Apparatus, computer program and method

Abstract

A user equipment configured to transmit signals using a number of antenna ports and a number of transmission layers, the user equipment comprising at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: applying a precoding matrix to an Uplink Demodulation Reference Signal, UL-DMRS to provide a weighted UL-DMRS, wherein the precoding matrix is invertible or pseudo-invertible, the precoding matrix has a num- ber of rows that is equal to the number of antenna ports, and the precoding matrix has a number of columns that is greater than the number of transmission layers and less than or equal to the number of rows of the precoding matrix; sending the weighted UL-DMRS to a network node.

Description

[0001] APPARATUS, COMPUTER PROGRAM AND METHOD

[0002] TECHNICAL FIELD

[0003] Various example embodiments relate to performance boosting in telecommunications systems. Some examples relate to performance boosting for Uplink (UL) transmissions.

[0004] BACKGROUND

[0005] Beamforming at a User Equipment (UE) or network node (e.g., a gNB) can be used to boost UL performance in a telecommunications network.

[0006] BRIEF DESCRIPTION

[0007] According to an aspect of the invention, there is provided a user equipment configured to transmit signals using a number of antenna ports and a number of transmission layers, the user equipment comprising at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: applying a precoding matrix to an Uplink Demodulation Reference Signal, UL-DMRS to provide a weighted UL-DMRS, wherein the precoding matrix is invertible or pseudo-invertible, the precoding matrix has a number of rows that is equal to the number of antenna ports, and the precoding matrix has a number of columns that is greater than the number of transmission layers and less than or equal to the number of rows of the precoding matrix; sending the weighted UL-DMRS to a network node.

[0008] According to some examples, the number of rows of the precoding matrix is equal to the number of columns of the precoding matrix and the precoding matrix is invertible.

[0009] According to some examples, the number of columns of the precoding matrix is less than the number of rows and the precoding matrix is pseudo-invertible.

[0010] According to some examples, the product of the precoding matrix with a Hermitian of the precoding matrix is invertible, and wherein the precoding matrix has a right inverse matrix.

[0011] According to some examples, the instructions, when executed by the at least one processor, cause the apparatus at least to perform: receiving, from the network node, a set of precoding matrices including the precoding matrix.

[0012] According to some examples, the instructions, when executed by the at least one processor, cause the apparatus at least to perform: selecting the precoding matrix based on at least one of: at least one rule or at least one indication received from the network node.

[0013] According to some examples, the UL DMRS signals are repeated before the precoding matrix is applied to the UL DMRS, wherein the result is multiplexed before to provide the weighted UL-DMRS.

[0014] According to an aspect of the invention, there is provided a method comprising: applying a precoding matrix to an Uplink Demodulation Reference Signal, UL-DMRS to provide a weighted UL-DMRS,wherein the precoding matrix is invertible or pseudo-invertible; sending the weighted UL-DMRS from a user equipment to a network node, wherein the user equipment is configured to transmit signals using a number of antenna ports and a number of transmission layers, wherein the precoding matrix has a number of rows that is equal to the number of antenna ports, and the precoding matrix has a number of columns that is greater than the number of transmissions layers and less than or equal to the number of rows of the precoding matrix.

[0015] According to some examples, the number of rows of the precoding matrix is equal to the number of columns of the precoding matrix and the precoding matrix is invertible.

[0016] According to some examples, the number of columns of the precoding matrix is less than the number of rows and the precoding matrix is pseudo-invertible.

[0017] According to some examples, the product of the precoding matrix with a Hermitian of the precoding matrix is invertible, and wherein the precoding matrix has a right inverse matrix.

[0018] According to some examples, the method comprises: receiving, from the network node, a set of precoding matrices including the precoding matrix.

[0019] According to some examples, the method comprises: selecting the precoding matrix based on at least one of: at least one rule or at least one indication received from the network node.

[0020] According to some examples, the UL DMRS signals are repeated before the precoding matrix is applied to the UL DMRS, wherein the result is multiplexed before to provide the weighted UL-DMRS.

[0021] According to an aspect of the invention, there is provided an apparatus comprising means for: applying a precoding matrix to an Uplink Demodulation Reference Signal, UL-DMRS to provide a weighted UL-DMRS, wherein the precoding matrix is invertible or pseudo-invertible; sending the weighted UL-DMRS from a user equipment to a network node, wherein the user equipment is configured to transmit signals using a number of antenna ports and a number of transmission layers, wherein the precoding matrix has a number of rows that is equal to the number of antenna ports, and the precoding matrix has a number of columns that is greater than the number of transmissions layers and less than or equal to the number of rows of the precoding matrix.

[0022] According to some examples, the number of rows of the precoding matrix is equal to the number of columns of the precoding matrix and the precoding matrix is invertible.

[0023] According to some examples, the number of columns of the precoding matrix is less than the number of rows and the precoding matrix is pseudo-invertible.

[0024] According to some examples, the product of the precoding matrix with a Hermitian of the precoding matrix is invertible, and wherein the precoding matrix has a right inverse matrix.

[0025] According to some examples, the method comprises: receiving, from the network node, a set of precoding matrices including the precoding matrix.According to some examples, the method comprises: selecting the precoding matrix based on at least one of: at least one rule or at least one indication received from the network node.

[0026] According to some examples, the UL DMRS signals are repeated before the precoding matrix is applied to the UL DMRS, wherein the result is multiplexed before to provide the weighted UL-DMRS.

[0027] According to an aspect of the invention, there is provided a computer program product embodied on a distribution medium readable by a computer and comprising program instructions which, when loaded into an apparatus, execute a method comprising: applying a precoding matrix to an Uplink Demodulation Reference Signal, UL-DMRS to provide a weighted UL-DMRS, wherein the precoding matrix is invertible or pseudo-invertible; sending the weighted UL-DMRS from a user equipment to a network node, wherein the user equipment is configured to transmit signals using a number of antenna ports and a number of transmission layers, wherein the precoding matrix has a number of rows that is equal to the number of antenna ports, and the precoding matrix has a number of columns that is greater than the number of transmissions layers and less than or equal to the number of rows of the precoding matrix.

[0028] According to an aspect of the invention, there is provided an apparatus comprising at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: receiving, from a user equipment, a weighted Uplink Demodulation Reference Signal, UL-DMRS, wherein the weighted UL-DMRS is determined by the user equipment by applying a precoding matrix to an UL-DMRS, wherein the precoding matrix is invertible or pseudo-invertible, and wherein the user equipment is configured to transmit signals using a first number of antenna ports and a second number of transmission layers wherein the precoding matrix has a number of rows that is equal to the number of antenna ports, and the precoding matrix has a number of columns that is greater than the number of transmissions layers and less than or equal to the number of rows of the precoding matrix.

[0029] According to some examples, the number of rows of the precoding matrix is equal to the number of columns of the precoding matrix and the precoding matrix is invertible.

[0030] According to some examples, the number of columns of the precoding matrix is less than the number of rows and the precoding matrix is pseudo-invertible.

[0031] According to some examples, the product of the precoding matrix with a Hermitian of the precoding matrix is invertible, and wherein the precoding matrix has a right inverse matrix.

[0032] According to some examples, the instructions, when executed by the at least one processor, cause the apparatus at least to perform: sending information indicative of at least one set of transmission precoding matrix indicators, TPMIs, wherein the precoding matrix corresponds to a TPMI in at least one of the at least two sets.

[0033] According to some examples, the instructions, when executed by the at least one processor, cause the apparatus at least to perform: sending information indicative of a subset of the at least one set of TPMIs.According to some examples, the instructions, when executed by the at least one processor, cause the apparatus at least to perform: sending information indicative of a specific TPMI in the at least one set of TPMIs.

[0034] According to some examples, the precoding matrix comprises an invertible matrix, wherein the instructions, when executed by the at least one processor, cause the apparatus at least to perform: determining a channel estimate based on the weighted UL-DMRS.

[0035] According to some examples, the precoding matrix comprises a pseudo-invertible matrix, wherein the instructions, when executed by the at least one processor, cause the apparatus at least to perform: determining a channel estimate based on the weighted UL-DMRS.

[0036] According to an aspect of the invention, there is provided a method comprising: receiving, from a user equipment, a weighted Uplink Demodulation Reference Signal, UL-DMRS, wherein the weighted UL-DMRS is determined by the user equipment by applying a precoding matrix to an UL-DMRS, wherein the precoding matrix is invertible or pseudo-invertible, and wherein the user equipment is configured to transmit signals using a first number of antenna ports and a second number of transmission layers wherein the precoding matrix has a number of rows that is equal to the number of antenna ports, and the precoding matrix has a number of columns that is greater than the number of transmissions layers and less than or equal to the number of rows of the precoding matrix.

[0037] According to some examples, the number of rows of the precoding matrix is equal to the number of columns of the precoding matrix and the precoding matrix is invertible.

[0038] According to some examples, the number of columns of the precoding matrix is less than the number of rows and the precoding matrix is pseudo-invertible.

[0039] According to some examples, the product of the precoding matrix with a Hermitian of the precoding matrix is invertible, and wherein the precoding matrix has a right inverse matrix.

[0040] According to some examples, the method comprises: sending information indicative of at least one set of transmission precoding matrix indicators, TPMIs, wherein the precoding matrix corresponds to a TPMI in at least one of the at least two sets.

[0041] According to some examples, the method comprises: sending information indicative of a subset of the at least one set of TPMIs.

[0042] According to some examples, the method comprises: sending information indicative of a specific TPMI in the at least one set of TPMIs.

