Apparatus, method, distribution medium and computer program product for communication

Abstract

A method is provided at a network node of a communication network, the method comprising: receiving an uplink reference signal from a user equipment; estimating, based on the received uplink reference signal, delay information about a delay profile of a communication channel between the user equipment and the network node and spatial information about the communication channel; applying both the delay information and the spatial information to precoding of at least one downlink reference signal; transmitting the at least one precoded downlink reference signal to the user equipment; and receiving, from the user equipment in response to the transmission of the at least one precoded downlink reference signal, channel information indicating at least a non-zero coefficient of at least one channel transmission layer.

Description

Technical Field

[0001] Various example implementations generally involve precoding based on partial reciprocity. Background Technology

[0002] To improve communication throughput and reliability, transmission directivity can be applied in radio communications. Directivity can increase signal strength at the receiver side, which can increase throughput and / or reduce transmission power. Precoding can be used to implement transmitter directivity. Precoding aims to match multi-antenna transmissions to current channel conditions. This is achieved by multiplying the signal with antenna-specific complex weights (phase and / or amplitude) that depend on the current channel conditions. Precoding can be codebook-based, in which a finite set of precoding vectors / matrices is defined and used for transmission. The number of vectors is a trade-off between performance and feedback overhead. An alternative to codebook-based precoding is non-codebook-based precoding, where any vectors / matrices can be used, or classical beamforming based on angle-of-arrival information that does not necessarily require channel knowledge.

[0003] In 5G NR, an Advanced Channel State Information (CSI) codebook is specified to accommodate both single-user and multi-user MIMO operations. Rel-15 specifies Type I and Type II codebooks, with the latter providing considerable accuracy in the Precoding Matrix Indicator (PMI). The PMI is fed back from the user equipment to the base station to convey information about which precoder(s) in the precoder codebook is appropriate from the user equipment's perspective. CSI enhancements continued in Rel-16, with a focus on reducing Type II overhead to alleviate pressure on uplink resources.

[0004] However, 3GPP determined that further improvements were needed. Summary of the Invention

[0005] The subject matter of the independent claims is provided according to several aspects. Additional aspects are defined in the dependent claims. Embodiments not falling within the scope of the claims are to be interpreted as examples useful for understanding this disclosure. Attached Figure Description

[0006] The present invention will now be described in more detail with reference to embodiments and accompanying drawings, in which...

[0007] Figure 1 A communication network according to one embodiment is shown;

[0008] Figure 2A and Figure 2B A spatial beam carrying a downlink reference signal and a subsequent report of channel state information from a user equipment are shown according to one embodiment.

[0009] Figure 3 and Figure 4 Methods according to some embodiments are shown;

[0010] Figure 5 A signaling flowchart according to one embodiment is shown;

[0011] Figure 6 and Figure 7 An apparatus according to some embodiments is shown;

[0012] Figure 8 and Figure 9 Methods according to some embodiments are shown;

[0013] Figure 10 A physical resource block carrying a downlink reference signal is shown according to one embodiment; and

[0014] Figure 11 and Figure 12 A signaling flowchart according to some embodiments is shown. Detailed Implementation

[0015] The following embodiments are exemplary. Although the specification may refer to "an," "one," or "some" embodiments in several places throughout the text, this does not necessarily mean that each reference points to the same embodiment(s), nor does it necessarily mean that a particular feature is applicable only to a single embodiment. Individual features of different embodiments may also be combined to provide other embodiments. For the purposes of this disclosure, the phrases "A or B" and "A and / or B" refer to (A), (B), or (A and B). For the purposes of this disclosure, the phrases "A, B, and / or C" refer to (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C).

[0016] The described embodiments can be implemented in radio systems, such as radio systems including at least one of the following radio access technologies (RATs): Global Microwave Access Interoperability (WiMAX), Global System for Mobile Communications (GSM, 2G), GSM EDGE Radio Access Network (GERAN), General Packet Radio Service (GRPS), Universal Mobile Telecommunications System based on Basic Wideband Code Division Multiple Access (W-CDMA) (UMTS, 3G), High-Speed ​​Packet Access (HSPA), Long Term Evolution (LTE), Advanced LTE, and Enhanced LTE (eLTE). The term "eLTE" here refers to LTE evolution connected to the 5G core. LTE is also known as Evolved UMTS Terrestrial Radio Access (EUTRA) or Evolved UMTS Terrestrial Radio Access Network (EUTRAN). The term "resource" can refer to radio resources, such as Physical Resource Blocks (PRBs), radio frames, subframes, time slots, subbands, frequency domains, subcarriers, beams, etc. The terms "transmit" and / or "receive" can refer to wireless transmission and / or reception over radio resources via a radio propagation channel.

[0017] However, the embodiments are not limited to the system / RAT given as an example, but those skilled in the art can apply the solution to other communication systems that provide the necessary attributes. An example of a suitable communication system is a 5G system. The 3GPP solution for 5G is called New Radio (NR). 5G is envisioned using multiple-input multiple-output (MIMO) multi-antenna transmission technology, more base stations or nodes than current LTE network deployments (the so-called small cell concept), including macro sites that cooperate with smaller local access nodes, and perhaps also employing various radio technologies to achieve better coverage and higher data rates. 5G may consist of more than one radio access technology / radio access network (RAT / RAN), each optimized for certain use cases and / or spectrum. 5G mobile communications may have a wider range of use cases and related applications, including video streaming, augmented reality, different data sharing methods, and various forms of machine-type applications, including vehicle safety, different sensors, and real-time control. 5G is expected to have multiple radio interfaces, namely sub-6GHz, cmWave, and mmWave, and can be integrated with existing legacy radio access technologies such as LTE.

[0018] The current architecture in LTE networks is distributed across radios and centralized in the core network. Low-latency applications and services in 5G require content to be closer to the radio, leading to local bursts and multi-access edge computing (MEC). 5G enables analytics and knowledge generation to occur at the data source. This approach requires leveraging resources that may not be continuously connected to the network, such as laptops, smartphones, tablets, and sensors. MEC provides a distributed computing environment for application and service hosting. It also enables the storage and processing of content closer to cellular subscribers to accelerate response times. Edge computing encompasses a wide range of technologies, such as wireless sensor networks, mobile data acquisition, mobile signature analytics, collaborative distributed peer-to-peer self-organizing networks and processing (which can also be categorized as local cloud / fog computing and grid / mesh computing), exposed computing, mobile edge computing, small clouds, distributed data storage and retrieval, autonomous and self-healing networks, remote cloud services, augmented and virtual reality, data caching, the Internet of Things (IoT) (massive connectivity and / or latency critical), and critical communications (autonomous vehicles, traffic safety, real-time analytics, time-critical control, healthcare applications). Edge clouds can be brought into the RAN by leveraging Network Functions Virtualization (NVF) and Software-Defined Networking (SDN). Using edge cloud may mean that access node operations are performed, at least in part, in servers, hosts, or nodes that are operationally coupled to remote radio heads or base stations, including radio components. Network slicing allows the creation of multiple virtual networks over a shared physical infrastructure. These virtual networks are then customized to meet the specific needs of applications, services, devices, customers, or operators.

[0019] In radio communications, node operations can be performed, at least partially, in a central / centralized unit (CU) (e.g., a server, host, or node) that is operatively coupled to a distributed unit (DU) (e.g., a radio head / node). Node operations may also be distributed among multiple servers, nodes, or hosts. It should also be understood that the workload distribution between core network operations and base station operations may vary from implementation to implementation. Therefore, 5G network architectures can be based on so-called CU-DU splitting. One gNB-CU controls several gNB-DUs. The term "gNB" in 5G can correspond to the eNB in ​​LTE. One or more gNBs can communicate with one or more UEs. A gNB-CU (central node) can control multiple spatially separated gNB-DUs to at least act as a transmit / receive (Tx / Rx) node. However, in some embodiments, the gNB-DU (also known as DU) may include, for example, the Radio Link Control (RLC), Media Access Control (MAC) layer, and Physical (PHY) layer, while the gNB-CU (also known as CU) may include layers above the RLC layer, such as the Packet Data Convergence Protocol (PDCP) layer, Radio Resource Control (RRC), and Internet Protocol (IP) layer. Other functional splits are also possible. It is assumed that those skilled in the art are familiar with the OSI model and the functions within each layer.

[0020] In one embodiment, the server or CU can generate a virtual network through which the server communicates with radio nodes. Typically, a virtual network can involve the process of combining hardware and software network resources and network functions into a single software-based management entity (i.e., the virtual network). Such a virtual network can provide flexible operational distribution between the server and the radio head end / node. In practice, any digital signal processing task can be performed in the CU or DU, and the boundary of responsibility transfer between the CU and DU can be chosen according to the implementation.

[0021] Other technological advancements that may be used include Software-Defined Networking (SDN), big data, and all-IP, to name just a few non-limiting examples. For instance, network slicing can be a form of virtual network architecture that uses the same principles as Software-Defined Networking (SDN) and Network Functions Virtualization (NFV) in fixed networks. SDN and NFV can provide greater network flexibility by allowing traditional network architectures to be segmented into virtual elements that can be linked (also via software). Network slicing allows the creation of multiple virtual networks on top of a shared physical infrastructure. These virtual networks are then customized to meet the specific needs of applications, services, devices, customers, or operators.

[0022] Multiple gNBs (access points / nodes), each comprising a CU and one or more DUs, can connect to each other via their negotiated Xn interfaces. The gNBs can also connect to the 5G core network (5GC) via a next-generation (NG) interface, which can be the 5G equivalent of the LTE core network. This 5G CU-DU split architecture can be implemented using a cloud / server architecture, allowing the higher-level CU to reside in the cloud while the DU is closer to or includes the actual radio and antenna units. Similar plans exist for LTE / LTE-A / eLTE. When both eLTE and 5G use a similar architecture in the same cloud hardware (HW), the next step could be to combine software (SW) to allow a single common SW to control two radio access networks / technologies (RAN / RAT). This would enable new ways to control the radio resources of both RANs. Furthermore, there could be configurations where the entire protocol stack is controlled by the same HW and processed by the same radio units as the CU.

[0023] It should also be understood that the workload allocation between core network operations and base station operations may differ from, or even not exist, in LTE. Another technological advancement that may be used is big data and all-IP, which can transform how networks are built and managed. 5G (or New Radio) networks are designed to support a multi-layered architecture, where MEC servers can be placed between the core and base stations or nodeBs (gNBs). It should be understood that MEC can also be applied to 4G networks.

[0024] 5G can also leverage satellite communications to enhance or supplement the coverage of 5G services, for example, by providing backhaul. Possible use cases include providing service continuity for machine-to-machine (M2M) or Internet of Things (IoT) devices or vehicle passengers, or ensuring the availability of critical communications and future rail / maritime / aviation communications. Satellite communications can utilize geostationary Earth orbit (GEO) satellite systems or low Earth orbit (LEO) satellite systems, particularly mega-constellations (systems deploying hundreds of (nano) satellites). Each satellite in a mega-constellation can cover several satellite-enabled network entities that create a ground cell. Ground cells can be created via ground relay nodes or by gNBs located on the ground or in satellites.

[0025] The implementation can also be applied to narrowband (NB) Internet of Things (IoT) systems, which enable a wide range of devices and services to connect using cellular telecommunications bands. NB-IoT is a narrowband radio technology designed for the Internet of Things (IoT) and is one of the technologies standardized by the 3rd Generation Partnership Project (3GPP). Other 3GPP IoT technologies suitable for implementing the implementation include Machine Type Communication (MTC) and eMTC (enhanced Machine Type Communication). NB-IoT focuses on low cost, long battery life, and support for a large number of connected devices. NB-IoT technology is deployed "in-band" in spectrum allocated for Long Term Evolution (LTE)—using resource blocks within ordinary LTE carriers, or in unused resource blocks within LTE carrier guard bands—or "independently" for deployment in dedicated spectrum.

[0026] The embodiments can also be applied to device-to-device (D2D), machine-to-machine, and peer-to-peer (P2P) communications. The embodiments can also be applied to vehicle-to-vehicle (V2V), vehicle-to-infrastructure (V2I), and infrastructure-to-vehicle (I2V), or generally to V2X or X2V communications.

[0027] Figure 1An example of a communication system to which embodiments of the present invention can be applied is shown. The system may include a control node 110 providing one or more cells (such as cell 100) and a control node 112 providing one or more other cells (such as cell 102). For example, each cell may be, for example, a macro cell, micro cell, femtocell, or picocell. In another view, a cell may define a coverage area or service area corresponding to an access node. Control nodes 110 and 112 may be evolved Node B (eNB) in LTE and LTE-A, ng-eNB in ​​eLTE, gNB in ​​5G, or any other means capable of controlling radio communications and managing radio resources within the cell. Control nodes 110 and 112 may be referred to as a base station, network node, or access node.

[0028] The system can be a cellular communication system consisting of a radio access network of access nodes, with each access node controlling one or more corresponding cells. Access node 110 can provide user equipment (UE) 120 (one or more UEs) with radio access to other networks such as the Internet. Radio access can include downlink (DL) communication from the control node to UE 120 and uplink (UL) communication from UE 120 to the control node.

[0029] Additionally, although not shown, one or more local access nodes may be arranged such that the cell provided by the local access node at least partially overlaps with the cell of access nodes 110 and / or 112. The local access node may provide radio access within a sub-cell. Examples of sub-cells may include microcells, picocells, and / or femtocells. Typically, a sub-cell provides a hotspot within a macrocell. The operation of the local access node may be controlled by an access node that provides sub-cells within its control area. Typically, the control node for a small cell may also be referred to as a base station, network node, or access node.

[0030] There can be multiple UEs 120 and 122 in the system. Each of them can be served by the same or different control nodes 110 and 112. If a D2D communication interface is established between UEs 120 and 122, then UEs 120 and 122 can communicate with each other.

[0031] The term "terminal device" or "UE" refers to any terminal device capable of wireless communication. As an example and not a limitation, a terminal device may also be referred to as a communication device, user equipment (UE), subscriber station (SS), portable subscriber station, mobile station (MS), or access terminal (AT). Terminal devices can include, but are not limited to, mobile phones, cellular phones, smartphones, Voice over IP (VoIP) phones, wireless local loop phones, tablets, wearable terminal devices, personal digital assistants (PDAs), portable computers, desktop computers, image acquisition terminal devices such as digital cameras, gaming terminal devices, music storage and playback devices, in-vehicle wireless terminal devices, wireless endpoints, mobile stations, laptop embedded devices (LEE), laptop mounted devices (LME), USB dongles, smart devices, wireless client devices (CPE), Internet of Things (IoT) devices, watches or other wearable devices, head-mounted displays (HMDs), vehicles, drones, medical devices and applications (e.g., remote surgery), industrial devices and applications (e.g., robots and / or other wireless devices operating in industrial and / or automated processing chain environments), consumer electronics devices, commercial equipment operations, and / or industrial wireless networks, etc. In the following description, the terms "terminal equipment", "communication equipment", "terminal", "user equipment" and "UE" are used interchangeably.

