Communication device, network device, and communication method

Abstract

A communication device comprising circuitry configured to receive downlink reference signals from a plurality of network nodes and estimate first channel state information and channel quality for each node. The circuitry is further configured to select a subset of the network nodes to which an uplink reference signal is transmitted based on the channel quality, and to transmit the uplink reference signal to the subset. The device receives feedback information including second channel state information estimated by the subset based on the uplink reference signal, and applies channel state information for communication with each of the plurality of network nodes based on at least one of the first channel state information and the second channel state information.

Description

COMMUNICATION DEVICE, NETWORK DEVICE, AND COMMUNICATION METHODCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of Japanese Priority Patent Application JP 2024-231077 filed on December 26, 2024, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a communication device, a network device, and a communication method.

[0003] Wireless access schemes and wireless networks for cellular mobile communication (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 TerrestrialRadio Access (EUTRA)”, or “Further EUTRA (FEUTRA)”) have been studied in the 3rd Generation Partnership Project (3GPP). Note that, 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 evolved NodeB (eNodeB). In NR, the base station device is also referred to as a gNodeB. Furthermore, in LTE and NR, a terminal device (mobile station, mobile station device, and terminal) is also referred to as user equipment (UE). LTE and NR are cellular communication systems in which a plurality of areas covered by the base station device is arranged in a cell shape. A single base station device may manage a plurality of cells.

[0004] NR is a radio access technology (RAT) different from LTE as a next-generation wireless access system for LTE. NR is an access technology that can cope with various use cases including enhanced mobile broadband (eMBB), massive machine type communications (mMTC), and ultra reliable and low latency communications (URLLC). In NR, standardization of supporting a technical framework corresponding to a usage scenario, a requirement condition, an arrangement scenario, and the like in those use cases has been advanced.

[0005] In recent years, in Release-19 of 3GPP, a next-generation wireless communication standard (6G, Beyond 5G) has been discussed, and there is a demand for further enhancements beyond NR, including high-speed communication, low-latency and high-reliability communication, high-dense massive communication, and simultaneous support of a plurality of these. In order to achieve the demand, further improvement in frequency utilization efficiency is required. Utilization of radio waves in a higher frequency band is one solution thereof, but since a propagation distance is shorter than that in a low frequency band, there is a problem that a communication area that can be covered by one base station device is reduced. As a means for solving this problem, a form of cell-free communication is promising.

[0006] In the conventional cellular wireless communication, a cell structure centered on one base station device is basic. A system in which each base station device covers a specific area (cell) and communicates with a terminal in the area has been common. However, particularly after 5G, not only one base station device but also network (NW) nodes by non-terrestrial network (NTN), integrated access and backhaul (IAB), or the like have been diversified for further communication requests.

[0007] In communication after 6G, it is expected that this diversification is further promoted, a large number of RUs are geographically dispersedly arranged by sharing roles (central unit (CU) / distributed unit (DU) / radio unit (RU) separation) of functions of one base station device, and use of an inter-terminal relay and a reconfigurable intelligent surface (RIS) is developed. Therefore, the terminal device is flexibly connected to surrounding communication resources without depending on a fixed cell structure, and an optimal communication path can be dynamically formed. Such communication or a mechanism thereof is called cell-free communication.

[0008] In 6G and later, as the cell-free communication, a form in which a plurality of NW nodes cooperatively performs communication with one terminal is expected.

[0009] In order to efficiently perform wireless communication, it is essential to estimate channel state information (CSI) between each NW node and the terminal device. CSI estimation enables appropriate selection of beamforming, precoding, and modulation / coding schemes, thereby achieving improvement in communication quality and maximization of system capacity.

[0010] Basically, the CSI is determined in a one-to-one relationship between the NW node and the terminal device, and in the existing standard, dedicated reference signals are defined for both the downlink and the uplink in order to estimate the CSI.

[0011] In the cell-free communication, it is assumed that the number of NW nodes communicating with the terminal device becomes large, but even in a case where the number of NW nodes increases as described above, estimation of CSI is important.

[0012] Japanese Translation of PCT International Application Publication No. 2024-504145WO 2019 / 168049 ASummary

[0013] The CSI is obtained by transmitting a specified specific reference signal and analyzing the signal at a receiving side. The reference signal transmitted in the downlink is referred to as a downlink reference signal, and the reference signal transmitted in the uplink is referred to as an uplink reference signal.

[0014] Examples of the downlink reference signal include channel state information reference signal (CSI-RS). The CSI-RS is a reference signal transmitted from the NW node, and the terminal device analyzes the received reference signal and feeds back an analysis result to the NW node. Therefore, the configuration of the downlink transmission is optimized on the NW node side.

[0015] In a situation in which the terminal device is connected to a plurality of NW nodes, the terminal device needs to analyze the downlink reference signal from each NW node and feed back a result. Therefore, in a form in which the number of NW nodes increases as in the cell-free communication, there is a concern that an overhead due to an increase in the amount of feedback accompanying an increase in the number of NW nodes causes a decrease in communication throughput.

[0016] Examples of the uplink reference signal include a sounding reference signal (SRS). The SRS is a reference signal transmitted from the terminal device, and the NW node analyzes the received signal and uses the analysis result (CSI estimation result) to optimize the configuration of uplink or downlink transmission. In a frequency division duplex (FDD) system using different frequency bands in the uplink and the downlink, the CSI estimation result is used only to optimize uplink communication. On the other hand, in a time division duplex (TDD) system using the same frequency band in the uplink and the downlink, the CSI estimation result can be used to optimize both uplink and downlink communication for channel complementarity.

[0017] In a situation where the terminal device is connected to a plurality of NW nodes, in a case where the uplink communication is optimized by using the estimation result for the uplink reference signal, it is necessary to feed back the CSI estimation result from each NW node to the terminal device. In this case, in a form in which the number of NW nodes connected to the terminal device increases as in the cell-free communication, there is a concern that an overhead due to an increase in the amount of feedback accompanying an increase in the number of NW nodes causes a decrease in the communication throughput.

[0018] In the case of the operation in the TDD system, the estimation result for the uplink reference signal can also be used for optimization of downlink transmission. In this case, since the received uplink reference signal is merely analyzed and used on the NW node side, feedback to the terminal side is not necessary, or the amount of feedback is extremely small.