[0043] According to some examples, the precoding matrix comprises an invertible matrix, wherein the method comprises: determining a channel estimate based on the weighted UL-DMRS.

[0044] According to some examples, the precoding matrix comprises a pseudo-invertible matrix, wherein the method comprises: determining a channel estimate based on the weighted UL-DMRS.According to an aspect of the invention, there is provided an apparatus comprising means for: receiving, from a user equipment, a weighted Uplink Demodulation Reference Signal, UL-DMRS, wherein the weighted UL-DMRS is determined by the user equipment by applying a precoding matrix to an UL-DMRS, wherein the precoding matrix is invertible or pseudo-invertible, and wherein the user equipment is configured to transmit signals using a first number of antenna ports and a second number of transmission layers wherein the precoding matrix has a number of rows that is equal to the number of antenna ports, and the precoding matrix has a number of columns that is greater than the number of transmissions layers and less than or equal to the number of rows of the precoding matrix.

[0045] According to some examples, the number of rows of the precoding matrix is equal to the number of columns of the precoding matrix and the precoding matrix is invertible.

[0046] According to some examples, the number of columns of the precoding matrix is less than the number of rows and the precoding matrix is pseudo-invertible.

[0047] According to some examples, the product of the precoding matrix with a Hermitian of the precoding matrix is invertible, and wherein the precoding matrix has a right inverse matrix.

[0048] According to some examples, the means are configured to perform: sending information indicative of at least one set of transmission precoding matrix indicators, TPMIs, wherein the precoding matrix corresponds to a TPMI in at least one of the at least two sets.

[0049] According to some examples, the means are configured to perform: sending information indicative of a subset of the at least one set of TPMIs.

[0050] According to some examples, the means are configured to perform: sending information indicative of a specific TPMI in the at least one set of TPMIs.

[0051] According to some examples, the precoding matrix comprises an invertible matrix, and the means are configured to perform: determining a channel estimate based on the weighted UL-DMRS.

[0052] According to some examples, the precoding matrix comprises a pseudo-invertible matrix, and the means are configured to perform: determining a channel estimate based on the weighted UL-DMRS.

[0053] According to an aspect of the invention, there is provided a computer program product embodied on a distribution medium readable by a computer and comprising program instructions which, when loaded into an apparatus, execute a method comprising: receiving, from a user equipment, a weighted Uplink Demodulation Reference Signal, UL-DMRS, wherein the weighted UL-DMRS is determined by the user equipment by applying a precoding matrix to an UL-DMRS, wherein the precoding matrix is invertible or pseudo-invertible, and wherein the user equipment is configured to transmit signals using a first number of antenna ports and a second number of transmission layers wherein the precoding matrix has a number of rows that is equal to the number of antenna ports, and the precoding matrix has a number of columns that is greater than the number of transmissions layers and less than or equal to the number of rows of the precoding matrix.According to an aspect of the invention, there is provided a user equipment comprising at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the user equipment at least to perform: determining, from at least two sets of transmission precoding matrix indicators, TPMIs, at least one TPMI to apply to uplink transmissions, wherein the determining is based on at least one of: at least one rule; at least one indication from a network node; applying at least one precoding matrix corresponding to the determined at least one TPMI to at least one uplink transmission; sending the at least one uplink transmission to the network node using a number of antenna ports and a number of transmission layers; wherein each precoding matrix corresponding to a TPMI in a first set of the at least two sets of TPMIs has a number of rows that is equal to the number of antenna ports and a number of columns that is equal to the number of transmissions layers; and wherein each precoding matrix corresponding to a TPMI in a second set of the at least two sets of TPMIs is invertible or pseudo-invertible and has a number of rows that is equal to the number of antenna ports and a number of columns that is greater than the number of transmission layers and less than or equal to the number of rows.

[0054] According to some examples, each of the at least two sets (or subsets of one of the at least two sets) may comprise one or more TPMIs.

[0055] According to some examples, a set of TPMIs of the at least two sets (or a subset of one of the at least two sets) is indicated from the network to the user equipment.

[0056] According to some examples, the at least one TPMI is determined from the indicated set of TPMIs based on the at least one rule.

[0057] According to some examples, the at least one TPMI is determined from the indicated set of TPMIs based on a second indication from the network node.

[0058] According to some examples, for a pseudo-invertible precoding matrix of the at least one precoding matrix, a product of the precoding matrix with a Hermitian of the precoding matrix is invertible, and wherein the precoding matrix has a right inverse matrix.

[0059] According to some examples, the instructions, when executed by the at least one processor, cause the user equipment at least to perform: receiving, from the network node, the at least one indication, wherein the at least one indication indicates which of the at least two sets of TPMIs should be used to determine the at least one TPMI.

[0060] According to some examples, the at least one indication is received in at least one of: a Medium Access Control Control Element, Downlink Control Information, a Radio Resource Control message.

[0061] According to some examples, the instructions, when executed by the at least one processor, cause the user equipment at least to perform: receiving a configured grant, CG, configuration for Physical Uplink Shared Channel, PUSCH, and / or Uplink, UL, transmissions, wherein the configuration includes or is associated with at least two TPMIs.According to some examples, the at least one rule is based on at least one of: a frequency resource allocation of the at least one uplink transmission; a Modulation and Coding Scheme, MCS, of the at least one uplink transmission; a DMRS pattern of the at least one uplink transmission; a waveform of the at least one uplink transmission; a mobility status of the user equipment; a number of transmission layers, of the at least one uplink transmission.

[0062] According to some examples, the at least one rule is based on at least one of: a threshold number of resource blocks and a number of resource blocks allocated for the at least one uplink transmission;

[0063] a threshold number of resource elements and a number of resource elements allocated for the at least one uplink transmission; a threshold number of resource block groups and a number of resource block groups allocated for the at least one uplink transmission.

[0064] According to some examples, the at least one rule is based on a threshold MCS index and an indicated MCS for the at least one uplink transmission.

[0065] According to some examples, the at least one rule is based on a DMRS pattern that is at least one of indicated to the user equipment or applicable at the user equipment; wherein a first DMRS pattern is associated with a third set of TPMIs of the at least two sets of TPMIs and a second DMRS pattern is associated with a fourth set of TPMIs of the at least two sets of TPMIs.

[0066] According to some examples, the third set of TPMIs or the fourth set of TPMIs is a subset of the first set of TPMIs and / or the second set of TPMIs.

[0067] According to some examples, the at least one rule is based on at least one of: a Transmission Configuration Indicator (TCI) state; a spatial relation.

[0068] According to some examples, the TCI state indicates mapping information fortransport blocks and / or codewords to the transmission layers.

[0069] According to some examples, the instructions, when executed by the at least one processor, cause the user equipment at least to perform: receiving information indicating an association between at least one TCI state and the at least one TPMI, wherein the information is received via at least one of: a Medium Access Control Control Element; a Radio Resource Control message.

[0070] According to some examples, the at least one uplink transmission comprises at least one Uplink Demodulation Reference Signal, UL-DMRS.

[0071] According to an aspect of the invention, there is provided an apparatus comprising means for: determining, from at least two sets of transmission precoding matrix indicators, TPMIs, at least one TPMI to apply to uplink transmissions, wherein the determining is based on at least one of: at least one rule; at least one indication from a network node; applying at least one precoding matrix corresponding to the determined at least one TPMI to at least one uplink transmission; sending the at least one uplink transmission to the network node using a number of antenna ports and a number of transmission layers; wherein each precoding matrix corresponding to a TPMI in a first set of the at least two sets of TPMIs has a number of rows that isequal to the number of antenna ports and a number of columns that is equal to the number of transmissions layers; and wherein each precoding matrix corresponding to a TPMI in a second set of the at least two sets of TPMIs is invertible or pseudo-invertible and has a number of rows that is equal to the number of antenna ports and a number of columns that is greater than the number of transmission layers and less than or equal to the number of rows.

[0072] According to some examples, each of the at least two sets (or subsets of one of the at least two sets) may comprise one or more TPMIs.

[0073] According to some examples, a set of TPMIs of the at least two sets (or a subset of one of the at least two sets) is indicated from the network to the user equipment.

[0074] According to some examples, the at least one TPMI is determined from the indicated set of TPMIs based on the at least one rule.

[0075] According to some examples, the at least one TPMI is determined from the indicated set of TPMIs based on a second indication from the network node.

[0076] According to some examples, for a pseudo-invertible precoding matrix of the at least one precoding matrix, a product of the precoding matrix with a Hermitian of the precoding matrix is invertible, and wherein the precoding matrix has a right inverse matrix.

[0077] According to some examples, the means are configured to perform: receiving, from the network node, the at least one indication, wherein the at least one indication indicates which of the at least two sets of TPMIs should be used to determine the at least one TPMI.

[0078] According to some examples, the at least one indication is received in at least one of: a Medium Access Control Control Element, Downlink Control Information, a Radio Resource Control message.

[0079] According to some examples, the means are configured to perform: receiving a configured grant, CG, configuration for Physical Uplink Shared Channel, PUSCH, and / or Uplink, UL, transmissions, wherein the configuration includes or is associated with at least two TPMIs.

[0080] According to some examples, the at least one rule is based on at least one of: a frequency resource allocation of the at least one uplink transmission; a Modulation and Coding Scheme, MCS, of the at least one uplink transmission; a DMRS pattern of the at least one uplink transmission; a waveform of the at least one uplink transmission; a mobility status of the user equipment; a number of transmission layers, of the at least one uplink transmission.

