ^^ ∈ {1, … , ^^}; determining a 3×3 matrixconsisting of three column vectors comprised by a respective group of the ^^ groups of column vectors; determining the precoding matrix based on the 3×3 matrix. The method may further comprise generating, based on the uplink data stream and the precoding matrix, a precoded uplink data stream. The method may further comprise transmitting the precoded uplink data stream to the network node using the three antenna ports. According to the second exemplary aspect, there is disclosed a method performed by a user equipment. The method may comprise obtaining a precoding matrix for precoding an uplink data stream to be transmitted to a network node by the user equipment using three antenna ports. The uplink data stream may comprise at most three uplink layers, wherein each of the at most three uplink layers is to be transmitted to the network node using the three antenna ports. The precoding matrix may comprise or may correspond to at least one of the following matrices: 1 1 1 1 − 1 1 [1] ;[− .1 1 1 1 1 1 05 0.866^^] ;[−0.5 + 0.866^^] ;[0.5 − 0.866^^ ] ;[ −1] ;[0.5 + 0.866^^ ] ;√31√3−0.5 + 0.866^^ √3−0.5 − 0.866^^ √3−0.5 − 0.866^^ √31√3−0.5 + 0.866^^; The method may further comprise generating, based on the uplink data stream and the precoding matrix, a precoded uplink data stream. The method may further comprise transmitting the precoded uplink data stream to the network node using the three antenna ports. According to the third exemplary aspect, there is disclosed a method performed by a network node. The method may comprise receiving a precoded uplink data stream. The precoded uplink data stream may have been transmitted to the network node by a user equipment using three antenna ports. The precoded uplink data stream may have been generated by the user equipment based on an uplink data stream and a precoding matrix. The uplink data stream may comprise at most three uplink layers, wherein each of the at most three uplink layers may have been transmitted to the network node by the user equipment using the three antenna ports. The precoding matrix may be obtainable based on performing at least the following: obtaining an oversampled 3×3^^ discrete Fourier transform, DFT, matrix with an oversampling factor ^^, wherein ^^ is an arbitrary natural number, wherein the oversampled 3×3^^ DFT matrix comprises 3^^ column vectors forming ^^ groups of column vectors, with each group ^^ of the ^^ groups ofcolumn vectors comprising the ^^^^ℎ, (^^ + column vector of the oversampled 3×3^^ DFTmatrix, with ^^ ∈ {1, … , ^^}; determining a 3×3 matrix consisting of three column vectors comprised by a respectivegroup of the ^^ groups of column vectors; determining the precoding matrix based on the 3×3 matrix. The method may further comprise determining, based on the received precoded uplink data stream, the uplink data stream. According to the fourth exemplary aspect, there is disclosed a method performed by a network node. The method may comprise receiving a precoded uplink data stream. The precoded uplink data stream may have been transmitted to the network node by a user equipment using three antenna ports. The precoded uplink data stream may have been generated by the user equipment based on an uplink data stream and a precoding matrix. The uplink data stream may comprise at most three uplink layers, wherein each of the at most three uplink layers may have been transmitted to the network node by the user equipment using the three antenna ports. The precoding matrix may comprise or may correspond to at least one of the following matrices: 1 1 1 1 −61 1 −. .1 1 0 1 1 6 1 1 [1] ;[05 8 ^^] ;[−0.5 + 0.866^^] ;[0.5 − 0.866^^ ] ;[ −1] ;[0.5 + 0.866^^ ] ;√31√3−0.5 + 0.866^^ √3−0.5 − 0.866^^ √3−0.5 − 0.866^^ √31√3−0.5 + 0.866^^- 1 1 1 [− . − . 61 1 1 00 61 1 1 15 8 ^^] ;[−0.5 − 0.866^^ −0.5 + 0.866^^] ;[1−0.5 + 0.866^^] ;√31−0.5 + 0.866^^√3−0.5 + 0.866^^ −0.5 − 0.866^^√31−0.5 − 0.866^^- 1 1 1 [05 08 61 1 1 .. ^1 1 1 −6 ^−1] ;[ −10.5 + 0.866^^ ] ;[0.5 − 0.866^^ 0.5 + 0.866^^ ] ;√3−0.5 − 0.866^^−1√31−0.5 + 0.866^^ √3−0.5 − 0.866^^ −0.5 + 0.866^^- 1 1 1 1 −. 61 1 1 1 [1−0.5 08 6^^ −0.5 + 0.866^^] ;[0.5 − 0.866^^−10.5 + 0.866^^] ;√31−0.5 + 0.866^^ −0.5 − 0.866^^ √3−0.5 − 0.866^^1−0.5 + 0.866^^The method may further comprise determining, based on the received precoded uplink data stream, the uplink data stream. According to the fifth exemplary aspect, there is disclosed a method performed by a user equipment. The method may comprise obtaining a precoding matrix for precoding an uplink data stream to be transmitted to a network node by the user equipment using three antenna ports. The uplink data stream may comprise at most three uplink layers, wherein each of the at most three uplink layers is to be transmitted to the network node using the three antenna ports. The precoding matrix may be obtainable based on performing at least the following: obtaining a 3^^×3^^ discrete Fourier transform, DFT, matrix with a matrix order parameter ^^, wherein ^^ is an arbitrary natural number,wherein the 3^^×3^^ DFT matrix comprises 3^^ rows forming 3^^ − 2 sub-matrices, with each of the 3^^ − 2 sub-matrices consisting of three consecutive rows of the 3^^×3^^ DFT matrix, wherein each of the 3^^ − 2 sub-matricescomprises 3^^ column vectors forming ^^ groups of column vectors, with each group ^^ of the ^^ groups of columnvectors comprising the ^^^^ℎ, (^^ + ^^)^^ℎ, and (2^^ + ^^)^^ℎ column vector of the respective sub-matrix, with ^^ ∈{1, … , ^^}; determining a 3×3 matrix based on a sub-matrix of the 3^^ − 2 sub-matrices, the 3×3 matrix consisting ofthree column vectors comprised by a respective group of the ^^ groups of column vectors comprised by the sub- matrix; determining the precoding matrix based on the 3×3 matrix. The method may further comprise generating, based on the uplink data stream and the precoding matrix, a precoded uplink data stream. The method may further comprise transmitting the precoded uplink data stream to the network node using the three antenna ports. According to the sixth exemplary aspect, there is disclosed a method performed by a user equipment. The method may comprise obtaining a precoding matrix for precoding an uplink data stream to be transmitted to a network node by the user equipment using three antenna ports. The uplink data stream may comprise at most three uplink layers, wherein each of the at most three uplink layers is to be transmitted to the network node using the three antenna ports. The precoding matrix may comprise or may correspond to at least one of the following matrices: 1 1 1 1 1 1 1 2^^^^ 1 −2^^^^ 1 −2^^^^ 1 1 1 2^^^^ [1] ;[ −^^6] ;[ −^^6] ;[ ^^ 6] ;[ −1] ;[ ^^ 6] ;√31 √3 −2^^^^ √3 2^^^^ √3 2^^^^ √3 6 6 1 √3 −2^^^^ −^^ −^^ −^^ 6 −^^ 6 2^^^^ −2^^^^ −2^^^^ 2^^^^ 1 1 1 −^^61 −^^ 6 1 ^^ 6 1 −1 1 ^^6[1] ;[ −2^^^^ 6] ;[ 2^^^^ 6] ;[ 2^^^^ −2^^^^ 6] ;[1] ;[] ;√3 √3 −^^ √3 −^^ 3 −^^ 1 √ √3 3 −^^ 6 −1 √ 1 1 −1 −1 The method may further comprise generating, based on the uplink data stream and the precoding matrix, a precoded uplink data stream. The method may further comprise transmitting the precoded uplink data stream to the network node using the three antenna ports. According to the seventh exemplary aspect, there is disclosed a method performed by a network node. The method may comprise receiving a precoded uplink data stream. The precoded uplink data stream may have been transmitted to the network node by a user equipment using three antenna ports. The precoded uplink data stream may have been generated by the user equipment based on an uplink data stream and a precoding matrix. The uplink data stream may comprise at most three uplink layers, wherein each of the at most three uplink layers may have been transmitted to the network node by the user equipment using the three antenna ports. The precoding matrix may be obtainable based on performing at least the following: obtaining a 3^^×3^^ discrete Fourier transform, DFT, matrix with a matrix order parameter ^^, wherein ^^ is an arbitrary natural number, wherein the 3^^×3^^ DFT matrix comprises 3^^rows forming 3^^ − 2 sub-matrices, with each of the 3^^ − 2 sub-matrices consisting of three consecutive rows ofthe 3^^×3^^ DFT matrix, wherein each of the 3^^ − 2 sub-matrices comprises 3^^ column vectors forming ^^ groupsof column vectors, with each group ^^ of the ^^ groups of column vectors comprising the ^^^^ℎ, andcolumn vector of the respective sub-matrix, with ^^ ∈ {1, … , ^^}; determining a 3×3 matrix based on asub-matrix of the 3^^ − 2 sub-matrices, the 3×3 matrix consisting of three column vectors comprised by a respectivegroup of the ^^ groups of column vectors comprised by the sub-matrix; determining the precoding matrix based on the 3×3 matrix. The method may further comprise determining, based on the received precoded uplink data stream, the uplink data stream. According to the eighth exemplary aspect, there is disclosed a method performed by a network node. The method may comprise receiving a precoded uplink data stream. The precoded uplink data stream may have been transmitted to the network node by a user equipment using three antenna ports. The precoded uplink data stream may have been generated by the user equipment based on an uplink data stream and a precoding matrix. The uplink data stream may comprise at most three uplink layers, wherein each of the at most three uplink layers may have been transmitted to the network node by the user equipment using the three antenna ports. The precoding matrix may comprise or may correspond to at least one of the following matrices: The method may further comprise determining, based on the received precoded uplink data stream, the uplink data stream. Any of the disclosed devices (user equipment, network node) may be a stationary device or a mobile device. The user equipment may in particular be a terminal device, e.g. a mobile device such as a smartphone, a tablet, a wearable, a smartwatch, a low power device, an IoT device, an IIoT device, a vehicle, a truck, a drone, an airplane, or the like. The user equipment may in particular be capable of communicating with (transmitting and / or receiving signals and / or data to / from) one or more other user equipments and / or with one or more network nodes, such as a base station of a wireless communication network. Generally, the user equipment may be any device enabled for communication with a wireless communication network and / or with another user equipment. A network node (e.g. the network node according to the third or fourth exemplary aspect) may be understood as a wireless communication station installed at a fixed or mobile location and may in particular be or comprise an entity of a radio access network of a wireless communication system. For instance, the network node may be, comprise, or be part of a base station of a wireless communication network of any generation (e.g. a gNB, eNodeB, NodeB, BTS or the like) of a 3GPP standard. Generally, the network node may be or comprise a hardware or software component implementing a certain functionality. In an example, the network node may be an entity as defined by 3GPP 5G or NR standard (also referred to as gNB). Accordingly, while the network node may be understood to be implemented in or be a single device or module, the network node may also be implemented across or comprise multiple devices or modules. As such, the network node may in particular be implemented in or be a stationary device. Multiple network nodes of the exemplary aspects may in particular establish a wireless communication system or network, which may in particular be an NR or 5G system (5GS) or any other wireless communications system defined by a past or future standard, in particular successors of the present 3GPP standards. The network nodes of the exemplary aspects may be capable of being in direct and / or indirect communication with the user equipment of the exemplary aspects. In general, the means or