Uplink precoding

Abstract

A method, apparatus, and computer program are described comprising: receiving, at a terminal device and from a network node, preconditioning information indicative of a preconditioning matrix; receiving, at the terminal device and from the network node, sounding reference signal, SRS, configuration information; transmitting, by the terminal device and to the network node, based at least in part on the SRS configuration information an SRS preconditioned using the preconditioning matrix.

Description

[0001] UPLINK PRECODING

[0002] Field

[0003] Example embodiments may relate to user equipment, network nodes, and methods for transmitting and / or receiving uplink reference signals.

[0004] Background

[0005] In the process of performing uplink transmissions, a terminal device may perform a precoding step. During precoding, the terminal device determines signals to send to antenna ports from at least one layer of input symbols. The terminal device may perform this precoding using a matrix.

[0006] As the size of the matrix or matrices used in precoding increases, the computational resources required to determine suitable matrices (e.g., from channel data) may increase. It is therefore desirable to provide methods by which suitable matrices for use in precoding can be indicated to terminal devices, so that a network with which a terminal device communicates may bear some of the computational burden in determining matrices for use in precoding. Further, a network may determine a precoding matrix based on uplink reference signals.

[0007] There is therefore an interest in providing improved methods of indicating matrices for use in precoding uplink transmissions, and improved methods for precoding uplink transmissions.

[0008] Summary

[0009] The scope of protection sought for various embodiments of the invention is set out by the independent claims. The embodiments and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments of the invention.

[0010] A first aspect provides a terminal device comprising: means for means for receiving, from a network node, preconditioning information indicative of a preconditioning matrix; means for receiving, from the network node, first scheduling information scheduling a first uplink transmission by the terminal device to the network node; means for receiving, from the network node, first precoding information indicative of a first transmit precoding matrix for use in precoding the first uplink transmission; means for precoding the first uplink transmission based on the first transmit precoding matrix and the preconditioning matrix; means for receiving, from the network node, second scheduling information scheduling a second uplink transmission by the terminal device to the network node; means for receiving, from the network node, second precoding information indicative of a second transmit precoding matrix for use in precoding the second uplink transmission; and means for precoding the second uplink transmission based on the second transmit precoding matrix and the preconditioning matrix.

[0011] In some example embodiments, the means for precoding the first uplink transmission is configured to determine a first matrix product of the first transmit precoding matrix and the preconditioning matrix, and precode the first uplink transmission based on the first matrix product; and the means for precoding the second uplink transmission is configured to determine a second matrix product of the second transmit precoding matrix and the preconditioning matrix, and precode the second uplink transmission based on the second matrix product.

[0012] In some example embodiments, the preconditioning matrix is based on long-term channel characteristics of a wireless communication channel between the terminal device and the network node; the first transmit precoding matrix is based on the preconditioning matrix and first short-term channel characteristics of the wireless communication channel between the terminal device and the network node; and the second transmit precoding matrix is based on the preconditioning matrix and second short-term channel characteristics of the wireless communication channel between the terminal device and the network node, wherein the second short-term channel characteristics are related to a later time period than the first short-term channel characteristics.

[0013] In some example embodiments, the first transmit precoding matrix is a NT x m matrix, the second transmit precoding matrix is a NT x n2 matrix, and the preconditioning matrix is a NT x NT matrix, wherein NT denotes a number of transmit antenna ports of the terminal device, and m and n2 denote a number of transmission layers of the first and second uplink transmissions respectively.

[0014] In some example embodiments, the means for receiving the first scheduling information is configured to receive the first scheduling information as part of downlink control information, DCI; and the means for receiving the second scheduling information is configured to receive the second scheduling information as part of DCI.

[0015] In some example embodiments, the means for receiving the first precoding information is configured to receive the first precoding information as part of the first scheduling information; and the means for receiving the second precoding information is configured to receive the second precoding information as part of the second scheduling information. In some example embodiments, the means for receiving the preconditioning information is configured to receive the preconditioning information as part of DCI, or as part a medium access control, MAC, control element, MAC-CE.

[0016] A second aspect provides a method comprising: receiving, at a terminal device and from a network node, preconditioning information indicative of a preconditioning matrix; receiving, at the terminal device and from the network node, first scheduling information scheduling a first uplink transmission by the terminal device to the network node; receiving, at the terminal device and from the network node, first transmit precoding information indicative of a first transmit precoding matrix for use in precoding the first uplink transmission; precoding, by the terminal device, the first uplink transmission based on the first transmit precoding matrix and the preconditioning matrix; receiving, at the terminal device and from the network node, second scheduling information scheduling a second uplink transmission by the terminal device to the network node; receiving, at the terminal device and from the network node, second transmit precoding information indicative of a second transmit precoding matrix for use in precoding the second uplink transmission; and precoding, by the terminal device, the second uplink transmission based on the second transmit precoding matrix and the preconditioning matrix.

[0017] In some example embodiments: precoding the first uplink transmission comprises determining a first matrix product of the first transmit precoding matrix and the preconditioning matrix, and precoding the first uplink transmission based on the first matrix product; and precoding the second uplink transmission comprises determining a second matrix product of the second transmit precoding matrix and the preconditioning matrix, and precoding the second uplink transmission based on the second matrix product.

[0018] In some example embodiments, the preconditioning matrix is based on long-term channel characteristics of a wireless communication channel between the terminal device and the network node; the first transmit precoding matrix is based on the preconditioning matrix and first short-term channel characteristics of the wireless communication channel between the terminal device and the network node; and the second transmit precoding matrix is based on the preconditioning matrix and second short-term channel characteristics of the wireless communication channel between the terminal device and the network node, wherein the second short-term channel characteristics are related to a later time period than the first short-term channel characteristics.

[0019] In some example embodiments, the first transmit precoding matrix is a NT x m matrix, the second transmit precoding matrix is a NT x n2 matrix, and the preconditioning matrix is a NT x NT matrix, wherein NT denotes a number of transmit antenna ports of the terminal device, and m and n2 denote a number of transmission layers of the first and second uplink transmissions respectively.

[0020] In some example embodiments, receiving the first scheduling information comprises receiving the first scheduling information as part of downlink control information, DCI; and receiving the second scheduling information comprises receiving the second scheduling information as part of DCI.

[0021] In some example embodiments, receiving the first precoding information comprises receiving the first precoding information as part of the first scheduling information; and receiving the second precoding information comprises receiving the second precoding information as part of the second scheduling information.

[0022] In some example embodiments, receiving the preconditioning information comprises receiving the preconditioning information as part of DCI, or as part a medium access control, MAC, control element, MAC-CE.

[0023] A third aspect provides a computer program comprising instructions which, when executed by at least one processor, cause an apparatus to perform: receiving, at the apparatus and from a network node, preconditioning information indicative of a preconditioning matrix; receiving, at the apparatus and from the network node, first scheduling information scheduling a first uplink transmission by the apparatus to the network node; receiving, at the apparatus and from the network node, first transmit precoding information indicative of a first transmit precoding matrix for use in precoding the first uplink transmission; precoding, by the apparatus, the first uplink transmission based on the first transmit precoding matrix and the preconditioning matrix; receiving, at the apparatus and from the network node, second scheduling information scheduling a second uplink transmission by the apparatus to the network node; receiving, at the apparatus and from the network node, second transmit precoding information indicative of a second transmit precoding matrix for use in precoding the second uplink transmission; and precoding, by the apparatus, the second uplink transmission based on the second transmit precoding matrix and the preconditioning matrix.

[0024] In some example embodiments, the third aspect may include any other feature mentioned with respect to the method of the second aspect.

[0025] A fourth aspect provides a non-transitory computer-readable medium having instructions stored thereon which, when executed by at least one processor, cause an apparatus to perform: receiving, at the apparatus and from a network node, preconditioning information indicative of a preconditioning matrix; receiving, at the apparatus and from the network node, first scheduling information scheduling a first uplink transmission by the apparatus to the network node; receiving, at the apparatus and from the network node, first transmit precoding information indicative of a first transmit precoding matrix for use in precoding the first uplink transmission; precoding, by the apparatus, the first uplink transmission based on the first transmit precoding matrix and the preconditioning matrix; receiving, at the apparatus and from the network node, second scheduling information scheduling a second uplink transmission by the apparatus to the network node; receiving, at the apparatus and from the network node, second transmit precoding information indicative of a second transmit precoding matrix for use in precoding the second uplink transmission; and precoding, by apparatus, the second uplink transmission based on the second transmit precoding matrix and the preconditioning matrix.

[0026] The fourth aspect may include any other feature mentioned with respect to the method of the second aspect.

[0027] A fifth aspect provides an apparatus, the apparatus having at least one processor and at least one memory having instructions stored thereon which, when executed by the at least one processor, cause the apparatus to perform: receiving, at the apparatus and from a network node, preconditioning information indicative of a preconditioning matrix; receiving, at the apparatus and from the network node, first scheduling information scheduling a first uplink transmission by the apparatus to the network node; receiving, at the apparatus and from the network node, first transmit precoding information indicative of a first transmit precoding matrix for use in precoding the first uplink transmission; precoding, by the apparatus, the first uplink transmission based on the first transmit precoding matrix and the preconditioning matrix; receiving, at the apparatus and from the network node, second scheduling information scheduling a second uplink transmission by the apparatus to the network node; receiving, at the apparatus and from the network node, second transmit precoding information indicative of a second transmit precoding matrix for use in precoding the second uplink transmission; and precoding, by the apparatus, the second uplink transmission based on the second transmit precoding matrix and the preconditioning matrix.

[0028] The fifth aspect may include any other feature mentioned with respect to the method of the second aspect.

[0029] A sixth aspect provides a network node comprising: means for sending, to a terminal device, preconditioning information indicative of a preconditioning matrix; means for sending, to the terminal device, first scheduling information scheduling a first uplink transmission by the terminal device to the network node; means for sending, to the terminal device, first precoding information indicative of a first transmit precoding matrix for use in precoding the first uplink transmission; means for receiving, from the terminal device, the first uplink transmission precoded based on the first transmit precoding matrix and the preconditioning matrix; means for sending, to the terminal device, second scheduling information scheduling a second uplink transmission by the terminal device to the network node; means for sending, to the terminal device, second precoding information indicative of a second transmit precoding matrix for use in precoding the second uplink transmission; and means for receiving, from the terminal device, the second uplink transmission precoded based on the second transmit precoding matrix and the preconditioning matrix.

[0030] In some example embodiments, the network node further comprises: means for selecting the preconditioning matrix based on long-term channel characteristics of a wireless communication channel between the terminal device and the network node; means for selecting the first transmit precoding matrix based on the preconditioning matrix and first short-term channel characteristics of the wireless communication channel between the terminal device and the network node; and means for selecting the second transmit precoding matrix based on the preconditioning matrix and second short-term channel characteristics of the wireless communication channel between the terminal device and the network node, wherein the second short-term channel characteristics are related to a later time period than the first short-term channel characteristics.

[0031] In some example embodiments, the means for selecting the preconditioning matrix is configured to select, from a codebook, a preconditioning matrix based on a long-term correlation between transmit and / or receive antenna ports.

[0032] In some example embodiments, the means for selecting the first transmit precoding matrix is configured to select, from a codebook, a transmit precoding matrix that optimises an objective function based on the first short-term channel characteristics and the preconditioning matrix; and the means for selecting the second transmit precoding matrix is configured to select, from a codebook, a transmit precoding matrix that optimises an objective function based on the second short-term channel characteristics and the preconditioning matrix.

