ENHANCED NEW RADIO (NR) TYPE II CHANNEL STATE INFORMATION (CSI) FEEDBACK USING ANGLE AND DELAY RECIPROCITY

Abstract

A method (800) performed by a base station (e.g., gNB). The method includes selecting (s802) a set of frequency domain (FD) basis vectors. The method also includes transmitting (s804) to a UE information identifying the selected FD basis vectors.

Claims

1-39. (canceled)

40. A method performed by a base station, the method comprising: selecting a set of frequency domain (FD) basis vectors; and transmitting to a user equipment (UE) information identifying the selected FD basis vectors.

41. The method of claim 40, wherein the selected FD basis vectors are selected based on measurements of a reference signal (RS) transmitted by the UE.

42. The method of claim 40, further comprising the base station, based on the reference signal transmitted by the UE, estimating angles of arrival and associated power delay profiles of the reference signal, wherein the base station selects the set of FD basis vectors based on the estimated angles and the associated power delay profiles of the reference signal; and the base station transmitting a plurality of down link (DL) reference signals based on: i) the estimated power delay profiles and/or ii) the estimated angles of arrival.

43. The method of claim 40, wherein the method further comprises transmitting a plurality of down link (DL) reference signals and requesting the UE to measure the DL reference signals and feedback a channel state information (CSI) report based on the DL reference signals and the set of FD basis vectors, and each of the plurality of DL reference signals is associated with one of the angles of arrival and one or more of delays associated with the power delay profiles.

44. The method of claim 40, further comprising, after transmitting to the UE the information identifying the set of FD basis vectors and DL reference signals, the base station receiving a CSI report message transmitted by the UE, wherein the message includes a set of coefficients each associated with one of the DL reference signals and one FD basis vector from a subset of the set of FD basis vectors selected by the UE.

45. The method of claim 40, wherein the set of FD basis vectors comprises adjacent DFT vectors.

46. The method of claim 40, wherein, when the set of FD basis vectors comprises one FD basis vector, the one FD basis vector may be predetermined as a DFT vector associated with zero hertz frequency.

47. The method of claim 40, wherein the set of FD basis vectors are commonly used for all transmission layers.

48. A non-transitory computer readable storage medium storing a computer program comprising instructions which when executed by processing circuitry of the base station causes the base station to perform the method of claim 40.

49. A base station, the base station being configured to: select a set of frequency domain (FD) basis vectors; and transmit to a user equipment, UE, information identifying the selected FD basis vectors

50. The base station of claim 49, wherein the base station is further configured to: based on the reference signal transmitted by the UE, estimate angles of arrival and associated power delay profiles of the reference signal, wherein the base station selects the set of FD basis vectors based on the estimated angles and the associated power delay profiles of the reference signal; and transmit a plurality of down link (DL) reference signals based on: i) the estimated power delay profiles and/or ii) the estimated angles of arrival.

51. A method performed by a user equipment (UE), the method comprising: transmitting a reference signal to a base station; receiving from the base station information identifying a set of FD basis vectors selected by the base station; receiving from the base station a plurality of downlink (DL) reference signals, RSs, and a request for channel state information (CSI) feedback based on the DL RSs and the set of FD basis vectors; selecting a subset of the set of FD basis vectors and estimating CSI based on the DL RSs and the selected subset of FD basis vectors; and transmitting to the base station a CSI report message including a set of coefficients each associated with one of the DL RSs and one of the FD basis vectors include in the selected subset of FD basis vectors.

52. The method of claim 51, wherein the selected subset is the same as the set of FD basis vectors.

53. The method of claim 51, wherein the set of FD basis vectors comprises adjacent DFT vectors.

54. The method of claim 53, wherein the set of adjacent DFT vectors are indicated by an index of the first DFT vector in the set and the total number of DFT vectors in the set.

55. The method of claim 51, wherein, when the set of FD basis vectors comprises one FD basis vector, the one FD basis vector may be predetermined as a DFT vector associated with zero hertz frequency.

56. The method of claim 51, wherein the set of FD basis vectors are commonly used for all transmission layers.

57. A non-transitory computer readable storage medium storing a computer program comprising instructions which when executed by processing circuitry of the UE causes the UE to perform the method of claim 51.