[0019] In the cell-free communication, operation in a high frequency band is assumed, ant thus the operation in the TDD system is expected. Thus, in estimating CSI in downlink communication, both methods using a downlink reference signal such as CSI-RS and an uplink reference signal such as SRS can be used. As described above, in a case where the CSI is estimated using the downlink reference signal, an increase in the amount of feedback from the terminal becomes a problem. However, in a case where the uplink reference signal is used not only for the optimization of the uplink transmission but also for the optimization of the downlink transmission, the problem of an increase in the amount of feedback from the terminal can be suppressed by omitting the transmission of the downlink reference signal. However, in this case, there is a concern about a problem such as an increase in power consumption of the terminal due to an increase in the number of times of transmission of the uplink reference signal.

[0020] On the other hand, in the existing standard, in the CSI estimation in the uplink communication, a rough channel state such as a spatial characteristic can be acquired by using the analysis result of the downlink reference signal such as the CSI-RS, but basically, the channel state information in the link communication can be obtained only by analyzing the uplink reference signal such as the SRS. Therefore, in a case where the terminal device is connected to a plurality of NW nodes, all the NW nodes need to feed back the analysis result of the uplink reference signal to the terminal device, and a feedback amount increases.

[0021] As described above, the existing standard is not sufficient in terms of the complementary use of downlink reference signal and uplink reference signal. In other words, in the existing standard, efficient CSI estimation is not performed, and in the cell-free communication in which the number of NW nodes increases, it is expected that the problem of an increase in the amount of feedback remarkably appears.

[0022] In view of such a situation, a method of improving the performance of the entire system and reducing the power consumption of the terminal by performing efficient CSI estimation is desired.

[0023] PTL 1 described above describes a method of measuring covariance of DL interference power by using a CSI-RS resource and precoding an SRS signal on the basis of the covariance. This method is described in terms of reducing the overhead by frequency complement of the SRS signal using the CSI-RS signal, and there is no description about an operation at the time of application to a case where there is a plurality of NW nodes.

[0024] PTL 2 described above describes a method of specifying a CSI-RS complementarily used in determining a precoder of an uplink signal on the basis of a temporal correlation. However, there is no description about an operation in a case where there is a plurality of NW nodes.

[0025] In short, PTL 1 and PTL 2 do not describe mutual complementation of CSI of uplink / downlink reference signals in a case where there is a plurality of NW nodes. In a case where the technologies of PTL 1 and PTL 2 are applied as they are in the cell-free communication, there is a possibility of causing a decrease in throughput.

[0026] In order to solve the above-described problem, the present disclosure provides a communication device, a network device, and a communication method capable of efficiently acquiring channel state information.

[0027] A communication device comprising circuitry configured to receive downlink reference signals from a plurality of network nodes and estimate first channel state information and channel quality for each node. The circuitry is further configured to select a subset of the network nodes to which an uplink reference signal is transmitted based on the channel quality, and to transmit the uplink reference signal to the subset. The device receives feedback information including second channel state information estimated by the subset based on the uplink reference signal, and applies channel state information for communication with each of the plurality of network nodes based on at least one of the first channel state information and the second channel state information.

[0028] Infrastructure equipment comprising circuitry configured to acquire first channel state information from uplink reference signals received by each of a plurality of network nodes from a communication device. The circuitry is further configured to select a subset of the network nodes to transmit a downlink reference signal to the communication device based on the first channel state information, and to cause the subset to transmit the downlink reference signal. The equipment acquires feedback information including second channel state information estimated by the communication device based on the downlink reference signal, and applies channel state information for communication with the communication device from each network node based on at least one of the first and second channel state information.

[0029] Fig. 1 is an explanatory diagram of a comparative example of the present disclosure.Fig. 2 is a block diagram illustrating an example of a network device according to the present embodiment.Fig. 3 is a block diagram illustrating an example of a terminal device as a communication device according to the present embodiment.Fig. 4 is a diagram illustrating a sequence example of a procedure in Case 1.Fig. 5 is a diagram illustrating an example of reference signal exchange between the terminal device and each NW node in Case 1.Fig. 6 is a diagram for explaining a first determination example.Fig. 7 is a diagram for explaining a second determination example.Fig. 8 is a diagram illustrating a sequence example of a procedure in Case 2.Fig. 9 is a diagram illustrating an example of reference signal exchange between the terminal device and each NW node in Case 2.

[0030] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Although main configuration parts of the present disclosure device will be mainly described below, the present disclosure may have a configuration part or function that is not illustrated or described. The following description is not intended to exclude components and functions that are not illustrated or described.

[0031] <Description of terms related to present disclosure> Terms used in the description of the present embodiment will be described.

[0032] <Channel state information (CSI)> Channel state information (CSI) is an index indicating the quality and characteristics of a wireless channel in a NR system. The CSI is used in both downlink and uplink. The CSI is utilized for various wireless resource management functions, such as adaptive modulation and coding (AMC), scheduling, and beamforming, to realize efficient communication.

[0033] Downlink CSI is mainly acquired by the terminal device through measurement of a reference signal such as a CSI-RS or an SSB. On the other hand, uplink CSI is mainly acquired by an NW node such as a base station on the basis of measurement of a sounding reference signal (SRS). The downlink CSI mainly includes elements (items) such as a channel quality indicator (CQI), a precoding matrix indicator (PMI), a rank indicator (RI), a CSI resource indicator (CRI), and a layer indicator (LI). The uplink CSI includes elements such as a transmitted precoding matrix indicator (TPMI), an SRS resource indicator (SRI), and a transmitted rank indicator (TRI).

[0034] A process of obtaining and utilizing the CSI starts with transmission of a reference signal, and proceeds in the following flow: estimation (calculation) of channel state information (CSI) at a receiving side, reporting of the CSI (or processing at a base station), optimization of transmission parameters, notification of optimized transmission parameters, and application of a CSI estimation result to a next transmission. This process is applied to both downlink and uplink, and is adjusted according to respective characteristics.

[0035] The CSI-related configuration is performed through RRC signaling. CSI-RS configuration or CSI report configuration are main targets in the downlink, and SRS configuration is main targets in the uplink. These configurations are designated by using a CSI-ReportConfig information element in NR-RRC-Definitions. There are three types of CSI reports: periodic, semi-persistent, and aperiodic, and the CSI reports are selectively used according to applications and situations.

[0036] The CSI also affects optimization of transmission parameters, selection of a transmission configuration indication (TCI) state, and selection of a TCI-UL state. The TCI state and the TCI-UL state designate a quasi co-location (QCL) relationship with a reference signal used for transmission of a downlink / uplink signal, and are dynamically indicated through the DCI. Therefore, optimal beam selection and precoding can be performed on the basis of the CSI, and the communication quality and efficiency of the entire system can be improved.

[0037] <Uplink reference signal> In the NR, a main uplink reference signal used to estimate channel state information (CSI) is a sounding reference signal (SRS). The SRS plays an important role for quality evaluation, proper scheduling, and precoding of the uplink channel.