[0081] According to some examples, the at least one rule is based on at least one of: a threshold number of resource blocks and a number of resource blocks allocated for the at least one uplink transmission;

[0082] a threshold number of resource elements and a number of resource elements allocated for the at least one uplink transmission; a threshold number of resource block groups and a number of resource block groups allocated for the at least one uplink transmission.According to some examples, the at least one rule is based on a threshold MCS index and an indicated MCS for the at least one uplink transmission.

[0083] According to some examples, the at least one rule is based on a DMRS pattern that is at least one of indicated to the user equipment or applicable at the user equipment; wherein a first DMRS pattern is associated with a third set of TPMIs of the at least two sets of TPMIs and a second DMRS pattern is associated with a fourth set of TPMIs of the at least two sets of TPMIs.

[0084] According to some examples, the third set of TPMIs or the fourth set of TPMIs is a subset of the first set of TPMIs and / or the second set of TPMIs.

[0085] According to some examples, the at least one rule is based on at least one of: a Transmission Configuration Indicator (TCI) state; a spatial relation.

[0086] According to some examples, the TCI state indicates mapping information fortransport blocks and / or codewords to the transmission layers.

[0087] According to some examples, the means are configured to perform receiving information indicating an association between at least one TCI state and the at least one TPMI, wherein the information is received via at least one of: a Medium Access Control Control Element; a Radio Resource Control message.

[0088] According to some examples, the at least one uplink transmission comprises at least one Uplink Demodulation Reference Signal, UL-DMRS.

[0089] According to an aspect of the invention, there is provided a method comprising: determining, from at least two sets of transmission precoding matrix indicators, TPMIs, at least one TPMI to apply to uplink transmissions, wherein the determining is based on at least one of: at least one rule; at least one indication from a network node; applying at least one precoding matrix corresponding to the determined at least one TPMI to at least one uplink transmission; sending the at least one uplink transmission to the network node using a number of antenna ports and a number of transmission layers; wherein each precoding matrix corresponding to a TPMI in a first set of the at least two sets of TPMIs has a number of rows that is equal to the number of antenna ports and a number of columns that is equal to the number of transmissions layers; and wherein each precoding matrix corresponding to a TPMI in a second set of the at least two sets of TPMIs is invertible or pseudo-invertible and has a number of rows that is equal to the number of antenna ports and a number of columns that is greater than the number of transmission layers and less than or equal to the number of rows.

[0090] According to some examples, each of the at least two sets (or subsets of one of the at least two sets) may comprise one or more TPMIs.

[0091] According to some examples, a set of TPMIs of the at least two sets (or a subset of one of the at least two sets) is indicated from the network to the user equipment.

[0092] According to some examples, the at least one TPMI is determined from the indicated set of TPMIs based on the at least one rule.According to some examples, the at least one TPMI is determined from the indicated set of TPMIs based on a second indication from the network node.

[0093] According to some examples, for a pseudo-invertible precoding matrix of the at least one precoding matrix, a product of the precoding matrix with a Hermitian of the precoding matrix is invertible, and wherein the precoding matrix has a right inverse matrix.

[0094] According to some examples, the method comprises: receiving, from the network node, the at least one indication, wherein the at least one indication indicates which of the at least two sets of TPMIs should be used to determine the at least one TPMI.

[0095] According to some examples, the at least one indication is received in at least one of: a Medium Access Control Control Element, Downlink Control Information, a Radio Resource Control message.

[0096] According to some examples, the method comprises: receiving a configured grant, CG, configuration for Physical Uplink Shared Channel, PUSCH, and / or Uplink, UL, transmissions, wherein the configuration includes or is associated with at least two TPMIs.

[0097] According to some examples, the at least one rule is based on at least one of: a frequency resource allocation of the at least one uplink transmission; a Modulation and Coding Scheme, MCS, of the at least one uplink transmission; a DMRS pattern of the at least one uplink transmission; a waveform of the at least one uplink transmission; a mobility status of the user equipment; a number of transmission layers, of the at least one uplink transmission.

[0098] According to some examples, the at least one rule is based on at least one of: a threshold number of resource blocks and a number of resource blocks allocated for the at least one uplink transmission;

[0099] a threshold number of resource elements and a number of resource elements allocated for the at least one uplink transmission; a threshold number of resource block groups and a number of resource block groups allocated for the at least one uplink transmission.

[0100] According to some examples, the at least one rule is based on a threshold MCS index and an indicated MCS for the at least one uplink transmission.

[0101] According to some examples, the at least one rule is based on a DMRS pattern that is at least one of indicated to the user equipment or applicable at the user equipment; wherein a first DMRS pattern is associated with a third set of TPMIs of the at least two sets of TPMIs and a second DMRS pattern is associated with a fourth set of TPMIs of the at least two sets of TPMIs.

[0102] According to some examples, the third set of TPMIs or the fourth set of TPMIs is a subset of the first set of TPMIs and / or the second set of TPMIs.

[0103] According to some examples, the at least one rule is based on at least one of: a Transmission Configuration Indicator (TCI) state; a spatial relation.

[0104] According to some examples, the TCI state indicates mapping information fortransport blocks and / or codewords to the transmission layers.According to some examples, the method comprises: receiving information indicating an association between at least one TCI state and the at least one TPMI, wherein the information is received via at least one of: a Medium Access Control Control Element; a Radio Resource Control message.

[0105] According to some examples, the at least one uplink transmission comprises at least one Uplink Demodulation Reference Signal, UL-DMRS.

[0106] According to an aspect of the invention, there is provided a computer program product embodied on a distribution medium readable by a computer and comprising program instructions which, when loaded into an apparatus, execute a method comprising: determining, from at least two sets of transmission precoding matrix indicators, TPMIs, at least one TPMI to apply to uplink transmissions, wherein the determining is based on at least one of: at least one rule; at least one indication from a network node; applying at least one precoding matrix corresponding to the determined at least one TPMI to at least one uplink transmission; sending the at least one uplink transmission to the network node using a number of antenna ports and a number of transmission layers; wherein each precoding matrix corresponding to a TPMI in a first set of the at least two sets of TPMIs has a number of rows that is equal to the number of antenna ports and a number of columns that is equal to the number of transmissions layers; and wherein each precoding matrix corresponding to a TPMI in a second set of the at least two sets of TPMIs is invertible or pseudo-invertible and has a number of rows that is equal to the number of antenna ports and a number of columns that is greater than the number of transmission layers and less than or equal to the number of rows.

[0107] According to an aspect of the invention, there is provided an apparatus comprising at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform: receiving, from a user equipment, at least one weighted uplink transmission is generated by the User Equipment applying at least one precoding matrix to the at least one uplink transmission, and wherein the at least one precoding matrix corresponds to at least one transmission precoding matrix indicator, TPMI, selected from at least two sets of TPMIs by the user equipment; determining an estimate of the at least one weighted uplink transmission based on the received uplink transmission and an inverse of the precoding matrix or a pseudo-inverse of the precoding matrix; wherein the at least one uplink transmission is sent by the user equipment using a number of antenna ports and a number of transmission layers; wherein each precoding matrix corresponding to a TPMI in a first set of the at least two sets of TPMIs has a number of rows that is equal to the number of antenna ports and a number of columns that is equal to the number of transmissions layers; and wherein each precoding matrix corresponding to a TPMI in a second set of the at least two sets of TPMIs is invertible or pseudo-invertible and has a number of rows that is equal to the number of antenna ports and a number of columns that is greater than the number of transmission layers and less than or equal to the number of rows.

[0108] According to some examples, each of the at least two sets (or a subset of one of the at least two sets) may comprise one or more TPMIs.According to some examples, for a pseudo-invertible precoding matrix of the at least one precoding matrix, a product of the precoding matrix with a Hermitian of the precoding matrix is invertible, wherein the precoding matrix has a right inverse matrix.

[0109] According to some examples, the instructions, when executed by the at least one processor, cause the user equipment at least to perform: sending, to the user equipment, the at least one indication, wherein the at least one indication indicates which of the at least two sets of TPMIs should be used to determine the at least one TPMI.

[0110] According to some examples, the at least one indication is received in at least one of: a Medium Access Control Control Element, Downlink Control Information, a Radio Resource Control message.

[0111] According to some examples, the instructions, when executed by the at least one processor, cause the user equipment at least to perform: sending a configured grant, CG, configuration for Physical Uplink Shared Channel, PUSCH, and / or Uplink, UL, transmissions, wherein the configuration includes or is associated with at least two sets of TPMIs.

[0112] According to some examples, the at least one rule is based on at least one of: a frequency resource allocation of the at least one uplink transmission; a Modulation and Coding Scheme, MCS, of the at least one uplink transmission; a DMRS pattern of the at least one uplink transmission; a waveform of the at least one uplink transmission; a mobility status of the user equipment; a number of transmission layers, of the at least one uplink transmission.

[0113] According to some examples, the at least one rule is based on at least one of: a threshold number of resource blocks and a number of resource blocks allocated for the at least one uplink transmission;

[0114] a threshold number of resource elements and a number of resource elements allocated for the at least one uplink transmission; a threshold number of resource block groups and a number of resource block groups allocated for the at least one uplink transmission.

[0115] According to some examples, the at least one is based on: a threshold MCS index and an indicated MCS for the at least one uplink transmission.

[0116] According to some examples, the at least one rule is based on: a DMRS pattern that is at least one of indicated to the user equipment or applicable at the user equipment; wherein a first DMRS pattern is associated with a third set of TPMIs of the at least two sets of TPMIs and a second DMRS pattern is associated with a fourth set of TPMIs of the at least two sets of TPMIs.

