Channel state information for reference signals in a wireless communication system

Abstract

According to some embodiments, a method is performed by a user equipment for reporting channel state information. The user equipment is configured with two or more channel state information reference signal, CSI-RS, resources in a CSI-RS resource set. The method comprises: selecting at least two CSI-RS resources from the CSI-RS resource set, wherein each of the at least two selected CSI-RS resources are associated to a set of spatially multiplexed layers, wherein different sets comprise different layers; determining a preferred precoder matrix for the selected CSI-RS resources; and transmitting a CSI report indicating the selected CSI-RS resources and the preferred precoder matrices. The method may further comprise calculating a channel estimate for the selected CSI-RS resources, and determining a channel quality indicator, CQI, corresponding to a hypothetical transmission from a plurality of effective channels where layers transmitted through the effective channels mutually interfere. The CSI report may indicate the determined CQI for the selected CSI-RS resources.

Claims

1. A method performed by a user equipment for reporting channel state information in a wireless communication system, wherein the user equipment is configured with two or more channel state information reference signal, CSI-RS, resources in a CSI-RS resource set, the method comprising: selecting at least two CSI-RS resources from the CSI-RS resource set, wherein each of the at least two selected CSI-RS resources are associated to a set of spatially multiplexed layers, wherein different sets comprise different layers; determining a preferred precoder matrix for each of the selected CSI-RS resources; and transmitting a CSI report indicating each of the selected CSI-RS resources and the determined preferred precoder matrix for each of the selected CSI-RS resources wherein a first one of the selected CSI-RS resources comprises a first set of layers and a second one of the selected CSI-RS resources comprises a second set of layers wherein the first set of layers and the second set of layers mutually interfere.

2. The method of any one of claim 1, further comprising: calculating a channel estimate for each of the selected CSI-RS resources; determining a channel quality indicator, CQI, corresponding to a hypothetical transmission on a plurality of effective channels, where the effective channels depend on the preferred precoder matrices and channel estimate for each of the selected CSI-RS resources, and where layers transmitted through the effective channels mutually interfere; and wherein the CSI report further indicates the determined CQI for each of the selected CSI-RS resources.

3. The method of claim 1, wherein each CSI-RS resource is associated with at least one of: a number of antenna ports (P); a multi-panel antenna array port layout parametrized by a number of vertical panels (M.sub.g) and a number of horizontal panels (N.sub.g); and a precoder codebook.

4. The method of claim 1, wherein each CSI-RS resource is associated with a different quasi co-location, QCL, assumption.

5. The method of claim 1, wherein the CSI-RS carried in each CSI-RS resource of the set of CSI-RS resources is transmitted from different antenna subsets.

6. The method of claim 5, wherein the different antenna subsets belong to different transmission points.

7. The method of claim 1, further comprising: obtaining a CSI report configuration comprising possible hypotheses for combinations of one or more CSI-RS resources; wherein: selecting the at least two CSI-RS resources comprises selecting the at least two CSI-RS resources according to a selected one of the possible hypotheses; and the CSI report indicates the selected CSI-RS resources by indicating the selected possible hypothesis.

8. The method of claim 1, wherein transmitting the CSI report comprises transmitting a first message associated with one of the selected CSI-RS resources and transmitting a second message associated with a second one of the selected CSI-RS resources.

9. The method of claim 8, wherein the first message is transmitted to a first transmission point and the second message is transmitted to a second transmission point.

10. The method of claim 1, wherein the determined preferred precoder matrix for at least one selected CSI-RS comprises a first preferred precoder matrix for a first subband; the method further comprises determining, for the at least one selected CSI-RS resource, a second preferred precoder matrix for a second subband; and wherein the CSI report indicates the first and second preferred precoder matrix for the at least one selected CSI-RS resource.

11. The method of claim 1, further comprising receiving an indication of a codeword-to-layer mapping for use when determining the CQI.

12. The method of claim 1, wherein: a set of demodulation reference signal, DMRS, antenna ports are numbered between 7-14; a set of CSI-RS antenna ports are numbered between 15-31; and a set of physical downlink shared channel, PDSCH, signals on antenna ports {p.sub.k, p.sub.k+1}, where p.sub.k=7+Σ.sub.l=1.sup.k−1v.sub.l, result in signals equivalent to corresponding symbols transmitted on antenna ports {15, . . . , 14+P.sub.k} corresponding to CSI-RS resource k in a set of K CSI-RS resources, as given by [y.sup.(15) . . . y.sup.(14+P.sup.k.sup.)].sup.T=W.sub.k[x.sup.(p.sup.k.sup.) . . . x.sup.(p.sup.k+1.sup.)].sup.T where x.sup.(7), . . . , x.sup.(6+v.sup.TOT.sup.) with v.sub.TOT×Σ.sub.k=1.sup.Kv.sub.k is a vector of symbols, where each symbol corresponds to a layer to be transmitted to the user equipment and contains all layers transmitting the PDSCH.

13. The method of claim 1, wherein the determined preferred precoder for a CSI-RS resource with index k of the selected CSI-RS resources is a matrix W.sub.k that is determined in accordance with a transmission vector y being equivalent to using W.sub.k on a set of layers in a vector x of physical downlink shared channel, PDSCH, signals transmitted to the user equipment according to y=W.sub.kx, wherein y is a transmission on antenna ports corresponding to the CSI-RS resource with index k.

14. The method of claim 1, wherein: the PDSCH signals are on a set of v.sub.k demodulation reference signal, DMRS, antenna ports that are indexed starting with a first port number D.sub.1; the CSI-RS resource with index k comprises P.sub.k antenna ports, and has a first antenna port with index C.sub.1; and the PDSCH signals on antenna ports {q.sub.k, q.sub.k+1}, where q.sub.k=D.sub.1+Σ.sub.l=1.sup.k−1v.sub.l , result in signals equivalent to transmission on antenna ports {C.sub.1, . . . , C.sub.1+P.sub.k} corresponding to CSI-RS resource k, as given by [y.sup.(15) . . . y.sup.(14+P.sup.k.sup.)].sup.T=W.sub.k[x.sup.(p.sup.k.sup.) . . . x.sup.(p.sup.k+1.sup.)].sup.T.

15. A user equipment capable of reporting channel state information in a wireless communication system, wherein the user equipment is configured with two or more channel state information reference signal, CSI-RS, resources in a CSI-RS resource set, and wherein the user equipment comprises processing circuitry operable to: select at least two CSI-RS resources from the CSI-RS resource set, wherein each of the at least two selected CSI-RS resources are associated to a set of spatially multiplexed layers, wherein different sets comprise different layers; determine a preferred precoder matrix for each of the selected CSI-RS resources; and transmit a CSI report indicating each of the selected CSI-RS resources and the determined preferred precoder matrix for each of the selected CSI-RS resources wherein a first one of the selected CSI-RS resources comprises a first set of layers and a second one of the selected CSI-RS resources comprises a second set of layers wherein the first set of layers and the second set of layers mutually interfere.

16. The user equipment of any one of claim 15, wherein the processing circuitry is further operable to: calculate a channel estimate for each of the selected CSI-RS resources; determine a channel quality indicator, CQI, corresponding to a hypothetical transmission from a plurality of effective channels, where the effective channels depend on the preferred precoder matrices and channel estimate for each of the selected CSI-RS resources, and where layers transmitted through the effective channels mutually interfere; and wherein the CSI report further indicates the determined CQI for each of the selected CSI-RS resources.

17. The user equipment of claim 15, wherein each CSI-RS resource is associated with at least one of: a number of antenna ports (P); a multi-panel antenna array port layout parametrized by a number of vertical panels (M.sub.g) and a number of horizontal panels (N.sub.g); and a precoder codebook.

18. The user equipment of claim 15, wherein each CSI-RS resource is associated with a different quasi co-location, QCL, assumption.

