Reference Signal Port Mapping

Abstract

A method for reducing the number of beams required per symbol. The method is implemented by a base station (gNB). The method includes transmitting a reference signal (RS) and receiving a report from a UE (302), where the report identifies a matrix. The method also includes using the identified matrix to transmit data to or schedule the UE. The matrix identified by the UE is equal to (I), where Wps is a port selection matrix, and (II) denotes a Kronecker product.

Description

[Technical field]

[0001] The present disclosure relates to reference signal port mapping. [Background technology]

[0002] 1. Codebook-based Precoding

[0003] Multi-antenna techniques can significantly increase the data rate and reliability of wireless communication systems. Performance is particularly improved when both the transmitter and receiver are equipped with multiple antennas, which results in a multiple-input multiple-output (MIMO) communication channel. Such systems and / or related techniques are typically referred to as MIMO.

[0004] The 3rd Generation Partnership Project (3GPP) New Radio (NR) standard is currently evolving with enhanced MIMO support. The core components in NR are MIMO antenna deployment and support for MIMO-related techniques, such as spatial multiplexing. The spatial multiplexing mode aims for high data rates in favorable channel conditions. An illustration of spatial multiplexing operation is provided in FIG. 1A.

[0005] As can be seen in FIG. 1A, the information carrying symbol vector s is N T ×r matrix W (hereafter referred to as the “precoder matrix”), which is expressed as (N T (N corresponding to antenna ports) TIt serves to distribute the transmission energy among subspaces of a x-dimensional vector space. The precoder matrix is ​​typically selected from a codebook of possible precoder matrices and is typically indicated by a precoder matrix indicator (PMI), which specifies a unique precoder matrix in the codebook for a given number of symbol streams. Each of the r symbols in s corresponds to a layer, and r is called the transmission rank. In this way, spatial multiplexing is achieved since multiple symbols can be transmitted simultaneously on the same time / frequency resource element (TFRE). The number of symbols r is typically adapted to suit the current channel properties.

[0006] NR uses orthogonal frequency division multiplexing (OFDM) in the downlink (and DFT-precoded OFDM in the uplink for rank-1 transmission), and therefore the received N R x1 vector y n But, therefore, y n =H n Ws n +e n It is modeled by, where e n is the noise / interference vector obtained as a realization of a random process. The precoder matrix W may be a wideband precoder, which is either constant over frequency or frequency selective.

[0007] The precoder matrix W is often R ×N T MIMO channel matrix H n , resulting in so-called channel-dependent precoding, which is also commonly referred to as closed-loop precoding, which essentially strives to concentrate the transmission energy in a subspace that is strong in the sense that it transfers most of the transmitted energy to the UE.

[0008] In closed-loop precoding for the NR downlink, the UE sends a recommendation to the NR base station (denoted as gNB) of a suitable precoder matrix to use based on channel measurements in the downlink. The gNB may configure the UE to provide feedback according to CSI-ReportConfig, transmit CSI-RS, and configure the UE to use measurements of the CSI-RS to feed back a recommended precoding matrix that the UE selects from a codebook. A single precoder matrix that is considered to cover a large bandwidth (wideband precoding) may be fed back. It may also be beneficial to feed back a frequency-selective precoding report instead, e.g., several precoder matrices, one per subband, that match the frequency variations of the channel. This is an example of a more general case of channel state information (CSI) feedback, which also encompasses feeding back other information besides the recommended precoder matrix to assist the gNode B in subsequent transmissions to the UE. Such other information may include a channel quality indicator (CQI) as well as a transmission rank indicator (RI). In NR, CSI feedback can be either wideband, where one CSI is reported for the entire channel bandwidth, or frequency-selective, where one CSI is reported for each subband, defined as a number of adjacent resource blocks spanning between 4 PRBs and 32 PRBs, depending on the size of the bandwidth part (BWP).

[0009] Given the CSI feedback from the UE, the gNB determines the transmission parameters it wants to use to transmit data to the UE, including the precoding matrix, transmission rank, and modulation and coding scheme (MCS). These transmission parameters may differ from the recommendation made by the UE. The transmission rank, and therefore the number of spatially multiplexed layers, is reflected in the number of columns of the precoder matrix W. For efficient performance, it is important that a transmission rank that matches the channel properties is selected.

[0010] 2. 2D Antenna Array

[0011] A two-dimensional antenna array has a number of antenna columns, N, corresponding to the horizontal dimension. h and the number of antenna rows corresponding to the vertical dimension, N v and the number of dimensions corresponding to different polarizations, N p Therefore, the total number of antennas is N = N h ×N v ×N p It should be pointed out that the antenna concept is non-limiting in the sense that it can refer to any virtualization (e.g., linear mapping) of a physical antenna element. For example, a pair of physical sub-elements may be fed with the same signal and therefore share the same virtualized antenna port. An example of a 4×4 array with dual polarized antenna elements is shown in FIG. 1B.

[0012] Precoding a signal can be interpreted as multiplying the signal with different precoding (aka "beamforming") weights for each antenna prior to transmission. A common approach is to tailor the precoder matrix to the antenna form factor, i.e., to use N precoder matrix codebooks when designing the codebook. h , N v , and N p The key is to take into account the following:

[0013] The codebook is designed with a particular antenna numbering in mind (or rather a port numbering scheme, where the mapping of antenna ports to physical antennas is up to each deployment). For a given P antenna ports, the precoding codebook is designed such that the P / 2 first antenna ports should map to a set of co-polarized antennas, and the P / 2 last antenna ports are mapped to another set of co-polarized antennas with orthogonal polarization to the first set. This is therefore targeted at dual-polarized antenna arrays. Figure 1C shows an example with 8 antenna ports.

[0014] 3. Channel State Information (CSI) Reference Signal (CSI-RS)

[0015] In CSI measurement and feedback, a CSI reference signal (CSI-RS) is defined. The CSI-RS is transmitted on each antenna port and is used by the UE to measure the downlink channel between each of the transmit antenna ports and each of its receive antenna ports. The transmit antenna ports are also referred to as CSI-RS ports. The supported number of antenna ports in NR is {1, 2, 4, 8, 12, 16, 24, 32}. By measuring the received CSI-RS, the UE can estimate the channel that the CSI-RS is traversing, including the radio propagation channel and the antenna gain. The CSI-RS for the above purpose is also referred to as non-zero power (NZP) CSI-RS.

[0016] CSI-RS may be configured to be transmitted in several resource elements (REs) in a slot and in several slots. Figure 2 shows an example of CSI-RS REs for 12 antenna ports, where one RE per RB per port is shown.

[0017] In addition, an interference measurement resource (IMR) for the UE to measure interference is also specified in NR. The IMR resource includes 4 REs, i.e., either 4 adjacent REs in frequency in the same OFDM symbol, or 2×2 adjacent REs in both time and frequency in a slot. By measuring both the channel based on the NZP CSI-RS and the interference based on the IMR, the UE can estimate the effective channel and noise plus interference to determine the CSI (i.e., rank, precoding matrix, and channel quality). Furthermore, a UE in NR can be configured to measure interference based on one or more NZP CSI-RS resources.