[0032] In a communication network with multiple access nodes, these nodes can connect to each other via interfaces. The LTE specification refers to such interfaces as the X2 interface. For IEEE 802.11 networks (i.e., wireless LANs, WLANs, WiFi), a similar interface, Xw, can be provided between access points. The interface between an eLTE access point and a 5G access point, or between two 5G access points, can be called Xn. Other communication methods between access nodes are also possible. Access nodes 110 and 112 can further connect to the core network 116 of the cellular communication system via another interface. The LTE specification designates the core network as the Evolved Packet Core (EPC), and the core network can include a Mobility Management Entity (MME) and gateway nodes. The MME handles the mobility of terminal devices in a tracking area containing multiple cells and handles signaling connections between the terminal devices and the core network. Gateway nodes handle data routing within the core network and data routing to / from terminal devices. The 5G specification designates the core network as the 5G Core (5GC), and the core network can include, for example, Access and Mobility Management Functions (AMF) and User Plane Functions / Gateways (UPF), to name just a few. AMF can handle Non-Access Stratum (NAS) signaling termination, NAS encryption and integrity protection, registration management, connection management, mobility management, access authentication and authorization, and security context management. For example, a UPF node can support packet routing and forwarding, packet inspection, and QoS processing.

[0033] As previously mentioned, 3GPP determined that further improvements could be achieved by leveraging partial uplink and downlink channel reciprocity. In Rel-17, work on NR CSI enhancement continued. In the description of the work item “Further Enhancement of MIMO for NR,” one topic is evaluating and specifying, where necessary, Type II port selection codebook enhancements (based on Type II port selection in Rel.15 / 16), where information related to angles and delays is estimated at the gNB by leveraging downlink / uplink (DL / UL) reciprocity of angles and delays, based on uplink sounding reference signals (SRS), and the remaining DL CSI is reported by the UE. This provides a better trade-off between UE complexity, performance, and reporting overhead, especially in Frequency Division Duplex (FDD) Frequency Range 1 (FR1) environments.

[0034] Incorporating reciprocity operations into the 5G NR CSI framework can be based on Type II port selection codebook enhancements. The Type II port selection codebook is based on the Spatial Beamforming CSI Reference Signal (RS). Spatial Beamforming CSI-RS, also known as Type B CSI feedback, has been introduced since LTE Release 13. Up to K=8 orthogonal (time or frequency) CSI-RS resources can be allocated to each user. Each CSI-RS resource consists of N in each spatial direction. k =Composed of 1..8 antenna ports (APs).

[0035] An antenna port (AP) (often simply called a port) can be understood as a logical abstraction of physical resources mapped to physical antennas. The number of available physical antenna elements is not necessarily equal to the number of APs. Each antenna port takes a resource grid as input. Resource grids can be different from each other. One antenna port can be mapped to multiple physical antennas. Furthermore, one physical antenna can be mapped to multiple antenna ports.

[0036] exist Figure 2B The diagram shows that UE 120 can send back a CSI-RS indicator (CRI), which informs gNB 110 of the optimal beam. UE 120 can also send a PMI, a rank indicator (RI), and a channel quality indicator (CQI). Once the “preferred” spatial direction for the channel between UE 120 and gNB 110 is determined via CRI feedback from UE 120 or via channel reciprocity on the UL using gNB 110, a spatial direction ( Figure 2B In the example, beam #2 completes the subsequent transmission.

[0037] Figure 2A An example embodiment of space beamforming CSI-RS is shown, wherein N k=4, with three frequency domain (FD) components (M=3), including , and The vertical dimension depicts the 12 subcarriers in frequency, while the horizontal dimension depicts the OFDM symbols in time. The depicted block can therefore be considered a Physical Resource Block (PRB) with 12 × 14 Resource Elements (REs). Blocks with waveform patterns depict the spatial domain (SD) beams 0-3 of FD component 0, blocks with dotted patterns depict the SD beams 0-3 of FD component 1, and blocks with brick-shaped patterns depict the SD beams 0-3 of FD component 2. For example, the top two waveform pattern blocks depict the SD beams 0-1 of FD component 0, and the bottom waveform pattern block depicts the SD beams 2-3 of FD component 0. The logic for other patterned blocks is the same. The gNB can transmit the depicted PRBs carrying at least these CSI-RS in a specific spatial direction. The gNB can be based on the same or different W1 and W2. f Another PRB with a different set of CSI-RS is transmitted in another spatial direction. The UE can receive these downlink reference signals, as described later.

[0038] For a spatial beamforming CSI-RS (e.g., beam #2) and assuming the transmitter (e.g., gNB) has N t >N k Each transceiver unit (TXRU) in CSI-RS uses a beam mesh (GoB) matrix. Pre-encoded. 1 PRB in N k The received signal at each resource point is

[0039] ,

[0040] in Figure 2A of and .

[0041] Therefore, the effective channel is In this example, this means that UE 120 effectively observes N k =4 <N t Channels of virtual antenna ports.

[0042] Assuming the CSI-RS density is 1, then across all n PRB Received signals of one PRB (horizontally stacked)

[0043] ,

[0044] in and .

[0045] On a path including the AP transmitting gNB 110 and the AP receiving UE 120, the correlation between subcarriers (subbands) in the frequency domain can be utilized to reduce the amount of CSI feedback overhead required. For example, in NR Rel.16, a linearly combined subband matrix W2 of size 2L×N3 is compressed in the frequency domain (FD) to... Where N3 is the number of sub-bands, and 2L is the number of spatial domain (SD) beams. The size is 2L×M

[0046]

[0047] FD basic subset The columns are taken from the DFT codebook. Similarly, for explicit CSI feedback in the time domain (TD), it has... Actual channel frequency response matrix (CFR) of 1 active subcarrier and 2L SD beams Compressed into a time-domain matrix

[0048]

[0049] in It is the length supported by the channel (i.e., the position of the active tap). The columns in the code are from the DFT codebook.

[0050] In one embodiment, code division multiplexing (CDM) can be applied within a PRB. For example, in each PRB, CDM is applied to a port close to the RE (time or frequency) to ensure orthogonality. Then, after receiving the CSI-RS pilot, the UE can "cancel" the CDM within the PRB and then operate as described above. In other words, CDM operates on top of the described scheme.

[0051] In frequency division duplex (FDD) 5G systems, the gNB uses downlink reference signal (e.g., CSI-RS) transmission and Type I or Type II codebook feedback from the UE to obtain CSI. While Type II in Rel-15 and Rel-16 provides significant accuracy, it comes at the cost of considerable feedback overhead and suffers some performance loss due to quantization errors.

[0052] The correct design of a CSI procedure based on partial reciprocity requires addressing several aspects, including downlink reference signal precoder design, uplink feedback format (uplink control information UCI design in NR), timely triggering of uplink reference signals (such as SRS), beamforming reference signal transmission in the downlink (such as CSI-RS), effective configuration of reciprocity-based CSI reports in radio resource allocation (RR) (such as reference signal configuration), and triggering status.

[0053] Although full-channel reciprocity does not hold in FDD systems, the gNB can rely on SRS transmissions from the UE to obtain broadband information that is typically similar for both uplink and downlink channels. In addition to path delay, reciprocal broadband parameters in FDD systems may also include the azimuth and elevation angles of the arriving and departing paths. However, errors can still occur when estimating reciprocal channel information, particularly for weaker paths, which can be problematic because the gNB might subsequently use erroneous information to beamform the downlink reference signal. Therefore, maintaining flexibility in defining the downlink reference signal precoder and subsequent operations on the UE side may be beneficial.

[0054] Furthermore, incorporating reciprocity-based CSI operation requires updating the uplink control information format to further reduce reporting overhead. In fact, after the UE transmission of the reference signal (e.g., SRS), a portion of the wideband channel characteristics may be available at the gNB side. Therefore, the uplink control information format needs to be optimized to avoid information redundancy and keep reporting overhead to a strict minimum. While the Type II port selection codebook covers the spatial reciprocity of the channel, it does not utilize delay reciprocity.

[0055] To at least partially address the aforementioned drawbacks, an efficient and flexible design for a downlink reference signal precoder is provided, leveraging both spatial and delay reciprocity between the uplink and downlink. Furthermore, an improved uplink control information format is proposed. In other words, a solution is proposed that can incorporate the estimated angle and delay information at gNB 110 based on the UE's uplink reference signal transmission (e.g., SRS in NR) during the precoding of the downlink reference signal (e.g., CSI-RS) for downlink CSI estimation at the UE side. The UE 120 can then report the remaining downlink CSI (e.g., frequency selectivity information) based on the received precoded downlink reference signal. This solution is built upon a Type II port selection enhancement framework.

[0056] Figure 3 and Figure 4 An example method for CSI measurement and reporting based on reciprocity is described. Figure 3 The method can be executed by network nodes, such as Figure 1 The gNB 110. The method of claim 4 can be performed by a user equipment, such as... Figure 1 UE 120.

[0057] like Figure 3 As shown, gNB 110 may receive a UL reference signal from UE 120 in step 300. In one embodiment, the UL reference signal includes a sounding reference signal (SRS). In one embodiment, UE 120 transmits periodic, aperiodic, or semi-persistent uplink reference signals to gNB 110.

[0058] In step 302, gNB 110 can estimate delay information regarding the delay distribution of the communication channel between UE 120 and gNB 110 based on the received UL reference signal. gNB 110 can further determine spatial information about the communication channel based on the received UL reference signal. That is, gNB 110 estimates the downlink channel spatial and frequency domain support based on the received uplink reference signal (one or more). For FDD, reciprocity is partial and may apply to angle and delay. In one embodiment, if the rank of the communication channel is >1, the estimation can be performed for each channel transmission rank.

[0059] In the Rel-16 Type II codebook, there is a correspondence between delay and so-called "frequency domain components." These two quantities can be defined in the DFT transform domain relative to the subcarrier domain where both SRS and CSI-RS are defined. The "frequency domain components" (also called "frequency domain supports" or "frequency domain basis vectors") are a set of vectors selected from the DFT basis. Recognizing the duality between the frequency and time domains, they indicate the location of the channel taps in the time domain.

[0060] In one embodiment, the delay information is determined based on channel reciprocity. In one embodiment, the delay information indicates the delay of each path of the communication channel relative to a reference time. The reference time may be the delay of the line-of-sight path. In one embodiment, the number of paths considered is limited by a predetermined power threshold. Due to the duality of time and frequency, the gNB110 can estimate the channel frequency response (CFR) based on the received SRS in order to obtain the delay information.

[0061] In one embodiment, spatial information indicates the angle of arrival of each path of the communication channel relative to a reference angle. For example, the reference angle could be zero. In practice, the physical direction corresponding to this zero angle can be determined by the gNB's reference system and can be a given specific direction of azimuth and / or elevation. The spatial information can be determined, for example, based on the angle of arrival information received from the ULSRS.

[0062] In step 304, gNB 110 may apply both delay information and spatial information to the precoding of at least one downlink reference signal. In one embodiment, the at least one downlink reference signal includes a Channel State Information Reference Signal (CSI-RS). In one embodiment, the at least one downlink reference signal includes another reference signal different from the CSI-RS, such as a Demodulation Reference Signal (DMRS). It is understood that, through precoding, specific types of information are added to the CSI-RS signal, which includes one or more PRB resource elements. By using delay information for precoding, the DL reference signal precoding on the gNB side differs from the precoding used for LTE Class B CSI and Rel-15 / Rel-16 Type II port selection codebooks. This step requires applying both spatial and delay information to the downlink reference signal precoding. The downlink reference signal precoder will be based on spatial domain beams (e.g., selected from an oversampled beam grid) and frequency domain components (e.g., selected from a codebook, typically based on DFT / IDFT, which may be oversampled). In step 302, the frequency domain components corresponding to the delay information due to time-frequency duality may be determined based on the received UL SRS. Spatial precoding can involve transmitting CSI-RS symbols through multiple antenna ports with a given complex multiplication factor (the set of these factors forming a precoding vector). The proposed "FD precoding" (also known as "delayed precoding") can be defined as applying a given complex multiplication factor to a spatial precoding vector of different frequency units (such as PRBs), for example, in... Figure 2A Therefore, in one embodiment, precoding includes applying a frequency-domain precoder to each DL reference signal (including one or more resource elements of the PRB), the frequency-domain precoder being based on a combination of a spatial beam and at least one frequency phase ramp, each phase ramp corresponding to a component of the corresponding delay distribution of the communication channel. Based on the frequency-time duality, the frequency phase ramp corresponds to the time-domain supported component of the channel.

[0063] In one embodiment, the processing of the CSI-RS signal / port (e.g., FD precoding) is performed before the transmitter's IFFT (i.e., in the frequency domain). In this context, the CSI-RS port to be beamformed (i.e., the CSI-RS signal) is windowed M times, where M represents the number of FD components. The goal of this operation may be to enable the UE 120 to estimate the non-zero coefficients of the linear combination by summing the beamformed CSI-RS over the configured subband for each AP. For example, in Figure 2A In an example embodiment, UE 120 can support S over all PRBs in many subbands. CSI-RS,0 (That is, channel estimation) is summed to achieve an S of the spatial beam.CSI-RS,0 As will be described. A subband may include, for example, multiple PRBs.

[0064] In step 306, gNB 110 may transmit at least one precoded DL reference signal to UE 120. gNB 110 may, for example, use the frequency-domain precoder described above to beamform each CSI-RS port (also referred to as a CSI-RS signal). There may be one or more DL reference signals (e.g., CSI-RS). Using only spatial precoding (as in Rel-16 Type II port selection), gNB 110 transmits one CSI-RS for each spatial beam, and this can be referred to as a CSI-RS port. After applying the "delayed precoding" in step 304, gNB 110 may transmit multiple CSI-RS for each spatial beam in step 306, such as... Figure 2A In this configuration, each spatial beam has M=3 FD components, and therefore, one spatial beam has three CSI-RS. In one embodiment, the gNB 110 transmits precoded CSI-RS ports in each configured subband. The subbands can be pre-configured to the UE 120 by the gNB 110 and / or pre-configured to the UE 120 according to the capabilities of the UE 120.

[0065] In one embodiment, after receiving the uplink reference signal, the gNB 110 can estimate a set of beams spanning the UE channel in the spatial domain. This set of beams can be used for beamforming of the DL reference signal.

