Type II Precoder Matrix Indicator (PMI) Extension for Coherent Joint Transmission (CJT)

Abstract

A method, system and apparatus for a type II precoder matrix indicator (PMI) for coherent joint transmission (CJT) is disclosed. According to one aspect, a method in a network node includes receiving from a wireless device (WD) a precoding matrix indicator (PMI) for coherent joint data transmission on a plurality of 5 transmit reception points (TRPs) and one or both of a time difference and a phase slope associated with each TRP of the plurality of TRPs relative to a reference timing (S144). The method also includes applying time pre-compensation to a physical downlink channel in each of the plurality of TRPs according to at least one of the time difference and the phase slope associated with the TRP. The method also includes applying 10 precoding matrices indicated by the PMI to a physical downlink channel in each of the plurality of TRPs.

Description

[Technical field]

[0001] The present disclosure relates to wireless communications, and in particular to precoder matrices such as Type II Precoder Matrix Indicators (PMIs) for coherent joint transmission (CJT). [Background technology]

[0002] The 3rd Generation Partnership Project (3GPP) has developed and is developing standards for fourth-generation (4G) wireless communication systems (also called Long Term Evolution (LTE)) and fifth-generation (5G) wireless communication systems (also called New Radio (NR)). Such systems provide, among other features, broadband communications between network nodes, such as base stations, and mobile wireless devices (WDs), as well as communications between network nodes and between WDs. Sixth-generation (6G) wireless communication systems are also under development.

[0003] Codebook-Based Precoding 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 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 one example of spatial multiplexing operation is provided in FIG.

[0005] As shown in Figure 1, the information carrying symbol vector s is N T ×r precoder matrix W, which is (N T (N corresponding to antenna ports)T It serves to distribute the transmission energy among subspaces of a -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, where 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 Discrete Fourier Transform (DFT) precoded OFDM in the uplink (for rank-1 transmission). Thus, the received N R x1 vector y n teeth, y n =H n Ws n +e n It can be modeled by: Here, e n is the noise / interference vector obtained as a realization of a random process. The precoder W may be a wideband precoder, which may be constant over frequency or frequency selective.

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

[0008] In closed-loop precoding for the NR downlink, the WD transmits a recommendation to a network node (e.g., gNB) of a suitable precoder to use based on channel measurements in the downlink. The network node may configure the WD to provide feedback according to the CSI-ReportConfig, transmit the CSI-RS, and configure the WD to use the measurements of the CSI-RS to feed back the recommended precoding matrix that the WD selects from the codebook. A single precoder that is considered to cover a large bandwidth (wideband precoding) may be fed back. It may also be beneficial to match the frequency variations of the channel and instead feed back a frequency-selective precoding report, e.g., several precoders, one per subband. 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 to assist the network node in subsequent transmissions to the WD. 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, where a subband is defined as a number of adjacent resource blocks ranging from 4 physical resource blocks (PRBs) to 32 PRBs, depending on the size of the bandwidth part (BWP).

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

[0010] 2D Antenna Array 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 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.

[0011] An example of a 4×4 array with dual polarized antenna elements is shown in FIG.

[0012] Precoding can be interpreted as multiplying the signal by a different beamforming weight for each antenna prior to transmission. A common approach is to tailor the precoder to the antenna form factor, i.e., to use N h , N v , and N p The key is to take into account the following:

[0013] Channel State Information Reference Signal (CSI-RS) In CSI measurement and feedback, a CSI reference signal (RS) is defined. The CSI-RS is transmitted on each antenna port and is used by the WD 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 called 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 WD 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 called non-zero power (NZP) CSI-RS.

[0014] CSI-RS may be configured to be transmitted in some REs in a slot and in some slots. Figure 3 shows an example of CSI-RS REs for 12 antenna ports, where one RE per RB per port is shown.

[0015] In addition, an interference measurement resource (IMR) for the WD to measure interference is also specified in NR. The IMR resource contains four resource elements (REs), i.e., either four adjacent REs in frequency in the same OFDM symbol, or a 2×2 block of adjacent REs in both time and frequency in a slot. By measuring both the channel based on the non-zero power (NZP) CSI-RS and the interference based on the IMR, the WD can estimate the effective channel and noise-plus-interference to determine the CSI (i.e., rank, precoding matrix, and channel quality).

[0016] Additionally, the WD in NR may be configured to measure interference based on one or more NZP CSI-RS resources.

[0017] CSI Framework in NR In NR, a WD 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 WD feeds back a CSI report.

[0018] Each CSI reporting setting contains at least the following information: A CSI-RS resource set for channel measurements; · IMR resource set for interference measurements; Optionally, a CSI-RS resource set for interference measurement; 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 rank indicator (RI), precoding matrix indicator (PMI), channel quality indicator (CQI), and CSI-RS resource indicator (CRI) in case of multiple CSI-RS resources in a resource set; Codebook type, i.e., type I or II, and codebook subset restriction, Measurement limits, and Subband size. One out of two possible subband sizes is indicated, the value range depends on the bandwidth of the BWP. One CQI / PMI is fed back per subband (if configured for subband reporting).

[0019] DFT-Based Precoder A common type of precoding is to use a DFT precoder, where the precoder vector used to precode a single layer transmission using a single-polarized uniform linear array (ULA) with N antennas is defined as follows: TIFF2025512727000002.tif28170, where k=0, 1, ... QN-1 are precoder indices and Q is an integer oversampling factor. By taking the Kronecker product of two precoder vectors, the corresponding precoder vector for a 2-D Uniform Planar Array (UPA) can be created as follows: TIFF2025512727000003.tif5170

[0020] In that case, extending the precoder for dual polarization UPA can be done as follows: TIFF2025512727000004.tif11170, where e jΦ is the quadrature phase shift keying (QPSK) alphabet A cophasing factor that can be selected from TIFF2025512727000005.tif8170.

[0021] Precoder matrix W for multi-layer transmission 2D,DP can be created by appending the columns of the DFT precoder vector as follows: W 2D,DP =[w 2D,DP (k1,l1,Φ1)w 2D,DP (k2,l2,Φ2) w 2D,DP (k R ,l R ,Φ R )], where R is the number of transmission layers (transmission rank). In the general special case for a rank-2 DFT precoder, k1=k2=k and l1=l2=l, which means that TIFF2025512727000006.tif11170Such a DFT-based precoder is used in NR Type I CSI feedback.

[0022] MU-MIMO In the case of Multi-User MIMO (MU-MIMO), two or more users in the same cell are co-scheduled on the same time-frequency resources. That is, two or more independent data streams are transmitted simultaneously to different WDs, and the spatial domain (SD) is used to separate each stream. By transmitting several streams simultaneously, the capacity of the system can be increased. However, this comes at the expense of reducing the signal-to-interference-plus-noise ratio (SINR) per stream, since power must be shared between the streams and the streams will interfere.

[0023] NR rel-15 Type II Codebook For the NR Type-II codebook in 3GPP Technology Release 15 (3GPP Rel-15), the precoding vector for each layer and subband is expressed in 3GPP Technical Standard (TS) 38.214 as follows: TIFF2025512727000007.tif38170

[0024] If this can be reconstructed and more simply represented as: RB -1 for the precoder vector w l,p (k) can be expressed as follows: TIFF2025512727000008.tif15170Here, if p=0, If TIFF2025512727000009.tif8170 and p=1, TIFF2025512727000010.tif8170, S is the subband size, N SB is the number of subbands in the CSI reporting bandwidth. Therefore, 2N SB parameters TIFF2025512727000011.tif8170 and Based on TIFF2025512727000012.tif6170 and frequency c l,iThe variation of the beam coefficients over (k) is determined, where, depending on the codebook setting, the subband amplitude parameters TIFF2025512727000013.tif8170 is quantized using 0 to 1 bits to obtain the subband phase parameters TIFF2025512727000014.tif5170 is quantized using 2 or 3 bits.

[0025] NR 3GPP Rel-16 Extended Type II Port Selection Codebook An enhanced Type II (eType II) port selection (PS) codebook was introduced in 3GPP 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 a high beamforming gain (compared to non-beamformed CSI-RS). Depending on the network node 16, e.g., gNB implementation, it is typically 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 WD. Based on measurements, the WD selects the best CSI-RS port and recommends the rank, precoding matrix, and CQI conditional on the rank and precoding matrix to the network node to use for downlink (DL) transmission. The precoding matrix includes a linear combination of the selected CSI-RS ports. The eType II PS codebook may be used by the WD to feed back the selected CSI-RS port and combining coefficients.

[0026] eType II PS codebook structure, configuration and reporting For a given transmission layer l, l ∈ {1,...,v}, where v is the rank indicated by the rank indicator (RI), and the precoder matrix is ​​of size P CSI-RS×N3 matrix W l where: P CSI-RS is the number of CSI-RS ports, N3=N SB × R is the number of subbands for PMI, where - the value R={1,2} (PMI subband size indicator) is configured by the Radio Resource Control (RRC), - N SB is the number of CQI subbands, which is also RRC configured. - The maximum RI value v is set according to the configured higher layer parameter typeII-RI-Restriction-r16. The WD shall not report v>4.

[0027] For each layer l, the precoding matrix W l (as shown in Figure 4) can be factorized as TIFF2025512727000015.tif7170, TIFF2025512727000016.tif6170 is TIFF2025512727000017.tif7170, l=1,...,v and t=0,1,...,N3-1,.

[0028] Port selection matrix W1: W1 is, Size P that can be factorized into TIFF2025512727000018.tif9170 CSI-RS × 2L port selection precoder matrix, where TIFF2025512727000019.tif6170 shows the Kronecker product, TIFF2025512727000020.tif7170 is the size Port selection matrix for TIFF2025512727000021.tif8170, where size TIFF2025512727000022.tif8170 TIFF2025512727000023.tif7170, i=0,1,...,L-1, contains one element indicating the selected CSI-RS port, and all other elements are 0. L is the number of selected CSI-RS ports from each polarization, and the same port is selected for both polarizations. - Supported L values ​​can be found in Table 1. - The selected CSI-RS port is This is represented by TIFF2025512727000024.tif8170, which is reported by the WD to the network nodes. ○ i 1,1 The value of is determined by WD based on CSI-RS measurements. The value of d is set by the upper layer parameter portSelectionSamplingSize, where d ∈ {1, 2, 3, 4}. The file is TIFF2025512727000025.tif8170. - W1 is common to all layers. Frequency domain (FD) compression matrix W f,l : W f,l is the size N3×M for layer l. v is the compression matrix of the FD, where ○ TIFF2025512727000026.tif8170 is the number of selected FD basis vectors, which is determined by the rank indicator v and the RRC configured parameter p v It depends on p v Supported values ​​of can be found in Table 1. TIFF2025512727000027.tif8170, where: TIFF2025512727000028.tif9170 is a set of N3 orthogonal DFT basis vectors M selected from TIFF2025512727000029.tif7170 v are the FD basis vectors, where TIFF2025512727000030.tif13170, (.) T indicates transposition. If N3≦19, one-step free selection is used. For each layer, the FD basis selection is TIFF2025512727000031.tif9170 bit combinatorial indicator. In TS38.214, the combinatorial indicator is the index i 1,6,l where l corresponds to the layer index. This combination index is reported by the WD to the network node for each layer. If N3>19, then a two-step selection using layer common intermediate subsets (IntS) is used. In this first step, a window base layer common IntS selection is used, which is initial IntS is a FD basis vector mod(M initial +n,N3), where: TIFF2025512727000032.tif5170, TIFF2025512727000033.tif5170. In TS38.214, the selected IntS is determined by the WD parameter i 1,5 to the network nodes via, which is reported layer by layer as part of the reported PMI. The second step of subset selection is The combination indicator is indicated by the 11170-bit combination indicator in 3GPP TS38.214. 1,6,l where l corresponds to the layer index. This combination index is reported by the WD to the network node for each layer. 〇 W f,l is layer specific. Linear combination coefficient matrix W 2,l : W 2,l is the selected M v 2LM for linearly combining the FD basis vectors with the selected 2L CSI-RS ports v Contains coefficients, size 2L×M v is a matrix of For layer l, Only a subset of 6,170 coefficients in TIFF2025512727000035.tif are non-zero and are reported. TIFF2025512727000036.tif6170 unreported coefficients are assumed to be 0. ○ TIFF2025512727000037.tif5170 is the maximum number of non-zero coefficients per layer, where β is an RRC configured parameter. Supported β values ​​are shown in Table 1. For v ∈ {2,3,4}, the total number of non-zero coefficients summed over all layers, TIFF2025512727000038.tif6170 is It shall satisfy TIFF2025512727000039.tif5170. The selected coefficient subset for each layer is of size 2LM v In the bitmap TIFF2025512727000040.tif6170 1's, i 1,7,l . The selected CSI-RS port associated with the strongest coefficient of layer l is i 1,8,l ,∈{0,1,...,2L-1}. W 2,l The amplitude coefficient in i 2,3,l and i 2,4,l It is shown by W 2,l The phase coefficient in i 2,5,l and / or W 2,l is layer specific. Table 1 - L,p v3GPP Rel-16 Type II PS Codebook Parameter Settings for and β TIFF2025512727000041.tif43170

