Type II precoder matrix indicator (PMI) enhancements for coherent joint transmission (CJT)

Abstract

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

Description

Technical Field

[0001] The present disclosure relates to wireless communications, and in particular to precoder matrices, such as a Type II Precoder Matrix Indicator (PMI) for Coherent Joint Transmission (CJT). Background Art

[0002] The 3rd Generation Partnership Project (3GPP) has developed and is developing standards for fourth generation (4G) (also known as Long Term Evolution (LTE)) and fifth generation (5G) (also known as New Radio (NR)) wireless communication systems. 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. Codebook-based precoding

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

[0004] The NR standard is currently evolving with enhanced MIMO support. A core component in NR is the support of MIMO-related technologies such as spatial multiplexing and MIMO antenna deployment. The spatial multiplexing mode is designed for high data rates under favorable channel conditions. Figure 1 An illustration of an example of spatial multiplexing operation is provided in .

[0005] like Figure 1 As shown in the figure, the information carrying symbol vector s is related to N T xr is multiplied by the precoder matrix W, which is used to multiply the precoder matrix W in N T (corresponding to N T The transmission energy is allocated in a subspace of a dimensional vector space (number of antenna ports). The precoder matrix is ​​typically selected from a codebook of possible precoder matrices and is typically indicated by a precoder matrix indicator (PMI), which specifies a unique precoder matrix in the codebook for a given number of symbol streams. Each of the r symbols in s corresponds to a layer, and r is called the transmission rank. In this way, spatial multiplexing is achieved because multiple symbols can be transmitted simultaneously on the same time / frequency resource element (TFRE). The number of symbols r is typically adapted to accommodate 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). Therefore, for a certain TFRE on subcarrier n (or alternatively data TFRE number n), the received N R x 1 vector y n It can be modeled as follows: y n =H n W n +e n Among them, e n is the noise / interference vector obtained as a realization of a random process. The precoder W can be a wideband precoder, which is constant in frequency, or can be frequency selective.

[0007] The precoder matrix W is often chosen to match N R x N T MIMO channel matrix H n This is also often referred to as closed-loop precoding and essentially strives to focus the transmit energy into a subspace that is strong in the sense that a large amount of the transmit energy is conveyed to the WD.

[0008] In closed-loop precoding for the NR downlink, based on channel measurements in the downlink, the WD transmits a recommendation of a suitable precoder to be used to the network node (e.g., gNB). The network node configures the WD to provide feedback according to the CSI-ReportConfig, and may transmit the CSI-RS, and configures the WD to use measurements of the CSI-RS to feedback the recommended precoding matrix selected by the WD from the codebook. A single precoder (wideband precoding) that should cover a large bandwidth may be fed back. It may also be beneficial to match the frequency variation 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 covers feedback of other information in addition to the recommended precoder to assist the network node in subsequent transmissions to the WD. Such other information may include a channel quality indicator (CQI) and 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 contiguous resource blocks ranging between 4-32 physical resource blocks (PRBs), depending on the bandwidth part (BWP) size.

[0009] Given the CSI feedback from the WD, the network node determines the transmission parameters it wishes to use to transmit to the WD, including the precoding matrix, transmission rank, and modulation and coding scheme (MCS). These transmission parameters may be different from the recommendation made by the WD. The transmission rank and therefore the number of spatial multiplexing layers is reflected in the number of columns of the precoder W. For efficient performance, the transmission rank that matches the channel properties should be selected. 2D Antenna Array

[0010] A two-dimensional antenna array can be represented by the number N of antenna columns corresponding to the horizontal dimension. h , the number of antenna rows corresponding to the vertical dimension N v , and the number of dimensions N corresponding to different polarizations p The total number of antennas is therefore N = N h N v N p The concept of an antenna is non-limiting in the sense that it may refer to any virtualization (e.g., linear mapping) of a physical antenna element. For example, pairs of physical sub-elements may be fed the same signal and thus share the same virtualized antenna port.

[0011] Figure 2 An example of a 4x4 array with dual polarized antenna elements is illustrated in FIG.

[0012] Precoding can be interpreted as multiplying the signal with different beamforming weights for each antenna before transmission. A typical approach is to adapt the precoder to the antenna shape factor, i.e., consider N when designing the precoder codebook. h 、N v and N p . Channel State Information Reference Signal (CSI-RS)

[0013] For CSI measurement and feedback, a CSI reference signal (RS) is defined. CSI-RS is transmitted on each antenna port and is used by WD to measure the downlink channel between each of the transmit antenna ports and each of its receive antenna ports. Transmit antenna ports are also called CSI-RS ports. The number of supported antenna ports in NR is {1, 2, 4, 8, 12, 16, 24, 32}. By measuring the received CSI-RS, WD can estimate the channel and antenna gain of the radio propagation channel that the CSI-RS is passing through. CSI-RS used for the above purpose is also called non-zero power (NZP) CSI-RS.

[0014] The CSI-RS may be configured to be transmitted in certain slots and certain REs in the slots. Figure 3An example of CSI-RS REs for 12 antenna ports is shown, where 1 RE per RB per port is shown.

[0015] In addition, interference measurement resources (IMR) are also defined in NR for WD to measure interference. IMR resources contain 4 resource elements (REs), 4 adjacent REs in frequency in the same OFDM symbol, or 2 by 2 blocks of adjacent REs in both time and frequency in a slot. By measuring the channel based on non-zero power (NZP) CSI-RS and measuring interference based on IMR, WD can estimate the effective channel and noise plus interference to determine CSI (i.e., rank, precoding matrix, and channel quality).

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

[0017] In NR, a WD can be configured with multiple CSI report settings and multiple CSI-RS resource settings. Each resource setting can contain multiple resource sets, and each resource set can contain up to 8 CSI-RS resources. For each CSI report setting, the WD feeds back a CSI report.

[0018] Each CSI report setting contains at least the following information: ●CSI-RS resource set for channel measurement; ●IMR resource set for interference measurement; ●Optionally, a set of CSI-RS resources for interference measurement; ●Time domain behavior, (i.e., periodic, semi-persistent, or aperiodic reporting); Frequency granularity, i.e. broadband or sub-band; ● In case of multiple CSI-RS resources in a resource set, the CSI parameters to be reported, such as rank indicator (RI), precoding matrix indicator (PMI), channel quality indicator (CQI) and CSI-RS resource indicator (CRI); Codebook type (i.e., Type I or II) and codebook subset constraints; ● measurement constraints; and ● Subband size. Indicates one of two possible subband sizes, the range of values ​​depends on the bandwidth of the BWP. One CQI / PMI is fed back per subband (if configured for subband reporting). DFT-based precoder

[0019] 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-polarization uniform linear array (ULA) with N antennas is defined as: Where k=0, 1, ... QN-1 is the precoder index and Q is an integer oversampling factor. The corresponding precoder vector for a two-dimensional uniform planar array (UPA) can be created by taking the Kronecker product of two precoder vectors as follows:

[0020] Extending the precoder for dual-polarization UPA can then be done as follows: where e jφ is available from the Quadrature Phase Shift Keying (QPSK) alphabet The co-phasing factor of choice.

[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 common special case, for a rank 2 DFT precoder, k1=k2=k and l1=l2=l, meaning:

[0022] Such DFT-based precoders are used in NR Type I CSI feedback. MU-MIMO

[0023] 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 to different WDs at the same time, and the spatial domain (SD) is used to separate the corresponding streams. 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, because power must be shared between streams and the streams will interfere. NR rel-15 Type II codebook

[0024] 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 Specification (TS) 38.214 as:

[0025] If this is reconstructed and expressed more simply, for some layer l=0,1, polarization p=0,1 and resource block k=0,...,N RB The precoder vector w is -1 l，p (k) can be expressed as: Among them, for p = 0, For p = 1, S is the subband size, and N SB is the number of subbands in the CSI reporting bandwidth. Therefore, the change in beam coefficient across frequency c l，i (k) Based on Parameters and is determined. It depends on the codebook configuration, the subband amplitude parameter 0-1 bits are used for quantization, and the subband phase parameters Use 2 or 3 bits for quantization. NR 3GPP Rel-16 enhanced Type II port selection codebook

[0026] In 3GPP Rel-16, an enhanced Type II (eType II) port selection (PS) codebook was introduced, which is intended to be used for beamformed CSI-RS, where each CSI-RS port covers a small portion of the cell coverage area with high beamforming gain (compared to non-beamformed CSI-RS). Although it depends on the network node 16 (e.g., gNB) implementation, it is generally assumed that each CSI-RS port is transmitted in a 2D spatial beam with a main lobe with azimuth and elevation pointing angles. The actual precoder matrix used for the CSI-RS is transparent to the WD. Based on the measurement, the WD selects the best CSI-RS port and recommends the rank, precoding matrix, and CQI adjusted on the rank and the precoding matrix to the network node for downlink (DL) transmission. The precoding matrix includes a linear combination of the selected CSI-RS ports. The eType II PS codebook can be used by the WD to feedback the selected CSI-RS port and the combination coefficients. eType II PS codebook reporting, configuration and structure

[0027] For a given transmission layer l, where l∈{1, .., v} and v is the rank indicated by the rank indicator (RI), the precoder matrix is ​​given by PCSI-RS ×N3 size matrix W l Given, 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; and - The maximum RI value v is set according to the configured higher layer parameter typeII-RI-Restriction-r16. WD shall not report v>4.

[0028] For each layer l, the precoding matrix W l Can be decomposed into (like Figure 4 shown in is normalized so that for l=1,...,v and t=0,1,....N3-1,

[0029] Port selection matrix W1: W1 is P CSI-RS ×2L size port selection precoder matrix, which can be decomposed into in represents the Kronecker product and yes The port selection matrix of size Size (for 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 CSI-RS port is selected by To indicate, which is reported by WD to the network node: ○i 1，1 The value of is determined by the WD based on CSI-RS measurement; The value of d is configured by the higher layer parameter portSelectionSamplingSize, where d∈{1, 2, 3, 4} and -W1 is common to all layers.

[0030] Frequency domain (FD) compression matrix W f，l : W f，l is N3×M for layer l v An FD compressed matrix of size ○ is the number of selected FD basis vectors, which depends on the rank indicator v and the RRC configured parameter p v . p v Supported values ​​of can be found in Table 1.

[0031] in is derived from N3 orthogonal DFT basis vectors Selected M v FD basis vectors, where (.) T Represents transpose: ○For N3≤19, use one-step free selection: ■For each layer, by The bit combination indicator indicates the FD basis selection. In TS38.214, the combination indicator is represented by index i 1，6，l Given, where l corresponds to the layer index. This combined index is reported to the network nodes by the WD at each layer; ○ For N3>19, a two-step selection with layer-shared intermediate subsets (IntS) is used: ■ In this first step, a window-based layer-shared IntS selection is used, which is obtained by M 初始 IntS is parameterized by the FD basis vector mod(M 初始 +n, N3), where n = 0, 1, ..., N'3-1 and N'3 = 2M v In TS 38.214, the selected IntS is determined by the WD via the parameter i 1，5 Report to the network node, the parameter i 1，5 Each layer is reported as part of the PMI report; ■For each layer, by The bit combination indicator is used to indicate the second step subset selection. In 3GPP TS 38.214, the combination indicator is indexed by i 1，6，l Given, where l corresponds to the layer index. This combined index is reported to the network nodes by the WD per layer; ○W f，l Is layer specific.