[0018] 3.1 CSI-RS Port Mapping

[0019] There are 18 different CSI-RS resource configurations in NR, where each has a specific number of ports X. See Table 1 below, which is a copy of Table 7.4.1.5.3-1 from 3GPP Technical Specification (TS) 38.211 V16.3.0 ("TS 38.211"). When Code Division Multiplexing (CDM) is applied, the index k i Let k denote the first subcarrier in the PRB used to map the CSI-RS sequence to resource elements, where k is the second subcarrier. i +1. This set of two subcarriers (k i, k i +1) is associated with CDM group j, where the CDM group covers one, two or four OFDM symbols. i’ or i’ +1 indicates the first OFDM symbol in the slot associated with the CDM group. i and l i’ is signaled from the gNB to the UE by RRC signaling when configuring CSI-RS resources.

[0020] When CDM is applied, the size of the CDM group (L) is either 2, 4 or 8, and the total number of CDM groups is given by the setting (k i ,l i’ ), (k i ,l i’ +1) pairs. Thus, a CDM group can refer to a set of two, four or eight antenna ports, where a set of two antenna ports occurs when only CDM in the frequency domain (FD) on two adjacent subcarriers is considered (FD-CDM2).

[0021] According to TS38.211 section 7.4.1.5.3, CSI-RS ports are numbered first within a CDM group and then across CDM groups. The UE shall assume that CSI-RS is transmitted using antenna port p numbered according to: p=3000+s+jL, j=0, 1, ..., N / L-1, s=0, 1,,..., L-1, (Equation 1) where s is the sequence index, L ∈ {1, 2, 4, 8} is the CDM group size, and N is the number of CSI-RS ports. The CDM group index j given in Table 7.4.1.5.3-1 in 38.211 corresponds to the time / frequency location for a given row of the table. TIFF0007652905000001.tif7170. This table is reproduced in Table 1 for convenience. For example, the CSI-RS resource configuration given by row 4 in Table 1 has two CDM groups (j=0, 1) of size L=2, where ports 3000 and 3001 map to the CDM group indicated by k0, and ports 3002 and 3003 map to the CDM group indicated by k0+2. TIFF0007652905000002.tif255170

[0022] 4. CSI Framework in NR

[0023] In NR, a UE may be configured with multiple CSI reporting settings and multiple CSI-RS resource settings. Each resource setting may include multiple resource sets, and each resource set may include up to eight CSI-RS resources. For each CSI reporting setting, the UE feeds back a CSI report. Each CSI reporting setting contains at least the following information: CSI-RS resource set for channel measurements, IMR resource set for interference measurements, CSI-RS resource set for interference measurements, time domain behavior, i.e. periodic, semi-persistent, or aperiodic reporting, frequency granularity, i.e. wideband or subband, CSI parameters to be reported, such as RI, PMI, CQI, and CSI-RS Resource Indicator (CRI), in case of multiple CSI-RS resources in the resource set, codebook type, i.e. Type I or Type II, and codebook subset restrictions, measurement restrictions, and subband size (one out of two possible subband sizes is indicated, the value range depends on the bandwidth of the BWP, and one CQI / PMI is fed back per subband (if configured for subband reporting)). and may contain.

[0024] When a CSI-RS resource set in a CSI reporting setting includes multiple CSI-RS resources, one of the CSI-RS resources is selected by the UE, and a CSI-RS Resource Indicator (CRI) is reported by the UE to indicate to the gNB regarding the selected CSI-RS resource in the resource set, along with the RI, PMI, and CQI associated with the selected CSI-RS resource.

[0025] In aperiodic CSI reporting in NR, two or more CSI reporting settings, each with a different CSI-RS resource set for channel measurements and / or a different resource set for interference measurements, may be configured and triggered simultaneously, in which case multiple CSI reports are aggregated and sent from the UE to the gNB in ​​a single physical uplink shared channel (PUSCH) transmission.

[0026] 5. NR Release 16 (Rel-16) Extended Type II Port Selection Codebook

[0027] An enhanced Type II (eType II) port selection (PS) codebook was introduced in Rel-16, which is intended to be used for beamformed CSI-RS, where each CSI-RS port covers a small portion of the cell coverage area with high gain (compared to non-beamformed CSI-RS). Depending on the gNB implementation, it is usually assumed that each CSI-RS port is transmitted in a 2D spatial beam with a main lobe with azimuth pointing angle and elevation pointing angle. The actual precoder matrix used for CSI-RS is transparent to the UE. Based on measurements, the UE selects and recommends the best CSI-RS port to the gNB to use for DL ​​transmission. The eType II PS codebook can be used by the UE to feedback the selected CSI-RS ports and the method for combining them.

[0028] 5.1 eType II PS Codebook Structure, Configuration and Reporting

[0029] For a given transmission layer l, l ∈ {1,...,v}, where v is the rank indicator (RI), the precoder matrix for all FD-units is of size P CSI-RS ×N3 matrix W lwhere P_CSI-RS is the number of CSI-RS ports, N_3=N_SB×R is the number of PMI subbands, where the value R={1,2} (PMI subband size indicator) is RRC configured, N_SB is the number of CQI bands, also RRC configured, and the RI value v is set according to the configured higher layer parameter typeII-RI-Restriction-r16. The UE shall not report v>4.

[0030] Precoder matrix W l teeth, TIFF0007652905000003.tif6170 can be factorized as W l teeth, TIFF0007652905000004.tif5170, normalized such that l=1,...,v. W1 can be written as CSI-RS × 2L port selection matrix. TIFF0007652905000005.tif10170, where W PS is a vector of size 0 and 1. TIFF0007652905000006.tif10170 is the port selection matrix. The selected ports are indicated by 1's that are common for both polarizations. L is the number of selected CSI-RS ports per polarization. Supported L values ​​can be found in Table 2. W1 is common to all layers.

[0031] W f,l is the size N3×M for layer l. v is the frequency domain (FD) compression matrix, where: TIFF0007652905000007.tif9170 is the number of selected FD precoding vectors, which is determined by the rank indicator v and the RRC configured parameter p v Depends on (p v Supported values ​​of can be found in Table 2), TIFF0007652905000008.tif6170, where: TIFF0007652905000009.tif8170 is a set of N3 orthogonal DFT basis vectors of size N3×1. Selected from TIFF0007652905000010.tif6170, M v is the size N3 × 1 FD precoding vector, W f,l is layer specific.