58. A user equipment (UE), the UE being configured to: transmit a reference signal to a base station; receive from the base station information identifying a set of FD basis vectors selected by the base station; receive from the base station a plurality of downlink (DL) reference signals (RSs) and a request for channel state information (CSI) feedback based on the DL RSs and the set of FD basis vectors; select a subset of the set of FD basis vectors and estimating CSI based on the DL RS and the selected subset of FD basis vectors; and transmit to the base station a CSI report message including a set of coefficients each associated with one of the DL RS and one of the selected subset of FD basis vectors

59. The UE of claim 58, wherein the selected subset is the same as the set of FD basis vectors, and the set of FD basis vectors comprises adjacent DFT vectors.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] FIG. 1 illustrates a spatial multiplexing operation.

[0059] FIG. 2 illustrates an example of a 4×4 array with dual-polarized antenna elements.

[0060] FIG. 3 illustrates an example of CSI-RS REs for 12 antenna ports, where 1RE per RB per port is shown.

[0061] FIG. 4 illustrates the agreed codebook structure utilizing both SD and FD compression.

[0062] FIG. 5 illustrates a procedure for reciprocity based FDD transmission scheme.

[0063] FIG. 6 illustrates an angle-delay power spectrum of a channel before and after spatial precoding.

[0064] FIG. 7 illustrates an angle-delay power spectrum of a channel before and after spatial precoding and delay pre-compensation.

[0065] FIG. 8 is a flowchart illustrating a process according to an embodiment.

[0066] FIG. 9 is a flowchart illustrating a process according to an embodiment.

[0067] FIG. 10 is a block diagram of a base station according to an embodiment.

[0068] FIG. 11 is a block diagram of a UE according to an embodiment.

DETAILED DESCRIPTION OF EXAMPLES

[0069] Enhanced Type II Port Selection Codebook for FDD System

[0070] FIG. 5 illustrates a procedure for reciprocity based FDD transmission scheme, assuming that NR Rel. 16 enhanced Type II port-select codebook is used.

[0071] In Step 1, a UE 102 transmits a sounding reference signal (SRS) in the UL to thereby allow a gNB 104 to estimate the angles and delays of different clusters, which are associated with different propagation paths.

[0072] In Step 2, gNB 104 selects dominant clusters according to the estimated angle-delay power spectrum profile, and, for each of the selected clusters, the gNB precodes one CSI-RS port according to the obtained angle and/or delay estimation. gNB also selects a set of frequency domain (FD) basis vectors and transmits to the UE information identifying the selected FD basis vectors. For example, the gNB may transmit to the UE a message comprising an index for each FD basis vector included in the selected set of FD basis vectors, wherein the index for a FD basis vector identifies (e.g., points to) the FD basis vector. The selected set of FD basis vectors is selected based on the estimated angle-delay power spectrum profile.

[0073] In Step 3 the UE measures the received CSI-RS ports and then determines a type II CSI including RI, PMI for each layer and CQI. The precoding matrix indicated by the PMI includes the best phase and amplitude for co-phasing the corresponding beams. The phase and amplitude for each beam are quantized and fed back to the gNB.

[0074] In Step 4, the gNB computes a DL precoding matrix per layer based on the selected beams and the corresponding amplitude and phase feedback and performs Physical Downlink Shared Channel (PDSCH) transmission based the precoding matrices directly (e.g., single user MIMO (SU-MIMO)) or a precoder derived based on the precoding matrices (including the CSI reports from co-scheduled UEs) (e.g., Zero-Forcing precoder in case of multiuser MIMO (MU-MIMO)).

[0075] In one embodiment, the gNB can assist the UE for selecting the best M FD basis vectors according to the estimated cluster angles and delays, in order to reduce the feedback overhead for CSI reporting as well as the computational complexity at the UE for selecting the best M FD basis vectors. The gNB can determine the angles and delays to different clusters by analyzing the angle-delay power spectrum of the channel.

[0076] For example, the 8×10 grid in left part of FIG. 6, shows the angle-delay power spectrum of an UL channel with 8 angle bins and 10 delay taps, where each shaded square represents the power level for a given cluster at certain angle and delay. Based on angle reciprocity, the gNB selects, in this example, 2 strongest clusters and precodes one CSI-RS port per polarization to each cluster (i.e., total 4 CSI-RS ports).

