Communication device, network device, and communication method

Abstract

The present invention provides a communication device, a network device, and a communication method for efficiently estimating channel status information. [Solution] The communication device of the present disclosure is a communication device that communicates with a wireless network including a plurality of communication points that can communicate in cooperation, and comprises: a receiving unit that receives downlink reference signals from each of the plurality of communication points; a control unit that calculates first channel state information based on the downlink reference signals and selects a communication point from the plurality of communication points to be used to transmit an uplink reference signal based on the first channel state information; and a transmitting unit that transmits the uplink reference signal to the selected communication point.

Description

Technical Field

[0001] This disclosure relates to a communication device, a network device, and a communication method.

Background Art

[0002] Wireless access methods and wireless networks for cellular mobile communications (hereinafter also referred to as "Long Term Evolution (LTE)", "LTE-Advanced (LTE-A)", "LTE-Advanced Pro (LTE-A Pro)", "New Radio (NR)", "New Radio Access Technology (NRAT)", "Evolved Universal Terrestrial Radio Access (EUTRA)", or "Further EUTRA (FEUTRA)") are being studied in the 3rd Generation Partnership Project (3GPP). In the following description, LTE includes LTE-A, LTE-A Pro, and EUTRA, and NR includes NRAT and FEUTRA. In LTE, a base station device (base station) is also referred to as an eNodeB (evolved NodeB). In NR, a base station device is also referred to as a gNodeB. Also, in LTE and NR, a terminal device (mobile station, mobile station device, terminal) is also referred to as a UE (User Equipment). LTE and NR are cellular communication systems in which a plurality of areas covered by base station devices are arranged in a cell shape. A single base station device may manage a plurality of cells.

[0003] NR is a Radio Access Technology (RAT) distinct from LTE, serving as the next-generation wireless access method. NR is an access technology capable of supporting various use cases, including Enhanced Mobile Broadband (eMBB), Massive Machine Type Communications (mMTC), and Ultra Reliable and Low Latency Communications (URLLC). Standardization efforts have focused on supporting a technical framework that addresses the usage scenarios, requirements, and deployment scenarios associated with these use cases.

[0004] In recent years, discussions on next-generation wireless communication standards (6G, Beyond 5G) have progressed in 3GPP's Release-19, with requirements for even faster communication than NR, low-latency, highly reliable communication, high-density communication for the majority of users, and simultaneous support for multiple of these. To meet these requirements, further improvements in frequency utilization efficiency are needed. Utilizing higher frequency bands is one solution, but because the propagation distance is shorter compared to lower frequency bands, there is a problem that the communication area that a single base station can cover becomes smaller. As a means of solving this problem, a form of communication called self-free communication is considered promising.

[0005] In conventional cellular wireless communication, the basic structure was a cell centered around a single base station. It was common for each base station to cover a specific area (cell) and communicate with terminals within that area. However, especially with 5G and beyond, to meet increasing communication demands, there has been a diversification of network nodes beyond a single base station, including NTN (Non-Terrestrial Network) and IAB (Integrated Access and Backhaul).

[0006] In 6G and beyond, this diversification is expected to be further advanced, with the functions of a single base station device being divided into roles (CU (Central Unit) / DU (Distributed Unit) / RU (Radio Unit) separation), allowing for the geographical distribution of numerous RUs, and the use of terminal-to-terminal relay and RIS (Reconfigurable Intelligent Surface) to advance. As a result, terminal devices can flexibly connect with surrounding communication resources and dynamically form optimal communication paths, without relying on a fixed cell structure. Such communication or its mechanism is called cell-free communication.

[0007] In 6G and beyond, a form of self-free communication is expected, where multiple network nodes cooperate to communicate with a single terminal.

[0008] To efficiently perform wireless communication, it is essential to estimate the channel state information (CSI) between each network node and terminal device. Estimating the CSI enables the selection of appropriate beamforming, precoding, and modulation / coding schemes, thereby improving communication quality and maximizing system capacity.

[0009] Basically, the CSI is determined in a one-to-one relationship between the network node and the terminal device, and existing standards specify dedicated reference signals for both the downlink and uplink to estimate the CSI.

[0010] In self-free communication, it is expected that there will be a large number of network nodes communicating with terminal devices. Even when the number of network nodes increases in this way, estimating the CSI (Center of Score) remains important. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Special Publication No. 2024-504145 [Patent Document 2] International Publication No. 2019 / 168049 [Overview of the Initiative] [Problems that the invention aims to solve]

[0012] CSI is obtained by transmitting a specific, defined reference signal and analyzing that signal at the receiving end. The reference signal transmitted over the downlink is called the downlink reference signal (downlink reference signal), and the reference signal transmitted over the uplink is called the uplink reference signal (uplink reference signal).

[0013] One example of a downlink reference signal is the CSI-RS (Channel State Information Reference Signal). The CSI-RS is a reference signal transmitted from the network node, and the terminal device analyzes the received reference signal and feeds the analysis results back to the network node. This allows the network node to optimize the downlink transmission configuration.

[0014] In situations where a terminal device is connected to multiple network nodes, the terminal device needs to analyze and feed back the downlink reference signal from each network node. Therefore, in configurations where the number of network nodes increases, such as self-free communication, there is a concern that the overhead caused by the increased amount of feedback due to the increase in network nodes will lead to a decrease in communication throughput.

[0015] One example of an uplink reference signal is the SRS (Sounding Reference Signal). The SRS is a reference signal transmitted from a terminal device, and the network node analyzes the received signal and uses the analysis result (CSI estimation result) to optimize the uplink or downlink transmission configuration. In frequency division duplex (FDD) schemes, which use different frequency bands for uplink and downlink, the CSI estimation result is used only to optimize uplink communication. On the other hand, in time division duplex (TDD) schemes, which use the same frequency band for uplink and downlink, the CSI estimation result can be used to optimize communication on both the uplink and downlink for channel complementarity.

[0016] In a scenario where a terminal device is connected to multiple network nodes, optimizing uplink communication using estimation results for the uplink reference signal requires feeding back the CSI estimation results from each network node to the terminal device. In this case, in configurations where the number of network nodes connected to the terminal device increases, such as in self-free communication, there is a concern that the overhead caused by the increased amount of feedback due to the increase in network nodes may lead to a decrease in communication throughput.

[0017] In TDD (Transmission-Driven) operation, the estimation results for the uplink reference signal can also be used to optimize downlink transmission. In this case, since the received uplink reference signal is simply analyzed and used on the network node side, feedback to the terminal side is unnecessary, or the amount of feedback is extremely small.

[0018] Since self-free communication is expected to operate in the high-frequency band, TDD operation is anticipated. Therefore, in estimating CSI in downlink communication, both methods using downlink reference signals such as CSI-RS and uplink reference signals such as SRS can be used. As explained above, when estimating CSI using downlink reference signals, an increase in the amount of feedback from the terminal becomes a problem. However, if the uplink reference signal is used not only for optimizing uplink transmission but also for optimizing downlink transmission, the problem of increased feedback from the terminal can be suppressed by omitting the transmission of the downlink reference signal. However, in this case, there are concerns about problems such as increased power consumption of the terminal due to an increase in the number of uplink reference signal transmissions.

[0019] On the other hand, in existing standards, while general channel conditions such as spatial characteristics can be obtained in CSI estimation for uplink communication using the analysis results of downlink reference signals like CSI-RS, the system is fundamentally designed so that channel condition information in link communication can only be obtained by analyzing uplink reference signals like SRS. Therefore, when a terminal device is connected to multiple network nodes, all network nodes need to feed back the analysis results of their uplink reference signals to the terminal device, which increases the amount of feedback.

[0020] Thus, existing standards are insufficient in terms of the complementary use of downlink and uplink reference signals. In other words, existing standards do not efficiently estimate the CSI, and this is expected to become particularly apparent in self-free communications where the number of network nodes increases, leading to a problem of increasing feedback.

[0021] Given this situation, there is a need for methods that improve overall system performance and reduce terminal power consumption by performing efficient CSI estimation.

[0022] In the above Patent Document 1, a method of measuring the covariance of DL interference power using CSI-RS resources and precoding the SRS signal based on the measurement is described. This method is described in terms of reducing the overhead by frequency complementing the SRS signal using the CSI-RS signal, and there is no description of the operation when applied to the case of multiple NW nodes.

[0023] In the above Patent Document 2, a method of specifying the CSI-RS that is complementarily used when determining the precoder of the uplink signal based on temporal correlation is described. However, there is no description of the operation when there are multiple NW nodes.

[0024] In short, in these Patent Documents 1 and 2, there is no description of the mutual complementation of the CSI of the uplink / downlink reference signals in the case of multiple NW nodes. If the technologies of these Patent Documents 1 and 2 are directly applied in self-free communication, there is a risk of throughput reduction.

[0025] The present disclosure provides a communication device, a network device, and a communication method that can efficiently acquire channel state information in order to solve the above-described problems.

Means for Solving the Problems

[0026] The communication device of the present disclosure is a communication device that communicates with a wireless network including a plurality of communication points that can communicate in cooperation, and includes a receiving unit that receives downlink reference signals from the plurality of communication points respectively, a control unit that calculates first channel state information based on the downlink reference signals and selects a communication point that is a transmission target of an uplink reference signal among the plurality of communication points based on the first channel state information, and a transmitting unit that transmits the uplink reference signal to the selected communication point.