[0029] The PMI reported by WD includes codebook indexes i1 and i2, where: TIFF2025512727000042.tif34170

[0030] The precoding matrix is ​​the PMI value according to Table 2. Table 2: Precoding matrices as indicated by PMI TIFF2025512727000043.tif31170, where TIFF2025512727000044.tif38170 · v m is the element (m mod P CSI-RS / 2) and 0 elsewhere, P CSI-RS / 2 element column vector, TIFF2025512727000045.tif11170· TIFF2025512727000046.tif7170 is i 1,6,l If N3>19, then i 1,5 is derived from · TIFF2025512727000047.tif8170 is i 2,3,l is the broadband amplitude coefficient denoted by · TIFF2025512727000048.tif8170 is i 2,4,l are the subband amplitude coefficients denoted by · TIFF2025512727000049.tif8170, TIFF2025512727000050.tif6170 is i 2,5,l is the phase coefficient given by:

[0031] In 3GPP Rel-16 Enhanced Type II CSI feedback, the CSI report contains two parts. Part 1 has a fixed payload size and is used to identify the number of information bits in Part 2. Part 1 contains the RI, CQI, and an indication of the overall number of non-zero amplitude coefficients across layers, i.e. TIFF2025512727000051.tif6170. Part 2 contains the PMI. Part 1 and Part 2 are coded separately.

[0032] FDD-based reciprocity operation and 3GPP Rel-17 Type II port selection codebook In Frequency Division Duplex (FDD) operation, uplink (UL) and DL transmissions are on different frequencies. Therefore, the propagation channels in UL and DL are not reciprocal as in Time Division Duplex (TDD). Despite this, some physical channel parameters, e.g., delay and angle for different clusters, which depend on the spatial properties of the channel and not on the carrier frequency, are reciprocal between UL and DL. Such properties can be exploited to obtain partial reciprocity based FDD transmission. 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 WD. In 3GPP RAN1, it was considered that in 3GPP Rel-17, the 3GPP Rel-16 Type II port selection codebook will be extended to support the above-mentioned FDD based reciprocity operation. In 3GPP RAN1#104e, the 3GPP Rel-17 Type II port selection codebook will adopt the same codebook structure as the 3GPP Rel-16 Type II port selection codebook, i.e., the codebook will be W1, W2, W3, W4, W5, W6, W7, W8, W9, W10, W11, W12, W13, W14, W15, W16, W17, W18, W19, W20, W21, W22, W23, W24, W25, W26, W27, W28, W29, W30, W31, W32, W33, W34, W35, W36, W37, W38, W39, W40, W41, W42, W43, W44, W45, W46, W47, W48, W49, W50 f The details of the codebook components, such as the dimensions of each matrix, are still being considered.

[0033] Procedures for FDD-based reciprocity operation One exemplary procedure for a reciprocity-based FDD transmission scheme is shown in FIG. 5 in four steps, assuming that the NR 3GPP Rel-16 extended Type II port selection codebook is used.

[0034] In step 1, a sounding reference signal (SRS) is configured by a network node in the WD, and the WD transmits the SRS in the UL for the network node to estimate the angles and delays of different clusters associated with different propagation paths.

[0035] In step 2, the network node selects a dominant cluster according to the estimated angular delay power spectral profile, and a set of spatial and frequency domain (SD-FD) basis pairs is calculated by the network node for CSI-RS beamforming based on the estimated angular delay power spectral profile. Each SD-FD pair corresponds to a CSI-RS port, and a certain delay is pre-compensated. Each CSI-RS port resource may contain one or more SD-FD basis pairs by applying different delays to different resource elements of the resource. The network node precodes all CSI-RS ports in the configured CSI-RS resource or multiple CSI-RS resources to the WD, and each configured CSI-RS resource contains the same number of SD-FD basis pairs.

[0036] In step 3, the network node configures the WD to measure the CSI-RS, and the WD measures the received CSI-RS ports and then determines Type-II CSI, including RI, PMI for each layer, and CQI. The precoding matrix indicated by the PMI includes the selected SD-FD basis pair / precoded CSI-RS port and the corresponding best phase and amplitude for cophasing the selected pair / port. The phase and amplitude for each pair / port are quantized and fed back to the network node.

[0037] In step 4, the network node implementation algorithm calculates the DL precoding matrix per layer based on the selected beam and the corresponding amplitude and phase feedback to perform PDSCH transmission. The transmission is based on the direct feedback (PMI) precoding matrix (e.g., SU-MIMO transmission) or the transmit precoding matrix is ​​obtained from an algorithm combining CSI feedback from multiple WDs (MU-MIMO transmission). In this case, a precoder is derived based on the precoding matrix (including CSI reports from co-scheduled WDs) (e.g., zero-forcing precoder or normalized ZF precoder). The final precoder is typically scaled so that the transmit power per power amplifier is not overridden.

[0038] Such reciprocity-based transmission can potentially be exploited 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 the reduced complexity of CSI calculation in the WD.

[0039] Note that Figure 5 shows only one example of a procedure for FDD-based reciprocity operation, where each CSI-RS port includes a single pair of SD-FD bases and the WD performs wideband averaging of the channel to obtain the corresponding coefficients. It is possible that each CSI-RS port includes multiple pairs of SD-FD bases and that the WD may compress channels with more FD components in addition to the DC DFT component.

[0040] Type-II Port Selection Codebook for FDD Operation Based on Angle and Delay Reciprocity When the 3GPP Rel-16 extended Type II port selection codebook is used for FDD operation based on angle and / or delay reciprocity, the frequency domain (FD) basis W fstill needs to be determined by the WD. Thus, in the CSI report, the feedback overhead to indicate which FD basis vector is selected may be large. This is especially true when the number of PMI subbands, N3, is large. Also, the computational complexity in the WD to evaluate and select the best FD basis vector increases as N3 increases. Furthermore, the channel experienced in the WD is frequency selective, which requires several FD basis vectors to be compressed in the PMI report. Reporting the coefficients for these FD basis vectors also consumes a large amount of UL overhead.

[0041] Based on the angle and delay reciprocity, the network node may determine a set of dominant clusters in the propagation channel by analyzing the angle-delay power spectrum of the UL channel. The network node may then utilize this information in such a way that each CSI-RS port is precoded towards a dominant cluster. In addition to SD beamforming, each of the CSI-RS ports will also be pre-compensated in time such that all precoded CSI-RS ports are aligned in the delay domain. As a result, the frequency selectivity of the channel is removed and the WD observes a frequency-flat channel that requires a very small number of FD basis vectors to compress. Ideally, if all beams can be perfectly aligned in time, the WD only needs to perform wideband filtering to obtain all the channel information on which the WD can calculate the 3GPP Rel-17 Type II PMI. Even if the delay is not actually perfectly pre-compensated at the network node, the frequencies selectively experienced at the WD may require a much smaller number of FD basis vectors, i.e., W, to compress the channel. f This can still be significantly reduced to require only the number of basis vectors in

[0042] The above procedure is further explained with reference to the example of FIG. 6. Based on the UL measurements, the network node identifies eight dominant clusters present in the original channel, tagged as A through G, which are distributed in four directions, each direction containing one or more taps. In this example, eight CSI-RS ports are precoded at the network node. Each CSI-RS port is precoded towards the dominant direction with a pre-compensated delay for a given cluster. The delay compensation can be achieved in different ways, for example, by applying a linear phase ramp across the occupied subcarriers. As a result, in the beamformed channel experienced at the WD, all dominant clusters are aligned at the same delay. Therefore, the WD only needs to apply a wideband filter (e.g., the DC component of the DFT matrix (i.e., W, which contains a single all-one vector over the frequency domain channel) to compress the channel and preserve all the channel information). f ) Based on the compressed channel, WD calculates the remaining parts of the Type II port selection codebook: W1 (the selected CSI-RS ports) and W2 (the complex coefficients for combining the selected ports).

[0043] The 3GPP Rel-17 Type II precoder follows the same structure as the 3GPP Rel-16 Type II port selection codebook, i.e., 3GPP Rel-17 uses W1, W2, and W3. f One difference between the 3GPP Rel-17 Type II precoder and the 3GPP Rel-16 Type II codebook is the W f is layer common, and the number of FD basis vectors may only be one or two.

[0044] PDSCH transmission from multiple TRPs NR 3GPP Rel-16 introduced non-coherent joint physical downlink shared channel (PDSCH) transmission from two transmitting and receiving points (TRPs), where a subset of the MIMO layers of the PDCCH for a WD is transmitted from a first TRP and the rest of the layers of the PDSCH are transmitted from a second TRP in the same time and frequency resources. The different layers are separated and received at the WD with a MIMO-enabled receiver.

[0045] An example is shown in Figure 7, where a physical downlink shared channel (PDSCH) with two layers is scheduled with the first layer transmitted from TRP1 and the second layer from TRP2. This is signaled in the corresponding downlink control information (DCI) by indicating two TCI states, the TCI code points associated with the first and second TCI states, and the DMRS ports x and y in the two CDM groups. Here, the demodulation reference signal (DMRS) port x in the first CDM group is associated with the first TCI state, and the DMRS port y in the second CDM group is associated with the second TCI state. The first TCI state may include TRS1 (tracking reference signal 1) as a quasi-colocated (QCL) source RS, and the second TCI state may include TRS1 as a QCL source RS.

[0046] SFN PDSCH In NR 3GPP Rel-17, an enhanced single frequency network (SFN) based PDSCH was also introduced for more robust PDSCH reception, where PDSCH is transmitted simultaneously from two TRPs in the same time and frequency resources.

[0047] An example in which the same PDSCH is transmitted from both TRPs with its DMRS is shown in Figure 8. This is indicated to the WD by both the RRC configuration of the system frame number (SFN) PDSCH and two transmission configuration indicator (TCI) states, which are indicated in the DCI that schedules the PDSCH. The first TCI state may include TRS1 as the QCL source RS, and the second TCI state may include TRS2 as the QCL source RS. Now the DMRS is associated with two TCI states, since the DMRS is transmitted from both TRPs. Summary of the Invention

[0048] Some embodiments advantageously provide methods, network nodes and wireless devices for a Type-II Precoder Matrix Indicator (PMI) for Coherent Joint Transmission (CJT).

[0049] In some embodiments, for coherent joint transmission (CJT), the WD receives downlink data coherently transmitted from multiple TRPs. In this case, the delay spread experienced by the WD for channels / signals transmitted from multiple TRPs via CJT may be much larger compared to the delay spread when the WD receives a channel / signal transmitted from a single TRP. This is because the multiple TRPs may be geometrically separated, which results in additional propagation delays that increase the delay spread between the WD and each individual TRP. Thus, the delay spread will increase with the number of TRPs and with their relative geometric distance.

[0050] This increase in observed delay spread due to WD for channels and signals transmitted by multiple TRPs via a CJT is further illustrated in FIG.

[0051] FIG. 9 is an example of an antenna delay domain power spectrum of a WD receiving coherent joint transmission channels / signals from two TRPs, “TRP1” and “TRP2”, each with 32 antenna elements. On the y-axis, antenna elements numbered “1” to “32” belong to “TRP2” and antenna elements numbered “33” to “64” belong to “TRP1”. On the x-axis, delay taps are represented that represent normalized propagation delays at the WD corresponding to different antenna elements. The shading in FIG. 9 represents the power for each particular antenna element at a particular delay tap. Most of the power of the antenna elements associated with “TRP1” is allocated in the first 10 delay taps, and most of the power of the antenna elements associated with “TRP2” is allocated from delay tap “65” to delay tap “75”. The distance between these two groups of delays comes from the propagation delay between the WD to the two TRPs. The overall delay spread is significantly increased with the introduction of the second TRP. In this example, the delay spread when only "TRP1" is considered is approximately 20 delay taps, and when "TRP2" is also considered, this increases the delay spread to approximately 80 delay taps.