[0117] According to some examples, the third set of TPMIs or the fourth set of TPMIs is a subset of the first set of TPMIs and / or the second set of TPMIs.

[0118] According to some examples, the at least one rule is based on at least one of: a Transmission Configuration Indicator (TCI) state; a spatial relation.

[0119] According to some examples, the TCI state indicates mapping information fortransport blocks and / or codewords to the transmission layers.According to some examples, the instructions, when executed by the at least one processor, cause the apparatus at least to perform: sending, to the user equipment information indicating an association between at least one TCI state and the at least one TPMI, wherein the information is received via at least one of: a Medium Access Control Control Element; a Radio Resource Control message.

[0120] According to some examples, the at least one uplink transmission comprises at least one Uplink Demodulation Reference Signal, UL-DMRS.

[0121] According to an aspect of, there is provided a method performed by a User Equipment, the method comprising: determining, from at least two sets of transmission precoding matrix indicators, TPMIs, at least one TPMI to apply to uplink transmissions, wherein the determining is based on at least one of: at least one rule; at least one indication from a network node; applying at least one precoding matrix corresponding to the determined at least one TPMI to at least one uplink transmission; sending the at least one uplink transmission to the network node using a number of antenna ports and a number of transmission layers; wherein each precoding matrix corresponding to a TPMI in a first set of the at least two sets of TPMIs has a number of rows that is equal to the number of antenna ports and a number of columns that is equal to the number of transmissions layers; and wherein each precoding matrix corresponding to a TPMI in a second set of the at least two sets of TPMIs is invertible or pseudo-invertible and has a number of rows that is equal to the number of antenna ports and a number of columns that is greater than the number of transmission layers and less than or equal to the number of row.

[0122] According to some examples, each of the at least two sets (or a subset of one of the at least two sets) may comprise one or more TPMIs.

[0123] According to some examples, for a pseudo-invertible precoding matrix of the at least one precoding matrix, a product of the precoding matrix with a Hermitian of the precoding matrix is invertible, wherein the precoding matrix has a right inverse matrix.

[0124] According to some examples, method comprises: sending, to the user equipment, the at least one indication, wherein the at least one indication indicates which of the at least two sets of TPMIs should be used to determine the at least one TPMI.

[0125] According to some examples, the at least one indication is received in at least one of: a Medium Access Control Control Element, Downlink Control Information, a Radio Resource Control message.

[0126] According to some examples, method comprises:: sending a configured grant, CG, configuration for Physical Uplink Shared Channel, PUSCH, and / or Uplink, UL, transmissions, wherein the configuration includes or is associated with at least two sets of TPMIs.

[0127] According to some examples, the at least one rule is based on at least one of: a frequency resource allocation of the at least one uplink transmission; a Modulation and Coding Scheme, MCS, of the at least one uplink transmission; a DMRS pattern of the at least one uplink transmission; a waveform of theat least one uplink transmission; a mobility status of the user equipment; a number of transmission layers, of the at least one uplink transmission.

[0128] According to some examples, the at least one rule is based on at least one of: a threshold number of resource blocks and a number of resource blocks allocated for the at least one uplink transmission;

[0129] a threshold number of resource elements and a number of resource elements allocated for the at least one uplink transmission; a threshold number of resource block groups and a number of resource block groups allocated for the at least one uplink transmission.

[0130] According to some examples, the at least one rule is based on: a threshold MCS index and an indicated MCS for the at least one uplink transmission.

[0131] According to some examples, the at least one rule is based on: a DMRS pattern that is at least one of indicated to the user equipment or applicable at the user equipment; wherein a first DMRS pattern is associated with a third set of TPMIs of the at least two sets of TPMIs and a second DMRS pattern is associated with a fourth set of TPMIs of the at least two sets of TPMIs.

[0132] According to some examples, the third set of TPMIs or the fourth set of TPMIs is a subset of the first set of TPMIs and / or the second set of TPMIs.

[0133] According to some examples, the at least one rule is based on at least one of: a Transmission Configuration Indicator (TCI) state; a spatial relation.

[0134] According to some examples, the TCI state indicates mapping information fortransport blocks and / or codewords to the transmission layers.

[0135] According to some examples, there is provided a method comprising: sending, to the user equipment information indicating an association between at least one TCI state and the at least one TPMI, wherein the information is received via at least one of: a Medium Access Control Control Element; a Radio Resource Control message.

[0136] According to some examples, the at least one uplink transmission comprises at least one Uplink Demodulation Reference Signal, UL-DMRS.

[0137] According to an aspect, there is provided an apparatus comprising means for: determining, from at least two sets of transmission precoding matrix indicators, TPMIs, at least one TPMI to apply to uplink transmissions, wherein the determining is based on at least one of: at least one rule; at least one indication from a network node; applying at least one precoding matrix corresponding to the determined at least one TPMI to at least one uplink transmission; sending the at least one uplink transmission to the network node using a number of antenna ports and a number of transmission layers; wherein each precoding matrix corresponding to a TPMI in a first set of the at least two sets of TPMIs has a number of rows that is equal to the number of antenna ports and a number of columns that is equal to the number of transmissions layers; and wherein each precoding matrix corresponding to a TPMI in a second set of the at least two sets of TPMIs is invertible or pseudo-invertible and has a number of rows that is equal to the number of antenna ports and anumber of columns that is greater than the number of transmission layers and less than or equal to the number of row.

[0138] According to some examples, each of the at least two sets (or a subset of one of the at least two sets) may comprise one or more TPMIs.

[0139] According to some examples, for a pseudo-invertible precoding matrix of the at least one precoding matrix, a product of the precoding matrix with a Hermitian of the precoding matrix is invertible, wherein the precoding matrix has a right inverse matrix.

[0140] According to some examples, the means are configured to perform: sending, to the user equipment, the at least one indication, wherein the at least one indication indicates which of the at least two sets of TPMIs should be used to determine the at least one TPMI.

[0141] According to some examples, the at least one indication is received in at least one of: a Medium Access Control Control Element, Downlink Control Information, a Radio Resource Control message.

[0142] According to some examples, the means are configured to perform: sending a configured grant, CG, configuration for Physical Uplink Shared Channel, PUSCH, and / or Uplink, UL, transmissions, wherein the configuration includes or is associated with at least two sets of TPMIs.

[0143] According to some examples, the at least one rule is based on at least one of: a frequency resource allocation of the at least one uplink transmission; a Modulation and Coding Scheme, MCS, of the at least one uplink transmission; a DMRS pattern of the at least one uplink transmission; a waveform of the at least one uplink transmission; a mobility status of the user equipment; a number of transmission layers, of the at least one uplink transmission.

[0144] According to some examples, the at least one rule is based on at least one of: a threshold number of resource blocks and a number of resource blocks allocated for the at least one uplink transmission;

[0145] a threshold number of resource elements and a number of resource elements allocated for the at least one uplink transmission; a threshold number of resource block groups and a number of resource block groups allocated for the at least one uplink transmission.

[0146] According to some examples, the at least one rule is based on: a threshold MCS index and an indicated MCS for the at least one uplink transmission.

[0147] According to some examples, the at least one rule is based on: a DMRS pattern that is at least one of indicated to the user equipment or applicable at the user equipment; wherein a first DMRS pattern is associated with a third set of TPMIs of the at least two sets of TPMIs and a second DMRS pattern is associated with a fourth set of TPMIs of the at least two sets of TPMIs.

[0148] According to some examples, the third set of TPMIs or the fourth set of TPMIs is a subset of the first set of TPMIs and / or the second set of TPMIs.

[0149] According to some examples, the at least one rule is based on at least one of: a Transmission Configuration Indicator (TCI) state; a spatial relation.According to some examples, the TCI state indicates mapping information fortransport blocks and / or codewords to the transmission layers.

[0150] According to some examples, the means are configured to perform: sending, to the user equipment information indicating an association between at least one TCI state and the at least one TPMI, wherein the information is received via at least one of: a Medium Access Control Control Element; a Radio Resource Control message.

[0151] According to some examples, the at least one uplink transmission comprises at least one Uplink Demodulation Reference Signal, UL-DMRS.

[0152] Some embodiments of the invention are defined in the dependent claims.

[0153] LIST OF THE DRAWINGS

[0154] In the following, the invention will be described in greater detail with reference to the embodiments and the accompanying drawings, in which:

[0155] Fig. 1 shows an example of a communication network to which examples disclosed herein may be applied;

[0156] Fig. 2 shows an example message flow;

[0157] Fig. 3 shows an example of a method;

[0158] Fig. 4 shows an example of a method;

[0159] Fig. 5 shows an example of a method;

[0160] Fig. 6 shows an example of a method;

[0161] Fig. 7 shows an example of an apparatus.

[0162] DESCRIPTION OF EMBODIMENTS

[0163] The following embodiments are exemplary. Although the specification may refer to “an”, “one”, or “some” embodiment(s) in several locations of the text, this does not necessarily mean that each reference is made to the same embodiment(s), or that a particular feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments. Further, when a particular feature, structure, or characteristic is described in connection of an embodiment, it is within the knowledge of one skilled in the art to apply such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. It shall be understood that although the terms “first,” “second” and the like may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another.