functionality of any of the disclosed devices or apparatuses (i.e. of any of the user equipment and the network node) can be implemented in hardware and / or software. They may comprise one or multiple modules or units providing the respective functionality. They may for instance comprise at least one processor for executing computer program code for performing the required functions, at least one memory storing the program code, or both. They could comprise for instance circuitry that is designed to implement the required functions, for instance implemented in a chipset or a chip, like an integrated circuit. In general, the means may comprise for instance one or more processing means or processors. Thus, according to the respective exemplary aspects of the present disclosure, there is in each case also disclosed a respective apparatus (i.e. a user equipment and a network node) comprising at least one processor and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause an apparatus at least to perform a method according to the respective aspect of the present disclosure. Specific means may be used to implement specific functions / functionalities / features, e.g. obtaining means for obtaining a precoding matrix for precoding an uplink data stream to be transmitted to a network node by the user equipment using three antenna ports, generating means for generating, based on the uplink data stream and the precoding matrix, a precoded uplink data stream, and / or transmitting means for transmitting the precoded uplink data stream to the network node using the three antenna ports (said means may for example be comprised by the user equipment). Further examples of specific means may comprise, e.g., receiving means for receiving a precoded uplink data stream having been transmitted to the network node by a user equipment using three antenna ports, and / or determining means for determining, based on the received precoded uplink data stream, the uplink data stream (said means may for example be comprised by the network node). Thus, according to the respective exemplary aspects of the present disclosure, there is in each case also disclosed a respective apparatus (i.e., a user equipment, a network node) comprising means for performing a method according to the respective aspect of the present disclosure. Any of the above-disclosed exemplary aspects may, however, in general be performed by an apparatus, which may be a module or a component for a device, for example a chip. The disclosed apparatus may comprise the disclosed components, for instance means, processor, memory, or may further comprise one or more additional components. According to the exemplary aspects of the present disclosure, there is in each case also disclosed a computer program comprising instructions, which, when executed by an apparatus, cause the apparatus to perform the method of the respective aspect. The computer program may in each case be stored on computer-readable storage medium, in particular a tangible and / or non-transitory medium. The computer readable storage medium could for example be a disk or a memory or the like. The computer program could be stored in the computer readable storage medium in the form of instructions encoding the computer-readable storage medium. The computer readable storage medium may be intended for taking part in the operation of a device, like an internal or external memory, for instance a Read-Only Memory (ROM) or hard disk of a computer, or be intended for distribution of the program, like an optical disc. Thus, according to the exemplary aspects of the present disclosure, there is in each case also disclosed a computer- readable storage medium having stored thereon the computer program of the respective aspect. The described aspects may be advantageous in terms of at least one of speed, efficiency or reliability of an uplink transmission, e.g. in 5G / NR. More specifically, by enabling three-port uplink transmission, in particular fully coherent three-port uplink transmission, the described aspects may allow UEs which are equipped with three or more transmission antennas / antenna ports to transmit UL data in a faster, more efficient and / or more reliable manner. In particular, the described aspects may enable transmission of each of one or more UL layers using three antennas / antenna ports of a corresponding UE. The aforementioned advantages may in particular be achieved by providing and / or using one or more precoding matrices obtainable in accordance with the first, third, fifth and / or seventh aspect and / or comprising or corresponding to one or more of the matrices provided in accordance with the second, fourth, sixth and / or eighth aspect. It has been found that the precoding matrices (obtainable) in accordance with the described aspects may be particularly advantageous for various physical and / or signaling reasons. For example, it has been found that a precoding matrix (obtainable) in accordance with the described aspects may allow to preserve and / or consistently distribute a transmission power of the transmitted UL signal, thereby enhancing power efficiency. Further, it has been found that using a precoding matrix (obtainable) in accordance with the described aspects may help in maintaining an orthogonality between the transmitted layers, thereby ensuring an optimal signal separation and interference management. Further, it has been found that using a precoding matrix (obtainable) in accordance with the described aspects may allow to simplify a design of a receiving network node, e.g. by making a complex power normalization dispensable and / or by allowing to simplify a design of analog components such as, e.g., amplifiers and / or antennas, of the receiving network node. In this way, the described aspects and in particular the precoding matrices (obtainable) in accordance with the described aspects may advantageously improve an uplink transmission, e.g. in 5G / NR. The means for obtaining the precoding matrix may for instance correspond to means for determining and / or computing the precoding matrix, e.g. by the user equipment itself. Alternatively or in addition, the means for obtaining the precoding matrix may correspond to means for retrieving the precoding matrix, e.g. from an internal memory of the user equipment. Alternatively or in addition, the means for obtaining the precoding matrix may correspond to means for receiving the precoding matrix from a further, e.g. external device. Obtaining the precoding matrix may thus comprise at least one of: - determining the precoding matrix by the user equipment; - retrieving the precoding matrix from an internal memory of the user equipment; - receiving the precoding matrix from an external device. The precoding matrix may be suitable and / or adapted for precoding an uplink data stream. To this end, the precoding matrix may for instance allow for generating, based on the precoding matrix and the uplink data stream, a precoded uplink data stream, e.g. as described in section 6.3.1.5 of 3GPP technical specification 38.211. In particular, the precoding matrix may be applied or applicable to an uplink data stream by means of a matrix multiplication (cf. e.g. the first equation in section 6.3.1.5 of 3GPP technical specification 38.211). The precoding matrix may be obtained as part of a precoding codebook comprising a plurality of precoding matrices. As used herein a (precoding) codebook may be understood, e.g., as a table comprising a plurality of precoding matrices (cf. e.g. the tables of precoding matrices in section 6.3.1.5 of 3GPP technical specification 38.211). As used herein, a precoding matrix may also be referred to as a precoder. The precoding matrix may be obtained based at least in part on a Transmitted Precoding Matrix Indicator, TPMI, index. For instance, the precoding matrix may be selected from a plurality of precoding matrices, e.g. a codebook, using the Transmitted Precoding Matrix Indicator (TPMI) index. The precoding matrix may in particular be obtained based on the TPMI index, e.g. as described in section 6.3.1.5 of 3GPP specification 38.211. The TPMI index may for example be obtained by the user equipment based on a downlink control information (DCI) transmitted to the user equipment by a network node. To this end, the network node may transmit precoding information to the user equipment. Correspondingly, the network node may comprise means for transmitting precoding information to the user equipment, the precoding information being indicative of the precoding matrix. Said precoding information may for example be part of said DCI and / or may comprise information based on which the TPMI index may be obtainable, e.g. by the user equipment. The uplink data stream, which is to be transmitted to the network node by the user equipment using three antenna ports, may in particular be transmitted to the network node by the user equipment using exactly three antenna ports. Further, the uplink data stream may comprise at least one and at most three uplink layers. In other words, the uplink data stream may comprise exactly one, exactly two or exactly three uplink layers. The precoding matrix may have three rows and a number of columns of the precoding matrix may correspond to a number of uplink layers comprised by the uplink data stream. Thus, the precoding matrix may in particular have exactly one, exactly two or exactly three columns. In other words, the precoding matrix may in particular be a 3x1, 3x2 or 3x3 matrix, e.g. depending on the number of uplink layers comprised by the uplink data stream. A 3x1 matrix may also be understood as a three-dimensional vector. The precoding matrix may comprise only non-zero entries. In other words, each entry of the precoding matrix may be unequal zero. Considering that the precoding matrix may be applied or applicable to the uplink data stream by means of a matrix multiplication, the precoding matrix comprising only non-zero entries may in particular result in each of the at most three uplink layers to be mathematically mapped to each of the three antenna ports. In particular in this way, each of the at most three uplink layers is transmitted to the network node using, e.g. all of, the three antenna ports. In other words, that each of the at most three uplink layers is to be transmitted to the network node using, e.g. all of, the three antenna ports may for example mean that at least a respective part of a respective data stream associated with each of the at most three uplink layers is to be transmitted via each of the three antenna ports. Thereby, an antenna port may be understood as a logical concept representing a set of transmission and / or receiving resources which are perceived by a receiver as having the same radio channel properties. Alternatively or in addition, an antenna port may comprise or correspond to an antenna. As mentioned, according to some of the described aspects, the precoding matrix may be obtainable based on performing at least the following: o obtaining an oversampled 3×3^^ discrete Fourier transform, DFT, matrix with an oversampling factor ^^, wherein ^^ is an arbitrary natural number, wherein the oversampled 3×3^^ DFT matrix comprises 3^^ column vectors forming ^^ groups of column vectors, with each group ^^ of the ^^ groups of column vectors comprising the ^^^^ℎ, (^^ + and (2^^ + ^^)^^ℎ column vector of theoversampled 3×3^^ DFT matrix, with ^^ ∈ {1, … , ^^};o determining a 3×3 matrix consisting of three column vectors comprised by a respective group of the ^^ groups of column vectors; o determining the precoding matrix based on the 3×3 matrix. For example, the precoding matrix may be or may have been obtained based on performing at least the recited steps. The recited steps may be or may have been performed by at least one of the user equipment, the network node, or a further device providing or having provided the precoding matrix to the user equipment and / or to the