19. The user equipment of claim 15, the processing circuitry further operable to: obtain a CSI report configuration comprising possible hypotheses for combinations of one or more CSI-RS resources; wherein: the processing circuitry is operable to select the at least two CSI-RS resources by selecting the at least two CSI-RS resources according to a selected one of the possible hypotheses; and the CSI report indicates the selected CSI-RS resources by indicating the selected possible hypothesis.

20. The user equipment of claim 15, the processing circuitry further operable to receive an indication of a codeword-to-layer mapping for use when determining the CQI.

21. A method performed by a network node of a wireless communication system, the method comprising: transmitting, to a user equipment, a first channel state information reference signal, CSI-RS, in a first CSI-RS resource of a set of at least two CSI-RS resources from a first antenna subset and a second CSI-RS in a second CSI-RS resource in the set of at least two CSI-RS resources from a second antenna subset, wherein the first and second antenna subsets comprise a first and second set of spatially multiplexed layers, respectively, and wherein the first and second set of layers are different; and receiving (956), from the user equipment, a CSI report comprising a first preferred precoder matrix associated with the first CSI-RS resource and a second preferred precoder matrix associated with the second CSI-RS resource wherein a transmission associated with the first set of layers and a transmission associated with the second set of layers mutually interfere.

22. The method of any one of claim 21, wherein the CSI report further comprises a channel quality indicator, CQI, associated with each of the first and second preferred precoder matrices.

23. The method of claim 21, wherein the first and second antenna subsets belong to different transmission points.

24. The method of claim 21, further comprising transmitting, to the user equipment, a CSI report configuration comprising possible hypotheses for combinations of CSI-RS resources.

25. The method of claim 21, further comprising transmitting, to the user equipment, an indication on a codeword-to-layer mapping for use when determining the CQI.

26. A network node of a wireless communication system, the network node comprising processing circuitry operable to: transmit, to a user equipment, a first channel state information reference signal, CSI-RS, in a first CSI-RS resource of a set of at least two CSI-RS resources from a first antenna subset and a second CSI-RS in a second CSI-RS resource in the set of at least two CSI-RS resources from a second antenna subset, wherein the first and second antenna subsets comprise a first and second set of spatially multiplexed layers, respectively, and wherein the first and second set of layers are different; and receive, from the user equipment, a CSI report comprising a first preferred precoder matrix associated with the first CSI-RS resource and a second preferred precoder matrix associated with the second CSI-RS resource wherein a transmission associated with the first set of layers and a transmission associated with the second set of layers mutually interfere.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For a more complete understanding of the embodiments and their features and advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which:

(2) FIG. 1 illustrates long term evolution (LTE) physical resources;

(3) FIG. 2 illustrates an example LTE time-domain structure with 15 kHz subcarrier spacing;

(4) FIG. 3 is an example transmission structure of precoded spatial multiplexing in New Radio (NR);

(5) FIG. 4 is an example two-dimensional array of cross-polarized antenna elements;

(6) FIG. 5 is an example multi-panel antenna array;

(7) FIG. 6 is an example of oversampled DFT beams;

(8) FIG. 7 is a block diagram illustrating an example wireless network, according to a particular embodiment;

(9) FIG. 8 is an example of a non-coherent multi-panel/TRP transmission, according to some embodiments;

(10) FIG. 9A is flow diagram illustrating an example method in a user equipment, according to some embodiments;

(11) FIG. 9B is flow diagram illustrating an example method in a network node, according to some embodiments;

(12) FIG. 10A is a block diagram illustrating an example embodiment of a wireless device;

(13) FIG. 10B is a block diagram illustrating example components of a wireless device;

(14) FIG. 11A is a block diagram illustrating an example embodiment of a network node;

(15) FIG. 11B is a block diagram illustrating example components of a network node; and

(16) FIG. 12 is a block diagram illustrating configuration of an example CSI framework for NC-JT.

DETAILED DESCRIPTION

(17) The next generation mobile wireless communication system (5G) or new radio (NR) supports a wide range of antenna setups, deployments, and use cases compared to long term evolution (LTE), such as multi-panel and multi-transmission reception point (TRP) operation in both the uplink and downlink. A particular problem is how to efficiently support such flexibility, yet avoid specifying separate channel state information (CSI) feedback format for each use case. In the downlink, a user equipment (UE) may be served by a transmit/receive point (TRP) equipped with multiple antenna panels, or it may be served by multiple TRPs, each equipped with one or more antenna panels. The panels may use different port layouts and would thus benefit from being associated with different precoder codebooks. If a single CSI-RS resource comprises the ports from multiple panels, a variety of different precoder codebooks corresponding to different combinations of panel sizes may have to be specified, which is infeasible.

(18) Particular embodiments obviate the problems described above and include a UE configured to measure on multiple CSI-RS resources, where each resource corresponds to a separate transmit/receive point (TRP) or antenna panel. The UE may select a number of channel state information reference signal (CSI-RS) resources to participate in a non-coherent joint transmission, as well as a preferred precoder matrix for each CSI-RS resource, on the basis that layers corresponding to different CSI-RS resources mutually interfere.

(19) A UE may jointly select a preferred precoder matrix and rank for each TRP/panel and calculate an appropriate channel quality indicator (CQI) under a non-coherent joint transmission (NC-JT) assumption. By associating each CSI-RS resource with a separate precoder codebook, particular embodiments may support a variety of different port layouts and antenna deployments.

(20) The following description sets forth numerous specific details. It is understood, however, that embodiments may be practiced without these specific details. In other instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure the understanding of this description. Those of ordinary skill in the art, with the included descriptions, will be able to implement appropriate functionality without undue experimentation.

(21) References in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to implement such feature, structure, or characteristic in connection with other embodiments, whether or not explicitly described.

(22) Particular embodiments are described with reference to FIGS. 7-11B of the drawings, like numerals being used for like and corresponding parts of the various drawings. LTE and NR are used throughout this disclosure as an example cellular system, but the ideas presented herein may apply to other wireless communication systems as well.

(23) FIG. 7 is a block diagram illustrating an example wireless network, according to a particular embodiment. Wireless network 100 includes one or more wireless devices 110 (such as mobile phones, smart phones, laptop computers, tablet computers, MTC devices, V2X devices, or any other devices that can provide wireless communication) and a plurality of network nodes 120 (such as base stations or eNodeBs). Wireless device 110 may also be referred to as a UE. Network node 120 serves coverage area 115 (also referred to as cell 115).

(24) In general, wireless devices 110 that are within coverage of network node 120 (e.g., within cell 115 served by network node 120) communicate with network node 120 by transmitting and receiving wireless signals 130. For example, wireless devices 110 and network node 120 may communicate wireless signals 130 containing voice traffic, data traffic, and/or control signals.

(25) A network node 120 communicating voice traffic, data traffic, and/or control signals to wireless device 110 may be referred to as a serving network node 120 for the wireless device 110. Communication between wireless device 110 and network node 120 may be referred to as cellular communication. Wireless signals 130 may include both downlink transmissions (from network node 120 to wireless devices 110) and uplink transmissions (from wireless devices 110 to network node 120). In LTE, the interface for communicating wireless signals between network node 120 and wireless device 110 may be referred to as a Uu interface.

(26) Each network node 120 may have a single transmitter or multiple transmitters for transmitting signals 130 to wireless devices 110. In some embodiments, network node 120 may comprise a multi-input multi-output (MIMO) system. For example, network node may include a multi-panel or multi-TRP antenna system. Similarly, each wireless device 110 may have a single receiver or multiple receivers for receiving signals 130 from network nodes 120 or other wireless devices 110.