[0066] In one embodiment, gNB 110 may transmit to UE 120 an indication of whether delay and spatial information are used for precoding of the DL reference signal at gNB 110. This allows UE 120 to know in advance how the CSI-RS is precoded on the gNB side. For example, UE 120 may be configured with a list of aperiodic CSI trigger states and / or a list of semi-persistent CSI trigger states, for example, by gNB 110. Each trigger state may be associated with a CSI report configuration set, which includes information / fields related to partial reciprocity operation. The information / fields related to partial reciprocity may include explicit or implicit indications regarding DL reference signal precoding (e.g., the number of CSI-RS ports) to specify whether the spatial domain, frequency domain, or a combination of both are used on the gNB side.

[0067] In one embodiment, upon receiving this indication (e.g., via RRC signaling), UE 120 can understand that the pilot has been windowed by a phase ramp. This may be why a simple summation (dot product) at the UE might suffice. If the pilot is not windowed and UE 120 still performs a summation, it will not provide the correct feedback.

[0068] In one embodiment, the precoded DL reference signal enables UE 120 to estimate the channel coefficients for each subband configured for UE 120, wherein the estimation may be based on at least one received precoded DL reference signal, and further enables UE 120 to perform a summation of the estimated channel coefficients over the subbands to derive non-zero coefficients in the frequency domain. For example, after receiving beamforming DL reference signals (precoded in both the spatial and frequency domains), UE 120 can process the measured channel coefficients of the received signal by summing over all configured subbands (the sums may be weighted) to derive at least one non-zero coefficient. In one embodiment, gNB 110 can configure the resolution of the window; for example, gNB 110 can allocate the window resolution within a subband in a certain configuration. CSI-RS All weights are set to the same value. In another embodiment, the weights can be different, such that S is given, for example, within a subband. CSI-RS The weights can have different values.

[0069] In step 308, gNB 110 may receive channel information from UE 120 in response to the transmission of at least one precoded DL reference signal. This channel information indicates at least one non-zero channel coefficient for at least one channel transport layer between UE 120 and gNB 110. For channels with a rank greater than 1, there may be multiple channel layers, each characterized by a corresponding channel matrix. Therefore, UE 120 may feed back channel coefficients for each transport layer. In one embodiment, the channel information includes channel state information (CSI). In one embodiment, the channel information includes a precoded matrix indicator (PMI). In one embodiment, the channel information is quantized by UE 120. The feedback channel information may explicitly or implicitly indicate the channel coefficients of the DL channel matrix. In one embodiment, the channel information may include channel coefficients in the frequency domain. In one embodiment, the channel information may include channel coefficients in the time domain, rather than in the frequency domain. However, it can be seen that these time-domain coefficients are transformed to convey coefficients in the FD, and vice versa.

[0070] In one embodiment, the non-zero coefficients in the frequency domain indicate the non-zero coefficients for each spatial beam and each frequency component or set of frequency components of the communication channel. It may be necessary to note, for example, regarding these domains, that... Figure 2AAmong them, two squares in each group represent two SD beams and one FD component. In the Rel-16 type II codebook, such a component is used by the UE for PMI frequency-domain compression. However, in the proposed solution, the compression does not need to be performed by the UE 120, but by the gNB 110 in the precoding of the CSI-RS in step 304. In one embodiment, for PMI feedback purposes, the UE may transmit only non-zero coefficients for each CSI-RS port.

[0071] In one embodiment, the UE 120 may refrain from transmitting, and thus the channel information may not include information indicating non-zero coefficients for any subbands respectively. That is, contrary to the Rel-16 type II codebook solution, the UE 120 may not feedback the frequency-based subset W f . Instead, the UE 120 may perform the summation of the estimated channel coefficients over the subbands. In the Rel-16 type II precoding, the relevant FD components are found by the UE and their indices are fed back to the gNB as part of the UCI. Due to the current proposal, this is no longer necessary because the gNB 110 estimates the frequency-domain components based on the UL SRS, as described in connection with step 302. Since these components are used for the precoding of the (multiple) DL reference signals in step 304, the UE 120 no longer needs to know the actual components or does not need to feed them back. In fact, when the proposed "FD precoding" (also referred to as "delayed precoding") in step 304 is applied to the CSI-RS port / signals, the UE 120 can still report non-zero coefficients for each FD component, but it does so blindly, that is, without knowing which FD component the coefficients correspond to. This information is known to the gNB 110, and the gNB 110 determines the set of weights applied to the corresponding spatial beams over the entire PRB.

[0072] Due to the windowing of the CSI-RS applied in advance on the gNB side, the summation operation can be possible. By using a phase ramp, the windowing shifts the channel impulse response (CIR) seen by the receiver (e.g., the UE 120), such that the delayed taps corresponding to the FD component m (where m < M) appear at the 0 position (DC) of the CIR. The DC component can be obtained by summation. In one embodiment, the summation can be extended to averaging. In one embodiment, before quantization, all FD coefficients are normalized by the strongest coefficient such that the strongest coefficient has a value of 1. The gNB 110 knows which phase ramp corresponds to which FD component used by the gNB 110 for precoding. Therefore, the gNB 110 can be able to determine the positions of the complex FD component coefficients fed back by the UE 120. In one embodiment, the channel information does not include a bitmap M indicating the positions of the non-zero coefficients within the precoding matrix indicator (PMI) INITIAL .

[0073] Therefore, in one embodiment, the uplink control information format carrying CSI is modified. Since both delay(s) and angle reciprocity(s) are included in the precoding of the downlink reference signal, UE 120 does not need to feed back a subset of the frequency domain. Furthermore, UE 120 can discard more fields from the previous Rel-16 Type II feedback, such as bitmaps indicating the positions of non-zero coefficients.

[0074] As a result of receiving such a CSI from UE 120, gNB 110 can recreate / determine the precoding matrix and / or downlink (spatial-time-frequency) channel matrix required for beamforming of data transmission to UE 120 in step 310. In one embodiment, the recreated channel can be depicted by a precoding matrix of the communication channel, indicating the spatial-time-frequency components of the communication channel. Based on one definition of CSI, UE 120 can report a precoding matrix indicator (PMI), which gNB 110 can use to reconstruct the precoding matrix. However, in another embodiment, UE 120 can report an explicit channel to gNB 110. This can indicate that UE 120 feeds back the compressed channel coefficients of the downlink spatial-time-frequency channel matrix. For each spatial delay basis component in step 308, the determination of the matrix in step 310 can be based on the spatial delay basis components (W1 and W2) of the UL SRS from step 302. f The knowledge of ) and further based on the feedback scaling factor (=CSI), such as W2. gNB 110 can then apply beamforming to the data transmission of UE 120 based on one or both of the matrices.

[0075] From UE 120's perspective, this method is... Figure 4 As described in the description. In step 400, UE 120 may transmit a UL reference signal to gNB 110, wherein the UL reference signal indicates the aforementioned delay information and spatial information of the communication channel between UE 120 and gNB 110. In step 402, in response to the transmission of the UL reference signal, UE 120 may receive at least one DL reference signal, wherein the at least one downlink reference signal is precoded in gNB 110 based at least on the delay information and spatial information. In step 404, UE 120 may determine channel information based on the received at least one precoded DL reference signal, the channel information indicating at least one channel transport layer / at least non-zero coefficients for at least one channel transport layer, and transmit the channel information to gNB 110 in step 406.

[0076] As described above, the determination / estimation of channel information by UE 120 in step 404 may include estimating channel coefficients for each subband configured for the user equipment, wherein the estimation may be based on at least one precoded downlink reference signal and the estimated channel coefficients are summed over the subband. In this way, UE 120 can calculate a scaling factor for each spatial delay basis component based on the precoded CSI-RS and then feed back the scaling factor without explicitly indicating the delay basis component.

[0077] The proposed reciprocity-based CSI measurement and reporting solution reduces the size of uplink control information (UCI in 5G NR) without affecting PMI accuracy. The proposed method reduces the computational burden on UE120 when measuring and reporting CSI because the CSI compression operation can be advantageously offloaded from UE120 to gNB110. For example, in Rel-16 II, the spatial delay basis component and corresponding scaling factor are calculated by UE120 and fed back at UL. In Rel-16 II port selection, the delay basis component and corresponding scaling factor are calculated by the UE and fed back at UL. Due to the currently proposed embodiment, the spatial delay basis component is calculated by gNB110, and the corresponding scaling factor is calculated and fed back by UE120. For example, the weighted summation operation inherent in FD compression is decoupled / distributed between gNB110 and UE120, respectively, instead of performing both operations at UE120. Any potential increase in DL resource overhead due to additional precoding can be controlled, for example, by assuming a lower CSI-RS density factor, such as per the second or third PRB pilot (CSI-RS). It can also be noted that UL resources are scarcer than their DL counterparts. Therefore, it may be beneficial to reduce UL resource usage at the expense of a slight increase in DL usage.

[0078] Let's now take a closer look at precoding. Starting with the case of an antenna port, the UE has a receive antenna, assuming n... PRB One PRB, and assume that gNB knows the DL from the UL SRS measurement. The effective compressed explicit channel on DL can be written as:

[0079]

[0080] Assuming the CSI-RS density is 1, the received signal can be written as:

[0081]

[0082] in

[0083]

[0084] It is the pilot signal transmitted on PRB x (e.g., CSI-RS).

[0085] consider A column within, for example, column m If the pilot sequence is windowed through this column, the received signal can be written as:

[0086]

[0087] in

[0088]

[0089] , making This is the transmitted pilot sequence after applying FD precoding, which includes multiplication with a diagonal matrix. This multiplies each pilot by a scalar number, i.e., performs windowing.

[0090] On the UE side, the inner product between the received signal and the pilot sequence is generated:

[0091]

[0092]

[0093] Therefore, on the UE side, the delay m of the compressed channel can be fed back by a simple dot product. This operation can be repeated M times to recover the entire compressed channel. .

[0094] Build on the gNB side In the next step, gNB can reconstruct the entire CSI using the following formula.

[0095]

[0096] To avoid overusing resources on the DL (Data Streaming Platform), multiple solutions can be used individually or in combination. For example:

[0097] • Maintain total CSI-RS density = 1. For example, assuming M = 4 and a CSI-RS density of 1 / 4 per delay tap, A column m inside, The pilot sequence is windowed every four PRBs. In this case, the DFT size can also be reduced accordingly.

[0098] • The entire process can be obtained using several CSI-RS transmissions at different times. .

[0099] • If each antenna port can be used differently with W f, then it is not necessary to detect all channel tap delays for each antenna port. In other words, even if M = 4 channel taps are active on all paths, each antenna port n only needs to report M n <the M strongest tap delays, which reduces the number of resources required in the DL.

[0100] When extending the above model to the multi-port case, for example, in the case of 1 PRB with N t ports (e.g., at PRB x), the beamformed CSI-RS can be written as:

[0101]

[0102] For N3 PRBs, the received signal can be written as:

[0103]

[0104]

[0105]

[0106] where .

[0107] On the UE side, then the inner product between the received signal and the pilot sequence is performed for each transmission antenna port (as written above, this inner product is performed for each tap delay m).

[0108] As described above, frequency windowing can be used. For example, if N t TXRUs are to be beamformed spatially into N k CSI ports, then

[0109]

[0110] the received signal can be written as:

[0111]

[0112] The analysis can also be extended to UEs with N rx > 1 receive antennas, where the effective channel for each transmission antenna port has the following size

[0113]

[0114] In this case, the UE will repeat the inner product between the received signal and the pilot sequence for each receive UE antenna and transmission gNB antenna port, as described above.

[0115] To account for the fact that only a portion of the channel bandwidth is active, the effective channel can be weighted using the correction matrix on the gNB side.

[0116]

[0117] Figure 5 An embodiment of the precoding and reporting method is shown. For Figure 3 and Figure 4 Each step, Figure 5 A possible embodiment for performing the corresponding steps is shown. In steps 300 and 400, the SRS is transmitted from UE 120 to gNB 110. In steps 302A and 302B, gNB 110 observes delay information in the form of channel frequency response (CFR). Parameter 𝑁 p It is the number of SD paths, equal to (2k × k). 𝑟𝑥 Based on this, gNB 110 can determine the frequency domain component W. f gNB can use the frequency domain component W in step 304. f The CSI-RS is windowed. In steps 306 and 402, the CSI-RS is transmitted to UE 120. In step 404, UE 120 then determines at least one transport layer / non-zero channel coefficients for at least one transport layer based on the CSI-RS. These may be referred to as scaling factors for the spatial delay basis components and denoted as W2. Alternatively, UE 120 may compute the channel matrix H. Then, in steps 308 and 406, either or both of these may be fed back to gNB for each transport layer / channel matrix (in the case of channel rank > 1). In step 310, gNB 110 estimates the CSI (e.g., CFR) to determine the precoding matrix and / or channel matrix for data transmission. If necessary, the precoding of CSI-RS, the transmission of CSI-RS, and the feedback of W2 and / or H may be repeated M times to recover the entire spatial-temporal-frequency channel. In step 500, the determined precoder matrix can then be used for beamforming data from gNB to UE.

[0118] Compared to the Rel.16 solution, the following points can be noted. The purpose of FD compression in Rel.16 is to reduce the overhead within the subband eigenvector matrix W2. This compression is achieved by combining matrix W2 with the compression matrix W... f This is achieved through multiplication and by selecting a subset of the coefficients of the matrix obtained as the compression result. Overall, the final structure of the PMI will be derived by multiplying the following three matrices:

[0119] • Matrix W1, which is responsible for space compression

[0120] · Matrix W2, which carries the selected compression factor

[0121] ·Matrix W f It is responsible for frequency domain (FD) compression.

[0122] Rel-16 supports two versions of the Type II codebook, namely:

[0123] • "Enhanced": In this case, all the computational burden is on the UE, which needs to identify and apply W1 and W2. f It then calculates W2 and feeds back an indicator carrying quantization information about the three matrices. The resulting overhead can be significant.

[0124] • Enhanced Port Selection: In this configuration, the CSI-RS port is beamformed at the gNB to pre-select a preferred spatial direction for transmission to the UE. Therefore, the UE does not need to identify and apply matrix W1, as spatial compression is not required in this case. Only W... f The identifier is used to calculate W2. Only the indicator carrying quantization information about these two matrices is fed back to the gNB. This results in a lower computational burden and less overhead for the UE.