[0164] For the purposes of the present disclosure, the phrases “at least one of A or B”, “at least one of A and B”, and “A and / or B” means (A), (B), or (A and B). For the purposes of the present disclosure, the phrase “A, B, and / or C” means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C).Embodiments described may be implemented in a communication network, such as any of the following radio access technologies (RATs): Worldwide Interoperability for Micro-wave Access (WiMAX), Global System for Mobile communications (GSM, 2G), GSM EDGE radio access Network (GERAN), General Packet Radio Service (GRPS), Universal Mobile Telecommunication System (UMTS, 3G) based on basic wideband-code division multiple access (W-CDMA), high-speed packet access (HSPA), Long Term Evolution (LTE), LTE-Advanced, and enhanced LTE (eLTE), 5G (also called NR), or any future RAT such as 6G. Moreover, communication within the communication network may utilize any proper wireless communication technology, comprising but not limited to: Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Frequency Division Duplex (FDD), Time Division Duplex (TDD), Multiple-Input Multiple-Output (MIMO), Orthogonal Frequency Division Multiple (OFDM), and / or Discrete Fourier Transform spread OFDM (DFT-s-OFDM).

[0165] As used herein, the term “network device” or “network node” refers to a node in a communication network via which user equipment may access the network and / or which is capable of controlling radio communication and managing radio resources within a cell. The network node or network device may be referred to as a base station (BS), an access point (AP) or an access node. The network device may be, depending on the applied technology, for example, a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), an NR NB (also referred to as a gNB), a Remote Radio Unit (RRU), a radio head (RH), a remote radio head (RRH), a relay, an Integrated Access and Backhaul (I AB) node, a low power node, a non-terrestrial network (NTN) or non-ground network device such as a satellite network device, a low earth orbit (LEO) satellite and a geosynchronous earth orbit (GEO) satellite, or an aircraft network device.

[0166] Moreover, in connection of split radio access network (RAN), the network device may refer to a centralised unit (CU) of a base station and / or a distributed unit (DU) of a base station. An interface between CU and DU may be referred to as an F1 interface in NR. In the split RAN architecture, node operations may be carried out, at least partly, in the central / centralized unit, CU, (e.g. server, host or node) operationally coupled to the DU, (e.g. a radio head / node). One CU may control one or more DUs, acting at least as trans-mit / receive (Tx / Rx) nodes. In some embodiments, the DUs may comprise e.g. a radio link control (RLC), medium access control (MAC) layer and a physical (PHY) layer, whereas the CU may comprise the layers above RLC layer, such as a packet data convergence protocol (PDCP) layer, a radio resource control (RRC) and an internet protocol (IP) layers. Other functional splits are possible too. In practice, any processing task may be performed in either the CU or the DU and the boundary where the responsibility is shifted between the CU and the DU may depend on the applied implementation.

[0167] The term “terminal device” refers to any end device that may be capable of wireless communication. By way of example, a terminal device may be referred to as a communication device, user equipment (UE), a Subscriber Station (SS), or a Mobile Station (MS). The terminal device may include a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones a tablet, a wearableterminal device, a personal digital assistant (PDA), portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehicle-mounted wireless terminal devices, USB dongles, an Internet of Things (loT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and / or other wireless devices operating in an industrial and / or an automated processing chain contexts), a consumer electronics device, a device operating on commercial and / or industrial wireless networks, and the like.

[0168] A term “resource”, as used herein, may refer to radio resources in time domain, in frequency domain, in space domain, and / or in code domain. Some examples of resources include e.g. a physical resource block (PRB), a radio frame, a subframe, a time slot, a subband, a frequency region, a sub-carrier, a beam, etc. The term “transmission” and / or “reception” may refer to wirelessly transmitting and / or receiving via a wireless propagation channel on radio resources.

[0169] Fig. 1 illustrates an example of a communication network to which examples disclosed herein may be applied. The communication network or a cellular communication network may comprise a network node 110 providing one or more cells, such as cell 100, and a network node 112 providing one or more other cells, such as cell 102. Each cell may be, e.g., a macro cell, a micro cell, femto, or a pico cell, for example. The cell may define a coverage area or a service area of the corresponding access node.

[0170] The network node 110 may provide a user equipment (UE) 120 (one or more UEs) with wireless access to the communication network. The wireless access may comprise downlink (DL) communication from the network node to the UE 120 and uplink (UL) communication from the UE 120 to the network node. Examples of uplink channels comprise physical uplink control channel (PUCCH) for transmitting control information and physical uplink shared channel (PUSCH) for transmitting data towards the network. Examples of downlink channels comprise physical downlink control channel (PDCCH) for transmitting control information and physical downlink shared channel (PDSCH) for transmitting data towards the user equipment.

[0171] There may be a plurality of UEs 120, 122 in the system. Each of them may be served by the same or by different network nodes 110, 112. UE may be configured with dual connectivity (DC), wherein the UE, e.g. UE 120, may be connected to multiple network nodes 110, 112. The UEs 120, 122 may communicate with each other, in case device-to-device (D2D) communication interface is established between them via a so-called sidelink (SL). Such D2D communications may be referred to as machine-to-machine, peer-to-peer (P2P) communications, or vehicle-to-vehicle (V2V), for example.

[0172] In the case of multiple network nodes in the communication network, the network nodes may be connected to each other via an interface. LTE specifications call such an interface as X2 interface. An interface between an LTE node and a 5G node, or between two 5G nodes may be called Xn interface.

[0173] The network nodes 110 and 112 may be further connected via another interface to a core network 116 of the communication network. The LTE specifications specify the core network as an evolvedpacket core (EPC), and the core network may comprise e.g. a mobility management entity (MME) and a gateway node. The MME may handle mobility of terminal devices in a tracking area encompassing a plurality of cells and handle signalling connections between the terminal devices and the core network. The gateway node may handle data routing in the core network and to / from the terminal devices. The 5G specifications specify the core network as a 5G core (5GC). The 5G core may comprise e.g. an access and mobility managementfunction (AMF) and a user plane function / gateway (UPF) and other functions. The AMF may handle termination of non-access stratum (NAS) signalling, NAS ciphering & integrity protection, registration management, connection management, mobility management, access authentication and authorization, security context management. The UPF node may support packet routing and forwarding, packet inspection and quality of service (QoS) handling, for example.

[0174] In the UL direction, two transmissions schemes are possible in NR; codebook-based transmission and non-codebook-based transmission.

[0175] In codebook-based UL transmission, the network node has control on the choice of precoding done by the UE. Codebook-based operation can be useful where channel reciprocity is not sustained. A UE can transmit several Sounding Reference Signal (SRS) resources to the network node (e.g., a gNB). The network node can estimate the UL channel based on these resources. Based on these measurements, the network node can compute the best SRS, which can be identified by the SRI (SRS Resource Indication) and also the rank and precoder (Transmitted Matrix Precoding Indicator (TPMI)) which should be used by the UE for the transmission. This precoder is selected from a predefined UL codebook over the SRS ports in the selected SRS resource by the SRI. At the end of these processing stages, the gNB has: the SRI, TPMI and rank, which can be used by the UE for the UL transmission. The gNB indicates to the UE the SRI, TPMI and the UE then has the necessary information for performing codebook-based UL transmission.

[0176] Under the codebook-based operation, three forms of transmission are possible in UL:

[0177] • Full coherence: where all the ports can be transmitted coherently.

[0178] • Partial coherence: where port pairs can be transmitted coherently.

[0179] • Non-coherent: where no port pairs can be transmitted coherently.

[0180] Non-codebook-based UL transmission fits more channel reciprocity. The UE computes the precoder based on the estimation of the CSI-RS. One or multiple SRSs are precoded and transmitted in UL while the network node estimates the best received SRS and its corresponding SRI, which is then indicated to the UE.

[0181] Three directions are considered for boosting UL performance:

[0182] • Beamforming at UE or at gNB (receiver)• Repetition and retransmission-based schemes.

[0183] • Channel coding.

[0184] Some examples described relate to a beamforming framework for improving UL performance. Under codebook-based transmission, the network node has a tight control on the choice of precoding done by the UE. The UE transmits several SRS resources to the gNB, which estimates the UL channel based on these resources. Based on these measurements, the gNB is able to compute the best SRS, which is identified by the SRI (SRS Resource indication) and also the rank and precoder (TPMI) which should be used by the UE for the transmission. This precoder is selected from a predefined UL codebook over the SRS ports in the selected SRS resource by the SRI. The Different TPMI table are specified for different coherency assumption. An example of a TPMI table used for single layer transmission using two antenna ports, is summarized in 3GPP TS 38.211 Section 6.3.1.5 “Precoding”, which states that the block of vectors

[0185]

[0186] - 1 shall be precoded according to:

[0187] <>

[0188]

[0189] Where

[0190]

[0191] The rest of theantenna ports {Po, ->Pp-i] can be determined according to the procedure in 3GPP TS 38.214.

[0192] For non-codebook transmission, the precoding matrix W equals the identity matrix. For codebook-based transmission, the precoding matrix l / l / is given by W= 1 for single-layer transmission o a single antenna port, otherwise by Tables 6.3.1.5-1 to 6.3.1.5-7 of 3GPP TS 38.211 with the TPMI index obtained form Downlink Control Information (DCI) scheduling the uplink transmission or the higher layer parameters according to the procedure in 3GPP TS 38.214.

[0193] SRS transmitted by a UE to a network node can be used by the network node to sound the UL channel and compute beamforming weights to be applied to UL received samples. Using the above, TPMI as a precoding can be applied at the UE prior to sending the SRS. This can be considered as digital precoding at the UE side.