[0032] Linear combination coefficient matrix W 2，l : W 2，l Contains 2LM v2L×M coefficients v A matrix of size M used for linear combination of the selected v FD basis vectors and the selected 2L CSI-RS ports. ●For layer l, only A subset of coefficients are nonzero and are reported. The remaining Unreported coefficients were considered zero; ○ is the maximum number of non-zero coefficients per layer, where β is a parameter configured by RRC. The supported β values ​​are shown in Table 1; ○ For v∈{2,3,4}, the total number of non-zero coefficients summed across all layers Should meet ○ In 2LM v Bitmap of size i 1，7，l Through 1 to indicate the selected coefficient subset for each layer; ○ The selected CSI-RS port associated with the strongest coefficient of layer l is represented by i 1，8，l ,∈{0,1,...,2L-1} to indicate; W 2，l The amplitude coefficient in is given by i 2，3，l and i 2，4，l To indicate, and W 2，l The phase coefficient in is given by i 2，5，l to instruct; and / or W 2，l Is layer specific. Table 1 For L, p v 3GPP Rel-16 Type II PS codebook parameter configuration for β and

[0033] The PMI reported by the WD contains codebook indices i1 and i2, where

[0034] The precoding matrix is ​​based on the PMI value in Table 2. Table 2: Precoding matrix indicated by PMI in: ● ● ●v m is the element (m mod P CSI-RS / 2) contains a value of 1 in the P and a value of zero elsewhere CSI-RS / 2-element column vector; ● ● From i 1，6，l , and if N3>19, then from i 1，5 ; ● By 2，3，l Indicated wideband amplitude coefficient; ● By 2，4，l the indicated sub-band amplitude coefficients; and ● c l，i，f ∈{0,...,15} is given by i 2，5，l Indicates the phase coefficient.

[0035] For 3GPP Re1-16 enhanced type IICSI 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 RI, CQI, and an indication of the total number of non-zero amplitude coefficients across layers, i.e. Part 2 contains the PMI. Parts 1 and 2 are coded separately. Reciprocity operation based on FDD and 3GPP Rel-17 Type II port selection codebook

[0036] In frequency division duplex (FDD) operation, uplink (UL) and DL transmissions are performed on different frequencies. Therefore, the propagation channels in UL and DL are not reciprocal as in the case of time division duplex (TDD). Nevertheless, some physical channel parameters (such as angles and delays to different clusters) that depend on the spatial properties of the channel rather than the carrier frequency are reciprocal between UL and DL. Such properties can be used to obtain FDD transmission based on partial reciprocity. The reciprocal part of the channel can be combined with the non-reciprocal part to obtain a complete channel. An estimate of the non-reciprocal part can be obtained by feedback from the WD. In 3GPP RAN1, it has been considered that in 3GPP Re1-17, the 3GPP Rel-16 type II port selection codebook will be enhanced to support the above-mentioned FDD-based reciprocity operation. It has been considered in 3GPP RAN1#104e that 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., a codebook consisting of W1, W2, and Wf. Details of the codebook components (such as the dimensions of each matrix) are still under consideration. Procedure for FDD-based reciprocity operation

[0037] exist Figure 5An example process for a reciprocity-based FDD transmission scheme is illustrated in 4 steps, assuming that the NR 3GPP Rel-16 enhanced Type II port selection codebook is used.

[0038] In step 1, the WD is configured with a sounding reference signal (SRS) by the network node, and the WD transmits the SRS in UL for the network node to estimate delays and angles of different clusters associated with different propagation paths.

[0039] In step 2, the network node selects a dominant cluster based on the estimated angle-delay power spectrum profile, based on which a set of spatial domain and frequency domain (SD-FD) basis pairs is calculated by the network node for CSI-RS beamforming. Each SD-FD pair corresponds to a CSI-RS port, where a certain delay is pre-compensated. By applying different delays on different resource elements of the resource, each CSI-RS port resource may contain one or more SD-FD basis pairs. The network node precodes all CSI-RS ports in a configured CSI-RS resource or multiple CSI-RS resources to the WD, where each configured CSI-RS resource contains the same number of SD-FD basis pairs.

[0040] In step 3, the network node has configured the WD to measure CSI-RS, and the WD measures the received CSI-RS port and then determines the type IICSI containing the PMI, RI and CQI of each layer. The precoding matrix indicated by the PMI contains the selected SD-FD basis pair / precoded CSI-RS port, and the corresponding optimal phase and amplitude for phasing the selected pair / port. The phase and amplitude of each pair / port are quantized and fed back to the network node.

[0041] In step 4, the network node implements an algorithm to calculate the DL precoding matrix for each layer based on the selected beam and the corresponding amplitude and phase feedback, and performs PDSCH transmission. The transmission is directly based on the feedback (PMI) precoding matrix (e.g., SU-MIMO transmission) or obtains the transmission precoding matrix (MU-MIMO transmission) from an algorithm that combines CSI feedback from multiple WDs. In this case, the precoder (e.g., a zero-forcing precoder or a regularized ZF precoder) is derived based on the precoding matrix (including CSI reports from co-scheduled WDs). The final precoder is usually scaled so that the transmit power per power amplifier is not overridden.

[0042] Such reciprocity-based transmission can potentially be used in codebook-based DL transmission for FDD to reduce feedback overhead in the UL, for example when using the NR Type II port selection codebook. Another potential benefit is to reduce the complexity of CSI calculation in the WD.

[0043] Notice, Figure 5 Only one example of a process for FDD-based reciprocity operation is shown, where each CSI-RS port contains a single pair of SD-FD basis and the WD performs wideband averaging of the channel to obtain the corresponding coefficients. It is possible that each CSI-RS port contains multiple pairs of SD-FD basis and it is possible that the WD can compress the channel by more FD components in addition to the DC DFT component. Type II port selection codebook for FDD operation based on angle and delay reciprocity

[0044] If the 3GPP Rel-16 enhanced type II port selection codebook is used for FDD operation based on angle and / or delay reciprocity, the frequency domain (FD) basis f It still needs to be determined by the WD. Therefore, in the CSI report, the feedback overhead for indicating which FD basis vectors are selected may be large. This is especially true when N3 (the number of PMI subbands) is large. Similarly, the computational complexity used by the WD to evaluate and select the best FD basis vectors also increases as N3 increases. In addition, the channel seen by the WD is frequency selective, which requires multiple FD basis vectors to be compressed in the PMI report. Reporting coefficients for these FD basis vectors also consumes a lot of UL overhead.

[0045] Based on angle and delay reciprocity, the network node can determine the set of dominant clusters in the propagation channel by analyzing the angle-delay power spectrum of the UL channel. The network node can then use this information in a way that each CSI-RS port is precoded toward the dominant cluster. In addition to SD beamforming, each CSI-RS port will also be precompensated in time so 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, which requires a very small number of FD bases for compression. Ideally, if all beams can be perfectly aligned in time, then the WD only needs to perform broadband filtering to obtain all channel information, based on which the WD can calculate the 3GPP Rel-17 type IIPMI. Even if it is not possible to perfectly precompensate delays at the network node in practice, the frequencies selectively seen by the WD can still be greatly reduced, so that the WD only requires a much smaller number of FD basis vectors (i.e., W f The number of basis vectors in ) is used to compress the channel.

[0046] refer to Figure 6The above process is further explained by the example of . Based on the UL measurement, the network node identifies 8 dominant clusters (labeled as AG) present in the original channel, which are distributed in 4 directions, each of which contains one or more taps. In this example, 8 CSI-RS ports are precoded at the network node. Each CSI-RS port is precoded toward the dominant direction with a precompensated delay for a given cluster. Delay precompensation can be achieved in different ways (e.g., by applying a linear phase slope across occupied subcarriers). As a result, in the beamformed channel (which is seen by the WD), all dominant clusters are aligned with the same delay. Therefore, the WD only needs to apply a broadband filter (e.g., applying the DC component of the DFT matrix (i.e., Wf containing a single all-one vector on the frequency domain channel)) to compress the channel and retain all channel information. Based on the compressed channel, the WD calculates W1 (the selected CSI-RS port) and W2 (the complex coefficients for combining the selected ports), which is the remainder of the type II port selection codebook.

[0047] 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 also contains W1, W2, and W f One difference between the 3GPP Rel-17 Type II precoder and the 3GPP Rel-16 Type II codebook is that Wf is layer-common and the number of FD basis vectors may be only 1 or 2. PDSCH transmission from multiple TRPs

[0048] In NR3GPP Rel-16, non-coherent joint physical downlink shared channel (PDSCH) transmission from two transmission and reception points (TRPs) is introduced, where a subset of the MIMO layers of the PDCCH to the WD is transmitted from the first TRP, and the remaining layers of the PDSCH are transmitted from the second TRP in the same time and frequency resources. The different layers are received at the WD by a MIMO-capable receiver and separated.

[0049] Figure 7An example is shown in which a physical downlink shared channel (PDSCH) with two layers is scheduled, where the first layer is transmitted from TRP1 and the second layer is transmitted from TRP2. This is signaled in the corresponding downlink control information (DCI) by indicating TCI code points associated with two TCI states (the first and second TCI states) and DMRS ports x and y in two CDM groups. Here, the demodulation reference signal (DMRS) port x in the first CDM group is associated with the first TCI state, while the DMRS port y in the second CDM group is associated with the second TCI state. The first TCI state may contain TRS1 (tracking reference signal 1) as a quasi-collocated (QCL) source RS, while the second TCI state may contain TRS1 as a QCL source RS. SFN PDSCH

[0050] In NR 3GPP Rel-17, enhanced single frequency network (SFN) based PDSCH is also introduced for more robust PDSCH reception, where PDSCH is transmitted simultaneously from two TRPs in the same time and frequency resources.

[0051] Figure 8 An example is shown in FIG, where the same PDSCH is transmitted from two TRPs along with its DMRS. This is indicated to the WD by both the two transmission configuration indicator (TCI) states indicated in the DCI that schedules the PDSCH and the RRC configuration of the system frame number (SFN) PDSCH. The first TCI state may contain TRS1 as the QCL source RS, while the second TCI state may contain TRS2 as the QCL source RS. The DMRS is now associated with two TCI states because the DMRS is transmitted from two TRPs. Summary of the invention

[0052] Some embodiments advantageously provide methods, network nodes, and wireless devices for Type II Precoder Matrix Indicator (PMI) for Coherent Joint Transmission (CJT).

[0053] In some embodiments, for coherent joint transmission (CJT), the WD receives downlink data coherently transmitted from multiple TRPs. In this case, the delay spread of the channel / signal transmitted from multiple TRPs via CJT as seen by the WD may be much larger than the delay spread when the WD receives the channel / signal transmitted from a single TRP. This is because the multiple TRPs may be geometrically separated, which introduces additional propagation delays that add to the delay spread between the WD and each individual TRP. Therefore, the delay spread will increase with the number of TRPs and their relative geometric distance.

[0054] Fig. 9 This increase in the delay spread observed by the WD for channels and signals transmitted via a CJT by multiple TRPs is further illustrated in .