[0125] In the current proposal, the identification and partial application of W are proposed. f The task is left to the gNB, taking a further step forward. In this case, the base station utilizes information obtained by evaluating the received SRS in the UL—that is, knowledge of the (multiple) delays and (multiple) angles of the UL channel—to further process the CSI-RS ports and window them before DL transmission. Therefore, due to the proposed method, summation at the UE is sufficient to obtain a set of compression coefficients after channel estimation. Finding W f The task of port selection is often a complex and lengthy process, which hinders the practical feasibility of using the Rel-16 Type II port selection codebook for low-end UEs. By transferring this complex part to the gNB, the computational and memory requirements of the UE are reduced. Therefore, there is no longer a need to communicate information about W... f The signaling of structural information is performed by the gNB independently of the PMI feedback, as the selection of the FD components is handled by the gNB. In other words, according to the proposed idea, the feedback overhead does not need to include information about FD compression, unlike its Rel-16 counterpart.

[0126] Next, let's look at some methods to improve W. f Examples of the accuracy and knowledge of [the subject].

[0127] In a Type II codebook, the precoding matrix of each layer can be written as:

[0128] (1)

[0129] The final precoder at gNB can be a weighted linear combination of L orthogonal beams for each polarization, as follows:

[0130]

[0131] The beam grid matrix W1 has a size of 2N1N2×2L and consists of L orthogonal vectors / beams for each polarization r from a set of oversampled O1O2N1N2 DFT beams, where N1 and N2 are the number of antenna ports in the horizontal and vertical domains, respectively. O1 and O2 are the oversampling factors in both dimensions. 'l' refers to the index of the transmission layer. This set of vectors can be used to approximate the eigenvectors of the channel covariance matrix through an appropriate weighted linear combination. This operation achieves compression in the spatial domain (SD), hence the resulting 2L beams are also called SD components.

[0132] A linear combination subband matrix W2 of size 2L×N3 (where N3 is the number of frequency subbands) is used to perform a weighted linear combination of the columns of W1 to generate the aforementioned channel covariance matrix. l The approximation of the strongest eigenvector.

[0133] The enhancement of Type II CSI feedback in Rel.16 can be based on utilizing the frequency correlation within W2. A frequency domain compression scheme is applied to the sub-band matrix W2. The precoders for each layer and across frequency domain units W are derived as follows.

[0134] (2)

[0135] in W is a 2L×M matrix of linear combination coefficients. f It is an N3×M FD compression matrix (similar to W1 in the frequency domain), where M is the number of frequency domain (FD) components.

[0136] For example, in Rel.16 Type II CSI, the UE can feed back to the gNB: beam grid matrix W1, FD basic subset W f And linear combination coefficients (LCC) On the UE side, It can be calculated as

[0137] (3)

[0138] As previously mentioned, Type II port selection enhancement can consider partial reciprocity of uplink and downlink channels in terms of (multiple) delays and (multiple) angles. For example, a CSI scheme can be used, where partial reciprocity of delay information is utilized to reduce complexity on the UE side, as illustrated above in Figure 2-. Figure 5The above. Let's call this proposal CSI Proposal #A. This can assume existing knowledge of the delay information of the DL on the gNB side (i.e., W). f The knowledge), and may include at least the following: on the gNB side, by using a phase ramp corresponding to each significant delay tap on the DL (i.e., using Windowing CSI-RS using columns in the table can be done using... CSI-RS are precoded. On the UE side, the inner product of the received signals in different frequency sub-bands with (multiple) known pilot sequences (CSI-RS) is obtained. The UE then provides feedback. Therefore, the UE is exempt from calculating the feature vector and DFT compression as required by Rel.16.

[0139] However, CSI scheme #A assumes that gNB has W f Sufficiently good (e.g., complete) knowledge (e.g., from measurements of the uplink reference signal, such as SRS). In reality, errors can still occur when estimating reciprocity channel information, especially for potentially problematic weaker paths or delays, because the gNB will subsequently use the erroneous information in the windowing (i.e., precoding) of the DL CSI-RS.

[0140] In Type II port selection CB, compared to Type II CB, the selected spatial beam matrix W1 is replaced by a port selection matrix indicating the selected port. It has been agreed that the same DFT-based compression scheme in Rel. 16 can be extended to the Type II port selection codebook. Therefore, when feeding back W1, the UE may only need to feed back the index of the selected port selection, rather than the index of the strongest beam from a fixed DFT-based codebook. An example of W1 with L=4 is shown below:

[0141] (4)

[0142] in This is a port selection vector, where the i-th element is 1 and the rest are 0. Note that the UE can be restricted to selecting L consecutive ports from all ports in the CSI-RS.

[0143] The advantage may lie in the fact that the gNB can utilize any prior knowledge it possesses regarding the DL spatial broadband CSI (e.g., from measurements of uplink reference signals such as SRS), allowing the UE to select a port set that does not span the entire angular range, thus potentially reducing the amount of required UL overhead or increasing the granularity of W1. As we have seen, port selection CB only assumes that spatial information knowledge exists in advance at the gNB.

[0144] In equation (3), Each element within can be calculated as a row (SD beam) in W2 and W f Weighted summation operation between a column (phase ramps corresponding to the major tap positions) within the column.

[0145] (5)

[0146] In CSI scheme #A, it is assumed that W exists at gNB. f Based on this knowledge, for each SD beam, the gNB pairs with different M-columns W f M CSI-RS applications with M windowing operations. Figure 2A An example of a resource block (RB) pilot format is depicted, which is designed to use M=3 FD components (including , and The 12 subcarriers in frequency and the four SD beams in each FD component are pre-coded. The vertical dimension depicts the 12 subcarriers in frequency, while the horizontal dimension depicts the OFDM symbols in time.

[0147] Before delving deeper, it may be helpful to review the pilot format used for traditional LTE / NR CSI-RS transmission. In a typical LTE / NR RB pilot format, two time-adjacent pilot resource elements (REs) carry two pilot symbols transmitted via code division multiplexing (CDM). Figure 2A In this context, these will include, for example, S CSI-RS,0 and S CSI-RS,1 . Figure 2A The illustrated RB contains four RE locations for each FD component and therefore carries four pilot symbols for each FD component, with each pilot symbol associated with a "CSI-RS port," for example, associated with an SD beam. Typically, as with typical LTE / NRCSI-RS formats, a certain number of these RBs are transmitted across the entire frequency band, and each "CSI-RS port" has an associated sequence of pilot symbols; one pilot symbol per RB across the entire frequency band of that "CSI-RS port." Within an RB, for each pair of adjacent REs, the UE cancels CDM and acquires the resulting two symbols, and acquires the "noisy" channel estimate for the two CSI-RS ports associated with that pair of adjacent REs. The noisy channel estimate for each CSI-RS port across all RBs can then be filtered / smoothed to obtain the estimated frequency response for that CSI-RS port. This type of channel estimation is commonly used in conventional LTE / NR CSI-RS channel estimation.

[0148] according to Figure 2AThe CSI scheme #A, partially depicted in the middle section, precodes each CSI-RS port using a combination of SD beams and FD components, thus ultimately resulting in 2LM virtual CSI ports, where 2L is the number of SD beams and M is the number of FD components. In this way, each virtual CSI port can be the result of pilot symbols first precoded with SD beams and then precoded with FD components (i.e., with phase ramps corresponding to the delays of the FD components), and the resulting symbols can be encoded according to the method described in the previous paragraph. In some embodiments of CSI scheme #A, SD precoding is optional, meaning that the scheme can also work with only FD precoding. Figure 2A In the example, we have a block that is marked differently, referring to different FD components. For each marked block, four pilot symbols are multiplexed, each corresponding to a different SD beam. The gNB can transmit at least the depicted PRB carrying these CSI-RS in the DL. The gNB can be based on the same or different W1 and W f Transmit another PRB with a different set of CSI-RS to another spatial direction and / or another UE. The UE can receive these downlink reference signals. The UE's task may be to estimate the effective channel frequency response for each CSI-RS port, where the effective channel frequency response is a combination of the FD and SD components associated with that CSI-RS port and the multipath channel. Note that in Figure 2A In the example, 12 pilot resource elements are used to enable the gNB to transmit a 4-port CSI-RS with M=3 windowing; in other words, there are 12 virtual CSI ports for 4 SD components × 3 FD components.

[0149] On the UE side, for each virtual CSI-RS port (i.e., the CSI-RS pilot sequence and corresponding pilot RE in the RB across the entire frequency band), the UE can estimate the channel response by calculating the complex channel gain, as previously described. The complex channel gain of the virtual CSI-RS port can be further averaged across the FD subband. In this way, for each virtual CSI-RS port, the UE can calculate the average channel gain / phase response across the FD subband. This can provide the UE with the value of the compressed channel component. This may mean that the weighted summation operation used to calculate the compressed channel component can be advantageously divided between the gNB and the UE, where weighting (windowing) is performed on the gNB side and summation is performed on the UE side. This may contrast with the standard scheme in the Rel-16 II codebook, where the entire weighted summation operation is performed on the UE side.

[0150] However, as mentioned earlier, CSI scheme #A or W-based schemes on the gNB side utilizing partial reciprocity... f Any other use case of W's knowledge can benefit from it.f Accurate knowledge is needed. Therefore, a mechanism is required whereby the W of partial reciprocity from the gNB side can be further refined or updated. f Prior knowledge is needed to avoid measurement errors on the gNB side.

[0151] To at least partially address this issue, a solution for delay scanning is proposed to refine the gNB's existing knowledge of delay information related to the DL channel, which can be obtained from UL SRS measurements, in order to acquire W. f More accurate knowledge. This can improve the estimation of W. f This improves the accuracy of the UL (Low Length) information and thus the accuracy of any subsequent use cases, such as for CSI scheme #A. Therefore, one advantage is that, similar to the port selection CB case, the gNB can utilize any prior knowledge it possesses about DL (Low Length) delay information so that the set of delays from which the UE selects does not span the entire delay range, thus reducing the amount of UL overhead required or increasing W (Wide Length) efficiency. f Granularity.

[0152] Figure 8 An example method is described. This method can be executed by network nodes, such as... Figure 1 The gNB 110. For simplicity, we assume the method is executed by the gNB 110. Therefore, as Figure 8 As shown, gNB 110 can determine a set of M' frequency domain components for the communication channel between the user equipment and the network node in step 800. In one embodiment, M' is a positive integer.

[0153] In one embodiment, M' is derived by gNB 110 based on measurements performed on received uplink reference signals (such as probe reference signals). However, other uplink reference signals, such as uplink DMRS, can be used alternatively. In one embodiment, UE 120 transmits multiple periodic, aperiodic, or semi-persistent uplink reference signals to gNB 110. gNB 110 can estimate delay information about the delay distribution of the communication channel between UE 120 and gNB 110, for example, based on UL RS. In one embodiment, knowledge of the M' FD components can be based on W already acquired based on early UE feedback. f .

[0154] In one embodiment, the delay information is determined based on channel reciprocity. Based on this delay information, gNB 110 can thus determine the set of M' frequency domain components.

[0155] In one embodiment, gNB 110 can also determine a set of 2L spatial domain components for the communication channel. In one embodiment, 2L is a positive integer. In one embodiment, gNB 110 can estimate spatial information about the communication channel based on the received uplink reference signal, and then determine the set of 2L spatial domain components based on the spatial information. The spatial information can be determined, for example, based on the angle of arrival information of the received UL SRS.

[0156] In one embodiment, the gNB 110 can select L' spatial domain components from 2L spatial domain components, where L' <= 2L. In one embodiment, the L' spatial domain components include the L' strongest spatial domain components out of the 2L spatial domain components. For example, what constitutes "strongest" can be based on received power.

[0157] In step 802, gNB 110 applies the set of M' FD components to the precoding of multiple downlink reference signals. These reference signals may be referred to as auxiliary or optional downlink reference signals, or a first set of downlink reference signals, in order to associate these reference signals with, for example, in Figures 3-4 The downlink reference signals mentioned above are separate. However, these auxiliary DL reference signals will be referred to simply as downlink reference signals below. The frequency domain component corresponding to the delay information caused by the time-frequency duality can be determined in step 802 based on the received UL SRS. In one embodiment, the downlink reference signal includes a channel state information reference signal (CSI-RS). In another embodiment, the downlink reference signal includes a different reference signal than CSI-RS, such as a demodulation reference signal (DMRS).

[0158] Precoding reveals that specific types of information are added to a CSI-RS signal that includes one or more PRB resource elements. The proposed "FD precoding" (also known as "delayed precoding") can be defined as applying a given complex multiplication factor to a spatial precoding vector of different frequency units (such as PRBs), as in, for example... Figure 2A In one embodiment, the FD precoding of the CSI-RS signal / port is performed before the transmitter's IFFT (i.e., in the frequency domain). In this case, the CSI-RS port (i.e., the CSI-RS signal) to be beamformed is windowed M' times.

[0159] In one embodiment, gNB 110 applies the same set of M' frequency domain components to each spatial domain component in precoding. This may mean that the same M' frequency domain components are used to precode downlink reference signals, even if different SD beams are used for these downlink reference signals.

[0160] In one embodiment, gNB 110 may further apply L' spatial domain components to precoding. Therefore, in addition to delay information, this step also requires applying spatial information to the downlink reference signal precoding. Spatial precoding may include transmitting CSI-RS symbols through multiple antenna ports having given complex multiplication factors (the set of these factors forms a precoding vector). Therefore, in one embodiment, precoding includes applying a frequency domain precoder to each DL reference signal including one or more resource elements of the PRB, the frequency domain precoder being based on a combination of a spatial beam and at least one frequency phase ramp, each phase ramp corresponding to a component of the corresponding delay distribution of the communication channel. Based on the frequency-time duality, the frequency phase ramp corresponds to the time-domain supported component of the channel.

[0161] Figure 8 The method can then proceed, with gNB 110 transmitting multiple precoded downlink reference signals to UE 120 in step 804. gNB 110 can, for example, beamform each CSI-RS port (also referred to as a CSI-RS signal) using the frequency-domain precoder described above. gNB 110 can then transmit multiple CSI-RS signals for each spatial beam in step 806, such as... Figure 2A In this configuration, each spatial beam has three FD components, thus one spatial beam has three CSI-RS. In one embodiment, the gNB 110 transmits pre-coded CSI-RS ports in each configured subband. The subbands can be pre-configured by the gNB 110 and / or configured to the UE 120 based on the capabilities of the UE 120. Assuming M' is greater than 1, there are at least two downlink RSs even when using a single beam.

[0162] In one embodiment, gNB 110 may transmit to UE 120 an indication of whether delay and / or spatial information is used for precoding of the DL reference signal at gNB 110. This allows UE 120 to know in advance how the CSI-RS is precoded on the gNB side. For example, UE 120 may be configured with a list of aperiodic CSI trigger states and / or a list of semi-persistent CSI trigger states, for example, by gNB 110. Each trigger state may be associated with a CSI report configuration set, which includes information / fields related to partial reciprocity operation. The information / fields related to partial reciprocity may include explicit or implicit indications regarding DL reference signal precoding (e.g., the number of CSI-RS ports) to specify whether the spatial domain, frequency domain, or a combination of both are used on the gNB side.