[0052] One approach is to use NR Type II PMI feedback for multiple TRP scenarios with coherent joint transmission where the coherence between TRPs can be implicitly reported via linear combination coefficients, but this requires the use of multiple frequency domain (FD) bases to be able to correctly estimate all propagation delays, which creates a very large CSI reporting overhead that grows rapidly with the number of TRPs and their geometric distance, which results in a larger delay spread as explained above.

[0053] When a WD is served by multiple geographically separated TRPs, the total delay spread of the combined channel is contributed by inter-TRP delay spread caused by different distances between the WD and the TRPs and intra-TRP delay spread caused by the multipath propagation environment. In some embodiments, the inter-TRP delay spread from the corresponding TRP is estimated and removed to obtain an effective channel based on which the Type-II PMI is calculated. The calculated Type-II report and the estimated inter-TRP delay spread, based on which the DL precoder for coherent joint transmission across multiple TRPs is derived, are reported together to the network node.

[0054] In some non-limiting embodiments, One or more of the following may be performed by the WD: The WD estimates the inter-TRP delay spread, which is determined by the distance between the WD and the serving TRP; The WD calculates the effective DL channel, which is obtained by removing the inter-TRP delay from the DL channel associated with the corresponding TRP; The WD calculates a Type II CSI report based on the obtained effective channel, and / or · WD reports Type II CSI together with intra-TRP delay spread. One or more of the following may be implemented by a network node: The network node calculates the DL precoder based on the reported Type II PMI and the inter-TRP delay spread; o In particular, for each subband, the network node may apply a de-phase rotation to the reported precoder according to the reported inter-TRP delay.

[0055] Some embodiments will still capture large delay spread in the CSI report, but reduce the Type II CSI reporting overhead when it is used for coherent joint transmission with multiple TRPs.

[0056] According to one aspect, a network node configured to communicate with a wireless device (WD) via a plurality of transmission and reception points (TRPs) is provided. The network node includes an air interface configured to receive from the WD a precoding matrix indicator (PMI) for coherent joint data transmission on the plurality of TRPs and one or both of a time difference and a phase slope associated with each TRP of the plurality of TRPs relative to a reference timing, and a processing circuit in communication with the air interface, the processing circuit configured to apply time pre-compensation to a physical downlink channel in each of the plurality of TRPs according to at least one of the time difference and the phase slope associated with the TRP, and apply a precoding matrix indicated by the PMI to the physical downlink channel in each of the plurality of TRPs.

[0057] According to this aspect, in some embodiments, the time difference is received as one of a phase change per resource block (RB), a phase change per subcarrier frequency, or a phase change per subband, where a subband consists of several RBs. In some embodiments, the time pre-compensation to the physical downlink channel is performed by applying a time advance or a time delay on the physical downlink channel according to the time difference. In some embodiments, the time pre-compensation to the physical downlink channel is performed by applying a phase shift per subcarrier, per RB, or per subband in the frequency domain to the physical downlink channel according to the phase ramp. In some embodiments, the PMI includes at least an indicator of one or both of a plurality of spatial beams and spatial domain (SD) basis vectors associated with each of the plurality of TRPs, an indicator of at least one of the frequency domain (FD) basis vectors, and a cophasing coefficient associated with one of the plurality of spatial beams or SD basis vectors associated with each of the plurality of TRPs and with one of the one or more FD basis vectors. In some embodiments, the phase slope is represented by a frequency domain (FD) basis vector, and an index of the FD basis vector is received as part of the PMI. In some embodiments, the reference timing is a downlink timing associated with a reference TRP, and the reference TRP is one of a plurality of TRPs. In some embodiments, the reference TRP is at least one of predefined and indicated by a WD. In some embodiments, each TRP of the plurality of TRPs is associated with a different channel state information reference signal (CSI-RS) resource.

[0058] According to another aspect, a method is provided in a network node configured to communicate with a wireless device (WD) via a plurality of transmission and reception points (TRPs). The method includes receiving from the WD a precoding matrix indicator (PMI) for coherent joint data transmission on the plurality of TRPs and one or both of a time difference and a phase slope associated with each TRP of the plurality of TRPs relative to a reference timing. The method also includes applying time pre-compensation to a physical downlink channel in each of the plurality of TRPs according to at least one of the time difference and the phase slope associated with the TRP. The method further includes applying a precoding matrix indicated by the PMI to a physical downlink channel in each of the plurality of TRPs.

[0059] According to this aspect, in some embodiments, the time difference is received as one of a phase change per resource block (RB), a phase change per subcarrier frequency, or a phase change per subband, where a subband consists of several RBs. In some embodiments, the time pre-compensation to the physical downlink channel is performed by applying a time advance or a time delay on the physical downlink channel according to the time difference. In some embodiments, the time pre-compensation to the physical downlink channel is performed by applying a phase shift per subcarrier, per RB, or per subband in the frequency domain to the physical downlink channel according to the phase ramp. In some embodiments, the PMI includes at least an indicator of one or both of a plurality of spatial beams and spatial domain (SD) basis vectors associated with each of the plurality of TRPs, an indicator of at least one of the frequency domain (FD) basis vectors, and a cophasing coefficient associated with one of the plurality of spatial beams or SD basis vectors associated with each of the plurality of TRPs and with one of the one or more FD basis vectors. In some embodiments, the phase slope is represented by a frequency domain (FD) basis vector, and an index of the FD basis vector is received as part of the PMI. In some embodiments, the reference timing is a downlink timing associated with a reference TRP, and the reference TRP is one of a plurality of TRPs. In some embodiments, the reference TRP is at least one of predefined and indicated by a WD. In some embodiments, each TRP of the plurality of TRPs is associated with a different channel state information reference signal (CSI-RS) resource.

[0060] According to yet another aspect, a wireless device (WD) configured to communicate with a network node is provided. The WD includes a radio interface configured to receive a CSI report configuration from the network node, the CSI report configuration including a plurality of downlink channel state information (CSI) reference signal (CSI-RS) resources, each of the plurality of CSI-RS resources representing one of a plurality of TRPs. The WD also includes a processing circuit in communication with the radio interface, the processing circuit configured to determine, for each TRP of the plurality of TRPs, at least one of a downlink time difference relative to a reference timing and a downlink phase slope representing the downlink time difference relative to the reference timing based at least in part on the measurement of the plurality of downlink CSI-RS resources. The processing circuit is also configured to report to the network node the determined at least one of the downlink time difference and the downlink phase slope associated with each TRP of the plurality of TRPs.

[0061] According to this aspect, in some embodiments, the processing circuit is further configured to determine, for each of the plurality of TRPs, an effective downlink channel based at least in part on removing an effect of at least one of a downlink time difference and a downlink phase tilt associated with the TRP from a channel measurement performed on a CSI-RS resource associated with the TRP, and to determine a precoder matrix indicator (PMI) based at least in part on the effective downlink channel for coherent joint data transmission from the plurality of TRPs to the WD, and the air interface is further configured to transmit the determined PMI to the network node. In some embodiments, the PMI indicates a precoding matrix for each of a plurality of subbands, the subband including a number of resource blocks (RBs). In some embodiments, the determining the PMI is based at least in part on the effective downlink channel of the plurality of TRPs. In some embodiments, the PMI includes at least an indicator of one or both of a plurality of spatial beams and spatial domain (SD) discrete Fourier transform (DFT) basis vectors associated with each of the plurality of TRPs, an indicator of at least one frequency domain (FD) DFT basis vector, and a cophasing coefficient associated with each one of the plurality of spatial beams and SD basis vectors associated with each of the plurality of TRPs and at least one of the at least one FD basis vector. In some embodiments, the phase slope associated with each TRP of the plurality of TRPs is reported as a phase change per subband. In some embodiments, the phase slope associated with each TRP of the plurality of TRPs is quantized and represented by a frequency domain (FD) discrete Fourier transform (DFT) basis vector, and the FD DFT basis vector is reported as part of the PMI for each of the plurality of TRPs. In some embodiments, the reference timing is a downlink timing previously collected by the WD based on a downlink reference signal (RS), and the downlink RS may be a tracking reference signal (TRS).In some embodiments, the reference timing is a downlink timing associated with a reference TRP, the downlink time difference associated with each TRP is a time delay difference in WD between the CSI-RS resources associated with the TRP and the CSI-RS resources associated with the reference TRP, and the time difference associated with the reference TRP is zero and is not reported. In some embodiments, the reference TRP is one of a plurality of TRPs. In some embodiments, the reference TRP is explicitly indicated by the network node. In some embodiments, the reference TRP is implicitly indicated by the network node. In some embodiments, the reference TRP is determined by the WD. In some embodiments, the reference TRP is pre-specified in a specification. In some embodiments, the radio interface is further configured to transmit to the network node an indication of which TRP of the plurality of TRPs is the reference TRP. In some embodiments, the time difference associated with each of the plurality of TRPs is reported as at least one of a phase change per resource block (RB) and a phase change per number of RBs. In some embodiments, determining the effective channel includes removing a delay factor from a channel measurement associated with a TRP of the plurality of TRPs, the delay factor being based at least in part on a time difference between the TRP and a reference TRP.

[0062] According to another aspect, a method is provided in a wireless device (WD) configured to communicate with a network node comprising a plurality of transmission and reception points (TRPs). The method includes receiving a CSI reporting configuration from the network node, the CSI reporting configuration including a plurality of downlink channel state information (CSI) reference signal (CSI-RS) resources, each of the plurality of CSI-RS resources representing one of the plurality of TRPs. The method includes determining (S150), for each TRP of the plurality of TRPs, at least one of a downlink time difference with respect to a reference timing and a downlink phase slope representing the downlink time difference with respect to the reference timing based at least in part on the measurement of the plurality of downlink CSI-RS resources. The method also includes reporting to the network node the determined at least one of the downlink time difference and the downlink phase slope associated with each TRP of the plurality of TRPs.

[0063] According to this aspect, in some embodiments, the processing circuit is further configured to determine, for each of the plurality of TRPs, an effective downlink channel based at least in part on removing an effect of at least one of a downlink time difference and a downlink phase tilt associated with the TRP from a channel measurement performed on a CSI-RS resource associated with the TRP, and to determine a precoder matrix indicator (PMI) based at least in part on the effective downlink channel for coherent joint data transmission from the plurality of TRPs to the WD, and the air interface is further configured to transmit the determined PMI to the network node. In some embodiments, the PMI indicates a precoding matrix for each of a plurality of subbands, the subband including a number of resource blocks (RBs). In some embodiments, the determining the PMI is based at least in part on the effective downlink channel of the plurality of TRPs. In some embodiments, the PMI includes at least an indicator of one or both of a plurality of spatial beams and spatial domain (SD) discrete Fourier transform (DFT) basis vectors associated with each of the plurality of TRPs, an indicator of at least one frequency domain (FD) DFT basis vector, and a cophasing coefficient associated with each one of the plurality of spatial beams and SD basis vectors associated with each of the plurality of TRPs and at least one of the at least one FD basis vector. In some embodiments, the phase slope associated with each TRP of the plurality of TRPs is reported as a phase change per subband. In some embodiments, the phase slope associated with each TRP of the plurality of TRPs is quantized and represented by a frequency domain (FD) discrete Fourier transform (DFT) basis vector, and the FD DFT basis vector is reported as part of the PMI for each of the plurality of TRPs. In some embodiments, the reference timing is a downlink timing previously collected by the WD based on a downlink reference signal (RS), and the downlink RS may be a tracking reference signal (TRS).In some embodiments, the reference timing is a downlink timing associated with a reference TRP, the downlink time difference associated with each TRP is a time delay difference in WD between the CSI-RS resources associated with the TRP and the CSI-RS resources associated with the reference TRP, and the time difference associated with the reference TRP is zero and is not reported. In some embodiments, the reference TRP is one of a plurality of TRPs. In some embodiments, the reference TRP is explicitly indicated by the network node. In some embodiments, the reference TRP is implicitly indicated by the network node. In some embodiments, the reference TRP is determined by the WD. In some embodiments, the reference TRP is pre-specified in a specification. In some embodiments, the method includes transmitting an indication to the network node of which TRP of the plurality of TRPs is the reference TRP. In some embodiments, the time difference associated with each of the plurality of TRPs is reported as at least one of a phase change per resource block (RB) and a phase change per number of RBs. In some embodiments, determining the effective channel includes removing a delay factor from a channel measurement associated with a TRP of the plurality of TRPs, the delay factor being based at least in part on a time difference between the TRP and a reference TRP.