[0077] In right part of FIG. 6, there are only 4 taps in the delay domain in the two beamformed channels, while in the original channel there are 10. Therefore, the 4 delay taps that remains, which can be translated to an FD basis with 4 vectors, {tilde over (W)}.sub.f=[f.sub.k.sub.0 f.sub.k.sub.1 . . . f.sub.k.sub.3], can be conveyed by the gNB to the UE, such that the UE only needs to select the best frequency basis vectors from the 4 FD basis vector candidates instead of 10. Thus, in this example, the overhead for indicating which FD bases can be selected can be decreased, and the computation complexity at UE for selecting the best FD bases can be reduced.

[0078] In one embodiment, the gNB pre-compensates the delays for each beamformed channel such that the strongest path in all beamformed channels arrive at UE at the same time. The delay pre-compensation can be done, for example, by applying a linear phase slope over frequency on the beamforming weights for each beam, where the slope is given by the delay for the strongest tap in each beam.

[0079] As seen in FIG. 7, after pre-compensating the delay for the beamformed channels, the number of delay taps reduces to 3, which in the raw channel there were 10 delay taps. Moreover, since the zeroth delay component (which corresponds to the zeroth FD basis vector, i.e., DC basis) always exists, the gNB only needs to signal to the UE the remaining 2 FD basis vectors {tilde over (W)}.sub.f=[f.sub.k.sub.0 f.sub.k.sub.1]. Hence, the UE only needs to select the best frequency basis vectors from the 2 FD basis vector candidates instead of 4. Thus, in this example, not only is the overhead for indicating which FD components that have been selected is reduced, but also the overhead in reporting corresponding LC coefficients. Additionally, the computational complexity at UE for selecting the best FD bases can be reduced.

[0080] In one embodiment, the gNB pre-determines and signals to the UE a layer-common set of M FD basis vectors {f.sub.k.sub.0, f.sub.k.sub.1, . . . , f.sub.k.sub.M−1}. The UE, for each transmission layer, may select a subset of respective best FD basis vectors from the set of layer-common FD basis vectors and report to the gNB (as used herein a set A is a subset of a set B whenever each element in set A is also in set B—accordingly, set A need not be smaller than set B (i.e., A may equal B), but set A may not be larger than set B). Note that with this embodiment, the UE does not need to perform a two-step FD-basis selection for large number of PMI subbands (i.e., N.sub.3>19) as in the Rel-16 type II enhanced codebooks. Because the gNB already predetermines and signals the layer-common set of M FD basis vectors {f.sub.k.sub.0, f.sub.k.sub.1, . . . , f.sub.k.sub.M−1}, the UE does not have to report an indication of which subset of FD-basis was selected by the UE. For instance, the index i.sub.1,5 (which is reported as part of the PMI in the NR Rel-16 enhanced type II CSI report for N.sub.3>19) does not need to be reported as part of the PMI report in this embodiment. Accordingly, in this embodiment CSI reporting overhead is reduced. In addition, there are complexity savings as well because the UE does not need to perform window-based Intermediary subset selection in this embodiment.

[0081] In one embodiment, the gNB pre-determines and signals to the UE multiple FD basis vector subsets. The UE, for each transmission layer, will select the respective best subset and the corresponding best FD basis vectors from the selected best subset and report to the gNB. In this embodiment, there are complexity savings as well since the UE does not need to perform window-based Intermediary subset selection as done by the UEs in Rel-16 NR enhanced type II CSI feedback.

[0082] In some embodiments, the same best FD basis vector subset is selected by the UE for all the layers (i.e., the selected best FD basis vector subset is layer common). In this case, the UE will report one index per PMI to the gNB to indicate the selected best FD basis vector subset.

[0083] In some embodiments, different best FD basis vector subsets can be selected by the UE for the different layers (i.e., the selected best FD basis vector subset is layer specific). In this case, the UE will report one index per layer per PMI to the gNB to indicate the selected best FD basis vector subset.