[0032] TIFF0007652905000011.tif6170 is the selected M for the selected 2L CSI-RS ports. v 2LM for linearly combining FD precoding vectors v Contains coefficients, size 2L×M v This is the linear combination coefficient matrix. For layer l, Only a subset of 5,170 coefficients in TIFF0007652905000012.tif are non-zero and are reported. TIFF0007652905000013.tif5170 unreported coefficients are assumed to be 0. The amplitudes and phases of the coefficients in TIFF0007652905000014.tif6170 shall be quantized for reporting. TIFF0007652905000015.tif6170 is layer specific. TIFF0007652905000016.tif52170 Summary of the Invention

[0033] Currently, there are several challenges. For example, there is an implementation complexity problem for transmitting in many different directions (e.g., many different beams if beamforming is used at the transmitter) at the same time (e.g., in the same OFDM symbol). Ideally, from a complexity point of view, a single beam with two ports (one per polarization) is transmitted in a wideband manner. That is, in one OFDM symbol, the same precoder / beamformer is used for both polarizations across the entire transmission bandwidth. The problem is that the current structure of the mapping of CSI-RS ports to resource elements and OFDM symbols in NR causes high implementation complexity.

[0034] Therefore, the present disclosure provides an alternative resource element mapping of CSI-RS ports so that ports corresponding to the same beam are mapped to the same OFDM symbol. In general, to reduce implementation complexity, the present disclosure aims to minimize the number of beams required per OFDM symbol. In general, since dual-polarized antennas and beams are typically used in NR, a beam contains two CSI-RS ports, one for each polarization, transmitted in the same beam direction. This mapping will reduce the number of different beamforming vectors (i.e., the number of beam directions) that need to be applied and transmitted per OFDM symbol. This also allows for the ideal case of a single wideband beamforming vector.

[0035] In one aspect, a method for reducing the number of beams required per symbol is provided. The method is implemented by a base station (gNB). The method includes transmitting a reference signal (RS) and receiving a report from a UE (302), the report identifying a matrix. The method also includes using the identified matrix to transmit data to or schedule the UE. The matrix identified by the UE is TIFF0007652905000017.tif9170, Wps is the port selection matrix, TIFF0007652905000018.tif5170 shows the Kronecker product.

[0036] In another embodiment, a method implemented by a base station includes transmitting CSI-RS using a configuration that maps CSI-RS ports such that CSI-RS ports corresponding to the same beam, but with different polarizations, are mapped to resource elements in the same symbol.

[0037] In another aspect, a method is provided that includes selecting a set of N transmission points (TPs), N≧2, for a UE. The method also includes, for each TP included in the set of TPs, employing the TP to transmit a CSI-RS in accordance with a CSI-RS resource configuration for the TP. The method also includes receiving a CSI report transmitted by the UE, the CSI report determined by the UE based on an aggregation of the CSI-RS resource configurations.

[0038] In another aspect, a computer program is provided that includes instructions that, when executed by processing circuitry of a base station, cause the base station to perform a base station method as disclosed herein. In another aspect, a carrier is provided that contains the computer program, the carrier being one of an electronic signal, an optical signal, a radio signal, and a computer readable storage medium.

[0039] In another aspect, a base station is provided, the base station adapted to perform the method of any base station embodiment disclosed herein. In some embodiments, the base station includes a processing circuit and a memory, the memory including instructions executable by the processing circuit such that the base station is operable to perform the base station method disclosed herein.

[0040] In one aspect, a method is provided for implementation by a UE. The method includes receiving a reference signal and transmitting a report to a base station. The report identifies a matrix. The identified matrix is TIFF0007652905000019.tif9170, Wps is the port selection matrix, TIFF0007652905000020.tif5170 indicates a Kronecker product. In another embodiment, a method performed by a UE includes estimating a downlink (DL) channel using a configuration that maps CSI-RS ports such that CSI-RS ports corresponding to the same beam with different polarizations are mapped to resource elements in the same symbol. In another aspect, a method performed by a UE includes, for each transmission point (TP) included in a selected set of N TPs, N≧2, obtaining a CSI-RS resource configuration for the TP, thereby obtaining N CSI-RS resource configurations. The method also includes receiving a CSI-RS from each of the N TPs. The method also includes generating a CSI report based on an aggregation of the N CSI-RS resource configurations. The method also includes transmitting the CSI report to a base station.

[0041] In another aspect, a computer program is provided that includes instructions that, when executed by processing circuitry in the UE, cause the UE to perform a UE method as disclosed herein. In another aspect, a carrier is provided that contains the computer program, the carrier being one of an electronic signal, an optical signal, a radio signal, and a computer readable storage medium.

[0042] In another aspect, a UE is provided, the UE adapted to perform the method of any UE embodiment disclosed herein. In some embodiments, the UE includes a processing circuit and a memory, the memory including instructions executable by the processing circuit such that the UE is operable to perform the UE method disclosed herein.

[0043] An advantage of this embodiment is that it allows for a simplified implementation of beamformed CSI-RS since fewer different beamforming vectors need to be applied per symbol. By reducing the number of different beamforming vectors per symbol, the freed processing resources can instead be used for, e.g., improved precoding of the PDDCH and / or PDSCH to increase performance.

[0044] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate various embodiments. [Brief description of the drawings]

[0045] [Figure 1A] FIG. 1 illustrates spatial multiplexing. [Figure 1B] FIG. 1 shows an antenna array with dual polarized antenna elements. [Figure 1C] FIG. 1 is a diagram showing an example of port numbering for eight antenna ports. [Diagram 2] A diagram showing CSI-RS resource elements. [Diagram 3] 1 illustrates an example procedure for reciprocity-based FDD transmission. [Figure 4] FIG. 1 illustrates port mapping in the prior art. [Diagram 5] FIG. 2 illustrates port mapping, according to one embodiment. [Figure 6] FIG. 2 illustrates port mapping, according to one embodiment. [Figure 7] FIG. 2 illustrates port mapping, according to one embodiment. [Figure 8] FIG. 2 illustrates port mapping, according to one embodiment. [Figure 9A] 1 is a flowchart illustrating a process according to one embodiment. [Figure 9B] 1 is a flowchart illustrating a process according to one embodiment. [Figure 10A]1 is a flowchart illustrating a process according to one embodiment. [Figure 10B] 1 is a flowchart illustrating a process according to one embodiment. [Figure 11] 1 is a flowchart illustrating a process according to one embodiment. [Figure 12] 1 is a flowchart illustrating a process according to one embodiment. [Figure 13] FIG. 2 is a block diagram of a base station according to one embodiment. [Figure 14] FIG. 2 is a block diagram of a base station according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0046] In frequency division duplex (FDD) operation, uplink (UL) and downlink (DL) transmissions are on different frequencies and therefore the propagation channels in the UL and DL are not reciprocal as in time division duplex (TDD). Despite this, some physical channel parameters (e.g., delays and angles for different clusters, which depend on the spatial properties of the channel rather than the carrier frequency) are reciprocal between the UL and DL. Such properties can be exploited to obtain partial reciprocity based FDD transmissions. The reciprocal part of the channel can be combined with the non-reciprocal part to obtain the complete channel. An estimate of the non-reciprocal part can be obtained by feedback from the user equipment (UE).