[0064] A more complete understanding of the present embodiments, together with their attendant advantages and features, will be more readily appreciated by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which: [Brief description of the drawings]

[0065] [Figure 1] FIG. 1 is a diagram of a transmission structure for precoded spatial multiplexing. [Diagram 2] FIG. 1 is a diagram of a two-dimensional antenna array. [Diagram 3] FIG. 2 is a diagram of an example of resource allocation. [Figure 4] FIG. 13 is a diagram showing matrix factors. [Diagram 5] FIG. 1 is a diagram of a procedure for codebook-based transmission for FDD. [Figure 6] FIG. 2 is a diagram of an example of CSI-RS precoding. [Figure 7] FIG. 1 is a diagram of an example of physical downlink control channel (PDCCH) repetition. [Figure 8] FIG. 1 is a diagram of an example of SFN PDCCH on two TRPs. [Figure 9] FIG. 1 is a diagram of an antenna delay power spectrum. [Figure 10] 1 is a schematic diagram of an exemplary network architecture illustrating a communication system connected to a host computer via an intermediate network in accordance with principles of the present disclosure; [Figure 11] 1 is a block diagram of a host computer communicating with a wireless device via a network node, at least partially over a wireless connection, in accordance with some embodiments of the present disclosure. [Figure 12] 1 is a flowchart illustrating an example method implemented in a communication system including a host computer, a network node, and a wireless device for executing a client application on a wireless device, according to some embodiments of the present disclosure. [Figure 13] 1 is a flowchart illustrating an example method implemented in a communication system including a host computer, a network node, and a wireless device for receiving user data at a wireless device, in accordance with some embodiments of the present disclosure. [Figure 14] 1 is a flowchart illustrating an example method implemented in a communication system including a host computer, a network node, and a wireless device for receiving user data at a host computer from a wireless device, in accordance with some embodiments of the present disclosure. [Figure 15]1 is a flowchart illustrating an exemplary method implemented in a communication system including a host computer, a network node, and a wireless device for receiving user data at a host computer, in accordance with some embodiments of the present disclosure. [Figure 16] 1 is a flowchart of an example process in a network node for a Type-II Precoder Matrix Indicator (PMI) for Coherent Joint Transmission (CJT). [Figure 17] 1 is a flowchart of an example process in a wireless device for a Type-II precoder matrix indicator (PMI) for coherent joint transmission (CJT). [Figure 18] 11 is a flowchart of another example process in a network node for a Type-II precoder matrix indicator (PMI) for coherent joint transmission (CJT). [Figure 19] 11 is a flowchart of another example process in a wireless device for a Type-II precoder matrix indicator (PMI) for coherent joint transmission (CJT). [Figure 20] FIG. 1 is a diagram of multi-TRP channels. [Figure 21] FIG. 13 is an example diagram of removing inter-TRP delay. [Figure 22] FIG. 1 is a diagram of an example of CSI-RS based delay measurement. [Figure 23] FIG. 1 is a diagram of an example of applying a precoding matrix with phase rotation per resource block. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0066] Before describing the exemplary embodiments in detail, it should be noted that the embodiments reside primarily in a combination of device components and processing steps related to a Type II precoder matrix indicator (PMI) for coherent joint transmission (CJT). Accordingly, where appropriate, components are represented by conventional symbols in the drawings and only those specific details relevant to understanding the embodiments are shown, so as not to obscure the present disclosure with details that would be readily apparent to those skilled in the art having the benefit of the description herein. Like numbers refer to like elements throughout the description.

[0067] As used herein, relational terms such as "first" and "second," "upper" and "lower" may be used merely to distinguish one entity or element from another entity or element without necessarily requiring or implying any physical or logical relationship or order between such entities or elements. The terminology used herein is merely for the purpose of describing particular embodiments and is not intended to limit the concepts described herein. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms unless the context clearly indicates otherwise. Furthermore, it will be understood that the terms "comprises," "comprising," "includes," and / or "including" as used herein specify the presence of stated features, wholes, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or groups thereof.

[0068] In the embodiments described herein, joining terms such as "in communication with" may be used to indicate electrical or data communication that may be accomplished, for example, by physical contact, induction, electromagnetic radiation, radio signaling, infrared signaling, or optical signaling. Those skilled in the art will appreciate that multiple components may interoperate and that modifications and variations are possible for accomplishing electrical and data communication.

[0069] In some embodiments described herein, the terms "coupled," "connected," and the like may be used herein to indicate a connection, although not necessarily direct, and may include a wired and / or wireless connection.

[0070] The term "network node" as used herein may be any type of network node comprised in a wireless network, which may further comprise any of a base station (BS), radio base station, base transceiver station (BTS), base station controller (BSC), radio network controller (RNC), gNode B (gNB), evolved Node B (eNB or eNodeB), Node B, MSR radio node such as a multi-standard radio (MSR) BS, a multi-cell / multicast coordination entity (MCE), an integrated transmission backhaul (IAB) node, a relay node, a donor node controlled relay, a radio access point (AP), a transmission point, a transmitting node, a remote radio unit (RRU), a remote radio head (RRH), a core network node (e.g., a mobility management entity (MME), a self-organizing network (SON) node, a coordination node, a positioning node, an MDT node, etc.), an external node (e.g., a third party node, a node outside the current network), a node in a distributed antenna system (DAS), a spectrum access system (SAS) node, an element management system (EMS), etc. The network nodes may also include test equipment. As used herein, the term "wireless node" may also be used to denote a wireless device (WD) such as a wireless device (WD) or a wireless network node.

[0071] In some embodiments, the non-limiting terms wireless device (WD) or user equipment (UE) are used interchangeably. A WD in this specification may be any type of wireless device capable of communicating with a network node or another WD via a wireless signal, such as a wireless device (WD). A WD may also be a wireless communication device, a target device, a D2D (device to device) WD, a machine-type WD or a WD capable of machine-to-machine communication (M2M), a low-cost and / or low-complexity WD, a sensor equipped with a WD, a tablet, a mobile terminal, a smartphone, a laptop embedded equipment (LEE), a laptop mounted equipment (LME), a USB dongle, a customer premises equipment (CPE), an Internet of Things (IoT) device, or a narrowband IoT (NB-IOT) device, etc.

[0072] Also, in some embodiments, the general term "radio network node" is used. The radio network node may be any type of radio network node, which may comprise a base station, a radio base station, a base transceiver station, a base station controller, a network controller, an RNC, an evolved Node B (eNB), a Node B, a gNB, a multi-cell / multicast coordination entity (MCE), an IAB node, a relay node, an access point, a radio access point, a remote radio unit (RRU), or a remote radio head (RRH).

[0073] It should be noted that, although terminology from one particular wireless system, such as, for example, 3GPP LTE and / or New Radio (NR), may be used in this disclosure, this should not be considered as limiting the scope of the disclosure to only the aforementioned systems. Other wireless systems, including, but not limited to, Wideband Code Division Multiple Access (WCDMA), Worldwide Interoperability for Microwave Access (WiMax), Ultra Mobile Broadband (UMB), and Global System for Mobile Communications (GSM), may also benefit from utilizing the ideas covered within this disclosure.

[0074] It should be further noted that functionality described herein as being performed by a wireless device or network node may be distributed over multiple wireless devices and / or network nodes. In other words, it is contemplated that the functionality of the network nodes and wireless devices described herein is not limited to implementation by a single physical device, but may in fact be distributed among several physical devices.

[0075] Unless otherwise specified, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art to which this disclosure belongs. It will be further understood that the terms used herein should be interpreted as having a meaning in accordance with the meaning of those terms in the context of this specification and related art, and are not to be interpreted in an ideal or overly formal sense unless expressly so defined herein.

[0076] Some embodiments provide a Type-II precoder matrix indicator (PMI) for coherent joint transmission (CJT).

[0077] Referring again to the drawings, in which like elements are referred to by like reference numerals, FIG. 10 shows a schematic diagram of a communication system 10, such as a 3GPP type cellular network that may support standards such as LTE and / or NR (5G), comprising an access network 12, such as a radio access network, and a core network 14, according to one embodiment. The access network 12 comprises a number of network nodes 16a, 16b, 16c (collectively referred to as network nodes 16), such as NBs, eNBs, gNBs or other types of wireless access points, each defining a corresponding coverage area 18a, 18b, 18c (collectively referred to as coverage area 18). Each network node 16a, 16b, 16c is connectable to the core network 14 over a wired or wireless connection 20. A first wireless device (WD) 22a located in the coverage area 18a is configured to wirelessly connect to or be paged by the corresponding network node 16a. A second WD 22b in the coverage area 18b can wirelessly connect to a corresponding network node 16b. Although multiple WDs 22a, 22b (collectively referred to as wireless devices 22) are shown in this example, the disclosed embodiments are equally applicable to situations where only one WD is in a coverage area or where only one WD connects to a corresponding network node 16. It should be noted that while only two WDs 22 and three network nodes 16 are shown for convenience, a communication system may include many more WDs 22 and network nodes 16.

[0078] It is also contemplated that the WD 22 may be in simultaneous and / or configured to communicate separately with more than one network node 16 and more than one type of network node 16. For example, the WD 22 may have dual connectivity with a network node 16 supporting LTE and the same or different network node 16 supporting NR. As an example, the WD 22 may be in communication with an eNB for LTE / E-UTRAN and a gNB for NR / NG-RAN.

[0079] The communication system 10 may itself be connected to a host computer 24, which may be embodied in hardware and / or software of a standalone server, a cloud-implemented server, a distributed server, or as a processing resource in a server farm. The host computer 24 may be owned or controlled by a service provider, or may be operated by or on behalf of the service provider. The connection 26, 28 between the communication system 10 and the host computer 24 may extend directly from the core network 14 to the host computer 24, or may extend through an optional intermediate network 30. The intermediate network 30 may be one of a public network, a private network, or a hosted network, or a combination of two or more of them. The intermediate network 30, if any, may be a backbone network or the Internet. In some embodiments, the intermediate network 30 may comprise two or more sub-networks (not shown).

[0080] The communication system of FIG. 10 as a whole enables connectivity between one of the connected WDs 22a, 22b and the host computer 24. The connectivity may be described as an over-the-top (OTT) connection. The host computer 24 and the connected WDs 22a, 22b are configured to communicate data and / or signaling via the OTT connection using the access network 12, the core network 14, any intermediate networks 30 and possible further infrastructure (not shown) as intermediaries. The OTT connection may be transparent in the sense that at least some of the participating communication devices through which the OTT connection passes are unaware of the routing of the uplink and downlink communications. For example, the network node 16 may not be or need not be informed regarding the past routing of an incoming downlink communication involving data originating from the host computer 24 to be forwarded (e.g., handed over) to the connected WD 22a. Similarly, network node 16 does not need to be aware of the future routing of outgoing uplink communications originating from WD 22 a and destined for host computer 24 .

[0081] The network node 16 is configured to include a phase derotator 32 that may be configured to determine a downlink precoder by applying a phase derotation for each subband of the precoder indicated by the received Type II PMI based at least in part on the received inter-TRP delay spread. The phase derotator 32 may also be configured to apply a phase rotation to each of a plurality of frequency domain (FD) basis vectors indicated by the Type II PMI, the phase rotation being based at least in part on a timing difference associated with the corresponding TRP. The phase derotator 32 may be configured to apply time precompensation to the physical downlink channel in each of the plurality of TRPs according to at least one of a time difference and a phase slope associated with the TRP. The wireless device 22 is configured to include an effective channel unit 34 that may be configured to determine an effective downlink channel based at least in part on removing the timing difference from the downlink channel for each TRP. More specifically, the effective channel unit 34 may be configured to determine an effective downlink channel based at least in part on removing an effect of timing differences from channel measurements performed on channel state information reference signal (CSI-RS) resources for each TRP of the at least one TRP. The effective channel unit 34 may also be configured to determine, for each TRP of the plurality of TRPs, at least one of a downlink time difference relative to a reference timing and a downlink phase slope representative of the downlink time difference relative to the reference timing based at least in part on measurements of the plurality of downlink CSI-RS resources.