[0038] The configuration of the SRS is performed through radio resource control (RRC) signaling. In the RRC signaling, the terminal device is notified of detailed configurations of the SRS resource set and the SRS resource by using an SRS-Config information element. These configurations include a transmission bandwidth, periodicity, a comb structure, the number of antenna ports, and the like.

[0039] After the configuration, the SRS is transmitted separately from a physical uplink shared channel (PUSCH) which is a physical layer channel. A transmission timing of the SRS is determined according to the configured periodicity. In the case of an aperiodic SRS, triggering is performed from the network through the DCI.

[0040] When the terminal device transmits the SRS, the NW node (for example, the base station) receives and analyzes the SRS. In the analysis, a channel impulse response is estimated by using the amplitude and phase information of the received SRS signal. In this procedure, channel characteristics such as path loss, large-scale fading, and small-scale fading are evaluated.

[0041] The NW node determines an optimum parameter (transmission parameter) for uplink transmission, on the basis of the analysis result of the received SRS. This includes resource allocation, a modulation and coding scheme (MCS), a precoding matrix, a transmission rank, and the like.

[0042] The terminal device is notified of the determined parameter mainly through downlink control information (DCI). The DCI is transmitted via a physical downlink control channel (PDCCH). Specifically, a DCI format 0_1, 0_2, or the like is used, and a parameter based on the SRS measurement result is indicated through a field such as SRS Resource Indicator (SRI) or Precoding information and number of layers. Furthermore, regarding the transmission power control, adjustment of the SRS transmission power is instructed through a transmit power control (TPC) command included in the DCI.

[0043] The parameter notified through the DCI is immediately interpreted by the terminal device and applied to the next uplink transmission. The terminal device uses a specific time-frequency resource on the basis of the instructed resource allocation, and selects an appropriate modulation scheme and coding rate according to the designated MCS. The transmission antenna is weighted by using the precoding information, and the number of layers is determined according to the designated transmission rank. Furthermore, transmission power is adjusted according to the TPC command, and a designated antenna port is used. Moreover, a reference signal is generated on the basis of the DMRS configuration and transmitted together with the data. By comprehensively applying these parameters, transmission of the uplink signal optimized for the channel state is realized.

[0044] On the other hand, the analysis result of the SRS is also applied to transmission of a downlink signal in the TDD system. Specifically, a transmission configuration indication (TCI) state is selected on the basis of received power of the SRS transmitted from the terminal device (UE). The TCI state designates a QCL relationship with a reference signal used for PDSCH transmission and is dynamically indicated through DCI. Therefore, by using the reciprocity of the channel, the uplink SRS measurement result is effectively utilized for downlink beam selection and precoding, and the communication quality and efficiency of the entire system are improved.

[0045] <Downlink reference signal> In the NR, main downlink reference signals used to estimate channel state information (CSI) are a channel state information reference signal (CSI-RS) and a synchronization signal block (SSB).

[0046] First, the CSI-RS will be described. The CSI-RS configuration is performed through radio resource control (RRC) signaling. Specifically, the network (for example, an NW node such as a base station) notifies the terminal device of the detailed configurations of the CSI-RS resource set and the CSI-RS resource by using CSI-RS-ResourceConfig and CSI-RS-Resource in the NR-RRC-Definitions. These configurations includes periodicity, an offset, resource mapping, the number of antenna ports, and the like of the CSI-RS.

[0047] The CSI-RS is transmitted separately from a physical downlink shared channel (PDSCH) which is a physical layer channel. A transmission timing of the CSI-RS is determined according to the configured periodicity and offset. Furthermore, in the case of an aperiodic CSI-RS, triggering is performed from an NW node through downlink control information (DCI).

[0048] When the terminal device receives the CSI-RS, the terminal device performs CSI estimation. In this procedure, amplitude and phase characteristics of the channel, a signal-to-noise ratio (SNR), an interference level, and the like are evaluated. The terminal device calculates CSI parameters such as a channel quality indicator (CQI), a precoding matrix indicator (PMI), a rank indicator (RI), and a CSI-RS resource indicator (CRI) on the basis of these measurement results.

[0049] The calculated CSI parameter is mainly reported to the network through a physical uplink control channel (PUCCH) or a physical uplink shared channel (PUSCH). The timing and content of the report are determined on the basis of the CSI report configuration configured by the RRC signaling. Furthermore, in the case of an aperiodic CSI report, triggering is performed through DCI.

[0050] The NW node analyzes the received CSI report and optimizes parameters of downlink transmission. Specifically, the result is used for scheduling, resource allocation, modulation and coding scheme (MCS) selection, determination of a precoding matrix, and the like. These optimized parameters are notified to the terminal device through DCI, and are applied to the next downlink transmission.

[0051] Next, the SSB will be described. The configuration of the SSB is mainly performed through a system information block (SIB1). The SSB includes a primary synchronization signal (PSS), a secondary synchronization signal (SSS), and a physical broadcast channel (PBCH), and is periodically transmitted. The SSB is mainly used for cell detection, initial access, and beam management, but is also used for CSI estimation.

[0052] When receiving the SSB, the terminal device first performs cell detection and initial synchronization by using the PSS and the SSS. Thereafter, reference signal received power (RSRP) and reference signal received quality (RSRQ) are measured. These measurement results are used not only for cell selection and handover determination but also for beam management.

[0053] The measurement result of the SSB is mainly reported to a network (for example, an NW node such as a base station) through RRC signaling (for example, measurement report). The trigger condition and content of the report are determined on the basis of the measurement configuration configured in the RRC signaling.

[0054] The NW node analyzes the received SSB measurement report and utilizes the result for inter-cell interference management, beam selection, mobility control, and the like. The measurement results of the SSB can be used for downlink beamforming. This is realized by using a quasi co-location (QCL) relationship between the SSB and the PDSCH.

[0055] The measurement results of the CSI-RS and SSB are reflected in downlink transmission through the TCI state. Therefore, the network can select an optimal beam direction and precoding on the basis of a measurement result of the terminal device, and improve performance of downlink transmission.

[0056] As described above, the CSI estimation using the CSI-RS and the SSB and the use of the result are realized by a series of flows: the configuration by RRC signaling, the transmission of the reference signal, the measurement by the terminal device, the report of the measurement result, the analysis by the network, and the parameter notification through DCI.