[0033] In some example embodiments, the first transmit precoding matrix is a NT x m matrix, the second transmit precoding matrix is a NT x n2 matrix, and the preconditioning matrix is a NT x NT matrix, wherein NT denotes a number of transmit antenna ports of the terminal device, and m and n2 denote a number of transmission layers of the first and second uplink transmissions respectively.

[0034] In some example embodiments the means for sending the first scheduling information is configured to send the first scheduling information as part of downlink control information, DCI; and the means for sending the second scheduling information is configured to send the second scheduling information as part of DCI.

[0035] In some example embodiments the means for sending the first precoding information is configured to send the first precoding information as part of the first scheduling information; and the means for sending the second precoding information is configured to send the second precoding information as part of the second scheduling information.

[0036] In some example embodiments, the means for sending the preconditioning information is configured to send the preconditioning information as part of DCI, or as part a medium access control, MAC, control element, MAC-CE.

[0037] A seventh aspect provides a method comprising: sending, from a network node and to a terminal device, preconditioning information indicative of a preconditioning matrix; sending, from the network node and to the terminal device, first scheduling information scheduling a first uplink transmission by the terminal device to the network node; sending, from the network node and to the terminal device, first precoding information indicative of a first transmit precoding matrix for use in precoding the first uplink transmission; receiving, at the network node and from the terminal device, a first uplink transmission precoded based on the first transmit precoding matrix and the preconditioning matrix; sending, from the network node and to the terminal device, second scheduling information scheduling a second uplink transmission by the terminal device to the network node; sending, from the network node and to the terminal device, second precoding information indicative of a second transmit precoding matrix for use in precoding the second uplink transmission; and receiving, at the network node and from the terminal device, a second uplink transmission precoded based on the second transmit precoding matrix and the preconditioning matrix.

[0038] In some example embodiments, the method further comprises: selecting the preconditioning matrix based on long-term channel characteristics of a wireless communication channel between the terminal device and the network node; selecting the first transmit precoding matrix based on the preconditioning matrix and first short-term channel characteristics of the wireless communication channel between the terminal device and the network node; and selecting the second transmit precoding matrix based on the preconditioning matrix and second short-term channel characteristics of the wireless communication channel between the terminal device and the network node, wherein the second short-term channel characteristics are related to a later time period than the first short-term channel characteristics.

[0039] In some example embodiments, selecting the preconditioning matrix comprises selecting, from a codebook, a preconditioning matrix based on a long-term correlation between transmit and / or receive antenna ports.

[0040] In some example embodiments selecting the first transmit precoding matrix comprises selecting, from a codebook, a transmit precoding matrix that optimises an objective function based on the first short-term channel characteristics and the preconditioning matrix; and selecting the second transmit precoding matrix comprises selecting, from a codebook, a transmit precoding matrix that optimises an objective function based on the second short-term channel characteristics and the preconditioning matrix.

[0041] In some example embodiments the first transmit precoding matrix is a NT x m matrix, the second transmit precoding matrix is a NT x n2 matrix, and the preconditioning matrix is a NT x NT matrix, wherein NT denotes a number of transmit antenna ports of the terminal device, and m and n2 denote a number of transmission layers of the first and second uplink transmissions respectively.

[0042] In some example embodiments, sending the first scheduling information comprises sending the first scheduling information as part of downlink control information, DCI; and sending the second scheduling information comprises sending the second scheduling information as part of DCI.

[0043] In some example embodiments, sending the first precoding information comprises sending the first precoding information as part of the first scheduling information; and sending the second precoding information comprises sending the second precoding information as part of the second scheduling information.

[0044] In some example embodiments sending the preconditioning information comprises sending the preconditioning information as part of DCI, or as part a medium access control, MAC, control element, MAC- CE.

[0045] An eighth aspect provides a computer program comprising instructions which, when executed by at least one processor, cause an apparatus to perform: sending, from the apparatus and to a terminal device, preconditioning information indicative of a preconditioning matrix; sending, from the apparatus and to the terminal device, first scheduling information scheduling a first uplink transmission by the terminal device to the apparatus; sending, from the apparatus and to the terminal device, first precoding information indicative of a first transmit precoding matrix for use in precoding the first uplink transmission; receiving, at the apparatus and from the terminal device, a first uplink transmission precoded based on the first transmit precoding matrix and the preconditioning matrix; sending, from the apparatus and to the terminal device, second scheduling information scheduling a second uplink transmission by the terminal device to the apparatus; sending, from the apparatus and to the terminal device, second precoding information indicative of a second transmit precoding matrix for use in precoding the second uplink transmission; and receiving, at the apparatus and from the terminal device, a second uplink transmission precoded based on the second transmit precoding matrix and the preconditioning matrix. In some example embodiments, the eighth aspect may include any other feature mentioned with respect to the method of the seventh aspect.

[0046] A ninth aspect provides a non-transitory computer-readable medium having instructions stored thereon which, when executed by at least one processor, cause an apparatus to perform: sending, from a network node and to a terminal device, preconditioning information indicative of a preconditioning matrix; sending, from the network node and to the terminal device, first scheduling information scheduling a first uplink transmission by the terminal device to the network node; sending, from the network node and to the terminal device, first precoding information indicative of a first transmit precoding matrix for use in precoding the first uplink transmission; receiving, at the network node and from the terminal device, a first uplink transmission precoded based on the first transmit precoding matrix and the preconditioning matrix; sending, from the network node and to the terminal device, second scheduling information scheduling a second uplink transmission by the terminal device to the network node; sending, from the network node and to the terminal device, second precoding information indicative of a second transmit precoding matrix for use in precoding the second uplink transmission; and receiving, at the network node and from the terminal device, a second uplink transmission precoded based on the second transmit precoding matrix and the preconditioning matrix.

[0047] The ninth aspect may include any other feature mentioned with respect to the method of the seventh aspect.

[0048] A tenth aspect provides an apparatus, the apparatus having at least one processor and at least one memory having instructions stored thereon which, when executed by the at least one processor, cause the apparatus to perform: sending, from the apparatus and to a terminal device, preconditioning information indicative of a preconditioning matrix; sending, from the apparatus and to the terminal device, first scheduling information scheduling a first uplink transmission by the terminal device to the apparatus; sending, from the apparatus and to the terminal device, first precoding information indicative of a first transmit precoding matrix for use in precoding the first uplink transmission; receiving, at the apparatus and from the terminal device, a first uplink transmission precoded based on the first transmit precoding matrix and the preconditioning matrix; sending, from the apparatus and to the terminal device, second scheduling information scheduling a second uplink transmission by the terminal device to the apparatus; sending, from the apparatus and to the terminal device, second precoding information indicative of a second transmit precoding matrix for use in precoding the second uplink transmission; and receiving, at the apparatus and from the terminal device, a second uplink transmission precoded based on the second transmit precoding matrix and the preconditioning matrix.

[0049] The tenth aspect may include any other feature mentioned with respect to the method of the seventh aspect. An eleventh aspect provides a terminal device comprising: means for receiving, from a network node, preconditioning information indicative of a preconditioning matrix; means for receiving, from the network node, sounding reference signal, SRS, configuration information; and means for transmitting, to the network node, based at least in part on the SRS configuration information, an SRS preconditioned using the preconditioning matrix.

[0050] In some example embodiments, the means for transmitting the preconditioned SRS is configured to transmit the preconditioned SRS periodically based at least in part on the configuration information.

[0051] In some example embodiments, the terminal device further comprises means for receiving, from the network node, an instruction to transmit the preconditioned SRS, wherein the means for transmitting the preconditioned SRS is configured to transmit the preconditioned SRS based on the SRS configuration and responsive to the instruction.

[0052] In some example embodiments, the terminal device further comprises means for receiving, from the network node, further preconditioning information indicative of a further preconditioning matrix.

[0053] In some example embodiments, the terminal device further comprises means for, responsive to receiving the further preconditioning information, preconditioning a further SRS using the further preconditioning matrix.

[0054] In some example embodiments, the terminal device further comprises: means for receiving, from the network node, first scheduling information scheduling a first uplink transmission by the terminal device to the network node; means for receiving, from the network node, first precoding information indicative of a first transmit precoding matrix for use in precoding the first uplink transmission; and means for precoding the first uplink transmission based on the first transmit precoding matrix and the preconditioning matrix.

[0055] In some example embodiments, the means for receiving the first scheduling information is configured to receive the first scheduling information following the transmission of the preconditioned SRS, and the first transmit precoding matrix, indicated by the first precoding information, is based on or derived from the preconditioned SRS.

[0056] In some example embodiments, the preconditioning matrix is based on long-term channel characteristics of a wireless communication channel between the terminal device and the network node; and the first transmit precoding matrix is based on the preconditioning matrix and first short-term channel characteristics of the wireless communication channel between the terminal device and the network node. In some example embodiments, the means for precoding the first uplink transmission is configured to determine a matrix product of the first transmit precoding matrix and the preconditioning matrix, and precode the first uplink transmission based on the matrix product.

[0057] In some example embodiments the means for receiving the first scheduling information is configured to receive the first scheduling information as part of downlink control information, DCI.

[0058] In some example embodiments the means for receiving the first precoding information is configured to receive the first precoding information as part of the first scheduling information.

[0059] In some example embodiments, the terminal device further comprises means for receiving, from the network node, second scheduling information scheduling a second uplink transmission by the terminal device to the network node; means for receiving, from the network node, second precoding information indicative of a second transmit precoding matrix for use in precoding the second uplink transmission; and means for precoding the second uplink transmission based on the second transmit precoding matrix and the preconditioning matrix.

[0060] In some example embodiments, the terminal device further comprises means for, based at least in part on receiving the further preconditioning information, precoding a further uplink transmission based at least partly on the further preconditioning matrix.

[0061] In some example embodiments, the means for receiving the preconditioning information is configured to receive the preconditioning information as part of DCI, or as part a medium access control, MAC, control element, MAC-CE.

[0062] In some example embodiments, the preconditioned SRS is an SRS resource with NT antenna ports, and wherein the preconditioning matrix is an Ni-by-Ni matrix for preconditioning an NT dimensional baseband transmit signal vector.

[0063] A twelfth aspect provides a method comprising: receiving, at a terminal device and from a network node, preconditioning information indicative of a preconditioning matrix; receiving, at the terminal device and from the network node, sounding reference signal, SRS, configuration information; transmitting, by the terminal device and to the network node, based at least in part on the SRS configuration information, an SRS preconditioned using the preconditioning matrix. In some example embodiments, transmitting the preconditioned SRS comprises transmitting the preconditioned SRS periodically based at least in part on the configuration information.

[0064] In some example embodiments, the method further comprises receiving, from the network node, an instruction to transmit the preconditioned SRS, wherein transmitting the preconditioned SRS comprises transmitting the preconditioned SRS based on the SRS configuration and responsive to the instruction.

[0065] In some example embodiments, the method further comprises receiving, from the network node, further preconditioning information indicative of a further preconditioning matrix.

[0066] In some example embodiments, the method further comprises, responsive to receiving the further preconditioning information, preconditioning a further SRS using the further preconditioning matrix.