[0047] One procedure for a reciprocity-based FDD transmission scheme is shown in FIG. 3 in four steps, assuming that the NR Rel-16 extended Type II port selection codebook is used.

[0048] In step 1, the UE 302 is configured with a sounding reference signal (SRS) by the gNB 404, and the UE transmits the SRS in the UL for the gNB to estimate the angles and delays of different clusters associated with different propagation paths.

[0049] In step 2, the gNB selects a dominant cluster according to the estimated angle-delay power spectral profile, and for each selected cluster, the gNB precodes (e.g., beamforms) and transmits one CSI-RS port per polarization according to the obtained angle and / or delay estimates to the UE.

[0050] In step 3, the gNB configures the UE to measure CSI-RS, and the UE measures the received CSI-RS port and then determines Type II CSI, including RI, PMI for each layer, and CQI. The precoding matrix indicated by the PMI includes the selected beam (i.e., the precoded CSI-RS port) and the corresponding best phase and amplitude for cophasing the selected beam. The phase and amplitude for each beam are quantized and fed back to the gNB.

[0051] In step 4, the gNB calculates DL precoding matrices per layer based on the selected beam and the corresponding amplitude and phase feedback, and performs physical downlink shared channel (PDSCH) transmission. The transmission is based on a direct feedback (PMI) precoding matrix (e.g., SU-MIMO transmission), or the transmit precoding matrix is ​​obtained from an algorithm that combines CSI feedback from multiple UEs (MU-MIMO transmission). In this case, a precoder is derived based on the precoding matrix (including CSI reports from co-scheduled UEs) (e.g., a zero-forcing precoder or a normalized ZF precoder). The final precoder is typically scaled so that the transmit power per power amplifier is not overridden.

[0052] Such reciprocity-based transmission can potentially be utilized in codebook-based DL transmission for FDD, for example, to reduce feedback overhead in the UL when an NR Type II port selection codebook is used. Another potential benefit is reduced complexity of CSI computation at the UE. Another potential benefit is reduced complexity of CSI computation at the UE.

[0053] As shown in the above section, there is an implementation complexity problem for transmitting in many different directions (e.g., many different beams if beamforming is used at the transmitter) at the same time (e.g., in the same OFDM symbol). Ideally, from a complexity point of view, a single beam with two ports (one per polarization) is transmitted in a wideband manner, i.e., in one OFDM symbol, the same precoder / beamformer is used across the entire transmission bandwidth for both polarizations. The problem is that the current structure of the mapping of CSI-RS ports to resource elements and OFDM symbols in NR causes high implementation complexity.

[0054] More specifically, from the structure of W1 in the NR precoding codebook, two CSI-RS ports associated with two different polarizations of the same beam are denoted by port numbers n and TIFF0007652905000021.tif10170. This, together with the port numbering convention in (1) and the CSI-RS locations in Table 1, implies that it is not possible to map two CSI-RS ports associated with different polarizations to the same OFDM symbol. Instead, CSI-RS ports in the same symbol are associated with beams pointing in different directions in the current NR standard.

[0055] For example, in row 5 in Table 1, there are four ports divided into two CDM groups, where each CDM group spans two subcarriers and different CDM groups are located in different symbols. According to the port numbering convention, ports 0-1 correspond to a first polarization and ports 2-3 correspond to a second polarization. Ports 0-1 belong to CDM group 0 that is mapped to symbol l0, and ports 2-3 belong to CDM group 1 that is mapped to the next OFDM symbol, symbol l0+1. This is illustrated in Figure 4, where CSI-RS ports 0 and 2 are assumed to correspond to beams pointing in a direction Φ1 with a first polarization +45° (indicated by " / " in the figure) and a second polarization -45° (indicated by "\" in the figure), respectively. Furthermore, CSI-RS ports 1 and 3 are assumed to correspond to beams pointing in a direction Φ2 with a first polarization +45° and a second polarization -45°, respectively.

[0056] This is consistent with the underlying assumption regarding the structure of W1, i.e., that the beam of the first polarization is TIFF0007652905000022.tif9170 ports (lowest port index) are associated with the same beam in the second polarization, It is consistent with the fact that 9170 ports (highest port index) are associated with each other. Thus, ports corresponding to different polarizations are mapped to different symbols, and ports corresponding to different beam directions but the same polarization are mapped to the same symbol.

[0057] A typical transmission is to transmit ports 0 and 2 in one beam direction and ports 1 and 3 in another direction, which means that in one OFDM symbol both beam directions are represented, leading to high implementation complexity.

[0058] Having different beam directions in the same symbol is problematic for gNB hardware implementations, since having multiple beamformers in the same symbol is costly. In the above example, and as mentioned above, two different beamforming vectors need to be applied in each resource block (when density is 1). For other CSI-RS configurations with more than four ports (NR supports up to 32 ports of CSI-RS resources), this problem can be more pronounced. For example, for a configuration according to row 16 in Table 1, there are eight ports associated with eight different beam directions in one symbol.

[0059] In the extended Type-II port selection codebook for 3GPP Release 17 (Rel-17), this problem may be exacerbated because CSI-RS beamforming will mostly be UE-specific and will use up to 32 ports. This means that for each UE, a CSI-RS port will be beamformed to the dominant channel cluster for that UE. Thus, the total number of CSI-RS beamforming directions may be increased compared to previous releases.

[0060] Therefore, the present disclosure provides an alternative resource element mapping of CSI-RS ports such that ports corresponding to the same beam are mapped to the same OFDM symbol. The objective is to reduce or minimize the number of different beams per OFDM symbol. This objective can be achieved in at least two different ways: (1) modifying the structure of W1 in the Type II port selection codebook, and (2) modifying the mapping of CSI-RS ports to time-frequency resources (e.g., resource elements (REs)).

[0061] 1. Modifying the codebook structure

[0062] According to 3GPP TS38.214 V16.3.0 ("TS 38.214"), W1 may be factored as follows: CSI-RS× 2L port selection matrix. TIFF0007652905000024.tif9170

[0063] W PS is a size of 0 and 1 TIFF0007652905000025.tif9170 Port selection matrix, where P CSI-RS is the total number of beamformed CSI-RS ports, L is the number of selected CSI-RS ports per polarization, TIFF0007652905000026.tif4170 shows the Kronecker product. CSI-RS In one embodiment where =8 (4 for each polarization) and L=2, and therefore 2 is chosen for the ports, Wps may be given as: TIFF0007652905000027.tif16170

[0064] The selected port is denoted by 1, which is, by assumption, common for both polarizations. This structure of W1 means that if port n is selected, then port This implies that TIFF0007652905000028.tif9170 is also selected. This implies that port n and port This also means that TIFF0007652905000029.tif9170 correspond to the same beam with different polarizations.