[0055] Fig. 9 FIG. 1 is an example of an antenna-delay domain power spectrum of a WD receiving a coherent joint transmission channel / signal from two TRPs (“TRP 1” and “TRP 2”), each with 32 antenna elements. On the y-axis, antenna elements numbered from “1” to “32” belong to “TRP 2”, while antenna elements numbered from “33” to “64” belong to “TRP 1”. On the x-axis, delay taps representing the normalized propagation delay at the WD corresponding to different antenna elements are represented. Fig. 9 The shading in represents the power for each specific antenna element at a specific delay tap. Most of the power for the antenna element associated with "TRP 1" is allocated in the first 10 delay taps, while most of the power for the antenna element associated with "TRP 2" 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. With the introduction of the second TRP, the overall delay spread is greatly increased. In this example, if only "TRP 1" is considered, the delay spread is about 20 delay taps, while if "TRP 2" is also considered, this will increase the delay spread to about 80 delay taps.

[0056] One approach is to use NR type IIPMI feedback for multi-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 a large number of frequency domain (FD) bases to be able to correctly estimate all propagation delays. As explained above, this will result in a very large CSI reporting overhead, which will increase rapidly with the number of TRPs that will create higher delay spreads and the geometric distance of these TRPs.

[0057] When a WD is served by multiple TRPs that are geographically separated, the total delay spread of the combined channel is contributed by the inter-TRP delay spread caused by the different distances between the WD and the TRP and the 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 the effective channel, based on which the Type I IPMI is calculated. The calculated Type II report and the estimated inter-TRP delay spread are jointly reported to the network node, based on which the DL precoder for coherent joint transmission across multiple TRPs is derived.

[0058] In some non-limiting examples: WD may perform one or more of the following: The WD estimates the inter-TRP delay spread, which is determined by the distance between the WD and the serving TRP; The WD computes 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 IICSI report based on the obtained effective channels; and / or • WD reports Type IICSI and Inter-TRP delay spread jointly. One or more of the following may be performed by a network node: The network node calculates the DL precoder based on the reported Type IIPMI and Inter-TRP delay spread: ○ In particular, for each subband, the network node may apply phase derotation for the reported precoder based on the reported inter-TRP delay.

[0059] Some embodiments reduce the Type IICSI reporting overhead when it is used for coherent joint transmission of multiple TRPs while still capturing the large delay spread in the CSI reports.

[0060] 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 comprises: a radio 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 phase slope and a time difference relative to a reference timing associated with each of the plurality of TRPs; and a processing circuit, the processing circuit communicating with the radio interface and configured to: apply time precompensation to a physical downlink channel at each of the plurality of TRPs according to at least one of the phase slope and the time difference associated with the TRP; and apply the precoding matrix indicated by the PMI to the physical downlink channel at each of the plurality of TRPs.

[0061] 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, wherein a subband is composed of a plurality of RBs. In some embodiments, time precompensation of 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, time precompensation of the physical downlink channel is performed by applying a phase shift per subband, per RB, or per subcarrier in the frequency domain to the physical downlink channel according to the phase slope. In some embodiments, the PMI includes at least an indicator of one or both of a plurality of spatial beams and a spatial domain SD basis vector associated with each of the plurality of TRPs, and an indicator of at least one of the frequency domain FD basis vectors and a common phase coefficient associated with one of the plurality of spatial beams or SD basis vectors associated with each of the plurality of TRPs and associated 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, wherein 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, wherein the reference TRP is one of the plurality of TRPs. In some embodiments, the reference TRP is at least one of predefined and indicated by the WD. In some embodiments, each of the plurality of TRPs is associated with a different channel state information reference signal CSI-RS resource.

[0062] 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 comprises: 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 phase slope and a time difference relative to a reference timing associated with each of the plurality of TRPs. The method further comprises: applying a time precompensation to a physical downlink channel at each of the plurality of TRPs according to at least one of the phase slope and the time difference associated with the TRP. The method further comprises: applying a precoding matrix indicated by the PMI to the physical downlink channel at each of the plurality of TRPs.

[0063] 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, wherein a subband is composed of a plurality of RBs. In some embodiments, time precompensation of 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, time precompensation of the physical downlink channel is performed by applying a phase shift per subband, per RB, or per subcarrier in the frequency domain to the physical downlink channel according to the phase slope. In some embodiments, the PMI includes at least an indicator of one or both of a plurality of spatial beams and a spatial domain SD basis vector associated with each of the plurality of TRPs, and an indicator of at least one of the frequency domain FD basis vectors and a common phase coefficient associated with one of the plurality of spatial beams or SD basis vectors associated with each of the plurality of TRPs and associated 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, wherein 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, wherein the reference TRP is one of the plurality of TRPs. In some embodiments, the reference TRP is at least one of predefined and indicated by the WD. In some embodiments, each of the plurality of TRPs is associated with a different channel state information reference signal CSI-RS resource.

[0064] 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 configuration of a CSI report including a plurality of downlink channel state information CSI reference signal CSI-RS resources from the network node, wherein each of the plurality of CSI-RS resources represents one of the plurality of TRPs. The WD also includes a processing circuit that communicates with the radio interface and is configured to: determine, based at least in part on the measurement of the plurality of downlink CSI-RS resources, for each of the plurality of TRPs at least one of the following items: a downlink time difference relative to a reference timing; and a downlink phase slope representing the downlink time difference relative to the reference timing. The processing circuit is also configured to report to the network node at least one of the determined downlink phase slope and the downlink time difference associated with each of the plurality of TRPs.

[0065] According to this aspect, in some embodiments, the processing circuit is further configured to: determine an effective downlink channel for each TRP in the plurality of TRPs based at least in part on removing the effect of at least one of a downlink phase slope and a downlink time difference associated with the TRP from a channel measurement performed on a CSI-RS resource associated with the TRP; determine a precoder matrix indicator PMI based at least in part on an effective downlink channel for coherent joint data transmission from the plurality of TRPs to the WD; and the radio interface is further configured to transmit the determined PMI to a network node. In some embodiments, the PMI indicates a precoding matrix for each of a plurality of subbands, wherein the subband comprises a plurality of resource blocks RBs. In some embodiments, determining the PMI is based at least in part on the effective downlink channels 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 common phase coefficient associated with each of the plurality of spatial beams and one or both of the SD basis vectors and at least one of the at least one FD basis vectors associated with each of the plurality of TRPs. In some embodiments, a phase slope associated with each of the plurality of TRPs is reported as a phase change per subband. In some embodiments, the phase slope associated with each of the plurality of TRPs is quantized and represented by a frequency domain FD discrete Fourier transform DFT basis vector, wherein the FD DFT basis vector is reported for each of the plurality of TRPs as part of the PMI. In some embodiments, the reference timing is a downlink timing previously acquired by the WD based on a downlink reference signal RS, wherein 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, wherein the downlink time difference associated with each TRP is the time delay difference at the WD between the CSI-RS resource associated with the TRP and the CSI-RS resource associated with the reference TRP, and wherein the time difference associated with the reference TRP is zero and is not reported. In some embodiments, the reference TRP is one of the multiple 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 the specification. In some embodiments, the radio interface is also configured to transmit to the network node an indication of which of the multiple TRPs is the reference TRP.In some embodiments, the time difference associated with each TRP in the plurality of TRPs is reported as at least one of a number of RBs per resource block and a phase change per RB. In some embodiments, determining the effective channel comprises removing a delay factor from a channel measurement associated with a TRP in the plurality of TRPs, the delay factor being based at least in part on the time difference between the TRP and a reference TRP.

[0066] According to another aspect, a method is provided in a wireless device WD configured to communicate with a network node including a plurality of transmission and reception points TRPs. The method comprises: receiving a configuration of a CSI report including a plurality of downlink channel state information CSI reference signal CSI-RS resources from the network node, wherein each of the plurality of CSI-RS resources represents one of the plurality of TRPs. The method comprises determining, based at least in part on the measurement of the plurality of downlink CSI-RS resources, for each of the plurality of TRPs at least one of the following items: a downlink time difference relative to a reference timing; and a downlink phase slope representing the downlink time difference relative to the reference timing. The method further comprises reporting to the network node at least one of the determined downlink phase slope and the downlink time difference associated with each of the plurality of TRPs.

[0067] According to this aspect, in some embodiments, the processing circuit is further configured to: determine an effective downlink channel for each TRP in the plurality of TRPs based at least in part on removing the effect of at least one of a downlink phase slope and a downlink time difference associated with the TRP from a channel measurement performed on a CSI-RS resource associated with the TRP; determine a precoder matrix indicator PMI based at least in part on an effective downlink channel for coherent joint data transmission from the plurality of TRPs to the WD; and the radio interface is further configured to transmit the determined PMI to a network node. In some embodiments, the PMI indicates a precoding matrix for each of a plurality of subbands, wherein the subband comprises a plurality of resource blocks RBs. In some embodiments, determining the PMI is based at least in part on the effective downlink channels 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 common phase coefficient associated with each of the plurality of spatial beams and one or both of the SD basis vectors and at least one of the at least one FD basis vectors associated with each of the plurality of TRPs. In some embodiments, a phase slope associated with each of the plurality of TRPs is reported as a phase change per subband. In some embodiments, the phase slope associated with each of the plurality of TRPs is quantized and represented by a frequency domain FD discrete Fourier transform DFT basis vector, wherein the FD DFT basis vector is reported for each of the plurality of TRPs as part of the PMI. In some embodiments, the reference timing is a downlink timing previously acquired by the WD based on a downlink reference signal RS, wherein 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, wherein the downlink time difference associated with each TRP is the time delay difference at the WD between the CSI-RS resource associated with the TRP and the CSI-RS resource associated with the reference TRP, and wherein the time difference associated with the reference TRP is zero and is not reported. In some embodiments, the reference TRP is one of the multiple 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 the specification. In some embodiments, the method includes transmitting to the network node an indication of which of the multiple TRPs is the reference TRP.In some embodiments, the time difference associated with each TRP in the plurality of TRPs is reported as at least one of a number of RBs per resource block and a phase change per RB. In some embodiments, determining the effective channel comprises removing a delay factor from a channel measurement associated with a TRP in the plurality of TRPs, the delay factor being based at least in part on the time difference between the TRP and a reference TRP. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] A more complete understanding of the present embodiments and the attendant advantages and features thereof will be more readily appreciated by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which: Figure 1 It is a transmission structure for precoded spatial multiplexing; Figure 2 It is a two-dimensional antenna array; Figure 3 is an example of resource allocation; Figure 4 Graph the matrix factors; Figure 5 It is the codebook-based transmission process for FDD; Figure 6 is an example of CSI-RS precoding; Figure 7 is an example of physical downlink control channel (PDCCH) repetition; Figure 8 is an example of SFN PDCCH on two TRPs; Fig. 9 is the antenna delayed power spectrum; Fig.10 is a schematic diagram illustrating an example network architecture of a communication system connected to a host computer via an intermediate network according to the principles of the present disclosure; Fig.11 is a block diagram of a host computer communicating with a wireless device via a network node over an at least partially wireless connection according to some embodiments of the present disclosure; Fig.12 is a flow chart illustrating an example method for executing a client application at a wireless device implemented in a communication system including a host computer, a network node, and a wireless device according to some embodiments of the present disclosure; Fig.13 is a flow chart illustrating an example method for receiving user data at a wireless device implemented in a communication system including a host computer, a network node, and a wireless device according to some embodiments of the present disclosure; Fig.14is a flow chart illustrating an example method for receiving user data from a wireless device at a host computer implemented in a communication system including a host computer, a network node, and a wireless device according to some embodiments of the present disclosure; Fig.15 is a flow chart illustrating an example method for receiving user data at a host computer implemented in a communication system including a host computer, a network node, and a wireless device according to some embodiments of the present disclosure; Fig.16 is a flow chart of an example process for a Type II Precoder Matrix Indicator (PMI) for Coherent Joint Transmission (CJT) in a network node; Fig.17 is a flow chart of an example process for a Type II Precoder Matrix Indicator (PMI) for Coherent Joint Transmission (CJT) in a wireless device; Fig.18 is a flow chart of another example process for a Type II Precoder Matrix Indicator (PMI) for Coherent Joint Transmission (CJT) in a network node; Fig.19 is a flow chart of another example process for a Type II Precoder Matrix Indicator (PMI) for Coherent Joint Transmission (CJT) in a wireless device; Fig. 20 It is a multi-TRP channel; Fig.21 It is a diagram of removing the delay between TRPs; Fig. 22 is an example based on CSI-RS delay measurement; and Fig.23 is an example of applying a precoding matrix with per resource block phase rotation. DETAILED DESCRIPTION