[0067] In some example embodiments, the method further comprises: receiving, from the network node, first scheduling information scheduling a first uplink transmission by the terminal device to the network node; receiving, from the network node, first precoding information indicative of a first transmit precoding matrix for use in precoding the first uplink transmission; and precoding the first uplink transmission based on the first transmit precoding matrix and the preconditioning matrix.

[0068] In some example embodiments, receiving the first scheduling information comprises receiving the first scheduling information following the transmission of the preconditioned SRS, and the first transmit precoding matrix, indicated by the first precoding information, is based on or derived from the preconditioned SRS.

[0069] In some example embodiments, the preconditioning matrix is based on long-term channel characteristics of a wireless communication channel between the terminal device and the network node; and the first transmit precoding matrix is based on the preconditioning matrix and first short-term channel characteristics of the wireless communication channel between the terminal device and the network node.

[0070] In some example embodiments precoding the first uplink transmission comprises determining a matrix product of the first transmit precoding matrix and the preconditioning matrix, and precoding the first uplink transmission based on the matrix product.

[0071] In some example embodiments receiving the first scheduling information comprises receiving the first scheduling information as part of downlink control information, DCI. In some example embodiments, receiving the first precoding information comprises receiving the first precoding information as part of the first scheduling information.

[0072] In some example embodiments, the method further comprises: receiving, from the network node, second scheduling information scheduling a second uplink transmission by the terminal device to the network node; receiving, from the network node, second precoding information indicative of a second transmit precoding matrix for use in precoding the second uplink transmission; and precoding the second uplink transmission based on the second transmit precoding matrix and the preconditioning matrix.

[0073] In some example embodiments, the method further comprises based at least in part on receiving the further preconditioning information, precoding a further uplink transmission based at least partly on the further preconditioning matrix.

[0074] In some example embodiments, receiving the preconditioning information comprises receiving the preconditioning information as part of DCI, or as part a medium access control, MAC, control element, MAC- CE.

[0075] In some example embodiments, a preconditioned SRS is an SRS resource with NT antenna ports, and the preconditioning matrix is an NT-by-NT matrix for preconditioning an NT dimensional baseband transmit signal vector.

[0076] A thirteenth aspect provides a computer program comprising instructions which, when executed by at least one processor, is configured to cause an apparatus to perform: receiving, at the apparatus and from a network node, preconditioning information indicative of a preconditioning matrix; receiving, at the apparatus and from the network node, sounding reference signal, SRS, configuration information; transmitting, by the apparatus and to the network node, based at least in part on the SRS configuration information, an SRS preconditioned using the preconditioning matrix.

[0077] In some example embodiments, the thirteenth aspect may include any other feature mentioned with respect to the method of the twelfth aspect.

[0078] A fourteenth aspect provides a non-transitory computer-readable medium having instructions stored thereon which, when executed by at least one processor, cause an apparatus to perform: receiving, at the apparatus and from a network node, preconditioning information indicative of a preconditioning matrix; receiving, at the apparatus and from the network node, sounding reference signal, SRS, configuration information; transmitting, by the apparatus and to the network node, based at least in part on the SRS configuration information, an SRS preconditioned using the preconditioning matrix.

[0079] The fourteenth aspect may include any other feature mentioned with respect to the method of the twelfth aspect.

[0080] A fifteenth aspect provides an apparatus, the apparatus having at least one processor and at least one memory having instructions stored thereon which, when executed by the at least one processor, cause the apparatus to perform: receiving, at the apparatus and from a network node, preconditioning information indicative of a preconditioning matrix; receiving, at the apparatus and from the network node, sounding reference signal, SRS, configuration information; transmitting, by the apparatus and to the network node, based at least in part on the SRS configuration information, an SRS preconditioned using the preconditioning matrix.

[0081] The fifteenth aspect may include any other feature mentioned with respect to the method of the twelfth aspect.

[0082] A sixteenth aspect provides a network node comprising: means for sending, to a terminal device, preconditioning information indicative of a preconditioning matrix; means for sending, to the terminal device, sounding reference signal, SRS, configuration information; and means for receiving, from the terminal device, an SRS preconditioned using the preconditioning matrix.

[0083] In some example embodiments, the configuration information indicates that the terminal device is to transmit the preconditioned SRS periodically; and the means for receiving the preconditioned SRS is configured to receive preconditioned SRS transmitted periodically.

[0084] In some example embodiments, the network node further comprises means for instructing the terminal device to transmit the preconditioned SRS.

[0085] In some example embodiments, the network node further comprises means for selecting the preconditioning matrix based on long-term channel characteristics of a wireless communication channel between the terminal device and the network node.

[0086] In some example embodiments, the network node further comprises: means for selecting a further preconditioning matrix based on further long-term channel characteristics of the wireless communication channel between the terminal device and the network node, wherein the further long-term channel characteristics are related to a later time period than the long-term channel characteristics; and means for sending, to the terminal device, further preconditioning information indicative of the further preconditioning matrix.

[0087] In some example embodiments, the network node further comprises means for receiving, from the terminal device, a further SRS preconditioned using the further preconditioning matrix.

[0088] In some example embodiments, the network node further comprises: means for sending, to the terminal device, first scheduling information scheduling a first uplink transmission by the terminal device to the network node; means for sending, to the terminal device, first precoding information indicative of a first transmit precoding matrix for use in precoding the first uplink transmission; and means for receiving, from the terminal device, a first uplink transmission precoded based on the first transmit precoding matrix and the preconditioning matrix.

[0089] In some example embodiments, the network node further comprises: means for selecting the first transmit precoding matrix based on the preconditioning matrix and first short-term channel characteristics of the wireless communication channel between the terminal device and the network node.

[0090] In some example embodiments, the network node further comprises: means for selecting the first transmit precoding matrix based at least in part on the received preconditioned SRS.

[0091] In some example embodiments, the network node further comprises: means for selecting a second transmit precoding matrix based on the received preconditioned SRS; means for sending, to the terminal device, second scheduling information, the second scheduling information scheduling a second uplink transmission by the terminal device to the network node; means for sending, to the terminal device, second precoding information indicative of the second transmit precoding matrix for use in precoding the second uplink transmission; and means for receiving, from the terminal device, a second uplink transmission precoded based on the second transmit precoding matrix and the preconditioning matrix.

[0092] In some example embodiments, the network node further comprises means for receiving, from the terminal device, a further uplink transmission precoded based at least partly on the further preconditioning matrix.

[0093] A seventeenth aspect provides a method comprising: sending, from a network node and to a terminal device, preconditioning information indicative of a preconditioning matrix; sending, from the network node and to the terminal device, sounding reference signal, SRS, configuration information; and receiving, at the network node and from the terminal device, an SRS preconditioned using the preconditioning matrix.

[0094] In some example embodiments, the configuration information indicates that the terminal device is to transmit the preconditioned SRS periodically; and receiving the preconditioned SRS comprises receiving preconditioned SRS transmitted periodically.

[0095] In some example embodiments, the method further comprises instructing the terminal device to transmit the preconditioned SRS.

[0096] In some example embodiment, the method further comprises selecting the preconditioning matrix based on long-term channel characteristics of a wireless communication channel between the terminal device and the network node.

[0097] In some example embodiments, the method further comprises: selecting a further preconditioning matrix based on further long-term channel characteristics of the wireless communication channel between the terminal device and the network node, wherein the further long-term channel characteristics are related to a later time period than the long-term channel characteristics; and sending, to the terminal device, further preconditioning information indicative of the further preconditioning matrix.

[0098] In some example embodiments, the method further comprises receiving, from the terminal device, a further SRS preconditioned using the further preconditioning matrix.

[0099] In some example embodiments, the method, further comprises: sending, to the terminal device, first scheduling information scheduling a first uplink transmission by the terminal device to the network node; sending, to the terminal device, first precoding information indicative of a first transmit precoding matrix for use in precoding the first uplink transmission; and receiving, from the terminal device, a first uplink transmission precoded based on the first transmit precoding matrix and the preconditioning matrix.

[0100] In some example embodiments, the method further comprises selecting the first transmit precoding matrix based on the preconditioning matrix and first short-term channel characteristics of the wireless communication channel between the terminal device and the network node.

[0101] In some example embodiments, the method further comprises selecting the first transmit precoding matrix based at least in part on the received preconditioned SRS. In some example embodiments, the method further comprises: selecting a second transmit precoding matrix based on the received preconditioned SRS; sending, to the terminal device, second scheduling information, the second scheduling information scheduling a second uplink transmission by the terminal device to the network node; sending, to the terminal device, second precoding information indicative of the second transmit precoding matrix for use in precoding the second uplink transmission; and receiving, from the terminal device, a second uplink transmission precoded based on the second transmit precoding matrix and the preconditioning matrix.

[0102] In some example embodiments, the method further comprises receiving, from the terminal device, a further uplink transmission precoded based at least partly on the further preconditioning matrix.

[0103] An eighteenth aspect provides a computer program comprising instructions which, when executed by at least one processor, cause an apparatus to perform: sending, from the apparatus and to a terminal device, preconditioning information indicative of a preconditioning matrix; sending, from the apparatus and to the terminal device, sounding reference signal, SRS, configuration information; and receiving, at the apparatus and from the terminal device, an SRS preconditioned using the preconditioning matrix.

[0104] In some example embodiments, the eighteenth aspect may include any other feature mentioned with respect to the method of the seventeenth aspect.

[0105] A nineteenth aspect provides a non-transitory computer-readable medium having instructions stored thereon which, when executed by at least one processor, cause an apparatus to perform: sending, from the apparatus and to a terminal device, preconditioning information indicative of a preconditioning matrix; sending, from the apparatus and to the terminal device, sounding reference signal, SRS, configuration information; and receiving, at the apparatus and from the terminal device, an SRS preconditioned using the preconditioning matrix.

[0106] The nineteenth aspect may include any other feature mentioned with respect to the method of the seventeenth aspect.

[0107] A twentieth aspect provides an apparatus, the apparatus having at least one processor and at least one memory having instructions stored thereon which, when executed by the at least one processor, cause the apparatus to perform: sending, from the apparatus and to a terminal device, preconditioning information indicative of a preconditioning matrix; sending, from the apparatus and to the terminal device, sounding reference signal, SRS, configuration information; and receiving, at the apparatus and from the terminal device, an SRS preconditioned using the preconditioning matrix.

[0108] The twentieth aspect may include any other feature mentioned with respect to the method of the seventeenth aspect.

[0109] Brief Description of the Drawings

[0110] Example embodiments will now be described by way of non-limiting example, with reference to the accompanying drawings, in which:

[0111] Fig. 1 illustrates an example of a communication system to which examples disclosed herein may be applied;

[0112] Fig. 2 is a message flow sequence of an example codebook-based precoding method;

[0113] Fig. 3 is a schematic illustration of an example 4-antenna port UE 150;

[0114] Fig. 4 is a message flow sequence of a method in accordance with example embodiments;

[0115] Fig. 5 is a flow diagram of a method in accordance with example embodiments;

[0116] Fig. 6 is a message flow sequence of a method in accordance with example embodiments;

[0117] Fig. 7 is a flow diagram illustrating a method in accordance with example embodiments;

[0118] Fig. 8 is a schematic diagram of a system that may be used to implement one or more of the example embodiments; and

[0119] Fig. 9 shows tangible media for storing computer-readable code which when run by a computer may perform methods according to example embodiments described herein.