[0194] For SRS based beamforming, the SRS consume resources from data to sound the channel. This increases the UL overhead. In particular, for aperiodic UL SRS, SRS resources are used in every slot carrying Uplink Shared Channel (UL-SCH) data. Further, there are issues with SRS aging, in particular for periodic SRS, where UL beamforming (e.g., beamforming weights) derived from SRS samples that received at slot N while the beamforming is applied at time N+X. The aging depends on SRS periodicity. In additionto aging, UL beamforming weights will not reflect the noise and interference level measured at slot N+X where the beamforming is applied.

[0195] UL Demodulation Reference Signal (DMRS) based beamforming (sometimes referred to as “UL boost feature” can be used to avoid the issues of SRS beamforming discussed in the above paragraph. UL DMRS based beamforming allows:

[0196] • Using UL DMRS to derive UL beamforming weights - there is no need to UL SRS, resulting in less overhead and higher data resources utilizations;

[0197] • No aging as UL DMRS is scheduled in the same slot as UL-SCH data;

[0198] • Accurate and up-to-date noise plus interference captured in UL beamforming weight computation as UL DMRS in the same slot as UL-SCH.

[0199] UL DMRS based beamforming is currently assumed transparent to the UE, however this introduces some restrictions on its applicability and can require more NW processing, as discussed below. To extend the range of UL DMRS based beamforming, some examples described herein use a framework for UL DMRS based beamforming.

[0200] UL DMRS based beamforming feature is based on UL DMRS symbols. These can be front loaded or additional DMRS. Front loaded DMRS symbols may be used for channel estimation, and additional DMRS can be used to enhance estimation. For examples, additional DMRS symbols can be used to with front loaded DMRS to estimate Doppler measurements. The UL receiver in each PUSCH slot can compute beamforming weights based on DMRS In-phase and Quadrature (l / Q) samples and applies the weighting factors to UL OFDM symbols for UL-SCH data.

[0201] The transmission precoding matrix applied for data is the same that is applied to DMRS symbols, as defined in 3GPP TS 38.211 section 6.4.1.1.3 “Precoding and mapping to physical resources”. As the DMRS is therefore already pre-coded along with the data, this precoding must be removed from the DMRS channel before using these DRMS channel estimates, (H^RS* W) for UL beamforming. Without removing DMRS precoding W, the UL DMRS-based beamforming weights are pre-coded. As the data is precoded with precoding matrix W, applying DMRS-based beamforming weights to data leads to the data being pre-coded twice. Reverting the pre-coding applied to DMRS for the purpose of UL beamforming is not always possible, as the matrix W is not always invertible.

[0202] To avoid the issue of not being able to remove the matrix W, UL DMRS-based beamforming can be applied to only single antenna port and single layer for UL and Frequency Range 1 (FR1). As the number of rows of the precoding matrix is the same as the number of transmission layers and as the number of columns of the precoding matrix is the same as the number of layers in this scenario, the precoding matrix only has one row and one column and will therefore be invertible. However, this approach does not work forUEs with two or more antenna ports for UL transmissions, or where a UE has a rank (i.e., a number of transmission layers) greater than 1.

[0203] Some examples described herein provide a UL DRMS framework that can be used where the number of antenna ports equal or greater than 1 and / or number of layers, i.e. rank, >=1

[0204] For a UE with M transmission antennas and N transmission layers, when M = N an invertible M x N precoding matrix l / l / may be used for UL DMRS beamforming. An invertible matrix may be considered to be a matrix that has an inverse matrix. For example, if there are 2 antenna ports and 2, a 2 x 2 matrix may be used as a precoding matrix W, or the following matrix may be used:

[0205] ra a i

[0206] la —al

[0207] where a is non-zero.

[0208] The NW can remove the invertible precoding matrix W applied to the UL DMRS by applying the inverse of matrix l / l / .

[0209] For a UE with M transmission antennas and N transmission layers, when M does not equal N, a pseudo-invertible precoding matrix l / l / may be used for UL DMRS beamforming. A pseudo-invertible matrix has a pseudo-inverse matrix (often referred to as a Moore-Penrose matrix). A pseudo-invertible matrix l / l / satisfies the following criteria:

[0210] Criterion 1: W * WH* W = W or W * WHis invertible

[0211] Criterion 2: W has a right inverse matrix V , i.e., W * V = Identity

[0212] As such, when M = N and the matrix is invertible, the matrix l / l / that is used to precode the UL DMRS has an inverse. When M does not equal N, the matrix l / l / that is used to precode the UL DMRS is pseudo-invertible and has a right inverse.

[0213] When M does not equal N and the precoding matrix is pseudo-invertible, the network (e.g., the network node, such as base station / gNB) can use the following processing on the DMRS channel estimates (CE) to remove precoding matrix l / l / :

[0214]

[0215] In some situations where there are M transmission antennas and N transmission layers, an M x N matrix will not be invertible or pseudo-invertible, due to the dimensions of the matrix. For example, the 4 x 1 matrices in table 6.5.1.5-3 of 3GPP TS 38.211, shown in Table 1 below, are not invertible or pseudo-invertible. According to example described herein, the dimensions of the matrix 1 / 1 / are increased so that the matrix is invertible or pseudo-invertible. According to some examples, the number of columns is increased to be more than the number of transmission layers while being less than or equal to the number of rows of the matrix 1 / 1 / As such, an invertible matrix or pseudo-invertible matrix can be used for precoding by the UE and can be removed at the network side.

[0216] As a further example, the following matrices are not satisfying criteria 1 and 2:

[0217]

[0218] I * WHis not invertible, this is because the rank of these 2x1 matrices equal to 1.

[0219] To achieve a higher rank, the dimension of the matrices W should be modified. For example, NW may configure a 2x2 W matrices for the case of single layer and two antenna ports. For example, W =

[0220] in this case the DMRS samples are repeated and then multiplexed:

[0221]

[0222]

[0223] this vector is transmitted over two ports.

[0224] The same principle can be applied to a case with a single transmission layer and four antenna ports. The 4 x 1 matrices shown in Table 1 below are not invertible. New matrices can built with higher dimensions 4 x 2, 4 x 3 or 4 x 4 to achieve criteria 1 and 2 (for a pseudo-invertible) or so that the matrix is invertible. In this examples, the 4 x 2 matrix and the 4 x 3 matrix may be pseudo-invertible, and the 4 x 4 matrix may be invertible.

[0225]

[0226] Table 1 : Precoding matrix IV for single-layer transmission using four antenna ports with transform precoding disabled (as detailed in Table 6.3.1.5-3 of 3GPP TS 38.211).Fig. 2 shows an example method. UE 200 can be configured with at least two sets of TPMIs at 201. Each set may comprise at least one TPMI. These may be configured by base station 202 (e.g., a gNB). Or, this may be preconfigured at the UE or indicated from another network node.

[0227] At 203, UE 200 receives an indication of which TPMI set to apply. The indication received at 203 may be indicated through a Medium Access Control (MAC) Control Element (CE). In other examples, the indication may be received in Downlink Control Information (DCI) or a Radio Resource Configuration (RRC) message.

[0228] At 205, UE 200 determines a TPMI from a set of TPMIs (which may be one of the at least sets of TPMIs mentioned above). UE 200 can then use the determined TPMI for PUSCH / UL transmission. At least one of the configured TPMI sets may comprise one or more TPMIs that correspond with an invertible matrix or a pseudo-invertible matrix.

[0229] The indication received at 203 of which TPMI set is applicable may be indicated through UL DCI scheduling or activating the PUSCH / UL transmission on which to apply the indicated TPMI.

[0230] In some examples, a set of TPMIs can be configured at UE 200 using a semi-static configuration by the network (e.g., by base station 202). In some examples, the TPMI set to be activated from the configured set may be dynamically activated using signalling at 203. Or, the TPMI set to be activated from the configured set may be determined at UE 200 based on a rule or condition being satisfied at UE 200.

[0231] In some examples, for configured PUSCH / UL transmissions, such as for configured grant (CG) type 1 , the corresponding CG configuration may include or be associated with at least two TPMIs in a set of TPMIs.

[0232] In some examples, base station 202 may indicate that a first set of TPMIs is applicable for UE 200. The first set of TPMIs may be considered to be “legacy” TPMIs that where on or more of the precoding matrices W corresponding to the respective TPMIs are not invertible or pseudo-invertible. The first set of TPMIs may have M N matrices that are not invertible or pseudo-invertible (due to the dimensions of the matrix), where there are M transmission antennas and N transmission layers, an M x N matrix will not be invertible or pseudo-invertible, due to the dimensions of the matrix. Base station 202 may indicate to use a second set of TPMIs, where the number of columns in at least one of the precoding matrices corresponding to the TPMIs is greater than the number of transmission layers, such that the precoding matrix is pseudo-invertible or invertible.

[0233] In some examples, UE 200 may be configured or specified with (e.g., from base station 202 with a rule or condition in which UE 200 should not apply a precoding matrix, or apply an identity matrix as a precoding matrix l / l / .

[0234] From the perspective of UE 200, TPMI sets may be provided by a semi-static configuration, e.g., by RRC configuration or reconfiguration. The TPMI sets may be pre-configured (specified) for UE 200. UE 200 may use this semi-static configuration to determine which TPMI set to apply, and in some examplesmay use the semi-static configuration to determine which TPMI to use.