[0082] Next, an exemplary implementation of the WD 22, the network node 16 and the host computer 24 described in the previous paragraph according to an embodiment will be described with reference to FIG. 11. In the communication system 10, the host computer 24 comprises hardware (HW) 38 including a communication interface 40 configured to set up and maintain wired or wireless connections with interfaces of different communication devices of the communication system 10. The host computer 24 further comprises a processing circuit 42, which may have storage and / or processing capabilities. The processing circuit 42 may include a processor 44 and a memory 46. In particular, in addition to or instead of a processor and memory such as a central processing unit, the processing circuit 42 may comprise an integrated circuit for processing and / or control, for example, one or more processors and / or processor cores and / or FPGAs (field programmable gate arrays) and / or ASICs (application specific integrated circuits) adapted to execute instructions. The processor 44 may be configured to access (e.g., write to and / or read from) the memory 46, which may include any type of volatile and / or non-volatile memory, such as cache and / or buffer memory and / or RAM (random access memory) and / or ROM (read only memory) and / or optical memory and / or EPROM (erasable programmable read only memory).

[0083] The processing circuitry 42 may be configured to control any of the methods and / or processes described herein and / or cause such methods and / or processes to be performed, for example, by the host computer 24. The processor 44 corresponds to one or more processors 44 for performing the host computer 24 functions described herein. The host computer 24 includes a memory 46 configured to store data, programmatic software code, and / or other information described herein. In some embodiments, the software 48 and / or host application 50 may include instructions that, when executed by the processor 44 and / or the processing circuitry 42, cause the processor 44 and / or the processing circuitry 42 to perform the processes described herein with respect to the host computer 24. The instructions may be software associated with the host computer 24.

[0084] The software 48 may be executable by the processing circuitry 42. The software 48 includes a host application 50. The host application 50 may be operable to provide services to a remote user, such as the WD 22 connecting via an OTT connection 52 that terminates at the WD 22 and the host computer 24. In providing services to the remote user, the host application 50 may provide user data that is transmitted using the OTT connection 52. "User data" may be data and information, described herein as implementing the described functionality. In one embodiment, the host computer 24 may be configured to provide control and functionality to a service provider and may be operated by or on behalf of the service provider. The processing circuitry 42 of the host computer 24 may enable the host computer 24 to observe, monitor, control, transmit to, and / or receive from the network nodes 16 and / or wireless devices 22.

[0085] The communication system 10 further includes a network node 16 provided therein, the network node 16 including hardware 58 that enables the network node 16 to communicate with the host computer 24 and the WD 22. The hardware 58 may include a communication interface 60 for setting up and maintaining wired or wireless connections with interfaces of different communication devices of the communication system 10, as well as a wireless interface 62 for setting up and maintaining at least a wireless connection 64 with the WD 22 located in the coverage area 18 served by the network node 16. The wireless interface 62 may be formed as or include, for example, one or more RF transmitters, one or more RF receivers, and / or one or more RF transceivers. The communication interface 60 may be configured to facilitate a connection 66 to the host computer 24. The connection 66 may be direct, or the connection 66 may pass through the core network 14 of the communication system 10 and / or one or more intermediate networks 30 outside the communication system 10.

[0086] In the embodiment shown, the hardware 58 of the network node 16 further includes processing circuitry 68. The processing circuitry 68 may include a processor 70 and a memory 72. In particular, in addition to or instead of a processor and memory, such as a central processing unit, the processing circuitry 68 may comprise integrated circuits for processing and / or control, e.g., one or more processors and / or processor cores and / or FPGAs (field programmable gate arrays) and / or ASICs (application specific integrated circuits), adapted to execute instructions. The processor 70 may be configured to access (e.g., write to and / or read from) the memory 72, which may include any type of volatile and / or non-volatile memory, e.g., cache and / or buffer memory and / or RAM (random access memory) and / or ROM (read only memory) and / or optical memory and / or EPROM (erasable programmable read only memory).

[0087] Thus, the network node 16 further has software 74 stored, for example, internally in the memory 72 or in an external memory accessible by the network node 16 via an external connection (e.g., a database, a storage array, a network storage device, etc.). The software 74 may be executable by the processing circuitry 68. The processing circuitry 68 may be configured to control any of the methods and / or processes described herein and / or cause such methods and / or processes to be performed, for example, by the network node 16. The processor 70 corresponds to one or more processors 70 for performing the network node 16 functions described herein. The memory 72 is configured to store data, programmatic software code and / or other information described herein. In some embodiments, the software 74 may include instructions that, when executed by the processor 70 and / or the processing circuitry 68, cause the processor 70 and / or the processing circuitry 68 to perform the processes described herein with respect to the network node 16. For example, the processing circuitry 68 of the network node 16 may include a phase derotator 32 configured to determine a downlink precoder by applying a phase derotation for each subband of the precoder indicated by the received Type II PMI based at least in part on the received inter-TRP delay spread. The phase derotator 32 may also be configured to apply a phase rotation to each of a plurality of frequency domain (FD) basis vectors indicated by the Type II PMI, the phase rotation being based at least in part on a timing difference associated with the corresponding TRP. The phase derotator 32 may be configured to apply time pre-compensation to the physical downlink channel in each of the plurality of TRPs according to at least one of a time difference and a phase tilt associated with the TRP.

[0088] The communication system 10 further includes the already mentioned WD 22. The WD 22 may have hardware 80, which may include a wireless interface 82 configured to set up and maintain a wireless connection 64 with a network node 16 serving the coverage area 18 in which the WD 22 is currently located. The wireless interface 82 may be formed as or may include, for example, one or more RF transmitters, one or more RF receivers, and / or one or more RF transceivers.

[0089] The hardware 80 of the WD 22 further includes a processing circuit 84. The processing circuit 84 may include a processor 86 and a memory 88. In particular, in addition to or instead of a processor and memory, such as a central processing unit, the processing circuit 84 may include integrated circuits for processing and / or control, for example, one or more processors and / or processor cores and / or FPGAs (field programmable gate arrays) and / or ASICs (application specific integrated circuits) adapted to execute instructions. The processor 86 may be configured to access (e.g., write to and / or read from) the memory 88, which may include any type of volatile and / or non-volatile memory, for example, cache and / or buffer memory and / or RAM (random access memory) and / or ROM (read only memory) and / or optical memory and / or EPROM (erasable programmable read only memory).

[0090] Thus, the WD 22 may further comprise software 90, which may be stored, for example, in memory 88 in the WD 22 or in an external memory accessible by the WD 22 (e.g., a database, a storage array, a network storage device, etc.). The software 90 may be executable by the processing circuitry 84. The software 90 may include a client application 92. The client application 92 may be operable to provide services to a human or non-human user via the WD 22 with the support of the host computer 24. At the host computer 24, a running host application 50 may communicate with the running client application 92 via an OTT connection 52 that terminates at the WD 22 and the host computer 24. In providing services to the user, the client application 92 may receive request data from the host application 50 and provide user data in response to the request data. The OTT connection 52 may transfer both the request data and the user data. The client application 92 may interact with the user to generate the user data that the client application 92 provides.

[0091] The processing circuitry 84 may be configured to control any of the methods and / or processes described herein and / or cause such methods and / or processes to be performed, for example, by the WD 22. The processor 86 corresponds to one or more processors 86 for performing the WD 22 functions described herein. The WD 22 includes a memory 88 configured to store data, programmatic software code, and / or other information described herein. In some embodiments, the software 90 and / or the client application 92 may include instructions that, when executed by the processor 86 and / or the processing circuitry 84, cause the processor 86 and / or the processing circuitry 84 to perform the processes described herein with respect to the WD 22. For example, the processing circuitry 84 of the wireless device 22 may include an effective channel unit 34 configured to determine an effective downlink channel based at least in part on removing the timing difference from the downlink channel for each TRP. The effective channel unit 34 may be configured to determine an effective downlink channel based at least in part on removing the effect of timing differences from channel measurements performed on channel state information reference signal (CSI-RS) resources for each TRP of the at least one TRP. The effective channel unit 34 may also be configured to determine at least one of a downlink time difference relative to a reference timing and a downlink phase slope representing the downlink time difference relative to the reference timing based at least in part on measurements of the multiple downlink CSI-RS resources for each TRP of the multiple TRPs. In some embodiments, the internal workings of the network node 16, the WD 22, and the host computer 24 may be as shown in FIG. 11, and separately, the surrounding network topology may be that of FIG. 10.

[0092] 11, OTT connection 52 is depicted abstractly to show communication between host computer 24 and wireless device 22 via network nodes 16, without explicit reference to intermediary devices and the exact routing of messages through those devices. The network infrastructure may determine the routing, and the network infrastructure may be configured to hide the routing from WD 22 or from the service provider operating host computer 24, or both. While OTT connection 52 is active, the network infrastructure may also make decisions to dynamically change the routing (e.g., based on load balancing considerations or reconfiguration of the network).

[0093] The wireless connection 64 between the WD 22 and the network node 16 follows the teachings of the embodiments described throughout this disclosure. One or more of the various embodiments improve the performance of the OTT services provided to the WD 22 using the OTT connection 52, of which the wireless connection 64 may form the final segment. More precisely, the teachings of some of these embodiments may improve data rates, latency, and / or power consumption, thereby providing benefits such as reduced user latency, relaxed limits on file sizes, better responsiveness, extended battery life, etc.

[0094] In some embodiments, measurement procedures may be provided for the purpose of monitoring data rates, latencies, and other factors that one or more embodiments improve upon. There may further be an optional network function for reconfiguring the OTT connection 52 between the host computer 24 and the WD 22 in response to fluctuations in the measurement results. The measurement procedures and / or the network function for reconfiguring the OTT connection 52 may be implemented in the software 48 of the host computer 24 or in the software 90 of the WD 22, or both. In an embodiment, sensors (not shown) may be deployed in or in association with the communication devices through which the OTT connection 52 passes, and the sensors may participate in the measurement procedures by providing values ​​of the monitored quantities exemplified above, or other physical quantities from which the software 48, 90 may calculate or estimate the monitored quantities. The reconfiguration of the OTT connection 52 may include message formats, retransmission settings, preferred routing, etc., and the reconfiguration need not affect the network node 16, and the reconfiguration may be unknown or imperceptible to the network node 16. Some such procedures and functions may be known and practiced in the art. In some embodiments, the measurements may involve proprietary WD signaling that facilitates host computer 24 measurements of throughput, propagation time, latency, etc. In some embodiments, the measurements may be implemented in that software 48, 90 causes OTT connection 52 to be used to send messages, particularly empty or "dummy" messages, while software 48, 90 monitors propagation times, errors, etc.

[0095] Thus, in some embodiments, host computer 24 includes processing circuitry 42 configured to provide user data and communication interface 40 configured to forward the user data to the cellular network for transmission to WD 22. In some embodiments, the cellular network also includes network node 16 having a wireless interface 62. In some embodiments, network node 16 is configured to implement, and / or processing circuitry 68 of network node 16 is configured to implement, the functions and / or methods described herein for preparing / initiating / maintaining / supporting / terminating transmissions to WD 22 and / or preparing / terminating / maintaining / supporting / terminating in receipt of transmissions from WD 22.

[0096] In some embodiments, host computer 24 includes processing circuitry 42 and communications interface 40 configured to receive user data originating from a transmission from WD 22 to network node 16. In some embodiments, WD 22 includes a wireless interface 82 and / or processing circuitry 84 configured to implement and / or perform functions and / or methods described herein for preparing / initiating / maintaining / supporting / terminating a transmission to network node 16 and / or preparing / terminating / maintaining / supporting / terminating in receipt of a transmission from network node 16.

[0097] 10 and 11 show various "units," such as the phase derotator 32 and the effective channel unit 34, as being within their respective processors, it is contemplated that these units may be implemented such that portions of the units are stored in corresponding memories within the processing circuitry. In other words, the units may be implemented in hardware or a combination of hardware and software within the processing circuitry.

[0098] FIG. 12 is a flow chart illustrating an exemplary method implemented in a communication system, such as the communication system of FIG. 10 and FIG. 11, according to one embodiment. The communication system may include a host computer 24, a network node 16, and a WD 22, which may be as described with reference to FIG. 11. In a first step of the method, the host computer 24 provides user data (block S100). In an optional sub-step of the first step, the host computer 24 provides the user data by executing a host application, such as the host application 50, for example (block S102). In a second step, the host computer 24 initiates a transmission carrying the user data to the WD 22 (block S104). In an optional third step, the network node 16 transmits the user data carried in the transmission initiated by the host computer 24 to the WD 22 (block S106), according to the teachings of the embodiments described throughout this disclosure. In an optional fourth step, the WD 22 executes a client application, such as, for example, client application 92, associated with the host application 50 executed by the host computer 24 (block S108).