network node, or may have been performed for deriving precoding matrices of a standardized codebook, such as a codebook defined by 3GPP. Obtaining the precoding matrix based on the recited steps may for example comprise or correspond to determining and / or computing the precoding matrix based on the recited steps. The precoding matrix may thus be determinable and / or computable based on performing at least the recited steps. In other words, the precoding matrix may result from or may be a result of performing at least the recited steps. Yet put differently, the precoding matrix may be obtained or may have been obtained by performing at least the recited steps. Obtaining the oversampled 3×3^^ discrete Fourier transform (DFT) matrix may comprise at least one of determining (e.g. computing), retrieving and receiving the oversampled 3×3^^ DFT matrix. As used herein, a DFT matrix may refer to a transformation matrix representing a discrete Fourier transform.The (^^, ^^)th term aij of the oversampled 3×3^^ DFT matrix may be given by:1,2, … ,3^^ Thereby, ^^ may denote the row and ^^ may denote the column of the (^^, ^^)th term aij within the oversampled 3×3^^DFT matrix and ^^ may correspond to the oversampling factor. As mentioned, the oversampling factor ^^ may correspond to an arbitrary natural number and may be greater than or equal to one. Thus, the oversampling factor ^^ may be equal to one, two, three, four, and so forth. That the oversampled DFT matrix is a 3×3^^ matrix may e.g. mean that, with an oversampling factor ^^ of one, two, three, or four, the oversampled DFT matrix may be a 3×3, 3×6, 3×9 and 3×12 matrix, respectively. It is to be understood that the ^^ before the 2^^ expression may correspond tothe imaginary unit such that, for reasons of consistency, the ^^ for denoting the (^^, ^^)th term aij may alternatively bedenoted as ^^′. The (^^, ^^)th term aij of the oversampled 3×3^^ DFT matrix may thus in particular be definable using thecomplex exponential function ^^^^^^. As mentioned, the oversampled 3×3^^ DFT matrix may comprise 3^^ column vectors. Each of the 3^^ column vectors may comprise or correspond to a three-dimensional column vector, e.g. a vector consisting of one column with three entries (or rows). As mentioned, the 3^^ column vectors may form ^^ groups of column vectors. In other words, the oversampled 3×3^^ DFT matrix may be conceptually divided into the ^^ groups of column vectors. A number ^^ of groups of column vectors may correspond to the oversampling factor ^^. Each group ^^ of the ^^ groupsof column vectors may comprise the ^^^^ℎ, (^^ + and (2^^ + ^^)^^ℎ column vector of the oversampled DFTmatrix, with ^^ ∈ {1, … , ^^}. Each group ^^ of the ^^ groups of column vectors may thus comprise exactly threecolumn vectors. In other words, each group ^^ of the ^^ groups of column vectors may comprise or correspond to a set of three, in particular three-dimensional, column vectors. As mentioned, a 3×3 matrix may be determined, e.g. based on the oversampled 3×3^^ DFT matrix. Determining the 3×3 matrix based on the oversampled 3×3^^ DFT matrix may for instance comprise or correspond to computing or deriving the 3×3 matrix from the oversampled 3×3^^ DFT matrix. In particular, the 3×3 matrix may consist of three column vectors comprised by a respective group of the ^^ groups of column vectors (e.g. by one of the ^^ groups). As mentioned, the precoding matrix may be determined, e.g. computed, based on the 3×3 matrix. The further steps according to which the precoding matrix is determined based on the 3×3 matrix may for example depend on a number of uplink layers comprised by the uplink data stream, as further described below. As mentioned, according to some of the described aspects, the precoding matrix may be obtainable based on performing at least the following: o obtaining a 3^^×3^^ discrete Fourier transform, DFT, matrix with a matrix order parameter ^^, wherein ^^ is an arbitrary natural number, wherein the 3^^×3^^ DFT matrix comprises 3^^ rows forming 3^^ − 2 sub-matrices, with each of the 3^^ − 2 sub-matrices consisting of threeconsecutive rows of the 3^^×3^^ DFT matrix, wherein each of the 3^^ − 2 sub-matrices comprises3^^ column vectors forming ^^ groups of column vectors, with each group ^^ of the ^^ groups of column vectors comprising the ^^^^ℎ, (^^ + column vector of the respectivesub-matrix, with ^^ ∈ {1, … , ^^};o determining a 3×3 matrix based on a sub-matrix of the 3^^ − 2 sub-matrices, the 3×3 matrixconsisting of three column vectors comprised by a respective group of the ^^ groups of column vectors comprised by the sub-matrix; o determining the precoding matrix based on the 3×3 matrix. For example, the precoding matrix may be or may have been obtained based on performing at least the recited steps. The recited steps may be or may have been performed by at least one of the user equipment, the network node, or a further device providing or having provided the precoding matrix to the user equipment and / or to the network node, or may have been performed for deriving precoding matrices of a standardized codebook, such as a codebook defined by 3GPP. Obtaining the precoding matrix based on the recited steps may for example comprise or correspond to determining and / or computing the precoding matrix based on the recited steps. The precoding matrix may thus be determinable and / or computable based on performing at least the recited steps. In other words, the precoding matrix may result from or may be a result of performing at least the recited steps. Yet put differently, the precoding matrix may be obtained or may have been obtained by performing at least the recited steps. Obtaining the 3^^×3^^ discrete Fourier transform (DFT) matrix may comprise at least one of determining (e.g. computing), retrieving and receiving the 3^^×3^^ DFT matrix. The 3^^×3^^ DFT matrix may be given by: Thereby, ^^3^^may denote the 3^^×3^^ DFT matrix and ^^ may correspond to the matrix order parameter. As mentioned, the matrix order parameter ^^ may correspond to an arbitrary natural number and may be greater than or equal to one. Thus, the matrix order parameter ^^ may be equal to one, two, three, four, and so forth. For example, with a matrix order parameter ^^ of one, two, three, or four, the 3^^×3^^ DFT matrix may be a 3×3, 6×6, 9×9 and 12×12 matrix, respectively. For differentiation from the oversampling factor, the matrix order parameter may also be denoted as ^^′. It is to be understood that the ^^ after the 2^^ expression in the definition of ^^3^^may correspond to the imaginary unit. Thus, at least some entries of the 3^^×3^^ DFT matrix may in particular be definable using the complex exponential function ^^^^^^.As mentioned, the 3^^×3^^ DFT matrix may comprise 3^^ rows. The 3^^ rows may form 3^^ − 2 sub-matrices. Eachof the 3^^ − 2 sub-matrices may consist of three consecutive rows of the 3^^×3^^ DFT matrix. Thereby, the rows ofwhich a particular sub-matrix consists may not have to be pairwise different. In other words, different sub-matricesmay share one or more, in particular two, rows. As mentioned, each of the 3^^ − 2 sub-matrices may comprise 3^^column vectors forming ^^ groups of column vectors. In other words, each of the 3^^ − 2 sub-matrices may beconceptually divided into the ^^ groups of column vectors. A number ^^ of groups of column vectors may correspond to the matrix order parameter ^^. Each group ^^ of the ^^ groups of column vectors may comprise the ^^^^ℎ,(^^ + ^^)^^ℎ, and (2^^ + ^^)^^ℎ column vector of the respective sub-matrix, with ^^ ∈ {1, … , ^^}. Each group ^^ of the ^^groups of column vectors may thus comprise exactly three column vectors. In other words, each group ^^ of the ^^ groups of column vectors may comprise or correspond to a set of three, in particular three-dimensional, column vectors.As mentioned, a 3×3 matrix may be determined based on a sub-matrix of the 3^^ − 2 sub-matrices. Determining the3×3 matrix based on the sub-matrix may for instance comprise or correspond to computing or deriving the 3×3 matrix from the sub-matrix. In particular, the 3×3 matrix may consist of three column vectors comprised by a respective group of the ^^ groups of column vectors comprised by the sub-matrix (e.g. by one of the ^^ groups). As mentioned, the precoding matrix may be determined, e.g. computed, based on the 3×3 matrix. Further steps according to which the precoding matrix is determined based on the 3×3 matrix may for example depend on a number of uplink layers comprised by the uplink data stream. In an example, the uplink data stream may comprise exactly three uplink layers and the precoding matrix may correspond to the 3×3 matrix. Thus, when the uplink data stream for instance comprises exactly three uplink layers, the precoding matrix may correspond to the 3×3 matrix. Yet put differently, in this case, the 3×3 matrix may represent the precoding matrix. In an example, the uplink data stream may comprise exactly two uplink layers and the precoding matrix may be obtainable based on further performing at least the following: o determining a 3×2 matrix consisting of two different column vectors of the three column vectors forming the 3×3 matrix. Thus, when the uplink data stream for instance comprises exactly two uplink layers, the precoding matrix may correspond to a 3×2 matrix. Said 3×2 matrix may be determined based on the 3×3 matrix. In particular, said 3×2 matrix may consist of two different column vectors of the three column vectors forming the 3×3 matrix. In an example, the uplink data stream may comprise exactly one uplink layer and the precoding matrix may be obtainable based on further performing at least the following: o determining a 3×1 matrix consisting of one column vector of the three column vectors forming the 3×3 matrix. Thus, when the uplink data stream for instance comprises exactly one uplink layer, the precoding matrix may correspond to a 3×1 matrix. Said 3×1 matrix may be determined based on the 3×3 matrix. In particular, said 3×1 matrix may consist of one column vector of the three column vectors forming the 3×3 matrix. Alternatively or in addition, said 3×1 matrix may be determined based on a 3×2 matrix having been determined based on the 3×3 matrix, as described above. It has been found that precoding matrices obtainable in accordance with the described aspects have mathematical properties that are advantageous for various physical and / or signaling reasons. In an example, the precoding matrix may be unitary. A unitary matrix may for instance be understood as a matrix whose inverse is equal to its conjugate transpose. In other words, a unitary matrix may be a complex square matrix^^ which satisfies the condition U†U = UU† = I with U† denoting the conjugate transpose of matrix ^^ and Idenoting the identity matrix. In an example, the precoding matrix may comprise one or more column vectors, the one or more column vectors being pairwise orthogonal and / or having unit length. Two vectors may for instance be understood to be pairwise orthogonal if their dot product (also referred to as inner product) is zero. This may for instance mean that the vectors are perpendicular to each other in the vector space. Pairwise orthogonal vectors may be referred to as vectors independent from each other. A vector may be said to have unit length if a magnitude (also referred to as a norm) of the vector is equal to one. Precoding matrices being unitary and / or comprising column vectors being pairwise orthogonal and / or having unit length may preserve and / or consistently distribute a transmission power of the transmitted uplink data stream, thereby enhancing power efficiency. Further, such precoding matrices may help in maintaining an orthogonality between the transmitted layers, thereby ensuring an optimal signal separation and interference management. Further, such precoding matrices may allow to simplify a design of a receiving network node, e.g. by making a complex power