[0069] Before describing the example embodiments in detail, it is noted that the embodiments reside primarily in a combination of processing steps and device components related to a Type II precoder matrix indicator (PMI) for coherent joint transmission (CJT). Accordingly, in the accompanying drawings, components have been represented by conventional symbols where appropriate, and only those specific details relevant to understanding the embodiments are shown so as not to obscure the disclosure with details that will be readily apparent to one of ordinary skill in the art having the benefit of the description herein. Like numbers refer to like elements throughout this description.

[0070] As used herein, relational terms such as "first" and "second", "top" and "bottom", etc., may be used only 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 terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the concepts described herein. Unless the context clearly indicates otherwise, as used herein, the singular forms "a", "an", and "the" are also intended to include the plural forms. It will be further understood that the terms "comprises, comprising" and / or "includes, including", when used herein, specify the presence of the features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0071] In the embodiments described herein, the conjunction term "in communication with" and the like may be used to indicate electrical or data communication, which may be accomplished, for example, by physical contact, induction, electromagnetic radiation, radio signaling, infrared signaling, or optical signaling. Those of ordinary skill in the art will appreciate that the various components may interoperate and that modifications and variations in achieving electrical and data communication are possible.

[0072] In some embodiments described herein, the terms "coupled," "connected," and the like may be used herein to indicate a connection (although not necessarily a direct one) and may include wired and / or wireless connections.

[0073] The term "network node" used herein may be any kind of network node included in a radio network, which may also include any of the following items: a base station (BS), a radio base station, a base transceiver station (BTS), a base station controller (BSC), a radio network controller (RNC), a gNode B (gNB), an evolved Node B (eNB or eNodeB), a Node B, a multi-standard radio (MSR) radio node (such as an MSR BS), a multi-cell / multicast coordination entity (MCE), an integrated access and backhaul (IAB) node, a relay node, a donor node controlling a relay, a radio access point (AP), a transmission point, a transmission node, a remote radio unit (RRU) remote radio head (RRH), a core network node (e.g., a mobile 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 node may also include a test device. As used herein, the term "radio node" may also be used to refer to a wireless device (WD) such as a wireless device (WD) or a radio network node.

[0074] In some embodiments, the non-limiting terms wireless device (WD) or user equipment (UE) are used interchangeably. The WD herein may be any type of wireless device capable of communicating with a network node or another WD via a radio signal, such as a wireless device (WD). The WD may also be a radio communication device, a target device, a device-to-device (D2D) 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 smart phone, a laptop embedded device (LEE), a laptop mounted device (LME), a USB dongle, a customer premises equipment (CPE), an Internet of Things (IoT) device, or a narrowband IoT (NB-IOT) device, etc.

[0075] In addition, in some embodiments, the general term "radio network node" is used. It can be any kind of radio network node, which may include any of the following items: base station, radio base station, base transceiver station, base station controller, network controller, RNC, evolved Node B (eNB), Node B, gNB, multi-cell / multicast coordination entity (MCE), IAB node, relay node, access point, radio access point, remote radio unit (RRU) remote radio head (RRH).

[0076] Note that although terminology from one particular wireless system such as, for example, 3GPP LTE and / or New Radio (NR) may be used in the present disclosure, this should not be viewed as limiting the scope of the present 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 applying the ideas encompassed within this disclosure.

[0077] Note also that the functions described herein as being performed by a wireless device or network node may be distributed across multiple wireless devices and / or network nodes. In other words, it is contemplated that the functions of the network nodes and wireless devices described herein are not limited to being performed by a single physical device and may (in fact) be distributed across several physical devices.

[0078] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those commonly understood by those of ordinary skill in the art to which the present disclosure belongs. It will be further understood that, unless explicitly defined as such herein, the terms used herein should be interpreted as having a meaning consistent with their meaning in the context of the relevant art and this specification, and will not be interpreted in an idealized or overly formal sense.

[0079] Some embodiments provide a Type II Precoder Matrix Indicator (PMI) for Coherent Joint Transmission (CJT).

[0080] Referring again to the drawings, wherein like elements are referred to by like reference numerals, Fig.101 shows a schematic diagram of a communication system 10 according to an embodiment, such as a 3GPP type cellular network that can support standards such as LTE and / or NR (5G), including an access network 12 such as a radio access network and a core network 14. The access network 12 includes a plurality 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 of which defines 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 via a wired or wireless connection 20. A first wireless device (WD) 22a located in the coverage area 18a is configured to be wirelessly connected to the corresponding network node 16a, or to be paged by the corresponding network node 16a. A second WD 22b in the coverage area 18b is wirelessly connectable to the corresponding network node 16b. Although multiple WDs 22a, 22b (collectively referred to as wireless devices 22) are illustrated in this example, the disclosed embodiments are equally applicable to situations where only a single WD is in the coverage area or a single WD is connecting to a corresponding network node 16. Note that although only two WDs 22 and three network nodes 16 are shown for convenience, the communication system may include more WDs 22 and network nodes 16.

[0081] Furthermore, it is contemplated that the WD 22 may communicate with more than one network node 16 and more than one type of network node 16 simultaneously, and / or be configured to communicate with them alone. For example, the WD 22 may have dual connectivity with a network node 16 that supports LTE and the same or different network node 16 that supports NR. As an example, the WD 22 may communicate with an eNB of LTE / E-UTRAN and a gNB of NR / NG-RAN.

[0082] The communication system 10 itself may be connected to a host computer 24, which may be embodied in hardware and / or software as a stand-alone server, a cloud-implemented server, a distributed server, or as processing resources in a server farm. The host computer 24 may be under the ownership or control of a service provider, or may be operated by or on behalf of the service provider. The connections 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 via an optional intermediate network 30. The intermediate network 30 may be a public network, a private network, or a combination of one or more of a managed network. The intermediate network 30, if any, may be a backbone network or the Internet. In some embodiments, the intermediate network 30 may include two or more subnetworks (not shown).

[0083] Fig.10 The communication system as a whole can realize the connectivity between one of the connected WD 22a, 22b and the host computer 24. This connectivity can be described as an over-the-top (OTT) connection. The host computer 24 and the connected WD 22a, 22b are configured to use the access network 12, the core network 14, any intermediate network 30 and possible additional infrastructure (not shown) as intermediaries to transfer data and / or signaling via the OTT connection. The OTT connection can be transparent in the sense that at least some of the participating communication devices through which the OTT connection passes do not know the routing of the uplink and downlink communications. For example, the past routing of the incoming downlink communication may not or need not be notified to the network node 16, and the downlink communication has data to be forwarded (e.g., handed over) to the connected WD 22a originating from the host computer 24. Similarly, the network node 16 does not need to know the future routing of the outgoing uplink communication originating from the WD 22a toward the host computer 24.

[0084] The network node 16 is configured to include a phase derotator 32, which may be configured to determine a downlink precoder by applying a phase derotation to each subband of the precoder indicated by the received type IIPMI 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 IIPMI, the phase rotation being based at least in part on the timing difference associated with the corresponding TRP. The phase derotator 32 may be configured to apply a time precompensation to a physical downlink channel at each of the plurality of TRPs based on at least one of a phase slope and a time difference associated with the TRP. The wireless device 22 is configured to include an effective channel unit 34, which may be configured to determine an effective downlink channel for each TRP based at least in part on removing the timing difference from the downlink channel. More specifically, the effective channel unit 34 may be configured to determine an effective downlink channel for each TRP in at least one TRP based at least in part on removing the effect of the timing difference from the channel measurement performed on the channel state information reference signal CSI-RS resource. The effective channel unit 34 may also be configured to determine, based at least in part on measurements of a plurality of downlink CSI-RS resources, for each 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.

[0085] Now refer to Fig.1110 is used to describe an example implementation of the WD 22, network node 16, and host computer 24 discussed in the preceding paragraphs according to one embodiment. In the communication system 10, the host computer 24 includes hardware (HW) 38, and the HW 38 includes a communication interface 40, which is configured to establish and maintain a wired or wireless connection with the interface of different communication devices of the communication system 10. The host computer 24 further includes 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 in place of a processor such as a central processing unit and a memory, the processing circuit 42 may also include 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) suitable for executing instructions. The processor 44 may be configured to access (e.g., write to and / or read from) a memory 46, which may include any kind 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).

[0086] Processing circuit 42 may be configured to control any of the methods and / or processes described herein, and / or to cause such methods and / or processes to be performed, for example, by host computer 24. Processor 44 corresponds to one or more processors 44 for performing the functions of host computer 24 described herein. Host computer 24 includes memory 46, which is configured to store data, programmatic software code, and / or other information described herein. In some embodiments, software 48 and / or host application 50 may include instructions that, when executed by processor 44 and / or processing circuit 42, cause processor 44 and / or processing circuit 42 to perform the processes described herein with respect to host computer 24. The instructions may be software associated with host computer 24.

[0087] The software 48 may be executable by the processing circuit 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 a WD 22 connected via an OTT connection 52 terminated at the WD 22 and the host computer 24). When providing services to the remote user, the host application 50 may provide user data transmitted using the OTT connection 52. "User data" may be data and information described herein as implementing the 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 circuit 42 of the host computer 24 may enable the host computer 24 to observe, monitor, control, transmit and / or receive from the network node 16 and / or the wireless device 22 to the network node 16 and / or the wireless device 22.

[0088] The communication system 10 also includes a network node 16, which is arranged in the communication system 10 and includes hardware 58, which enables it to communicate with the host computer 24 and the WD 22. The hardware 58 may include a communication interface 60 for establishing and maintaining a wired or wireless connection to the interface of different communication devices of the communication system 10, and a radio interface 62 for establishing and maintaining a wireless connection 64 with the WD 22 located in the coverage area 18 served by the network node 16. The radio interface 62 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. The communication interface 60 may be configured to facilitate a connection 66 to the host computer 24. The connection 66 may be direct, or it may pass through the core network 14 of the communication system 10 and / or through one or more intermediate networks 30 external to the communication system 10.