[0027] The network device of this disclosure is one of a plurality of network devices that constitute a wireless network including a plurality of network devices capable of coordinating communication, and comprises: a receiving unit that receives an uplink reference signal transmitted from a communication device to the plurality of network devices; a control unit that acquires first channel status information based on the uplink reference signal and determines whether or not to transmit a downlink reference signal to the communication device based on the first channel status information; and a transmitting unit that transmits the downlink reference signal to the communication device in response to the decision to transmit the downlink reference signal. [Brief explanation of the drawing]

[0028] [Figure 1] Diagram illustrating the comparative example in this disclosure. [Figure 2] A block diagram showing an example of a network device according to this embodiment. [Figure 3] This block diagram shows an example of a terminal device as a communication device according to this embodiment. [Figure 4] A diagram showing an example of the procedure sequence in Case 1. [Figure 5] This diagram shows an example of the exchange of reference signals between the terminal device and each network node in Case 1. [Figure 6] A diagram illustrating example 1 of the judgment. [Figure 7] A diagram illustrating example 2 of the judgment. [Figure 8] A diagram showing an example of the procedure sequence in Case 2. [Figure 9] This diagram shows an example of the exchange of reference signals between the terminal device and each network node in Case 2. [Modes for carrying out the invention]

[0029] Embodiments of this disclosure will be described below with reference to the drawings. The following description will focus on the main components of this disclosure, but there may be components and functions not shown or described. The following description does not exclude any components or functions not shown or described.

[0030] <Explanation of terms related to this disclosure> The terms used in this embodiment will be explained below.

[0031] <Channel Status Information (CSI)> Channel Status Information (CSI) is an indicator in NR systems that represents the quality and characteristics of a radio channel. CSI is used for both downlink and uplink. CSI is utilized in various radio resource management functions such as adaptive modulation and coding (AMC), scheduling, and beamforming to achieve efficient communication.

[0032] Downlink CSI is primarily acquired by terminal equipment through measurement of reference signals such as CSI-RS and SSB. On the other hand, uplink CSI is primarily acquired by network nodes such as base stations based on measurement of SRS (Sounding Reference Signal). Downlink CSI mainly includes elements (items) such as CQI (Channel Quality Indicator), PMI (Precoding Matrix Indicator), RI (Rank Indicator), CRI (CSI Resource Indicator), and LI (Layer Indicator). Uplink CSI includes elements such as TPMI (Transmitted Precoding Matrix Indicator), SRI (SRS Resource Indicator), and TRI (Transmitted Rank Indicator).

[0033] The process of acquiring and using CSI begins with the transmission of a reference signal, followed by the estimation (calculation) of Channel Status Information (CSI) at the receiving end, CSI reporting (or processing at the base station), optimization of transmission parameters, notification of the optimized transmission parameters, and application of the CSI estimation results to the next transmission. This process applies to both downlink and uplink, and is adjusted according to the characteristics of each.

[0034] CSI-related settings are configured through RRC signaling. On downlinks, the main settings are CSI-RS and CSI reporting settings, while on uplinks, the main settings are SRS settings. These settings are specified using the CSI-ReportConfig information element within NR-RRC-Definitions. There are three types of CSI reports: periodic, semi-persistent, and aperiodic, which are used depending on the application and situation.

[0035] CSI influences the optimization of transmission parameters, as well as the selection of the TCI (Transmission Configuration Indication) state and the TCI-UL state. The TCI state and TCI-UL state specify the QCL (Quasi Co-Location) relationship with the reference signal used for transmitting downlink / uplink signals, and are dynamically indicated via DCI. This enables optimal beam selection and precoding based on CSI, improving the overall communication quality and efficiency of the system.

[0036] <Uplink reference signal> In NR (Noise Reduction), the primary uplink reference signal used to estimate channel status information (CSI) is the Sounding Reference Signal (SRS). The SRS plays a crucial role in evaluating the quality of uplink channels, ensuring proper scheduling, and precoding.

[0037] SRS configuration is performed through RRC (Radio Resource Control) signaling. RRC signaling uses SRS-Config information elements to notify terminal devices of the SRS resource set and detailed settings for SRS resources. These settings include transmission bandwidth, periodicity, comb structure, and number of antenna ports.

[0038] After configuration, SRS is transmitted separately from the physical layer channel, PUSCH (Physical Uplink Shared Channel). The timing of SRS transmission is determined according to the configured periodicity. In the case of aperiodic SRS, it is triggered from the network via DCI.

[0039] When a terminal device transmits an SRS signal, a network node (e.g., a base station) receives and analyzes it. The analysis uses the amplitude and phase information of the received SRS signal to estimate the channel impulse response. During this process, channel characteristics such as path loss, large-scale fading, and small-scale fading are evaluated.

[0040] At the network node, the optimal parameters (transmission parameters) for uplink transmission are determined based on the analysis results of the received SRS. These include resource allocation, modulation coding scheme (MCS), precoding matrix, and transmission rank.

[0041] The determined parameters are primarily communicated to terminal devices via DCI (Downlink Control Information). DCI is transmitted via PDCCH (Physical Downlink Control Channel). Specifically, DCI formats such as 0_1 and 0_2 are used, and parameters based on SRS measurement results are indicated through fields such as SRS Resource Indicator (SRI) and Precoding information and number of layers. Regarding transmit power control, adjustments to the SRS transmit power are instructed through the TPC (Transmit Power Control) command included in the DCI.

[0042] Parameters notified via DCI are immediately interpreted by the terminal device and applied to the next uplink transmission. The terminal device uses specific time-frequency resources based on the instructed resource allocation and selects the appropriate modulation scheme and coding rate according to the specified MCS. It weights the transmitting antenna using precoding information and determines the number of layers according to the specified transmit rank. It also adjusts the transmit power according to the TPC command and uses the specified antenna port. Furthermore, it generates a reference signal based on the DMRS settings and transmits it along with the data. By comprehensively applying these parameters, uplink signal transmission optimized for the channel state is achieved.

[0043] On the other hand, the SRS analysis results are also applied to the transmission of downlink signals in TDD systems. Specifically, the TCI (Transmission Configuration Indication) state is selected based on the received power of the SRS transmitted from the terminal equipment (UE). The TCI state specifies the QCL relationship with the reference signal used for PDSCH transmission and is dynamically indicated via DCI. This allows for the effective use of uplink SRS measurement results for downlink beam selection and precoding by utilizing channel reciprocity, thereby improving the overall communication quality and efficiency of the system.

[0044] <Downlink Reference Signal> In NR, the main downlink reference signals used to estimate channel state information (CSI) are CSI-RS (Channel State Information Reference Signal) and SSB (Synchronization Signal Block).

[0045] First, let's explain CSI-RS. CSI-RS configuration is performed through RRC (Radio Resource Control) signaling. Specifically, detailed settings for CSI-RS resource sets and CSI-RS resources are notified from the network (e.g., NW nodes such as base stations) to terminal devices using CSI-RS-ResourceConfig and CSI-RS-Resource within NR-RRC-Definitions. These settings include CSI-RS periodicity, offset, resource mapping, and the number of antenna ports.

[0046] CSI-RS is transmitted separately from the physical layer channel, PDSCH (Physical Downlink Shared Channel). The transmission timing of CSI-RS is determined according to the configured periodicity and offset. In the case of aperiodic CSI-RS, it is triggered from the network node via DCI (Downlink Control Information).

[0047] When a terminal device receives CSI-RS, it performs CSI estimation. During this process, the channel amplitude, phase characteristics, SNR (Signal-to-Noise Ratio), and interference level are evaluated. Based on these measurement results, the terminal device calculates CSI parameters such as CQI (Channel Quality Indicator), PMI (Precoding Matrix Indicator), RI (Rank Indicator), and CRI (CSI-RS Resource Indicator).

[0048] The calculated CSI parameters are primarily reported to the network via PUCCH (Physical Uplink Control Channel) or PUSCH (Physical Uplink Shared Channel). The timing and content of the report are determined based on the CSI report settings configured in RRC signaling. In the case of aperiodic CSI reports, they are triggered via DCI.

[0049] The network node analyzes the received CSI report and optimizes the parameters for downlink transmission. Specifically, these parameters are used for scheduling, resource allocation, MCS (Modulation and Coding Scheme) selection, and precoding matrix determination. These optimized parameters are communicated to the terminal device via DCI and applied to the next downlink transmission.

[0050] Next, we will explain SSB. SSB configuration is primarily done through the System Information Block (SIB1). SSB includes the Primary Synchronization Signal (PSS), Secondary Synchronization Signal (SSS), and Physical Broadcast Channel (PBCH), which are transmitted periodically. SSB is mainly used for cell detection, initial access, and beam management, but it is also used for CSI estimation.

[0051] Upon receiving an SSB signal, the terminal device first performs cell detection and initial synchronization using PSS and SSS. Subsequently, it measures the SSB signal strength (RSRP: Reference Signal Received Power) and signal quality (RSRQ: Reference Signal Received Quality). These measurement results are used for cell selection and handover decisions, as well as for beam management.

[0052] SSB measurement results are primarily reported to the network (e.g., NW nodes such as base stations) through RRC signaling (e.g., measurement reports). The trigger conditions and content of the reports are determined based on the measurement settings configured in the RRC signaling.