(27) Wireless devices 110 may communicate with each other (i.e., D2D operation) by transmitting and receiving wireless signals 140. For example, wireless device 110a may communicate with wireless device 110b using wireless signal 140. Wireless signal 140 may also be referred to as sidelink 140. Communication between two wireless devices 110 may be referred to as D2D communication or sidelink communication. In LTE, the interface for communicating wireless signal 140 between wireless devices 110 may be referred to as a PC5 interface.

(28) Wireless signals 130 and 140 may be transmitted on time-frequency resources. The time-frequency resources may be partitioned into radio frames, subframes, slots, and/or mini-slots. Data may be scheduled for transmission based on the partitions. For example, data transmissions may be scheduled based on subframe, slot, or mini-slot.

(29) Wireless device 110, network node 120, or any other component of network 100 that transmits wireless signals may be referred to as a wireless transmitter. Wireless device 110, network node 120, or any other component of network 100 that receives wireless signals may be referred to as a wireless receiver.

(30) Wireless signals 130 may include reference signals, such as CSI-RS. Network node 120 may transmit one or more CSI-RS signal on a set of time-frequency resource elements (REs) associated with an antenna port. Wireless device 110 may be configured to receive and measure the CSI-RS. Wireless device 110 may transmit CSI reports to one or more network nodes 120.

(31) For example, network node 120 may transmit, to wireless device 110, a first CSI-RS in a first CSI-RS resource of a set of at least two CSI-RS resources from a first antenna subset and a second CSI-RS in a second CSI-RS resource in the set of at least two CSI-RS resources from a second antenna subset. An antenna subset is one or more antenna elements comprised on at least a single antenna panel comprising an antenna array. A single antenna panel may be associated with a single TRP. A multi-panel array may be associated with a single TRP, wherein an antenna subset may comprise one or more antenna panels.

(32) In particular embodiments, wireless device 110 may configured (e.g., preconfigured, or dynamically configured via signaling from another network element, such as network node 120) with two or more CSI-RS resources in a CSI-RS resource set. Wireless device 110 may select at least two CSI-RS resources from the CSI-RS resource set, determine a preferred precoder matrix for each of the selected CSI-RS resources, and transmit a CSI report to network node 120 indicating each of the selected CSI-RS resources and the determined preferred precoder matrix for each of the selected CSI-RS resources. Wireless device 110 may calculate a channel estimate for each of the selected CSI-RS resources and determine a CQI corresponding to a hypothetical transmission from a plurality of effective channels. The effective channels depend on the preferred precoder matrices and channel estimate for each of the selected CSI-RS resources. Layers transmitted through the effective channels mutually interfere. The CSI report further indicates the determined CQI for each of the selected CSI-RS resources.

(33) Network node 120 may receive, from wireless device 110, a CSI report comprising a first preferred precoder matrix associated with the first CSI-RS resource and a second preferred precoder matrix associated with the second CSI-RS resource. The CSI report may further comprise a CQI associated with each of the first and second preferred precoder matrices. The antenna subsets belong to different transmission points or belong to different antenna panels of the same transmission point. In particular embodiments, wireless device 110 may receive CSI-RS and report CSI according to any of the examples and embodiments described with respect to FIGS. 8-11B.

(34) In wireless network 100, each network node 120 may use any suitable radio access technology, such as long term evolution (LTE), 5G NR, LTE-Advanced, UMTS, HSPA, GSM, cdma2000, NR, WiMax, WiFi, and/or other suitable radio access technology. Wireless network 100 may include any suitable combination of one or more radio access technologies. For purposes of example, various embodiments may be described within the context of certain radio access technologies. However, the scope of the disclosure is not limited to the examples and other embodiments could use different radio access technologies.

(35) As described above, embodiments of a wireless network may include one or more wireless devices and one or more different types of radio network nodes capable of communicating with the wireless devices. The network may also include any additional elements suitable to support communication between wireless devices or between a wireless device and another communication device (such as a landline telephone). A wireless device may include any suitable combination of hardware and/or software. For example, in particular embodiments, a wireless device, such as wireless device 110, may include the components described with respect to FIG. 10A below. Similarly, a network node may include any suitable combination of hardware and/or software. For example, in particular embodiments, a network node, such as network node 120, may include the components described with respect to FIG. 11A below.

(36) Particular embodiments include CSI feedback to support non-coherent joint transmission (NC-JT) from multiple panels or multiple transmission points. With NC-JT, separate layers are transmitted from each antenna panel or transmission/reception point (TRP) to increase the transmission rank at the UE and correspondingly increase the achievable data rate. A particular benefit of non-coherent JT is to facilitate higher rank transmission in the case where the UE is rank-constrained, e.g. by being line-of-sight (LOS) to the serving transmission point or if the serving transmission point only supports a few layers. By transmitting additional layers from a non-serving transmission point, the UE's peak rate can be increased.

(37) For NC-JT to be beneficial, accurate link adaptation is required as there can be significant inter-layer interference between the transmissions from the multiple TRPs or panels. Furthermore, it is beneficial to select the transmission rank and precoding of the participating TRPs jointly so that an optimal transmission setting may be used.

(38) In some embodiments, a UE is configured to measure on a number of non-zero power (NZP) CSI-RS resources, where each CSI-RS resource comprises a number of CSI-RS antenna ports. Each CSI-RS resource may be associated with a different TRP or antenna panel. In some embodiments, the CSI-RS carried in a CSI-RS resource may be transmitted from different antenna subsets of the antenna array of a TRP in a non-precoded fashion, while in other embodiments, the CSI-RS are transmitted from all antennas of the antenna array of a TRP in a beamformed fashion.

(39) Some embodiments use the NR CSI framework and configure the UE with a CSI Report Setting that is linked with one Resource Setting for channel measurement. The Resource Setting may comprise a resource set with multiple CSI-RS resources, where each CSI-RS resource corresponds to a separate TRP.

(40) In other embodiments, the UE is configured with a CSI Report Setting linked with several Resource Settings for channel measurement where each Resource Setting is associated with a separate TRP. Each Resource Setting may comprise a set of multiple CSI-RS resources, or they may comprise a set of a single CSI-RS resource.

(41) Regardless of how the CSI-RS resources are configured in the CSI framework and whether they belong to the same Resource Setting, the UE may in some embodiments, select a number of CSI-RS resources corresponding to a number of TRPs to indicate that a NC-JT from the TRPs is desired. In some embodiments, the selection is made with one or more CSI-RS Resource Indicator (CRI).

(42) For example, the UE may report a “Number of Resources Indicator” (NRI), which indicates how many resources are selected along with a set of the selected CRIs: {CRI.sub.1, . . . , CRI.sub.NRI}. Alternatively, the CRI selection may be reported using a bitmap with each bit corresponding to a CSI-RS resource. Setting the corresponding bit to one indicates that the resource is selected.

(43) In other embodiments, each TRP transmits CSI-RS in several CSI-RS resources (if for example each TRP corresponds to a Resource Setting which in turn comprises one or more set of CSI-RS resources) corresponding to different beams in a beam sweep transmitted from a TRP. The UE may select both which TRPs it desires to participate in the NC-JT as well as which CSI-RS resource should be used per TRP. In some such embodiments, the TRP selection is made with one or more separate Resource Setting Indicator (RSI), while the selection of a CSI-RS resource per TRP (i.e., within the set of CSI-RS resources within a Resource Setting) is made with a CRI.

(44) In some embodiments, the TRP selection is made with a single hypothesis indicator (HI). In some embodiments, the UE is configured with a set of possible hypotheses for dynamic (transmission) point selection and NC-JT in the CSI Report Setting, for example according to Table 1 below where a ‘1’ indicates that a TRP is transmitting and a ‘0’ indicates the opposite. In the example, the selection of HI indicates which TRPs the UE desires to participate in the transmission.