[0089] In the illustrated embodiment, the hardware 58 of the network node 16 also includes a processing circuit 68. The processing circuit 68 may include a processor 70 and a memory 72. In particular, in addition to or in place of a processor such as a central processing unit and a memory, the processing circuit 68 may also include an integrated circuit for processing and / or control, such as one or more processors and / or processor cores and / or an FPGA (field programmable gate array) and / or an ASIC (application-specific integrated circuit) adapted to execute instructions. The processor 70 may be configured to access the memory 72 (e.g., write to the memory 72 and / or read from the memory 72), and the memory 72 may include any kind of volatile and / or non-volatile memory, such as a cache and / or buffer memory and / or a RAM (random access memory) and / or a ROM (read-only memory) and / or an optical memory and / or an EPROM (erasable programmable read-only memory).

[0090] Thus, the network node 16 also has software 74, which is stored internally, for example, in the memory 72, or in an external memory (e.g., a database, a storage array, a network storage device, etc.) accessible by the network node 16 via an external connection. The software 74 is executable by the processing circuit 68. The processing circuit 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, programmed 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 circuit 68, cause the processor 70 and / or the processing circuit 68 to perform the processes described herein with respect to the network node 16. For example, the processing circuit 68 of the network node 16 may include a phase derotator 32 configured to determine a downlink precoder by applying a phase derotation to each subband of the precoder indicated by the received type I 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 the timing difference associated with the corresponding TRP. The phase derotator 32 may be configured to apply a time precompensation to the physical downlink channel at each of the plurality of TRPs based on at least one of a phase slope and a time difference associated with the TRP.

[0091] The communication system 10 also includes the already mentioned WD 22. The WD 22 may have hardware 80, which may include a radio interface 82 configured to establish 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 radio 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.

[0092] The hardware 80 of the WD 22 also includes a processing circuit 84. The processing circuit 84 may include a processor 86 and a memory 88. In particular, in addition to or in place of a processor and a memory such as a central processing unit, the processing circuit 84 may include an integrated circuit for processing and / or control, such as one or more processors and / or processor cores and / or an FPGA (field programmable gate array) and / or an ASIC (application-specific integrated circuit) suitable for executing instructions. The processor 86 may be configured to access the memory 88 (e.g., write to the memory 88 and / or read from the memory 88), and the memory 88 may include any kind of volatile and / or non-volatile memory, such as a cache and / or buffer memory and / or a RAM (random access memory) and / or a ROM (read-only memory) and / or an optical memory and / or an EPROM (erasable programmable read-only memory).

[0093] Therefore, WD 22 may also include software 90 stored in, for example, a memory 88 at WD 22 or stored in an external memory (e.g., a database, a storage array, a network storage device, etc.) accessible by WD 22. Software 90 may be executable by processing circuit 84. Software 90 may include client application 92. Client application 92 may be operable to provide services to human or non-human users via WD 22 under the support of host computer 24. In host computer 24, the executed host application 50 may communicate with the executed client application 92 via an OTT connection 52 terminated at WD 22 and host computer 24. When providing services to users, client application 92 may receive request data from host application 50 and provide user data in response to the request data. OTT connection 52 may transmit both request data and user data. Client application 92 may interact with the user to generate the user data it provides.

[0094] The processing circuit 84 may be configured to control any method and / or process described herein and / or to cause such a method and / or process 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, programming 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 circuit 84, cause the processor 86 and / or the processing circuit 84 to perform the process described herein with respect to the WD 22. For example, the processing circuit 84 of the wireless device 22 may include an effective channel unit 34, which is configured to determine an effective downlink channel for each TRP based at least in part on removing the timing difference from the downlink channel. The effective channel unit 34 may be configured to determine an effective downlink channel for each TRP in at least one TRP based at least in part on the effect of removing the timing difference from the channel measurement performed on the channel state information reference signal CSI-RS resource. The effective channel unit 34 may also be configured to determine, based at least in part on the measurement of the plurality of downlink CSI-RS resources, for each 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. In some embodiments, the internal workings of the network node 16, the WD 22, and the host computer 24 may be as follows: Fig.11 As shown in , and independently, the surrounding network topology can be Fig.10 network topology.

[0095] exist Fig.11 , the OTT connection 52 has been abstractly drawn to illustrate communications between the host computer 24 and the wireless device 22 via the network node 16, without explicit reference to any intermediary devices and the precise routing of messages via these devices. The network infrastructure may determine the routing, which may be configured to be hidden from the WD 22 or the service provider operating the host computer 24, or both. When the OTT connection 52 is active, the network infrastructure may further make decisions by which it dynamically changes the routing (e.g., based on reconfiguration of the network or load balancing considerations).

[0096] The wireless connection 64 between the WD 22 and the network node 16 is in accordance with the teachings of the embodiments described throughout this disclosure. One or more of the various embodiments improves the performance of the OTT service provided to the WD 22 using the OTT connection 52, where the wireless connection 64 may form the last leg. More specifically, the teachings of some of these embodiments may improve data rates, latency, and / or power consumption, and thereby provide benefits such as reduced user waiting time, relaxed restrictions on file size, better responsiveness, extended battery life, and the like.

[0097] In some embodiments, a measurement process may be provided for the purpose of monitoring the data rate, latency, and other factors improved by one or more embodiments. There may further be optional network functionality for reconfiguring the OTT connection 52 between the host computer 24 and the WD 22 in response to changes in the measurement results. The measurement process and / or network functionality for reconfiguring the OTT connection 52 may be implemented with the software 48 of the host computer 24, or with the software 90 of the WD 22, or with both. In an embodiment, a sensor (not shown) may be deployed in or associated with a communication device through which the OTT connection 52 passes; the sensor may participate in the measurement process by supplying the values ​​of the monitored quantities exemplified above, or supplying the values ​​of other physical quantities from which the software 48, 90 can calculate or estimate the monitored quantities. The reconfiguration of the OTT connection 52 may include message formats, retransmission settings, preferred routes, etc.; the reconfiguration does not need to affect the network node 16, and it may be unknown or imperceptible to the network node 16. Some such processes and functionalities may be known and practiced in the art. In some embodiments, the measurements may involve proprietary WD signaling that facilitates the host computer 24's measurements of throughput, propagation time, latency, etc. In some embodiments, the measurements may be achieved because the software 48, 90 uses the OTT connection 52 to cause messages (particularly empty or "dummy" messages) to be transmitted while it monitors propagation time, errors, etc.

[0098] Thus, in some embodiments, the host computer 24 includes processing circuitry 42 configured to provide user data and a communication interface 40 configured to forward the user data to a cellular network for transmission to the WD 22. In some embodiments, the cellular network further includes a network node 16 having a radio interface 62. In some embodiments, the network node 16 is configured and / or the processing circuitry 68 of the network node 16 is configured to perform the functions and / or methods described herein for preparing / initiating / maintaining / supporting / ending transmissions to the WD 22 and / or preparing / terminating / maintaining / supporting / ending reception of transmissions from the WD 22.

[0099] In some embodiments, host computer 24 includes processing circuitry 42 and communication interface 40 configured to receive user data originating from a transmission from WD 22 to network node 16. In some embodiments, WD 22 is configured to and / or includes a radio interface 82 and / or processing circuitry 84 configured to perform the functions and / or methods described herein for preparing / initiating / maintaining / supporting / ending transmissions to network node 16 and / or preparing / terminating / maintaining / supporting / ending reception of transmissions from network node 16.

[0100] although Fig.10 and 11 Various "units" such as phase derotator 32 and effective channel unit 34 are shown as being within a corresponding processor, but it is contemplated that these units may be implemented so that a portion of the unit is stored in a corresponding memory within the processing circuit. In other words, these units may be implemented within the processing circuit in hardware or a combination of hardware and software.

[0101] Fig.12 is a diagram illustrating a communication system (such as, for example, Fig.10 and Fig.11 Flowchart of an example method implemented in a communication system of FIG. 1 . The communication system may include a host computer 24, a network node 16, and a WD 22, which may be reference Fig.11 Those host computers, network nodes and WDs described herein. In the first step of the method, the host computer 24 provides user data (box S100). In an optional sub-step of the first step, the host computer 24 provides user data by executing a host application (such as, for example, the host application 50) (box S102). In the second step, the host computer 24 initiates a transmission to the WD 22 carrying the user data (box S104). In an optional third step, in accordance with the teachings of the embodiments described throughout the present disclosure, the network node 16 transmits the user data carried in the transmission initiated by the host computer 24 to the WD 22 (box S106). In an optional fourth step, the WD 22 executes a client application (such as, for example, the client application 92) associated with the host application 50 executed by the host computer 24 (box S108).

[0102] Fig.13 is a diagram illustrating a communication system (such as, for example, Fig.10 Flow chart of an example method implemented in a communication system of FIG. 1 . The communication system may include a host computer 24, a network node 16, and a WD 22, which may be reference Fig.10 and Fig.111 and 2. In the first step of the method, host computer 24 provides user data (block S110). In an optional substep (not shown), host computer 24 provides user data by executing a host application (such as, for example, host application 50). In a second step, host computer 24 initiates a transmission to WD 22 carrying user data (block S112). According to the teachings of the embodiments described throughout this disclosure, the transmission can be transmitted via network node 16. In an optional third step, WD 22 receives the user data carried in the transmission (block S114).

[0103] Fig.14 is a diagram illustrating a communication system (such as, for example, Fig.10 A flow chart of an example method implemented in a communication system of FIG. 1 . The communication system may include a host computer 24, a network node 16, and a WD 22, which may be a reference Fig.10 and Fig.11 Those host computers, network nodes, and WDs described herein. In an optional first step of the method, WD 22 receives input data provided by host computer 24 (box S116). In an optional sub-step of the first step, WD 22 executes client application 92, which provides user data as a reaction to the received input data provided by host computer 24 (box S118). Additionally or alternatively, in an optional second step, WD 22 provides user data (box S120). In an optional sub-step of the second step, WD 22 provides user data (box S122) by executing a client application (such as, for example, client application 92). When providing user data, the executed client application 92 may further consider user input received from the user. Regardless of the specific manner in which the user data is provided, in an optional third sub-step, WD 22 may initiate transmission of user data to host computer 24 (box S124). In a fourth step of the method, host computer 24 receives user data transmitted from WD 22 (block S126 ) in accordance with the teachings of the embodiments described throughout this disclosure.

[0104] Fig.15 is a diagram illustrating a communication system (such as, for example, Fig.10 A flow chart of an example method implemented in a communication system of FIG. 1 . The communication system may include a host computer 24, a network node 16, and a WD 22, which may be a reference Fig.10 and Fig.11In an optional first step of the method, network node 16 receives user data from WD 22 in accordance with the teachings of the embodiments described throughout this disclosure (block S128). In an optional second step, network node 16 initiates transmission of the received user data to host computer 24 (block S130). In a third step, host computer 24 receives user data carried in the transmission initiated by network node 16 (block S132).

[0105] Fig.16 Flowchart of an example process of a type II precoder matrix indicator (PMI) for coherent joint transmission (CJT) in a network node 16. One or more blocks described herein may be performed 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 radio interface 62, and / or the communication interface 60. The network node 16 is configured to receive a type II precoder matrix indicator PMI and a transmission reception point TRP inter-delay spread (block S134) from a WD, such as via the processing circuit 68 and / or the processor 70 and / or the radio interface 62 and / or the communication interface 60. The process also includes determining a downlink precoder (block S136) by applying phase derotation to each subband of the precoder indicated by the received type I IPMI based at least in part on the received inter-TRP delay spread. In some embodiments, 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.