[0057] <Antenna port> An antenna port is a logical entity defined in the 3GPP technical specification, and is different from a physical antenna port. Basically, in the case of being referred to as an antenna port, the antenna port refers to a logical antenna port, and is a concept used to recognize the identity of propagation path characteristics. For example, in the same antenna port, it can be recognized that a propagation path characteristic in one symbol is the same as a propagation path characteristic in another symbol. In the same antenna port, the propagation path characteristics are recognized as the same even between different symbols, but between different antenna ports, the propagation path characteristics are regarded as different unless there is a quasi-co-location (QCL) relationship. The antenna port can associate a specific reference signal with a specific channel, and these are regarded as having the same propagation path characteristic. With this characteristic, the receiving side can estimate the propagation path characteristic by using the reference signal and apply the propagation path characteristic to the reception processing of the related channel.

[0058] <Quasi-co-location> Two antenna ports can be represented as being in quasi-co-location (QCL) in a case where a predetermined condition is satisfied. The predetermined condition is that a global characteristic of a propagation channel carrying a symbol at one antenna port can be inferred from a propagation channel carrying a symbol at another antenna port. The global characteristic includes a delay variance, a Doppler spread, a Doppler shift, an average gain, and / or a mean delay.

[0059] QCL between antenna ports is defined by a transmission configuration indicator (TCI) state. For example, the TCI state includes a parameter that configures a QCL relationship between a downlink reference signal (DMRS) and an antenna port of a PDSCH, a QCL relationship between a downlink reference signal (DMRS) and an antenna port of a PDCCH, or a QCL relationship between a downlink reference signal (DMRS) and an antenna port of a non-zero-power (NZP) CSI-RS resource. The TCI state is defined by following types (1) to (4): (1) QCL-TypeA: {Doppler shift, Doppler broadening, mean delay, delay broadening} (2) QCL-TypeB: {Doppler shift, Doppler broadening} (3) QCL-TypeC: {Doppler broadening, mean delay} (4) QCL-TypeD: {Spatial Rx (Receiver, Reception) parameter} The terminal device designates the TCI state by downlink control information (DCI), medium access control control element (MAC-CE), or radio resource control (RRC) signaling.

[0060] <Resource> The resource represents a frequency, a time, a resource element (including REG, CCE, CORESET), a resource block, a bandwidth part, a component carrier, a symbol, a sub-symbol, a slot, a mini-slot, a subslot, a subframe, a frame, a PRACH occasion, an occasion, a code, a multi-access physical resource, a multi-access signature, a subcarrier spacing (numerology), or the like.

[0061] <CL-CSI(Cross-Link CSI)> In this specification, the CSI obtained by using uplink / downlink reference signals complementarily with each other may be referred to as cross-link CSI (CL-CSI) for convenience sake in order to be distinguished from conventional CSI. The CL-CSI is an extended concept that also includes conventional CSI. Uplink or downlink CSI obtained only from the uplink reference signal is also included in the CL-CSI, and downlink or uplink CSI obtained only from the downlink reference signal is also included in the CL-CSI. Furthermore, the downlink or uplink CSI obtained from both the uplink reference signal and the downlink reference signal is also included in the CL-CSI. Another naming method besides CL-CSI is also possible.

[0062] <NW Node> An NW node is, for example, a node such as a cell, a gNB (base station), a transmission and reception point (TRP), an antenna port, an RU, a set of antenna ports, an IAB node, a relay terminal, or a beam. Furthermore, the NW node may be a node such as a central unit (CU), a distributed unit (DU), or a radio unit (RU). Note that the base station can be implemented not only by a ground base station device but also, for example, by a non-ground base station device that operates as a communication device, such as a satellite station, a drone, a balloon, or an airplane.

[0063] The NW node may be a set of antenna ports that are in the same quasi-co-location (QCL). That is, a set of antenna ports that are in the same quasi-co-location (QCL) may be defined as one node, and this node may be defined as NW.

[0064] The NW node need not be fixed and may be a moving node.

[0065] The NW node does not need to be a node on the ground (terrestrial), and may be a node on the non-ground (non-terrestrial, satellite, drone, UAV).

[0066] Furthermore, the term “NW node group” refers to a set of NW nodes including at least one or more of the NW nodes described above.

[0067] <Uplink signal> The uplink signal refers to a signal and a channel transmitted from the terminal device to the NW node group. In particular, the estimated CSI refers to all signals and channels that are applied during transmission. Examples of the uplink signal 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)

[0068] <Downlink signal> The downlink signal refers to a signal and a channel transmitted from the NW node group to the terminal device. In particular, the estimated CSI refers to all signals and channels that are applied during transmission. Examples of the downlink signal 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)

[0069] <Uplink reference signal> The uplink reference signal refers to a signal and a channel transmitted from the terminal device to the NW node group for CSI estimation. Examples of the uplink reference signal include the following. ・SRS (Sounding Reference Signal)

[0070] <Downlink reference signal> The downlink reference signal refers to a signal and a channel transmitted from the NW node group to the terminal device for CSI estimation. Examples of the downlink reference signal include the following. ・SSB (Synchronization Signal Block) ・CSI-RS (Channel State Information Reference Signal)

[0071] Hereinafter, prior to describing the details of the embodiments of the present technology, a comparative example of the present disclosure will be described in order to understand the problems to be solved by the present embodiment.

[0072] Fig. 1 is an explanatory diagram of the comparative example. A plurality of NW nodes 100, a terminal device 200, and a control device 300 are illustrated. The plurality of NW nodes 100 is nodes on the wireless network side including a plurality of communication points capable of communicating in cooperation, and function as communication points in the cell-free communication. The terminal device 200 can communicate with a wireless network including the plurality of NW nodes 100. In this example, four NW nodes 100 are illustrated, and are also referred to as an NW node 1, an NW node 2, an NW node 3, and an NW node 4 in the case of being distinguished from each other. The control device 300 is, for example, a device which controls the plurality of NW nodes 100, and is, for example, a base station, a DU, or a CU. A downlink reference signal is transmitted to the terminal device 200 from each of the plurality of NW nodes 100 under the control of the control device 300, and the terminal device 200 feeds back the CSI calculated (estimated) from the downlink reference signal, to the plurality of NW nodes 100. The feedback information obtained by the NW node 100 may be analyzed by the NW node 100 or may be provided to the control device 300 and analyzed by the control device 300. Here, a case is assumed in which analysis is performed by the NW node 100. A direction of communication from the NW node 100 to the terminal device 200 corresponds to downstream, and a direction of communication from the terminal device 200 to the NW node 100 corresponds to upstream.

[0073] The transmission parameter of the downlink signal at the time of transmission from the NW node 100 can be optimized on the basis of the CSI report fed back by the terminal device 200, which analyzes the downlink reference signal transmitted by NW node 100. At this time, the CSI report fed back from the terminal device 200 to the NW node 100 is mainly transmitted via the PUCCH or the PUSCH.