[0084] In one embodiment, the gNB signals the UE a layer-specific FD basis subset. The UE, for each transmission layer, will either use all signaled FD basis vectors for the respective layer or select the best FD basis vectors from the respective layer-specific FD basis subset and report to the gNB. If all signaled FD basis vectors for the respective layer are used by the UE, then neither index i.sub.1,5 (which indicates the selected intermediary subset of FD basis vectors to the gNB in rel-16 type II CSI report) nor the index i.sub.1,6,l (which indicates the selected subset of FD basis vectors to the gNB in rel-16 type II CSI report) need to be reported by the UE to the gNB as part of the PMI report. This amounts to notable CSI report overhead savings compared to the Rel-16 type II enhanced CSI reporting.

[0085] In some variants of the above embodiment, N.sub.3=N.sub.SB×R and M=┌p×N.sub.3/R┐ where R is an RRC configured PMI subband size indicator and p is rank dependent higher layer parameter are assumed. For instance, for the embodiment where the whole set of FD basis vectors signaled by the gNB are used by the UE, then the gNB's signaling is expected to have M FD basis vectors. Note that in this case N.sub.3 and M are semi-static since they are determined by the RRC configured parameters R, p, and N.sub.SB. In an alternative embodiment, the gNB may more dynamically signal M′ FD basis vectors depending on the angle-delay power spectrum it measured on the uplink. In this case the number of FD basic vectors may also be explicitly indicate to the gNB by the UE. In some embodiments the corresponding N.sub.3 (i.e., PMI subband size) can also be indicated to the UE by the gNB. In general, the number of selected beams by the gNB can be indicated to the UE by a number of CSI-RS ports in a CSI request. One method to accomplish this is to configure multiple CSI-RS resources for aperiodic CSI feedback reporting where different resources have different number of CSI-RS antenna ports X. The aperiodic CSI trigger points in the DCI are as in Rel. 15 used to select which of the CSI-RS should be used for CSI reporting, i.e. gNB is selecting an X port CSI-RS resource for the feedback. The UE shall determine the number of FD basis vectors for the CSI feedback based on the value X of the indicated CSI-RS resource.

[0086] The amount of delay spread across the selected beams can be translated into channel coherence bandwidth in the frequency domain, which can be used to determine the number of frequency units or subbands (i.e., N.sub.3) required in the type II CSI feedback. The determined number of frequency units may be signaled to the UE to adapt the UE channel delay spread.

[0087] Furthermore, the power delay profile may also be used to determine a dominant M (M<N.sub.3) {f.sub.k.sub.0, f.sub.k.sub.1, . . . , f.sub.k.sub.M−1} frequency domain basis vectors out of an FD basis {f.sub.0, f.sub.1, . . . , f.sub.N.sub.3.sub.−1} for UE to feedback type II CSI. In one embodiment, M adjacent vectors from the FD basis may be selected starting from a basis vector f.sub.k.sub.0.

[0088] FIG. 8 is a flowchart illustrating a process 800 according to an embodiment. Process 800 may begin in step s802. Step s802 comprises selecting a set of frequency domain (FD) basis vectors. Step s804 comprises transmitting to a UE (e.g., UE 102) information identifying the selected FD basis vectors.

[0089] In some embodiments, the selected FD basis vectors are selected based on measurements of a reference signal (RS) transmitted by the UE. In some embodiments, the RS is a sounding reference signal (SRS).

[0090] In some embodiments process 800 further includes the base station, based on the reference signal transmitted by the UE, estimating angles of arrival and associated power delay profiles of the reference signal, wherein the base station selects the set of FD basis vectors based on the estimated angles and the associated power delay profiles of the reference signal. In some embodiments process 800 further includes the base station transmitting a plurality of down link, DL, reference signals based on: i) the estimated power delay profiles and/or ii) the estimated angles of arrival.

[0091] In some embodiments the process further includes transmitting a plurality of down link, DL, reference signals, each associated with one of the angles of arrival and one or more of delays associated with the power delay profiles, and requesting the UE to measure the DL reference signals and feedback a channel state information (CSI) report based on the DL reference signals and the set of FD basis vectors. In some embodiments the DL reference signals are channel state information reference signals (CSI-RS).

[0092] In some embodiments the process further includes, after transmitting to the UE the information identifying the set of FD basis vectors and DL reference signals, the base station receiving a CSI report message transmitted by the UE, wherein the message includes a set of coefficients each associated with one of the DL reference signals and one FD basis vector from a subset of the set of FD basis vectors selected by the UE.