[0065] It is observed that consecutive ports 2n and 2n+1 are generally mapped to the same OFDM symbol. The main idea is to ensure that consecutive ports 2n and 2n+1 correspond to different polarizations transmitted in the same beam.

[0066] In one embodiment, the structure of W1 is modified according to the following: TIFF0007652905000030.tif8170

[0067] This means that if port 2n is selected for a beam (column W1), port 2n+1 is also selected. It is still assumed that the port selection is common for both polarizations.

[0068] Thus, in this embodiment, the port numbering is effectively changed such that ports corresponding to the same beam with different polarizations have consecutive port numbers, i.e., 2n and 2n+1, and therefore these ports will belong to the same CDM group, which allows these ports to be mapped to the same OFDM symbol, which reduces the number of beam directions in a symbol compared to legacy NR mapping.

[0069] 2. Corrected CSI-RS port mapping

[0070] According to section 7.4.1.5.3 in TS38.211, CSI-RS ports are numbered first within a CDM group and then across CDM groups. Furthermore, the CDM groups are numbered first in ascending order of frequency domain allocation and then in ascending order of time domain allocation. The codebook structure is defined as port n and port The assumption is based on the assumption that the two ports correspond to the same beam with different polarizations, so that two ports associated with different polarizations of the same beam are not mapped to the same symbol.

[0071] In the following, three embodiments are disclosed that allow for mapping the CSI-RS ports such that CSI-RS ports corresponding to the same beam with different polarizations are mapped to resource elements in the same symbol. For these embodiments, the codebook structure and port numbering are maintained as in legacy NR, and instead, the CSI-RS port mapping is modified.

[0072] 2.1 Port Number Reordering

[0073] In one embodiment, the CSI-RS port numbering order is modified so that ports are numbered first across CDM groups and then within a CDM group, but the numbering order within a CDM group follows the current NR standard. Table 3 shows an example of current and proposed port numbering for the case of eight ports divided into four CDM groups. TIFF0007652905000032.tif35170

[0074] Figure 5 shows a proposed modification of the CSI-RS port mapping using the same example as in Figure 4. As explained before, the problem with the current mapping shown in Figure 4 is that the two CSI-RS ports in a symbol are beamformed in different directions. This means that in every resource block (or every second resource block if density is 0.5), two different beamforming weight vectors need to be applied on two adjacent subcarriers. This is complicated from a hardware implementation point of view.

[0075] According to this embodiment, ports 0 and 2 are instead mapped to symbol l0, and ports 1 and 3 are mapped to symbol l0+1. With this mapping, the same beamforming weight vector can be applied at all CSI-RS resource elements in a symbol, which simplifies the implementation of CSI-RS beamforming compared to legacy mapping.

[0076] An example with eight CSI-RS ports is shown in Figure 6. Figure 6 shows the port mapping for row 7 in Table 1 according to the current specification and according to one embodiment. In this case, there are four CDM groups spread across both the frequency and time domains. For the mapping according to the current specification, there will be four different beam directions in each symbol carrying a CS-RS resource element. For the mapping proposed in this embodiment, the number of beam directions is reduced by half to only two directions. Although the CSI-RS beamformer cannot be wideband with the proposed mapping for this case, it is still a significant reduction in complexity compared to the current specification.

[0077] 2.2 CDM Group Numbering Reordering

[0078] In another embodiment, instead of port ordering, the ordering of CDM groups is modified. According to TS38.211, CDM groups are numbered first in ascending order of frequency domain allocation, then in ascending order of time domain allocation. In this embodiment, CDM groups are instead numbered first in ascending order of time domain allocation, then in ascending order of frequency domain allocation. An example of this for row 7 in Table 1 is shown in Figure 7. Also, in this case, the number of beamforming directions per symbol is reduced from 4 to 2.

[0079] 2.3 Introducing new CSI-RS resource configuration

[0080] In one embodiment, Table 1 is extended with new CSI-RS resource configurations that give more possibilities for mapping CSI-RS ports with different beamforming directions to different symbols. Alternatively, alternative tables for CSI-RS resources with desired properties are defined.

[0081] The new CSI-RS resource configuration uses CDM groups that span only subcarriers, not time, and therefore l′ in Table 1 only has the value l′=0. This ensures that one CSI-RS port is only present in one OFDM symbol, which reduces implementation complexity.

[0082] For example, for 8 CSI-RS ports, there is currently no mapping that gives a single beamforming direction per symbol. This can be achieved by introducing the FD-cdm2 setting on the 4 OFDM symbols according to the following: TIFF0007652905000033.tif29170

[0083] This setup combined with the renumbering embodiment is shown in Figure 8. It can be seen that in this case there is only one beamforming direction per symbol.

[0084] In another example, for 16 CSI-RS ports, there is currently no mapping that gives at most two beamforming directions per symbol. This can be achieved by introducing a FD-cdm4 setting on four OFDM symbols according to the following: TIFF0007652905000034.tif29170

[0085] In this case, there are only two beamforming directions per symbol.

[0086] 2.4 Aggregating CSI-RS Resource Configurations

[0087] In yet another embodiment, a new CSI-RS resource configuration for a larger number of ports is obtained by aggregating multiple instances of a legacy (e.g., Rel-15) CSI-RS resource configuration of fewer ports (mapped to different OFDM symbols) to achieve a desired number of ports in the new resource configuration. The fewer port resources have the desired property of having only two or four ports per symbol to minimize the number of beams per symbol to one or two. For example, using K OFDM symbols, K multiples of rows 3 or 4 in Table 1 may be aggregated into a new 2K or 4K port CSI-RS resource, respectively.

[0088] 2.5 Coherent Joint Transmission (CJT)

[0089] In another embodiment, aggregation of CSI-RS resource configurations is used for coherent joint transmission (CJT) from multiple transmission points (TPs). In this case, the UE is configured with one (or more) CSI-RS resource configurations for each transmission point participating in the CJT. The UE then computes a type-II CSI report for all transmission points together by aggregating the CSI-RS resource configurations for all transmission points. The UE then feeds back the computed CSI report to the base station, which can use the CSI report, for example, to determine a precoder for the coherent joint transmission from the transmission point.

[0090] For example, the gNB configures the UE with two CSI-RS resource configurations (e.g., CSI-RS resource settings), one for each TP (e.g., TP1 and TP2). That is, the gNB network provides the UE (e.g., via an RRC configuration) with a CSI resource configuration identifying a first CSI resource for TP1 and a second CSI resource for TP2. Based on measurements of the CSI-RS transmitted using the first CSI-RS resource, the UE generates a first channel estimate (H1) for the channel between the UE and TP1, and based on measurements of the CSI-RS transmitted using the second CSI-RS resource, the UE generates a second channel estimate (H2) for the channel between the UE and TP2.