[0074] The CSI report reported by the terminal device 200 mainly includes the following contents. ・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 downlink reference signal measurement result

[0075] The transmission parameter optimized on the basis of the CSI report is mainly indicated from the NW node 100 to the terminal device 200 through downlink control information (DCI) in the PDCCH. Examples of the indicated transmission parameter include the following. ・Parameters for time-frequency resource allocation ・Periodicity and offset ・Density (CDM type) ・QCL information ・MCS (Modulation and Coding Scheme) ・Resource such as antenna port used

[0076] Furthermore, it is also possible to designate a reference signal having a quasi co-location (QCL) relationship by using a concept of a transmission configuration indication (TCI) state and to perform efficient beam management. This enables transmission in an appropriate beam direction particularly in communication in a high frequency band.

[0077] Furthermore, in the TDD system, the analysis result of the uplink reference signal is also applied to the transmission parameter optimization of the downlink signal by using the reciprocity of the channel. That is, in this case, the transmission parameter of the downlink signal at the time of transmission from the NW node 100 is optimized on the basis of the CSI report obtained by the NW node 100 analyzing the uplink reference signal transmitted by the terminal device 200.

[0078] (Problems in comparative example) In an environment in which the terminal device 200 is connected to a large number of NW nodes 100, in the operation of transmitting the CSI report from the terminal device 200 on the basis of the analysis result of the downlink reference signal, it is considered that a phenomenon in which the feedback amount increases as the number of NW nodes 100 increases remarkably occurs. In the TDD system, in principle, in a case where the CSI is estimated for the uplink reference signal, it is possible to obtain a CSI estimation result having contents similar to those in a case where CSI is estimated for the downlink reference signal. Therefore, it is also conceivable to suppress the transmission of the downlink reference signal and solve the problem of an increase in the feedback amount by actively using the CSI obtained from the uplink reference signal for the transmission of the downlink signal. However, frequent transmission of the uplink reference signal increases power consumption of the terminal device 200, leading to compression by other uplink data channels.

[0079] In view of the above problems, the present embodiment provides a mechanism for estimating the CSI by complementarily using the uplink reference signal and the downlink reference signal. Therefore, effects such as improvement in communication quality of the entire system and reduction in power consumption of the terminal device 200 are obtained.

[0080] <Configuration of network device> Fig. 2 is a block diagram illustrating an example of a network device 10 according to the present embodiment. The network device 10 is one of a plurality of network devices constituting a wireless network including the plurality of network devices capable of communicating in cooperation. The network device 10 is, for example, a communication device such as the NW node 100 or the control device 300. The network device 10 may be a device which includes both the NW node 100 and the control device 300. In this case, for example, the NW node 100 may be an antenna device including a radio unit (RU), and the control device 300 may be a base station including a central unit (CU) / a distributed unit (DU). 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 forms may be used. The communication device to be communicated by the network device 10 is, for example, the terminal device 200.

[0081] The network device 10 includes 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. Each of the wireless communication unit 120, the network communication unit 130, and the control unit 150 is implemented by, for example, a processor (hardware processor) such as a central processing unit (CPU) or a micro-processing unit (MPU), a processor such as an application specific integrated circuit (ASIC) or a field-programmable gate array (FPGA), or an integrated circuit. The storage unit 140 is implemented by an arbitrary recording medium such as a memory, a hard disk device, an optical disk, or a magnetic recording device. The memory may be a volatile memory or a nonvolatile memory.

[0082] For example, in a case where the network device 10 is the NW node 100 or the control device 300, the communication point 110 may be an antenna. Furthermore, in a case where the network device 10 includes a plurality of NW nodes 100 and the control device 300, each of the communication points 110 may correspond to one NW node 100. Note that the definition of the NW node 100 is as described above.

[0083] The wireless communication unit 120 transmits and receives signals via one or more communication points 110. The signal includes data or information. The wireless communication unit 120 includes a signal transmission unit 121 which transmits a signal and a signal reception unit 122 which receives a signal. For example, the signal transmission unit 121 transmits a downlink signal or a downlink reference signal to the terminal device 200, and the signal reception unit 122 receives an uplink signal or an uplink reference signal from the terminal device 200. The wireless communication unit 120 may form a plurality of beams by a plurality of communication points 110 to communicate with the terminal device 200.

[0084] The network communication unit 130 transmits and receives information to and from another communication device. For example, the network communication unit 130 transmits information to another communication device and receives information from another communication device. The other communication device includes, for example, at least one of the terminal device 200, the NW node 100, the control device 300, the core network, or a node on the Internet.

[0085] The storage unit 140 temporarily or permanently stores programs and data for the operation of the network device 10. Furthermore, the storage unit 140 temporarily or permanently stores information regarding another communication device (the terminal device 200, the NW node 100, the control device 300, or the like) to be communicated.

[0086] The control unit 150 includes a reception unit 152 and a transmission unit 151. The reception unit 152 of the control unit 150 receives data or information from the terminal device 200 via the wireless communication unit 120. The transmission unit 151 of the control unit 150 transmits data or information addressed to the terminal device 200 via the wireless communication unit 120.

[0087] 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 performs control related to the operation performed by the NW node 100 or the control device 300 in the sequence of Fig. 4 or Fig. 8 as described later. For example, the control unit 150 performs control related to acquisition of uplink or downlink channel state information (CSI) from the terminal device 200. For example, control is performed to transmit a downlink reference signal and acquire feedback information (downlink CSI estimation result) from the terminal device 200. Furthermore, control is performed to acquire the uplink CSI estimation result by receiving and analyzing the uplink reference signal from the terminal device 200.

[0088] The control unit 150 acquires information regarding another communication device (the terminal device 200, the NW node 100, the control device 300, or the like). Examples of the information to be acquired by the control unit 150 include, but are not limited to, uplink or downlink channel state information (CSI estimation result) between the terminal device 200 and the NW node 100, and information regarding specifications and capabilities of the terminal device 200.

[0089] <Configuration of terminal device 200> Fig. 3 is a block diagram illustrating an example of the terminal device 200 as the communication device according to the present embodiment. In the present embodiment, the communication device is the terminal device 200, but may be a device, other than the terminal device, such as a device having a relay function (relay device). The terminal device 200 can communicate with a wireless network including a plurality of communication points capable of communicating in cooperation. The terminal device 200 includes one or more antennas 210, a wireless communication unit 220 (transceiver), a storage unit 240, and a control unit 250. Each of the wireless communication unit 220 and the control unit 250 is implemented by, for example, a processor such as a central processing unit (CPU), a micro-processing unit (MPU), an application specific integrated circuit (ASIC), or a field-programmable gate array (FPGA) or an integrated circuit. The storage unit 240 is implemented by an arbitrary recording medium such as a memory, a hard disk device, an optical disk, or a magnetic recording device. The memory may be a volatile memory or a nonvolatile memory.