[0163] One objective of this operation could be to enable the UE 120 to estimate the non-zero coefficients of the linear combination by summing the CSI-RS of beamforming over the configured subbands for each spatial beam, where the summation can be weighted. For example, in Figure 2A In an example embodiment, UE 120 can support S over all PRBs in many subbands. CSI-RS,0 (That is, channel estimation) is summed to achieve an S of the spatial beam. CSI-RS,0 A subband can include, for example, multiple PRBs. Upon receiving this indication (e.g., via RRC signaling), it can be understood that the pilot has been windowed via a phase ramp. This may be why a simple summation (dot product) might be sufficient at the UE. If the pilot is not windowed and the UE 120 still performs a summation, it will not provide the correct feedback.

[0164] Therefore, when performing steps 800-804, the gNB may have selected L'≤2L of the strongest SD beams and transmitted M' windowed CSI-RS sequences from L'M' CSI-RS ports on DL. In one embodiment, L'M'<2LM. Each of the L'M' virtual CSI-RS ports is precoded with a combination of an SD beam and an FD component / phase ramp. M represents the refinement number of the FD components, as will be explained later. Note that the channel support for all 2L SD beams is substantially the same as that for the L' strongest beams.

[0165] In step 806, in response to the transmission of multiple precoded downlink reference signals, gNB 110 can receive feedback from UE 120, and in step 808, modify the set of frequency domain components based on the feedback.

[0166] In one embodiment, for each spatial domain component of a plurality of downlink reference signals, UE 120 may transmit feedback and gNB 110 may receive feedback individually.

[0167] Based on some embodiments, let's take a closer look at the UE's reception and processing of precoded reference signals. (make) ) is the transmission pilot vector of the m-th FD component across the PRB, where n PRB This is the total number of PRBs allocated for UE 120, and It is the n measured / acquired for the bandwidth configured for CSI reporting. PRB A vector of channel coefficients. Note that W is assumed here. f From size n PRB ×n PRBThe DFT codebook is different from the one assumed above, which is from a DFT codebook of size N3×N3.

[0168] Assuming a CSI-RS density of 1 and an SD beam with L'=1 used for scanning, the received OFDM signal (without applying the proposed embodiment) can be written as:

[0169] , (6)

[0170] Where r is n PRB A vector of size, and

[0171] (7)

[0172] is n PRB ×n PRB A matrix of size W. f n PRB The m-th column of the size, using This indicates that if the pilot sequence is windowed through this column, the transmitted pilot sequence can be written as:

[0173] (8)

[0174] in

[0175] (8b)

[0176] It is (n) PRB ×n PRB A matrix of size W. Note that W f The resolution is configured by gNB 110. For example, if N3 is the number of subbands and the system has [specific resolution] for each subband... For a PRB, for Type II CSI feedback, the gNB 110 can be designed to derive W from an N3×N3 DFT codebook. f In other words, all within a sub-band Each PRB is multiplied by the same windowing factor. For example, for a subband index s, the windowing coefficients within subband index s in equation (8b) are all equal.

[0177]

[0178] The received signal can be written as:

[0179] (9)

[0180] On the UE 120 side, the simple inner product between the received signal and the pilot sequence (i.e., Generate effective channel coefficients associated with the m-th FD component (or delay):

[0181] , (10)

[0182] It can be extended to

[0183] . (11)

[0184] Figure 10 Depicts an example of the proposed delay scan scheme, where the nth PRB is considered, assuming L' = 1 SD beam, and M' = 8 windowed CSI-RS sequences (i.e., ) are transmitted from gNB 110 to UE 120. The UE can be configured to select M strongest FD components from the M' CSI-RS sequences. By performing the dot product in equation (10) on all M' CSI-RS sequences, UE 120 can identify the M strongest FD components and may feedback their indices to gNB 110.

[0185] Note that (11) calculates the channel coefficients assuming 1 SD beam. In the general case, L'≥1 can be used. For each FD component m, the effective channel coefficient l on each beam is calculated according to (11), and the final stacked vector of FD component m can be written as

[0186] (12)

[0187] In one embodiment, the feedback indicates the indices of M strongest frequency-domain components among the M' frequency-domain components, where M < M'. One benefit can be that the UL overhead is reduced because the feedback can include only the indices and not the quantized complex coefficients. In other words, UE 120 can determine the M strongest FD components of the received downlink RS. For example, UE 120 can first perform the summation of the channel estimation S CSI-RS,0 over all PRBs to obtain an S CSI-RS,0 for that spatial beam. Then, the values of the summated frequency-domain components can be compared, and only M strongest components are selected. Then, the indices of those FD components can be feedback to gNB110. However, UE 120 can have other ways to select the M strongest FD components.

[0188] In one embodiment, oversampling can be used for the M' frequency-domain components. In that case, UE 120 can transmit the oversampling group index and the indices of the M strongest frequency-domain components within the indicated oversampling group as feedback.

[0189] For example, an oversampling factor O3>1 can be introduced on the gNB side. In this case, the size of the DFT codebook from which W f is obtained is In this case, UE 120 can select only the orthogonal FD components. If the UE is configured such that O3 > 1, then UE 120 can provide two indicators: 1) Oversampling group index. : The selected group The indices of the M FD components within. For example, if O3=2 and M=2, and assuming the two oversampled groups are... and Then UE 120 sends k=0 or k=1 to reference one of the two groups, and selects M=2 additional FD components within the selected group (0 or 1).

[0190] The aforementioned limitation at UE 120 of selecting only M FD components within the selected group may require the UE to know which FD components belong to which groups. This can be achieved in, for example, two possible ways:

[0191] 1. With a fixed configuration (i.e., pre-configured) as specified in the specification, in which case the gNB 110 can use a pre-configured mapping between M' FD components and oversampled groups. For example, two oversampled groups can be obtained in the order of CSI-RS resource elements, such that the two oversampled groups are respectively and .

[0192] 2. The mapping between the oversampled groups and the M' FD components is configured to the UE120 by the gNB 110, for example, during RRC signaling. In this case, the gNB 110 can notify the UE120 which CSI-RS are mapped to which M' FD components (and therefore to which oversampled groups).

[0193] In one embodiment, the proposed delayed scanning procedure is configured with M'=O3M. In this case, the gNB only needs to find the oversampled group index k and all FD components within that group will be selected, so the UE will not need to provide feedback i. M .

[0194] While some example embodiments assume the same FD component selection for all SD beams, in other embodiments, such as when operating with very large bandwidths, it may be meaningful to select different channel supports (i.e., FD components) for different SD components / beams. Consequently, and depending on the W required by the gNB side... f In some embodiments, the UE 120 may also be configured to report a different set of oversampled group indices and / or M FD component indices for each SD beam, i.e., k l and / or i l,M For each . In this case, in one embodiment, the number of M' FD components can vary between different SD components / beams.

[0195] Figure 11 Depicts the proposed gNB-UE procedure for delay scanning. For L' SD beams, is computed for each of the M' possible sequences according to equation (12), i.e., . Then it is constructed by horizontally stacking on its columns to obtain an L'×M' matrix:

[0196] (13)

[0197] One way to perform delay selection is to average over all L' SD beam pairs to obtain a of size 1×M'. Then M strongest FD components can be selected according to , as shown in Figure 11 . This Figure 11 assumes an oversampling factor O3 is used, but the general principle shown in this figure also applies to the case without oversampling.

[0198] Figure 11 Provides a framework in which the knowledge of W f is required at the gNB 110 side for any purpose, e.g., in addition to FD precoding in DL. One purpose can be to perform port-specific phase ramps to align all taps within a window such that the equivalent channels across different beams have all taps within a small window. This can reduce the remaining CSI after tap selection.

[0199] In one embodiment, the feedback indicates the values of M strongest frequency-domain components out of M' frequency-domain components, where M < M'. That is, UE 120 can also be configured to feedback the complex coefficients of the selected M FD components over L' SD beams, e.g., in addition to and these two indicators. In this case, Figure 11 the UE-gNB procedure shown in Figure 12 may be different in the last step, as shown in , where in addition to the feedback of the indicators, UE 120 also feedbacks the quantized compressed channels measured for L' SD beams and the selected M FD components is constructed by selecting the columns in corresponding to the selected M FD components. gNB 110 can use this information to update its knowledge of W fAnd knowledge of compressed channel information.

[0200] However, although L'<2L in some embodiments, L'=2L is possible, in which case the entire spatial domain based on UL RS is used for precoding. In this case, gNB 110 can transmit M' windowed CSI-RS over 2L beams (2LM' virtual ports), and UE 120 can feed back W f The indicator of the optimal FD component and the corresponding scaling factor corresponding to the combination with W1.

[0201] After gNB 110 receives knowledge of M FD components (e.g., indexes and / or LC coefficients), gNB 110 can modify this set of FD components. One modification could be to reduce the number of FD components in the set from M' FD components to M FD components. In other words, gNB 110 can, for example, first determine M' FD components based on the received UL RS, where M' is a relatively large number to accurately depict the delay distribution of the channel. Then, UE 120 can feed back information on only M (less than M') FD components. Based on this information, gNB 110 can determine a set of M FD components (i.e., modify this set of M' components by removing one or more FD components not fed back by UE 120). It is considered that M FD components sufficiently depict the delay distribution of the channel.

[0202] In one embodiment, gNB 110 may notify UE 120 (or UE 120 may be pre-configured with the following information) that UE 120 needs to determine and return only M of the received M' FD components. For example, such configuration information may be provided to UE 120 from gNB 110 via RRC signaling. Similarly, the value of M may be indicated to UE 120, or UE 120 may be pre-configured with such information.

[0203] In one embodiment, once gNB knows W based on the refined M FD components f Furthermore, based on the 2L SD components, W1 is known, and the gNB 110 can follow any method that utilizes this knowledge at the gNB 110, such as the process of CSI scheme #A. Typically, once a set of refined M FD components is known, the gNB 110 can apply this set of M FD components to communication with the UE 120. Additionally, the 2L SD components can be used for communication with the UE 120. It should be noted that in some embodiments, only the set of refined M FD components is needed, and the 2L SD components are not required. Therefore, the delayed scanning proposal described in the embodiments of this application can at least partially address how to obtain W1 on the gNB side. f Or W based on UL RSf How to refine the estimate?

[0204] As described above, M'L' is less than 2LM in one embodiment. For example, in CSI scheme #A, assuming 2L spatial beams and M FD components, the gNB needs to allocate 2LM DL resources to receive all M FD components on the UL. If gNB is against W f If the understanding is insufficient, then it can be based on The received quantized values ​​are used to send a larger number of windowed CSI-RS sequences, assuming M' > M FD components. Then gNB will refine its parameters with respect to W. f This knowledge is relevant. However, the required number of DL CSI-RS is proportional to 2L, which may limit the maximum number of FD components that can be scanned, i.e., M'. Furthermore, the number of unselected 2L (M'-M) FD components... The quantization coefficients may not be utilized at gNB. This could translate into inefficient use of UL resources. This is likely because the application's proposed delayed scan process refines W based primarily on M'L' selection rather than M'2L. f That could be a beneficial reason.

[0205] Figure 9 An example method is described. This method can be executed by a user device, such as... Figure 1 UE 120. For simplicity, we assume that the method is executed by UE 120. Therefore, as Figure 9 As shown, UE 120 may receive multiple downlink reference signals from gNB 110 in step 900, wherein the precoding of the multiple downlink reference signals is based on M' frequency domain components. In one embodiment, UE 120 may transmit a UL RS, such as SRS, to gNB 110, which indicates delay information of the communication channel and thus enables the determination of M' frequency domain components at gNB 110. In one embodiment, the UL RS further indicates spatial information about the communication channel, which enables the determination of 2L SD components at gNB 110. Then, as already explained, the multiple downlink reference signals may be further precoded with L' spatial domain components out of the 2L spatial domain components, where L' <= 2L.

[0206] In step 902, UE 120 can estimate the M strongest frequency domain components among M' frequency domain components based on the received multiple downlink reference signals, where M is less than M', and in step 404 transmit feedback of the received multiple DL reference signals to gNB 110, the feedback providing information on the determined M strongest FD components.

[0207] In one embodiment, UE 120 determines the indices of the M strongest frequency domain components out of the M' frequency domain components and provides these indices as feedback in step 904. In another embodiment, UE 120 additionally or alternatively determines the values ​​of the coefficients of the M strongest frequency domain components and provides the values ​​of the M strongest FD components in the feedback.

[0208] In one embodiment, UE 120 detects that oversampling has been applied to M' frequency domain components. This may occur, for example, via RRC signaling from gNB 110. UE 120 can then provide an oversampling group indication and indices of the M strongest FD components within the indicated oversampling group as feedback. In one embodiment, UE 120 may receive a mapping configuration between the oversampling group and the M' FD components from gNB 110.

[0209] In one embodiment, when different sets of M' frequency domain components are applied to at least two different spatial domain components in precoding, the UE can determine the M strongest frequency domain components of each spatial beam, and then provide a different set of M frequency domain components as feedback for each of the corresponding at least two spatial beams.

[0210] Once gNB 110 has received knowledge of M FD components based on feedback, UE 120 can perform communication with gNB 110 based at least in part on the M FD components and / or on 2L SD components.

[0211] In one embodiment, the delayed scan can be performed iteratively multiple times before, for example, CSI scheme #A is applied. This allows for updating the accuracy of the FD components. For example, in the second iteration, M' FD components may differ from those in the first round because a period of time may have elapsed between them. Furthermore, gNB 110 may not necessarily decide to change W after the delayed scan operation. f For example, if the feedback from the UE does not change W f The existing estimate. In other words, the refined W f Its use may not be as refined as that used for W f The delayed scanning process is not as frequent.