[0053] The NW node analyzes the received SSB measurement reports and uses them for inter-cell interference management, beam selection, and mobility control. The SSB measurement results can be used for downlink beam formation. This is achieved by utilizing the QCL (Quasi Co-Location) relationship between the SSB and PDSCH.

[0054] The measurement results for CSI-RS and SSB are reflected in downlink transmission via TCI state. This allows the network to select the optimal beam direction and precoding based on the measurement results of the terminal equipment, thereby improving downlink transmission performance.

[0055] Thus, CSI estimation using CSI-RS and SSB, and the utilization of the results, are achieved through a series of steps: setup via RRC signaling, transmission of a reference signal, measurement at a terminal device, reporting of measurement results, analysis over the network, and parameter notification via DCI.

[0056] <Antenna port> An antenna port is a logical entity defined in the 3GPP technical specifications and is distinct from a physical antenna port. Essentially, when we refer to an antenna port, we are referring to a logical antenna port, a concept used to recognize the identity of propagation path characteristics. For example, within the same antenna port, the propagation path characteristics of one symbol can be recognized as the same as those of another symbol. Within the same antenna port, propagation path characteristics are recognized as the same even between different symbols, but between different antenna ports, propagation path characteristics are considered different unless there is a quasi-co-location (QCL) relationship. An antenna port can associate a specific reference signal with a specific channel, and these are considered to have the same propagation path characteristics. This characteristic allows the receiver to estimate the propagation path characteristics using the reference signal and apply this to the reception processing of the associated channel.

[0057] <quasi-co-location> Two antenna ports can be described as quasi-co-location (QCL) if they satisfy certain conditions. These conditions are that the global characteristics of the propagation channel carrying symbols at one antenna port can be inferred from the propagation channel carrying symbols at the other antenna port. The global characteristics include delay dispersion, Doppler spread, Doppler shift, average gain, and / or average delay.

[0058] QCL between antenna ports is defined by the TCI (Transmission Configuration Indicator) state. For example, the TCI state includes parameters that set the QCL relationship between the downlink reference signal (DMRS) and the PDSCH antenna port, the QCL relationship between the downlink reference signal (DMRS) and the PDCCH antenna port, or the QCL relationship between the downlink reference signal (DMRS) and the NZP (Non-Zero-Power) CSI-RS resource antenna port. The TCI state is defined by the following types (1) to (4). (1) QCL-TypeA: {Doppler shift, Doppler spread, mean delay, delay spread} (2) QCL-Type B: {Doppler shift, Doppler spread} (3) QCL-TypeC: {Doppler spread, mean delay} (4) QCL-TypeD: {Spatial Rx (Receiver, Reception) parameters} The terminal device's TCI state is specified by DCI (Downlink Control Information), MAC-CE (Medium Access Control Control Element), or RRC (Radio Resource Control) signaling.

[0059] <Resources> Resources include Frequency, Time, Resource Element (including REG, CCE, and CORESET), Resource Block, Bandwidth Part, Component Carrier, Symbol, Sub-Symbol, Slot, Mini-Slot, Subslot, Subframe, Frame, PRACH occasion, Occasion, Code, Multi-access physical resource, Multi-access signature, and Subcarrier Spacing (Numerology).

[0060] <CL-CSI(Cross-Link CSI)> In this specification, CSI obtained by mutually complementarily utilizing uplink / downlink reference signals may be referred to as Cross-Link CSI (CL-CSI) for convenience, in order to distinguish it from conventional CSI. CL-CSI is an extended concept that also includes conventional CSI. Uplink or downlink CSI obtained from uplink reference signals alone are included in CL-CSI, as are downlink or uplink CSI obtained from downlink reference signals alone. Furthermore, downlink or uplink CSI obtained from both uplink and downlink reference signals are also included in CL-CSI. Other names besides CL-CSI are also possible.

[0061] <NWノード> Network nodes include, for example, cells, gNBs (base stations), TRPs (Transmission and reception points), antenna ports, RUs, sets of antenna ports, IAB nodes, relay terminals, and beams. Network nodes may also include CUs (Central Units), DUs (Distributed Units), and RUs (Radio Units). Base stations can be not only ground-based base station equipment, but also non-ground base station equipment that operates as communication devices, such as satellite stations, drones, balloons, and airplanes.

[0062] A network node may be a set of antenna ports sharing the same Quasi-co-location (QCL). In other words, a set of antenna ports sharing the same Quasi-co-location (QCL) can be defined as a single node, and this node can be defined as a network.

[0063] Network nodes do not need to be fixed in place; they can be mobile nodes.

[0064] Network nodes do not need to be terrestrial nodes; they can also be non-terrestrial nodes (satellites, drones, UAVs).

[0065] Furthermore, when referring to a group of network nodes, it means a collection of network nodes that include at least one of the aforementioned network nodes.

[0066] <Uplink signal> Uplink signals refer to the signals and channels transmitted from terminal equipment to a group of network nodes. In particular, they refer to all signals and channels to which the estimated CSI is applied during transmission. Examples of uplink signals include the following: ·PUSCH (Physical Uplink Shared Channel) ·PUCCH (Physical Uplink Control Channel) ·PRACH (Physical Random Access Channel) ·SRS (Sounding Reference Signal) ·DMRS (Demodulation Reference Signal) ·PT-RS (Phase Tracking Reference Signal)

[0067] <Downlink signal> Downlink signals refer to the signals and channels transmitted from the network node group to terminal devices. In particular, it refers to all signals and channels to which the estimated CSI is applied during transmission. Examples of downlink signals include the following: ·PDSCH (Physical Downlink Shared Channel) ·PDCCH (Physical Downlink Control Channel) ·PBCH (Physical Broadcast Channel) ·SSB (Synchronization Signal Block) ·CSI-RS (Channel State Information Reference Signal) ·DMRS (Demodulation Reference Signal) ·PT-RS (Phase Tracking Reference Signal) ·TRS (Tracking Reference Signal) ·PRS (Positioning Reference Signal)

[0068] <Uplink reference signal> Uplink reference signals refer to the signals and channels transmitted from terminal devices to the network node group for CSI estimation. Examples of uplink reference signals include the following: ·SRS (Sounding Reference Signal)

[0069] <Downlink Reference Signal> Downlink reference signals refer to the signals and channels transmitted from the network node group to terminal devices for CSI estimation. Examples of downlink reference signals include the following: ·SSB (Synchronization Signal Block) ·CSI-RS (Channel State Information Reference Signal)

[0070] Before describing the details of embodiments of the present invention, comparative examples of this disclosure will be described in order to understand the problems that this embodiment solves.

[0071] Figure 1 is an explanatory diagram of a comparative example. It shows multiple NW nodes 100, terminal devices 200, and a control device 300. The multiple NW nodes 100 are nodes on the wireless network side that include multiple communication points capable of coordinating communication, and function as communication points in self-free communication. The terminal device 200 can communicate with the wireless network including these multiple NW nodes 100. In this example, four NW nodes 100 are shown, and when distinguishing them, they are also referred to as NW node 1, NW node 2, NW node 3, and NW node 4. The control device 300 is a device that controls multiple NW nodes 100, for example, a base station, DU, or CU. The multiple NW nodes 100 under the control device 300 each transmit downlink reference signals to the terminal device 200, and the terminal device 200 provides feedback of the CSI calculated (estimated) from the downlink reference signals to the multiple NW nodes 100. Feedback information acquired at NW node 100 can be analyzed at NW node 100, or it can be provided to control device 300 and analyzed at control device 300. Here, we assume that the analysis is performed at NW node 100. The direction of communication from NW node 100 to terminal device 200 corresponds to downlink, and the direction of communication from terminal device 200 to NW node 100 corresponds to uplink.

[0072] The transmission parameters of the downlink signal transmitted from the NW node 100 can be optimized based on the CSI report that the terminal device 200 analyzes and feeds back from the downlink reference signal transmitted by the NW node 100. In this case, the CSI report fed back from the terminal device 200 to the NW node 100 is mainly transmitted via PUCCH or PUSCH.

[0073] The CSI report submitted by terminal device 200 mainly contains the following information: ·CQI (Channel Quality Indicator) ·PMI (Precoding Matrix Indicator) · RI (Rank Indicator) ·CRI(CSI-RS Resource Indicator) ·L1-RSRP (Layer 1 Reference Signal Received Power) · LI (Layer Indicator) ·SSBRI (SS / PBCH Block Resource Indicator) • Difference information of the downlink reference signal measurement results

[0074] The optimized transmission parameters based on the CSI report are primarily communicated from the network node 100 to the terminal device 200 via DCI (Downlink Control Information) within the PDCCH. Examples of the transmitted parameters communicated include the following: • Parameters related to time-frequency resource allocation • Periodicity and offset ·Density (CDM type) QCL Information ·MCS (Modulation and Coding Scheme) • Resources such as the antenna port to be used

[0075] Furthermore, by using the concept of TCI (Transmission Configuration Indication) state, it is possible to specify a reference signal in a QCL (Quasi Co-Location) relationship and perform efficient beam management. This enables transmission in the appropriate beam direction, especially in high-frequency communications.

[0076] Furthermore, in TDD systems, channel incompatibility is utilized to apply the analysis results of the uplink reference signal to the optimization of the downlink signal transmission parameters. In this case, the transmission parameters of the downlink signal transmitted from NW node 100 are optimized based on the CSI report obtained by NW node 100 from analyzing the uplink reference signal transmitted by terminal device 200.