[0091] The UE aggregates channel H=[H1;H2]. That is, the UE stacks channels H1 and H2 along the CSI-RS port dimension. For example, consider the case of a single-antenna UE, i.e., the channel to TP1, H1, is of dimension P1×N, where P1 is the number of CSI-RS ports and N is the number of frequency subbands. The channel to TP2, H2, is of dimension P2×N. Then, H=[H1;H2] is obtained by stacking H1 on H2, such that H is of dimension (P1+P2)×N.

[0092] Based on the aggregated channel H, the UE calculates a Type-II PMI, denoted by W, which may be decomposed as W=[W(1);W(2)], where W(1) is the PMI for TRP1 and W(2) is the PMI for TRP(2). The UE includes the calculated Type-II PMI in a CSI report and sends the report to the gNB.

[0093] 3. Settings

[0094] The embodiments of the present disclosure introduce alternative CSI-RS resource configurations, or alternative definitions of the MIMO precoding codebook. In all these alternatives, it is assumed that the UE supports the embodiments described herein and informs the network that the UE has this capability. If the UE supports these new alternative solutions, the network can subsequently configure the UE to use the new configuration, for example using RRC signaling. In one embodiment, before receiving such signaling from the network, the UE shall use the legacy description.

[0095] 9A is a flow chart illustrating a process 900 for reducing the number of beams required per symbol. Process 900 may be performed by the gNB 304 and may begin at step s902. Step s902 includes transmitting a reference signal (RS). Step s904 includes receiving a report from the UE 302, the report identifying a matrix indicative of a selected CSI-RS port. Step s906 includes using the identified matrix to transmit data to or schedule the UE. The matrix identified by the UE may be TIFF0007652905000035.tif9170, Wps is the port selection matrix, TIFF0007652905000036.tif5170 shows the Kronecker product.

[0096] In some embodiments, Wps is of size P / 2×L, where P represents the total number of beamformed CSI-RS ports and L represents the number of selected CSI-RS ports per polarization. In an embodiment, Wps consists of 0 and 1.

[0097] FIG. 9B is a flow chart illustrating a process 920. The process 920 may be performed by the gNB 304 and may begin at step s922. Step s922 includes transmitting the CSI-RS using a configuration that maps the CSI-RS ports such that CSI-RS ports corresponding to the same beam with different polarizations are mapped to resource elements in the same symbol. In some embodiments, the CSI-RS ports are numbered first across CDM groups and then within the CDM groups. In some embodiments, the CDM groups are numbered first in ascending order of time domain allocation and then in ascending order of frequency domain allocation. In some embodiments, two CSI-RS ports in a symbol are beamformed in the same direction. In some embodiments, a single beamforming weight vector is applied in all CS-RS resource elements in a symbol.

[0098] 10A is a flow chart illustrating a process 1000. The process 1000 may be performed by the UE 302 and may begin at step s1002. Step s1002 includes receiving a reference signal. Step s1004 includes transmitting a report to the base station (304), the report identifying a matrix, the identified matrix being TIFF0007652905000037.tif9170, where Wps is the port selection matrix, tif5170 indicates the Kronecker product. In some embodiments, Wps is of size P / 2×L, where P represents the total number of beamformed CSI-RS ports and L represents the number of selected CSI-RS ports per polarization. In some embodiments, Wps consists of 0 and 1.

[0099] FIG. 10B is a flow chart illustrating a process 1020. The process 1020 may be performed by the UE 302 and may begin at step s1022. Step s1022 includes estimating a downlink (DL) channel using a configuration that maps CSI-RS ports such that CSI-RS ports corresponding to the same beam with different polarizations are mapped to resource elements in the same symbol. In some embodiments, the CSI-RS ports are numbered first across CDM groups and then within the CDM groups. In some embodiments, the CDM groups are numbered first in ascending order of time domain allocation and then in ascending order of frequency domain allocation. In some embodiments, two CSI-RS ports in a symbol are beamformed in the same direction. In some embodiments, a single beamforming weight vector is applied in all CS-RS resource elements in the symbol.

[0100] 11 is a flowchart illustrating a process 1100. Process 1100 may begin at step s1102. Step s1102 includes selecting a set of N transmission points (TPs) (e.g., base stations or antennas), N≧2, for the UE 302. Step s1104 includes, for each TP included in the set of TPs, employing the TP to transmit CSI-RS according to a CSI-RS resource configuration for the TP. Step s1106 includes receiving a CSI report transmitted by the UE, the CSI report determined by the UE based on an aggregation of the CSI-RS resource configuration.

[0101] In some embodiments, the process also includes, for each TP included in the selected set of N TPs, configuring, in the UE, a CSI-RS resource configuration for the TP, thereby configuring the UE with N CSI-RS resource configurations.

[0102] In some embodiments, the process also includes determining a precoder for coherent joint transmission from the N TPs to the UE based on the CSI report.

[0103] In some embodiments, the CSI report is a Type II CSI report.

[0104] In some embodiments, the CSI report comprises a precoding matrix indicator (PMI) determined by the UE based on an aggregation of CSI-RS resource configurations.

[0105] FIG. 12 is a flow chart illustrating a process 1200. The process 1200 may be performed by the UE 302 and may begin at step s1202. Step s1202 includes, for each TP included in a selected set of N TPs, N≧2, obtaining a CSI-RS resource configuration for the TP, thereby obtaining N CSI-RS resource configurations. Step s1204 includes receiving a CSI-RS from each of the N TPs. Step s1206 includes generating a CSI report based on an aggregation of the N CSI-RS resource configurations. Step s1208 includes transmitting the CSI report to a base station (e.g., base station 304).

[0106] In some embodiments, the process also includes receiving, from each of the N TPs, a precoded data signal generated using a precoder determined based on the CSI report, In some embodiments, the CSI report is a Type II CSI report.

[0107] In some embodiments, receiving a CSI-RS from each of the N TPs includes the UE receiving a first CSI-RS from a first TP and the UE receiving a second CSI-RS from a second TP. In some embodiments, generating a CSI report based on an aggregation of the N CSI-RS resource configurations includes the UE generating a first channel estimate (H1) based on measurements of the first CSI-RS, the UE generating a second channel estimate (H2) based on measurements of the second CSI-RS, the UE aggregating H1 and H2, thereby producing an aggregated channel estimate (H), and the UE generating a CSI report based on H. In some embodiments, generating a CSI report based on H includes the UE calculating a Type II PMI based on H and including the Type II PMI in the CSI report.

[0108] In some embodiments, N=2, and generating a CSI report based on an aggregation of the N CSI-RS resource configurations includes the UE obtaining (e.g., by generating, selecting, etc.) a first precoder matrix indicator (PMI) based on measurements of the first CSI-RS and the second CSI-RS, the UE obtaining a second PMI based on the measurements of the first CSI-RS and the second CSI-RS, the UE aggregating the first PMI and the second PMI, thereby generating an aggregated PMI, and the UE generating a CSI report based on the aggregated PMI.