(45) In some embodiments, the HI selection corresponds to selection of one or more Resource Setting, where additionally a CSI-RS resource within each Resource Setting may be selected. In other embodiments, the HI selection corresponds to selection of one or more CSI-RS resources and is functionally equivalent to indicating multiple CRIs. However, by preconfiguring a number of hypotheses, the signaling overhead may be reduced and additionally the number of possible hypotheses a UE may select can be constrained. For example, the network may only support NC-JT from a smaller number of TRPs than what the UE is configured to measure on (for instance, maximum two TRPs out of the three in the example below, in that case, the network may not configure HI=7). In another embodiment, the UE is configured to report multiple CSIs corresponding to multiple hypotheses in the same CSI report.

(46) TABLE-US-00001 TABLE 1 Example of DPS and NC-JT hypotheses Hypothesis Indicator (HI) TRP #1 TRP #2 TRP #3 1 1 0 0 2 0 1 0 3 0 0 1 4 1 1 0 5 0 1 1 6 1 0 1 7 1 1 1

(47) In other embodiments, the UE is configured to report CSI for a certain NC-JT hypothesis and on the basis that the configured Resource Settings or NZP CSI-RS resources shall participate in the NC-JT.

(48) Each CSI-RS resource may be associated with a separate quasi-colocation (QCL) assumption. For example, it may be assumed that antenna ports within a CSI-RS resource are transmitted from a single TRP, and thus are quasi-colocated, but ports in different CSI-RS resources cannot be assumed to be transmitted from a single TRP, and therefore cannot be assumed quasi-colocated.

(49) Each CSI-RS resource is associated with a precoder codebook. In some embodiments, the precoder codebook is a parametrized codebook that depends of the port layout (N.sub.1, N.sub.2) of the CSI-RS resource, where the number of ports in the CSI-RS resource is P=2N.sub.1N.sub.2. In some embodiments, the port layout is associated with the CSI-RS resource in the Resource Setting and only a codebook Type (such as NR Type I or Type II) is identified in the Report Setting. In some embodiments, a codebook (which may be a function of the port layout) is identified for each linked Resource Setting in the CSI Report Setting.

(50) For each of the selected CSI-RS resources, the UE calculates a preferred precoder matrix from the associated codebook, under the assumption that transmission occurs from all of the CSI-RS resources simultaneously. The resulting rank the UE shall select for the hypothetical transmission is thus the sum of the per-resource ranks: ν.sub.TOT=Σ.sub.k×1.sup.Kν.sub.k, where ν.sub.k is the rank of the precoder hypothesis for the selected CSI-RS resource k and K is the number of selected resources. The UE makes the precoder selection, on the basis that the layers corresponding to different CSI-RS resources mutually interfere.

(51) For example, if W.sub.k is the desired precoder matrix of rank ν.sub.k for CSI-RS resource k∈{1 . . . K} and H.sub.k is the channel estimate of the CSI-RS ports of resource k, the following effective channel is used for the hypothetical PDSCH transmission when determining PMI and CQI:

(52) $H_{e f f} = [H_{1} ... H_{K}] [\begin{matrix} W_{1} & .Math. & 0 \\ .Math. & ⋱ & .Math. \\ 0 & .Math. & W_{K} \end{matrix}] = [H_{1} W_{1} ... H_{K} W_{K}] .$

(53) In specification language, this may be described as what correspondence between CSI-RS ports and DMRS ports shall be assumed by the UE for the hypothetical transmission when determining CQI. Assuming LTE port numbering such that DMRS antenna ports are numbered between 7-14 and CSI-RS antenna ports are numbered between 15-31, the specification text may look as follows:

(54) PDSCH signals on antenna ports {p.sub.k, p.sub.k+1}, where p.sub.k=7+Σ.sub.l=1.sup.k−1v.sub.l would result in signals equivalent to corresponding symbols transmitted on antenna ports {15, . . . , 14+P.sub.k} corresponding to CSI-RS resource k in a set of K CSI-RS resources, as given by
[y.sup.(15) . . . y.sup.(14+P.sup.k.sup.)].sup.T=W.sub.k[x.sup.(p.sup.k.sup.). . . x.sup.(p.sup.k+1.sup.)].sup.T
where x.sup.(7), . . . , x.sup.(6+v.sup.TOT.sup.) with v.sub.TOT×Σ.sub.k=1.sup.Kv.sub.k is a vector of symbols, where each symbol corresponds to a layer to be transmitted to the UE and contains all layers from all TRPs transmitting the PDSCH to the UE. In some embodiments, the vector x may correspond to the vector x from the layer mapping in Subclause 6.3.3.2 of 3GPP technical specification 36.211, e.g. a set of layers being a subset of all layers from all TRPs.

(55) In some embodiments, indicating the preferred precoder matrix may comprise determining a PMI and RI for each selected CSI-RS resource. If a multi-stage codebook and frequency-selective precoding is used, several precoder matrices may be indicated with multiple PMI, for instance, W.sub.k(f)=W.sub.1,k W.sub.2,k (f).

(56) The UE will then calculate a Channel Quality Indicator (CQI) corresponding to the preferred precoders and under the assumption that layers corresponding to the selected CSI-RS resources mutually interfere. Such mutual interference may be calculated based on Equation 1 using y=H.sub.effx, where y is a hypothesized received signal of a PDSCH comprising the mutual interference among the MIMO layers in x transmitted on the TRPs hypothesized to be transmitting the PDSCH to the UE.

(57) In NR, NC-JT transmission from one or more TRPs can be achieved in two ways: either a single PDSCH is transmitted, where the layers within the PDSCH are transmitted from different TRPs, or multiple PDSCHs are transmitted each from a separate TRP. As a codeword-to-layer mapping is applied within a PDSCH, different number of layers per codeword, and correspondingly per CQI (where one codeword maps to one CQI), may be used for the same number of layers, depending on which way is used. Thus, in an embodiment, the codeword-to-layer mapping as well as the number of CQIs to calculate is indicated in the Report Setting, so that the reported CQI correspond to the subsequent PDSCH transmission.

(58) In another embodiment, a non-ideal backhaul link between the TRPs participating in the NC-JT is assumed. In this case, a separate CSI report may be transmitted to each TRP, comprising only the PMI(s), RI and CQI(s) corresponding to that TRP. In other embodiments, a single CSI report is transmitted comprising the PMIs, RIs and CQIs corresponding to the different resources.

(59) FIG. 8 illustrates an example of non-coherent multi-panel/TRP transmission, according to some embodiments. The UE is configured with five 2-port CSI-RS resources and selects two resources (resources #1 and #5).

(60) The examples and embodiments described above may be generalized by the flowcharts in FIGS. 9A and 9B.

(61) FIG. 9A is flow diagram illustrating an example method in a user equipment, according to some embodiments. In particular embodiments, one or more steps of FIG. 9A may be performed by wireless device 110 of network 100 described with respect to FIG. 7.

(62) The method may begin at step 910, where the UE obtains a CSI report configuration. For example, in some embodiments wireless device 110 may receive a report configuration from network node 120. The CSI report configuration may include any suitable configuration information for instructing the UE how to measure CSI-RS resources and how to report the measurements to the network node.

(63) In some embodiments, the CSI report configuration may include possible hypotheses for combinations of one or more CSI-RS resources. For example, the report configuration may include a Hypothesis Indicator (HI) as described above with respect to Table 1. In another example, the UE network may transmit CSI-RS in four CSI-RS resources. The CSI report configuration may include an indicator with values 1, 2, or 3. If the indicator value is 2, for example, then the UE reports CSI information (e.g., PMI/CQI/RI) for two CSI-RS resources.

(64) In some embodiments, the UE may be preconfigured with CSI report configuration information and obtaining the CSI report configuration may comprise reading the CSI report configuration information from memory or storage.

(65) In some embodiments, the configuration information may include an indication of a codeword-to-layer mapping for use when determining the CQI.