[0120] Detailed Description

[0121] 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. 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).

[0122] Embodiments described may be implemented in a communication system, such as any of the following radio access technologies (RATs): World-wide 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 system 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 Duplexing (FDD), Time Division Duplexing (TDD), Multiple-Input Multiple-Output (MIMO), Orthogonal Frequency Division Multiplexing (OFDM), and / or Discrete Fourier Transform spread OFDM (DFT-s-OFDM).

[0123] As used herein, the term “network device” or “network node” refers to a node in a communication system 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 (IAB) node, a low power node, a non-terrestrial network (NTN) node 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.

[0124] 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 transmit / receive (Tx / Rx) nodes. In some embodiments, the DUs may comprise e.g. a radio link control (RLC), medium access control (MAC) layer and a physical (PHY) layer, whereas the CU may comprise the layers above RLC layer, such as a packet data convergence protocol (PDCP) layer, Service Data Application Protocol (SDAP) layer and a radio resource control (RRC) layer. Other functional splits are possible too. In practice, any processing task may be performed in either the CU and / or the DU and the boundary where the responsibility is shifted between the CU and the DU may depend on the applied implementation.

[0125] 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 wearable terminal device, a personal digital assistant (PDA), portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and play-back appliances, vehiclemounted 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.

[0126] 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.

[0127] Fig. 1 illustrates an example of a communication system to which examples disclosed herein may be applied. The communication system or a cellular communication system 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.

[0128] The network node 110 may provide a user equipment (UE) 120 (one or more UEs) with wireless access to the communication system. 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. 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, 1 12. 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.

[0129] In the case of multiple network nodes in the communication system, 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 is called Xn interface.

[0130] The network nodes 110 and 112 may be further connected via another interface to a core network 116 of the communication system. The LTE specifications specify the core network as an evolved packet 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 management function (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.

[0131] Uplink precoding

[0132] When performing uplink (UL) MIMO, a UE (or other terminal device) sends information bearing symbols for transmission to a set of antenna ports.

[0133] The UE may determine which of the available antenna ports to transmit the symbols via. If multiple antenna ports are selected, the UE may determine whether to apply a phase shift between the antenna ports. In the case of multi-layer UL MIMO (e.g., in which the UE transmits multiple symbols over the same frequency / time resource to increase throughput), the UE may perform this determination for each layer. This selection of antenna ports for the layers, and the phase shifts, etc. can be represented by a precoding matrix. The below signal model includes exemplary precoding matrix P.

[0134] X = Ps is a column vector of dimension v x 1 which contains information bearing symbols, n is the number of transmit layers, and snrepresents the symbol for the nthlayer. pEQNTXVjs apreceding matrix. The dimension of P is NTx v where NTand v denote the number of transmit antenna ports and the number of transmit layers, respectively. x e CNTX 1is a baseband transmit signal vector (e.g., a complex vector) of dimension equal to the number of transmit antenna ports.

[0135] For example, for two-layer UL MIMO over four Tx antenna ports, the precoding may be represented as follows:

[0136] Taking the example of symbol and port xltthe precoding may correspond to the transmission of a signal based on symbol via port by giving P1a non-zero amplitude (or magnitude), while giving P1an amplitude of zero may correspond to not transmitting a signal based on via port x . Using real, complex, and imaginary values for the elements of P, the precoding may introduce phase differences. Power control can be simplified by ensuring that each of the elements of P have one of two amplitudes (i.e. the elements have a zero “off” amplitude or a non-zero “on” amplitude).

[0137] Aspects of the present disclosure relate to codebook-based UL precoding (e.g., single-layer or multi-layer codebook-based UL precoding). In codebook-based precoding, a matrix used in precoding is selected from a codebook. Selecting the matrix from a codebook may allow for efficient communication of the matrix over the radio channel, but relies on the codebook comprising suitable matrices, and the selection of suitable matrices from the codebook.

[0138] In some examples, codebooks of precoding matrices may assume:

[0139] 1 ) Isotropic antennas at the UE, and

[0140] 2) A uniform Linear Array (ULA) structure If these assumptions do not hold, then a codebook design based on these assumptions may be sub-optimal. For example, the codebook may not account for antenna link degradation (for example, due to signal blockage / attenuation resulting from a user’s hand gripping a UE handset, or due to directional antennas pointing in an undesirable direction).

[0141] Moreover, the wireless channel shows characteristics that do not change quickly (e.g., compared to faster changing characteristics) and can be exploited to improve communications. Such characteristics may result from a hand grip position, building reflections, etc.

[0142] Aspects of the present disclosure relate to methods for exploiting the long-standing electromagnetic conditions of the channel to improve transmission.

[0143] FIG. 2 shows a message flow sequence of a codebook-based method for precoding UL MIMO transmissions, designated generally by the reference numeral 200.

[0144] In method 200, a network node 212 (e.g., a gNB) indicates a transmit precoding matrix to UE 210.

[0145] At step 212 of method 200, UE 210 transmits non-precoded sounding reference signal (SRS), for receipt by the network node 212.

[0146] The SRS can be transmitted sequentially or simultaneously, depending on UE capabilities. Simultaneously transmitted SRS may be lower in power than sequential SRS, to satisfy a maximum combined transmission power limitation, which may reduce coverage.

[0147] At step 214, network node 212 estimates the channel (between UE antenna ports and network node antenna ports) based on the received SRS. Network node 212 determines a suitable transmit precoding matrix indicator (TPMI), corresponding to a transmit precoding matrix, from a pre-defined codebook.

[0148] In some examples, additional information determines which pre-defined codebook of a set of codebooks is used. For example, the codebook used may be based on rank indicator (Rl), indicating the number of UL MIMO layers to be used, and / or a number of antenna ports (e.g., defining the dimensions of the matrix P above).

[0149] At step 216, network node 212 schedules a PUSCH transmission, or other uplink transmission, by UE 210. Network node 212 sends scheduling information to UE 210, including the selected TPML The information also includes a rank indicator (Rl), indicating the number of UL MIMO layers to be used. This information may include an SRS resource indicator (SRI).

[0150] At step 218, UE 210 sends the scheduled PUSCH transmission. The UE precodes the transmission based on the indicated TMPI.

[0151] Method 200 may be repeated (although SRS can be transmitted more or less often than once per scheduled PUSCH), with subsequent scheduling information indicating a TPMI for use in precoding a subsequent PUSCH.

[0152] Aspects of the present disclosure relate to improving precoding gains of codebook-based UL precoding.

[0153] FIG. 3 is a schematic illustration of an example 4-antenna port UE 150. UE 150 is modelled with different radiation patterns per antenna port, resulting in different antenna gains for each antenna port at different angles of arrival. UE 150 has antenna ports AP1 , AP2, AP3, and AP4. Antenna ports AP1 - AP4 may by used to emit SRS. UE 150’s SRS may be received by base station 160. Base station 160 may receive the SRS via two beams, Beaml and Beam2. The radiation patterns of AP1 - AP4 may not have their strongest gain in the direction of the strongest angles of arrival (AoA) for Beaml or Beam2. There may therefore be a gain direction (a, b, c, or d, respectively for AP1 , AP2, AP3, or AP4), and a substantial gain delta between the direction of the strongest angle of arrival for the base station 160 beams and the direction of strongest directional antenna gain for the antenna ports.

[0154] The radiation patterns at each port may result from antenna design and / or other conditions. Among other factors, user hand grip (for handset UEs) may hinder signal transmission (e.g., non-isotropically), affecting the effective radiation pattern. Additionally or alternatively, the antennas may have a directional gain that is greatest in a direction different from the direction of the gNB. These factors can result in unbalanced port to port path losses.

[0155] It can be seen that coverage limitations and delta max min gains depend on the angle of arrival of the radio signal at UE 150. A codebook with limited resolution or granularity may not be able to account for this angle of arrival and antenna port dependence of the gains. The performance of a precoding matrix codebook therefore depends at least partly on the granularity or resolution of the codebook, as this may allow the codebook to account for the electromagnetic properties of the radio channel. With a low-granularity codebook, it may be difficult to correctly compensate for or exploit such scenarios. One option for improving precoding gains comprises increasing the size of the codebook of precoding matrices. This would allow for more granular precoding, which may allow for the selection and indication to a terminal device of a precoding matrix providing better performance (e.g., SNR gains). For example, increasing the granularity of the precoding could comprise allowing the selection (e.g., by expanding the codebook) of a larger number of precoding matrices that use the “on” or “off’ approach to amplitude. Additionally or alternatively, increasing the granularity of the precoding could comprise allowing the selection of precoding matrices having more amplitude granularity (e.g., so that elements of the precoding matrix may take more than two amplitudes). Similarly, increasing granularity could comprise allowing the selection of precoding matrices with additional phase differences between matrix elements (e.g., the codebook may comprise matrices having matrix elements with a larger number of possible complex arguments).

[0156] While increasing the size of the codebook of precoding matrices may provide gains, applying this to the system of method 200 may result in unacceptable signaling overhead.

[0157] Increasing the size of the codebook to improve granularity would increase the size of the information needed to indicate the matrix from the codebook. If this is combined with an increase in the number of transmit antenna ports and the number of UL MIMO layers (which affect the dimensions of the precoding matrix), the size of the TMPI could be increased by several orders of magnitude.

[0158] It may therefore be advantageous to increase the granularity of codebook-based precoding, while reducing the impact of this increase on signaling overhead.

[0159] At least a portion of the properties of a radio channel may be “durable”, or (relatively) slowly changing. As discussed above, these characteristics may derive from building reflections, user hand grip, and antenna directionality.

[0160] We can consider a realization of a wireless communication channel as the product of two matrices, one of which changes slowly (e.g., on the order of tens of seconds), and changes to this matrix may be referred to as “slow fading”. The other matrix changes quickly (on the order of milliseconds), and these changes may be referred to as “fast fading”. The product of these matrices changes with the speed of the quickest.

[0161] In example 200, the “consistent” part of the channel is disregarded, in favor of estimating (through SRS) the overall product, and thus selecting a precoder based on the resulting channel. However, by selecting a precoder for the two parts separately, it is possible to improve precoding performance (with similar overhead). In aspects of the present disclosure, a network node estimates long-term channel characteristics, and selects a matrix based on these long-term channel characteristics, on which the “full” precoder can be at least partly based.

[0162] For example, the network node may store long-term channel information, such as a plurality of channel estimates, estimated at different time instances (e.g., the N most recent channel estimates, or channel estimates obtained within a time interval T), and determine long-term channel characteristics from the longterm channel information.

[0163] Returning to the signal model: x = Ps

[0164] Used above to illustrate the precoder, P, aspects of this disclosure propose an additional matrix, referred to as the durable preconditioning matrix (DPM), which will impact the precoding operation as follows: x = I / l / DPs.

[0165] The matrix WDcaptures the long-term / durable characteristics of the wireless channel.

[0166] Reusing the same matrix WDfor a length of time may have a lower impact on precoding performance than reusing the same matrix P for that same length of time, as matrix WDis based on long-standing channel characteristics.

[0167] Therefore, matrix P (e.g., a precoding matrix indicated by the TPMI) may be selected by the network node and indicated to a terminal device every transmission time interval (TTI) (e.g., in downlink control information scheduling a PUSCH), while the durable preconditioning matrix WDbe reused for a number of consecutive TTIs ND).