[0093] In some embodiments the set of FD basis vectors comprises one or more FD basis vectors. In some embodiments the set of FD basis vectors comprises adjacent DFT vectors. In some embodiments the set of adjacent DFT vectors are indicated by an index of the first DFT vector in the set and the total number of DFT vectors in the set.

[0094] In some embodiments, when the set of FD basis vectors comprises one FD basis vector, the one FD basis vector may be predetermined as a DFT vector associated with zero hertz frequency.

[0095] In some embodiments the length of the DFT vectors is derived from configured parameters.

[0096] In some embodiments the set of FD basis vectors are commonly used for all transmission layers. In other embodiments the set of FD basis vectors can be different for different transmission layers.

[0097] In some embodiments the transmitting can be via one of radio resource control (RRC) signaling or dynamic signaling in a Physical Downlink Control Channel (PDCCH) or in a Medium Access Control Element (MAC CE).

[0098] FIG. 9 is a flowchart illustrating a process 900, according to an embodiment, that is performed by a UE (e.g., UE 102). Process 900 may begin in step s902. Step s902 comprises the UE transmitting a reference signal (e.g., an SRS) to a base station (e.g., gNB 104). Step s904 comprises receiving from the base station information identifying a set of FD basis vectors selected by the base station. Step s906 comprises receiving from the base station a plurality of downlink (DL) reference signals (RSs) (e.g., CSI-RS), and a request for channel state information (CSI) feedback based on the DL RSs and the set of FD basis vectors. Step s908 comprises selecting a subset of the set of FD basis vectors and estimating CSI based on the DL RS and the subset of the set of FD basis vectors. Step s910 comprises transmitting (s910) to the base station a CSI report message including a set of coefficients each associated with at least one of the DL reference signals and at least one of the selected FD basis vectors.

[0099] FIG. 10 is a block diagram of base station 104, according to some embodiments. As shown in FIG. 10, base station 104 may comprise: processing circuitry (PC) 1002, which may include one or more processors (P) 1055 (e.g., one or more general purpose microprocessors and/or one or more other processors, such as an application specific integrated circuit (ASIC), field-programmable gate arrays (FPGAs), and the like), which processors may be co-located in a single housing or in a single data center or may be geographically distributed (i.e., base station 104 may be a distributed computing apparatus); a network interface 1068 comprising a transmitter (Tx) 1065 and a receiver (Rx) 1067 for enabling base station 104 to transmit data to and receive data from other nodes connected to a network 110 (e.g., an Internet Protocol (IP) network) to which network interface 1068 is connected; communication circuitry 1048, which is coupled to an antenna arrangement 1049 comprising one or more antennas and which comprises a transmitter (Tx) 1045 and a receiver (Rx) 1047 for enabling base station 104 to transmit data and receive data (e.g., wirelessly transmit/receive data); and a local storage unit (a.k.a., “data storage system”) 1008, which may include one or more non-volatile storage devices and/or one or more volatile storage devices. In embodiments where PC 1002 includes a programmable processor, a computer program product (CPP) 1041 may be provided. CPP 1041 includes a computer readable medium (CRM) 1042 storing a computer program (CP) 1043 comprising computer readable instructions (CRI) 1044. CRM 1042 may be a non-transitory computer readable medium, such as, magnetic media (e.g., a hard disk), optical media, memory devices (e.g., random access memory, flash memory), and the like. In some embodiments, the CRI 1044 of computer program 1043 is configured such that when executed by PC 1002, the CRI causes base station 104 to perform steps described herein (e.g., steps described herein with reference to the flow charts). In other embodiments, base station 104 may be configured to perform steps described herein without the need for code. That is, for example, PC 1002 may consist merely of one or more ASICs. Hence, the features of the embodiments described herein may be implemented in hardware and/or software.