normalization dispensable and / or by allowing to simplify a design of analog components of the network node such as, e.g., amplifiers and / or antennas. In this way, in particular precoding matrices being unitary and / or comprising column vectors being pairwise orthogonal and / or having unit length may advantageously improve an uplink transmission, e.g. in 5G / NR. The means for generating, based on the uplink data stream and the precoding matrix, the precoded uplink data stream may for instance correspond to means for determining and / or computing the precoded uplink data stream, e.g. by the user equipment itself. Generating the precoded uplink data stream based on the uplink data stream and the precoding matrix may for instance comprise multiplying the precoding matrix with the uplink data stream by means of matrix multiplication, e.g. as reflected in the first equation in section 6.3.1.5 of 3GPP technical specification 38.211. The means for generating the precoded uplink data stream may thus correspond to means suitable and / or adapted for performing at least one matrix multiplication. The means for transmitting the precoded uplink data stream to the network node using the three antenna ports may for instance comprise or correspond to one or more radio transmission means such as, e.g., a transmitter, a transceiver and / or one or more antennas or antenna ports. The means for receiving the precoded uplink data stream (such means being comprised, e.g., by a network node) may for instance comprise or correspond to one or more radio receiving means such as, e.g., a receiver, a transceiver and / or one or more antennas or antenna ports. The means for determining the uplink data stream based on the received precoded uplink data stream (such means being comprised, e.g., by a network node) may for instance comprise or correspond to means for computing the uplink data stream, e.g. by the network node, based on the precoded uplink data stream. Computing the uplink data stream based on the precoded uplink data stream may for instance comprise at least one of: determining a radio channel used by the user equipment for transmitting the precoded uplink data stream; determining the precoding matrix based on which the user equipment has generated the precoded uplink data stream; decoding (also referred to as postcoding and / or equalizing) the precoded uplink data stream; signal processing the precoded uplink data stream; and / or applying one or more error correction algorithms to the precoded uplink data stream. In this way, an (e.g. original) uplink data stream having been transmitted to the network node by a user equipment may be accurately recovered. As used herein, based on a number of antenna ports a user equipment is capable of using for transmitting one or more uplink layers, the user equipment may be categorized as non-coherent, partially coherent or fully coherent. A non-coherent UE may be capable of using only one antenna port to transmit each uplink layer. A partially coherent user equipment may be capable of using more than one but not all available antenna ports to transmit each uplink layer. A fully coherent user equipment may be capable of using all available antenna ports to transmit each uplink layer. Considering that, according to the described aspects, each of the at most three uplink layers is to be or has been transmitted to the network node using, e.g. all of, the three antenna ports, a user equipment in accordance with the described aspects may be considered a fully coherent user equipment. As used herein, performing a second step based on a first step may for example mean that the second step may be performed, e.g. directly, in response to the first step, e.g. without any intermediate steps in between the first step and the second step. Alternatively, performing a second step based on a first step may mean that the second step may be performed (merely) after the first step, e.g. such that there may be at least one intermediate step in between the first step and the second step. It is to be understood that the presentation of the embodiments disclosed herein is merely by way of examples and non-limiting. Herein, the disclosure of a method step shall also be considered as a disclosure of means for performing the respective method step. Likewise, the disclosure of means for performing a method step shall also be considered as a disclosure of the method step itself. Other features of the present disclosure will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the present disclosure, for which reference should be made to the appended claims. It should be further understood that the drawings are not drawn to scale and that they are merely intended to conceptually illustrate the structures and procedures described herein. BRIEF DESCRIPTION OF THE FIGURES Some example embodiments will now be described with reference to the accompanying drawings in which FIG.1 exemplarily illustrates a user equipment and a network node in wireless communication; FIG.2 shows an example embodiment of a method according to the present disclosure; FIG.3 shows another example embodiment of a method according to the present disclosure; FIG.4A shows an example of a method for obtaining a precoding matrix related to example embodiments of the present disclosure; FIG.4B shows another example of a method for obtaining a precoding matrix related to example embodiments of the present disclosure; FIG.5 shows a schematic illustration of various uplink layers and antenna ports related to example embodiments of the present disclosure; FIG.6 shows an example of a signaling flow chart according to example embodiments of the present disclosure; FIG.7 shows a block diagram of an example of a user equipment; FIG.8 shows a block diagram of an example of a network node; and FIG.9 shows a schematic illustration of examples of tangible and non-transitory computer-readable storage media. DETAILED DESCRIPTION OF THE FIGURES The following description serves to deepen the understanding of the present disclosure and shall be understood to complement and be read together with the description of example embodiments of the present disclosure as provided in the above SUMMARY section of this specification. In the following, an example wireless communication system, within which the present disclosure may be applied, is described. While the specific radio system in the examples below is a 5G / NR system, this is only to be considered a non-limiting example. FIG.1 exemplarily illustrates a UE 100 (an example of a user equipment according to the described aspects) in wireless communication with a gNB 200 (an example of a network node according to the described aspects) via a radio link 10. Radio link 10 may enable transmitting / receiving information and / or signals in between the UE 100 and the gNB 200. For example, UE 100 may transmit a precoded uplink data stream to gNB 200 via the radio link 10. Correspondingly, gNB 200 may receive a precoded uplink data stream via the radio link 10. Further, gNB 200 may transmit DCI to the UE 100 via the radio link 10. FIG.2 shows an example embodiment 300 of a method according to at least one of the first, second, fifth or sixth exemplary aspect. Method 300 may for example be performed by a user equipment according to at least one of said aspects. First, a precoding matrix for precoding an uplink data stream to be transmitted to a network node by the user equipment using three antenna ports may be obtained (action 310). Further, based on the uplink data stream and the precoding matrix, a precoded uplink data stream may be generated (action 320). Further, the precoded uplink data stream may be transmitted to the network node using the three antenna ports (action 330). FIG.3 shows an example embodiment 400 of a method according to at least one of the third, fourth, seventh or eighth exemplary aspect. Method 400 may for example be performed by a network node according to at least one of said aspects. First, a precoded uplink data stream having been transmitted to the network node by a user equipment using three antenna ports may be received (action 410). Further, based on the received precoded uplink data stream, the uplink data stream may be determined (action 420). FIG.4A shows an example of a method 500 for obtaining a precoding matrix related to at least one of the first, second, third, or fourth exemplary aspect. First, an oversampled 3×3^^ DFT matrix may be obtained (action 510). Further, e.g. based on the oversampled 3×3^^ DFT matrix, a 3×3 matrix may be determined (action 520). Further, based on the 3×3 matrix, the precoding matrix may be determined (action 530). Generally, method 500 may be or may have been performed by a user equipment according to the described aspects. In particular, however, method 500 may be or may have been performed by an external device before any of the methods according to the described aspects is performed. In other words, the precoding matrix may be or may have been precomputed using method 500 and may, subsequently, be or have been provided to the user equipment, e.g. as part of a future 3GPP specification. For instance, method 500 may have been performed for deriving precoding matrices of a standardized codebook, such as a codebook defined by 3GPP. Example implementations of method 500 will be described in detail further below. FIG.4B shows an example 600 of a method for obtaining a precoding matrix related to at least one of the fifth, sixth, seventh, or eighth exemplary aspect. First, a 3^^×3^^ DFT matrix may be obtained (action 610), wherein the3^^×3^^ DFT matrix comprises 3^^ rows forming 3^^ − 2 sub-matrices. Further, based on a sub-matrix of the 3^^ − 2sub-matrices, a 3×3 matrix may be determined (action 620). Further, based on the 3×3 matrix, the precoding matrix may be determined (action 630). Generally, method 600 may be or may have been performed by a user equipment according to the described aspects. In particular, however, method 600 may be or may have been performed by an external device before any of the methods according to the described aspects is performed. In other words, the precoding matrix may be or may have been precomputed using method 600 and may, subsequently, be or have been provided to the user equipment, e.g. as part of a future 3GPP specification. For instance, method 600 may have been performed for deriving precoding matrices of a standardized codebook, such as a codebook defined by 3GPP. Example implementations of method 600 will be described in detail further below. FIG.5 shows a schematic illustration of a set 20 of three uplink layers 21, 22, 23 and a set 30 of three antenna ports 31, 32, 33. As schematically illustrated by the lines connecting each of the three uplink layers 21, 22, 23 with each of the three antenna ports 31, 32, 33, each of the three uplink layers 21, 22, 23 may be transmitted using, e.g. all of, the three antenna ports 31, 32, 33. To this end, the three uplink layers 21, 22, 23 may be mapped onto the three antenna ports 31, 32, 33 using a mapping 25. Mathematically, mapping 25 may correspond to a precoding matrix. Mapping 25 may in particular correspond to a fully coherent precoding matrix, e.g. a precoding matrix comprising only non-zero entries. Correspondingly, generating a precoded uplink data stream to be transmitted via the three antenna ports 31, 32, 33 may for instance comprise multiplying the precoding matrix corresponding to mapping 25 with a matrix or block of vectors representing the three uplink layers 21, 22, 23 by means of matrix multiplication, e.g. as reflected in the first equation in section 6.3.1.5 of 3GPP technical specification 38.211. FIG.6 shows an example of a signaling flow chart between a UE 100 and a gNB 200 according to example embodiments of the present disclosure. First, gNB 200 may transmit downlink control information (DCI) to UE 100 (action 701). The DCI may comprise precoding information. The