[0077] (Problems in the comparative example) In an environment where terminal device 200 is connected to numerous network nodes 100, the operation of sending a CSI report from terminal device 200 based on the analysis results of the downlink reference signal is likely to result in a significant increase in the amount of feedback as the number of network nodes 100 increases. In a TDD system, in principle, when estimating CSI for an uplink reference signal, it is possible to obtain the same CSI estimation result as when estimating CSI for a downlink reference signal. Therefore, it is conceivable that the problem of increased feedback can be solved by actively utilizing the CSI obtained from the uplink reference signal for transmitting the downlink signal, thereby suppressing the transmission of the downlink reference signal. However, frequently transmitting the uplink reference signal increases the power consumption of terminal device 200, which can put pressure on other uplink data channels.

[0078] In light of the above issues, this embodiment provides a mechanism for estimating the CSI by complementaryly utilizing the uplink reference signal and the downlink reference signal. This results in improvements to the overall communication quality of the system and a reduction in the power consumption of the terminal device 200.

[0079] <Network device configuration> Figure 2 is a block diagram showing an example of a network device 10 according to this embodiment. The network device 10 is one of a plurality of network devices that constitute a wireless network including a plurality of network devices capable of coordinating communication. The network device 10 is, for example, a communication device such as an NW node 100 or a control device 300. The network device 10 may be a device that includes both an NW node 100 and a control device 300. In this case, for example, the NW node 100 may be an antenna device including an RU (Radio Unit), and the control device 300 may be a base station including a CU (Central Unit) / DU (Distributed Unit). Alternatively, the NW node 100 may be a base station including an RU and a DU, and the control device 300 may be a base station including a CU. Other configurations are also possible. The communication device that the network device 10 communicates with is, for example, a terminal device 200.

[0080] The network device 10 comprises one or more communication points 110, a wireless communication unit 120 (transceiver), a network communication unit 130, a storage unit 140, and a control unit 150. The wireless communication unit 120, the network communication unit 130, and the control unit 150 are each implemented by a processor (hardware processor) such as a CPU (Central Processing Unit) or MPU (Micro-Processing Unit), an ASIC (Application Specific Integrated Circuit), or an FPGA (Field-Programmable Gate Array), or an integrated circuit. The storage unit 140 is implemented by any recording medium such as memory, a hard disk drive, an optical disk, or a magnetic recording device. The memory may be volatile or non-volatile memory.

[0081] The communication point 110 may be an antenna, for example, if the network device 10 is an NW node 100 or a control device 300. Alternatively, if the network device 10 includes multiple NW nodes 100 and control devices 300, each communication point 110 may correspond to one NW node 100. The definition of an NW node 100 is as described above.

[0082] The wireless communication unit 120 transmits and receives signals via one or more communication points 110. The signals include data or information. The wireless communication unit 120 includes a signal transmitting unit 121 that transmits signals and a signal receiving unit 122 that receives signals. For example, the signal transmitting unit 121 transmits a downlink signal or downlink reference signal to the terminal device 200, and the signal receiving unit 122 receives an uplink signal or uplink reference signal from the terminal device 200. The wireless communication unit 120 may communicate with the terminal device 200 by forming multiple beams using multiple communication points 110.

[0083] The network communication unit 130 sends and receives information with other communication devices. For example, the network communication unit 130 sends information to other communication devices and receives information from other communication devices. Other communication devices include, for example, at least one of a terminal device 200, an NW node 100, a control device 300, a core network, or a node on the internet.

[0084] The storage unit 140 temporarily or permanently stores programs and data for the operation of the network device 10. The storage unit 140 also temporarily or permanently stores information about other communication devices that are to be communicated with (such as terminal devices 200, NW nodes 100, or control devices 300).

[0085] The control unit 150 comprises a receiving unit 152 and a transmitting unit 151. The receiving unit 152 of the control unit 150 receives data or information from the terminal device 200 via the wireless communication unit 120. The transmitting unit 151 of the control unit 150 transmits data or information destined for the terminal device 200 via the wireless communication unit 120.

[0086] The control unit 150 controls the operation of the entire network device 10 and provides various functions of the network device 10. The control unit 150 controls the operations performed by the NW node 100 or the control device 300 in the sequence shown in Figure 4 or Figure 8, which will be described later. For example, the control unit 150 controls the acquisition of channel status information (CSI) for the uplink or downlink between the terminal device 200 and the terminal device 200. For example, it controls the acquisition of feedback information (downlink CSI estimation result) from the terminal device 200 by transmitting a downlink reference signal. It also controls the acquisition of uplink CSI estimation result by receiving and analyzing an uplink reference signal from the terminal device 200.

[0087] The control unit 150 acquires information about other communication devices (such as terminal devices 200, NW nodes 100, or control devices 300). Examples of information acquired by the control unit 150 include, but are not limited to, channel status information (CSI estimation results) for the uplink or downlink between terminal devices 200 and NW nodes 100, and information about the specifications and capabilities of terminal devices 200.

[0088] <Configuration of terminal device 200> Figure 3 is a block diagram showing an example of a terminal device 200 as a communication device according to this embodiment. In this embodiment, the communication device is a terminal device 200, but it may be a device other than a terminal device, such as a device with a relay function (relay device). The terminal device 200 is capable of communicating with a wireless network that includes multiple communication points capable of coordinating communication. The terminal device 200 comprises one or more antennas 210, a wireless communication unit 220 (transceiver), a storage unit 240, and a control unit 250. The wireless communication unit 220 and the control unit 250 are each implemented by a processor or integrated circuit such as a CPU (Central Processing Unit), MPU (Micro-Processing Unit), ASIC (Application Specific Integrated Circuit), or FPGA (Field-Programmable Gate Array), for example. The storage unit 240 is implemented by any recording medium such as a memory, hard disk drive, optical disk, or magnetic recording device. The memory may be volatile memory or non-volatile memory.

[0089] Antenna 210 radiates the signal output by the wireless communication unit 220 into space as radio waves. Antenna 210 converts the radio waves in space into a signal and outputs the signal to the wireless communication unit 220. Antenna 210 may be an array antenna having multiple antenna elements.

[0090] The wireless communication unit 220 transmits and receives signals. The signals include data or information. The wireless communication unit 220 comprises a signal transmitting unit 221 that transmits signals and a signal receiving unit 222 that receives signals. For example, the signal receiving unit 222 receives downlink signals from one or more NW nodes 100. The signal transmitting unit 221 transmits uplink signals to one or more NW nodes 100.

[0091] The storage unit 240 temporarily or permanently stores programs and various data for the operation of the terminal device 200. The storage unit 240 may also store information related to the network device 10.

[0092] The control unit 250 comprises a transmitting unit 251 and a receiving unit 252. The receiving unit 252 receives data or information from the network device 10 or one or more NW nodes 100 via the wireless communication unit 220. The transmitting unit 251 transmits data or information destined for the network device 10 or one or more NW nodes 100 via the wireless communication unit 120.

[0093] The control unit 250 of the terminal device 200 controls the overall operation of the terminal device 200 and provides various functions of the terminal device 200. The control unit 250 controls the operations performed by the terminal device 200 in the sequence shown in Figure 4 or Figure 8, which will be described later. For example, the control unit 250 controls the acquisition of channel status information (CSI) for the uplink or downlink between each NW node 100. For example, it controls the transmission of an uplink reference signal to acquire feedback information (uplink CSI estimation result) from the NW node 100. It also controls the reception and analysis of a downlink reference signal from the NW node 100 to acquire the downlink CSI estimation result and provide feedback to the NW node 100.

[0094] <A mechanism that estimates CSI by complementaryly utilizing uplink / downlink reference signals> As described above, this embodiment provides a mechanism for estimating the CSI by complementaryly utilizing the uplink / downlink reference signals. This mechanism will be explained in the following two cases. • Case 1: Procedure for applying the estimated CL-CSI to the transmission of downlink signals. Case 2: Procedure for applying the estimated CL-CSI to the transmission of the uplink signal.

[0095] (Case 1: Procedure for applying the estimated CL-CSI to the transmission of downlink signals)

[0096] Figure 4 shows an example of the procedure sequence in Case 1. More specifically, Figure 4 shows the CL-CSI estimation sequence when multiple NW nodes 100 (NW nodes 1 to N) exist. The operation of this sequence is controlled by the control unit 150 of the network device 10 (NW node 100 or control device 300) and the control unit 250 of the terminal device 200. Figure 5 shows an example of the exchange of reference signals (downlink reference signal and uplink reference signal) between the terminal device 200 and each NW node 100 when the procedure in Figure 4 is applied. The multiple NW nodes 100 correspond to multiple communication points in a wireless network that includes multiple communication points capable of coordinating communication.

[0097] In Figure 4, the control unit 150 of the control device 300 sets the transmission settings for the uplink reference signal and downlink reference signal via at least one NW node 100 using RRC / MAC-CE / DCI, etc. (S110). The receiving unit 252 of the terminal device 200 transmits the uplink reference signal at a timing or period according to the transmission settings (S120). The uplink reference signal may be transmitted for each frequency domain in which CSI is to be estimated, or it may be transmitted in a single frequency domain that encompasses these frequency domains. The uplink reference signal is received by the receiving units 152 of all NW nodes 100 present around the terminal device 200. That is, in self-free communication, multiple NW nodes are present around the terminal and are wirelessly connected to the terminal device 200 during the initial procedure performed in advance or during the subsequent handover (switching some of the multiple connected NW nodes). These NW nodes receive the uplink reference signal transmitted from the terminal device 200 with their respective receiving units 152.