[0100] FIG. 11 is a block diagram of UE 102, according to some embodiments. As shown in FIG. 11, UE 102 may comprise: processing circuitry (PC) 1102, which may include one or more processors (P) 1155 (e.g., one or more general purpose microprocessors and/or one or more other processors, such as an application specific integrated circuit (ASIC), field-programmable gate arrays (FPGAs), and the like); communication circuitry 1148, which is coupled to an antenna arrangement 1149 comprising one or more antennas and which comprises a transmitter (Tx) 1145 and a receiver (Rx) 1147 for enabling UE 102 to transmit data and receive data (e.g., wirelessly transmit/receive data); and a local storage unit (a.k.a., “data storage system”) 1108, which may include one or more non-volatile storage devices and/or one or more volatile storage devices. In embodiments where PC 1102 includes a programmable processor, a computer program product (CPP) 1141 may be provided. CPP 1141 includes a computer readable medium (CRM) 1142 storing a computer program (CP) 1143 comprising computer readable instructions (CRI) 1144. CRM 1142 may be a non-transitory computer readable medium, such as, magnetic media (e.g., a hard disk), optical media, memory devices (e.g., random access memory, flash memory), and the like. In some embodiments, the CRI 1144 of computer program 1143 is configured such that when executed by PC 1102, the CRI causes UE 102 to perform steps described herein (e.g., steps described herein with reference to the flow charts). In other embodiments, UE 102 may be configured to perform steps described herein without the need for code. That is, for example, PC 1102 may consist merely of one or more ASICs. Hence, the features of the embodiments described herein may be implemented in hardware and/or software.

[0101] Summary of Various Embodiments:

[0102] A1. A method (800) performed by a base station (e.g., gNB 104), the method comprising: selecting (s802) a set of frequency domain, FD, basis vectors; and transmitting (s804) to a UE (e.g., UE 102) information identifying the selected FD basis vectors.

[0103] A2. The method of embodiment A1, wherein the selected FD basis vectors are selected based on measurements of a reference signal, RS, transmitted by the UE.

[0104] A3. The method of embodiment A2, wherein the RS is a sounding reference signal, SRS.

[0105] A4. The method of embodiment A1, A2, or A3, further comprising the base station, based on the reference signal transmitted by the UE, estimating angles of arrival and associated power delay profiles of the reference signal, wherein the base station selects the set of FD basis vectors based on the estimated angles and the associated power delay profiles of the reference signal.

[0106] A5. The method of embodiment A4, further comprising the base station transmitting a plurality of down link, DL, reference signals based on: i) the estimated power delay profiles and/or ii) the estimated angles of arrival.

[0107] A6. The method of any one of embodiments A1-A5, wherein the method further comprising transmitting a plurality of down link, DL, reference signals and requesting the UE to measure the DL reference signals and feedback a channel state information, CSI, report based on the DL reference signals and the set of FD basis vectors.

[0108] A6a. The method of embodiment A6, wherein each of the plurality of DL reference signals is associated with one of the angles of arrival and one or more of delays associated with the power delay profiles.

[0109] A7. The method of A6 or A6a, wherein the DL reference signals are channel state information reference signals, CSI-RS.

[0110] A8. The method of any one of embodiments A1-A7, further comprising, after transmitting to the UE the information identifying the set of FD basis vectors and DL reference signals, the base station receiving a CSI report message transmitted by the UE, wherein the message includes a set of coefficients each associated with one of the DL reference signals and one FD basis vector from a subset of the set of FD basis vectors selected by the UE.

[0111] A9. The method of any one of embodiments A1-A8, wherein the set of FD basis vectors comprises one or more FD basis vectors.

[0112] A10. The method of any one of embodiments A1-A9, wherein the set of FD basis vectors comprises adjacent DFT vectors.

[0113] A11. The method of embodiment A10, wherein the set of adjacent DFT vectors are indicated by an index of the first DFT vector in the set and the total number of DFT vectors in the set.

[0114] A12. The method of any one of embodiments A1-A11, wherein, when the set of FD basis vectors comprises one FD basis vector, the one FD basis vector may be predetermined as a DFT vector associated with zero hertz frequency.

[0115] A13. The method of any one of embodiments A1-A12, wherein the length of the DFT vectors is derived from configured parameters.

[0116] A14. The method of any one of embodiments A1-A13, wherein the set of FD basis vectors are commonly used for all transmission layers.

[0117] A15. The method of any one of embodiments A1-A13, wherein the set of FD basis vectors can be different for different transmission layers.

[0118] A16. The method of any one of embodiments A1-A14, where the transmitting can be via one or more of: radio resource control, RRC, signaling,

dynamic signaling in a Physical Downlink Control Channel, PDCCH, Downlink Control Information, DCI, or a Medium Access Control Element, MAC CE.