[0212] In one embodiment, Figure 8 and Figure 9 The proposed delayed scanning can be applied in conjunction with CSI scheme #A. In this case, the gNB can receive the uplink reference signal from the user equipment. The gNB can determine a set of M' frequency domain components for the channel between the UE and the gNB. This can be based on the received UL RS. Then the gNB can perform... Figure 8The remaining steps. Once the gNB has acquired knowledge of the delay information, it can apply the delay information to the precoding of at least one DL reference signal and transmit at least one precoded DL reference signal to the UE. In one embodiment, the gNB can also apply spatial information to the precoding (e.g., based on 2L spatial components). The UE can then determine channel information based on the received at least one precoded downlink reference signal, which indicates at least non-zero coefficients of at least one channel transport layer, and transmit the channel information to the gNB. Determining the channel information may include estimating the channel coefficients for each subband configured for the UE based on at least one precoded downlink reference signal, and summing the estimated channel coefficients over the subbands. The non-zero coefficients of at least one channel transport layer may indicate non-zero coefficients for each spatial beam and each frequency domain component or a set of frequency domain components of the communication channel. Therefore, in response to the transmission of at least one precoded downlink reference signal, the gNB can receive channel information from the user equipment indicating at least non-zero coefficients of at least one channel transport layer. In this way, the gNB can determine at least one of the precoding matrix and the channel matrix of the communication channel based on the received channel information, and apply beamforming to the data transmission of the user equipment based at least in part on one or both of the matrices.

[0213] gNB 110 can execute only Figure 3 The method (and may execute one or more embodiments related to the method) only performs Figure 8 The method (and may execute one or more embodiments related to the method), or in combination Figure 8 Method execution Figure 3 The methods (and possibly one or more embodiments related to one or both of these methods). UE 120 may only perform... Figure 4 The method (and possibly one or more embodiments related to the method) only performs Figure 9 The method (and may execute one or more embodiments related to the method), or in combination Figure 9 Method execution Figure 4 The methods (and one or more embodiments that may be performed in connection with one or both of these methods).

[0214] like Figure 6As shown, one embodiment provides an apparatus 10 including a control circuitry system (CTRL) 12 (such as at least one processor) and at least one memory 14 including computer program code (software), wherein the at least one memory and the computer program code (software) are configured, together with the at least one processor, to cause the apparatus to perform any of the processes described above. The memory can be implemented using any suitable data storage technology, such as semiconductor-based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory, and removable memory. The memory may include a database for storing data.

[0215] In one embodiment, device 10 may be a network node or be included therein, such as in a 5G gNB / gNB-CU / gNB-DU. In one embodiment, the device is network node 110 or is included therein. The device may be caused to perform some functions that perform the above-described processes, such as Figure 3 and / or Figure 8 The steps.

[0216] In one embodiment, a CU-DU (Central Unit-Distributed Unit) architecture is implemented. In this case, device 10 may be included in a central unit (e.g., control unit, edge cloud server, server) operatively coupled (e.g., via a wireless or wired network) to a distributed unit (e.g., a remote radio head end / node). That is, the central unit (e.g., the edge cloud server) and the radio nodes may be independent devices that communicate with each other via a radio path or via a wired connection. Alternatively, they may communicate within the same entity via a wired connection, etc. The edge cloud or edge cloud server may serve multiple radio nodes or a radio access network. In one embodiment, at least some of the described processes may be performed by the central unit. In another embodiment, the device may alternatively be included in a distributed unit, and at least some of the described processes may be performed by the distributed unit. In one embodiment, the execution of at least some functions of device 10 may be shared between two physically separate devices (DU and CU) forming an operational entity. Thus, the device can be viewed as an operational entity comprising one or more physically separate devices for performing at least some of the described processes. In one embodiment, the device controls the execution of the process regardless of the location of the device and where the process / function is performed.

[0217] The device may also include a radio interface (TRX) 16, which includes hardware and / or software for establishing a communication connection according to one or more communication protocols. For example, the TRX can provide the device with the communication capability to access a radio access network.

[0218] The device may also include a user interface 18, including, for example, at least one keypad, microphone, touch display, display, speaker, etc. The user interface can be used by a user to control the device.

[0219] According to any embodiment, the control circuitry system 12 may include an estimation circuitry system 20 for estimating delay and spatial information based on the received UL reference signal. The estimation circuitry system 20 may also estimate a precoding matrix based at least in part on the received CSI. According to any embodiment, the circuitry system 20 or additional circuitry (not shown) may be further used to refine the delay information. According to any embodiment, the control circuitry system 12 may also include a precoding circuitry system 22 for precoding the DL reference signal using a frequency domain subset. According to any embodiment, the control circuitry system 12 may also include a DL reference signal circuitry 24 for transmitting the DL reference signal to one or more UEs.

[0220] like Figure 7 As shown, one embodiment provides an apparatus 50 including a control circuitry system (CTRL) 52 (such as at least one processor) and at least one memory 54 including computer program code (software), wherein the at least one memory and the computer program code (software) are configured, together with the at least one processor, to cause the apparatus to perform any of the processes described above. The memory can be implemented using any suitable data storage technology, such as semiconductor-based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory, and removable memory. The memory may include a database for storing data.

[0221] In one embodiment, device 50 may include a terminal device of a communication system, such as a user terminal (UT), computer (PC), laptop, newsletter, cellular phone, mobile phone, communicator, smartphone, handheld computer, mobile vehicle (such as a car), home appliance, or any other communication device, which is generally referred to as UE in the specification. Alternatively, the device is included within such a terminal device. Furthermore, the device may be or include a module providing connectivity (to be attached to the UE), such as a plug-in unit, a "USB dongle," or any other type of unit. This unit may be installed inside the UE or connected to the UE via a connector or even wirelessly. In one embodiment, device 50 is or is included within UE 120. The device may be caused to perform some of the functions described above, such as Figure 4 and / or Figure 9 The steps.

[0222] The device may also include a communication interface (TRX) 56, which includes hardware and / or software for establishing a communication connection according to one or more communication protocols. For example, the TRX can provide the device with the communication capability to access a radio access network. The device may also include a user interface 58, including, for example, at least one keypad, microphone, touch display, monitor, speaker, etc. The user interface can be used for user control of the device.

[0223] According to any embodiment, the control circuitry 52 may include a UL reference signal circuitry 60 for compiling and transmitting UL reference signals such as SRS to the gNB. According to any embodiment, this circuitry 60 or additional circuitry (not shown) may be further used to refine delay information. For example, the control circuitry 52 may include, for example, a channel information determination circuitry 62 for determining the CSI based on the received CSI-RS.

[0224] In one embodiment, an apparatus for performing at least some of the described embodiments includes at least one processor and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured, together with the at least one processor, to cause the apparatus to perform the functions according to any of the above embodiments. According to one aspect, when the at least one processor executes the computer program code, the computer program code causes the apparatus to perform the functions according to any of the described embodiments. According to another embodiment, the apparatus for performing at least some embodiments includes at least one processor and at least one memory including computer program code, wherein the at least one processor and the computer program code perform at least some functions according to any of the described embodiments. Thus, at least one processor, memory, and computer program code form a processing component for performing at least some of the described embodiments. According to yet another embodiment, the apparatus for performing at least some embodiments includes a circuit system including at least one processor and at least one memory including computer program code. When activated, the circuit system causes the apparatus to perform at least some functions according to any of the described embodiments.

[0225] As used in this application, the term "circuit system" refers to all of the following: (a) hardware circuitry implementations only, such as implementations only in analog and / or digital circuitry systems; and (b) combinations of circuitry and software (and / or firmware), such as (if applicable): (i) combinations of (multiple) processors, or (ii) portions of (multiple) processors / software (including (multiple) digital signal processors), software, and (multiple) memories that work together to cause a device to perform various functions; and (c) circuitry, such as (multiple) microprocessors or portions of (multiple) microprocessors that require software or firmware to perform operations, even if the software or firmware does not actually exist. This definition of "circuit system" applies to all uses of the term in this application. As another example, as used in this application, the term "circuit system" will also cover implementations of processors (or multiple processors) or portions of processors and their accompanying software and / or firmware. For example, if applicable to a particular element, the term "circuit system" will also cover baseband integrated circuits or application processor integrated circuits for mobile phones, or similar integrated circuits in servers, cellular network devices, or other network devices.

[0226] In one embodiment, at least some of the described processes may be performed by a device including corresponding components for performing at least some of the described processes. Some example components for performing the processes may include at least one of the following: a detector, a processor (including dual-core and multi-core processors), a digital signal processor, a controller, a receiver, a transmitter, an encoder, a decoder, a memory, RAM, ROM, software, firmware, a display, a user interface, a display circuit system, a user interface circuit system, user interface software, display software, a circuit, an antenna, an antenna circuit system, and a circuit system.

[0227] The techniques and methods described herein can be implemented in various ways. For example, these techniques can be implemented using hardware (one or more devices), firmware (one or more devices), software (one or more modules), or a combination thereof. For hardware implementation, the embodiments may be implemented within one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, other electronic units designed to perform the functions described herein, or combinations thereof. For firmware or software, the implementation may be executed by a module (e.g., process, function, etc.) of at least one chipset performing the functions described herein. Software code may be stored in memory cells and executed by a processor. The memory cells may be implemented within or outside the processor. In the latter case, it may be communicatively coupled to the processor in various ways known in the art. Furthermore, the components of the systems described herein may be rearranged and / or supplemented by additional components to facilitate the implementation of various aspects described herein, and they are not limited to the precise configurations illustrated in the given figures, as will be understood by those skilled in the art.

[0228] The embodiments described can also be performed as a computer process defined by a computer program or parts thereof. Embodiments of the described methods can be performed by executing at least a portion of a computer program including corresponding instructions. The computer program can be in source code form, object code form, or some intermediate form, and can be stored in a carrier, which can be any entity or device capable of carrying the program. For example, the computer program can be stored on a computer or processor-readable computer program distribution medium. The computer program medium can be, for example, but not limited to, recording media, computer memory, read-only memory, electrical carrier signals, telecommunication signals, and software distribution packages. The computer program medium can be a non-transitory medium. The software code used to perform the embodiments shown and described is entirely within the scope of those skilled in the art.

[0229] The following is a first list of some aspects of the present invention.

[0230] According to a first aspect, an apparatus is provided, the apparatus comprising: at least one processor and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured, together with the at least one processor, to cause the apparatus to perform operations including: receiving an uplink reference signal from a user equipment; estimating delay information and spatial information about a communication channel between the user equipment and the apparatus based on the received uplink reference signal; applying both the delay information and the spatial information to precoding at least one downlink reference signal; transmitting the at least one precoded downlink reference signal to the user equipment; and receiving channel information from the user equipment in response to the transmission of the at least one precoded downlink reference signal, the channel information indicating at least non-zero coefficients of at least one channel transport layer.

[0231] Various embodiments of the first aspect may include at least one feature from the following bulleted list:

[0232] • The uplink reference signal includes a sounding reference signal (SRS), the downlink reference signal includes a channel state information reference signal (CSI-RS), the channel information is channel state information (CSI), and the delay information is determined based on channel reciprocity.

[0233] • The delay information indicates the delay of each path of the communication channel relative to a reference time.

[0234] • The spatial information therein indicates the angle of arrival of each path of the communication channel relative to a reference angle.

[0235] • The precoding includes applying a frequency domain precoder to each downlink reference signal, the frequency domain precoder being based on a combination of a spatial beam and at least one frequency phase ramp, each phase ramp corresponding to a component of the corresponding delay distribution of the communication channel.

[0236] • The precoded downlink reference signal enables the user equipment to estimate the channel coefficients of each subband configured for the user equipment based on the at least one precoded downlink reference signal and to perform a summation of the estimated channel coefficients over the subbands to derive the nonzero coefficients of the at least one channel transport layer.

[0237] • The non-zero coefficients of the at least one channel transmission layer indicate the non-zero coefficients for each spatial beam and each frequency domain component or a set of frequency domain components of the communication channel.

[0238] • The channel information mentioned therein does not include information indicating the non-zero coefficients for any subband.

[0239] • The channel information mentioned therein does not include a bitmap indicating the position of the non-zero coefficients within the precoding matrix indicator.

[0240] • Determine at least one of the precoding matrix of the communication channel and the channel matrix of the communication channel based on the received channel information; and apply beamforming to the data transmission to the user equipment based at least in part on one or both of the matrices.

[0241] • Transmit to the user equipment an indication of whether the delay and the spatial information are used for precoding the downlink reference signal at the device.

[0242] According to a second aspect, an apparatus is provided, the apparatus comprising: at least one processor and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured, together with the at least one processor, to cause the apparatus to perform operations including: transmitting an uplink reference signal to a network node, the uplink reference signal indicating delay information about a delay distribution of a communication channel between the apparatus and the network node and spatial information about the communication channel; receiving at least one downlink reference signal in response to transmitting the uplink reference signal, wherein the at least one downlink reference signal is precoded at least based on the delay information and the spatial information; determining channel information based on the received at least one precoded downlink reference signal, the channel information indicating at least non-zero coefficients of at least one channel transport layer; and transmitting the channel information to the network node.

[0243] Various embodiments of the second aspect may include at least one feature from the following bulleted list:

[0244] • The uplink reference signal includes a sounding reference signal (SRS), and the downlink reference signal includes a channel state information reference signal (CSI-RS), and the channel information includes channel state information (CSI).

[0245] • Determining the channel information includes estimating the channel coefficients for each subband configured for the device based on the at least one precoded downlink reference signal and summing the estimated channel coefficients over the subbands.

[0246] • The non-zero coefficients of the at least one channel transmission layer indicate the non-zero coefficients for each spatial beam and each frequency domain component or a set of frequency domain components of the communication channel.

[0247] • Receive from the network node an indication of whether the delay and the spatial information are used for the precoding of the downlink reference signal at the network node.

[0248] According to a third aspect, a method is provided at a network node, the method comprising: receiving an uplink reference signal from a user equipment; estimating delay information and spatial information about a communication channel between the user equipment and the network node based on the received uplink reference signal; applying both the delay information and the spatial information to precoding at least one downlink reference signal; transmitting the at least one precoded downlink reference signal to the user equipment; and receiving channel information from the user equipment in response to the transmission of the at least one precoded downlink reference signal, the channel information indicating at least non-zero coefficients of at least one channel transport layer. Various embodiments of the third aspect may include at least one feature from the bulleted list under the first aspect.

[0249] According to a fourth aspect, a method is provided at a user equipment, the method comprising: transmitting an uplink reference signal to a network node of the communication network, the uplink reference signal indicating delay information about a delay distribution of a communication channel between the user equipment and the network node and spatial information about the communication channel; receiving at least one downlink reference signal in response to the transmission of the uplink reference signal, wherein the at least one downlink reference signal is precoded at least based on the delay information and the spatial information; determining channel information based on the received at least one precoded downlink reference signal, the channel information indicating at least non-zero coefficients of at least one channel transport layer; and transmitting the channel information to the network node. Various embodiments of the fourth aspect may include at least one feature from the bulleted list under the second aspect.

[0250] According to the fifth aspect, a computer program product embodied on a computer-readable distribution medium and including program instructions that, when loaded into a device, execute the method according to the third aspect.