[0090] The antenna 210 radiates, as a radio wave, a signal output from the wireless communication unit 220 into space. The antenna 210 converts a radio wave in space into a signal and outputs the signal to the wireless communication unit 220. The antenna 210 may be an array antenna having a plurality of antenna elements.

[0091] The wireless communication unit 220 transmits and receives a signal. The signal includes data or information. The wireless communication unit 220 includes a signal transmission unit 221 which transmits a signal and a signal reception unit 222 which receives a signal. For example, signal reception unit 222 receives downlink signals from one or more NW nodes 100. The signal transmission unit 221 transmits uplink signals to one or more NW nodes 100.

[0092] The storage unit 240 temporarily or permanently stores programs and various types of data for the operation of the terminal device 200. The storage unit 240 may store information regarding the network device 10.

[0093] The control unit 250 includes a transmission unit 251 and a reception unit 252. The reception 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 transmission unit 251 transmits data or information addressed to the network device 10 or one or more NW nodes 100, via the wireless communication unit 120.

[0094] The control unit 250 of the terminal device 200 controls the operation of the entire terminal device 200 and provides various functions of the terminal device 200. The control unit 250 performs control related to the operation performed by the terminal device 200 in the sequence of Fig. 4 or Fig. 8 as described later. For example, the control unit 250 performs control related to acquisition of uplink or downlink channel state information (CSI) from each NW node 100. For example, control is performed to transmit an uplink reference signal and acquire feedback information (uplink CSI estimation result) from the NW node 100. Furthermore, control is performed to acquire the downlink CSI estimation result and feed back the result to the NW node 100 by receiving and analyzing the downlink reference signal from the NW node 100.

[0095] <Mechanism for estimating CSI by complementarily using uplink / downlink reference signals> As described above, the present embodiment provides a mechanism for estimating the CSI by complementarily using the uplink / downlink reference signals. This mechanism will be described in following two cases. ・Case 1: Procedure for applying result of estimating CL-CSI in transmission of downlink signal ・Case 2: Procedure for applying result of estimating CL-CSI in transmission of uplink signal

[0096] (Case 1: Procedure for applying result of estimating CL-CSI in transmission of downlink signal)

[0097] Fig. 4 illustrates a sequence example of a procedure in Case 1. More particularly, Fig. 4 illustrates a sequence of CL-CSI estimation in a case where there is a plurality of NW nodes 100 (NW nodes 1 to N). The operation of this sequence is controlled by the control unit 150 of the network device 10 (the NW node 100 or the control device 300) and the control unit 250 of the terminal device 200. Fig. 5 illustrates an example of exchange of reference signals (downlink reference signal and uplink reference signal) between the terminal device 200 and each NW node 100 in a case where the procedure of Fig. 4 is applied. The plurality of NW nodes 100 correspond to a plurality of communication points in a wireless network including the plurality of communication points capable of communicating in cooperation.

[0098] In Fig. 4, the control unit 150 of the control device 300 performs transmission configurations of the uplink reference signal and the downlink reference signal by RRC / MAC-CE / DCI or the like via at least one NW node 100 (S110). The reception unit 252 of the terminal device 200 transmits the uplink reference signal at a timing or a period according to the transmission configuration (S120). The uplink reference signal may be transmitted for every frequency domain in which the CSI is desired to be estimated, or may be transmitted in one frequency domain including these frequency domains. The uplink reference signal is received by the reception units 152 of all the NW nodes 100 existing around the terminal device 200. That is, in the cell-free communication, a plurality of NW nodes is present around the terminal, and are wirelessly connected to the terminal device 200 at the time of an initial procedure performed in advance or at the time of handover (at the time of switching a part of a plurality of connected NW nodes) thereafter. Each of these NW nodes receives the uplink reference signal transmitted from the terminal device 200 by each reception unit 152.

[0099] Here, the NW nodes 100 are disposed at physically different positions, or at least there is no QCL relationship between the antenna ports of these NW nodes 100. Thus, the channel states of these NW nodes 100 are completely different, and the quality of the uplink reference signals received by the NW nodes 100 are also different.

[0100] The control unit 150 of each NW node 100 estimates the CSI on the basis of the received uplink reference signal (S130). The CSI can be estimated by the control device 300. The CSI estimated by the NW node 100 on the basis of the uplink reference signal corresponds to the first channel state information of the present disclosure.

[0101] The control device 300 or the control unit 150 of each NW node 100 determines the channel quality (the reception quality of the uplink reference signal) on the basis of the CSI estimated by each NW node 100, and determines the NW node 100 which transmits the downlink reference signal to the terminal device 200 among the plurality of NW nodes 100 (S140). That is, the control device 300 determines, for every NW node, whether to use the CSI estimated from the uplink reference signal or the CSI estimated from the downlink reference signal as described later, as the CSI estimation result applied to the transmission of the downlink signal in step S190 as described later.

[0102] That is, the transmission power of the terminal device 200 is basically smaller than the transmission power of the NW node 100. Therefore, even if the quality of the uplink reference signal received by the NW node 100 is poor, sufficient quality can be obtained in the downlink signal at the time of downlink signal transmission even if the same channel condition as that at the time of transmission of the uplink reference signal is assumed. In addition, a situation is conceivable in which even if the quality of the uplink reference signal is poor due to other reasons, sufficient quality can be obtained at the time of downlink signal transmission. Therefore, in a case where it is not suitable to use the CSI estimated from the uplink reference signal, the CSI is acquired by using the downlink reference signal as described later.

[0103] As a specific processing example, the control unit 150 of the control device 300 or the control unit 150 of each NW node 100 determines whether or not to transmit the downlink reference signal for every NW node 100, on the basis of the channel quality (reception quality) of the uplink reference signal received by every NW node 100. In this case, for example, it is determined whether the channel quality satisfies the quality condition, and the NW node 100 in which the channel quality does not satisfy the quality condition is selected as the NW 100 which transmits the downlink reference signal.

[0104] For another example, the channel quality of the uplink reference signals received by all the NW nodes 100 are comprehensively determined, and the NW node 100 which transmits the downlink reference signal is determined. Details of the processing of determining the NW node 100, which transmits the downlink reference signal, based on comprehensive determination will be described later.