[0106] Fig.17 is a flow chart of an example process in a wireless device 22 according to some embodiments of the present disclosure. One or more blocks described herein may be performed 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 radio interface 82, and / or the communication interface 60. The wireless device 22 is configured, such as via the processing circuit 84 and / or the processor 86 and / or the radio interface 82, to determine a timing difference between a downlink channel and the TRP for each of at least two transmission reception points TRPs (block S138). The process also includes determining an effective downlink channel for each TRP based at least in part on removing the timing difference from the downlink channel (block S140). The process also includes determining a type II precoder matrix indicator PMI based at least in part on the effective channel (block S142).

[0107] 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 at least one TRP, the delay factor being based at least in part on the 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 two TRPs. In some embodiments, the process further includes determining a quantized phase slope based at least in part on the timing difference between the TRPs. In some embodiments, the process further includes reporting n-1 timing differences to a network node for n TRPs used for coherent joint transmission.

[0108] Fig.18 Flowchart of an example process of a type II precoder matrix indicator (PMI) for coherent joint transmission (CJT) in a network node 16. One or more of the blocks described herein may be performed 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 radio interface 62, and / or the communication interface 60. The network node 16 is configured to receive from the WD a precoding matrix indicator PMI for coherent joint data transmission over the plurality of TRPs, and one or both of a phase slope and a time difference associated with each of the plurality of TRPs relative to a reference timing (block S144). The method also includes applying time precompensation to a physical downlink channel at each of the plurality of TRPs according to at least one of the phase slope and the time difference associated with the TRP (block S146). The method also includes applying a precoding matrix indicated by the PMI to a physical downlink channel at each TRP in the plurality of TRPs (block S148).

[0109] 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, wherein the subband is composed of multiple RBs. In some embodiments, time precompensation of 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, time precompensation of the physical downlink channel is performed by applying a phase shift per subband, per RB, or per subcarrier in the frequency domain to the physical downlink channel according to the phase slope. In some embodiments, the PMI includes at least an indicator of one or both of a plurality of spatial beams and a spatial domain SD basis vector associated with each of the plurality of TRPs, and an indicator of at least one of the frequency domain FD basis vectors and a common phase 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, wherein the 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, wherein the reference TRP is one of the plurality of TRPs. In some embodiments, the reference TRP is at least one of predefined and indicated by WD 22. In some embodiments, each of the plurality of TRPs is associated with a different channel state information reference signal CSI-RS resource.

[0110] Fig.19 is a flow chart of an example process in a wireless device 22 according to some embodiments of the present disclosure. One or more blocks described herein may be performed 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 radio interface 82, and / or the communication interface 60. The wireless device 22 is configured, such as via the processing circuit 84 and / or the processor 86 and / or the radio interface 82, to receive a configuration of a channel state information CSI report from the network node 16, which includes a plurality of downlink CSI reference signal CSI-RS resources, wherein each of the plurality of CSI-RS resources represents one of the plurality of TRPs (block S150). The method includes determining, based at least in part on the measurement of the plurality of downlink CSI-RS resources, for each of the plurality of TRPs, at least one of the following items: a downlink time difference relative to a reference timing; and a downlink phase slope representing the downlink time difference relative to the reference timing (block S152). The method also includes reporting to the network node 16 at least one of the determined downlink phase slope and downlink time difference associated with each of the plurality of TRPs (block S154).

[0111] According to this aspect, in some embodiments, the processing circuit is further configured to: determine an effective downlink channel for each of the plurality of TRPs based at least in part on removing the effect of at least one of a downlink phase slope and a downlink time difference associated with the TRP from a channel measurement performed on a CSI-RS resource associated with the TRP; 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 radio 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, wherein a subband comprises a plurality of resource blocks RBs. In some embodiments, determining the PMI is based at least in part on the effective downlink channels for 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 common phase coefficient associated with each of the plurality of said spatial beams and one or both of the SD basis vectors and at least one of the at least one FD basis vectors associated with each of the plurality of TRPs. In some embodiments, the phase slope associated with each of the plurality of TRPs is reported as a phase change per subband. In some embodiments, the phase slope associated with each of the plurality of TRPs is quantized and represented by a frequency domain FD discrete Fourier transform DFT basis vector, wherein the FD DFT basis vector is reported for each of the plurality of TRPs as part of the PMI. In some embodiments, the reference timing is a downlink timing previously acquired by the WD 22 based on a downlink reference signal RS, wherein 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, wherein the downlink time difference associated with each TRP is a time delay difference at WD 22 between a CSI-RS resource associated with the TRP and a CSI-RS resource associated with a reference TRP, and wherein the time difference associated with the reference TRP is zero and is not reported. In some embodiments, the reference TRP is one of the multiple 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 WD 22. 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 of the multiple TRPs is the reference TRP.In some embodiments, the time difference associated with each TRP in the plurality of TRPs is reported as at least one of a number of RBs per resource block and a phase change per RB. In some embodiments, determining the effective channel comprises removing a delay factor from a channel measurement associated with a TRP in the plurality of TRPs, the delay factor being based at least in part on the time difference between the TRP and a reference TRP.

[0112] Having described the general process flow of the arrangements of the present disclosure and having provided examples of hardware and software arrangements for implementing the processes and functions of the present disclosure, the following sections provide examples and details of arrangements of a Type II precoder matrix indicator (PMI) for coherent joint transmission (CJT).

[0113] The term TRP may be represented by a TCI state, an NZP CSI-RS resource, or a subset of ports within an NZP CSI-RS resource.

[0114] For coherent joint transmission, a user receives coherently transmitted channels / signals from multiple TRPs. The total delay spread of the channels between WD 22 and the multiple TRPs is generally greater than the delay spread when WD 22 receives the channel / signal from a single TRP, especially when the average propagation delays from the multiple TRPs to WD 22 are different.

[0115] The above Fig. 20 The example shown in is further illustrated, where WD 22 receives channels / signals from two geometrically separated TRPs. Between WD 22 and each individual TRP, there are three propagation paths in the channel, which introduces delay spread. As seen in the figure, t1, t2, and t3 are the three delay taps associated with TRP 1, while t4, t5, and t6 are the delay taps associated with TRP 2. The total delay spread for the combined channel between WD 22 and TRP 1 and TRP 2 is determined by all 6 delay taps. However, if only the channel between WD 22 and each individual TRP is considered, there are only three channel taps, which means a much lower delay spread.

[0116] The NR Type II codebook, including the enhanced Type II codebook (CB) and enhanced Type II port selection (PS) CB in 3GPP Rel-16, and the further enhanced Type IIPS CB in 3GPP Rel-17 (referred to as 3GPP Rel-16 Type II CB, 3GPP Rel-16 PS CB and 3GPP Rel-17 PS CB, respectively, hereinafter for simplicity) may be used to compress and report channel state information (CSI) in the delay domain (or equivalently, the frequency domain).

[0117] More specifically, the enhanced type II precoding matrix W f Each selected frequency domain (FD) basis vector in W2 may be associated with a dominant delay tap. For the example above, if the existing enhanced type II codebook is used for CSI reporting, a total of 6 FD basis vectors are required to capture all taps in the combined channel. Because the number of linear combination coefficients in W2 (which is the heaviest payload of the type I CSI report) is proportional to the number of FD basis vectors, having more FD basis vectors also means more overhead for reporting W2.

[0118] refer to Fig.21 , the total delay spread has two contributions: the intra-TRP delay spread caused by multipath propagation between WD 22 and each individual TRP, and the inter-TRP delay spread caused by the propagation delay difference (also referred to herein as timing difference) due to the two TRPs being geometrically separated (and therefore having different distances to WD 22). The effect of the inter-TRP delay spread essentially adds a shared offset to the intra-TRP delay spread.

[0119] Based on the above observations, it is reasonable to treat intra-TRP (i.e., within the same TRP) delay spread and inter-TRP (i.e., between different TRPs) delay spread separately in order to reduce the overhead required to capture the large total delay spread of the combined channel. In particular, the inter-TRP delay spread can be estimated and reported separately. Then, the inter-TRP delay spread can be removed from the portion of the combined channel associated with the corresponding TRP, and an effective channel can be obtained. Finally, the intra-TRP delay spreads associated with multiple TRPs can be jointly compressed based at least in part on the effective channel with fewer FD basis vectors.

[0120] Fig.21 The above method for separately handling inter-TRP and 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 hand side, while Fig.21 The effective delay spread of the effective channel after removing the inter-TRP delay (i.e., the propagation delay difference between different TRPs to WD 22) is shown on the right hand side of . In this example, the inter-TRP delay is given by τ=t4-t1. After removing the inter-TRP delay τ for TRP 2, the effective channel contains only 4 delay taps compared to 6 delay taps in the original channel. Therefore, 4 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.

[0121] Furthermore, a larger delay spread means a more frequency selective channel and thus a smaller coherence bandwidth. A smaller coherence bandwidth requires a smaller subband size for CSI feedback so that the channel (both amplitude and phase) does not change significantly within a subband. This results in more subbands for a given bandwidth. General Process for Proposed Type II Reporting Enhancements

[0122] The general process of the proposed Type IICSI reporting enhancement for multi-TRP coherent joint transmission can be summarized in the following steps: Step 1: WD 22 estimates the timing difference between the DL channel and the TRP of the service, such as via processing circuit 84; Step 2: WD 22 removes the timing difference for the corresponding TRP and obtains a valid DL channel; Step 3: Based on the valid DL channels, WD 22 calculates type IIPMI; Step 4: WD 22 reports Type II CSI containing the timing difference between the PMI and the serving TRP; and / or Step 5: The network node 16 (e.g., gNB) applies a precoding matrix associated with Type IIPMI, together with a phase rotation, based at least in part on the timing difference between the reported TRPs of the services.

[0123] In step 1, WD 22 estimates the timing difference between the DL channel and also the served TRPs. The timing difference may be the inter-TRP delay between two given TRPs.

[0124] When estimating the timing difference, a reference TRP may be used so that 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 it may be inferred from the CSI report configuration. For example, when it is explicitly specified in the NR 3GPP specification, it may be associated with an explicitly configured CSI-RS resource; when it is implicitly inferred, it may be associated with a predetermined CSI-RS resource (such as the first CSI-RS resource in the CSI report configuration). In some cases, instead of the term "reference TRP", the 3GPP specification may use "reference CSI-RS resource for deriving the timing difference between TRPs".

[0125] Fig. 22 An example is shown in FIG. 1 , where two CSI-RS resources are transmitted from two TRPs in an OFDM system. τ1 and τ2 are the time delays associated with the first delay taps corresponding to TRP1 and TRP2, respectively. The delay may result in a phase slope of The observed channel in WD is TRP1 and TRP2 τ2-τ1 is the timing difference between TRP2 and TRP1.

[0126] In the above embodiments, the timing differences 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 differences between TRPs may be estimated based at least in part on a subset of ports within a single CSI-RS resource. For example, in some embodiments, different subsets of ports may correspond to different TRPs, and on one port in the subset of ports within the single CSI-RS resource, WD22 estimates the channel corresponding to each TRP.