[0099] FIG. 13 is a flow chart illustrating an exemplary method implemented in a communication system, such as the communication system of FIG. 10, according to one embodiment. The communication system may include a host computer 24, a network node 16, and a WD 22, which may be as described with reference to FIGS. 10 and 11. In a first step of the method, the host computer 24 provides user data (block S110). In an optional sub-step (not shown), the host computer 24 provides the user data by executing a host application, such as, for example, a host application 50. In a second step, the host computer 24 initiates a transmission carrying the user data to the WD 22 (block S112). The transmission may proceed via the network node 16 in accordance with the teachings of the embodiments described throughout this disclosure. In an optional third step, the WD 22 receives the user data carried in the transmission (block S114).

[0100] FIG. 14 is a flow chart illustrating an exemplary method implemented in a communication system, such as the communication system of FIG. 10, according to one embodiment. The communication system may include a host computer 24, a network node 16, and a WD 22, which may be as described with reference to FIGS. 10 and 11. In an optional first step of the method, the WD 22 receives input data provided by the host computer 24 (block S116). In an optional sub-step of the first step, the WD 22 executes a client application 92, which provides user data in response to the received input data provided by the host computer 24 (block S118). Additionally or alternatively, in an optional second step, the WD 22 provides the user data (block S120). In an optional sub-step of the second step, the WD provides the user data by executing a client application, such as the client application 92 (block S122). In providing the user data, the executed client application 92 may further take into account user input received from a user. Regardless of the particular manner in which the user data was provided, WD 22 may, in an optional third sub-step, initiate transmission of the user data to host computer 24 (block S124). In a fourth step of the method, host computer 24 receives the user data transmitted from WD 22 (block S126) in accordance with the teachings of the embodiments described throughout this disclosure.

[0101] 15 is a flow chart illustrating an exemplary method implemented in a communication system, such as the communication system of FIG. 10, according to one embodiment. The communication system may include a host computer 24, a network node 16, and a WD 22, which may be as described with reference to FIG. 10 and FIG. 11. In an optional first step of the method, the network node 16 receives user data from the WD 22 (block S128), in accordance with the teachings of the embodiments described throughout this disclosure. In an optional second step, the network node 16 initiates a transmission of the received user data to the host computer 24 (block S130). In a third step, the host computer 24 receives the user data carried in a transmission initiated by the network node 16 (block S132).

[0102] FIG. 16 is a flow chart of an example process in the network node 16 for a type II precoder matrix indicator (PMI) for coherent joint transmission (CJT). One or more blocks described herein may be implemented by one or more elements of the network node 16, such as by one or more of the processing circuit 68 (including the phase derotator 32), the processor 70, the air interface 62 and / or the communication interface 60. The network node 16 is configured to receive (block S134) a type II precoder matrix indicator (PMI) and a transmit-receive point (TRP)-to-transmit-receive point (TRP) delay spread from the WD, such as via the processing circuit 68 and / or the processor 70 and / or the air interface 62 and / or the communication interface 60. The process also includes determining a downlink precoder by applying a phase derotation for each subband of the precoder indicated by the received type II PMI based at least in part on the received TRP-to-TRP delay spread (block S136). In some embodiments, applying the phase de-rotation includes applying phase rotation to a physical downlink shared channel (PDSCH) transmitted from a first TRP and applying no phase rotation to the same PDSCH transmitted from a second TRP.

[0103] FIG. 17 is a flowchart of an example process in the wireless device 22 according to some embodiments of the present disclosure. One or more blocks described herein may be implemented by one or more elements of the wireless device 22, such as by one or more of the processing circuit 84 (including the effective channel unit 34), the processor 86, the air interface 82, and / or the communication interface 60. The wireless device 22, such as via the processing circuit 84 and / or the processor 86 and / or the air interface 82, is configured to determine (block S138) for each of at least two transmit reception points (TRPs) a downlink channel and a timing difference between the TRPs. The process also includes determining an effective downlink channel (block S140) based at least in part on removing the timing difference from the downlink channel for each TRP. The process further includes determining a type II precoder matrix indicator (PMI) based at least in part on the effective channel (block S142).

[0104] In some embodiments, the timing difference is determined relative to a reference TRP. In some embodiments, the reference TRP is associated with a channel state information reference signal (CSI-RS) resource. In some embodiments, determining the effective channel includes removing a delay factor from at least one channel of the at least one TRP, the delay factor being based at least in part on a timing difference between the at least one TRP and another TRP. In some embodiments, determining a Type II precoder matrix indicator (PMI) is based at least in part on a cascaded channel matrix of the two TRPs. In some embodiments, the process also includes determining a quantized phase slope based at least in part on a timing difference between the TRPs. In some embodiments, the process also includes reporting n-1 timing differences to the network node for the n TRPs used for the coherent joint transmission.

[0105] FIG. 18 is a flow chart of an example process in the network node 16 for a type II precoder matrix indicator (PMI) for coherent joint transmission (CJT). One or more blocks described herein may be implemented by one or more elements of the network node 16, such as by one or more of the processing circuit 68 (including the phase derotator 32), the processor 70, the air interface 62 and / or the communication interface 60. The network node 16, such as via the processing circuit 68 and / or the processor 70 and / or the air interface 62 and / or the communication interface 60, is configured to receive from the WD (block S144) a precoding matrix indicator (PMI) for coherent joint data transmission on the multiple TRPs and one or both of a time difference and a phase slope associated with each TRP of the multiple TRPs relative to a reference timing. The method also includes applying time pre-compensation to a physical downlink channel in each of the multiple TRPs according to at least one of the time difference and the phase slope associated with the TRP (block S146). The method further includes applying the precoding matrix indicated by the PMI to a physical downlink channel in each of the multiple TRPs (block S148).

[0106] According to this aspect, in some embodiments, the time difference is received as one of a phase change per resource block (RB), a phase change per subcarrier frequency, or a phase change per subband, where a subband consists of several RBs. In some embodiments, the time pre-compensation to the physical downlink channel is performed by applying a time advance or a time delay on the physical downlink channel according to the time difference. In some embodiments, the time pre-compensation to the physical downlink channel is performed by applying a phase shift per subcarrier, per RB, or per subband in the frequency domain to the physical downlink channel according to the phase ramp. In some embodiments, the PMI includes at least an indicator of one or both of a plurality of spatial beams and spatial domain (SD) basis vectors associated with each of the plurality of TRPs, an indicator of at least one of the frequency domain (FD) basis vectors, and a cophasing coefficient associated with one of the plurality of spatial beams or SD basis vectors associated with each of the plurality of TRPs and with one of the one or more FD basis vectors. In some embodiments, the phase slope is represented by a frequency domain (FD) basis vector, and an index of the FD basis vector is received as part of the PMI. In some embodiments, the reference timing is a downlink timing associated with a reference TRP, and the reference TRP is one of a plurality of TRPs. In some embodiments, the reference TRP is at least one of predefined and indicated by WD22. In some embodiments, each TRP of the plurality of TRPs is associated with a different channel state information reference signal (CSI-RS) resource.

[0107] FIG. 19 is a flowchart of an example process in the wireless device 22 according to some embodiments of the disclosure. One or more blocks described herein may be implemented by one or more elements of the wireless device 22, such as by one or more of the processing circuit 84 (including the effective channel unit 34), the processor 86, the air interface 82 and / or the communication interface 60. The wireless device 22 is configured to receive, from the network node 16, a CSI reporting configuration including a plurality of downlink channel state information (CSI) reference signal (CSI-RS) resources, each of the plurality of CSI-RS resources representing one of the plurality of TRPs (block S150). The method includes, for each TRP of the plurality of TRPs, determining at least one of a downlink time difference relative to a reference timing and a downlink phase slope representing the downlink time difference relative to the reference timing based at least in part on the measurements of the plurality of downlink CSI-RS resources (block S152). The method also includes reporting to the network node 16 the determined at least one of the downlink time difference and the downlink phase tilt associated with each TRP of the plurality of TRPs (block S154).

[0108] According to this aspect, in some embodiments, the processing circuit is further configured to determine, for each of the plurality of TRPs, an effective downlink channel based at least in part on removing an effect of at least one of a downlink time difference and a downlink phase tilt associated with the TRP from a channel measurement performed on a CSI-RS resource associated with the TRP, and to determine a precoder matrix indicator (PMI) based at least in part on the effective downlink channel for coherent joint data transmission from the plurality of TRPs to the WD 22, and the air interface is further configured to transmit the determined PMI to the network node 16. In some embodiments, the PMI indicates a precoding matrix for each of a plurality of subbands, the subband including a number of resource blocks (RBs). In some embodiments, determining the PMI is based at least in part on the effective downlink channel of the plurality of TRPs. In some embodiments, the PMI includes at least an indicator of one or both of a plurality of spatial beams and spatial domain (SD) discrete Fourier transform (DFT) basis vectors associated with each of the plurality of TRPs, an indicator of at least one frequency domain (FD) DFT basis vector, and a cophasing coefficient associated with each one of the plurality of spatial beams and SD basis vectors associated with each of the plurality of TRPs and at least one of the at least one FD basis vector. In some embodiments, the phase slope associated with each TRP of the plurality of TRPs is reported as a phase change per subband. In some embodiments, the phase slope associated with each TRP of the plurality of TRPs is quantized and represented by a frequency domain (FD) discrete Fourier transform (DFT) basis vector, and the FD DFT basis vector is reported as part of the PMI for each of the plurality of TRPs. In some embodiments, the reference timing is downlink timing previously collected by the WD22 based on a downlink reference signal (RS), and the downlink RS may be a tracking reference signal (TRS).In some embodiments, the reference timing is a downlink timing associated with a reference TRP, the downlink time difference associated with each TRP is a time delay difference in WD22 between the CSI-RS resources associated with the TRP and the CSI-RS resources associated with the reference TRP, and the time difference associated with the reference TRP is zero and is not reported. In some embodiments, the reference TRP is one of a plurality of TRPs. In some embodiments, the reference TRP is explicitly indicated by the network node 16. In some embodiments, the reference TRP is implicitly indicated by the network node 16. In some embodiments, the reference TRP is determined by the WD22. In some embodiments, the reference TRP is pre-specified in a specification. In some embodiments, the method includes transmitting to the network node 16 an indication of which TRP of the plurality of TRPs is the reference TRP. In some embodiments, the time difference associated with each of the plurality of TRPs is reported as at least one of a phase change per resource block (RB) and a phase change per number of RBs. In some embodiments, determining the effective channel includes removing a delay factor from a channel measurement associated with a TRP of the plurality of TRPs, the delay factor being based at least in part on a time difference between the TRP and a reference TRP.

[0109] Having described the general process flows of the configurations of the present disclosure and provided example hardware and software configurations for implementing the processes and functions of the present disclosure, the following sections provide configuration details and examples for a Type-II Precoder Matrix Indicator (PMI) for Coherent Joint Transmission (CJT).

[0110] The term TRP may be represented by a TCI state, an NZP CSI-RS resource, or a subset of ports within the NZP CSI-RS resource.

[0111] In coherent joint transmission, a user receives channels / signals coherently transmitted from multiple TRPs. The total delay spread of the channels between the WD22 and the multiple TRPs is generally larger than when the WD22 receives channels / signals from a single TRP, especially when the average propagation delays from the multiple TRPs to the WD22 are different.

[0112] The above is further illustrated with an example shown in FIG. 20, where WD22 receives channels / signals from two geometrically separated TRPs. Between WD22 and each individual TRP, there are three propagation paths in the channel resulting in a delay spread. As seen in this figure, t1, t2 and t3 are the three delay taps associated with TRP1, and t4, t5 and t6 are the delay taps associated with TRP2. The total delay spread for the combined channel between WD22 and TRP1 and TRP2 is determined by all six delay taps. However, if only the channel between WD22 and each individual TRP is considered, there are only three channel taps, which means a much lower delay spread.

[0113] NR type-II codebooks, including an extended type-II codebook (CB) and an extended type-II port selection (PS) CB in 3GPP Rel-16, as well as a further extended type-II PS CB in 3GPP Rel-17 (for simplicity, hereinafter referred to as 3GPP Rel-16 type-II CB, 3GPP Rel-16 PS CB, and 3GPP Rel-17 PS CB, respectively), can be applied to compress and report channel state information (CSI) in the delay domain (or equivalently, in the frequency domain).

[0114] More specifically, the extended type II precoding matrix W fEach selected frequency-domain (FD) basis vector in may be associated with a dominant delay tap. For the above example, if the existing extended type-II codebook is used for CSI reporting, a total of six FD basis vectors are needed to capture all taps in the combined channel. Having more FD basis vectors also means a larger overhead for reporting W2, since the number of linear combination coefficients in W2, the most pay-load heavy part of Type-II CSI reporting, scales with the number of FD basis vectors.