(66) At step 912, the UE may receive an instruction to measure a set of CSI-RS resources. For example, wireless device 110 may receive an instruction from network node 120 to measure CSI-RS on a set of N CSI-RS resources. In some embodiments, each CSI-RS resource may carry one or more CSI-RS.

(67) In some embodiments, wireless device 110 may be preconfigured with a set of CSI-RS resources and a schedule for measuring the CSI-RS resources. In some embodiments, wireless device 110 may be preconfigured with a default configuration and may receive instructions to override the default configuration.

(68) At step 914, the UE may calculate a channel estimate for each of the CSI-RS resources in the set. For example, wireless device 110 may measure and determine a channel estimate for each CSI-RS.

(69) At step 916, the UE selects at least two CSI-RS resources from the set of CSI-RS resources. For example, wireless device 110 may select a subset K of CSI-RS from a set of N CSI-RS. K is less than or equal to N (e.g., in some embodiments the subset may include the entire set) and greater than or equal to 2. Wireless device 100 may select the subset according to any of the examples or embodiments described above. For example, selecting the subset of CSI-RS resources may comprise selecting a plurality of CSI-RS resource indicators (CRIs), or selecting a plurality of Resource Settings. The selection may be determined based on a hypothesis indicator.

(70) At step 918, the UE determines, for each of the selected CSI-RS resources, one or more preferred precoder matrices. For example, wireless device 110 may determine one or more preferred precoder matrices according to any of the examples or embodiments described above.

(71) As one example, the determined precoder may be a single wideband precoder for the entire system bandwidth. As another example, the UE may determine multiple precoders for a CSI-resource. The multiple precoders may each comprise frequency selective (or subband) precoders.

(72) At step 920, the UE may determine a CQI corresponding to a hypothetical transmission from a number of effective channels. The effective channels depend on the preferred precoder matrices and channel estimate for each of the CSI-RS resources in the subset. Layers transmitted through the effective channels mutually interfere. For example, wireless device 110 may determine a CQI based on the preferred precoder matrices and channel estimate for the subset of CSI-RS resources according to any of the examples or embodiments described above.

(73) At step 922, the UE transmits a CSI report to one or more network nodes. Each CSI report may comprise one or more preferred precoder matrices and the one or more CQI. For example, wireless device 110 may transmit a CSI report to network node 120 according to any of the embodiments and examples described above. In some embodiments, the CSI report may include multiple messages (e.g., one message per CSI-RS resource). The multiple message may be sent to one network element, or the message may be sent to different network elements, each one responsible for one or more of the TRPs or antenna panels.

(74) Modifications, additions, or omissions may be made to method 900 of FIG. 9A. Additionally, one or more steps in the method of FIG. 9A may be performed in parallel or in any suitable order. The steps may be repeated over time as necessary.

(75) FIG. 9B is flow diagram illustrating an example method in a network node, according to some embodiments. In particular embodiments, one or more steps of FIG. 9B may be performed by network node 120 of network 100 described with respect to FIG. 7.

(76) The method may begin at step 952, where the network node transmits a CSI report configuration to user equipment. For example, network node 120 may transmit a CSI report configuration to wireless device 110. The CSI report configuration is described in more detail above with respect to step 910 of FIG. 9A.

(77) At step 954, the network node transmits a set of CSI-RS resources from a plurality of transmission points to a wireless device, for example, a first CSI-RS in a first CSI-RS resource of a set of at least two CSI-RS resources from a first antenna subset and a second CSI-RS in a second CSI-RS resource in the set of at least two CSI-RS resources from a second antenna subset. For example, network node 120 may transmit a set of CSI-RS to wireless device 110 using three transmission points. A transmission point may refer to a TRP, an antenna panel, etc. Network node 120 may transmit a first CSI-RS in a first CRI-RS resource from the first TRP, a second CSI-RS in a second CSI-RS resource from the second TRP, and so on. Since the first and second antenna subsets may comprise a first and second set of spatially multiplexed layers, respectively, wherein the first and second set of layers are different, each of the transmissions may be joint (i.e., at the same time) and non-coherent (i.e., may interfere with each other).

(78) At step 956, the network node receives, from the wireless device, a CSI report comprising a first preferred precoder matrix associated with the first CSI-RS resource and a second preferred precoder matrix associated with the second CSI-RS resource. The CSI report may further comprise a CQI associated with each of the first and second preferred precoder matrices. For example, network node 120 may receive a CSI report from wireless device 110. Wireless device 110 may determine the CSI report according to any of the examples and embodiments described above.

(79) Modifications, additions, or omissions may be made to method 950 of FIG. 9B. Additionally, one or more steps in the method of FIG. 9B may be performed in parallel or in any suitable order. The steps may be repeated over time as necessary.

(80) FIG. 10A is a block diagram illustrating an example embodiment of a wireless device. The wireless device is an example of the wireless devices 110 illustrated in FIG. 7. In particular embodiments, the wireless device is capable of receiving an instruction to measure a set of CSI-RS resources. Each CSI-RS resource of the set of CSI resources carries a CSI-RS. The wireless device may be further capable of calculating a channel estimate for each of the CSI-RS resources in the set; determining, for each of the CSI-RS resources in the set, one or more preferred precoder matrices; determining CQI corresponding to a hypothetical transmission from a number of effective channels, where the effective channels depend on the preferred precoder matrices and channel estimate for each of the CSI-RS resources, and layers transmitted through the effective channels mutually interfere; and transmitting one or more CSI reports to one or more network nodes. Each CSI report may comprise a plurality of one or more preferred precoder matrices and the one or more CQI.

(81) Particular examples of a wireless device include a mobile phone, a smart phone, a PDA (Personal Digital Assistant), a portable computer (e.g., laptop, tablet), a sensor, a modem, a machine type (MTC) device/machine to machine (M2M) device, laptop embedded equipment (LEE), laptop mounted equipment (LME), USB dongles, a device-to-device capable device, a vehicle-to-vehicle device, or any other device that can provide wireless communication. The wireless device includes transceiver 1010, processing circuitry 1020, memory 1030, and power source 1040. In some embodiments, transceiver 1010 facilitates transmitting wireless signals to and receiving wireless signals from wireless network node 120 (e.g., via an antenna), processing circuitry 1020 executes instructions to provide some or all of the functionality described herein as provided by the wireless device, and memory 1030 stores the instructions executed by processing circuitry 1020. Power source 1040 supplies electrical power to one or more of the components of wireless device 110, such as transceiver 1010, processing circuitry 1020, and/or memory 1030.

(82) Processing circuitry 1020 includes any suitable combination of hardware and software implemented in one or more integrated circuits or modules to execute instructions and manipulate data to perform some or all of the described functions of the wireless device. In some embodiments, processing circuitry 1020 may include, for example, one or more computers, one more programmable logic devices, one or more central processing units (CPUs), one or more microprocessors, one or more applications, and/or other logic, and/or any suitable combination of the preceding. Processing circuitry 1020 may include analog and/or digital circuitry configured to perform some or all of the described functions of wireless device 110. For example, processing circuitry 1020 may include resistors, capacitors, inductors, transistors, diodes, and/or any other suitable circuit components.

(83) Memory 1030 is generally operable to store computer executable code and data. Examples of memory 1030 include computer memory (e.g., Random Access Memory (RAM) or Read Only Memory (ROM)), mass storage media (e.g., a hard disk), removable storage media (e.g., a Compact Disk (CD) or a Digital Video Disk (DVD)), and/or or any other volatile or non-volatile, non-transitory computer-readable and/or computer-executable memory devices that store information.

(84) Power source 1040 is generally operable to supply electrical power to the components of wireless device 110. Power source 1040 may include any suitable type of battery, such as lithium-ion, lithium-air, lithium polymer, nickel cadmium, nickel metal hydride, or any other suitable type of battery for supplying power to a wireless device.