[0105] The transmission unit 151 of the NW node 100 (in the example of Fig. 4, the NW nodes 1 and 2) determined to transmit the downlink reference signal in step S140 transmits the downlink reference signal to the terminal device 200 in response to the determination 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 of the NW nodes 1 and 2, and the transmission unit 251 of the terminal device 200 transmits (feeds back) the CSI estimation result (the analysis result of the downlink reference signal) to the NW nodes 1 and 2 (S170). The CSI estimated by the terminal device 200 on the basis of the downlink reference signal corresponds to the second channel state information according to the present disclosure.

[0106] The control unit 150 of the control device 300 or the control unit 150 of each NW node 100 determines, for every NW node 100 (NW nodes 1 to N), which one of the CSI estimation results of the uplink reference signal and the downlink reference signal is used (S180). That is, it is determined which CSI application result is applied to subsequent transmission of the downlink signal. Basically, the CSI estimation result of the uplink reference signal is selected for the NW node 100 that has not transmitted the downlink reference signal, and the CSI estimation result of the downlink reference signal is selected for the NW node 100 that has transmitted the downlink reference signal. However, even for the NW node 100 that has transmitted the downlink reference signal, in a case where there is a reason, for example, that feedback cannot be obtained from the terminal device 200, the uplink reference signal may be selected also for the NW node 100. Furthermore, for the NW node 100 that has transmitted the 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, an average of both or the like, may be used as the CSI estimation result between the NW node 100 and the terminal device 200. Determining the CSI estimation result to be used for every NW node 100 in this manner may be referred to as CL-CSI estimation.

[0107] Each NW node 100 transmits the downlink signal by applying the determined CSI estimation result (S190). As described above, the transmission unit 151 of the NW node 100 transmits the downlink signal on the basis of the CSI estimation result of the uplink reference signal in a case where the downlink reference signal is not transmitted to the terminal device 200, and transmits the downlink signal on the basis of the CSI estimation result of the downlink reference signal in a case where the downlink reference signal is transmitted to the terminal device 200.

[0108] Hereinafter, a specific example of processing of determining the NW node 100 which transmits the downlink reference signal will be described, the processing being performed in step S140.

[0109] (Example of determining whether or not to transmit downlink reference signal for every NW node) The control unit 150 of the control device 300 or the control unit 150 of each NW node 100 determines whether or not the channel quality (reception quality) of the uplink reference signal received by each NW node 100 satisfies a quality condition. For example, it is determined whether or not the path loss of the uplink reference signal is less than a threshold. The threshold is, for example, P [dBm]. P is an arbitrary real number. For the NW nodes 100 with a path loss equal to or greater than the threshold, it is determined to use the CSI estimation result by the uplink reference signal (not to transmit the downlink reference signal), and for the NW nodes 100 with a path loss less than the threshold, it is determined to transmit the downlink reference signal.

[0110] The threshold described above may be set in the terminal device 200 by notification from a higher layer such as RRC signaling. At this time, the terminal device 200 may be notified of a different value for every NW node. The threshold may be an average path loss including past measurements. How much past measurement is included may be set by notification from an upper layer such as RRC signaling. Furthermore, the threshold does not need to be a single value, and may be a range of values. Channel quality (reception quality) is not limited to a path loss as long as it is an index indicating quality of a certain channel. Examples other than the 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)

[0111] (Example of determining NW node which transmits downlink reference signal, based on comprehensive determination) The control device 300 determines the NW node 100 which transmits the downlink reference signal, based on the comprehensive determination of the channel quality of the uplink reference signals received by all the NW nodes 100. An example of determining the NW node 100 based on the comprehensive determination will be described as a first determination example and a second determination example.

[0112] Fig. 6 is a diagram for describing the first determination example. As a precondition, a case where there are two NW nodes 100 is treated for the sake of simplicity (NW nodes 1 and 2, respectively). The channel quality (SINR) of the uplink reference signal measured at each NW node 100 is shown in the drawing over three frequency domains. A threshold for determining the channel quality is indicated by a horizontal line. In this example, a case where the same threshold value is used in each NW node 100 is described. The channel quality (SINR) is included in the CSI measured on the basis of the uplink reference signal in each NW node 100. The CSI is obtained by measuring the uplink reference signal received at each NW node 100 over a plurality of frequency domains (frequency resources), and the distribution of channel quality (SINR) over the plurality of frequency domains is illustrated. Due to the influence of the frequency selectivity, the channel quality varies for every NW node 100 over the frequency domains. The average value of the channel quality for every frequency domain may be treated as the channel quality of the frequency domain.

[0113] In both the NW node 1 and the NW node 2, the channel quality (SINR) is lower than the threshold in the frequency domains 1 and 3. In the frequency domain 2, the channel quality of the NW node 2 is higher than the threshold, and the channel quality of the NW node 1 is lower than the threshold. Therefore, it is determined to acquire the CSI estimation result by using the CSI estimation result of the uplink reference signal of the NW node 2 for the frequency domain 2 and transmitting the downlink reference signal to the NW node 1 for the frequency domains 1 and 3. It is determined that the downlink reference signal is not transmitted to the NW node 2. The reason for determining the NW node as the NW node 1 which transmits the downlink reference signal is that the channel quality of the uplink reference signal in the frequency domains 1 and 3 is higher for the NW node 1. Due to the symmetry of the propagation path, it is assumed that the channel quality of the downlink reference signal is also higher for the NW node 1. In this manner, the NW node with channel quality which is the highest or equal to or higher than a predetermined value is determined (selected). However, it is also possible to determine the NW node 2 as the NW node which transmits the downlink reference signal.

[0114] Here, a situation is assumed in which it is sufficient that at least one NW node 100 can acquire the CSI estimation result for every frequency domain. Therefore, in the case of the example of Fig. 6, in the subsequent downlink signal transmission step (S190), it is assumed that the downlink signal is transmitted in the frequency domain 1 and 3 by applying the CSI estimation result of the downlink reference signal from the NW node 1, and the downlink signal is transmitted in the frequency domain 2 by applying the CSI estimation result of the uplink reference signal from the NW node 2.

[0115] For only the frequency domains 1 and 3 in which the CSI estimation result of sufficient channel quality cannot be obtained by the uplink reference signal, the CSI estimation result is obtained by the downlink reference signal. At this time, the downlink reference signal is transmitted only to the NW node 1, and the downlink reference signal is not transmitted to the NW node 2, so that the resource amount and the feedback amount for transmitting the downlink reference signal are reduced.