[0109] 13 is a block diagram of a base station 304, according to some embodiments. As shown in FIG. 13, the base station 304 includes a processing circuit (PC) 1302, which may include one or more processors (P) 1355 (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 array (FPGA), etc.), which may be co-sited in a single housing or in a single data center or may be geographically distributed (i.e., the base station 304 may be a distributed computing device), and a network interface 1368, which enables the base station 304 to communicate with the network 110 ( For example, the PC 1302 may comprise a network interface 1368 comprising a transmitter (Tx) 1365 and a receiver (Rx) 1367 for enabling the base station 304 to transmit data to and receive data from other nodes connected to the network (e.g., an Internet Protocol (IP) network); a communication circuit 1348 coupled to an antenna configuration 1349 comprising one or more antennas and comprising a transmitter (Tx) 1345 and a receiver (Rx) 1347 for enabling the base station 304 to transmit data to and receive data from (e.g., transmit / receive data wirelessly); and a local storage unit (a.k.a. "data storage system") 1308, which may include one or more non-volatile storage devices and / or one or more volatile storage devices. In an embodiment in which the PC 1302 comprises a programmable processor, a computer program product (CPP) 1341 may be provided. The CPP 1341 comprises a computer readable medium (CRM) 1342, which stores a computer program (CP) 1343 comprising computer readable instructions (CRI) 1344. The CRM 1342 may be a non-transitory computer-readable medium, such as a magnetic medium (eg, a hard disk), an optical medium, a memory device (eg, a random access memory, a flash memory), or the like.In some embodiments, the CRI 1344 of the computer program 1343, when executed by the PC 1302, is configured such that the CRI causes the base station 304 to perform steps described herein (e.g., steps described herein with reference to flow charts). In other embodiments, the base station 304 may be configured to perform steps described herein without the need for code; that is, for example, the PC 1302 may simply consist of one or more ASICs. Thus, features of the embodiments described herein may be implemented in hardware and / or software.

[0110] FIG. 14 is a block diagram of a UE 302, according to some embodiments. As shown in FIG. 14, the UE 302 may include a processing circuit (PC) 1402, which may include one or more processors (P) 1455 (e.g., one or more general-purpose microprocessors and / or one or more other processors, such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), etc.), a communication circuit 1448, coupled to an antenna configuration 1449, which may include one or more antennas, a transmitter (Tx) 1445 and a receiver (Rx) 1447 to enable the UE 302 to transmit data and receive data (e.g., transmit / receive data wirelessly), and a local storage unit (a.k.a. "data storage system") 1408, which may include one or more non-volatile storage devices and / or one or more volatile storage devices. In embodiments in which the PC 1402 includes a programmable processor, a computer program product (CPP) 1441 may be provided. The CPP 1441 includes a computer readable medium (CRM) 1442, which stores a computer program (CP) 1443 including computer readable instructions (CRI) 1444. The CRM 1442 may be a non-transitory computer readable medium, such as a magnetic medium (e.g., hard disk), an optical medium, a memory device (e.g., random access memory, flash memory), etc. In some embodiments, the CRI 1444 of the computer program 1443, when executed by the PC 1402, is configured such that the CRI causes the UE 302 to perform steps described herein (e.g., steps described herein with reference to flow charts). In other embodiments, the UE 302 may be configured to perform steps described herein without the need for code. That is, for example, the PC 1402 may simply consist of one or more ASICs. Thus, features of the embodiments described herein may be implemented in hardware and / or software.

[0111] Overview of Various Embodiments

[0112] A1. A method implemented by a base station 304 for reducing the number of beams required per symbol, the method comprising: transmitting a reference signal (RS); receiving a report from a UE 302, the report identifying a matrix; receiving the report; and using the identified matrix to transmit data to or schedule the UE, the matrix identified by the UE being: TIFF0007652905000039.tif9170, where Wps is the port selection matrix, and using the identified matrix, where TIFF0007652905000040.tif5170 indicates a Kronecker product.

[0113] A2. The method of embodiment A1, in which Wps is of size P / 2×L, where P represents the total number of beamformed CSI-RS ports and L represents the number of selected CSI-RS ports per polarization.

[0114] The method of embodiment A1 or A2, wherein Wps consists of 0 and 1.

[0115] A4. A method implemented by a base station 304, the method including transmitting CSI-RS using a CSI-RS configuration that maps CSI-RS ports such that CSI-RS ports corresponding to the same beam, but with different polarizations, are mapped to resource elements in the same symbol.

[0116] A5. The method of embodiment A4, in which CSI-RS ports are numbered first across CDM groups and then within CDM groups.

[0117] A6. The method of embodiment A4, in which the CDM groups are numbered first in ascending order of time domain allocation and then in ascending order of frequency domain allocation.

[0118] A7. The method of any one of embodiments A4 to A6, wherein two CSI-RS ports in a symbol are beamformed in the same direction.

[0119] A8. The method of embodiment A7, in which a single beamforming weight vector is applied across all CSI-RS resource elements in a symbol.

[0120] A9. The method of any one of embodiments A4 to A8, further comprising receiving a message sent by a user equipment (UE), the message including UE capability information indicating that the UE supports a CSI-RS configuration. A10. The method of any one of embodiments A4 to A9, further comprising configuring a user equipment (UE) to use a CSI-RS configuration for channel measurements.

[0121] A11. The method of any one of embodiments A4 to A10, wherein the CSI-RS configuration configures code division multiplexing groups (CDM) only across subcarriers and not across time.

[0122] A12. The method of any one of embodiments A4 to A11, wherein the CSI-RS ports are conveyed on a plurality of CSI-RS resources, each CSI-RS resource including a subset of the CSI-RS ports.

[0123] A13. A method according to any one of claims A4 to A12, wherein the CSI-RS configuration has X ports, and the method further comprises obtaining a CSI-RS resource configuration by aggregating multiple instances of the CSI-RS resource configuration for fewer than X ports.

[0124] A14. A method comprising: selecting a set of N transmission points (TPs), N≧2, for a user equipment (UE); for each TP included in the set of TPs, employing the TP to transmit a channel state information reference signal (CSI-RS) in accordance with a CSI-RS resource configuration for the TP; and receiving a channel state information (CSI) report transmitted by the UE, the CSI report determined by the UE based on an aggregation of the CSI-RS resource configuration.

[0125] A15. The method of claim A14, further comprising: for each TP included in the selected set of N TPs, configuring, in the UE, a CSI-RS resource configuration for the TP, thereby configuring N CSI-RS resource configurations in the UE.

[0126] A16. The method of claim A14 or A15, further comprising determining a precoder for coherent joint transmission from the N TPs to the UE based on the CSI report.

[0127] A17. The method of any one of claims A14 to A16, wherein the CSI report is a Type II CSI report.

[0128] A18. The method of any one of claims A1 to A17, wherein the CSI report comprises a precoding matrix indicator (PMI) determined by the UE based on an aggregation of CSI-RS resource configurations.