[0127] In step 2, WD 22 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 relative to TRP1, i.e., τ2-τ1. By removing the estimated timing difference from the measured channel and Remove the delay factors separately and To obtain effective channels H1 and H2.

[0128] Alternatively, the effective channel for TRP2 is obtained by calculating the measured channel Remove the timing difference factor Obtained as 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 determined by the measured channel Give directly.

[0129] In step 3, WD 22 calculates a Type IIPMI based at least in part on the concatenated effective DL channel (e.g., H=[H1 H2] in the example shown in step 2). Type IIPMI 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 become a block diagonal matrix, where each block corresponds to the SD basis vector of one of the TRPs. In the example discussed in step 2, the precoding matrix for PMI subband n (n=1, ..., N3) associated with Type IIPMI may be expressed as Where W1(n) is associated with TRP1 and W2(n) is associated with TRP2, and N3 is the number of PMI subbands.

[0130] In addition to the above Type II PMI component from the existing 3GPP Rel-16 / 17 Type II codebook, WD22 may also report the timing difference between each of the configured TRPs for Type-II based CJT CSI feedback and the reference TRP among the configured TRPs. For example, τ2 - τ1 in the example discussed in step 2.

[0131] For a given frequency, the timing difference between two TRPs may result in a phase difference between the signals received from the two TRPs, i.e., This phase difference changes linearly with frequency, and the phase slope is sufficient to characterize the timing difference.

[0132] In one embodiment, the phase slope is quantized between 0 and 2π and reported to the network node 16 as part of the Type II CSI report. Since for each CSI-RS port, there is one channel sample per RB for CSI-RS, the phase change or slope may only be measured at the granularity of per RB. Therefore, in one embodiment, the phase change on one RB between the measured channels associated with two CSI-RS resources may be reported, i.e., where Δf is the bandwidth per RB in Hertz. can be quantized between 0 and 2π.

[0133] In another embodiment, the quantized phase slope may be represented by FD basis vectors, which are taken from the DFT matrix, possibly by oversampling in frequency (e.g., sampling per RB instead of per PMI subband in the 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 of the FD basis vector used for compressing the effective channel. A larger DFT matrix size can more accurately remove the inter-TRP delay.

[0134] Let the number of TRPs used for coherent joint transmission be represented as n. Then, in some embodiments, at least n - 1 timing differences need to be reported. In some embodiments, which timing differences are reported from WD 22 to the network node 16 depends on which TRPs are selected as part of the Type II CSI feedback. In some embodiments, WD 22 may be configured for n different CSI-RS resources (i.e., n TRPs), and WD 22 only selects a subset n′ < n of the CSI-RS resources (i.e., n′ TRPs are selected by WD 22 for coherent joint transmission) of SD basis vectors or CSI-RS ports as part of the Type II CSI feedback. In this case, only n′ - 1 timing differences need to be reported, and one of the above embodiments can be used to identify the reference CSI-RS resource (or reference TRP) for calculating the timing difference.

[0135] The timing difference may result in frequency selectivity. In some other embodiments, a per-FD subband phase change between each TRP in the plurality of TRPs and a reference TRP is reported to the network node 16 due to the timing difference.

[0136] In step 4 , WD 22 includes the timing difference(s) as part of a Type IICSI report and reports the timing difference(s) to network node 16 .

[0137] The timing difference(s) may be reported to the network node 16 in the CSI report part 1 since it is a large scale fading channel property.

[0138] In step 5, the network node 16 determines based at least in part on the reported timing difference To apply the per-subband precoding matrix together with the per-RB phase rotation. Fig.23 , where the per-subband precoder {W1(n), n=1, ..., N3} reported by WD 22 is applied to the PDSCH transmitted from TRP1, and the per-subband precoder {W2(n), n=1, ..., N3} reported by WD 22 is combined with the per-RB phase derotation factor The combining is applied 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 actually a delay precompensation for the timing difference between the two TRPs. Alternatively, phase derotation can be applied per subcarrier instead of per RB, where the phase derotation amount per subcarrier is Where N sc is the number of subcarriers per RB.

[0139] Although two TRPs are used for discussion in the above example, the ideas can be easily extended to more than two TRPs.

[0140] Some embodiments may include one or more of the following: Embodiment A1. A network node configured to communicate with a wireless device WD, the network node being configured to and / or comprising a radio interface and / or comprising a processing circuit configured to: receiving a type II precoder matrix indicator PMI and an inter-transmission reception point TRP delay spread from the WD; and Based at least in part on the received inter-TRP delay spread, a downlink precoder is determined by applying phase derotation to each subband of the precoder indicated by the received Type IIPMI. Embodiment A2. A network node as described in Embodiment A1, wherein applying the phase derotation comprises applying a phase rotation to a physical downlink shared channel PDSCH transmitted from a first TRP, and not applying a 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 an inter-transmission reception point TRP delay spread from the WD; and Based at least in part on the received inter-TRP delay spread, a downlink precoder is determined by applying phase derotation to each subband of the precoder indicated by the received Type IIPMI. Embodiment B2. A method as described in Embodiment B1, wherein applying the 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 C1. A wireless device (WD) configured to communicate with a network node, the WD being configured to, and / or comprising a radio interface and / or a processing circuit configured to: determining, for each of at least two transmission reception points TRP, a timing difference between a downlink channel and the TRP; determining an effective downlink channel for each TRP based at least in part on removing the timing difference from the downlink channel; and A type II precoder matrix indicator (PMI) is determined based at least in part on the effective channel. Embodiment C2. The WD of embodiment C1, wherein the timing difference is determined relative to a reference TRP. Embodiment C3. A WD as described in Embodiment C2, wherein the reference TRP is associated with a channel state information reference signal CSI-RS resource. Embodiment C4. A WD as described in any of Embodiments C1-C3, wherein determining the valid channel includes removing a delay factor from at least one channel of at least one TRP, and the delay factor is at least partially based on a timing difference between the at least one TRP and another TRP. Embodiment C5. A WD as described in any of Embodiments C1-C4, wherein determining the type II precoder matrix indicator PMI is at least partially based on the cascaded channel matrix of two TRPs. Embodiment C6. A WD as described in any of Embodiments C1-C5, wherein the WD, radio interface and / or processing circuit is also configured to determine a quantized phase slope based at least in part on a timing difference between TRPs. Embodiment C7. A WD as described in any of Embodiments C1-C6, wherein the WD, radio interface and / or processing circuit is also configured to report n-1 timing differences to the network node for n TRPs used for coherent joint transmission. Embodiment D1. A method implemented in a wireless device (WD), the method comprising: determining, for each of at least two transmission reception points TRP, a timing difference between a downlink channel and the TRP; determining an effective downlink channel for each TRP based at least in part on removing the timing difference from the downlink channel; and A type II precoder matrix indicator (PMI) is determined based at least in part on the effective channel. Embodiment D2. A method as described in Embodiment D1, wherein the timing difference is determined relative to a reference TRP. Embodiment D3. A method as described in Embodiment D2, wherein the reference TRP is associated with a channel state information reference signal CSI-RS resource. Embodiment D4. A method as described in any of embodiments D1-D3, wherein determining the valid channel includes removing a delay factor from at least one channel of at least one TRP, and the delay factor is at least partially based on a timing difference between the at least one TRP and another TRP. Embodiment D5. A method as described in any of Embodiments D1-D4, wherein determining a type II precoder matrix indicator PMI is at least partially based on a cascaded channel matrix of two TRPs. Embodiment D6. The method as described in any of Embodiments D1-D5 also includes determining a quantized phase slope based at least in part on a timing difference between TRPs. Embodiment D7. The method as described in any one of embodiments D1-D6 further includes reporting n-1 timing differences to the network node for n TRPs used for coherent joint transmission.

[0141] As will be appreciated by those skilled in the art, the concepts described herein may be embodied as methods, data processing systems, computer program products, and / or computer storage media storing executable computer programs. Thus, the concepts described herein may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware aspects, all of which are collectively referred to herein as "circuits" or "modules". Any process, step, action, and / or functionality described herein may be performed and / or associated with a corresponding module, which may be implemented in software and / or firmware and / or hardware. In addition, the present disclosure may take the form of a computer program product on a tangible computer-usable storage medium having a computer program code embodied in the medium that may be executed by a computer. Any suitable tangible computer-readable medium may be utilized, including a hard disk, a CD-ROM, an electronic storage device, an optical storage device, or a magnetic storage device.

[0142] Some embodiments are described herein with reference to flowchart illustrations and / or block diagrams of methods, systems, and computer program products. It will be understood that each frame of the flowchart illustration and / or block diagram and the combination of frames in the flowchart illustration and / or block diagram can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer (thereby creating a special-purpose computer), a special-purpose computer, or other programmable data processing device to produce a machine, so that instructions executed via a processor of a computer or other programmable data processing device create components for implementing the functions / actions specified in one or more flowcharts and / or block diagram frames.

[0143] These computer program instructions may also be stored in a computer-readable memory or storage medium, which can direct a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article containing instruction components, which implement the functions / actions specified in one or more flowcharts and / or block diagrams.

[0144] The computer program instructions may also be loaded onto a computer or other programmable data processing device to cause a series of operable steps to be performed on the computer or other programmable device to produce a computer-implemented process, so that the instructions executed on the computer or other programmable device provide steps for implementing the functions / actions specified in one or more flowcharts and / or block diagram blocks.

[0145] It is to be understood that the functions / actions indicated in the blocks may not occur in the order indicated in the operational diagrams. For example, two blocks shown in succession may actually be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending on the functionality / actions involved. Although some of the diagrams in the figures contain arrows on communication paths to illustrate the primary direction of communication, it is to be understood that communication may occur in the opposite direction of the arrows depicted.

[0146] Computer program code for carrying out operations of the concepts described herein may be used in languages ​​such as Python, The computer program code for performing the operations of the present disclosure may be written in an object-oriented programming language such as C++ or C++. However, the 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 be executed entirely on the user's computer, partially on the user's computer, as an independent 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 via a local area network (LAN) or a wide area network (WAN), or a connection may be established with an external computer (e.g., by using the Internet of an Internet Service Provider).

[0147] In conjunction with the above description and the accompanying drawings, many different embodiments have been disclosed herein. It will be understood that it would be overly repetitive and confusing to literally describe and illustrate every combination and subcombination of these embodiments. Thus, all embodiments can be combined in any manner and / or combination, and this specification including the accompanying drawings should be interpreted as constituting a complete written description of all combinations and subcombinations of the embodiments described herein and the manner and process of making and using them, and should support claims to any such combination or subcombination.

[0148] Abbreviations that may be used in the preceding description include: abbreviation explain DFT Discrete Fourier Transform eType II Enhanced Type II, 3GPP Rel-16 Type II feType II Further enhanced 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 Transmission and Reception Point W1 is the matrix containing all space-domain basis vectors for type II PMI W f The matrix containing all frequency domain basis vectors for type II PMI W2 contains the f The matrix of the composite common factors

[0149] Those skilled in the art will appreciate that the embodiments described herein are not limited to what has been specifically shown and described herein above. In addition, unless otherwise mentioned above, it should be noted that all drawings are not to scale. Various modifications and variations are possible in view of the above teachings without departing from the scope of the appended claims.