precoding information may comprise information based on which the TPMI index may be obtainable by UE 100. Based on and / or in response to the DCI, UE 100 may transmit a precoded uplink data stream to the gNB 200 (action 702). To this end, UE 100 may obtain a TPMI index based on the DCI. Based on the TPMI index, UE 100 may obtain a precoding matrix. Based on the obtained precoding matrix and an uplink data stream to be transmitted to gNB 200, UE 100 may then generate the precoded uplink data stream which may then be transmitted to gNB 200. As mentioned, current 5G / NR supports 1-port, 2-port, 4-port and 8-port PUSCH transmission but the typical commercial mobile UEs are equipped with only 1 or 2 transmit (Tx) antennas. Anticipating advancements in hardware and design technology, future UEs may be equipped with 3 Tx antennas, thereby enhancing the uplink (UL) performance. Generally, three different types of UE phase coherence capabilities may be assumed: (1) non-coherent UE, (2) partially coherent UE, and (3) fully coherent UE. A non-coherent UE may for instance be understood as a UE that cannot use more than one antenna port coherently to transmit each layer. The corresponding codebook vector / matrix can have only a single non-zero entry in each column. For partially coherent UEs, each layer can be transmitted from a subset of total available antenna ports over which the coherent precoding can be performed. The allowed subset of antennas may be called an “Antenna Group” and may typically be fixed. The number of antenna groups may be denoted Ng. For example, for 4 antenna port, UEs with partially coherent architecture, only two groups may be supported in 5G (Ng = 2) and a layer can be transmitted only from one of the two possible groups. A partially coherent codebook vector / matrix can have multiple non-zero entries along with at least one zero entry in each column of the codebook. A partially coherent UE can also support the codebooks corresponding to non-coherent UE. For fully coherent UEs, each layer can be coherently transmitted either from all or a subset of the antenna ports. The corresponding precoder vector / matrix can have all non-zero entries in each column of the codebook. A fully coherent UE can support the precoders for partially coherent UE as well as non-coherent UE. In order to improve at least one of speed, efficiency or reliability of an uplink transmission, it may be desirable to enable fully coherent three-port uplink transmission. Further, it may be desirable to obtain codebook(s) having unitary properties / orthogonal vectors where each vector has constant modulus elements. However, the design of a 3-port fully coherent codebook (e.g. comprising one or more fully coherent precoding matrices) may be considered not straight-forward at least because of the following reasons: (1) Using an antenna port muting concept on one of the ports of 4-port codebooks to create 3-port codebook(s) may lose the orthogonality between the codebook vectors. (2) The existing codebook design by using Kronecker product between lower dimension orthogonal codebooks to create the corresponding higher dimension orthogonal codebooks may not be possible because of the dimension of 3-port codebook (target / outcome codebook) being an odd number. Hence, there may be a need for 3-port fully coherent codebook(s) having unitary properties / orthogonal vectors where each vector has constant modulus elements. In view of the above, the present disclosure proposes various 3-port fully coherent orthogonal codebooks to support single-layer, dual-layer and three-layer uplink transmission. The proposed codebook designs supporting 3-layer uplink transmission may be understood to exploit the properties of an oversampled DFT matrix (generated with an oversampling factor ^^ where ^^ is a positive integer and is of size 3×3^^) to create the required 3-port 3-layer fully coherent orthogonal precoders with constant modulus elements. To design 3-port 2-layer fully coherent orthogonal codebook with constant modulus elements, the 3-port 3-layer fully coherent orthogonal precoders with constant modulus elements may be exploited. By deleting one column at a time of each 3-port 3-layer fully coherent orthogonal precoder (3x3), 3 orthogonal precoder matrices of size 3x2 supporting the 3-port 2-layer fully coherent UL transmission can be obtained. To design the 3-port 1-layer fully coherent codebook with constant modulus elements, the designed 3-port 3-layer fully coherent orthogonal precoders with constant modulus elements may again be exploited. By deleting two columns at a time of each 3-port 3-layer fully coherent orthogonal precoder (3x3), 3 precoder vectors of size 3x1 supporting the 3-port 1-layer fully coherent UL transmission can be obtained. Below, two alternatives for the 3-port fully coherent codebooks for single-layer, 2-layer and 3-layer UL transmission are proposed. As 3 antenna ports can simultaneously support a maximum of three-layer transmission and each layer can be precoded by a unique precoding vector, the following codebook cases are possible for a 3-port fully coherent UE: 1. Single-layer three-port transmission, 2. Two-layer three-port transmission, 3. Three-layer three-port transmission. The present disclosure proposes multiple 3-port fully coherent codebooks which have constant modulus / magnitude constraint on each of its elements. For a given number of layers L (i.e., rank L), the goal is to design a set of precoder matrices for the given L, where each precoder matrix is 3xL. For L=1 (Rank 1), the precoder matrices are column vectors (3x1). Mathematically, finding a fully coherent precoding matrix with the desired properties may be formulated as follows: Let, the three precoding vectors of the codebook, to support 3-port 3-layer UL transmission, are: which have unit / constant modulus elements. Defining the matrix the problem of obtaining the orthogonal / unitary fully coherent 3-port codebook (for up to 3-layer UL transmission)is equivalent to finding a matrix ^^ which satisfies ^^^^^^ = ^^3 where ^^3 is a 3 × 3 identity matrix. Design of 3-port 3-layer fully coherent codebook(s)Designing a 3-port-3-layer fully coherent codebook may involve determining a set of 3 × 3 precoder matrices,where it is preferable that the 3 columns in each precoder matrix are orthogonal to each other. The ‘size’ of a codebook may refer to the number of precoder matrices in the codebook. In the following, we start by showing how a single 3 x 3 precoder can be created from the DFT matrix and then we show how to construct multiple precoders by leveraging the concept of oversampled DFT matrix. Final set of 3-port 3-layer precoders is the set of one or more precoders constructed from the oversampled DFT matrix. A single 3x3 precoder matrix One solution to the above problem is to exploit each column of a 3×3 DFT matrix to be one column vector of the precoder matrix which will have constant modulus elements and the vectors are also orthogonal to each other. Such a precoder matrix is given below: A general construction procedure to design multiple precoder matrices for 3-port 3-layer fully coherent UL transmission is given below which exploits the principle of oversampled DFT so that the columns within a given precoder matrix are all orthogonal to each other. The following is an example implementation of method 500: Step 1: Decide the number of 3-port 3-layer fully coherent precoders with constant modulus elements to be generated. Let N be the number of 3 x 3 precoder matrices to be generated / designed for the 3-layer 3-port fully coherent codebook. With this construction, the maximum number of precoder matrices that we can have in the rank 3 codebook would be N. Step 2: Generate an oversampled DFT matrix (of size 3 x 3N) with an oversampling factor of ‘N’ where ‘N’ is a positive integer (an example of action 510). Step 3: Divide the ‘3N’ column vectors of the generated oversampled DFT matrix into ‘N’ different groups such that each group has 3 column vectors and ^ Group ‘1’ contains the 1st, (N+1)th, and (2N +1)thcolumn vectors of the oversampled DFT matrix, ^ Group ‘2’ contains the 2nd, (N+2)th, and (2N +2)thcolumn vectors of the oversampled DFT matrix, ^ Group ‘3’ contains the 3rd, (N+3)th, and (2N +3)thcolumn vectors of the oversampled DFT matrix, ^ … ^ Group ‘N’ contains the Nth, (2N)th, and (3N)thcolumn vectors of the oversampled DFT matrix. Step 4: Define a 3 x 3 matrix for each Group ‘n’ where n = 1, …, N such that the 3 columns vectors of the 3 x 3 matrix for each Group are the 3 column vectors in the corresponding group (an example of action 520). Step 5: We now have ‘N’ 3 x 3 matrices which are also unitary and hence have orthogonal column vectors. The codebook of precoder matrices for rank 3 can consist of all N of the constructed matrices. Alternatively, we can choose ‘P’ matrices from the available ‘N’ 3 x 3 matrices as being the required size ‘P’ fully coherent 3-port 3-layer codebook. The (i,j)thterm (i.e., ^^^^^^) of a 3x3N matrix (A) generated by oversampling a 3x3 DFT matrix with the oversampling factor N is given by ^^ = 1,2,3 and ^^ = 1,2, … ,3^^ 2-layer fully coherent matrices Designing a 3-port-2-layer fully coherent codebook involves determining a set of 3x2 precoder matrices, where it is preferable that the 2 columns in each precoder matrix are orthogonal to each other. Three 3x2 precoders derived from a single 3x3 precoder Using the single 3-layer 3-port fully coherent precoder matrix derived above (a 3x3 DFT matrix with oversampling=1), 3 different 3x2 precoders can be obtained to support 3-port 2-layer fully coherent UL transmission by removing one column at a time from the 3x3 precoder. This can equivalently be viewed as constructing the codebook by selecting all possible pairs of columns in the 3x3 precoder matrix. The 3 possible 3-port 2-layer fully coherent precoders obtained by removing the one column at a time from the 3-layer 3-port codebook are as follows: 1111 ^^3,2 =[1 −0.5 − 0.866^^] , √31 −0.5 + 0.866^^which is obtained by removing the third column of ^^3,3(equivalent to pairing columns 1 and 2 of ^^3,3), 1−0.5 + 0.866^^] , −0.5 − 0.866^^ which is obtained by removing the second column of ^^3,3(equivalent to pairing columns 1 and 3 of ^^3,3), and 11 1^^33,2 =[−0.5 − 0.866^^ −0.5 + 0.866^^] , √3−0.5 + 0.866^^ −0.5 − 0.866^^which is obtained by removing the first column of ^^3,3(equivalent to pairing columns 2 and 3 of ^^3,3). This solution provides a set of three precoder matrices, each being 3x2. For each precoder matrix, the two columns are orthogonal to each other. The result is a size 3 fully coherent codebook for the rank 2 case for 3 ports. Generic Solution (Derived from Multiple 3x3 precoders) The basic solution provided a size 3 codebook for the rank 2 case and was derived from a 3-port DFT matrix with an oversampling factor of N=1. A more generic solution that will create a larger size codebook is to leverage the 3-port DFT matrix with oversampling of N>1, as follows: Step 1: Select a value of N (oversampling factor) and select the N fully coherent 3-port 3-layer precoder matrices as set out above Step 2: For each of the N precoder matrices (i.e., Precoder matrix ‘i'; i = 1, … , N), generate 3 fully coherent 3-port 2-layer precoders (3x2 matrices) by removing one of the columns at a time, i.e., if the ith3x3 precoder is [^^1^^^^2^^^^3^^] where ^^^^^^is the jthcolumn of the ith3x3 precoder, then the corresponding 3 precoders for 3-port 2-layer UL transmission can be derived as: (1) [^^1^^^^2^^], (2) [^^2^^^^3^^], (3) [^^1^^^^3^^]. This construction can be viewed equivalently as constructing the three precoders by selecting the three possible pairs of columns in the corresponding 3x3 precoder matrix. Step 3: We now have 3N 3x2 matrices which have orthogonal column vectors, i.e., [^^11^^21], [^^21^^31], [^^11^^31], …, ^^2^^], [^^2^^^^3^^], [^^1^^^^3^^]. These 3N matrices are the possible 3N fully