[0168] Reusing the DPM may provide an increase in precoding granularity with a disproportionately small impact on signaling overhead. One factor limiting the granularity of the precoding in codebook-based precoding is the number of bits provided for indicating a selected precoder. In an illustrative example, if 10 bits are used to indicate each of WDand P, and the network node indicates each of these matrices to a terminal device each TTI, then 20 bits are required to indicate WDand P each TTI. However, if the DPM is indicated once every 10 consecutive TTIs / reused for 10 consecutive TTIs, then on average only 1 1 bits are required to indicate WDand P each TTI (as for one TTI 20 bits are used, and for the other 9 TTI only 10 bits are used). Reusing the DPM may therefore allow for an increase in precoding granularity with a disproportionately small increase in signaling overhead (or, if this method were compared to a relatively high-granularity scheme, applying this method may allow a maintenance of the same granularity with a reduction in signaling overhead, etc.)

[0169] The above discussed increases in granularity, and the above discussed exploitation of long-term channel electromagnetic characteristics may improve the performance of codebook-based precoding.

[0170] FIG. 4 shows a message flow sequence of a method for precoding UL MIMO transmissions, designated generally by the reference numeral 400. In this example, a UE 210 sends precoded UL transmissions to a gNB 212, but this method is applicable to terminal devices sending UL transmissions to network nodes more generally.

[0171] At step 412, UE 210 indicates to gNB 212 that it supports DPM based precoding. In some examples, gNB 212 may assume that UE 210 supports DPM based precoding, and this step may be omitted.

[0172] At step 414, UE 210 transmits SRS, for reception by gNB 212.

[0173] At step 416, gNB 212 performs channel estimation based on the SRS transmitted at step 414.

[0174] In some examples, to determine the long-term characteristics of the channel, the gNB collects long-term channel data. The gNB 212 may therefore collect channel data and perform channel estimation before it has collected sufficient data to enable precoding using a DPM. Therefore, in some examples precoding according to method 200 may be used before sufficient data to enable precoding using a DPM is collected. Therefore, in some examples, steps 412 and 414 are preceded by UL transmissions according to method 200 (e.g., short-term channel data, such as the most recent estimated channel matrix, is used to identify an appropriate UL transmit precoding matrix, without using a DPM, and the UE performs at least one UL transmission using the transmit precoding matrix).

[0175] Once gNB 212 is able to determine the long-term characteristics of the channel gNB 212 may determine a DPM. For example, gNB 212 may determine a DPM once a threshold amount of channel data or number of estimated channel matrices is obtained by the gNB, or when the obtained channel data or number of estimated channel matrices spans a threshold amount of time.

[0176] The Durable Preconditioning Matrix (DPM) is a precoding matrix to be used by the UE for a number of consecutive transmissions, together with a more frequently selected precoding matrix (e.g., with a precoding matrix selected and indicated to the UE at each TTI). This allows the DPM to account for long-standing electromagnetic conditions of the communication channel (i.e., buildings, hand grip, specific antenna patterns) and leaves accounting for fast fading to the “fine” precoding matrix.

[0177] The gNB selects the DPM from a pre-defined codebook, common to the UE and the gNB. The UE and gNB may be preconfigured with this matrix (e.g., the gNB may infer from the indication at step 412 that the UE is configured with this matrix).

[0178] The DPM may be indicated to the UE using an index, which may be referred to as the Durable Preconditioning Matrix Index (DPMI).

[0179] In the following, the DPM is denoted by WDand the precoding matrix selected by the TPMI as Wn(t). The time index for the TPMI is explicitly marked (t), as it changes with a higher time-granularity than the DPM.

[0180] Computation

[0181] One method of determining long-term channel characteristics is to use long-term data. In one example, gNB 212 computes the DPM based on a set of channel estimates The number of channel estimates N is larger than the number of channel estimates used to select the TPMI. Using a large number of channel estimates to select the TPMI may provide insufficient time granularity for the TPMI to account for fast fading, so a smaller number of channel estimates (e.g., one) may be used to select the TPMI.

[0182] The specific number of consecutive instances of channel realization used to determine the DPM may depend on a balance of factors. For example, in some examples as few as two consecutive instances of channel realization may be used to determine the DPM (if the TPMI is based on only one), while in other examples hundreds or thousands of consecutive instances of channel realization may be used to determine the DPM.

[0183] Using a small number of channel realizations (e.g., using two channel realizations, while the TPMI is selected based on one) may result in the DPM reflecting longer term channel characteristics than the TPMI, but these may still be relatively shortterm, and the DPM may need to be frequently updated, which may affect signaling overhead. Using a large number of channel realizations (e.g., -10 seconds worth of channel realizations, while the TPMI is selected based on one channel realization) may result in the DPM reflecting long term channel characteristics, but being less responsive to medium term changes, which may affect precoding performance.

[0184] Based on this sequence of channel matrices (channel estimates), the gNB 212 may extract the long-term characteristics of the channel. The computation of the DPM can be performed in different ways, and the computation used may be tailored to the codebook design (or vice versa).

[0185] Covariance matrix

[0186] One method of selecting a DPM comprises calculating a covariance matrix.

[0187] The covariance matrix captures statistically long-term correlation between transmit or receive antennas. If the Kronecker model holds, one possible way is to compute the transmit covariance or transmit correlation matrix such as:

[0188] Where £"{-} represents the expectation operation and represents the variance of the channel elements. =TRACE<'H HHHis the Hermitian adjoint of the channel matrix H.

[0189] N

[0190] In order to implement the formula CT 2, gNB 212 may memorize N successive channel estimations aH

[0191] (of the channel between the gNB and the same UE, UE 212) and compute the moving average, e.g., according to the below formula.

[0192] CTis a Hermitian matrix, and can be represented by a matrix with the following form:

[0193] ■ 1 a2c 1 a .a2«j 1 .

[0194] A three by three matrix is shown above for illustrative purposes, but12Jis an NTby NTmatrix, and can aH therefore be multiplied with the NTby v matrix P (to generate an NTby v combined precoding matrix using the DPM and the matrix indicated by TPMI), or the NTby 1 product of P and s (to further modify a generated NTdimensional transmit vector).

[0195] The above Hermitian matrix can be indicated by a vector

[0196] The entries of this vector may be complex valued and may therefore be indicated by an amplitude and phase. The gNB may therefore represent matrix CTby indicating amplitude and phase vectors (e.g., from separate codebooks), to indicate the amplitude and phase of the matrix entries a i-

[0197] In one example, for an Nyport system the amplitude codebook may be composed of amplitude vectors:

[0198] For an amplitude granularity of 2: Vn ane {1, 0} . For an amplitude granularity of 3: Vn ane {1, 0.5, 0}. For an amplitude granularity of 4: Vn ane {1, 0.66, 0.33, 0}. For an amplitude granularity of 5: Vn anG {1,0.75, 0.5, 0.25, 0}.

[0199] The phase codebook may be composed of phase vectors:

[0200] As can be appreciated, the codebook could include amplitude and phase granularities other than those shown explicitly above, and different amplitude and phase granularities can be combined (e.g., to achieve a balance between precoding performance and signaling overhead).

[0201] As discussed above, the preconditioning matrix may have increased granularity due to an increase in the number of possible amplitude and phase values of the elements, which may result in a more granular overall precoding.

[0202] Alternatively, CTmay be of the following form:

[0203] That is to say, CTis characterized by NT(NT- l) / 2 matrix elements, and the amplitude and phase vectors are of dimension NTNT- 1) / 2.

[0204] Additionally, or alternatively, the precoding may have increased frequency granularity. In the above discussion, the channel matrix is considered to be a function of time. However, the channel matrix also has a degree of frequency dependence, which may vary depending on the frequency band. The importance of this frequency dependence may vary with the width and frequency of the frequency range in which a UE operates. For example, the delay spread of a channel may influence (at least partly) the frequency dependence of the channel. One way to account for this frequency dependence would be to provide different precoders for different frequency ranges. For example, if gNB 212 determines that the frequency dependence of the precoding matrix is significant, it could indicate different precoders for use in different frequency ranges.

[0205] In some examples, different precoders may be provided for different frequency ranges by selecting different preconditioning matrices for different frequency ranges. For example, a first sub-band or set of sub-bands could be associated with a first frequency range, and a second sub-band or set of sub-bands could be associated with a second frequency range. gNB 212 may determine the long-term channel properties for the sub-bands or sets of sub-bands (e.g., based on long-term data for respective sub-bands or sets of subbands) and select respective DPMI for the sub-bands or sets of sub-bands. For example, the above described transmit-correlation matrix based method could be applied using data specific to a respective sub-band / set of sub-bands / frequency range.

[0206] The above described matrices may be normalized by their Frobenius norms (e.g., by the gNB and / or UE) to reduce the impact of the precoding on the total power budget.

[0207] General form In some examples, the DPM codebook may take a more general form. This formulation does not rely on the matrix being Hermitian. Any (square preconditioning) matrix can be expressed (at a level of approximation) by a linear combination of a DFT (discrete Fourier transform) matrices.

[0208] In this case, the codebook is a basic DFT codebook with arbitrary phase resolution. The DPM selected will be the linear combination of a set of matrices. A maximum of Netelements can be combined. The scalars are fed back to the UE using a DPMLscalars field.

[0209] DPM = n=!anMn where Mnare matrices belonging to a DFT codebook, and anare scalars belonging to the DPMLscalars field.

[0210] The general form may be used to indicate a DPM determined using the formula for CTabove (e.g., by indicating the linear combination of matrices that best approximates CT). The general form is not limited to indicating DPM matrices determined in this manner.

[0211] Precoding matrix

[0212] As discussed above, gNB 212 may estimates a matrix based on the long-term channel characteristics, and selects a codebook matrix based on this estimate. For example, gNB 212 may select the “closest” matrix of the codebook to CT, or the matrix of the codebook that best approximates CT. The selected matrix is referred to as WD.

[0213] While the DPM (WDin this example) captures the long-term characteristics of the wireless channel, fast fading characteristics may still affect the channel. gNB 212 may therefore select a TPMI for use with the DPM, to reflect the short-term characteristics of the channel. The transmission precoding matrix (indicated by the TPMI) is denoted here by WT.

[0214] To select the TPMI, gNB may address the below optimization problem, identifying the matrix Wnof the codebook of possible WTthat maximizes some objective function:

[0215] WT= argmax HWDWn

[0216] WnECB

[0217] In examples, the gNB expects the UE to generate the overall precoding matrix by cascading the DPM (corresponding to the received DPMI) and the legacy precoder (corresponding to the received TPMI). In this case the resulting overall DPM based precoder utilized during time-instant ‘n’ is expected to be P(n) = pWrCn).

[0218] Therefore, once the DPM that will be used for a transmission is known, the TPMI can computed as the one that maximizes an objective function (e.g., signal to noise ratio, signal to noise plus interference ratio, etc.) considering an equivalent channel that includes the DPM:

[0219] Heq(n) = H(n)WD

[0220] The TPMI reflects shorter-term channel characteristics than the DPM. Therefore, in some examples, this optimization is based on shorter-term data (e.g., one channel estimate, or a smaller number of channel estimates than are used to select the DPM).