[0098] Here, each NW node 100 is located in a physically different position, or at least there is no QCL relationship between the antenna ports of these NW nodes 100. Therefore, the channel states of these NW nodes 100 are completely different, and the quality of the uplink reference signal received by each is also different.

[0099] The control unit 150 of each NW node 100 estimates the CSI based on the received uplink reference signal (S130). The CSI estimation can also be performed by the control device 300. The CSI estimated by the NW node 100 based on the uplink reference signal corresponds to the first channel status information of this disclosure.

[0100] The control device 300 or the control unit 150 of each NW node 100 determines the channel quality (reception quality of the uplink reference signal) based on the CSI estimated at each NW node 100, and determines which of the multiple NW nodes 100 will transmit the downlink reference signal to the terminal device 200 (S140). That is, the control device 300 determines for each NW node whether to use the CSI estimated from the uplink reference signal or the CSI estimated from the downlink reference signal, as the CSI estimation result to be applied to the transmission of the downlink signal in step S190, which will be described later.

[0101] In other words, the transmission power of terminal device 200 is basically smaller than the transmission power of NW node 100. Therefore, even if the quality of the uplink reference signal received by NW node 100 is poor, sufficient quality can be obtained for the downlink signal transmission, even if the same channel conditions as for the uplink reference signal transmission are assumed. Furthermore, for other reasons, it is possible that even if the quality of the uplink reference signal is poor, sufficient quality can be obtained for the downlink signal transmission. For this reason, if it is not suitable to use the CSI estimated from the uplink reference signal, the CSI is obtained using the downlink reference signal, as described later.

[0102] As a specific example of processing, the control unit 150 of the control device 300 or the control unit 150 of each NW node 100 decides whether or not to transmit a downlink reference signal for each NW node 100 based on the channel quality (reception quality) of the uplink reference signal received at each NW node 100. In this case, for example, it is determined whether the channel quality meets the quality conditions, and the NW node 100 whose channel quality does not meet the quality conditions is selected as the NW 100 to transmit the downlink reference signal.

[0103] As another example, the channel quality of the uplink reference signal received by all NW nodes 100 is comprehensively assessed to determine which NW node 100 should transmit the downlink reference signal. Details of the process for determining which NW node 100 should transmit the downlink reference signal based on this comprehensive assessment will be described later.

[0104] In step S140, the NW node 100 (NW nodes 1 and 2 in the example of Figure 4) that has been decided to transmit a downlink reference signal transmits the downlink reference signal to the terminal device 200 in accordance with the decision to transmit the downlink reference signal (S150). The control unit 250 of the terminal device 200 estimates the CSI of the downlink reference signal for each NW node 1 and 2, and the transmission unit 251 of the terminal device 200 transmits (feeds back) the CSI estimation result (analysis result of the downlink reference signal) to NW nodes 1 and 2 (S170). The CSI estimated by the terminal device 200 based on the downlink reference signal corresponds to the second channel status information according to this disclosure.

[0105] The control unit 150 of the control device 300 or the control unit 150 of each NW node 100 determines which CSI estimation result to use for each NW node 100 (NW nodes 1 to N)—the uplink reference signal or the downlink reference signal (S180). That is, it determines which CSI application result to apply to the subsequent transmission of the downlink signal. Basically, for NW nodes 100 that did not transmit a downlink reference signal, the CSI estimation result of the uplink reference signal is selected, and for NW nodes 100 that transmitted a downlink reference signal, the CSI estimation result of the downlink reference signal is selected. However, even for NW nodes 100 that transmitted a downlink reference signal, if there is a reason such as not being able to get feedback from the terminal device 200, the uplink reference signal may also be selected for that NW node 100. Furthermore, for NW nodes 100 that transmitted a downlink reference signal, both the CSI estimation result of the uplink reference signal and the CSI estimation result of the downlink reference signal, for example, the average of the two, may be used as the CSI estimation result between the NW node 100 and the terminal device 200. This process of determining the CSI estimation result to be used for each of the 100 network nodes can also be called CL-CSI estimation.

[0106] Each NW node 100 transmits a downlink signal by applying the determined CSI estimation result (S190). In this way, the transmitting unit 151 of the NW node 100 transmits a downlink signal based on the CSI estimation result of the uplink reference signal if it has not transmitted a downlink reference signal to the terminal device 200, and transmits a downlink signal based on the CSI estimation result of the downlink reference signal if it has transmitted a downlink reference signal to the terminal device 200.

[0107] The following is a specific example of the process of determining which NW node 100 will transmit the downlink reference signal, which is performed in step S140.

[0108] (Example of determining whether or not to send a downlink reference signal for each network node) The control unit 150 of the control device 300 or the control unit 150 of each NW node 100 determines whether the channel quality (received quality) of the uplink reference signal received at each NW node 100 satisfies the quality conditions. For example, it determines whether the path loss of the uplink reference signal is less than a threshold. The threshold is, for example, P [dBm], where P is any real number. For NW nodes 100 whose path loss is above the threshold, it is decided to use the CSI estimation result from the uplink reference signal (and not transmit the downlink reference signal), and for NW nodes 100 whose path loss is below the threshold, it is decided to transmit the downlink reference signal.

[0109] The above threshold may be set in the terminal device 200 by notification from a higher layer such as RRC signaling. In this case, the terminal device 200 may be notified of different values ​​for each NW node. The threshold may also be the average path loss including past measurements. How far back in time the past measurements should be included may be set by notification from a higher layer such as RRC signaling. Also, the threshold does not have to be a single value, but may be a range of values. Channel quality (reception quality) is not limited to path loss, as long as it is an indicator of the quality of some channel. Examples other than path loss are shown below. ·RSRP (Reference Signal Received Power) ·RSRQ (Reference Signal Received Quality) ·RSSI (Received Signal Strength Indicator) ·SINR (Signal-to-Interference-plus-Noise Ratio) • SNR (Signal-to-Noise Ratio) ·SIR (Signal-to-Interference Ratio)

[0110] (An example of determining which network node should transmit the downlink reference signal based on an overall assessment.) The control device 300 determines which NW node 100 should transmit the downlink reference signal by comprehensively determining the channel quality of the uplink reference signal received by all NW nodes 100. Examples of determining the NW node 100 by comprehensive determination are shown as Determination Example 1 and Determination Example 2.

[0111] Figure 6 illustrates the first example of judgment. For simplicity, the case of two NW nodes 100 is used as a prerequisite (referred to as NW node 1 and NW node 2, respectively). The figure shows the channel quality (SINR) of the uplink reference signal measured at each NW node 100 across three frequency domains. The threshold for determining channel quality is indicated by a horizontal line. This example describes the case where the same threshold is used at each NW node 100. Channel quality (SINR) is included in the CSI, which is measured at each NW node 100 based on the uplink reference signal. The CSI is calculated by measuring the uplink reference signal received at each NW node 100 across multiple frequency domains (frequency resources), and the distribution of channel quality (SINR) across multiple frequency domains is illustrated. Due to the influence of frequency selectivity, the channel quality differs for each NW node 100 in each frequency domain. The average value of the channel quality for each frequency domain may be treated as the channel quality for that frequency domain.

[0112] Both NW Node 1 and NW Node 2 have channel quality (SINR) below the threshold in frequency domains 1 and 3. In frequency domain 2, NW Node 2 has channel quality above the threshold, while NW Node 1 has channel quality below the threshold. Therefore, it is decided to use the CSI estimation result of the uplink reference signal from NW Node 2 for frequency domain 2, and to obtain the CSI estimation result by transmitting the downlink reference signal to NW Node 1 for frequency domains 1 and 3. It is decided not to transmit the downlink reference signal to NW Node 2. NW Node 1 is chosen as the NW node to transmit the downlink reference signal because NW Node 1 has better channel quality for the uplink reference signal in frequency domains 1 and 3. Due to the symmetry of the propagation path, it is assumed that NW Node 1 also has higher channel quality for the downlink reference signal. Thus, the NW node with the highest channel quality or a higher value than the predetermined value is determined (selected). However, it is also possible to decide that NW Node 2 is the NW node to transmit the downlink reference signal.

[0113] Here, we assume a situation where it is sufficient to obtain CSI estimation results from at least one NW node 100 in each frequency domain. Therefore, in the example in Figure 6, in the subsequent downlink signal transmission step (S190), it is assumed that the downlink signal is transmitted in frequency domains 1 and 3 by applying the CSI estimation results of the downlink reference signal from NW node 1, and the downlink signal is transmitted in frequency domain 2 by applying the CSI estimation results of the uplink reference signal from NW node 2.

[0114] For frequency domains 1 and 3, where sufficient channel quality CSI estimation results could not be obtained using the uplink reference signal, the CSI estimation results are obtained using the downlink reference signal. In this process, the downlink reference signal is transmitted only to NW node 1, and not to NW node 2, thereby reducing the resources and feedback required for transmitting the downlink reference signal.