coherent 3-port 2-layer precoders derived from the N 3x3 precoder matrices. This solution provides a set of 3N precoder matrices for 2 layers and 3-ports, where each precoder matrix is 3x2. For each precoder matrix, the two columns are orthogonal to each other. The result is a size 3N fully coherent codebook for the rank 2 case for 3 ports. An optional example is to have Step 2 be restricted to a subset (size P rather than size N) of the precoder matrices from above. Design of 3-port 1-layer fully coherent codebook(s) Designing a 3-port-1-layer fully coherent codebook involves determining a set of 3x1 precoder vectors that balance the tradeoff between performance and the size of the codebook (which corresponds to the required feedback overhead). Three 3x1 precoders derived from a single 3x3 precoder Using the single 3-layer 3-port fully coherent precoder (3x3 matrix) derived above, 3 different 3x1 precoders can be obtained to support 3-port 1-layer fully coherent UL transmission by removing two columns at a time from the 3x3 precoder from above, i.e., keeping only one column vector. Furthermore, the 3 possible 1-layer 3-port fully coherent codebook vectors can be obtained as: 1 1 1 1 1 [] −0.5 − 0.866^^1 1, ^^2 =[], ^^3 =[−0.5 + 0.866^^], 1√3−0.5 + 0.866^^ √3−0.5 − 0.866^^which are obtained by removing two columns from the above 3x3 precoder or equivalently one column from the above 3x2 precoders. This construction can be viewed as being equivalent to setting a precoder vector to be equal to one of the columns of the 3-port DFT matrix (with no oversampling). The basic solution provides a codebook of size 3, where each precoder vector is one of the columns of the 3-port DFT matrix (no oversampling). Generic Solution (Derived from Multiple 3x3 precoders) The basic solution provided a size 3 codebook for the rank 1 case and was derived from a 3-port DFT matrix with an oversampling factor of N=1. A more generic solution that will create a larger size codebook is to leverage the 3-port DFT matrix with oversampling of N>1. Then each column of the oversampled DFT matrix would be a possible precoding vector. Step 1: Select the N fully coherent 3-port 3-layer precoder matrices as set out above. (Alternatively, select a subset of size P of the precoder matrices as set out above) Step 2: For each of the N precoders (i.e., Precoder ‘i'; i = 1, … , N), generate 3 fully coherent 3-port 1-layer precoders (3x1 matrices) by removing two column at a time, i.e., if the ith3x3 precoder is [^^1^^^^2^^^^3^^] where ^^^^^^is the jthcolumn of the ith3x3 precoder, then the corresponding 3 precoders for 3-port 1-layer UL transmission can be derived as: (1) [^^1^^], (2) [^^2^^], (3) [^^3^^]. This construction is equivalent to selecting each of the columns of the precoder matrices as rank 1 precoders for the single layer 3-port codebook. Alternatively, we can use the subset of size ‘P’ as mentioned in the previous step. Step 3: We now have 3N 3x1 matrices which have all non-zero elements, i.e., [^^11], [^^21], [^^31], …, [^^1^^], [^^2^^], [^^3^^]. These 3N vectors are the possible 3N fully coherent 3-port 1-layer precoder vectors derived from the N 3x3 precoders. Alternatively, if we are leveraging the subset of size ‘P’, then we would have 3P fully coherent 3-port 1- layer precoder vectors. Examples In the following, various examples will be provided to explain the proposed general construction procedure for codebook design. Example 1 In Example 1, generate 2 fully coherent 3-port 3-layer precoder matrices using an oversampled DFT with an oversampling factor of 2: Step 1: Number of fully coherent 3-port 3-layer precoders required = 2 Step 2: An oversampled DFT matrix (of order 3 x 6) generated with an oversampling factor of N = 2 is given by 11 1 1 1 1 1^^^^^^^^=3,^^=2 =[1 0.5 − 0.866^^ −0.5 − 0.866^^ −1 −0.5 + 0.866^^ 0.5 + 0.866^^] 1 −0.5 − 0.866^^ −0.5 + 0.866^^ 1 −0.5 − 0.866^^ −0.5 + 0.866^^Step 3: As N = 2, there will be 2 groups: st rd thGroup 1: Set of 1, 3 and 5 column vectors of ^^^^^^^^=3,^^=21 11 1 Therefore, Group [] ,[−0.5 − 0.866^^] ,1 1 √3−0.5 + 0.866^^−0. + . 6 ^√3[ ]} 508 6^ −0.5 − 0.866^^ 1 nd th thGroup 2: Set of 2 , 4 and 6 column vectors of ^^^^^^^^=3,^^=21 111 1 10.5 − 0.866^^ 0.5 + 0.866^^Therefore, Group 2 = { [ ], [ ], [ ]} −1√ √ √3 3 3−0.5 − 0.866^^ −0.5 + 0.866^^1 Step 4: Matrix (3 x 3) corresponding to Group 1, i.e., ^^ is given by11 1 −0.5 − 0.866^^ −0.5 + 0.866^^^^ = ]1−0.5 + 0.866^^ −0.5 − 0.866^^ And the matrix (3 x 3) corresponding to Group 2, i.e., ^^ is given by21 111 0.5 − 0.866^^ 0.5 + 0.866^^^^ = [ ] −12√3−0.5 − 0.866^^ −0.5 + 0.866^^1 ^^ ^^^^ = ^^ and ^^ ^^ = ^^ where ^^ is an identityStep 5: Now we have 2 matrices ^^ and ^^ which are unitary, i.e., ^^1 2 1 1 3 2 2 3 3matrix of order 3. Therefore, the required 2 precoders for this Example 1 are: stst^ 1 precoder = ^^ (Note that ^^ = ^^ where ^^ is given above. Hence, ^^ is same as the 13-port 3-layer1 1 3,3 3,3 1fully coherent codebook ^^ as proposed earlier.)3,3nd^ 2 precoder = ^^2In case only 1 precoder is required, any of the matrices ^^ or ^^ can be selected. Note that without loss of1 2generality, a scaling factor can be suitable determined different from that shown in the proposed codebooks. Example 2 In Example 2, generate 3 fully coherent 3-port 3-layer precoder matrices using an oversampled DFT with an oversampling factor of 3. Step 1: Number of fully coherent 3-port 3-layer precoder matrices required = 3 Step 2: An oversampled DFT matrix (of order 3 x 6) generated with an oversampling factor of N = 2 is given by^^^^ ^ ^ 3 ^ = =1 ^^ = , ^ 3√3 × Step 3: As N = 3, there will be 3 groups: Group 1: Set of 1st, 4thand 7thcolumn vectors of Group 2: Set of 2nd, 5thand 8thcolumn vectors of ^^^^^^^^=3,^^=3Group 3: Set of 3rd, 6thand 9thcolumn vectors of ^^^^^^^^=3,^^=3Step 4: Matrix (3 x 3) corresponding to Group 1, i.e., ^^1is given by 1 1 −0.5 − 0.866^^ −0.5 + 0.866^^] −0.5 + 0.866^^ −0.5 − 0.866^^The matrix (3 x 3) corresponding to Group 2, i.e., ^^2is given by ^^2=− − 0.9848^^] √30.1736 − 0.9848^^ 0.766 + 0.6428^^ −0.9397 − 0.342^^And the matrix (3 x 3) corresponding to Group 3, i.e., ^^3is given by 1 1 1 1 ^^3= [0.1736 − 0.9848^^ −0.9397 + 0.342^^ 0.766 + 0.6428^^] √3−0.9397 − 0.342^^ 0.766 − 0.6428^^ 0.1736 + 0.9848^^Step 5: Now we have 3 matrices ^^1 , ^^ and ^^ which are unitary and satisfy ^^ ^^^^ = ^^ ^^^^ = ^^ ^^2 3 1 1 2 2 3 ^^3 = ^^3.Therefore, the required 3 precoders for this Example 2 are ^1st precoder = ^^1 (Note that ^^1 = ^^1 = ^^3,3 where ^^1 is derived in Example 1 and ^^3,3 is given above andis the proposed 1st3-port 3-layer fully coherent codebook) ^ 2ndprecoder = ^^2^ 3rdprecoder = ^^3In case only 1 or 2 precoder are required, any of the matrices ^^1and / or ^^2and / or ^^3can be selected. Example 3 Example 3 relates to an example of TPMI based 3-port UL transmission codebooks. We assume P = 2 in this example due to which the codebooks defined in Example 1 will be used as two 3x3 precoders as shown in Table 3 below. Thereafter, 3-port 2-layer and 3-port single-layer codebooks can be obtained by deleting the one and two columns from each of the two 3x3 precoders, respectively (which gives six 3x2 precoders and six 3x1 precoders). Proposed single-layer, 2-layer and 3-layer 3-port codebooks are highlighted in grey. Table 1: Precoding matrix W for single-layer transmission using three antenna ports with transform precoding disabled. TPMI ‘7’ to ‘12’ are used here (proposed) to indicate the 6 new 3-port single-layer precoders. Table 2: Precoding matrix W for two-layer transmission using three antenna ports with transform precoding disabled. TPMI ‘9’ to ‘14’ are used here (proposed) to indicate the 6 new 3-port 2-layer precoders. Table 3: Precoding matrix W for three-layer transmission using three antenna ports with transform precoding disabled. TPMI ‘3’ and ‘4’ are used here (proposed) to indicate the 2 new 3-port 3-layer precoders. If 3GPP defines a new fully coherent 3-port 3-layer codebook of size ‘P’ (i.e., having ‘P’ precoders), and hence we will have ‘3P’ new fully coherent 3-port 2-layer precoders (3-port 2-layer codebook of size ‘3P’) and ‘3P’ new fully coherent 3-port single-layer precoders (3-port single-layer codebook of size ‘3P’). Therefore, assuming that 3GPP has already defined the: ^ ‘X’ 3-port single-layer precoders (non-coherent + partial-coherent) with the TPMI ‘0’ to ‘(X-1)’ in use, ^ ‘Y’ 3-port 2-layer precoders (non-coherent + partial-coherent) with the TPMI ‘0’ to ‘(Y-1)’ in use, ^ ‘Z’ 3-port 3-layer precoders (non-coherent + partial-coherent) with the TPMI ‘0’ to ‘(Z-1)’ in use. Therefore, the TPMI for the proposed 3-port fully coherent precoders will be: ^ TPMI ‘X’ to ‘(X+3P-1)’ for ‘3P’ 3-port single-layer fully coherent precoders (proposed), ^ TPMI ‘Y’ to ‘(Y+3P-1)’ for ‘3P’ 3-port 2-layer fully coherent precoders (proposed), ^ TPMI ‘Z’ to ‘(Z+P-1)’ for ‘P’ 3-port 3-layer fully coherent precoders (proposed). In an example, the codebooks in Tables 1, 2 and 3 are combined in a common table (e.g., Table 1) so that the bits for TPMI feedback spans the entries for all ranks 1, 2 and 3 (as shown in Table 4 below). In this alternative, a separate rank indicator (RI) is not needed as the TPMI implicitly contains the rank that was selected. More alternatives may be generated by using the permutation of entries in Table 4. Table 4: Precoding matrix W for single, dual and three-layer transmission using three antenna ports with transform precoding disabled. Alternate An alternative (to the codebook design presented above) to design the 3-port fully coherent codebooks is to exploit the 3Nx3N DFT matrix (by using the definition of Discrete Fourier Transform) as: Using the above equation of ^^3^^, we discuss the following cases for N = 1, N = 2 and N = 3 which represents the 3x3, 6x6 and 9x9 DFT matrices, respectively. These will then be used to construct a fully coherent codebook design algorithm: For N = 1: For N = 2: For N = 3:= + = +Proposed Codebook Construction MethodFor a chosen value of N where ^^ ∈ {1,2,3, … }, the number of 3x3 fully coherent orthogonal precoders will be equalto N*(3N – 2). The procedure to obtain N*(3N – 2) such 3-port 3-layer orthogonal precoders is as follows. The following is an example implementation of method 600: Step 1: Generate a 3Nx3N DFT matrix for the chosen value of N (an example of action 610). For example, DFT matrix is of size 3 x 3, 6 x 6, and 9 x 9 for N = 1, N = 2, and N = 3, respectively. Similarly, higher values of N can also be selected. Step 2: Obtain / extract the (3N-2) sub-matrix groups from the 3Nx 3N DFT matrix where each sub-matrix group is the (3 x 3N) sub-matrix of any 3 consecutive rows of the 3N x 3N DFT matrix. Examples: For N = 1, there is 3N – 2 = 3(1) – 2 = 1 sub-matrix group as shown below. For N = 2, there are 3N – 2 = 3(2) – 2 = 4 sub-matrix groups as shown below. For N = 3, there are 3N – 2 = 3(3) – 2 = 7 sub-matrix groups as shown below. Step 3: For each of the (3N-2) sub-matrix groups (i.e., sub-matrix group ‘i’ where i = 1,2, …, (3N-2)), obtain N codebooks (3 x 3), each with 3 orthogonal column vectors, as follows (an example of action 620): ^ 3 column vectors in Precoder ‘1’ of sub-matrix group ‘i’ = Column ‘1’, Column ‘(N+1)’ and Column '(2N+1)’ of sub-matrix group ‘i’. ^ 3 column vectors in Precoder ‘2’ of sub-matrix group ‘i’ = Column ‘2’, Column ‘(N+2)’ and Column '(2N+2)’ of sub-matrix group ‘i’. ^ … ^ 3 column vectors in Precoder ‘N’ of sub-matrix group ‘i’ = Column ‘N’, Column ‘2N’ and Column '3N’ of sub-matrix group ‘i’. Step 4: Select the required / desired number of precoders from the obtained N(3N – 2) codebooks (an example of action 630). N Number of Possible Codebooks = 3(3N – 2) 1 N(3N – 2) = 1(3 – 2) = 1 2 N(3N – 2) = 2(6 – 2) = 8 3 N(3N – 2) = 3(9 – 2) = 21 … … Examples: N = 1: Number of Possible Codebooks = 1 N = 2: Number of Possible Precoders = 8 N*(3N-2) Precoders Check: Is this precoder unique? (Check by converting the first row to