[0119] B1. A method (900) performed by a UE, the method comprising: transmitting (s902) a reference signal to a base station; receiving (s904) from the base station information identifying a set of FD basis vectors selected by the base station; receiving (s906) from the base station a plurality of downlink, DL, reference signals, RSs, and a request for channel state information, CSI, feedback based on the DL RSs and the set of FD basis vectors; selecting (s908) a subset of the set of FD basis vectors and estimating CSI based on the DL RS and the selected subset of FD basis vectors; and transmitting (s910) to the base station a CSI report message including a set of coefficients each associated with one of the DL RS and one of the selected subset of FD basis vectors.

[0120] B2. The method of embodiment B1, wherein the DL RS is a channel state information RS, CSI-RS.

[0121] B3. The method of embodiment B1, wherein the reference signal transmitted by the UE is a sounding Reference Signal, SRS.

[0122] B4. The method of embodiment B1, B2, or B3, wherein the selected subset is the same as the set the FD basis vectors.

[0123] B5. The method of any one of embodiments B1-B4, wherein the DL RS is a channel state information RS, CSI-RS.

[0124] B6. The method of any one of embodiments B1-B5, wherein the reference signal transmitted by the UE is a sounding Reference Signal, SRS.

[0125] B7. The method of any one of embodiments B1-B6, wherein the set of FD basis vectors comprises one or more FD basis vectors.

[0126] B8. The method of any one of embodiments B1-B7, wherein the set of FD basis vectors comprises adjacent DFT vectors.

[0127] B9. The method of embodiment B8, wherein the set of adjacent DFT vectors are indicated by an index of the first DFT vector in the set and the total number of DFT vectors in the set.

[0128] B10. The method of any one of embodiments B1-B9, wherein, when the set of FD basis vectors comprises one FD basis vector, the one FD basis vector may be predetermined as a DFT vector associated with zero hertz frequency.

[0129] B11. The method of any one of embodiments B1-610, wherein the length of the DFT vectors is derived from configured parameters.

[0130] B12. The method of any one of embodiments B1-611, wherein the set of FD basis vectors are commonly used for all transmission layers.

[0131] B13. The method of any one of embodiments B1-B12, wherein the set of FD basis vectors can be different for different transmission layers.

[0132] B14. The method of any one of embodiments B1-B13, where the receiving from the base station the information identifying the set of FD basis vectors can be via one or more of: radio resource control, RRC, signaling, dynamic signaling in a Physical Downlink Control Channel, PDCCH, a Medium Access Control Element, MAC CE, or Downlink Control Information, DCI.

[0133] C1. A computer program (1043) comprising instructions (1044) which when executed by processing circuitry (1002) causes the processing circuitry (1002) to perform the method of any one of embodiments A1-A16.

[0134] C2. A computer program (1143) comprising instructions (1144) which when executed by processing circuitry (1102) causes the processing circuitry (1102) to perform the method of any one of embodiments B1-B3.

[0135] C3. A carrier containing the computer program of embodiment C1 or C2, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a computer readable storage medium (1042, 1142).

[0136] D1. A base station (104), the base station being adapted to perform the method of any one of embodiments A1-A16.

[0137] D2. A base station (104), the base station comprising: processing circuitry (1002); and a memory (1042), the memory containing instructions (1044) executable by the processing circuitry, whereby the apparatus is operative to perform the method of any one of the embodiments A1-A6.

[0138] E1. A UE (102), the UE being adapted to perform the method of any one of embodiments B1-B3.

[0139] E2. A UE (102), the UE comprising: processing circuitry (1102); and a memory (1142), the memory containing instructions (1144) executable by the processing circuitry, whereby the apparatus is operative to perform the method of any one of the embodiments B1-B3.

[0140] While various embodiments are described herein, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of this disclosure should not be limited by any of the above described exemplary embodiments. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

[0141] Additionally, while the processes described above and illustrated in the drawings are shown as a sequence of steps, this was done solely for the sake of illustration.

[0142] Accordingly, it is contemplated that some steps may be added, some steps may be omitted, the order of the steps may be re-arranged, and some steps may be performed in parallel.