[0115] In this determination example 1, it is determined whether the channel quality of multiple NW nodes 100 meets the quality conditions for each of the multiple frequency domains, and based on the determination results for each frequency domain, it is decided whether or not to transmit a downlink reference signal to the terminal device 200. As an example, the control unit 150 of the control device 300 or the control unit 150 of the NW node 100 decides whether or not to transmit a downlink reference signal to the terminal device 200, or determines which NW node to transmit the downlink reference signal to, based on the determination results for each frequency domain of each NW node, including the NW node 100. At this time, a frequency domain in which none of the NW nodes 100 meet the quality conditions is identified, and based on the channel quality of each NW node 100 in the identified frequency domain, it is decided which NW node 100 to transmit the downlink reference signal to the terminal device 200 from. Then, control is performed to transmit the downlink reference signal from the determined NW node 100. For example, in the identified frequency domain, the NW node 100 with the highest channel quality or above a predetermined value may be determined.

[0116] Figure 7 illustrates Judgment Example 2. The preconditions are the same as those for Judgment Example 1 in Figure 6. In frequency domains 1 and 3, the channel quality (SINR) of NW node 1 is higher than the threshold, and in frequency domain 2, the channel quality of NW node 2 is higher than the threshold. In other words, unlike in judgment example 1, when all NW nodes 100 are considered together, a channel quality above the threshold is always obtained in every frequency band. Therefore, in this case, there are no NW nodes that should transmit the downlink reference signal, meaning that it is decided that no NW node should transmit the downlink reference signal. In the subsequent downlink signal transmission step (S190), the downlink signal may be transmitted in frequency domains 1 and 3 by applying the CSI estimation result of the uplink reference signal from NW node 1, and the downlink signal may be transmitted in frequency domain 2 by applying the CSI estimation result of the uplink reference signal from NW node 2.

[0117] As shown in the example in Figure 7, since channel quality above the threshold is always obtained in all frequency bands, there is no need to transmit a downlink reference signal. Therefore, the amount of resources and feedback required to transmit the downlink reference signal can be reduced.

[0118] As shown in Judgment Example 1 and Judgment Example 2, in self-free communication with multiple network nodes, it is possible to combine the multiple network nodes for each frequency domain and assign the best MCS (CSI estimation result) to the network node with the best quality. Therefore, overall throughput is improved compared to when there is only one network node and an MCS (Modulation and Coding Scheme) is assigned to that network node according to its frequency characteristics (CSI estimation result).

[0119] In Judgment Example 1 and Judgment Example 2, one NW node 100 was selected for each frequency domain, but two or more NW nodes 100 may be selected for each frequency domain. Furthermore, the CSI estimation results for both the uplink reference signal and the downlink reference signal may be used for the same NW node 100. Also, as mentioned above, the threshold may not be a single value but a range of values.

[0120] For the NW node 100 determined in step S140, the transmission period of the downlink reference signal (i.e., the period of feedback from the terminal device 200 to the downlink reference signal) may be dynamically adjusted according to the channel quality measured from the uplink reference signal transmitted in step S120. Periodic transmission of the downlink reference signal may occur, for example, after the transmission of the downlink signal (S190). NW node 100 that was not determined to transmit a downlink reference signal in step S140 may periodically transmit an uplink reference signal.

[0121] When adjusting the transmission period of the downlink reference signal, the adjusted period may be dynamically notified to the terminal device 200 using DCI or similar. For example, the period may be 20ms if the path loss is less than 100dB, 10ms if the path loss is between 100dB and 120dB, and 5ms if the path loss is 120dB or more. By adjusting the transmission period of the downlink reference signal according to the channel quality of the uplink reference signal, the transmission frequency of the downlink reference signal and feedback can be appropriately reduced. In addition to DCI, the adjusted period may be notified using RRC or MAC-CE or similar methods.

[0122] After the NW node 100 that will transmit the downlink reference signal is determined in step S140, and before the downlink reference signal is transmitted from that NW node 100, the control device 300 may notify the terminal device 200 of the transmission settings for the downlink reference signal via DCI through at least one of the NW nodes 100. For example, the notification may be made using DCI Format0_0, Format0_1, etc. In this case, the control device 300 may apply different transmission settings to each NW node 100 that transmits the downlink reference signal.

[0123] As described above, according to the Case 1 method shown in Figures 4 and 5, each NW node 100 can reduce the number of unnecessary feedbacks and unnecessary reference signal transmissions by using the CSI estimated using an appropriate reference signal (uplink reference signal or downlink reference signal).

[0124] (TCI state update) A procedure for updating the TCI state may be added to the sequence of Case 1 shown in Figure 4. For example, the processing of this procedure may be additionally performed in step S140. According to this procedure, based on the uplink reference signal transmitted by the terminal device 200, the control unit 150 of the control device 300 or the control unit 150 of each NW node 100 updates the TCI state that defines the QCL relationship between antenna ports for the downlink and notifies the terminal device 200 of the updated TCI state. This improves the flexibility of TCI state management, which was previously determined only by feedback information for downlink reference signals (e.g., CSI-RS and SSB) transmitted from NW nodes. It is expected that the amount of signaling will be reduced because the information from the uplink reference signal, which was not previously used, will be used for downlink transmission as an update to the TCI state.

[0125] In light of the fact that this disclosure will actively utilize uplink reference signals such as SRS for the transmission of downlink signals, new indices related to uplink reference signals such as SRS may be defined in the TCI state, which was previously defined only by CSI-RS and SSB. For example, the following extensions are possible.

[0126] (Example of extension 1: Introduction of a new QCL-Type to the TCI state table) For example, if we designate a new QCL-Type as QCL-Type E, we may include the following parameters in QCL-Type E. • Spatial RX / TX beam information ·Angle of arrival (AoA) • Delayed spread Doppler shift / spread

[0127] Explicitly adding QCL-Type, defined by an uplink reference signal such as SRS, allows for more flexible and broader use than Example 2 of the extension below (where an uplink reference signal is added as an extension of the TCI state).

[0128] (Example of extension 2: Adding SRS resources as reference signals through TCI state extension) For example, add a new reference signal type "srs-RefSignal". Here, srs-RefSignal may include the following information: • srs-ResourceId: An ID that uniquely identifies the SRS resource. • srs-ResourceSetId: The ID of the associated SRS resource set • srs-QclInfo: A new information element containing QCL information based on SRS. Examples of new information elements include: spatial relationship information timingOffset: Timing offset based on SRS frequencyOffset: Frequency offset based on SRS

[0129] (Case 2: Procedure for applying the estimated CL-CSI to the transmission of the uplink signal) First, as a comparative example of this disclosure, we will describe an example in which CSI is estimated and applied to the transmission of an uplink signal.

[0130] The transmission parameters for the uplink signal are primarily optimized based on the CSI obtained by the NW node 100 through analysis of the uplink reference signal transmitted by the terminal device 200. In a TDD system, channel incompatibility is sometimes utilized to apply the CSI obtained by the terminal device 200 through analysis of the downlink reference signal transmitted by the NW node 100 to the optimization of the uplink signal transmission parameters.

[0131] Here, a prime example of an uplink reference signal is the SRS (Sounding Reference Signal). NW node 100 estimates the CSI (Channel Status) by receiving and analyzing the SRS.

[0132] The CSI estimated by NW node 100 mainly includes the following items: Channel coefficient • Signal-to-noise ratio (SNR) • Signal-to-noise ratio (SINR) • Path Loss ·Angle of Arrival (AoA) • Delayed spread Doppler spread

[0133] Based on these CSI estimation results, the optimized transmission parameters for the uplink signal are instructed or notified to the terminal device 200 from the control unit 300 or the network node 100, primarily through DCI (Downlink Control Information) within the PDCCH.

[0134] Examples of transmission parameters instructed to the terminal device 200 are shown below. • Parameters related to time-frequency resource allocation • Transmit Power Control (TPC) command ·TPMI(Transmitted Precoding Matrix Indicator) ·TRI(Transmitted Rank Indicator) ·MCS (Modulation and Coding Scheme) • SRI (SRS Resource Indicator)

[0135] Furthermore, using the TCI-UL (Transmission Configuration Indication for Uplink) state concept, the control unit 300 or the NW node 100 can specify the QCL (Quasi Co-Location) relationship of the uplink, enabling efficient beam management. This allows for transmission in the appropriate beam direction, especially in high-frequency communications.

[0136] When there are many NW nodes 100 connected, such as in self-free communication, a problem arises where the amount of feedback increases when a terminal device 200 transmits an uplink reference signal. Case 2 solves this problem.

[0137] Figure 8 shows an example of the procedure sequence in Case 2. More specifically, Figure 8 shows the CL-CSI estimation sequence when multiple NW nodes 100 (NW nodes 1 to N) exist. The operation of this sequence is controlled by the control unit 150 of the network device 10 (NW node 100 or control device 300) and the control unit 250 of the terminal device 200. Figure 9 shows an example of the exchange of reference signals (downlink reference signal and uplink reference signal) between the terminal device 200 and each NW node 100 when the procedure in Figure 8 is applied.

[0138] In the following explanation, we will omit explanations that overlap with Case 1. In other words, the content explained in the method of Case 1 can be applied to the method of Case 2.

[0139] First, the control device 300 configures the transmission settings for the uplink reference signal and downlink reference signal via at least one NW node 100 using RRC / MAC-CE / DCI or the like (S210). The transmitting unit 151 of each NW node 100 transmits the downlink reference signal at a timing or period according to the transmission settings, and the receiving unit 252 of the terminal device 200 receives these downlink reference signals (S220).