[0129] B1. A method implemented by a UE 302, the method comprising receiving a reference signal and transmitting a report to a base station 304, the report identifying a matrix, the identified matrix being TIFF0007652905000041.tif9170, Wps is the port selection matrix, and sending a report, where TIFF0007652905000042.tif5170 indicates a Kronecker product.

[0130] B2. The method of embodiment B1, in which Wps is of size P / 2×L, where P represents the total number of beamformed CSI-RS ports and L represents the number of selected CSI-RS ports per polarization.

[0131] The method of embodiment B1 or B2, wherein Wps consists of 0 and 1.

[0132] B4. A method implemented by a UE 302, the method including estimating a downlink (DL) channel using a CSI-RS configuration that maps CSI-RS ports such that CSI-RS ports corresponding to the same beam with different polarizations are mapped to resource elements in the same symbol.

[0133] B5. The method of embodiment B4, in which CSI-RS ports are numbered first across CDM groups and then within CDM groups.

[0134] B6. The method of embodiment B4, wherein the CDM groups are numbered first in ascending order of time domain allocation and then in ascending order of frequency domain allocation.

[0135] B7. The method of any one of embodiments B4-B6, wherein two CSI-RS ports in a symbol are beamformed in the same direction.

[0136] B8. The method of embodiment B7, in which a single beamforming weight vector is applied across all CS-RS resource elements in a symbol.

[0137] B9. The method of any one of embodiments B4 to B8, further comprising sending a message to a serving base station, the message including UE capability information indicating that the UE supports CSI-RS configuration.

[0138] B10. The method of any one of embodiments B4-B9, further comprising using a CSI-RS configuration for channel measurements.

[0139] B11. The method of any one of embodiments B4 to B10, wherein the CSI-RS configuration configures code division multiplexing groups (CDM) only across subcarriers and not across time.

[0140] B12. The method of any one of embodiments B4 to B11, wherein the CSI-RS ports are conveyed on a plurality of CSI-RS resources, each CSI-RS resource including a subset of the CSI-RS ports.

[0141] B13. A method according to any one of claims B4 to B12, wherein the CSI-RS configuration has X ports and the CSI-RS resource configuration is obtained by aggregating multiple instances of CSI-RS resource configurations of fewer than X ports.

[0142] B14. A method implemented by a UE, the method including: for each transmission point (TP) included in a selected set of N TPs, N≧2, obtaining a channel state information reference signal (CSI-RS) resource configuration for the TP, thereby obtaining N CSI-RS resource configurations; receiving a CSI-RS from each of the N TPs; generating a CSI report based on an aggregation of the N CSI-RS resource configurations; and transmitting the CSI report to a base station.

[0143] B15. The method of claim B14, further comprising receiving, from each of the N TPs, a precoded data signal generated using a precoder determined based on the CSI report.

[0144] B16. The method of claim B14 or B15, wherein the CSI report is a Type II CSI report.

[0145] B17. A method according to any one of claims B14 to B16, wherein receiving a CSI-RS from each of the N TPs includes the UE receiving a first CSI-RS from a first TP and the UE receiving a second CSI-RS from a second TP.

[0146] B18. The method of claim B17, wherein generating a CSI report based on an aggregation of N CSI-RS resource configurations includes the UE generating a first channel estimate (H1) based on measurements of a first CSI-RS, the UE generating a second channel estimate (H2) based on measurements of a second CSI-RS, the UE aggregating H1 and H2, thereby producing an aggregated channel estimate (H), and the UE generating the CSI report based on H.

[0147] The method of claim B18, wherein generating a CSI report based on H includes, by the UE, calculating a Type II PMI based on H and including the Type II PMI in the CSI report.

[0148] B20. The method of claim B17, wherein N=2, and generating a CSI report based on an aggregation of N CSI-RS resource configurations includes: the UE obtaining a first precoder matrix indicator (PMI) based on measurements of the first CSI-RS and the second CSI-RS; the UE obtaining a second PMI based on measurements of the first CSI-RS and the second CSI-RS; the UE aggregating the first PMI and the second PMI, thereby generating an aggregated PMI; and the UE generating a CSI report based on the aggregated PMI.

[0149] C1a. A computer program 1343 comprising instructions 1344 that, when executed by the processing circuitry 1302 of a base station 304, cause the base station 304 to perform a method according to any one of embodiments A1 to A18.

[0150] C1b. A computer program 1443 including instructions 1444 that, when executed by the processing circuit 1402 of the UE 320, cause the UE 302 to perform a method according to any one of embodiments B1 to B20.

[0151] C2. A carrier containing the computer program of embodiment C1a or C1b, the carrier being one of an electronic signal, an optical signal, a radio signal, and a computer readable storage medium 1342, 1442.

[0152] D1. A base station 304, wherein the base station 304 is adapted to implement the method of any one of embodiments A1 to A18.

[0153] D2. A base station 304, the base station 304 comprising a processing circuit 1302 and a memory 1342, the memory including instructions 1344 executable by the processing circuit, such that the base station 304 is operable to perform a method according to any one of embodiments A1 to A18.

[0154] E1. A UE 302, wherein the UE 302 is adapted to perform a method according to any one of embodiments B1 to B20.

[0155] E2. A UE 302, the UE 302 comprising a processing circuit 1402 and a memory 1442, the memory including instructions 1444 executable by the processing circuit, thereby enabling the UE 302 to operate to perform a method according to any one of embodiments B1 to B20.

[0156] Although various embodiments have been described herein, it should be understood that the embodiments have been presented by way of example only, and not by way of limitation. Thus, the breadth and scope of the present disclosure should not be limited by any of the exemplary embodiments described above. Moreover, unless otherwise indicated herein or clearly contradicted by context, any combination of the above-described elements in all possible variations thereof is encompassed by the present disclosure.

[0157] Additionally, while the processes described above and illustrated in the Figures have been shown as a sequence of steps, this has been done for purposes of illustration only, and it is therefore contemplated that some steps may be added, some steps may be omitted, the order of the steps may be rearranged, and some steps may be performed in parallel.

Claims

1. A method (1000) implemented by a UE (302), comprising: Receiving a reference signal (s1002); and transmitting (s1004) a report to a base station (304), the report identifying a matrix, the identified matrix being where Wps is the port selection matrix, shows the Kronecker product, and The method (1000).

2. Wps is of size P / 2×L, where P represents the total number of beamformed CSI-RS ports and L represents the number of selected CSI-RS ports per polarization; Wps consists of 0 and 1; The method of claim 1.

3. A computer program (1443) comprising instructions (1444) which, when executed by a processing circuit (1402) of a UE (320), cause the UE (302) to perform a method according to claim 1 or 2.

4. A UE (302), comprising: Receiving a reference signal (s1002); and transmitting (s1004) a report to a base station (304), the report identifying a matrix, the identified matrix being where Wps is the port selection matrix, shows the Kronecker product, and A UE (302) adapted to perform a method including:

5. The UE of claim 4, wherein the UE is further configured to perform the method of claim 2.

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