[0221] Some user equipment may, in order to simplify power control systems, only allow limited “on” and “off” granularity of the amplitude of the matrix elements of the overall product P(n) = WDWT(n). In some examples, this can be addressed by setting a threshold value T. If an element of the product WDWT(n) has amplitude < r, then its amplitude is set to 0, in case it is > r its amplitude is set to 1 .

[0222] In some examples, gNB 212 may perform the above optimization on the basis that this threshold will be applied. For example, UE 210 may indicate (e.g., at step 412) that it will apply this threshold. In some examples, gNB 212 does not account for the application of this threshold when selecting the TPMI.

[0223] UE capabilities may additionally or alternatively be relevant to DPM selection. For example, a DPM matrix having only diagonal elements may be simpler for a UE to implement, as this may simplify to per antenna port control (e.g., per antenna port power control). A UE may indicate it’s DPM capabilities to the gNB (e.g. at step 412). Different codebooks may therefore be defined for UEs having different capabilities. The gNB may select from a codebooks of DPM matrices based at least in part on the indicated capabilities. For example, the gNB may select from a codebook containing diagonal DPM when selecting a DPM for a less capable UE, and the gNB may select from a codebook containing DPM with off-diagonal elements when selecting a DPM for a more capable UE.

[0224] At step 418, the gNB 212 sends scheduling information to UE 210, scheduling an uplink transmission (e.g., a PUSCH). gNB 212 also sends the TPMI and DPMI (indicating WTand WDrespectively) at this stage. The scheduling information may be sent via DCI. The TPMI may also be sent via DCI (e.g., with the scheduling information). The DPMI may also be sent via DCI, or via MAC CE (medium access control, MAC, control element, MAC CE). The DPMI may alternatively be sent via RRC signalling.

[0225] In method 400, the channel estimation, DPMI selection, and TPMI selection are shown to all take place before the scheduling information, TPMI, and DPMI are sent to UE 210. In some examples, gNB 212 does not wait for TPMI to be selected, and sends the DPMI to the UE before the scheduling information. In some examples, gNB 212 selects a DPMI and sends the DPMI to UE before gNB determines scheduling information and selects a TPMI. For example, gNB may select a DPMI for the purpose of SRS preconditioning (as discussed later in the specification) and indicate this to the UE, and “reuse” this DPMI for the purpose of UL transmission preconditioning.

[0226] UE 210, having received the DPMI, TPMI, and scheduling information then sends the scheduled UL transmission at step 420. The UE may infer that DPM based precoding is to be performed based on receiving the DPMI, or based on a different indication.

[0227] Based on at least on the TPMI (e.g. based on the TPMI and a rank indicator), the UE selects the matrix WTfrom a preconfigured codebook. Based on the DPMI the UE selects the DPM matrix WDfrom a preconfigured codebook. The UE may precode the UL transmission using precoder P(n) = WDWT(n), although, the UE may optionally modify this matrix further. For example, the UE may perform a normalization operation on WDWT(e.g., if WDWTis not already normalized by its Frobenius norm), and / or adapt the matrix to have elements with two amplitude values (e.g., based on threshold r as discussed above), to determine a matrix for use in precoding. Precoding may be performed by multiplying non-precoded data (e.g., vector of symbols s) with the precoding matrix to obtain precoded data (e.g., transmit signal vector x). gNB 212 receives the UL transmission at step 420.

[0228] At step 422, UE 210 sends further SRS. The SRS may be similar to the SRS of step 414, or these SRS may be preconditioned as discussed later in this specification.

[0229] At step 424, gNB 212 performs channel estimation based on the received SRS. gNB may estimate the shortterm channel characteristics (e.g., one channel estimate), but does not necessarily estimate long-term channel characteristics. gNB 212 selects a TPMI in a similar manner to step 416, based on the short-term channel characteristics and the DPM. At step 426, gNB 212 sends second scheduling information and a second TPMI to UE 210. It is not necessary to send the DPMI again, as this is selected based on long-term channel characteristics that are unlikely to change in the interval between the scheduled transmissions.

[0230] At step 428, UE 210 precodes an UL transmission based on the second TPMI and the DPMI received at step 418. In this instance, the precoding has been made more granular through the use of the DPM, and has taken into account the long-term characteristics of the channel, but because the DPM is reused from a previous instance, the impact on the signaling overhead has been reduced.

[0231] In some examples, the DPM may be reused for a fixed number of instances, or until the gNB indicates that the UE 210 is to stop using the DPM in precoding (e.g., either by indicating an updated DPM, or by indicating that DPM based precoding should no longer be used).

[0232] The gNB 212 may use any suitable scheme for updating the DPM. For example, the gNB may select and transmit an updated DPMI after a fixed number of TTIs, or the gNB may monitor the long-term channel characteristics and / or the precoding performance, and select and transmit to the UE 210 an updated DPMI based on, for example, a change in the channel characteristics or a change in precoding performance.

[0233] Fig. 5 is a flow diagram of a method in accordance with example embodiments, designated generally by the reference numeral 500. Method 500 takes place between a terminal device (such as a UE) and a network node (such as a gNB).

[0234] At step 510, the terminal device receives from the network node preconditioning information indicative of a preconditioning matrix from the network node. Corresponding steps of selecting a preconditioning matrix and sending the indication to the terminal device may be undertaken by a network node.

[0235] In some examples, the preconditioning matrix selected (e.g., at the network node) based on long-term characteristics of the wireless channel between antenna ports of the terminal device and antenna ports of the network node. In some examples, the characteristics may be long-term because the characteristics are longer-term than short-term characteristics (e.g., the characteristics may change over a longer time scale than the channel characteristics upon which a transmit precoding matrix is based). In some examples, the characteristics may be long-term because the characteristics change over a time period that is relatively longer than a transmission time interval. For example, the characteristics may change over a plurality of transmission time intervals, 10 or more transmission time intervals, etc. In some examples, a preconditioning matrix may be based on long-term channel characteristics by being derived from long-term data. For example, the long-term channel characteristics may be derived from a larger number of measurements, measurements taken at a larger number of time instances, or measurements spanning a larger time interval than the measurements based upon which a transmit precoding matrix may be selected. For example, the preconditioning matrix may be based on an average of channel estimates at different time instances (e.g. a moving average of the channel matrix), or an average of some property derived from channel estimates at different time instances (e.g., a moving average of the transmit correlation matrix).

[0236] In some examples, the preconditioning matrix may be a matrix selected based on the following formula, which is discussed in further detail elsewhere in this specification:

[0237] In some examples, receiving the preconditioning information comprises receiving an indication of a matrix in a pre-defined codebook.

[0238] In some examples, the preconditioning matrix is selected based on the long-term channel characteristics and the codebook (e.g., by determining a matrix based on long-term channel characteristics, and selecting a matrix within the codebook that approximates or most closely approximates the determined matrix).

[0239] In some examples, the preconditioning information is received via physical layer signaling. In some examples, the preconditioning information is received via downlink control information. In some examples, the preconditioning information is received via medium access control (MAC) layer signaling. In some examples, the preconditioning information is received via MAC control element (MAC CE) signaling. In some examples, the preconditioning information is received via RRC signaling.

[0240] At step 512, the terminal device receives from the network node first scheduling information, which schedules a first uplink transmission by the terminal device to the network node. A corresponding step of determining to send the scheduling information and / or sending the scheduling information may take place at a network node.

[0241] In some examples, this scheduling information may be received as part of physical layer signaling. In some examples, this scheduling information may be received as part of downlink control information. In some examples, the transmission scheduled by this scheduling information may carry uplink data. In some examples, the transmission scheduled by this scheduling information may be a PUSCH transmission.

[0242] At step 514, the terminal device receives from the network node first precoding information indicative of a first transmit precoding matrix for use in precoding the first uplink transmission. A corresponding step of selecting the first transmit precoding matrix and / or sending the first precoding information may take place at a network node.

[0243] In some examples, the first transmit precoding matrix is selected (e.g., by the network node) based on the preconditioning matrix and first short-term channel characteristics of the wireless communication channel between the terminal device and the network node.

[0244] In some examples, the short-term channel characteristics may be considered short-term by comparison to the long-term channel characteristics used to determine the preconditioning matrix. For example, the shortterm channel characteristics may be based on channel estimations at fewer time instances (e.g., at one time instance), based on a smaller set of data, and / or based on data collected over a shorter period, etc.

[0245] In some examples, receiving the first precoding information comprises receiving an indication of a matrix in a pre-defined codebook.

[0246] In some examples, the first transmit precoding matrix may be selected by determining a precoding matrix of the codebook that optimizes some value (such as signal to noise ratio, signal to noise plus interference ratio, etc.) based on a channel estimate and the selected preconditioning matrix.

[0247] In some examples, the first precoding information is received with or as part of the scheduling information.

[0248] At step 516, the terminal device precodes the first uplink transmission based on the first precoding matrix and the preconditioning matrix. A corresponding step of receiving the precoded first uplink transmission may take place at a network node.

[0249] Precoding the uplink transmission may comprise determining a precoding matrix based on the transmit precoding matrix and the preconditioning matrix and precoding the uplink transmission using the determined precoding matrix. For example, determining a precoding matrix may comprise determining a matrix product of the preconditioning matrix and first transmit precoding matrix. In some examples, this matrix product may be used directly in precoding. In other examples, this matrix product undergoes further processing, such as a normalization step, or some other step to adapt the matrix product to the power control systems of the terminal device.

[0250] In some examples the first transmit precoding matrix is an NT X m matrix and the preconditioning matrix is an NT X NT matrix, wherein NT denotes the number of transmit antenna ports of the terminal device, and m denotes the number of transmission layers of the first uplink transmission.

[0251] At step 518, the terminal device receives from the network node second scheduling information, scheduling a second uplink transmission by the terminal device to the network node. In some examples, the second scheduling information may have similar features to the first scheduling information, although the uplink data for transmission may be different, and the second uplink transmission may be scheduled at a different time to the first uplink transmission. A corresponding step of determining to send the scheduling information and / or sending the scheduling information may take place at a network node.

[0252] At step 520, the terminal device receives from the network node second precoding information, indicative of a second transmit precoding matrix, for use in precoding the second uplink transmission. A corresponding step of selecting the second transmit precoding matrix and / or sending the second precoding information may take place at a network node.

[0253] In some examples, the second transmit precoding information may be provided to the terminal device in a similar manner to the first transmit precoding information, and may be selected by the network node in a similar manner to the first transmit precoding information.

[0254] In some examples the second transmit precoding matrix is an NT X n2 matrix and the preconditioning matrix is an NT X NT matrix, wherein NT denotes the number of transmit antenna ports of the terminal device, and n2 denotes the number of transmission layers of the second uplink transmission. n2 may be different or equal to ni.

[0255] In some examples, the second transmit precoding matrix is based on the preconditioning matrix and second short-term channel characteristics of the wireless communication channel between the terminal device and the network node, wherein the second short-term channel characteristics are related to a later time period and / or different time instance than the first short-term channel characteristics. For example, the second uplink transmission may be scheduled for a later time than the first uplink transmission, and the transmit precoding matrix may be based on a later channel estimate, based on later collected channel data. At step 522, the terminal device precodes the second uplink transmission based on the second transmit precoding matrix and the preconditioning matrix. In some examples, the precoding of the second uplink transmission may be performed similarly to the precoding of the first uplink transmission, using the second transmit precoding matrix rather than the first. A corresponding step of receiving the precoded first uplink transmission may take place at a network node.