(85) Other embodiments of the wireless device may include additional components (beyond those shown in FIG. 10A) responsible for providing certain aspects of the wireless device's functionality, including any of the functionality described above and/or any additional functionality (including any functionality necessary to support the solution described above).

(86) FIG. 10B is a block diagram illustrating example components of a wireless device 110. The components may include receiving module 1050, determining module 1052, and transmitting module 1054.

(87) Receiving module 1050 may perform the receiving functions of wireless device 110. For example, receiving module 1050 may receive a CSI configuration and/or an instruction to measure a set of CSI-RS resources according to any of the examples and embodiments described above (e.g., steps 910 and 912 of FIG. 9A). In certain embodiments, receiving module 1050 may include or be included in processing circuitry 1020. In particular embodiments, receiving module 1050 may communicate with determining module 1052 and transmitting module 1054.

(88) Determining module 1052 may perform the determining functions of wireless device 110. For example, determining module 1052 may select two or more CSI-RS resources from a set of CSI-RS resources, determine a precoder matrix for each of the selected CSI-RS resources, determine a channel estimate for each of the selected CSI-RS resources, and/or determine a CQI corresponding to a hypothetical transmission from a number of effective channels, where the effective channels depend on the determined precoder matrices and channel estimate for each of the selected CSI-RS resources, and layers transmitted through the effective channels mutually interfere (e.g., steps 916-920 of FIG. 9A). In certain embodiments, determining module 1052 may include or be included in processing circuitry 1020. In particular embodiments, determining module 1052 may communicate with receiving module 1050 and transmitting module 1054.

(89) Transmitting module 1054 may perform the transmitting functions of wireless device 110. For example, transmitting module 1054 may transmit one or more CSI reports to one or more network nodes according to any of the examples and embodiments described above (e.g., step 922 of FIG. 9A). In certain embodiments, transmitting module 1054 may include or be included in processing circuitry 1020. In particular embodiments, transmitting module 1054 may communicate with receiving module 1050 and determining module 1052.

(90) FIG. 11A is a block diagram illustrating an example embodiment of a network node. The network node is an example of the network node 120 illustrated in FIG. 7. In particular embodiments, the network node is capable of transmitting two or more CSI-RS to a wireless device and receiving a CSI report from a wireless device with different channel state information for two or more CSI-RS.

(91) Network node 120 can be an eNodeB, a nodeB, gNB, a base station, a wireless access point (e.g., a Wi-Fi access point), a low power node, a base transceiver station (BTS), a transmission point or node, a remote RF unit (RRU), a remote radio head (RRH), or other radio access node. The network node includes at least one transceiver 1110, processor or processing circuitry 1120, at least one memory 1130, and at least one network interface 1140. Transceiver 1110 facilitates transmitting wireless signals to and receiving wireless signals from a wireless device, such as wireless devices 110 (e.g., via an antenna); processing circuitry 1120 executes instructions to provide some or all of the functionality described above as being provided by a network node 120; memory 1130 stores the instructions executed by processing circuitry 1120; and network interface 1140 communicates signals to backend network components, such as a gateway, switch, router, Internet, Public Switched Telephone Network (PSTN), controller, and/or other network nodes 120. Processing circuitry 1120 and memory 1130 can be of the same types as described with respect to processing circuitry 1020 and memory 1030 of FIG. 10A above.

(92) In some embodiments, network interface 1140 is communicatively coupled to processing circuitry 1120 and refers to any suitable device operable to receive input for network node 120, send output from network node 120, perform suitable processing of the input or output or both, communicate to other devices, or any combination of the preceding. Network interface 1140 includes appropriate hardware (e.g., port, modem, network interface card, etc.) and software, including protocol conversion and data processing capabilities, to communicate through a network.

(93) Other embodiments of network node 120 include additional components (beyond those shown in FIG. 11A) responsible for providing certain aspects of the network node's functionality, including any of the functionality described above and/or any additional functionality (including any functionality necessary to support the solution described above). The various different types of network nodes may include components having the same physical hardware but configured (e.g., via programming) to support different radio access technologies, or may represent partly or entirely different physical components.

(94) FIG. 11B is a block diagram illustrating example components of a network node 120. The components may include transmitting module 1150 and receiving module 1152.

(95) Transmitting module 1150 may perform the transmitting functions of network node 120. For example, transmitting module 1150 may transmit a set of CSI-RS resources to a wireless device according to any of the examples and embodiments described above (e.g., step 954 of FIG. 9A). Transmitting module 1150 may transmit a CSI report configuration to a wireless device (e.g., step 952 of FIG. 9A). In certain embodiments, transmitting module 1150 may include or be included in processing circuitry 1120. In particular embodiments, transmitting module 1150 may communicate with receiving module 1152.

(96) Receiving module 1152 may perform the receiving functions of network node 120. For example, receiving module 1152 may receive a CSI report according to any of the examples and embodiments described above (e.g., step 956 of FIG. 9A). In certain embodiments, receiving module 1152 may include or be included in processing circuitry 1120. In particular embodiments, receiving module 1152 may communicate with transmitting module 1150.

(97) Modifications, additions, or omissions may be made to the systems and apparatuses disclosed herein without departing from the scope of the invention. The components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses may be performed by more, fewer, or other components. Additionally, operations of the systems and apparatuses may be performed using any suitable logic comprising software, hardware, and/or other logic. As used in this document, “each” refers to each member of a set or each member of a subset of a set.

(98) Modifications, additions, or omissions may be made to the methods disclosed herein without departing from the scope of the invention. The methods may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order.

(99) Although this disclosure has been described in terms of certain embodiments, alterations and permutations of the embodiments will be apparent to those skilled in the art. Accordingly, the above description of the embodiments does not constrain this disclosure. Other changes, substitutions, and alterations are possible without departing from the spirit and scope of this disclosure, as defined by the claims below.

(100) The examples below provide a non-limiting example of how certain aspects of the embodiments may be implemented within the framework of a specific communication standard. In particular, the examples provide a non-limiting example of how particular embodiments could be implemented within the framework of a 3GPP TSG RAN standard. The changes are merely intended to illustrate how certain aspects of the embodiments could be implemented in a particular standard. However, the embodiments could also be implemented in other suitable manners, both in the 3GPP Specification and in other specifications or standards.

(101) For example, a standard may include the following attributes related to a CSI framework. Regarding RS and interference measurement setting, a specification may rename ‘RS setting” as “Resource setting,” which comprises configuration for a signal used for channel and/or interference measurement.

(102) Regarding other terminology, a UE can be configured with N≥1 CSI reporting settings, M≥1 Resource settings, and 1 CSI measurement setting, where the CSI measurement setting includes L≥1 links. Each of the L links corresponds to a CSI reporting setting and a Resource setting.

(103) The following configuration parameters may be signaled via radio resource control (RRC) at least for CSI acquisition. N, M, and L may be indicated either implicitly or explicitly. In each CSI reporting setting, at least reported CSI parameter(s), CSI Type (I or II) if reported, codebook configuration including codebook subset restriction, time-domain behavior, frequency granularity for CQI and PMI, measurement restriction configurations may be signaled. In each Resource setting, a configuration of S≥1 CSI-RS resource set(s) may be signaled. Each set may correspond to different selections from a pool of all CSI-RS resources configured to the UE. A configuration of Ks≥1 CSI-RS resources for each set s, including at least mapping to REs, the number of ports, time-domain behavior, etc., may be signaled. In each of the L links in CSI measurement setting, CSI reporting setting indication, Resource setting indication, and/or quantity to be measured (either channel or interference) may be signaled. One CSI reporting setting can be linked with one or multiple Resource settings. Multiple CSI reporting settings can be linked with the same Resource setting.