[0115] 21, the total delay spread has two contributions: the intra-TRP delay spread caused by multipath propagation between the WD 22 and each individual TRP, and the inter-TRP delay spread caused by propagation delay differences (also referred to herein as timing differences) due to the two TRPs being geometrically separated (and thus having different distances to the WD 22). The impact of the inter-TRP delay spread essentially adds a common offset for the intra-TRP delay spread.

[0116] Based on the above observations, in order to reduce the required overhead for capturing a large total delay spread for the combined channel, it is reasonable to treat the intra-TRP (i.e., within the same TRP) delay spread and the inter-TRP (i.e., between different TRPs) delay spread separately. In particular, the inter-TRP delay spread may be estimated and reported separately. The inter-TRP delay spread may then be removed from the part of the combined channel associated with the corresponding TRP, and an effective channel may be obtained. Finally, the intra-TRP delay spreads associated with multiple TRPs may be compressed together based at least in part on the effective channel with fewer FD basis vectors.

[0117] The above method for separately processing the inter-TRP delay spread and the intra-TRP delay spread is further explained in FIG. 21. The total delay spread of the original combined multi-TRP channel is shown on the left side of FIG. 21, and the effective delay spread of the effective channel after removing the inter-TRP delay (i.e., the propagation delay difference between different TRPs and WD22) is shown on the right side of FIG. 21. In this example, the inter-TRP delay is given by τ=t4-t1. After removing the inter-TRP delay τ for TRP2, the effective channel contains only four delay taps compared to six delay taps in the original channel. Thus, four FD basis vectors are sufficient to capture all delay taps in the effective channel. Therefore, the number of coefficients in W2 can also be reduced accordingly.

[0118] Furthermore, a larger delay spread means a more frequency selective channel and therefore a smaller coherent bandwidth, which requires a smaller subband size for the CSI feedback so that the channel (both amplitude and phase) does not vary significantly within a subband. This results in more subbands for a given bandwidth.

[0119] Proposed general procedure for Type II reporting extension The general procedure of the proposed Type-II CSI reporting extension for multi-TRP coherent joint transmission can be summarized in the following steps. Step 1: The WD 22, such as via the processing circuitry 84, estimates the timing difference between the DL channel and the served TRP; Step 2: The WD22 removes the timing difference for the corresponding TRP to obtain an effective DL channel; Step 3: Based on the effective DL channel, the WD22 calculates the Type II PMI; Step 4: The WD22 reports a Type II CSI that includes both the PMI and the timing difference between the served TRP, and / or Step 5: The network node 16, e.g., a gNB, applies a precoding matrix associated with the Type II PMI along with a phase rotation based at least in part on the reported timing difference between the served TRPs.

[0120] In step 1, the WD 22 estimates the DL channel and also the timing difference between the served TRPs. The timing difference may be the inter-TRP delay between two given TRPs.

[0121] When estimating the timing difference, a reference TRP may be used, and thus the reported timing difference is calculated relative to a common reference TRP. The reference TRP may be explicitly specified in the NR 3GPP specification, or the reference TRP may be inferred from the CSI reporting configuration. For example, when the reference TRP is explicitly specified in the NR 3GPP specification, the reference TRP may be associated with an explicitly configured CSI-RS resource, and when the reference TRP is implicitly inferred, the reference TRP may be associated with a pre-determined CSI-RS resource, such as the first CSI-RS resource in the CSI reporting configuration. In some cases, instead of the term "reference TRP", "reference CSI-RS resource for deriving timing difference between TRPs" may be used in the 3GPP specification.

[0122] An example in which two CSI-RS resources are transmitted from two TRPs in an OFDM system is shown in Figure 22. τ1 and τ2 are the time delays associated with the first delay taps corresponding to TRP1 and TRP2, respectively. The delays are The observed channels in WD are shown in Fig. 2 for TRP1. TIFF2025512727000053.tif6170, and for TRP2 TIFF2025512727000054.tif6170. τ2-τ1 is the timing difference between TRP2 and TRP1.

[0123] In the above embodiments, the timing difference between different TRPs may be estimated based at least in part on different CSI-RS resources (i.e., each TRP corresponds to a different CSI-RS resource). Note that in some alternative embodiments, the timing difference between TRPs may be estimated based at least in part on subsets of ports within a single CSI-RS resource. For example, in some embodiments, different subsets of ports may correspond to different TRPs, and WD22 estimates a channel corresponding to each TRP on one of the subsets of ports within a single CSI-RS resource.

[0124] In step 2, the WD22 obtains the effective DL channel after removing the estimated timing difference from the channel associated with the corresponding TRP. In the above example, the timing difference may be estimated for TRP1, i.e., τ2-τ1. Let the effective channels, H1 and H2, be the measured channels, respectively. TIFF2025512727000055.tif6170 and From TIFF2025512727000056.tif6170, Delay Factor TIFF2025512727000057.tif5170 and Obtained by removing TIFF2025512727000058.tif5170.

[0125] Alternatively, the effective channel for TRP2 is the measured channel Timing difference factor from TIFF2025512727000059.tif6170 By removing TIFF2025512727000060.tif5170, TIFF2025512727000061.tif6170. In this case, TRP1 is used as the reference TRP and the timing difference is calculated relative to TRP1. Therefore, the effective channel for TRP1 is the measured channel This is given directly by TIFF2025512727000062.tif6170.

[0126] In step 3, WD22 calculates the Type-II PMI based at least in part on the cascaded effective DL channel, e.g., H=[H1H2] in the example shown in step 2. The Type-II PMI may follow the same general structure as the 3GPP Rel-16 Type-II codebook or the 3GPP Rel-17 Type-II codebook. However, the spatial domain (SD) basis vectors are block diagonal matrices, with each block corresponding to an SD basis vector for one of the TRPs. In the example described in step 2, the precoding matrix in PMI subband n (n=1,...,N3) associated with the Type-II PMI is TIFF2025512727000063.tif10170, where W1(n) is associated with TRP1, W2(n) is associated with TRP2, and N3 is the number of PMI subbands.

[0127] In addition to the above Type II PMI components from the existing 3GPP Rel-16 / 17 Type II codebook, the WD22 may also report the timing difference between each of the configured TRPs for Type II based CJT CSI feedback and the reference TRP in the configured TRP, e.g., τ2-τ1 in the example described in step 2.

[0128] For a given frequency, the timing difference between two TRPs is the phase difference between the signals received from the two TRPs, i.e., TIFF2025512727000064.tif6170. The phase difference varies linearly over frequency, and the phase slope is sufficient to characterize this timing difference.

[0129] In one embodiment, the phase slope is quantized between 0 and 2π and reported to the network node 16 as part of a Type II CSI report. Since CSI-RS has one channel sample per RB for each CSI-RS port, the phase change or phase slope may only be measured at a per-RB granularity. Thus, in one embodiment, the phase change over one RB between the measured channels associated with two CSI-RS resources may be reported, i.e. TIFF2025512727000065.tif5170, where Δf is the bandwidth per RB in Hertz. TIFF2025512727000066.tif4170 can be quantized between 0 and 2π.

[0130] In another embodiment, the quantized phase slope may be represented by an FD basis vector taken from a DFT matrix, possibly with oversampling in frequency (e.g., sampled per RB instead of per PMI subband in existing Type II CSI). The index of the corresponding FD basis vector is reported to the network node 16. The length of the FD basis vector, i.e., the size of the DFT matrix, may be different from the length for the FD basis vector used to compress the effective channel. A larger DFT matrix size may remove the inter-TRP delay more accurately.

[0131] Let n denote the number of TRPs used for coherent joint transmission. In some embodiments, at least n - 1 timing differences need to be reported. In some embodiments, which timing differences are reported from WD22 to network node 16 depends on which TRPs are selected as part of type II CSI feedback. In some embodiments, WD22 can be configured for n different CSI-RS resources (i.e., n TRPs), and WD22 selects SD basis vectors or CSI-RS ports from only a subset n' < n of the CSI-RS resources as part of type II CSI feedback (i.e., n' TRPs are selected by WD22 for coherent joint transmission). In this case, only n' - 1 timing differences need to be reported, and a reference CSI-RS resource (or reference TRP) for calculating the timing differences can be identified using one of the above embodiments.

[0132] The timing differences can give rise to frequency selectivity. In some other embodiments, the phase change for each of the plurality of TRPs with respect to the reference TRP for each FD sub-band due to the timing differences is reported to network node 16.

[0133] In step 4, WD22 includes the (one or more) timing differences as part of type II CSI reporting and reports the (one or more) timing differences to network node 16.

[0134] Since the (one or more) timing differences are large-scale fading channel characteristics, they can be reported to network node 16 in CSI reporting part 1.

[0135] In step 5, network node 16 uses the reported timing differences 23, where the per-subband precoder {W1(n),n=1,...,N3} reported by WD22 is applied to the PDSCH transmitted from TRP1, and the per-subband precoder {W2 ...3(n),n=1,...,N3} reported by WD22 is applied to the PDSCH transmitted from TRP1, and the per-subband precoder {W4(n),n=1,...,N3} reported by WD22 is applied to the PDSCH transmitted from TRP1, and the per-RB phase derotation factor TIFF2025512727000068.tif5170 and applies to the same PDSCH transmitted from TRP2 for CJT, where N3 is the number of PMI subbands and n RB is the RB index. Phase derotation is effectively a delay pre-compensation for the timing difference between the two TRPs. Alternatively, phase derotation can be expressed as With the per-subcarrier phase derotation amount of TIFF2025512727000069.tif5170, it can be applied per subcarrier rather than per RB, where N sc is the number of subcarriers per RB.

[0136] In the above example, two TRPs were used for illustration purposes, but the ideas can easily be extended to three or more TRPs.

[0137] Some embodiments may include one or more of the following. A1. A network node configured to communicate with a wireless device (WD), the network node comprising: receiving a type II precoder matrix indicator (PMI) and a transmit-receive-point (TRP) delay spread from a WD; determining a downlink precoder by applying a phase derotation for each subband of the precoder indicated by the received Type II PMI based at least in part on the received inter-TRP delay spread; a network node configured to perform the above and / or comprising a wireless interface configured to perform the above and / or comprising processing circuitry configured to perform the above. Embodiment A2. The network node of embodiment A1, wherein applying phase derotation includes applying phase rotation to a physical downlink shared channel (PDSCH) transmitted from a first TRP and not applying phase rotation to the same PDSCH transmitted from a second TRP. Embodiment B1. A method implemented in a network node configured to communicate with a wireless device (WD), the method comprising: receiving a type II precoder matrix indicator (PMI) and a transmit-receive-point (TRP) delay spread from a WD; determining a downlink precoder by applying a phase derotation for each subband of the precoder indicated by the received Type II PMI based at least in part on the received inter-TRP delay spread; A method comprising: Embodiment B2. The method of embodiment B1, wherein applying phase derotation includes applying phase rotation to a physical downlink shared channel (PDSCH) transmitted from a first TRP and applying no phase rotation to the same PDSCH transmitted from a second TRP. Embodiment C1. A wireless device (WD) configured to communicate with a network node, the WD comprising: determining, for each of at least two transmit reception points (TRPs), a timing difference between a downlink channel and the TRP; determining an effective downlink channel based at least in part on removing the timing difference from the downlink channel for each TRP; determining a type II precoder matrix indicator (PMI) based at least in part on the effective channel; A wireless device (WD) configured to perform the above and / or comprising a wireless interface configured to perform the above and / or comprising a processing circuit configured to perform the above. Embodiment C2. The WD of embodiment C1, wherein the timing difference is determined relative to a reference TRP. Embodiment C3. The WD of embodiment C2, wherein the reference TRP is associated with a channel state information reference signal (CSI-RS) resource. Embodiment C4. The WD of any one of embodiments C1 to C3, wherein determining an effective channel includes removing a delay factor from at least one channel of at least one TRP, the delay factor being based at least in part on a timing difference between the at least one TRP and another TRP. Embodiment C5. The WD of any one of embodiments C1 to C4, wherein determining the type II precoder matrix indicator (PMI) is based at least in part on cascaded channel matrices of two TRPs. Embodiment C6. A WD as described in any one of embodiments C1 to C5, wherein the WD, wireless interface and / or processing circuitry are further configured to determine a quantized phase slope based at least in part on a timing difference between the TRPs. Embodiment C7. A WD as described in any one of embodiments C1 to C6, wherein the WD, the radio interface and / or the processing circuitry are further configured to report n-1 timing differences to the network node for the n TRPs used for coherent joint transmission. Embodiment D1. A method implemented in a wireless device (WD), comprising: determining, for each of at least two transmit reception points (TRPs), a timing difference between a downlink channel and the TRP; determining an effective downlink channel based at least in part on removing the timing difference from the downlink channel for each TRP; determining a type II precoder matrix indicator (PMI) based at least in part on the effective channel; A method comprising: Embodiment D2. The method of embodiment D1, in which the timing difference is determined relative to a reference TRP. Embodiment D3. The method of embodiment D2, in which the reference TRP is associated with a channel state information reference signal (CSI-RS) resource. Embodiment D4. The method of any one of embodiments D1 to D3, wherein determining an effective channel includes removing a delay factor from at least one channel of at least one TRP, the delay factor being based at least in part on a timing difference between the at least one TRP and another TRP. Embodiment D5. The method of any one of embodiments D1 to D4, wherein determining a Type II precoder matrix indicator (PMI) is based at least in part on cascaded channel matrices of two TRPs. Embodiment D6. The method of any one of embodiments D1 to D5 further comprising determining a quantized phase ramp based at least in part on a timing difference between the TRPs. Embodiment D7. The method of any one of embodiments D1 to D6, further comprising reporting n-1 timing differences to the network node for the n TRPs used for coherent joint transmission.