[0140] The control unit 250 of the terminal device 200 estimates the CSI based on the downlink reference signal received from each NW node 100 (S230). The CSI estimated by the terminal device 200 from the downlink reference signal corresponds to the first channel status information according to this disclosure.

[0141] The control unit 250 of the terminal device 200 determines the channel quality (received quality of the downlink reference signal) based on the CSI estimation result of the downlink reference signal received from each NW node 100, and selects or determines the NW node 100 to which the uplink reference signal will be transmitted (S240). In other words, the terminal device 200 decides whether to use the CSI estimated from the downlink reference signal or the CSI estimated from the uplink reference signal, as the CSI estimation result to be applied to the transmission of the uplink signal (S290), which will be described later. Even if the quality of the downlink reference signal received from the NW node 100 is poor (including cases where the downlink reference signal cannot be received), it is assumed that a situation (propagation path environment) in which a more suitable quality can be obtained when transmitting the uplink signal is possible.

[0142] As a concrete example of processing, based on the channel quality of the downlink reference signal received from each NW node 100, it is determined whether or not each NW node 100 is eligible to receive an uplink reference signal. Alternatively, the channel quality of the downlink reference signals received from all NW nodes 100 is comprehensively assessed to determine which NW nodes 100 are eligible to receive an uplink reference signal. These detailed operational examples can be performed using the same methods as in Case 1.

[0143] The transmitting unit 251 of the terminal device 200 transmits an uplink reference signal to the NW node 100 (NW nodes 1 and 2 in the example of Figure 8) determined in step S140 (S250). Upon receiving the uplink reference signal, each NW node 100 estimates the CSI of the uplink reference signal and transmits (feeds back) the estimation result (analysis result of the uplink reference signal) to the terminal device 200 (S270). The CSI estimated at each NW node 100 based on the uplink reference signal corresponds to the second channel status information according to this disclosure.

[0144] The control unit 250 of the terminal device 200 determines for each NW node 100 whether to use the CSI estimation result for the uplink reference signal or the downlink reference signal (S280). That is, it determines which CSI application result to apply to the subsequent transmission of the uplink signal (S290). Basically, for NW nodes 100 that were not targeted to transmit the uplink reference signal (i.e., NW nodes other than the NW node selected in step S240), the CSI estimation result for the downlink reference signal is selected. For NW nodes 100 that were targeted to transmit the uplink reference signal (i.e., the NW node selected in step S240), the CSI estimation result for the uplink reference signal is selected.

[0145] However, even if an NW node 100 is the target of transmitting an uplink reference signal, if there are reasons such as the inability to obtain feedback from the NW node 100, the downlink reference signal may also be selected for that NW node 100. Furthermore, for an NW node 100 that is the target of transmitting an uplink reference signal, it is possible to use both the CSI estimation result of the uplink reference signal and the CSI estimation result of the downlink reference signal, for example, the average of the two, as the CSI estimation result between the NW node 100 and the terminal device 200. This process of determining the CSI estimation result to be used for each NW node 100 may be called CL-CSI estimation.

[0146] The transmitting unit 251 of the terminal device 200 transmits an uplink signal to each NW node 100 by applying the determined CSI estimation result to each NW node (S290). That is, the transmitting unit 251 of the terminal device 200 transmits an uplink signal to the NW node selected in step S240 based on the CSI estimation result of the uplink reference signal, and transmits an uplink signal to the NW node not selected in step S240 based on the CSI estimation result of the downlink reference signal.

[0147] The specific example of the process performed in step S240 described above may be the same as the specific example of step S140 (Figures 6 and 7) described in detail in Figure 4. In the explanation of the specific example of step S140 (Figures 6 and 7), you can read it by swapping the upstream link and the downstream link.

[0148] For example, the control unit 250 of the terminal device 200 may select an NW node 100 whose channel quality does not meet the quality criteria. Alternatively, the control unit 250 of the terminal device 200 may determine whether the channel quality of the NW node 100 meets the quality criteria for each of several frequency domains, and select an NW node 100 to which the uplink reference signal will be transmitted based on the determination results for each frequency domain. For example, the control unit 250 of the terminal device 200 may identify a frequency domain in which none of the NW nodes 100 meet the quality criteria, and select an NW node 100 to which the uplink reference signal will be transmitted based on the channel quality of each NW node 100 in the identified frequency domain. For example, the control unit 250 of the terminal device 200 may select an NW node 100 with the highest channel quality or a channel quality above a predetermined value in the identified frequency domain.

[0149] As described above, according to the sequence in Case 2, the terminal device 200 can estimate the CSI with each NW node 100 using an appropriate reference signal (uplink reference signal or downlink reference signal).

[0150] According to this embodiment, it becomes possible to estimate channel state information by mutually complementarily utilizing the uplink / downlink reference signals, thereby enabling efficient estimation of channel state information.

[0151] (Other embodiments: Control of the transmission timing of the reference signal by a terminal device) In existing standards, the transmission timing of the downlink reference signal and the uplink reference signal is determined by the NW node 100 and notified to the terminal device 200 via RRC / MAC-CE / DCI. The terminal device 200 does not have the authority to determine the transmission timing of the downlink reference signal and the uplink reference signal. However, in self-free communication, it is important to reduce the transmission of reference signals, and for this purpose, a mechanism in which the terminal device 200 determines the transmission timing is considered effective.

[0152] As an example of such a mechanism, particularly in the case of the uplink reference signal, the transmitter 151 of the control device 300 or the transmitter 151 of the NW node 100 may transmit information (control information) indicating a basic period (e.g., 5ms period) to the terminal device 200, and the terminal device 200 may be allowed to freely transmit the uplink reference signal at multiples of that basic period (e.g., 40ms period). Such operation is controlled by the control unit 150 of the network device 10 (NW node 100 or control device 300) and the control unit 250 of the terminal device 200.

[0153] In this case, the NW node 100 or the control device 300 may notify the terminal device 200 in advance of parameters related to period adjustment via RRC / MAC-CE / DCI. Here, these parameters are referred to as Adaptive Periodicity Range (ASPR). The ASPR parameters are added to the existing Periodicity parameters and include, for example, the following basic period, maximum period, maximum multiple, and minimum multiple. Each pair of integers in the range from the minimum multiple to the maximum multiple and the basic period corresponds to multiple candidate values ​​of periods available to the terminal device 200. ·Basic period: Example 5ms ·Maximum cycle: e.g. 40ms • Maximum multiple: Example 8 • Minimum multiple: Example 1 (same as the fundamental period)

[0154] In this example, terminal device 200 can arbitrarily select a period from eight candidates: 5ms, 10ms, 15ms, 20ms, 25ms, 30ms, 35ms, and 40ms. The period setting may differ for each NW node 100.

[0155] Thus, if the terminal device 200 transmits at a frequency that is increased from the basic period by any multiple within the range of minimum multiple and maximum multiple, it can autonomously adjust the transmission frequency of the uplink reference signal without receiving control information (e.g., RRC / MAC-CE / DCI) from the downlink signal. This efficiently reduces the number of uplink reference signal transmissions and thus reduces power consumption. Reducing the number of uplink reference signal transmissions is also effective in suppressing interference to other terminal devices and other NW nodes 100.

[0156] According to this embodiment, the terminal device 200 can semi-autonomously control the transmission timing of the uplink reference signal without relying on control information from the downlink signal, thereby reducing the number of uplink reference signal transmissions.

[0157] The embodiments described above are merely examples of how to implement this disclosure, and it is possible to implement this disclosure in various other forms. For example, various modifications, substitutions, omissions, or combinations thereof are possible without departing from the gist of this disclosure. Such modified, substituted, or omission forms are included within the scope of this disclosure, as well as within the scope of the invention described in the claims and its equivalents.

[0158] Furthermore, the effects described herein are merely illustrative, and other effects may also occur.