(104) The following may be dynamically selected by L1 or L2 signaling, if applicable: (a) one or multiple CSI reporting settings within the CSI measurement setting; (b) one or multiple CSI-RS resource sets selected from at least one Resource setting; and (c) one or multiple CSI-RS resources selected from at least one CSI-RS resource set.

(105) Regarding NR reception, a single NR-PDCCH may schedule a single NR-PDSCH where separate layers are transmitted from separate TRPs. Multiple NR-PDCCHs each may schedule a respective NR-PDSCH where each NR-PDSCH is transmitted from a separate TRP. The case where a single NR-PDCCH schedules a single NR-PDSCH where each layer is transmitted from all TRPs jointly can be done in a specification-transparent manner. CSI feedback details for the above case can be specified separately.

(106) With non-coherent joint transmission (NC-JT), separate layers are transmitted from each antenna panel or transmission point (TRP) to increase the transmission rank at the UE and correspondingly increase the achievable data rate. The primary benefit of non-coherent JT is to facilitate higher rank transmission where the UE is rank-constrained (e.g., by being line-of-sight (LOS) to the serving transmission point or if the serving transmission point only supports a few layers). By transmitting additional layers from a non-serving transmission point, the UE's peak rate can be increased. For NC-JT to be beneficial though, accurate link adaptation is required as there can be significant inter-layer interference between the transmissions from the multiple TRPs or panels. Furthermore, it is beneficial to select the transmission rank and precoding of the participating TRPs jointly so that an optimal transmission setting can be used.

(107) NC-JT can be supported using the existing CSI framework in NR. For example, a UE could be configured with two CSI Report Settings, each corresponding to a separate TRP, and to feed back a PMI/RI/CQI report corresponding to each TRP corresponding to a single-TRP hypothesis. The reported PMIs can be used directly to precode the transmission from each TRP. However, there are several issues with using the standard-transparent approach: (a) the RIs will likely be chosen too aggressively because they correspond to single-TRP hypothesis and are not selected jointly corresponding to NC-JT hypothesis; (b) the CQIs will be too optimistic because inter-TRP interference is not taken into account; and (c) because PMIs for each TRP are determined independently, PMIs that cause large mutual interference could be selected by the UE.

(108) Thus, a CSI Report Setting that supports NC-JT in the NR CSI framework is beneficial. For optimal performance, the UE may dynamically select between single-TRP (i.e., DPS) or NC-JT transmission from multiple TRPs. The selection may be fed back in a single CSI report. Even if the UE indicates that it prefers NC-JT transmission, however, the UE cannot be certain that the network can accommodate NC-JT transmission and single-TRP transmission may be applied instead. Thus, the network needs CSI available for both NC-JT and single-TRP hypothesis, which means that several CSI Report Settings may be configured for the UE.

(109) Particular 3GPP working groups considered the following options for CSI enhancements for NC-JT CSI feedback. Option 1 uses a single CSI process with K>1 CSI-RS resources. Channel measurement and inter-TP interference measurement can be flexibly configured based on the selection of these K CSI-RS resource for different hypothesis.

(110) Option 2 uses a single CSI process with enhanced codebook and an aggregated CSI resource from multiple CSI-RS resources. CSI-RS resources from multiple TPs are aggregated to form one CSI-RS resource. An enhanced codebook with the codeword structure considering non-coherent joint transmission can be applied to the aggregated channel measured from the aggregated CSI-RS. An example of the codeword structure considering two-TP joint transmission is

(111) $W = [\begin{matrix} W_{a} & 0 \\ 0 & W_{b} \end{matrix}],$
where W.sub.a and W.sub.b are the precoding matrices applied to the two TPs respectively.

(112) Option 3 uses multiple CSI processes with dependency among CSI processes. For the multiple CSI processes mechanism, dependency among the CSI-processes can be considered. In this way, different interference assumption for each TP is indicated. More specially, the calculated CSI of one CSI process, e.g., PMI, from the first TP can be treated as configuration of interferer during the CSI calculation for another CSI process (i.e., for another TP). This indication may be used to improve the CSI accuracy assuming advanced receiver, e.g., SIC.

(113) Because NR uses a flexible CSI framework, a preferred approach to support NC-JT CSI feedback may be a mixture of the first two options above. Thus, a particular CSI framework may include TRPs or antenna panels that transmit their CSI-RS in separate CSI resources rather than with different ports in the same CSI-RS resource, because the CSI-RS from different TRPs cannot be assumed to be QCL, and further, a QCL indication between CSI-RS ports and DMRS ports for each TRP may be needed. To indicate QCL with corresponding DMRS, each TRP may transmit separate CSI-RS resources.

(114) Different TRPs may be equipped with different antennas (e.g., having a different number of ports or port layouts). Therefore, following the Option 2 above directly may be cumbersome, because a variety of different codebooks for multi-TRP would have to be defined. Rather, it is simpler to define a separate codebook for each TRP that is applied with a CSI-RS resource associated with the TRP, rather than aggregating the CSI-RS resources and applying a joint codebook. TRPs participating in NC-JT can be equipped with different antennas and require different codebooks.

(115) Another consideration is that even if the UE can recommend a NC-JT transmission, the recommendation may not always be optimal, because the UE may desire a low rank transmission. Thus, the UE may be able to dynamically indicate how many TRPs it desires to participate in the NC-JT (including single point transmission hypothesis). Accordingly, the network may configure a maximum number of TRPs/CSI-RS resources and the UE may dynamically select a number of CSI-RS resources to be included in the CSI report. It is beneficial for the UE to dynamically select how many TRPs shall participate in the NC-JT

(116) To calculate CSI for a NC-JT hypothesis, the UE can select a number of CSI-RS resources. Each CSI-RS resource can be associated with a precoder codebook (e.g., a port layout (N.sub.1, N.sub.2)). For each of the selected CSI-RS resources, the UE calculates a preferred precoder matrix from the associated codebook, under the assumption that transmission occurs from all of the CSI-RS resources simultaneously. The resulting rank the UE shall select for the hypothetical transmission is thus the sum of the per-resource ranks: ν.sub.TOT=Σ.sub.k=1.sup.Kν.sub.k, where ν.sub.k is the rank of the precoder hypothesis for selected CSI-RS resource index k and K is the number of selected resources.

(117) The UE makes the precoder selection on the basis that the layers corresponding to different CSI-RS resources mutually interfere. For instance, if W.sub.k is the desired precoder matrix of rank ν.sub.k for CSI-RS resource k∈{1 . . . . K} and H.sub.k is the channel estimate of the CSI-RS ports of resource k, the following effective channels is used for the hypothetical PDSCH transmission when determining PMI and CQI:

(118) $H_{e f f} = [H_{1} ... H_{K}] [\begin{matrix} W_{1} & .Math. & 0 \\ .Math. & ⋱ & .Math. \\ 0 & .Math. & W_{K} \end{matrix}] = [H_{1} W_{1} ... H_{K} W_{K}] .$
Thus, the inter-layer interference across selected CSI-RS resources may be considered. An example of multi-resource selection is illustrated in FIG. 8.

(119) Furthermore, each TRP may use either non-precoded CSI-RS or a set of beamformed CSI-RS. In the latter case, each TRP is associated with a number of CSI-RS resources that is selected with a CRI by the UE. Thus, the selection of a CSI-RS resource within a TRP (or panel) may be differentiated from the selection of multiple CSI-RS resources corresponding to different TRPs for NC-JT.