[0138] As will be appreciated by those skilled in the art, the concepts described herein may be embodied as a method, a data processing system, a computer program product, and / or a computer storage medium storing an executable computer program. Thus, the concepts described herein may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects, all of which may be generally referred to herein as a "circuit" or "module." Any process, step, action, and / or function described herein may be performed by and / or associated with a corresponding module, which may be implemented in software and / or firmware and / or hardware. Furthermore, the present disclosure may take the form of a computer program product on a tangible computer usable storage medium having computer program code embodied in the medium that can be executed by a computer. Any suitable tangible computer readable medium may be utilized, including hard disks, CD-ROMs, electronic storage devices, optical storage devices, or magnetic storage devices.

[0139] Some embodiments have been described herein with reference to flowchart illustrations and / or block diagrams of methods, systems and computer program products. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general purpose computer (to create a special purpose computer), a special purpose computer, or other programmable data processing apparatus to create a machine, such that the instructions, executing via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions / acts specified in one or more blocks of the flowchart and / or block diagram.

[0140] These computer program instructions may also be stored in a computer-readable memory or storage medium that may direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory create an article of manufacture that includes instruction means that implement the functions / acts specified in one or more blocks of the flowcharts and / or block diagrams.

[0141] Computer program instructions may also be loaded into a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, such that the instructions executing on the computer or other programmable apparatus provide steps for implementing the functions / acts specified in one or more blocks of the flowcharts and / or block diagrams.

[0142] It should be understood that the functions / acts noted in the blocks may occur out of the order noted in the operational illustrations. For example, two blocks shown in succession may in fact be performed substantially concurrently, or the blocks may sometimes be performed in the reverse order, depending on the functions / acts involved. Although some of the figures include arrows on communication paths to indicate the primary direction of communication, it should be understood that communication may occur in the opposite direction to that of the illustrated arrows.

[0143] Computer program code for performing the operations of the concepts described herein may be written in an object-oriented programming language, such as Python, Java, or C++. However, computer program code for performing the operations of the present disclosure may also be written in a conventional procedural programming language, such as the "C" programming language. The program code may run entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer. In the latter scenario, the remote computer may be connected to the user's computer through a local area network (LAN) or wide area network (WAN), or the connection may be made to an external computer (e.g., through the Internet using an Internet Service Provider).

[0144] Many different embodiments have been disclosed herein with reference to the above description and drawings. It will be understood that literally describing and illustrating every combination and subcombination of these embodiments would be unduly repetitive and unclear. Thus, all embodiments may be combined in any manner and / or combination, and the present specification, including the drawings, is intended to constitute a complete written description of every combination and subcombination of the embodiments described herein and of the manner and process of making and using them, and to support claims to any such combination or subcombination.

[0145] Abbreviations that may be used in the foregoing description include the following:

[0146] Abbreviation Description DFT Discrete Fourier Transform eType II Extended Type II, 3GPP Rel-16 Type II feType II Further extension type II, 3GPP Rel-17 type II FD frequency domain LCC Linear combination coefficient SCI Strongest Coefficient Indicator SD spatial domain TD time domain TRP Sending and Receiving Points W1 A matrix containing all the space-domain basis vectors for Type II PMI W f A matrix containing all frequency-domain basis vectors for Type-II PMI W2W1 and W f A matrix containing the complex cophasing factors for

[0147] It will be appreciated by those skilled in the art that the embodiments described herein are not limited to what has been particularly shown and described herein above. Furthermore, unless otherwise noted above, it should be noted that all of the accompanying drawings are not necessarily to scale. Various modifications and variations are possible in light of the above teachings without departing from the scope of the following claims.

Claims

1. A method in a network node (16) configured to communicate with a wireless device (WD) (22) via a plurality of transmit and receive points (TRPs), the method comprising: receiving (S144) from the WD (22), a precoding matrix indicator (PMI) for coherent joint data transmission on the plurality of TRPs, and one or both of a time difference and a phase tilt associated with each TRP of the plurality of TRPs with respect to a reference timing; applying (S146) time pre-compensation to a physical downlink channel in each of the plurality of TRPs according to at least one of the time difference and the phase tilt associated with the TRP; applying (S148) the precoding matrix indicated by the PMI to the physical downlink channel in each of the plurality of TRPs A method comprising.

2. The method according to claim 1, wherein the time difference is received as one of a phase change per resource block (RB), a phase change per sub-carrier frequency, or a phase change per sub-band, and the sub-band consists of several RBs.

3. The method according to claim 1, wherein the time pre-compensation to the physical downlink channel is implemented by applying a time advance or a time delay on the physical downlink channel according to the time difference.

4. The method according to claim 1, wherein the time pre-compensation to the physical downlink channel is implemented by applying a phase shift per sub-carrier, per RB, or per sub-band in the frequency domain to the physical downlink channel according to the phase tilt.

5. The method according to claim 1, wherein the PMI includes at least an indicator of one or both of a plurality of spatial beams and spatial domain (SD) basis vectors associated with each of the plurality of TRPs, an indicator of at least one of the frequency domain (FD) basis vectors, and a co-phasing coefficient associated with one of the plurality of spatial beams or SD basis vectors associated with each of the plurality of TRPs and one of the one or more FD basis vectors, respectively.

6. The method according to claim 1, wherein the phase tilt is represented by a frequency domain (FD) basis vector, and an index of the FD basis vector is received as part of the PMI.

7. The method according to claim 1, wherein the reference timing is a downlink timing associated with a reference TRP, and the reference TRP is one of the plurality of TRPs.

8. The method according to claim 7, wherein the reference TRP is at least one of predefined and indicated by the WD.

9. The method according to claim 1, wherein each of the plurality of TRPs is associated with a different channel state information reference signal (CSI-RS) resource.

10. A network node (16) configured to communicate with a wireless device (WD) (22) via a plurality of transmit and receive points (TRPs), the network node (16) being a wireless interface (62) configured to receive, from the WD (22), a precoding matrix indicator (PMI) for coherent joint data transmission on the plurality of TRPs and one or both of a time difference and a phase tilt associated with each of the plurality of TRPs with respect to a reference timing; a processing circuit (68) communicating with the wireless interface (62), the processing circuit (68) being applying time pre-compensation to a physical downlink channel in each of the plurality of TRPs according to at least one of the time difference and the phase tilt associated with the TRP; applying a precoding matrix indicated by the PMI to the physical downlink channel in each of the plurality of TRPs A network node (16) configured to perform.

11. The network node (16) according to claim 10, wherein the processing circuit (68) is further configured to perform the method according to any one of claims 2 to 9.

12. A method in a wireless device (WD) (22) configured to communicate with a network node (16) comprising a plurality of transmit and receive points (TRPs), the method comprising Receiving, from the network node, a configuration of a CSI report including a plurality of downlink channel state information (CSI) reference signal (CSI-RS) resources (S150), wherein each of the plurality of downlink CSI-RS resources represents one of the plurality of TRPs, and receiving the configuration of the CSI report (S150); For each TRP of the plurality of TRPs, at least partially based on measurements of the plurality of downlink CSI-RS resources, a downlink time difference with respect to a reference timing, and a downlink phase slope representing the downlink time difference with respect to the reference timing Determining at least one of them (S152); Reporting to the network node at least one of the determined downlink time difference and the downlink phase slope associated with each TRP of the plurality of TRPs (S154); A method comprising.

13. For each of the plurality of TRPs, determining an effective downlink channel based at least in part on removing the influence of at least one of the downlink time difference and the downlink phase slope associated with the TRP from channel measurements performed on the CSI-RS resources associated with the TRP; Determining a precoder matrix indicator (PMI) based at least in part on the effective downlink channel for coherent joint data transmission from the plurality of TRPs to the WD; Transmitting the determined PMI to the network node The method according to claim 12, further comprising.

14. The method according to claim 13, wherein the PMI indicates a precoding matrix for each of a plurality of subbands, and the subbands include a plurality of resource blocks (RBs).

15. The method according to claim 13, wherein determining the PMI is based at least in part on the effective downlink channel of the plurality of TRPs.

16. The method according to claim 13, wherein the PMI includes at least an indicator of one or both of a plurality of spatial beam and spatial domain (SD) discrete Fourier transform (DFT) basis vectors associated with each of the plurality of TRPs, an indicator of at least one frequency domain (FD) DFT basis vector, and a co-phasing coefficient associated with at least one of each of one or both of the plurality of spatial beam and SD basis vectors associated with each of the plurality of TRPs and at least one of the at least one FD basis vector.

17. The method according to claim 12, wherein the phase tilt associated with each TRP of the plurality of TRPs is reported as a phase change for each sub-band.

18. The method according to claim 13, wherein the phase tilt associated with each TRP of the plurality of TRPs is quantized and represented by a frequency domain (FD) discrete Fourier transform (DFT) basis vector, and the FD DFT basis vector is reported as part of the PMI for each of the plurality of TRPs.

19. The method according to claim 12, wherein the reference timing is the downlink timing previously obtained by the WD based at least in part on a downlink reference signal (RS), and the downlink RS can be a tracking reference signal (TRS).

20. The method according to claim 12, wherein the reference timing is the downlink timing associated with a reference TRP, and the downlink time difference associated with each TRP is the time delay difference in the WD between the CSI-RS resource associated with the TRP and the CSI-RS resource associated with the reference TRP, and the time difference associated with the reference TRP is 0 and not reported.

21. The method according to claim 20, wherein the reference TRP is one of the plurality of TRPs.

22. The method according to claim 20, wherein the reference TRP is explicitly indicated by the network node.

23. The method according to claim 20, wherein the reference TRP is implicitly indicated by the network node.

24. The method according to claim 20, wherein the reference TRP is determined by the WD.

25. The method according to claim 20, wherein the reference TRP is pre-specified in the specification.

26. The method according to claim 20, further comprising transmitting to the network node (16) an indication of which of the plurality of TRPs is the reference TRP.

27. The method according to claim 12, wherein the time difference associated with each of the plurality of TRPs is reported as at least one of a phase change per resource block (RB) and a phase change per a certain number of RBs.

28. Determining the effective downlink channel includes removing a delay factor from channel measurements associated with a TRP among the plurality of TRPs, wherein the delay factor is at least partially based on a time difference between the TRP and a reference TRP. The method according to claim 13.

29. A wireless device (WD) (22) configured to communicate with a network node (16), the WD (22) A wireless interface (82) configured to receive from the network node a setting of a CSI report including a plurality of downlink channel state information (CSI) reference signal (CSI-RS) resources, each of the plurality of downlink CSI-RS resources representing one of a plurality of transmit and receive points (TRPs). Wireless interface (82), A processing circuit (84) communicating with the wireless interface (82), the processing circuit (84) For each TRP of the plurality of TRPs, at least partially based on measurements of the plurality of downlink CSI-RS resources, The downlink time difference with respect to the reference timing, and The downlink phase slope representing the downlink time difference with respect to the reference timing Determining at least one of; Reporting to the network node at least one of the determined downlink time difference and the downlink phase slope associated with each TRP of the plurality of TRPs A wireless device (WD) (22) configured to perform.

30. The WD (22) according to claim 29, wherein the processing circuit (84) is configured to perform the method according to any one of claims 13 to 28.

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