[0111] (if it is something else) stPrecoder ‘1’ = 1 row is already

[0111] . Yes, it is unique. 1 1 1 1 2^^^^ −2^^^^ √3[ 1 −^^6−^^6] −2^^^^ 2^^^^ 1 −^^6−^^6Precoder ‘2’ = 1strow is already

[0111] . Yes, it is unique as it is different from 1 1 1 Precoder ‘1’. 1 −2^^^^ 2^^^^ √3[ ^^6−1 ^^6] 2^^^^ −2^^^^ −^^61 −^^6Precoder ‘3’ = 2^^^^ −2^^^^ 2^^^^ −2^^^^ 1 0 0 1 1 −^^6−^^61 1 −^^6−^^6−2^^^^ −2^^^^ 2^[ ^^^ √31 −6 6] [ −2^^^^ 2^^^^ ^^] [0 −^^60 ] −^^6 61 −^^ −^^ 2^^^^3 √ 60 0 −^^ 1 1 1 1 1 1 1 1 1 2^^^^ −2^^^^ 1 66= [ ] = Precoder ‘1’ 1 −^^ −^^3 √ −2^^^^ 2^^^^ 661 −^^ −^^ Precoder ‘3’ is equivalent to Precoder ‘1’. −2^^^^ 2^^^^ 2^^^^ Precoder ‘4’ =66 6^^ −1 ^^ ^^ 0 0−2^^^^ 2^^^^ 1 2^^^^ −2^^^^] [[ ]6 6^^ −1 ^^ 0 −1 0616−^^ 1 −^^2^^^^ −2^^^^ 3 √ −2^^^^[ ] 6√63−^^ 1 −^^60 0 ^^ −1 −1 −1 −1 −1 −1 1 1 1 1 −2^^^^ 2^^^^ = [66 √3 ^^ −1 ^^ ] = Precoder ‘2’ 2^^^^ −2^^^^ −^^61 −^^6Precoder ‘4’ is equivalent to Precoder ‘2’. −2^^^^ 2^^^^ Precoder ‘5’ = 1 −^^6^61 0 0 −2^^^^ 2^^^^ 1 −^ 2^^^^ 16 6[] [0 −^^60 ] −^^ −^^ 1 1 11√−2^^^^2^^^^ −2^^^^3[ ] 1 1 1√630 0 −^^6 61 −^^ −^^2^^^^ −2^^^^ 1 1 16 61 −^^ −^^ 2^^^^ −2^^^^ 1 66= [ ] = Precoder ‘1’ 1 −^^ −^^√3−2^^^^ 2^^^^ 661 −^^ −^^ Precoder ‘5’ is equivalent to Precoder ‘1’. 2^^^^ −2^^^^ −2^^^^ Precoder ‘6’ =66 6−^^ 1 −^^ −^^ 0 02^^^^ −2^^^^ 1 ][[ ]6 6−^^ 1 −^^ −1 −1 −1 0 1 01√−2^^^^ 2^^^^ 2^^^^3[ ] −1 −1 −13 √6 6 6−^^ 1 −^^ 0 0 −^^−2^^^^ 2^^^^ 1 1 16 6−^^ 1 −^^ −2^^^^ 2^^^^ 1 66= [ ] = Precoder ‘2’ ^^ −1 ^^3 √ 2^^^^ −2^^^^ 66−^^ 1 −^^ Precoder ‘6’ is equivalent to Precoder ‘2’. stPrecoder ‘7’ = 1 row is already

[0111] . 1 1 1 = Precoder ‘1’ 2^^^^ −2^^^^ 1 66[ ] 1 −^^ −^^3 √ −2^^^^ 2^^^^ Precoder ‘7’ is same as Precoder ‘1’. 661 −^^ −^^ −1 −1 −1 Precoder ‘8’ = −1 0 0−2^^^^ 2^^^^ 1 −1 −1 −1] [[ ]6 6−^^ 1 −^^ 0 −1 0−2^^^^ 2^^^^ 1 2^^^^ −2^^^^3 √6 6[ ] −^^ 1 −^^ 0 0 −13 √6 6^^ −1 ^^2^^^^ −2^^^^ 1 1 16 6^^ −1 ^^ −2^^^^ 2^^^^ 1 66= [ ] = Precoder ‘2’ ^^ −1 ^^3 √ 2^^^^ −2^^^^ 66−^^ 1 −^^ Precoder ‘8’ is equivalent to Precoder ‘2’. Now turning to FIG.7, there is shown a block diagram of an example of a UE 100. For example, UE 100 may be one of a smartphone, a tablet computer, a notebook computer, a smart watch, a smart band, an IoT device or a vehicle or a part thereof. UE 100 comprises a processor 101. Processor 101 may represent a single processor or two or more processors, which are for instance at least partially coupled, for instance via a bus. Processor 101 executes a program code stored in program memory 102 (for instance program code causing UE 100 in connection with a network node 200 to perform one or more of the example embodiments of a method according to the present disclosure or parts thereof, when executed on processor 101, and interfaces with a main memory 103. Program memory 102 may also contain an operating system for processor 101. Some or all of memories 102 and 103 may also be included into processor 101. One of or both of a main memory and a program memory of a processor (e.g. program memory 102 and main memory 103) could be fixedly connected to the processor (e.g. processor 101) or at least partially removable from the processor, for instance in the form of a memory card or stick. A program memory (e.g. program memory 102) may for instance be a non-volatile memory. It may for instance be a FLASH memory (or a part thereof), any of a ROM, PROM, EPROM, MRAM or a FeRAM (or a part thereof) or a hard disc (or a part thereof), to name but a few examples. For example, a program memory may for instance comprise a first memory section that is fixedly installed, and a second memory section that is removable from, for instance in the form of a removable SD memory card. A main memory (e.g. main memory 103) may for instance be a volatile memory. It may for instance be a DRAM memory, to give non-limiting example. It may for instance be used as a working memory for processor 101 when executing an operating system, an application, a program, and / or the like. Processor 101 further controls a communication interface 104 (e.g. radio interface) configured to receive and / or transmit data and / or information. For instance, communication interface 104 may be configured to transmit and / or receive radio signals from a network node, in particular as described herein. It is to be understood that any computer program code based processing required for receiving and / or evaluating radio signals may be stored in an own memory of communication interface 104 and executed by an own processor of communication interface 104 and / or it may be stored for example in memory 103 and executed for example by processor 101. Communication interface 104 may in particular be configured to communicate according to a cellular communication system like a 2G / 3G / 4G / 5G or future generation cellular communication system. User equipment 100 may use radio interface 104 to communicate with a network node. For example, the communication interface 104 may further comprise a BLE and / or Bluetooth radio interface including a BLE transmitter, receiver or transceiver. For example, radio interface 104 may additionally or alternatively comprise a WLAN radio interface including at least a WLAN transmitter, receiver or transceiver. The components 102 to 104 of user equipment 100 may for instance be connected with processor 101 by means of one or more serial and / or parallel busses. It is to be understood that user equipment 100 may comprise various other components. For example, user equipment 100 may optionally comprise a user interface (e.g. a touch-sensitive display, a keyboard, a touchpad, a display, etc.). FIG.8 shows a block diagram of an example of a network node, such as a base station or gNB. For instance, network node 200 may be configured for scheduling and / or transmitting signals to the UE 100, as described above. Network node 200 comprises a processor 201. Processor 201 may represent a single processor or two or more processors, which are for instance at least partially coupled, for instance via a bus. Processor 201 executes a program code stored in program memory 202 (for instance program code causing network node 200 to perform alone or together with user equipment 100 example embodiments according to the present disclosure or parts thereof), and interfaces with a main memory 203. Program memory 202 may also comprise an operating system for processor 201. Some or all of memories 202 and 203 may also be included into processor 201. Moreover, processor 201 controls a communication interface 204 which is for example configured to communicate according to a cellular communication system like a 2G / 3G / 4G / 5G cellular communication system. Communication interface 204 of apparatus 200 may be realized by radio heads for instance and may be provided for communication between network node and user equipment. The components 202 to 204 of apparatus 200 may for instance be connected with processor 201 by means of one or more serial and / or parallel busses. It is to be understood that apparatuses 100, 200 may comprise various other components. FIG.9 shows a schematic illustration of examples of tangible and non-transitory computer-readable storage media according to the present disclosure that may for instance be used to implement memory 102 of FIG.7 or memory 202 of FIG.8. To this end, FIG.9 displays a flash memory 1000, which may for instance be soldered or bonded to a printed circuit board, a solid-state drive 1001 comprising a plurality of memory chips (e.g. Flash memory chips), a magnetic hard drive 1002, a Secure Digital (SD) card 1003, a Universal Serial Bus (USB) memory stick 1004, an optical storage medium 1005 (such as for instance a CD-ROM or DVD) and a magnetic storage medium 1006. Any presented connection in the described embodiments is to be understood in a way that the involved components are operationally coupled. Thus, the connections can be direct or indirect with any number or combination of intervening elements, and there may be merely a functional relationship between the components. Further, as used in this text, the term ‘circuitry’ may refer to one or more or all of the following: (a) hardware-only circuit implementations (such as implementations in only analog and / or digital circuitry) and (b) combinations of hardware circuits and software (and / or firmware), 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 (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(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 in this text, including in any claims. As a further example, as used in this text, the term ‘circuitry’ also covers an implementation of merely a hardware circuit or processor (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 processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device. Any of the processors mentioned in this text, in particular but not limited to processors 101 and 201 of FIGS.7 and 8, could be a processor of any suitable type. Any processor may comprise but is not limited to one or more microprocessors, one or more processor(s) with accompanying digital signal processor(s), one or more processor(s) without accompanying digital signal processor(s), one or more special-purpose computer chips, one or more field- programmable gate arrays (FPGAS), one or more controllers, one or more application-specific integrated circuits (ASICS), or one or more computer(s). The relevant structure / hardware has been programmed in such a way to carry out the described function. Moreover, any of the actions or steps described or illustrated herein may be implemented using executable instructions in a general-purpose or special-purpose processor and stored on a computer-readable storage medium (e.g., disk, memory, or the like) to be executed by such a processor. References to ‘computer-readable storage medium’ should be understood to encompass specialized circuits such as FPGAs, ASICs, signal processing devices, and other devices. As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements. The wording “A, or B, or C, or a combination thereof” or “at least one of A, B and C” or “at least one of A, B or C” or “A, B, and / or C” may be understood to be not exhaustive and to include at least the following: (i) A, or (ii) B, or (iii) C, or (iv) A and B, or (v) A and C, or (vi) B and C, or (vii) A and B and C. It will be understood that the embodiments disclosed herein are only exemplary, and that any feature presented for a particular example embodiment may be used with any aspect of the present disclosure on its own or in combination with any feature presented for the same or another particular example embodiment and / or in combination with any other feature not mentioned. It will further be understood that any feature presented for an example embodiment in a particular category may also be used in a corresponding manner in an example embodiment of any other category.