Claims

1. A network node (16) configured to communicate with a wireless device WD (22) via a plurality of transmission and reception points TRP, the network node (16) comprising: a radio interface (62) configured to receive from the WD (22) a precoding matrix indicator PMI for coherent joint data transmission over the plurality of TRPs, and one or both of a phase slope and a time difference relative to a reference timing associated with each of the plurality of TRPs; and a processing circuit (68) in communication with the radio interface (62) and configured to: applying a time precompensation to a physical downlink channel at each TRP of the plurality of TRPs based on at least one of the phase slope and the time difference associated with the TRP; as well as A precoding matrix indicated by the PMI is applied to the physical downlink channel at each TRP in the plurality of TRPs.

2. The network node (16) according to claim 1, wherein: 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, wherein a subband consists of a plurality of RBs.

3. The network node (16) as claimed in any one of claims 1 and 2, wherein: The time precompensation of 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.

4. The network node (16) as claimed in any one of claims 1 and 2, wherein: The time precompensation of the physical downlink channel is performed by applying a per-subband, per-RB or per-subcarrier phase shift in the frequency domain to the physical downlink channel according to the phase slope.

5. The network node (16) according to any one of claims 1 to 4, 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, and an indicator of at least one of the frequency domain FD basis vectors and common phase coefficients each associated with one of the plurality of spatial beams or SD basis vectors associated with each of the plurality of TRPs and associated with one of the one or more FD basis vectors.

6. The network node (16) according to any one of claims 1 to 5, wherein: The phase slope is represented by frequency domain FD basis vectors, wherein the index of the FD basis vectors is received as part of the PMI.

7. The network node (16) according to any one of claims 1 to 6, wherein: The reference timing is a downlink timing associated with a reference TRP, wherein the reference TRP is one of the multiple TRPs.

8. The network node (16) according to any one of claims 1 to 7, wherein: The reference TRP is at least one of predefined and indicated by the WD.

9. The network node (16) according to any one of claims 1 to 8, wherein: Each TRP of the multiple TRPs is associated with a different channel state information reference signal CSI-RS resource.

10. A method in a network node (16) configured to communicate with a wireless device WD (22) via a plurality of transmission and reception points TRP, the method comprising: receiving (S144) from the WD (22) a precoding matrix indicator PMI for coherent joint data transmission over the plurality of TRPs, and one or both of a phase slope and a time difference relative to a reference timing associated with each of the plurality of TRPs; applying (S146) a time precompensation to a physical downlink channel at each TRP of the plurality of TRPs according to at least one of the phase slope and the time difference associated with the TRP; as well as A precoding matrix indicated by the PMI is applied (S148) to the physical downlink channel at each TRP in the plurality of TRPs.

11. The method of claim 10, wherein: 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, wherein a subband consists of a plurality of RBs.

12. The method according to any one of claims 10 and 11, wherein: The time precompensation of 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.

13. The method according to any one of claims 10 and 11, wherein: The time precompensation of the physical downlink channel is performed by applying a per-subband, per-RB or per-subcarrier phase shift in the frequency domain to the physical downlink channel according to the phase slope.

14. The method according to any one of claims 10 to 13, 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, and an indicator of at least one of the frequency domain FD basis vectors and common phase coefficients each associated with one of the plurality of spatial beams or SD basis vectors associated with each of the plurality of TRPs and associated with one of the one or more FD basis vectors.

15. The method according to any one of claims 10 to 14, wherein: The phase slope is represented by frequency domain FD basis vectors, wherein the index of the FD basis vectors is received as part of the PMI.

16. The method according to any one of claims 10 to 15, wherein: The reference timing is a downlink timing associated with a reference TRP, wherein the reference TRP is one of the multiple TRPs.

17. The method according to any one of claims 10 to 16, wherein: The reference TRP is at least one of predefined and indicated by the WD.

18. The method according to any one of claims 10 to 17, wherein: Each TRP of the multiple TRPs is associated with a different channel state information reference signal CSI-RS resource.

19. A wireless device WD (22) configured to communicate with a network node (16), the WD (22) comprising: a radio interface (82) configured to receive, from the network node, a configuration of a CSI report comprising a plurality of downlink channel state information (CSI) reference signal (CSI-RS) resources, wherein each of the plurality of CSI-RS resources represents one of the plurality of TRPs; and a processing circuit (84) in communication with the radio interface (82) and configured to: Based at least in part on the measurement of the plurality of downlink CSI-RS resources, determining, for each TRP in the plurality of TRPs, at least one of the following: downlink time difference relative to a reference timing; and a downlink phase slope representing the downlink time difference relative to a reference timing; and Reporting to the network node at least one of the determined downlink phase slope and the downlink time difference associated with each of the plurality of TRPs.

20. The WD (22) of claim 19, wherein: The processing circuit (84) is further configured to: determining an effective downlink channel for each TRP in the plurality of TRPs based at least in part on removing an effect of the at least one of the downlink phase slope and the downlink time difference associated with the TRP from a channel measurement performed on a CSI-RS resource associated with the TRP; as well as 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; and The radio interface (82) is further configured to transmit the determined PMI to the network node.

21. The WD (22) according to claim 20, wherein: The PMI indicates a precoding matrix for each subband in a plurality of subbands, wherein the subband includes a plurality of resource blocks RBs.

22. The WD (22) according to any one of claims 20 and 21, wherein Determining the PMI is based at least in part on the valid downlink channels of the multiple TRPs.

23. The WD (22) according to any one of claims 20 to 22, wherein 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 common phase coefficients associated with each of the plurality of spatial beams and one or both of the SD basis vectors associated with each of the plurality of TRPs and at least one of the at least one FD basis vectors.

24. The WD (22) according to any one of claims 19 to 23, wherein The phase slope associated with each TRP in the multiple TRPs is reported as a phase change per subband.

25. The WD (22) according to any one of claims 19 to 24, wherein The phase slope associated with each of the plurality of TRPs is quantized and represented by frequency domain FD Discrete Fourier Transform DFT basis vectors, wherein the FD DFT basis vectors are reported for each of the plurality of TRPs as part of the PMI.

26. The WD (22) according to any one of claims 19 to 25, wherein The reference timing is a downlink timing previously acquired by the WD at least partially based on a downlink reference signal RS, wherein the downlink RS may be a tracking reference signal TRS.

27. The WD (22) according to any one of claims 19 to 25, wherein The reference timing is a downlink timing associated with a reference TRP, wherein the downlink time difference associated with each TRP is a time delay difference at the WD between a CSI-RS resource associated with the TRP and a CSI-RS resource associated with the reference TRP, and wherein the time difference associated with the reference TRP is zero and is not reported.

28. The WD (22) according to any one of claims 19 to 27, wherein The reference TRP is one of the multiple TRPs.

29. The WD (22) according to any one of claims 19 to 28, wherein The reference TRP is explicitly indicated by the network node.

30. The WD (22) according to any one of claims 19 to 28, wherein The reference TRP is implicitly indicated by the network node.

31. The WD (22) according to any one of claims 19 to 28, wherein The reference TRP is determined by the WD.

32. The WD (22) of any one of claims 19 to 28, wherein The reference TRP is pre-specified in the specification.

33. The WD (22) according to any one of claims 19 to 32, wherein The radio interface is further configured to transmit to the network node (16) an indication of which TRP of the plurality of TRPs is the reference TRP.

34. The WD (22) according to any one of claims 19 to 33, wherein The time difference associated with each of the multiple TRPs is reported as at least one of a number of RBs per resource block and a phase change per RB.

35. The WD (22) of any one of claims 19 to 34, wherein Determining the valid channel includes removing a delay factor from a channel measurement associated with a TRP in the plurality of TRPs, the delay factor being based at least in part on a time difference between the TRP and the reference TRP.

36. A method in a wireless device WD (22) configured to communicate with a network node (16) comprising a plurality of transmission and reception points TRP, the method comprising: receiving (S150) from the network node a configuration of a CSI report comprising a plurality of downlink channel state information, CSI reference signal, CSI-RS resources, wherein each of the plurality of CSI-RS resources represents one of the plurality of TRPs; Based at least in part on the measurement of the plurality of downlink CSI-RS resources, determining (S152) for each of the plurality of TRPs at least one of the following: downlink time difference relative to a reference timing; and A downlink phase slope representing a downlink time difference relative to a reference timing; and reporting (S154) to the network node the determined downlink phase slope associated with each of the multiple TRPs and at least one of the downlink time differences.

37. The method of claim 36, further comprising: determining an effective downlink channel for each TRP in the plurality of TRPs based at least in part on removing an effect of the at least one of the downlink phase slope and the downlink time difference associated with the TRP from a channel measurement performed on a CSI-RS resource 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; and The determined PMI is transmitted to the network node.

38. The method of any one of claims 36 and 37, wherein: The PMI indicates a precoding matrix for each subband in a plurality of subbands, wherein the subband includes a plurality of resource blocks RBs.

39. The method of any one of claims 36 to 38, wherein: Determining the PMI is based at least in part on the valid downlink channels of the multiple TRPs.

40. The method of any one of claims 36 to 39, wherein: 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 common phase coefficients associated with each of the plurality of spatial beams and one or both of the SD basis vectors associated with each of the plurality of TRPs and at least one of the at least one FD basis vectors.

41. The method of any one of claims 36 to 40, wherein: The phase slope associated with each TRP in the multiple TRPs is reported as a phase change per subband.

42. The method of any one of claims 36 to 41, wherein: The phase slope associated with each of the plurality of TRPs is quantized and represented by frequency domain FD Discrete Fourier Transform DFT basis vectors, wherein the FD DFT basis vectors are reported for each of the plurality of TRPs as part of the PMI.

43. The method of any one of claims 36 to 42, wherein: The reference timing is a downlink timing previously acquired by the WD at least partially based on a downlink reference signal RS, wherein the downlink RS may be a tracking reference signal TRS.

44. The method of any one of claims 36 to 42, wherein: The reference timing is a downlink timing associated with a reference TRP, wherein the downlink time difference associated with each TRP is a time delay difference at the WD between a CSI-RS resource associated with the TRP and a CSI-RS resource associated with the reference TRP, and wherein the time difference associated with the reference TRP is zero and is not reported.

45. The method of any one of claims 36 to 44, wherein: The reference TRP is one of the multiple TRPs.

46. ​​The method of any one of claims 36 to 45, wherein: The reference TRP is explicitly indicated by the network node.

47. The method of any one of claims 36 to 45, wherein: The reference TRP is implicitly indicated by the network node.

48. The method of any one of claims 36-45, wherein: The reference TRP is determined by the WD.

49. The method of any one of claims 36 to 45, wherein: The reference TRP is pre-specified in the specification.

50. The method of any one of claims 36-49, further comprising transmitting to the network node (16) an indication of which of the plurality of TRPs is the reference TRP.

51. The method of any one of claims 36 to 50, wherein: The time difference associated with each of the multiple TRPs is reported as at least one of a number of RBs per resource block and a phase change per RB.

52. The method of any one of claims 36 to 51, wherein: Determining the valid channel includes removing a delay factor from a channel measurement associated with a TRP in the plurality of TRPs, the delay factor being based at least in part on a time difference between the TRP and the reference TRP.

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