[0235] The determination of a TPMI set to use, or the determination of a subset of a TPMI set when combined with at least one other determination factor, may be based on at least one of the following determination factors (which may be considered to be “rules”):

[0236] • Frequency resource allocation (number of resources, range, etc.). For example, if the PUSCH / UL resource corresponding to the PUSCH / UL transmission has a frequency domain allocation, in terms of number of resource blocks (RBs) or resource elements (REs) or RB groups, which is lower than or equal to a threshold, UE 200 may determine or fetch TPMI based on a first TPMI set / subset. Otherwise, if the frequency domain allocation is above the threshold, the UE may determine or fetch TPMI based on a second TPMI set / subset.

[0237] • Indicated Modulation Coding Scheme (MCS). For example, if indicated MCS is greater than or equal a threshold, or is within a first MCS range, the UE may determine or fetch TPMI based on a first TPMI set / subset. Otherwise, if the indicated MCS is lower than (or equal) to a threshold, or is within a second MCS range, the UE may determine or fetch TPMI based on a second TPMI set / subset.

[0238] • Applicable DMRS pattern. For example, if a first DMRS pattern is indicated or is applicable, the UE may determine or fetch TPMI based on a first TPMI set / subset. If a second DMRS pattern is indicated or is applicable, the UE may determine or fetch TPMI based on a second TPMI set / subset.

[0239] • Indicated or applicable waveform (e.g., Discrete Fourier Transform-Spread-Orthogonal Frequency Division Multiplexing (DFTS-OFDM), Cyclic Prefix (CP-OFDM), Pi / 2 Binary Phase-shift keying (BPSK) etc.). For example, if a first DMRS pattern is indicated or is applicable, the UE may determine or fetch TPMI based on a first TPMI set / subset. If a second DMRS pattern is indicated or is applicable, the UE may determine or fetch TPMI based on a second TPMI set / subset.

[0240] • A UE mobility status (note that in some examples, the mobility status may be determined by base station 202 based on UL reference signals (e.g., SRS or UL DMRS) and nay determine a set or subset of TPMIs to apply based on this determination). The UE mobility status may be determined based on a parameter related to speed, for example a doppler related parameter (such as doppler spread), time / frequency domain channel properties (such as delay offset, phase offset, frequency offset, etc.)

[0241] • The number of transmission layers.

[0242] • Information in DCI / PDCCH scheduling PUSCH, or even information provided via MAC CE.

[0243] Using the one or more rules, UE 200 can determine a TPMI to apply a precoding matrix l / l / for UL transmissions. This results in a weighted UL-DMRS that can be sent at 207.

[0244] At 209, if the precoding matrix W is invertible or pseudo-invertible, the precoding matrix can be removed from the UL-DMRS for channel estimation.

[0245] In a further example, UE 200 may be configured or specified with at least one set or subset of matrices or vectors. The UE may then further be indicated, through MAC CE or DCI, information indicativeof whether to apply a specific matrix or vector of the set or subset to the UL transmission. This further indication may be through a DCI indication or through RRC, for example. Applying a matrix / vector to an UL transmission may correspond to multiplying the TPMI of the UL transmission with the at least one matrix / vector. Specifically, the UE may be indicated, through MAC CE or DCI (or even RRC), indication indicative of whether the apply the at least one matrix or vector on top of the TPMI.

[0246] Alternatively, or additionally, the determination of whether to apply at least one matrix / vector, to the TPMI or on top of the TPMI, may be based on at least one (specified or configured) condition or rule. The at least one condition or rule may comprise one or more of the examples given above.

[0247] In some embodiments, the UE determines the TPMI and / or SRI to apply for an UL transmission (such as PUSCH transmission), through or based on indicated or applicable UL or joint TCI (transmission configuration indicator) state or spatial relation. In this case, there may be association of at least one TCI state (or spatial relation) to at least one TPMI and / or SRI, where such association may be configured / indi-cated via RRC or MAC CE.

[0248] In some embodiments, there may be at least two codewords or transport blocks carried in a same UL / PUSCH transmission. In this case, TPMI and / or SRI may be different (or same) for different / re-spective transmission layer groups or antenna port groups (where a group may contain one or more layers or ports). The determination of at least one TPMI and / or SRI to apply may be through (UL) TCI state or spatial relation info (such as indicated or applicable TCI state(s) or spatial relation). Alternatively, at least TPMI(s) may be determined based on any other way / approach proposed / covered in this invention. In addition, the association of at least one TCI state (or spatial relation info) to at least one TPMI and / or SRI may be configured via RRC, and / or may be updated / indicated via MAC CE or RRC. Hence, for an applicable / indicated TCI state(s) for an UL / PUSCH transmission, the UE applies the corresponding TPMI(s) and / or SRI(s).

[0249] In related embodiments, the TCI state may additionally (i.e., in addition to TPMI and / or SRI) or alternatively provide information about the mapping of transport blocks (or codewords) to transmission layers. For example, a TCI state(s) may be associated or may comprise, e.g., using a configuration / indication via RRC (or MAC CE), information about which and / or how many transport blocks (or codewords) to map to certain number of transmission layers. The association information for at least one TCI state to transport block(s) mapping information (i.e., mapping of transport block(s) to transmission layers) may be updated via (dedicated) MAC CE or via RRC (or even via DCI). Hence, for an applicable / indicated TCI state(s) for an UL / PUSCH transmission, the UE applies the corresponding mapping information. The Information about the mapping of transport block(s) to transmission layers may comprise for example: one transport block should be mapped to x layers (where x may be e.g., 1 , 2 or 4 layers), and the second / next transport block, if any, is mapped to remaining transmission layers if any; one transport block is mapped to each layer; etc.

[0250] Fig. 3 shows an example method. The method may be performed by a UE, such as UE 200, for example.At 300, the method comprises applying a precoding matrix to an Uplink Demodulation Reference Signal, UL-DMRS to provide a weighted UL-DMRS, wherein the precoding matrix is invertible or pseudo-invertible, the precoding matrix has a number of rows that is equal to the number of antenna ports, and the precoding matrix has a number of columns that is greater than the number of transmission layers and less than or equal to the number of rows of the precoding matrix

[0251] At 301, the method comprises sending the weighted UL-DMRS to a network node. Fig. 4 shows an example method. The method may be performed by a network node, such as base station 202, for example.

[0252] At 400, the method comprises receiving, from a user equipment, a weighted Uplink Demodulation Reference Signal, UL-DMRS, wherein the weighted UL-DMRS is determined by the user equipment by applying a precoding matrix to an UL-DMRS, wherein the precoding matrix is invertible or pseudo-invertible, and wherein the user equipment is configured to transmit signals using a first number of antenna ports and a second number of transmission layers wherein the precoding matrix has a number of rows that is equal to the number of antenna ports, and the precoding matrix has a number of columns that is greater than the number of transmissions layers and less than or equal to the number of rows of the precoding matrix.

[0253] Fig. 5 shows an example method. The method may be performed by a UE, such as UE 200 for example.

[0254] At 500, the method comprises determining, from at least two sets of transmission precoding matrix indicators, TPMIs, at least one TPMI to apply to uplink transmissions, wherein the determining is based on at least one of: at least one rule; at least one indication from a network node

[0255] At 501, the method comprises applying at least one precoding matrix corresponding to the determined at least one TPMI to at least one uplink transmission.

[0256] At 502, the method comprises sending the at least one uplink transmission to the network node using a number of antenna ports and a number of transmission layers. Each precoding matrix corresponding to a TPMI in a first set of the at least two sets of TPMIs may have a number of rows that is equal to the number of antenna ports and a number of columns that is equal to the number of transmissions layers. Each precoding matrix corresponding to a TPMI in a second set of the at least two sets of TPMIs is invertible or pseudo-invertible may have a number of rows that is equal to the number of antenna ports and a number of columns that is greater than the number of transmission layers and less than or equal to the number of rows Fig. 6 shows an example method. The method may be performed by a network node, such as base station 202, for example,

[0257] At 600, the method comprises receiving, from a user equipment, at least one weighted uplink transmission is generated by the User Equipment applying at least one precoding matrix to the at least one uplink transmission, and wherein the at least one precoding matrix corresponds to at least one transmission precoding matrix indicator, TPMI, selected from at least two sets of TPMIs by the user equipment.At 601, the method comprises determining an estimate of the at least one weighted uplink transmission based on the received uplink transmission and an inverse of the precoding matrix or a pseudoinverse of the precoding matrix; wherein the at least one uplink transmission is sent by the user equipment using a number of antenna ports and a number of transmission layers; wherein each precoding matrix corresponding to a TPMI in a first set of the at least two sets of TPMIs has a number of rows that is equal to the number of antenna ports and a number of columns that is equal to the number of transmissions layers; and wherein each precoding matrix corresponding to a TPMI in a second set of the at least two sets of TPMIs is invertible or pseudo-invertible and has a number of rows that is equal to the number of antenna ports and a number of columns that is greater than the number of transmission layers and less than or equal to the number of rows.

[0258] Fig. 7 shows, by way of example, a block diagram of an apparatus 10. The apparatus 10 comprises, for example, at least one processor 12 and at least one memory 14 storing instructions 15 that, when executed by the at least one processor, cause the apparatus 10 at least to perform the method or methods as disclosed herein, and any of the embodiments thereof. In an example, the at least one memory and the instructions (e.g. a computer program code, software), are configured, with the at least one processor, to cause the apparatus 10 to perform the method or methods as disclosed herein, and any of the embodiments thereof.

[0259] A processor 12 may comprise circuitry, or be constituted as circuitry or circuitries, the circuitry or circuitries being configured to perform phases of methods in accordance with example embodiments described herein. As used in this application, 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, 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 user equipment, to perform various functions) and (c) hardware circuit(s) and or processors), 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 application, including in any claims. As a further example, as used in this application, 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.