Claims

1. C l a i m s1. A user equipment comprising:- means for obtaining a precoding matrix for precoding an uplink data stream to be transmitted to a network node by the user equipment using three antenna ports, the uplink data stream comprising at most three uplink layers, wherein each of the at most three uplink layers is to be transmitted to the network node using the three antenna ports, wherein the precoding matrix is obtainable based on performing at least the following: o obtaining an oversampled 3×3^^ discrete Fourier transform, DFT, matrix with an oversampling factor ^^, wherein ^^ is an arbitrary natural number, wherein the oversampled 3×3^^ DFT matrix comprises 3^^ column vectors forming ^^ groups of column vectors, with each group ^^ of the ^^ groups of column vectors comprising the ^^^^ℎ,and (2^^ + ^^)^^ℎ columnvector of the oversampled 3×3^^ DFT matrix, with ^^ ∈ {1, … , ^^};o determining a 3×3 matrix consisting of three column vectors comprised by a respective group of the ^^ groups of column vectors; o determining the precoding matrix based on the 3×3 matrix; - means for generating, based on the uplink data stream and the precoding matrix, a precoded uplink data stream; and - means for transmitting the precoded uplink data stream to the network node using the three antenna ports.

2. The user equipment of claim 1, wherein theterm aij of the oversampled 3×3^^ DFT matrix isgiven by: ^^ = 1,2,3 and ^^ = 1,2, … ,3^^3. The user equipment of any of claims 1 or 2, wherein the precoding matrix comprises only non-zero entries.

4. The user equipment of any of claims 1 to 3, wherein the precoding matrix is unitary.

5. The user equipment of any of claims 1 to 4, wherein the precoding matrix comprises one or more column vectors, the one or more column vectors being pairwise orthogonal and / or having unit length.

6. The user equipment of any of claims 1 to 5, wherein the precoding matrix has three rows and wherein a number of columns of the precoding matrix corresponds to a number of uplink layers comprised by the uplink data stream.

7. The user equipment of any of claims 1 to 6, wherein the precoding matrix is obtained as part of a precoding codebook comprising a plurality of precoding matrices.

8. The user equipment of any of claims 1 to 7, wherein the precoding matrix is obtained based at least in part on a Transmitted Precoding Matrix Indicator, TPMI, index.

9. The user equipment of any of claims 1 to 8, wherein obtaining the precoding matrix comprises at least one of: - determining the precoding matrix by the user equipment; - retrieving the precoding matrix from an internal memory of the user equipment; - receiving the precoding matrix from an external device.

10. The user equipment of any of claims 1 to 9, wherein the uplink data stream comprises exactly three uplink layers, wherein the precoding matrix corresponds to the 3×3 matrix.

11. The user equipment of any of claims 1 to 9, wherein the uplink data stream comprises exactly two uplink layers, wherein the precoding matrix is obtainable based on further performing at least the following: - determining a 3×2 matrix consisting of two different column vectors of the three column vectors forming the 3×3 matrix.

12. The user equipment of any of claims 1 to 9, wherein the uplink data stream comprises exactly one uplink layer, wherein the precoding matrix is obtainable based on further performing at least the following: - determining a 3×1 matrix consisting of one column vector of the three column vectors forming the 3×3 matrix.

13. A user equipment comprising: - means for obtaining a precoding matrix for precoding an uplink data stream to be transmitted to a network node by the user equipment using three antenna ports, the uplink data stream comprising at most three uplink layers, wherein each of the at most three uplink layers is to be transmitted to the network node using the three antenna ports, wherein the precoding matrix comprises or corresponds to at least one of the following matrices:1 1 1 1 1 1 −^1 1 − 1 1 1 1 ^− ;- means for generating, based on the uplink data stream and the precoding matrix, a precoded uplink data stream; and - means for transmitting the precoded uplink data stream to the network node using the three antenna ports.

14. A network node comprising: - means for receiving a precoded uplink data stream having been transmitted to the network node by a user equipment using three antenna ports, the precoded uplink data stream having been generated by the user equipment based on an uplink data stream and a precoding matrix, the uplink data stream comprising at most three uplink layers, wherein each of the at most three uplink layers has been transmitted to the network node by the user equipment using the three antenna ports, wherein the precoding matrix is obtainable based on performing at least the following: o obtaining an oversampled 3×3^^ discrete Fourier transform, DFT, matrix with an oversampling factor ^^, wherein ^^ is an arbitrary natural number, wherein the oversampled 3×3^^ DFT matrix comprises 3^^ column vectors forming ^^ groups of column vectors, with each group ^^ of the ^^ groups of column vectors comprising the ^^^^ℎ,and (2^^ + ^^)^^ℎ columnvector of the oversampled 3×3^^ DFT matrix, with ^^ ∈ {1, … , ^^};o determining a 3×3 matrix consisting of three column vectors comprised by a respective group of the ^^ groups of column vectors; o determining the precoding matrix based on the 3×3 matrix; - means for determining, based on the received precoded uplink data stream, the uplink data stream.

15. The network node of claim 14, comprising:- means for transmitting precoding information to the user equipment, the precoding information being indicative of the precoding matrix.

16. A network node comprising:- means for receiving a precoded uplink data stream having been transmitted to the network node by a user equipment using three antenna ports, the precoded uplink data stream having been generated by the user equipment based on an uplink data stream and a precoding matrix, the uplink data stream comprising at most three uplink layers, wherein each of the at most three uplink layers has been transmitted to the network node by the user equipment using the three antenna ports, wherein the precoding matrix comprises or corresponds to at least one of the following matrices: ;- means for determining, based on the received precoded uplink data stream, the uplink data stream.

17. A method, performed by a user equipment, the method comprising: - obtaining a precoding matrix for precoding an uplink data stream to be transmitted to a network node by the user equipment using three antenna ports, the uplink data stream comprising at most three uplink layers, wherein each of the at most three uplink layers is to be transmitted to the network node using the three antenna ports, wherein the precoding matrix is obtainable based on performing at least the following: o obtaining an oversampled 3×3^^ discrete Fourier transform, DFT, matrix with an oversampling factor ^^, wherein ^^ is an arbitrary natural number, wherein the oversampled 3×3^^ DFT matrix comprises 3^^ column vectors forming ^^ groups of column vectors, with each group ^^ of the ^^ groups of column vectors comprising the ^^^^ℎ,and (2^^ + ^^)^^ℎ columnvector of the oversampled 3×3^^ DFT matrix, with ^^ ∈ {1, … , ^^};o determining a 3×3 matrix consisting of three column vectors comprised by a respective group of the ^^ groups of column vectors; o determining the precoding matrix based on the 3×3 matrix; - generating, based on the uplink data stream and the precoding matrix, a precoded uplink data stream; and - transmitting the precoded uplink data stream to the network node using the three antenna ports.

18. A method, performed by a network node, the method comprising:- receiving a precoded uplink data stream having been transmitted to the network node by a user equipment using three antenna ports, the precoded uplink data stream having been generated by the user equipment based on an uplink data stream and a precoding matrix, the uplink data stream comprising at most three uplink layers, wherein each of the at most three uplink layers has been transmitted to the network node by the user equipment using the three antenna ports, wherein the precoding matrix is obtainable based on performing at least the following: o obtaining an oversampled 3×3^^ discrete Fourier transform, DFT, matrix with an oversampling factor ^^, wherein ^^ is an arbitrary natural number, wherein the oversampled 3×3^^ DFT matrix comprises 3^^ column vectors forming ^^ groups of column vectors, with each group ^^ of the ^^ groups of column vectors comprising the ^^^^ℎ,and (2^^ + ^^)^^ℎ columnvector of the oversampled 3×3^^ DFT matrix, with ^^ ∈ {1, … , ^^};o determining a 3×3 matrix consisting of three column vectors comprised by a respective group of the ^^ groups of column vectors; o determining the precoding matrix based on the 3×3 matrix; - determining, based on the received precoded uplink data stream, the uplink data stream.

19. A computer program comprising instructions, which, when executed by an apparatus, cause the apparatus to perform the method of any of claims 17 or 18.

20. A computer-readable storage medium having stored thereon the computer program of claim 19.

Images