[0251] According to a sixth aspect, a computer program product embodied on a computer-readable distribution medium and including program instructions that, when loaded into a device, execute the method according to a fourth aspect.

[0252] According to the seventh aspect, a computer program product including program instructions is provided, which, when loaded into a device, execute the method according to the third aspect.

[0253] According to the eighth aspect, a computer program product including program instructions is provided, which, when loaded into a device, execute the method according to the fourth aspect.

[0254] According to a ninth aspect, an apparatus is provided, the apparatus comprising components for performing the method according to a third aspect, and / or components configured to cause network nodes to perform the method according to a third aspect.

[0255] According to a tenth aspect, an apparatus is provided, the apparatus comprising components for performing the method according to a fourth aspect, and / or components configured to cause a user equipment to perform the method according to a fourth aspect.

[0256] According to the eleventh aspect, a computer system is provided, the computer system comprising: one or more processors; at least one data storage device; and one or more computer program instructions, the one or more computer program instructions being executed by the one or more processors in association with the at least one data storage device to perform the method according to the third aspect and / or the method according to the fourth aspect.

[0257] This concludes the first part of the list.

[0258] The following is a second list of some aspects of the present invention.

[0259] According to a first aspect, an apparatus is provided, the apparatus comprising: at least one processor and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured, together with the at least one processor, to cause the apparatus to perform operations including: determining a set of M' frequency domain components for a communication channel between a user equipment and a network node; applying the set of M' frequency domain components to the precoding of a plurality of downlink reference signals; transmitting the plurality of precoded downlink reference signals to the user equipment; receiving feedback from the user equipment in response to the transmission of the plurality of precoded downlink reference signals; and modifying the set of M' frequency domain components based on the feedback.

[0260] Various embodiments of the first aspect may include at least one feature from the following bulleted list:

[0261] • Wherein the feedback indicates the indices of the M strongest frequency domain components out of the M' frequency domain components, where M <M'。

[0262] • Wherein the feedback indicates the values ​​of the M strongest frequency domain components out of the M' frequency domain components, where M <M'。

[0263] • Apply oversampling to the M' frequency domain components; receive an oversampling group index and indices of the M strongest frequency domain components within the indicated oversampling group from the user equipment as the feedback.

[0264] • Provide the user equipment with a mapping configuration between the oversampling groups and the M' frequency domain components.

[0265] • Apply the set of M' frequency domain components identically to each spatial domain component in the precoding.

[0266] • Apply a different set of M' frequency domain components to at least two spatial domain components in the precoding.

[0267] • Where the set of frequency domain components includes M' frequency domain components before the modification and M frequency domain components after the modification.

[0268] • Receive an uplink reference signal from the user equipment; estimate delay information regarding the communication channel based on the received uplink reference signal; determine the set of M' frequency domain components based on the delay information.

[0269] • Determine a set of 2L spatial domain components for the communication channel; select L' spatial domain components from the 2L spatial domain components, where L'<2L; apply the L' spatial domain components to the precoding.

[0270] • Apply the modified set of frequency domain components to the communication with the user equipment.

[0271] According to a second aspect, there is provided an apparatus, the apparatus comprising: at least one processor and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured to, together with the at least one processor, cause the apparatus to perform operations including: receiving a plurality of downlink reference signals from a network node, wherein the precoding of the plurality of downlink reference signals is based on M' frequency domain components; estimating M strongest frequency domain components among the M' frequency domain components based on the received plurality of downlink reference signals, where M<M'; and transmitting feedback of the received plurality of downlink reference signals, the feedback providing information on the determined M strongest frequency domain components.

[0272] Various embodiments of the second aspect may include at least one feature from the following bullet list:

[0273] • Determine indices of the M strongest frequency domain components among the M' frequency domain components; and provide the indices of the M strongest frequency domain components in the feedback.

[0274] • Determine the values ​​of the coefficients of the M strongest frequency domain components; and provide the values ​​of the M strongest frequency domain components in the feedback.

[0275] • Detect oversampling applied to the M' frequency domain components; provide an oversampling group indication and an index of the M strongest frequency domain components within the indicated oversampling group in the feedback.

[0276] • Receive the mapping configuration between the oversampled group and the M' frequency domain components from the network node.

[0277] • Provide the feedback for each spatial domain component of the plurality of downlink reference signals, respectively.

[0278] • When a different set of M' frequency domain components are applied to at least two different spatial domain components in the precoding, the M strongest frequency domain components are determined for each of the corresponding at least two spatial domain components; and a different set of M frequency domain components is provided for each of the corresponding at least two spatial domain components in the feedback.

[0279] • Transmit an uplink reference signal to a network node, the uplink reference signal indicating delay information of the communication channel between the device and the network node, the delay information enabling the determination of M' frequency domain components at the network node.

[0280] • Communication with network nodes is performed based at least in part on M frequency domain components.

[0281] According to a third aspect, a method is provided at a network node, the method comprising: determining a set of M' frequency domain components for a communication channel between a user equipment and the network node; applying the set of M' frequency domain components to the precoding of a plurality of downlink reference signals; transmitting the plurality of precoded downlink reference signals to the user equipment; receiving feedback from the user equipment in response to the transmission of the plurality of precoded downlink reference signals; and modifying the set of M' frequency domain components based on the feedback.

[0282] Various embodiments of the third aspect may include at least one feature from the bullet list under the first aspect.

[0283] According to a fourth aspect, a method at a user equipment is provided, the method comprising: receiving a plurality of downlink reference signals from a network node, wherein precoding of the plurality of downlink reference signals is based on M' frequency domain components; estimating M strongest frequency domain components among the M' frequency domain components based on the received plurality of downlink reference signals, wherein M < M'; and transmitting feedback of the received plurality of downlink reference signals to the network node, the feedback providing information on the determined M strongest frequency domain components.

[0284] Various embodiments of the fourth aspect may include at least one feature from the bullet list under the second aspect.

[0285] According to a fifth aspect, a computer program product embodied on a computer-readable distribution medium and comprising program instructions is provided, the program instructions when loaded into a device performing the method according to the third aspect.

[0286] According to a sixth aspect, a computer program product embodied on a computer-readable distribution medium and comprising program instructions is provided, the program instructions when loaded into a device performing the method according to the fourth aspect.

[0287] According to a seventh aspect, a computer program product comprising program instructions is provided, the program instructions when loaded into a device performing the method according to the third aspect.

[0288] According to an eighth aspect, a computer program product comprising program instructions is provided, the program instructions when loaded into a device performing the method according to the fourth aspect.

[0289] According to a ninth aspect, a device is provided, the device comprising components for performing the method according to the third aspect and / or components configured to cause a user equipment to perform the method according to the third aspect.

[0290] According to a tenth aspect, a device is provided, the device comprising components for performing the method according to the fourth aspect and / or components configured to cause a user equipment to perform the method according to the fourth aspect.

[0291] According to an eleventh aspect, a computer system is provided, the computer system comprising: one or more processors; at least one data storage device; and one or more computer program instructions, the one or more computer program instructions to be executed by the one or more processors in association with the at least one data memory to perform the method according to the third aspect and / or the method according to the fourth aspect.

[0292] The list of the second aspect ends here. One or more aspects of the second list may be performed in combination with one or more aspects of the first list.

[0293] Although the invention has been described above with reference to examples in conjunction with the accompanying drawings, it is apparent that the invention is not limited thereto, but can be modified in various ways within the scope of the appended claims. Therefore, all words and expressions should be interpreted broadly and are intended to illustrate rather than limit the embodiments. It will be apparent to those skilled in the art that the concepts of the invention can be implemented in various ways as technology advances. Furthermore, it will be understood by those skilled in the art that the described embodiments can, but are not required to, be combined with other embodiments in various ways.

Claims

1. A device for communication, comprising: At least one processor and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured together with the at least one processor to cause the device to perform operations including: Receive uplink reference signals from user equipment; Based on the received uplink reference signal, delay information about the delay distribution of the communication channel between the user equipment and the device, and spatial information about the communication channel are estimated, wherein the delay information indicates the delay of each path of the communication channel relative to a reference time, and the delay information is determined based on channel reciprocity, wherein the uplink reference signal includes a sounding reference signal (SRS). Both the delay information and the spatial information are applied to the precoding of multiple downlink reference signals; Transmit to the user equipment an indication of whether the delay and the spatial information are used for precoding of the plurality of downlink reference signals at the device; The user equipment is transmitted the plurality of precoded auxiliary downlink reference signals, the downlink reference signals including channel state information reference signals (CSI-RS); In response to the transmission of the plurality of precoded downlink reference signals, channel information is received from the user equipment, the channel information indicating at least non-zero coefficients of at least one channel transport layer, and the channel information is channel state information (CSI). Based on the delay information, a set of M' frequency domain components are determined for the communication channel; The set of M' frequency domain components is applied to the precoding of multiple auxiliary downlink reference signals; The plurality of precoded auxiliary downlink reference signals are transmitted to the user equipment; Feedback is received from the user equipment in response to the transmission of the plurality of precoded auxiliary downlink reference signals; as well as Based on the feedback, the set of M' frequency domain components are modified.

2. The apparatus of claim 1, wherein the spatial information indicates the angle of arrival of each path of the communication channel relative to a reference angle.

3. The apparatus of claim 1, wherein the precoding comprises applying a frequency domain precoder to each downlink reference signal, the frequency domain precoder being based on a combination of a spatial beam and at least one precoded frequency vector, each precoded frequency vector corresponding to a component of a corresponding delay distribution of the communication channel.

4. The apparatus of claim 1, wherein the at least one memory and the computer program code are configured, together with the at least one processor, to cause the apparatus to perform operations including: Transmit downlink reference signal resources, the downlink reference signal resources including a plurality of precoded downlink reference signals having a reduced density of 1 / d in the precoded downlink reference signals, wherein the density of a given precoded downlink reference signal in the downlink reference signal resources is defined as the number of resource blocks, the resource blocks containing the same precoded downlink reference signals in the total number of resource blocks in the frequency band configured for channel information reporting.

5. The apparatus of claim 4, wherein d is an integer greater than 1 and less than or equal to 4.

6. The apparatus of claim 1, wherein the precoded downlink reference signal enables the user equipment to estimate channel coefficients for each subband configured for the user equipment based on the at least one precoded downlink reference signal, and to perform a summation of the estimated channel coefficients over the subbands to derive the nonzero coefficients of the at least one channel transport layer.

7. The apparatus of claim 1, wherein the non-zero coefficients of the at least one channel transmission layer indicate non-zero coefficients for each spatial beam and each frequency domain component or a set of frequency domain components of the communication channel.

8. The apparatus of claim 1, wherein the channel information does not include the Discrete Fourier Transform (DFT) frequency domain compression matrix.

9. The apparatus of claim 1, wherein the channel information does not include information indicating non-zero coefficients for any subband.

10. The apparatus of claim 1, wherein the channel information does not include a bitmap indicating the position of the non-zero coefficients within a precoding matrix indicator.

11. The apparatus of claim 1, wherein the at least one memory and the computer program code are configured, together with the at least one processor, to cause the apparatus to perform operations including: Based on the received channel information, determine at least one of the precoding matrix and the channel matrix of the communication channel; and Beamforming is applied to data transmission to the user equipment, based at least in part on one or both of the matrices.

12. The apparatus of claim 1, wherein the feedback indicates the indices of the M strongest frequency domain components among the M' frequency domain components, wherein M... <M'。 13. The apparatus of claim 1 or 12, wherein the feedback indicates the values ​​of the M strongest frequency domain components among the M' frequency domain components, wherein M <M'。 14. The apparatus of claim 13, wherein the at least one memory and the computer program code are configured, together with the at least one processor, to cause the apparatus to perform operations including: Oversampling is applied to the M' frequency domain components; As feedback, the user equipment receives an oversampling group index and the indices of the M strongest frequency domain components within the indicated oversampling group.

15. The apparatus of claim 14, wherein the at least one memory and the computer program code are configured, together with the at least one processor, to cause the apparatus to perform operations including: Provide the user equipment with a mapping configuration between the oversampling group and the M' frequency domain components.

16. The apparatus of claim 1, wherein the at least one memory and the computer program code are configured, together with the at least one processor, to cause the apparatus to perform operations including: The set of M' frequency domain components are applied equally to each spatial domain component in the precoding of the plurality of auxiliary downlink reference signals.

17. The apparatus of claim 1, wherein the at least one memory and the computer program code are configured, together with the at least one processor, to cause the apparatus to perform operations including: A different set of M' frequency domain components are applied to at least two spatial domain components in the precoding of the plurality of auxiliary downlink reference signals.

18. The apparatus of claim 1, wherein the set of frequency domain components comprises M' frequency domain components before the modification and M frequency domain components after the modification.

19. The apparatus of claim 1, wherein the at least one memory and the computer program code are configured, together with the at least one processor, to cause the apparatus to perform operations including: Based on the estimated delay information, the set of M' frequency domain components are determined.

20. The apparatus of claim 1, wherein the at least one memory and the computer program code are configured, together with the at least one processor, to cause the apparatus to perform operations including: A set of 2L spatial domain components is determined for the communication channel; Select L' spatial domain components from the 2L spatial domain components, where L' < 2L; The L' spatial domain components are applied to the precoding of the plurality of downlink reference signals.

21. The apparatus of claim 1, wherein the at least one memory and the computer program code are configured, together with the at least one processor, to cause the apparatus to perform operations including: The modified frequency domain components are applied to the precoding of the at least one downlink reference signal.

22. An apparatus for communication, comprising: At least one processor and at least one memory including computer program code, wherein the at least one memory and the computer program code are configured together with the at least one processor to cause the device to perform operations including: Uplink reference signals are transmitted to network nodes, the uplink reference signals indicating delay information about the delay distribution of the communication channel between the device and the network node, and spatial information about the communication channel, wherein the delay information indicates the delay of each path of the communication channel relative to a reference time, and wherein the uplink reference signals include sounding reference signals (SRS). Receive from the network node an indication of whether the delay and the spatial information are used for precoding of multiple downlink reference signals at the network node; In response to the transmission of the uplink reference signal, the plurality of downlink reference signals, including a channel state information reference signal (CSI-RS), are received, wherein the plurality of downlink reference signals are pre-coded based at least on the delay information and the spatial information. Based on at least one received precoded downlink reference signal, channel information is determined, the channel information indicating at least one non-zero coefficient of at least one channel transport layer, the channel information including channel state information (CSI); The channel information is transmitted to the network node; Multiple auxiliary downlink reference signals are received from the network node, wherein the precoding of the multiple auxiliary downlink reference signals is based on a set of M' frequency domain components, wherein the set of M' frequency domain components is determined based on the delay information; Based on the received multiple auxiliary downlink reference signals, estimate the M strongest frequency domain components among the M' frequency domain components, where M... <M'; The network node transmits feedback on the received multiple auxiliary downlink reference signals, the feedback providing information on the determined M strongest frequency domain components.