[0256] In some examples, steps 518 - 522 may repeat for a number of uplink transmissions using the same preconditioning matrix.

[0257] By reusing the preconditioning matrix in multiple uplink transmissions, the granularity of the precoding may be improved with a disproportionately small increase in signaling overhead. Correspondingly, in some examples, this reuse may allow a degree of precoding granularity to be maintained while reducing signaling overhead.

[0258] Using a preconditioning matrix that is based on longer-term channel characteristics may provide a preconditioning matrix that provides precoding gains over the longer-term (e.g., precoding gains may be observed when using the same precoding matrix for a period of time, and this period of time may be greater if the preconditioning matrix is based on longer-term characteristics).

[0259] In some examples, the terminal device is not necessarily aware of how the preconditioning matrix is selected, and uses the preconditioning matrix as instructed or in a pre-defined manner. For example, the network node may have some flexibility in how the preconditioning matrix is determined (e.g., the mathematical method used to select a matrix from the codebook, the data upon which this selection is based, etc.). The use of the preconditioning matrix by the terminal device may therefore facilitate precoding gains (e.g., through an increase in granularity) and / or a reduction or disproportionately low increase in signaling overhead, and the network node may in some examples determine how the preconditioning matrix may be selected and / or indicated to achieve desired precoding gains and / or lower signaling overhead.

[0260] In some examples, the terminal device receives a further / updated preconditioning matrix from the network node, and precodes further uplink transmissions using the further preconditioning matrix. In some examples, the network node updates the preconditioning matrix based on an elapsed time or number of transmissions since the last update. In some examples, the network node updates the preconditioning matrix based on precoding performance of the terminal device.

[0261] A further preconditioning matrix may be based on long-term channel characteristics at a later time instance or period than the preconditioning matrix of step 510. For example, the further preconditioning matrix may be based on channel data and / or channel estimates collected over or corresponding to a later time period.

[0262] Sounding reference signals

[0263] Sounding reference signals (SRSs) are p ilot / trai ni ng symbols that are transmitted by a UE in UL and exploited by the gNB to estimate the UL channel and to select the respective TPMI. The gNB determines an SRS configuration including, for example, SRS physical resources, usage, transmission periodicity, and notifies the UE of the configuration via one of the RRC messages (e.g. RRCSetup, RRCReconfiguration).

[0264] In one example, UE may send non-precoded SRS for each of the configured SRS resources (e.g., 4 SRS per configured resource). These SRSs can be sent sequentially or simultaneously, depending on the UE capabilities. Simultaneously transmitted SRS’s will reduce the power of each SRS to comply with the requirements for maximum combined Tx power at the UE and thus will reduce the coverage.

[0265] Based on the received non-precoded SRS transmission, a gNB may estimate the channel matrix H.

[0266] Preconditioned SRS

[0267] Aspects of the present disclosure also relate to preconditioning SRS.

[0268] FIG. 6 shows a message flow sequence of a method for preconditioning SRS, designated generally by the reference numeral 600. In this example, a UE 210 sends preconditioned SRS to a gNB 212, but this method is applicable to terminal devices sending UL reference signals to network nodes more generally.

[0269] At step 612, UE 210 sends to the gNB an indication that it is capable of DPM based SRS preconditioning. This may be the same capability as the capability of step 412 of method 400, or a related capability.

[0270] At step 614, UE 210 transmits SRS. For example, as discussed above UE 210 may send non-preconditioned SRS for each of the configured SRS resources. As discussed in connection with method 400, the gNB 212 may rely on long-term data to select a DPM, so while this data is accrued, non-DPM based methods may be used, including non-DPM based UL MIMO precoding methods and non-preconditioned SRS transmissions.

[0271] At step 616, gNB 212 determines long-term channel characteristics (for example, using long-term channel data), and selects a DPM based on the long-term channel characteristics. For example, the DPM may be selected similarly to the selection performed at step 416 of method 400.

[0272] At step 618, gNB 212 indicates the DPM to UE 210 by sending the DPMI to UE 210. gNB 212 also configures a preconditioned SRS resource set. SRS transmitted based on this configuration are preconditioned. The configuration may further specify whether the configured SRS are transmitted periodically, in response to a gNB instruction (e.g. aperiodically), or periodically for a configured number of repetitions in response to a gNB instruction (e.g., semi-statically). The preconditioned SRS resource set may be configured via RRC signalling (e.g., via RRCSetup or RRCReconfiguration).

[0273] At step 620, UE 210 sends an SRS preconditioned using the preconditioning matrix indicated by the DPMI.

[0274] Taking the channel model to be: y = Hx

[0275] Where y is NRdimensional vector of received signals at NRantenna ports, a non-preconditioned SRS may allow the estimation of the channel matrix H through comparison of y and x.

[0276] When the UE sends preconditioned SRS, gNB 212 may instead estimate the effective channel HWDaccounting for the preconditioning. For example, the channel model may effectively be: y = HWDX

[0277] Preconditioning the SRS may therefore comprise preconditioning the NTdimensional baseband transmit vector of the SRS x by multiplying it with the preconditioning matrix WDto generate a preconditioned transmit vector WDx, where NTis the number of transmit antenna ports of the SRS resource.

[0278] As with the preconditioning matrix of DPM based precoding, this preconditioning matrix is based on longterm characteristics. This may allow the long-term characteristics of the channel to be exploited to provide gains. For example, the signal-to-noise ratio of the received preconditioned SRS may be greater than the signal-to-noise ratio of a non-preconditioned SRS under the same channel conditions.

[0279] Further, the preconditioned SRS is based on long-term channel characteristics, so may provide these gains over non-preconditioned SRS for a longer timescale than the fast fading timescale characteristic of the channel. A DPM may therefore be used to precondition SRS over multiple transmission time intervals, or for multiple rounds of transmission of the same SRS resource (e.g., in the case of periodic SRS).

[0280] The signaling overhead of gNB 212 indicating this preconditioning may therefore be reduced.

[0281] At step 622, gNB 212 performs channel estimation, and selects a TPMI for use in a subsequent UL transmission by UE 210.

[0282] While the preconditioned SRS may allow the prediction of the effective channel accounting for the preconditioning, HWD, it is not necessary for gNB 212 to determine / / and WDseparately to select a TPMI. As discussed in connection with step 416 of method 400, the TPMI can be selected by identifying a transmit precoding matrix Wnthat optimizes some property of HWDWnsuch as signal-to-noise ratio, or signal-to- noise plus interference ratio. It is not necessary to separately determine H WDto perform this optimization.

[0283] The gNB may therefore estimate the effective channel HWDbased on the preconditioned SRS, and select a TPMI based on the effective channel.

[0284] The gNB may additionally or alternatively estimate the channel H based on the preconditioned SRS and its knowledge of the preconditioning matrix.

[0285] The improvements in the signal to noise ratio of the preconditioned SRS may allow for more accurate channel (or effective channel) estimation, allowing for more accurate selection of an appropriate precoding matrix.

[0286] At step 624, gNB 212 sends scheduling information to UE 210. This step is similar to step 418 of method 400. gNB 212 may send the scheduling information without a DPMI at this stage, as UE 210 received a DPMI at step 618.

[0287] At step 626, UE 210 sends an uplink transmission, such as a PUSCH transmission, similar to step 422 of method 400.

[0288] The preconditioning matrix is based on long-term channel characteristics, so may remain valid for multiple TTIs. gNB 212 may therefore receive further preconditioned SRS transmissions preconditioned based on the DPMI received at step 618, and send further scheduling information and TPMIs scheduling transmissions to be precoded based on the DPMI received at step 618 and the TPMIs associated with respective scheduling information. Fig. 7 is a flow diagram illustrating a method in accordance with example embodiments, designated generally by the reference numeral 700. Method 700 takes place between a terminal device (such as a UE) and a network node (such as a gNB).

[0289] At step 710, the terminal device receives preconditioning information indicative of a preconditioning matrix. This preconditioning information may be determined and / or received similarly to step 510 of method 500. Corresponding steps of selecting a preconditioning matrix and sending the indication to the terminal device may be undertaken by a network node.

[0290] At step 712, the terminal device receives SRS configuration information. A corresponding step of sending the configuration information to the terminal device may be undertaken by a network node.

[0291] The SRS configuration information may in some examples configure one or more SRS resources or SRS resource sets for transmitting preconditioned SRS, preconditioned using the preconditioning matrix. The configuration information may indicate whether the preconditioned SRS are to be transmitted periodically (e.g., as in the case of periodic and semi-static transmission schemes), in response to an instruction from the network node (e.g., received via DCI as in the case of an aperiodic scheme or received via MAC CE as in the case of a semi-static scheme).

[0292] The preconditioned SRS is an SRS resource with NT antenna ports, and wherein the preconditioning matrix is an NT-by-NT matrix for preconditioning an NT dimensional baseband transmit signal vector.

[0293] At step 714, the terminal device transmits SRS preconditioned using the preconditioning matrix based on the SRS configuration information. A corresponding step of receiving the preconditioned SRS may be undertaken by a network node.

[0294] Preconditioning the SRS may provide improved SRS signal reception at the network node, allowing for improved channel estimation. Channel estimates based on the preconditioned SRS may effectively estimate the channel modified by the preconditioning. The preconditioning matrix may be known by the network node (e.g., as it is selected by the network node), so the network node may account for the preconditioning of the SRS.

[0295] Basing the preconditioning matrix on long-term channel properties may allow for reuse of the preconditioning matrix over a time period (e.g., for a number of transmission time intervals, such as at least 2, at least 10, etc., or for a plurality of consecutive transmissions of a preconditioned SRS resource). Reusing the preconditioning matrix reduces the average signaling overhead that may be required to indicate the preconditioning matrix to the terminal device.

[0296] In some examples, step 714 may be followed by a step of receiving a further preconditioning matrix (e.g., after a plurality of transmissions of the preconditioned SRS, after an elapsed time or number of transmission time intervals, or after a determination at the network node that the preconditioning performance of the preconditioning matrix has degraded). Further SRS may be preconditioned using the further preconditioning matrix. Aspects of the discussion of further preconditioning matrices in connection with method 500 are applicable to further preconditioning matrices in connection with method 700.

[0297] In some examples, step 714 may be followed by steps similar to steps 518 - 522 of method 500. The shortterm channel characteristics may be determined based at least partly on the preconditioned SRS, and the transmit precoding matrix may be selected (by the network node) based on the preconditioned SRS. These steps may be repeated a number of times using the preconditioning matrix of step 710 (e.g., at least a second time, by receiving second precoding information, receiving second scheduling information, and precoding a second transmission).

[0298] Basing SRS preconditioning and uplink transmission precoding on the same preconditioning information may also reduce the (average) signaling overhead of indicating the preconditioning matrix. This may also reduce the number of calculation steps needed at the network node to determine a precoding matrix for use with the uplink transmit preconditioning matrix, as an estimate of the channel preconditioned using the SRS preconditioning (e.g. HWD, which may be determined from preconditioned SRS) may then be used as an estimate the channel preconditioned with the uplink transmission preconditioning (e.g. HWD, which may be used in the selection of the transmit precoding matrix).

[0299] For completeness, FIG. 8 is a schematic diagram of components of one or more of the example embodiments described previously, which hereafter are referred to generically as a processing system 1800. The processing system 1800 may, for example, be comprised by the device referred to in the claims below.