[0260] The memory 14 may be implemented using any suitable data storage technology. The memory may comprise a database for storing data. The memory 14 may be at least in part external to apparatus 10but accessible to apparatus 10.

[0261] The instructions 15 may be comprised in a computer readable medium or a non-transitory computer readable medium. Aterm non-transitory, as used herein, is a limitation of the medium itself (i.e. tangible, not a signal) as opposed to a limitation on data storage persistency (e.g. random access memory, RAM, vs. read only memory, ROM).

[0262] For example, the apparatus 10 is a terminal device, such as UE 200 of Fig. 2. As another example, the apparatus is comprised in such a terminal device, e.g. as a chipset configured to control the terminal device. The apparatus 10 may be caused or configured to perform at least the method of Fig. 3 or 5 and / or any one or more of the embodiments described.

[0263] As another example, the apparatus 10 is a network node, e.g. 202 of Fig. 2. In another embodiment, the apparatus is comprised in such a network node, e.g. as a chipset configured to control the network node.

[0264] The apparatus may comprise one or more entities of any of protocol layers, such as a MAC entity, an RRC entity, an RLC entity, a PDCP entity or a PHY entity. In some embodiments, the entity is configured to perform at least the method of Fig. 3 to 6, and / or any one or more of the embodiments described.

[0265] The apparatus 10 comprises a radio interface 16. The radio interface 16 may provide the apparatus 10 with communication capabilities. The radio interface 16 may comprise a receiver configured to receive information in accordance with at least one cellular or non-cell ular standard. The radio interface 16 may comprise a transmitter configured to transmit information in accordance with at least one cellular or non-cellular standard. The receiver may comprise more than one receiver. The transmitter may comprise more than one transmitter. The radio interface 16 may comprise a transceiver configured to receive and transmit information in accordance with at least one cellular or non-cellular standard. The transceiver may comprise more than one transceiver.

[0266] The apparatus 10 may comprise a user interface 18 comprising, for example, at least one of a keypad, a microphone, a touch display, a display, a speaker, etc. The user interface 18 may be used to control the apparatus by the user. The user interface 18 may be external to the apparatus 10. For example, the apparatus 10 may be connected to another device, such as a computer, either via wireless or wired connection, and the apparatus 10 is controlled by the user via the computer.

[0267] In an embodiment, at least some of the processes described herein may be carried out by an apparatus comprising means for carrying out at least some of the described processes. Means for performing method steps as disclosed herein may include software and / or hardware components of the apparatus 10. For example, the at least one processor 12, the memory 14, and the computer program code form means for carrying out the method or methods as disclosed herein, and any of the embodiments thereof. As used herein the term “means” is to be construed in singular form, i.e. referring to a single element, or in plural form, i.e.referring to a combination of single elements. Therefore, terminology “means for [performing A, B, C]”, is to be interpreted to cover an apparatus in which there is only one means for performing A, B and C, or where there are separate means for performing A, B and C, or partially or fully overlapping means for performing A, B, C. Further, terminology “means for performing A, means for performing B, means for performing C” is to be interpreted to cover an apparatus in which there is only one means for performing A, B and C, or where there are separate means for performing A, B and C, or partially or fully overlapping means for performing A, B, C.

[0268] Even though the invention has been described above with reference to an example according to the accompanying drawings, it is clear that the invention is not restricted thereto but can be modified in several ways within the scope of the appended claims. Therefore, all words and expressions should be interpreted broadly and they are intended to illustrate, not to restrict, the embodiment. It will be obvious to a person skilled in the art that, as technology advances, the inventive concept can be implemented in various ways. Further, it is clear to a person skilled in the art that the described embodiments may, but are not required to, be combined with other embodiments in various ways.

Claims

1. CLAIMS1. A user equipment configured to transmit signals using a number of antenna ports and a number of transmission layers, the user equipment comprising at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform:applying a precoding matrix to an Uplink Demodulation Reference Signal, UL-DMRS to provide a weighted UL-DMRS, wherein the precoding matrix is invertible or pseudo-invertible, the precoding matrix has a number of rows that is equal to the number of antenna ports, and the precoding matrix has a number of columns that is greater than the number of transmission layers and less than or equal to the number of rows of the precoding matrix;sending the weighted UL-DMRS to a network node.

2. The user equipment according to claim 1 , wherein the number of rows of the precoding matrix is equal to the number of columns of the precoding matrix and the precoding matrix is invertible.

3. The user equipment according to claim 1, wherein the number of columns of the precoding matrix is less than the number of rows and the precoding matrix is pseudo-invertible.

4. The user equipment according to claim 3, wherein the product of the precoding matrix with a Hermitian of the precoding matrix is invertible, and wherein the precoding matrix has a right inverse matrix.

5. The user equipment according to any preceding claim, wherein the instructions, when executed by the at least one processor, cause the apparatus at least to perform:receiving, from the network node, a set of precoding matrices including the precoding matrix.

6. The user equipment according to any preceding claim, wherein the instructions, when executed by the at least one processor, cause the apparatus at least to perform:selecting the precoding matrix based on at least one of: at least one rule or at least one indication received from the network node.

7. The user equipment according to any preceding claim, wherein the UL DMRS signals are repeated before the precoding matrix is applied to the UL DMRS, wherein the result is multiplexed before to provide the weighted UL-DMRS.

8. A method comprising:applying a precoding matrix to an Uplink Demodulation Reference Signal, UL-DMRS to provide a weighted UL-DMRS, wherein the precoding matrix is invertible or pseudo-invertible;sending the weighted UL-DMRS from a user equipment to a network node, wherein the user equipment is configured to transmit signals using a number of antenna ports and a number of transmission layers, wherein the precoding matrix has a number of rows that is equal to the number of antenna ports, and the precoding matrix has a number of columns that is greater than the number of transmissions layers and less than or equal to the number of rows of the precoding matrix.

9. A computer program comprising instructions stored thereon for performing at least the following:applying a precoding matrix to an Uplink Demodulation Reference Signal, UL-DMRS to provide a weighted UL-DMRS, wherein the precoding matrix is invertible or pseudo-invertible;sending the weighted UL-DMRS from a user equipment to a network node, wherein the user equipment is configured to transmit signals using a number of antenna ports and a number of transmission layers, wherein the precoding matrix has a number of rows that is equal to the number of antenna ports, and the precoding matrix has a number of columns that is greater than the number of transmissions layers and less than or equal to the number of rows of the precoding matrix.

10. An apparatus comprising at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to perform:receiving, from a user equipment, a weighted Uplink Demodulation Reference Signal, UL-DMRS, wherein the weighted UL-DMRS is determined by the user equipment by applying a precoding matrix to an UL-DMRS, wherein the precoding matrix is invertible or pseudo-invertible, and wherein the user equipment is configured to transmit signals using a first number of antenna ports and a second number of transmission layers wherein the precoding matrix has a number of rows that is equal to the number of antenna ports, and the precoding matrix has a number of columns that is greater than the number of transmissions layers and less than or equal to the number of rows of the precoding matrix.

11. The user equipment according to claim 10, wherein the number of rows of the precoding matrix is equal to the number of columns of the precoding matrix and the precoding matrix is invertible.

12. The user equipment according to claim 10, wherein the number of columns of the precoding matrix is less than the number of rows and the precoding matrix is pseudo-invertible.

13. The apparatus according to claim 12, wherein the product of the precoding matrix with a Hermitian of the precoding matrix is invertible, and wherein the precoding matrix has a right inverse matrix.

14. The apparatus according to any of claims 10 to 13, wherein the instructions, when executed by the at least one processor, cause the apparatus at least to perform:sending information indicative of at least one set of transmission precoding matrix indicators, TPMIs, wherein the precoding matrix corresponds to a TPMI in at least one of the at least two sets.

15. The apparatus according to any of claims 10 to 14, wherein the precoding matrix comprises an invertible matrix, wherein the instructions, when executed by the at least one processor, cause the apparatus at least to perform:determining a channel estimate based on the weighted UL-DMRS.

16. The apparatus according to any of claims 10 to 15, wherein the precoding matrix comprises a pseudo-invertible matrix, wherein the instructions, when executed by the at least one processor, cause the apparatus at least to perform:determining a channel estimate based on the weighted UL-DMRS.

17. A method comprising:receiving, from a user equipment, a weighted Uplink Demodulation Reference Signal, UL-DMRS, wherein the weighted UL-DMRS is determined by the user equipment by applying a precoding matrix to an UL-DMRS, wherein the precoding matrix is invertible or pseudo-invertible, and wherein the user equipment is configured to transmit signals using a first number of antenna ports and a second number of transmission layers wherein the precoding matrix has a number of rows that is equal to the number of antenna ports, and the precoding matrix has a number of columns that is greater than the number of transmissions layers and less than or equal to the number of rows of the precoding matrix.

18. A computer program comprising instructions stored thereon for performing at least the following:receiving, from a user equipment, a weighted Uplink Demodulation Reference Signal, UL- DMRS, wherein the weighted UL-DMRS is determined by the user equipment by applying a precoding matrix to an UL-DMRS, wherein the precoding matrix is invertible or pseudo-invertible, and wherein the user equipment is configured to transmit signals using a first number of antenna ports and a second number of transmission layers wherein the precoding matrix has a number of rows that is equal to the number of antenna ports, and the precoding matrix has a number of columns that is greater than the number of transmissions layers and less than or equal to the number of rows of the precoding matrix.

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