23. The apparatus of claim 22, wherein determining the channel information comprises: The channel coefficients for each subband configured for the device are estimated based on the at least one precoded downlink reference signal, and the estimated channel coefficients are summed over the subbands.

24. The apparatus of claim 22, wherein the at least one memory and the computer program code are configured, together with the at least one processor, to cause the apparatus to perform operations including: Receive downlink reference signal resources, the downlink reference signal resources including a plurality of precoded downlink reference signals having a reduced density of 1 / d in the precoded downlink reference signals, wherein the density of a given precoded downlink reference signal in the downlink reference signal resources is defined as the number of resource blocks, the resource blocks containing the same precoded downlink reference signals in the total number of resource blocks in the frequency band configured for channel information reporting.

25. The apparatus of claim 24, wherein d is an integer greater than 1 and less than or equal to 4.

26. The apparatus of claim 22, wherein the non-zero coefficients of the at least one channel transmission layer indicate non-zero coefficients for each spatial beam and each frequency domain component or a set of frequency domain components of the communication channel.

27. The apparatus of claim 22, wherein the at least one memory and the computer program code are configured, together with the at least one processor, to cause the apparatus to perform operations including: Based on the received multiple downlink reference signals, estimate the M strongest frequency domain components among the M' frequency domain components, where M <M'; The network node transmits feedback on the received plurality of downlink reference signals, the feedback providing information on the determined M strongest frequency domain components.

28. The apparatus of claim 27, wherein the at least one memory and the computer program code are configured, together with the at least one processor, to cause the apparatus to perform operations including: Determine the indices of the M strongest frequency domain components among the M' frequency domain components; and The indices of the M strongest frequency domain components are provided in the feedback.

29. The apparatus of claim 27, wherein the at least one memory and the computer program code are configured, together with the at least one processor, to cause the apparatus to perform operations including: Determine the values ​​of the coefficients of the M strongest frequency domain components; and The values ​​of the M strongest frequency domain components are provided in the feedback.

30. The apparatus of claim 27, wherein the at least one memory and the computer program code are configured, together with the at least one processor, to cause the apparatus to perform operations including: Oversampling detection is applied to the M' frequency domain components; The feedback provides an oversampling group indication, as well as indices of the M strongest frequency domain components within the indicated oversampling group.

31. The apparatus of claim 30, wherein the at least one memory and the computer program code are configured, together with the at least one processor, to cause the apparatus to perform operations including: The network node receives the mapping configuration between the oversampled group and the M' frequency domain components.

32. The apparatus of claim 27, wherein the at least one memory and the computer program code are configured, together with the at least one processor, to cause the apparatus to perform operations including: The feedback is provided for each spatial domain component of the plurality of downlink reference signals.

33. The apparatus of claim 27, wherein the at least one memory and the computer program code are configured, together with the at least one processor, to cause the apparatus to perform operations including: When a different set of M' frequency domain components is applied to at least two different spatial domain components in the precoding, the M strongest frequency domain components are determined for each of the corresponding at least two spatial domain components; and In the feedback, a different set of M frequency domain components are provided for each of the corresponding at least two spatial domain components.

34. The apparatus of claim 27, wherein the at least one memory and the computer program code are configured, together with the at least one processor, to cause the apparatus to perform operations including: Communication with network nodes is performed based at least in part on M frequency domain components.

35. The apparatus of claim 22, wherein the apparatus includes a user terminal.

36. A method at a network node of a communication network, comprising: Receive uplink reference signals from user equipment; Based on the received uplink reference signal, delay information about the delay distribution of the communication channel between the user equipment and the network node, and spatial information about the communication channel are estimated, wherein the delay information indicates the delay of each path of the communication channel relative to a reference time, and the delay information is determined based on channel reciprocity, wherein the uplink reference signal includes a sounding reference signal (SRS). Both the delay information and the spatial information are applied to the precoding of multiple downlink reference signals; Transmit to the user equipment an indication of whether the delay and the spatial information are used for precoding of the plurality of downlink reference signals at the network node; The user equipment is transmitted the plurality of precoded auxiliary downlink reference signals, the downlink reference signals including channel state information reference signals (CSI-RS); In response to the transmission of the plurality of precoded downlink reference signals, channel information is received from the user equipment, the channel information indicating at least non-zero coefficients of at least one channel transport layer, and the channel information is channel state information (CSI). Based on the delay information, a set of M' frequency domain components are determined for the communication channel; The set of M' frequency domain components is applied to the precoding of multiple auxiliary downlink reference signals; The plurality of precoded auxiliary downlink reference signals are transmitted to the user equipment; Feedback is received from the user equipment in response to the transmission of the plurality of precoded auxiliary downlink reference signals; as well as Based on the feedback, the set of M' frequency domain components are modified.

37. A method at a user equipment in a communication network, comprising: Uplink reference signals are transmitted to network nodes, the uplink reference signals indicating delay information about the delay distribution of the communication channel between the user equipment and the network node, and spatial information about the communication channel, wherein the delay information indicates the delay of each path of the communication channel relative to a reference time, and wherein the uplink reference signals include sounding reference signals (SRS). Receive from the network node an indication of whether the delay and the spatial information are used for precoding of multiple downlink reference signals at the network node; In response to the transmission of the uplink reference signal, the plurality of downlink reference signals, including a channel state information reference signal (CSI-RS), are received, wherein the plurality of downlink reference signals are pre-coded based at least on the delay information and the spatial information. Based on at least one received precoded downlink reference signal, channel information is determined, the channel information indicating at least one non-zero coefficient of at least one channel transport layer, the channel information including channel state information (CSI); The channel information is transmitted to the network node; Multiple auxiliary downlink reference signals are received from the network node, wherein the precoding of the multiple auxiliary downlink reference signals is based on a set of M' frequency domain components, wherein the set of M' frequency domain components is determined based on the delay information; Based on the received multiple auxiliary downlink reference signals, estimate the M strongest frequency domain components among the M' frequency domain components, where M... <M'; The network node transmits feedback on the received multiple auxiliary downlink reference signals, the feedback providing information on the determined M strongest frequency domain components.

38. An apparatus for communication, comprising components for performing the following: Receive uplink reference signals from user equipment; Based on the received uplink reference signal, delay information about the delay distribution of the communication channel between the user equipment and the device, and spatial information about the communication channel are estimated, wherein the delay information indicates the delay of each path of the communication channel relative to a reference time, and the delay information is determined based on channel reciprocity, wherein the uplink reference signal includes a sounding reference signal (SRS). Both the delay information and the spatial information are applied to the precoding of multiple downlink reference signals; Transmit to the user equipment an indication of whether the delay and the spatial information are used for precoding of the plurality of downlink reference signals at the device; The user equipment is transmitted the plurality of precoded auxiliary downlink reference signals, the downlink reference signals including channel state information reference signals (CSI-RS); In response to the transmission of the plurality of precoded downlink reference signals, channel information is received from the user equipment, the channel information indicating at least non-zero coefficients of at least one channel transport layer, and the channel information is channel state information (CSI). Based on the delay information, a set of M' frequency domain components are determined for the communication channel; The set of M' frequency domain components is applied to the precoding of multiple auxiliary downlink reference signals; The plurality of precoded auxiliary downlink reference signals are transmitted to the user equipment; Feedback is received from the user equipment in response to the transmission of the plurality of precoded auxiliary downlink reference signals; as well as Based on the feedback, the set of M' frequency domain components are modified.

39. An apparatus for communication, comprising components for performing the following: Uplink reference signals are transmitted to network nodes, the uplink reference signals indicating delay information about the delay distribution of the communication channel between the device and the network node, and spatial information about the communication channel, wherein the delay information indicates the delay of each path of the communication channel relative to a reference time, and wherein the uplink reference signals include sounding reference signals (SRS). Receive from the network node an indication of whether the delay and the spatial information are used for precoding of multiple downlink reference signals at the network node; The plurality of downlink reference signals are received in response to the transmission of the uplink reference signal, the plurality of downlink reference signals including a channel state information reference signal (CSI-RS), wherein the plurality of downlink reference signals are pre-coded based at least on the delay information and the spatial information; Based on at least one received precoded downlink reference signal, channel information is determined, the channel information indicating at least one non-zero coefficient of at least one channel transport layer, the channel information including channel state information (CSI); The channel information is transmitted to the network node; Multiple auxiliary downlink reference signals are received from the network node, wherein the precoding of the multiple auxiliary downlink reference signals is based on a set of M' frequency domain components, wherein the set of M' frequency domain components is determined based on the delay information; Based on the received multiple auxiliary downlink reference signals, estimate the M strongest frequency domain components among the M' frequency domain components, where M... <M'; as well as The network node transmits feedback on the received multiple auxiliary downlink reference signals, the feedback providing information on the determined M strongest frequency domain components.

40. A computer program product embodied on a computer-readable distribution medium and including program instructions that, when loaded into a device, perform a method, the method comprising: Receive uplink reference signals from user equipment; Based on the received uplink reference signal, delay information about the delay distribution of the communication channel between the user equipment and the device, and spatial information about the communication channel are estimated, wherein the delay information indicates the delay of each path of the communication channel relative to a reference time, and the delay information is determined based on channel reciprocity, wherein the uplink reference signal includes a sounding reference signal (SRS). Both the delay information and the spatial information are applied to the precoding of multiple downlink reference signals; Transmit to the user equipment an indication of whether the delay and the spatial information are used for precoding of the plurality of downlink reference signals at the device; The user equipment is transmitted the plurality of precoded auxiliary downlink reference signals, the downlink reference signals including channel state information reference signals (CSI-RS); In response to the transmission of the plurality of precoded downlink reference signals, channel information is received from the user equipment, the channel information indicating at least non-zero coefficients of at least one channel transport layer, and the channel information is channel state information (CSI). Based on the delay information, a set of M' frequency domain components are determined for the communication channel; The set of M' frequency domain components is applied to the precoding of multiple auxiliary downlink reference signals; The plurality of precoded auxiliary downlink reference signals are transmitted to the user equipment; Feedback is received from the user equipment in response to the transmission of the plurality of precoded auxiliary downlink reference signals; as well as Based on the feedback, the set of M' frequency domain components are modified.

41. A computer program product embodied on a computer-readable distribution medium and including program instructions that, when loaded into a device, execute a method, the method comprising: Uplink reference signals are transmitted to network nodes, the uplink reference signals indicating delay information about the delay distribution of the communication channel between the device and the network node, and spatial information about the communication channel, wherein the delay information indicates the delay of each path of the communication channel relative to a reference time, and wherein the uplink reference signals include sounding reference signals (SRS). Receive from the network node an indication of whether the delay and the spatial information are used for precoding of multiple downlink reference signals at the network node; The plurality of downlink reference signals are received in response to the transmission of the uplink reference signal, the plurality of downlink reference signals including a channel state information reference signal (CSI-RS), wherein the plurality of downlink reference signals are pre-coded based at least on the delay information and the spatial information; Based on at least one received precoded downlink reference signal, channel information is determined, the channel information indicating at least one non-zero coefficient of at least one channel transport layer, the channel information including channel state information (CSI); The channel information is transmitted to the network node; Multiple auxiliary downlink reference signals are received from the network node, wherein the precoding of the multiple auxiliary downlink reference signals is based on a set of M' frequency domain components, wherein the set of M' frequency domain components is determined based on the delay information; Based on the received multiple auxiliary downlink reference signals, estimate the M strongest frequency domain components among the M' frequency domain components, where M... <M'; as well as The network node transmits feedback on the received multiple auxiliary downlink reference signals, the feedback providing information on the determined M strongest frequency domain components.

42. A computer program product including program instructions that, when loaded into a device, execute a method, the method comprising: Receive uplink reference signals from user equipment; Based on the received uplink reference signal, delay information about the delay distribution of the communication channel between the user equipment and the device, and spatial information about the communication channel are estimated, wherein the delay information indicates the delay of each path of the communication channel relative to a reference time, and the delay information is determined based on channel reciprocity, wherein the uplink reference signal includes a sounding reference signal (SRS). Both the delay information and the spatial information are applied to the precoding of multiple downlink reference signals; Transmit to the user equipment an indication of whether the delay and the spatial information are used for precoding of the plurality of downlink reference signals at the device; The user equipment is transmitted the plurality of precoded auxiliary downlink reference signals, the downlink reference signals including channel state information reference signals (CSI-RS); In response to the transmission of the plurality of precoded downlink reference signals, channel information is received from the user equipment, the channel information indicating at least non-zero coefficients of at least one channel transport layer, and the channel information is channel state information (CSI). Based on the delay information, a set of M' frequency domain components are determined for the communication channel; The set of M' frequency domain components is applied to the precoding of multiple auxiliary downlink reference signals; The plurality of precoded auxiliary downlink reference signals are transmitted to the user equipment; Feedback is received from the user equipment in response to the transmission of the plurality of precoded auxiliary downlink reference signals; as well as Based on the feedback, the set of M' frequency domain components are modified.

43. A computer program product including program instructions that, when loaded into a device, execute a method, the method comprising: Uplink reference signals are transmitted to network nodes, the uplink reference signals indicating delay information about the delay distribution of the communication channel between the device and the network node, and spatial information about the communication channel, wherein the delay information indicates the delay of each path of the communication channel relative to a reference time, and wherein the uplink reference signals include sounding reference signals (SRS). Receive from the network node an indication of whether the delay and the spatial information are used for precoding of multiple downlink reference signals at the network node; In response to the transmission of the uplink reference signal, the plurality of downlink reference signals, including a channel state information reference signal (CSI-RS), are received, wherein the plurality of downlink reference signals are pre-coded based at least on the delay information and the spatial information. The precoding of the plurality of downlink reference signals is applied with a set of M' frequency domain components, and the M' frequency domain components are determined by the network node based on the delay information; Based on at least one received precoded downlink reference signal, channel information is determined, the channel information indicating at least one non-zero coefficient of at least one channel transport layer, the channel information including channel state information (CSI); The channel information is transmitted to the network node; Multiple auxiliary downlink reference signals are received from the network node, wherein the precoding of the multiple auxiliary downlink reference signals is based on a set of M' frequency domain components, wherein the set of M' frequency domain components is determined based on the delay information; Based on the received multiple auxiliary downlink reference signals, estimate the M strongest frequency domain components among the M' frequency domain components, where M... <M'; as well as The network node transmits feedback on the received multiple auxiliary downlink reference signals, the feedback providing information on the determined M strongest frequency domain components.

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