(120) To efficiently facilitate the differentiation, a CSI Report Setting for NC-JT hypothesis can be linked with several NZP CSI-RS Resource Settings for channel measurement, where each Resource Setting corresponds to a TRP. Within each Resource Setting, the UE could for example be configured with multiple CSI-RS resource sets, each comprising a number of CSI-RS resources, in case the TRP is utilizing beamformed CSI-RS with resource pooling, or, on the other extreme, a single NZP CSI-RS resource in case the TRP utilizes non-precoded CSI-RS. For each (channel) Resource Setting in the CSI Report Setting, there is an association with a precoder codebook (or simply a port layout) to use for the CSI-RS resources within that Resource Setting. The TRP selection is performed by selecting one or more of the configured Resource Settings and for each selected Resource Setting, a PMI/RI and possibly a CRI is determined.

(121) The Resource Setting selection can be performed with a Hypothesis Indicator (HI). For example, a UE may be configured with a set of possible hypotheses for DPS and NC-JT in the CSI Report Setting, for example, according to Table 2 where a ‘1’ indicates that a Resource Setting is selected and a ‘0’ indicates the opposite.

(122) TABLE-US-00002 TABLE 2 Example of DPS and NC-JT hypotheses Hypothesis Resource Setting Resource Setting Resource Setting Indicator (HI) #1 (TRP #1) #2 (TRP #2) #2 (TRP #3) 0 (DPS) 1 0 0 1 (DPS) 0 1 0 2 (DPS) 0 0 1 3 (NC-JT) 1 1 0 4 (NC-JT) 0 1 1 5 (NC-JT) 1 0 1 6 (NC-JT) 1 1 1

(123) By configuring which hypotheses a UE is able to select from in the CSI Report Setting, the network can configure different CSI Report Settings for e.g. DPS and NC-JT and trigger different CSI reports for the different sets of hypotheses. Another possibility is to configure only a single hypothesis, in that case, the UE does not need to feed back an HI.

(124) An example of how the CSI framework supports multi-TRP NC-JT CSI feedback is illustrated in FIG. 12. Each CSI Report Setting corresponds to different sets of configured channel hypotheses.

(125) In general, to support NC-JT CSI feedback, a CSI Report Setting can be linked with more than one Resource Setting for channel measurement. The CSI Report Setting associates each Resource Setting with a precoder codebook. A CSI Report Setting is further configured with a set of hypotheses for channel measurement, wherein each hypothesis selects a subset of the linked Resource Settings for channel measurement and where the UE selects one hypothesis from the set as part of the CSI report. For the selected Resource Settings, the UE determines PMI, RI and if applicable CRI for each Resource Setting jointly, on the basis that the layers from CSI-RS resources in different Resource Settings mutually interfere.

(126) NC-JT may be supported either within a PDSCH, where the different layers of the PDSCH correspond to different TRPs, or using multiple PDSCH each transmitted from a separate TRP. The same CSI framework may be used for both cases, but a difference is what codeword-to-layer mapping to assume and how many CQIs to calculate, because e.g. a rank-4 NC-JT transmission where each TRP transmits two layers each can either be mapped to 1 or 2 codewords depending on if 1 or 2 PDSCH(s) is used. Thus, the UE needs to know what is assumed. This could be configured in the Resource Setting. For CSI feedback with NC-JT hypothesis, the CSI Report Setting may contain information on whether single or multiple PDSCH is assumed for CQI calculation.

(127) Regarding feedback of the CSI report, it simple to consider transmission of a single CSI feedback report containing all PMIs/CQIs, even if multiple PDCCH/PDSCH operation is used (i.e., CSI report is not split up into several per-TRP CSI reports). Even if the TRPs are not perfectly synchronized and, for example, manage their own HARQ buffers requiring independent HARQ-ACK feedback on separate PUCCH transmissions, CSI feedback generally is not as delay-sensitive as HARQ feedback and may be shared by the TRPs over a non-ideal backhaul link (or scheduling information of the uplink resource allocation of the physical channel carrying the CSI report could be shared and the TRPs could independently receive the uplink transmission). Because CSI feedback for NC-JT most likely is aperiodically triggered, and thus carried on PUSCH, the UE may transmit several PUSCHs simultaneously if per-TRP CSI feedback is used, which could become cumbersome from e.g. a power control perspective and should be avoided. Accordingly, CSI feedback for NC-JT may be contained in a single report, and not split up in per-TRP CSI reports on separate PUCCH/PUSCH transmissions.

(128) Abbreviations used in the preceding description include:

(129) 3GPP Third Generation Partnership Project

(130) BTS Base Transceiver Station

(131) CoMP Coordinated Multiple Transmission Point

(132) CQI Channel Quality Indicator

(133) CRC Cyclic Redundancy Check

(134) CRI CSI-RS Resource Indicator

(135) C-RNTI Cell Radio Network Temporary Identifier

(136) CSI Channel State Information

(137) CSI-RS Channel State Information Reference Signal

(138) D2D Device to Device

(139) DCI Downlink Control Information

(140) DFT Discrete Fourier Transform

(141) eNB eNodeB

(142) FDD Frequency Division Duplex

(143) HARQ Hybrid Automatic Repeat Request

(144) LTE Long Term Evolution

(145) MAC Medium Access Control

(146) M2M Machine to Machine

(147) MCS Modulation and Coding Scheme

(148) MIMO Multi-Input Multi-Output

(149) MTC Machine Type Communication

(150) NC-JT Non-Coherent Joint Transmission

(151) NR New Radio

(152) OFDM Orthogonal Frequency Division Multiplexing

(153) PDCCH Physical Downlink Control Channel

(154) PDSCH Physical Downlink Shared Channel

(155) PMI Precoder Matrix Index

(156) PRB Physical Resource Block

(157) PUCCH Physical Uplink Control Channel

(158) PUSCH Physical Uplink Shared Channel

(159) QAM Quadrature Amplitude Modulation

(160) QCL Quasi-Colocation

(161) QPSK Quadrature Phase-Shift Keying

(162) RAN Radio Access Network

(163) RAT Radio Access Technology

(164) RB Resource Block

(165) RBS Radio Base Station

(166) RI Rank Indicator

(167) RNC Radio Network Controller

(168) RRC Radio Resource Control

(169) RRH Remote Radio Head

(170) RRU Remote Radio Unit

(171) SINR Signal-to-Interference-plus-Noise Ratio

(172) SPS Semi Persistent Scheduling

(173) TDD Time Division Duplex

(174) UCI Uplink Control Information

(175) UE User Equipment

(176) UL Uplink

(177) URLLC Ultra-Reliable Low-Latency Communication

(178) UTRAN Universal Terrestrial Radio Access Network

(179) WAN Wireless Access Network

Channel state information for reference signals in a wireless communication system

Assignee

Inventors

Cpc classification

Classification Explorer

H04B7/0456

ELECTRICITY

Classification Explorer

H04B7/0417

ELECTRICITY

Classification Explorer

H04W72/046

ELECTRICITY

Classification Explorer

H04B7/0626

ELECTRICITY

Classification Explorer

H04W72/1273

ELECTRICITY

Classification Explorer

H04B7/0608

ELECTRICITY

Classification Explorer

H04W72/23

ELECTRICITY

Classification Explorer

H04B7/0697

ELECTRICITY

Classification Explorer

H04B7/0691

ELECTRICITY

Classification Explorer

H04B7/0639

ELECTRICITY

Classification Explorer

H04L5/005

ELECTRICITY

Classification Explorer

H04L5/0057

ELECTRICITY

Classification Explorer

H04B7/0802

ELECTRICITY

Classification Explorer

H04W72/541

ELECTRICITY

International classification

Classification Explorer

H04W4/00

ELECTRICITY

Classification Explorer

H04B7/06

ELECTRICITY

Classification Explorer

H04W72/04

ELECTRICITY

Classification Explorer

H04L5/00

ELECTRICITY

Classification Explorer

H04B7/0417

ELECTRICITY

Classification Explorer

H04W72/12

ELECTRICITY

Classification Explorer

H04W72/08

ELECTRICITY

Abstract

Claims

Description