[0300] The processing system 1800 may have a processor 1802, a memory 1804 closely coupled to the processor and comprised of a Random Access Memory (RAM) 1814 and a Read Only Memory (ROM) 1812, and, optionally, a user input 1810 and a display 1818. The processing system 1800 may comprise one or more network / apparatus interfaces 1808 for connection to a network / apparatus, e.g., a modem which may be wired or wireless. The network / apparatus interface 1808 may also operate as a connection to other apparatus such as device / apparatus which is not network side apparatus. Thus, direct connection between devices / apparatus without network participation is possible.

[0301] The processor 1802 is connected to each of the other components in order to control operation thereof.

[0302] The memory 1804 may comprise a non-volatile memory, such as a hard disk drive (HDD) or a solid-state drive (SSD). The ROM 1812 of the memory 1804 stores, amongst other things, an operating system 1815 and may store software applications 1816. The RAM 1814 of the memory 1804 is used by the processor 1802 for the temporary storage of data. The operating system 1815 may contain code which, when executed by the processor implements aspects of the methods 200, 400, 500, 600, and 700 described above. Note that in the case of small device / apparatus the memory can be most suitable for small size usage i.e. , not always a hard disk drive (HDD) or a solid state drive (SSD) is used.

[0303] The processor 1802 may take any suitable form. For instance, it may be a microcontroller, a plurality of microcontrollers, a processor, or a plurality of processors.

[0304] The processing system 1800 may be a standalone computer, a server, a console, or a network thereof. The processing system 1800 and needed structural parts may be all inside device / apparatus such as loT device / apparatus i.e., embedded to very small size.

[0305] In some example embodiments, the processing system 1800 may also be associated with external software applications. These may be applications stored on a remote server device / apparatus and may run partly or exclusively on the remote server device / apparatus. These applications may be termed cloud-hosted applications. The processing system 1800 may be in communication with the remote server device / apparatus in order to utilize the software application stored there.

[0306] FIG. 9 shows a tangible media, in the form of a removable memory unit 1910, storing instructions which, when executed by at least one processor, may perform methods according to example embodiments described above. The removable memory unit 1910 may be a memory stick, e.g., a Universal Serial Bus (USB) memory stick, having internal memory 1930 storing the instructions. The internal memory 1930 may be accessed by the at least one processor via a connector 1920. Of course, other forms of tangible storage media may be used, as will be readily apparent to those of ordinary skilled in the art. Tangible media can be any device / apparatus capable of storing data / information which data / information can be exchanged between devices / apparatus / network. Embodiments of the present invention may be implemented in software, hardware, application logic or a combination of software, hardware and application logic. The software, application logic and / or hardware may reside on memory, or any computer media. In an example embodiment, the application logic, software or an instruction set is maintained on any one of various conventional computer-readable media. In the context of this document, a “memory” or “computer-readable medium” may be any non-transitory media or means that can contain, store, communicate, propagate or transport the instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer.

[0307] Reference to, where relevant, “computer-readable medium”, “computer program product”, “tangibly embodied computer program” etc., or a “processor” or “processing circuitry” etc. should be understood to encompass not only computers having differing architectures such as single / multi-processor architectures and sequencers / parallel architectures, but also specialised circuits such as field programmable gate arrays (FPGA), application specific integrated circuits (ASIC), signal processing devices / apparatus and other devices / apparatus. References to computer program, instructions, code etc. should be understood to express software for a programmable processor firmware such as the programmable content of a hardware device / apparatus as instructions for a processor or configured or configuration settings for a fixed function device / apparatus, gate array, programmable logic device / apparatus, etc.

[0308] If desired, the different functions discussed herein may be performed in a different order and / or concurrently with each other. Furthermore, if desired, one or more of the above-described functions may be optional or may be combined. Similarly, it will also be appreciated that the flow and signalling diagrams of Figures 2 and 4 - 7 are examples only and that various operations depicted therein may be omitted, reordered and / or combined.

[0309] It will be appreciated that the above-described example embodiments are purely illustrative and are not limiting on the scope of the invention. Other variations and modifications will be apparent to persons skilled in the art upon reading the present specification.

[0310] Moreover, the disclosure of the present application should be understood to include any novel features or any novel combination of features either explicitly or implicitly disclosed herein or any generalization thereof and during the prosecution of the present application or of any application derived therefrom, new claims may be formulated to cover any such features and / or combination of such features.

[0311] Although various aspects of the invention are set out in the independent claims, other aspects of the invention comprise other combinations of features from the described example embodiments and / or the dependent claims with the features of the independent claims, and not solely the combinations explicitly set out in the claims. It is also noted herein that while the above describes various examples, these descriptions should not be viewed in a limiting sense. Rather, there are several variations and modifications which may be made without departing from the scope of the present invention as defined in the appended claims.

Claims

48ClaimsWhat is claimed is:1 . A terminal device comprising: means for receiving, from a network node, preconditioning information indicative of a preconditioning matrix; means for receiving, from the network node, sounding reference signal, SRS, configuration information; and means for transmitting, to the network node, based at least in part on the SRS configuration information, an SRS preconditioned using the preconditioning matrix.

2. The terminal device of claim 1 , wherein the means for transmitting the preconditioned SRS is configured to transmit the preconditioned SRS periodically based at least in part on the configuration information.

3. The terminal device of claim 1 , further comprising means for receiving, from the network node, an instruction to transmit the preconditioned SRS, wherein the means for transmitting the preconditioned SRS is configured to transmit the preconditioned SRS based on the SRS configuration and responsive to the instruction.

4. The terminal device of any preceding claim, further comprising means for receiving, from the network node, further preconditioning information indicative of a further preconditioning matrix.

5. The terminal device of claim 4, further comprising means for, responsive to receiving the further preconditioning information, preconditioning a further SRS using the further preconditioning matrix.

6. The terminal device of any preceding claim, further comprising: means for receiving, from the network node, first scheduling information scheduling a first uplink transmission by the terminal device to the network node; means for receiving, from the network node, first precoding information indicative of a first transmit precoding matrix for use in precoding the first uplink transmission; and means for precoding the first uplink transmission based on the first transmit precoding matrix and the preconditioning matrix.

497. The terminal device of claim 6, wherein: the means for receiving the first scheduling information is configured to receive the first scheduling information following the transmission of the preconditioned SRS, and the first transmit precoding matrix, indicated by the first precoding information, is based on or derived from the preconditioned SRS.

8. The terminal device of claim 6 or claim 7, wherein: the preconditioning matrix is based on long-term channel characteristics of a wireless communication channel between the terminal device and the network node; and the first transmit precoding matrix is based on the preconditioning matrix and first short-term channel characteristics of the wireless communication channel between the terminal device and the network node.

9. The terminal device of any of claims 6 - 8, wherein: the means for precoding the first uplink transmission is configured to determine a matrix product of the first transmit precoding matrix and the preconditioning matrix, and precode the first uplink transmission based on the matrix product.

10. The terminal device of any of claims 6 - 9, wherein: the means for receiving the first scheduling information is configured to receive the first scheduling information as part of downlink control information, DCI.11 . The terminal device of any of claims 6 - 10, wherein: the means for receiving the first precoding information is configured to receive the first precoding information as part of the first scheduling information.

12. The terminal device of any of claims 6 - 11 , further comprising: means for receiving, from the network node, second scheduling information scheduling a second uplink transmission by the terminal device to the network node; means for receiving, from the network node, second precoding information indicative of a second transmit precoding matrix for use in precoding the second uplink transmission; and means for precoding the second uplink transmission based on the second transmit precoding matrix and the preconditioning matrix.

13. The terminal device of any of claims 6 - 12 when dependent on claim 4, further comprising means50 for, based at least in part on receiving the further preconditioning information, precoding a further uplink transmission based at least partly on the further preconditioning matrix.

14. The terminal device of any preceding claim, wherein the means for receiving the preconditioning information is configured to receive the preconditioning information as part of DCI, or as part a medium access control, MAC, control element, MAC-CE.

15. The terminal device of any preceding claim, wherein the preconditioned SRS is an SRS resource with NT antenna ports, and wherein the preconditioning matrix is an NT-by-N? matrix for preconditioning an NT dimensional baseband transmit signal vector.

16. A network node comprising: means for sending, to a terminal device, preconditioning information indicative of a preconditioning matrix; means for sending, to the terminal device, sounding reference signal, SRS, configuration information; and means for receiving, from the terminal device, an SRS preconditioned using the preconditioning matrix.

17. The network node of claim 16, wherein: the configuration information indicates that the terminal device is to transmit the preconditioned SRS periodically; and the means for receiving the preconditioned SRS is configured to receive preconditioned SRS transmitted periodically.

18. The network node of claim 16, further comprising means for instructing the terminal device to transmit the preconditioned SRS.

19. The network node of any of claims 16 - 18, further comprising means for selecting the preconditioning matrix based on long-term channel characteristics of a wireless communication channel between the terminal device and the network node.

20. The network node of claim 19, further comprising: means for selecting a further preconditioning matrix based on further long-term channel characteristics of the wireless communication channel between the terminal device and the network node,51 wherein the further long-term channel characteristics are related to a later time period than the long-term channel characteristics; and means for sending, to the terminal device, further preconditioning information indicative of the further preconditioning matrix.21 . The network node of claim 20, further comprising means for receiving, from the terminal device, a further SRS preconditioned using the further preconditioning matrix.

22. The network node of any of claims 16 - 21 , further comprising: means for sending, to the terminal device, first scheduling information scheduling a first uplink transmission by the terminal device to the network node; means for sending, to the terminal device, first precoding information indicative of a first transmit precoding matrix for use in precoding the first uplink transmission; and means for receiving, from the terminal device, a first uplink transmission precoded based on the first transmit precoding matrix and the preconditioning matrix.

23. The network node of claim 22, further comprising: means for selecting the first transmit precoding matrix based on the preconditioning matrix and first short-term channel characteristics of the wireless communication channel between the terminal device and the network node.

24. The network node of claim 22, further comprising: means for selecting the first transmit precoding matrix based at least in part on the received preconditioned SRS.

25. The network node of any of claims 22 - 24, further comprising: means for selecting a second transmit precoding matrix based on the received preconditioned SRS; means for sending, to the terminal device, second scheduling information, the second scheduling information scheduling a second uplink transmission by the terminal device to the network node; means for sending, to the terminal device, second precoding information indicative of the second transmit precoding matrix for use in precoding the second uplink transmission; and means for receiving, from the terminal device, a second uplink transmission precoded based on the second transmit precoding matrix and the preconditioning matrix.

26. The network node of any of claims 22 - 25 when dependent on claim 20, further comprising means for receiving, from the terminal device, a further uplink transmission precoded based at least partly on the further preconditioning matrix.

27. A method comprising: receiving, at a terminal device and from a network node, preconditioning information indicative of a preconditioning matrix; receiving, at the terminal device and from the network node, sounding reference signal, SRS, configuration information; transmitting, by the terminal device and to the network node, based at least in part on the SRS configuration information an SRS preconditioned using the preconditioning matrix.

28. A method comprising: sending, from a network node and to a terminal device, preconditioning information indicative of a preconditioning matrix; sending, from the network node and to the terminal device, sounding reference signal, SRS, configuration information; and receiving, at the network node and from the terminal device, an SRS preconditioned using the preconditioning matrix.

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