[0159] Furthermore, this disclosure may also take the following form. [Item 1] A communication device that communicates with a wireless network including multiple communication points capable of coordinating communication, A receiving unit that receives downlink reference signals from each of the aforementioned multiple communication points, A control unit calculates first channel status information based on the downlink reference signal, and selects a communication point from among the plurality of communication points to be used to transmit the uplink reference signal based on the first channel status information. A transmitting unit that transmits the uplink reference signal to the selected communication point, A communication device equipped with this device. [Item 2] The receiving unit receives second channel status information based on the uplink reference signal from the selected communication point. The transmitting unit transmits an uplink signal to a selected communication point from among the plurality of communication points based on the second channel status information, and transmits the uplink signal to a communication point different from the selected communication point based on the first channel status information. The terminal device described in item 1. [Item 3] The first channel status information includes a value relating to the channel quality of the downlink reference signal, The control unit selects a communication point where the channel quality does not meet the quality requirements. The terminal device described in item 1 or 2. [Item 4] The first channel state information includes a value relating to the channel quality of the downlink reference signal, The control unit determines whether the channel quality of the plurality of communication points satisfies the quality conditions for each of the plurality of frequency domains included in the downlink reference signal, and selects the communication point to be transmitted the uplink reference signal based on the determination result for each frequency domain. A terminal device as described in any one of items 1 to 3. [Item 5] The control unit identifies a frequency range in which none of the communication points meet the quality conditions, and selects a communication point to which the uplink reference signal will be transmitted, based on the channel quality of the identified frequency range for each communication point. The terminal device described in item 4. [Item 6] The control unit selects a communication point in the specified frequency range where the channel quality is highest or equal to or greater than a predetermined value. The terminal device described in item 5. [Item 7] The control unit selects one period from a plurality of candidate values ​​for the period for transmitting the uplink reference signal, based on the first channel state information or the second channel state information of the selected communication point. The transmitting unit transmits the uplink reference signal to the selected communication point at the selected period. The terminal device described in item 2. [Item 8] The receiving unit receives control information specifying a plurality of candidate values ​​for the period with respect to the selected communication point. The control unit acquires a plurality of candidate values ​​for the period based on the control information. The terminal device described in item 7. [Item 9] One of the multiple network devices that constitute a wireless network including multiple network devices capable of coordinating communication, A receiving unit that receives an uplink reference signal transmitted from a communication device to the plurality of network devices, A control unit that acquires first channel status information based on the uplink reference signal and determines whether or not to transmit a downlink reference signal to the communication device based on the first channel status information, A transmitting unit that transmits the downlink reference signal to the communication device in response to the decision to transmit the downlink reference signal, A network device equipped with the following features. [Item 10] The receiving unit receives second channel status information based on the downlink reference signal from the communication device. The transmitting unit transmits a downlink signal based on the first channel status information if the downlink reference signal has not been transmitted to the communication device, and transmits the downlink signal based on the second channel status information if the downlink reference signal has been transmitted to the communication device. The network device described in item 9. [Item 11] The first channel status information includes a value relating to the channel quality of the uplink reference signal, The control unit decides to transmit the downlink reference signal to the communication device if the channel quality does not meet the quality requirements. Network devices as described in item 9 or 10. [Item 12] The first channel status information includes a value relating to the channel quality of the uplink reference signal, The control unit determines whether the channel quality satisfies the quality conditions for each of the multiple frequency domains included in the uplink reference signal, and determines whether or not to transmit the downlink reference signal to the communication device based on the determination result for each frequency domain for each network device. A network device as described in any one of items 9-11. [Item 13] The control unit identifies the frequency range in which none of the network devices meet the quality requirements, determines which network device will transmit the downlink reference signal to the communication device based on the channel quality of each network device in the identified frequency range, and controls the device to transmit the downlink reference signal from the determined network device. The network device described in item 12. [Item 14] The control unit selects a network device with the highest or above-predetermined channel quality in the specified frequency range. The network device described in item 13. [Item 15] The transmitting unit transmits control information specifying a plurality of candidate values ​​for the period of transmission of the uplink reference signal, thereby causing the communication device to transmit the uplink reference signal at a period arbitrarily selected from the plurality of candidate values. A network device as described in any one of items 9-14. [Item 16] The control unit updates the TCI (Transmission Configuration Indicator) state, which defines the QCL (Quasi Co-Location) relationship between antenna ports for the downlink, based on the uplink reference signal. A network device as described in any one of items 9 through 15. [Item 17] A communication method for communicating with a wireless network that includes multiple communication points capable of coordinating communication, The downlink reference signal is received from each of the aforementioned multiple communication points. Based on the downlink reference signal, first channel status information is calculated, and based on the first channel status information, a communication point is selected from the plurality of communication points to be the target of transmission of the uplink reference signal. The uplink reference signal is transmitted to the selected communication point. Communication method. [Item 18] A communication method performed on one of the multiple network devices that constitute a wireless network including multiple network devices capable of coordinating communication, The communication device receives the uplink reference signal transmitted to the plurality of network devices, Based on the aforementioned uplink reference signal, first channel status information is acquired, and based on the aforementioned first channel status information, it is determined whether or not to transmit a downlink reference signal to the communication device. In response to the decision to transmit the downlink reference signal, the communication device is instructed to transmit the downlink reference signal. Communication method. [Explanation of Symbols]

[0160] 1 NW node 2 NW nodes 3 Network Nodes 4 Network Nodes 10 Network devices 100 Network Nodes 110 communication points 120 Wireless Communication Section 121 Signal transmission unit 122 Signal receiving section 130 Network Communications Department 140 Storage section 150 Control Unit 151 Transmitter 152 Receiving Unit 200 terminal devices 300 Control device 210 Antenna 220 Wireless Communication Section 221 Signal transmission unit 222 Signal receiving section 240 Storage section 250 Control Unit 251 Transmitter 252 Receiving Unit

Claims

1. A communication device that communicates with a wireless network including multiple communication points capable of coordinating communication, A receiving unit that receives downlink reference signals from each of the aforementioned multiple communication points, A control unit calculates first channel status information based on the downlink reference signal, and selects a communication point from among the plurality of communication points to be used to transmit the uplink reference signal based on the first channel status information. A transmitting unit that transmits the uplink reference signal to the selected communication point, A communication device equipped with this device.

2. The receiving unit receives second channel status information based on the uplink reference signal from the selected communication point. The transmitting unit transmits an uplink signal to a selected communication point from among the plurality of communication points based on the second channel status information, and transmits the uplink signal to a communication point different from the selected communication point based on the first channel status information. The communication device according to claim 1.

3. The first channel status information includes a value relating to the channel quality of the downlink reference signal, The control unit selects a communication point where the channel quality does not meet the quality requirements. The communication device according to claim 1.

4. The first channel status information includes a value relating to the channel quality of the downlink reference signal, The control unit determines whether the channel quality of the plurality of communication points satisfies the quality conditions for each of the plurality of frequency domains included in the downlink reference signal, and selects the communication point to be transmitted the uplink reference signal based on the determination result for each frequency domain. The communication device according to claim 1.

5. The control unit identifies a frequency range in which none of the communication points meet the quality conditions, and selects a communication point to which the uplink reference signal will be transmitted, based on the channel quality of the identified frequency range for each communication point. The communication device according to claim 4.

6. The control unit selects a communication point in the specified frequency range where the channel quality is highest or equal to or greater than a predetermined value. The communication device according to claim 5.

7. The control unit selects one period from a plurality of candidate values ​​for the period of transmission of the uplink reference signal, based on the first channel state information or the second channel state information of the selected communication point. The transmitting unit transmits the uplink reference signal to the selected communication point at the selected period. The communication device according to claim 2.

8. The receiving unit receives control information specifying a plurality of candidate values ​​for the period with respect to the selected communication point. The control unit acquires a plurality of candidate values ​​for the period based on the control information. The communication device according to claim 7.

9. One of the multiple network devices that constitute a wireless network including multiple network devices capable of coordinating communication, A receiving unit that receives an uplink reference signal transmitted from a communication device to the plurality of network devices, A control unit that acquires first channel status information based on the uplink reference signal and determines whether or not to transmit a downlink reference signal to the communication device based on the first channel status information, A transmitting unit that transmits the downlink reference signal to the communication device in response to the decision to transmit the downlink reference signal, A network device equipped with the following features.

10. The receiving unit receives second channel status information based on the downlink reference signal from the communication device. The transmitting unit transmits a downlink signal based on the first channel status information if the downlink reference signal has not been transmitted to the communication device, and transmits the downlink signal based on the second channel status information if the downlink reference signal has been transmitted to the communication device. The network device according to claim 9.

11. The first channel status information includes a value relating to the channel quality of the uplink reference signal, The control unit decides to transmit the downlink reference signal to the communication device if the channel quality does not meet the quality requirements. The network device according to claim 9.

12. The first channel status information includes a value relating to the channel quality of the uplink reference signal, The control unit determines whether the channel quality satisfies the quality conditions for each of the multiple frequency domains included in the uplink reference signal, and determines whether or not to transmit the downlink reference signal to the communication device based on the determination result for each frequency domain for each network device. The network device according to claim 9.

13. The control unit identifies the frequency range in which none of the network devices meet the quality requirements, determines which network device will transmit the downlink reference signal to the communication device based on the channel quality of each network device in the identified frequency range, and controls the device to transmit the downlink reference signal from the determined network device. The network device according to claim 12.

14. The control unit selects a network device with the highest or above-predetermined channel quality in the specified frequency range. The network device according to claim 13.

15. The transmitting unit transmits control information specifying a plurality of candidate values ​​for the period of transmission of the uplink reference signal, thereby causing the communication device to transmit the uplink reference signal at a period arbitrarily selected from the plurality of candidate values. The network device according to claim 9.

16. The control unit updates the TCI (Transmission Configuration Indicator) state, which defines the QCL (Quasi Co-Location) relationship between antenna ports for the downlink, based on the uplink reference signal. The network device according to claim 9.

17. A communication method for communicating with a wireless network that includes multiple communication points capable of coordinating communication, The downlink reference signal is received from each of the aforementioned multiple communication points. Based on the downlink reference signal, first channel status information is calculated, and based on the first channel status information, a communication point is selected from the plurality of communication points to be the target of transmission of the uplink reference signal. The uplink reference signal is transmitted to the selected communication point. Communication method.

18. A communication method performed on one of the multiple network devices that constitute a wireless network including multiple network devices capable of coordinating communication, The communication device receives the uplink reference signal transmitted to the plurality of network devices, Based on the aforementioned uplink reference signal, first channel status information is acquired, and based on the aforementioned first channel status information, it is determined whether or not to transmit a downlink reference signal to the communication device. In response to the decision to transmit the downlink reference signal, the communication device is instructed to transmit the downlink reference signal. Communication method.

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