[0116] As described above, in the first determination example, it is determined whether or not the channel quality of the plurality of NW nodes 100 satisfies the quality condition for the plurality of frequency domains, and it is determined whether or not to transmit the downlink reference signal to the terminal device 200 on the basis of the determination result for every frequency domain. As an example, the control unit 150 of the control device 300 or the control unit 150 of the NW node 100 determines whether or not to transmit the downlink reference signal to the terminal device 200 or determines the NW node which transmits the downlink reference signal, on the basis of the determination result of each NW node including the NW node 100 for every frequency domain. At this time, a frequency domain that does not satisfy the quality condition is specified in any NW node 100, and it is determined which NW node 100 transmits the downlink reference signal to the terminal device 200, on the basis of the channel quality of each NW node 100 in the specified frequency domain. Then, control is performed such that the downlink reference signal is transmitted from the determined NW node 100. For example, the NW node 100 with channel quality which is the highest or equal to or higher than the predetermined value in the specified frequency domain may be determined.

[0117] Fig. 7 is a diagram for explaining second determination example. A precondition is the same as that in the first determination example of Fig. 6. The channel quality (SINR) of the NW node 1 is higher than the threshold in the frequency domains 1 and 3, and the channel quality of the NW node 2 is higher than the threshold in the frequency domain 2. That is, unlike first determination example, when all the NW nodes 100 are combined, channel quality equal to or higher than the threshold value is always obtained in any frequency band. Thus, in this case, it is determined that there is no NW node which transmits the downlink reference signal, that is, no NW node transmits the downlink reference signal. In the subsequent downlink signal transmission step (S190), the NW node 1 may transmit the downlink signal in the frequency domain 1 or 3 by applying the CSI estimation result of the uplink reference signal, and the NW node 2 may transmit the downlink signal in the frequency domain 2 by applying the CSI estimation result of the uplink reference signal.

[0118] As described above, in the example of Fig. 7, channel quality equal to or higher than the threshold is always obtained in any frequency band, so that it is not necessary to transmit the downlink reference signal. Thus, the resource amount and the feedback amount for transmitting the downlink reference signal can be reduced.

[0119] As described in the first determination example and the second determination example, in the cell-free communication in which there is a plurality of NW nodes, it is possible to allocate an excellent MCS (CSI estimation result) to the NW node with the best quality by combining a plurality of NW nodes for every frequency domain. Therefore, as compared with a case where a single NW node is used and a modulation and coding scheme (MCS) corresponding to the frequency characteristic (CSI estimation result) of the NW node is allocated to the NW node, the throughput is improved as a whole.

[0120] Here, in the first determination example and the second determination example, one NW node 100 is selected for every frequency domain, but two or more NW nodes 100 may be selected for every frequency domain. Furthermore, the CSI estimation results of both the uplink reference signal and the downlink reference signal may be used for the same NW node 100. Furthermore, as described above, the threshold value may be a range of values instead of a single value.

[0121] For the NW node 100 determined in step S140, the transmission period of the downlink reference signal (that is, the period of feedback from the terminal device 200 for the downlink reference signal) may be dynamically adjusted according to the channel quality measured from the uplink reference signal transmitted in step S120. The periodic downlink reference signal may be transmitted, for example, after the downlink signal is transmitted (S190). The NW node 100 for which it is not determined to transmit the downlink reference signal in step S140 may periodically transmit the uplink reference signal.

[0122] In a case where the transmission period of the downlink reference signal is adjusted, the terminal device 200 may be dynamically notified of the adjusted period by DCI or the like. For example, the period may be 20 ms in a case where the path loss is less than 100dB, the period may be 10 ms in a case where the path loss is 100dB or more and less than 120dB, and the period may be 5 ms in a case where the path loss is 120dB or more. The transmission frequency of the downlink reference signal and the feedback can be appropriately reduced by adjusting the transmission period of the downlink reference signal according to the channel quality of the uplink reference signal. The notification of the adjusted period may be performed by RRC, MAC-CE, or the like in addition to the DCI.

[0123] After the NW node 100 which transmits the downlink reference signal is determined in step S140 and before the downlink reference signal from the NW node 100 is transmitted, the control device 300 may notify the terminal device 200 of the transmission configuration of the downlink reference signal by the DCI via at least one NW node 100. For example, the notification is performed by DCI Format0_0, Format0_1, or the like. At that time, the control device 300 may apply different transmission configuration for every NW node 100 which transmits the downlink reference signal.

[0124] As described above, according to the method of Case 1 illustrated in Figs. 4 and 5, by using the CSI estimated by each NW node 100 using an appropriate reference signal (uplink reference signal or downlink reference signal), it is possible to reduce the number of times of wasteful feedback and wasteful reference signal transmission.

[0125] (Update of TCI state) A TCI state update procedure may be added to the sequence of Case 1 illustrated in Fig. 4. For example, in step S140, the processing of this procedure may be additionally performed. 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 a TCI state that defines a QCL relationship between the antenna ports related to the downlink, and notifies the terminal device 200 of the updated TCI state. Therefore, it is possible to improve flexibility in managing the TCI state which has been defined only by the feedback information for the downlink reference signal (for example, the CSI-RS and the SSB) transmitted from the NW node in the related art. The information of the uplink reference signal that has not been used in the related art is used for the downlink transmission as the update of the TCI state, so that the amount of signaling is expected to be reduced.

[0126] In view of the fact that the uplink reference signal such as the SRS is actively used for the downlink signal transmission according to the present disclosure, an index related to the uplink reference signal such as the SRS may be newly defined in the TCI state which has been defined only by the CSI-RS and the SSB in the related art. For example, following extension methods are conceivable.

[0127] (Extension example 1: introduction of new QCL-Type to TCI state table) For example, when a new QCL-Type is QCL-Type E, the following parameters may be included in QCL-Type E. ・Spatial RX / TX beam information ・Angle of Arrival (AoA) ・Delay spread ・Doppler shift / spread

[0128] By explicitly adding QCL-Type defined by the uplink reference signal such as the SRS, it is possible to perform flexible and wide use as compared with following extension example 2 (a case where the uplink reference signal is added as an extension of the TCI state).

[0129] (Extension example 2: addition as reference signal of SRS resource by extension of TCI state) For example, a new reference signal type “srs-RefSignal” is added. Here, the srs-RefSignal may include the following information or the like. ・srs-ResourceId: ID for uniquely identifying SRS resource ・srs-ResourceSetId: ID of associated SRS resource set ・srs-QclInfo: new information element containing QCL information based on SRS. Examples of new information elements include the following. spatialRelation: spatial relation information timingOffset: Timing offset based on SRS frequencyOffset: frequency offset based on SRS

[0130] (Case 2: procedure for applying result of CL-CSI estimation to transmission of uplink signal) First, as a comparative example of the present disclosure, an example will be described in which the CSI is estimated and applied to the transmission of the uplink signal.

[0131] The transmission parameter of the uplink signal is optimized mainly on the basis of CSI obtained by the NW node 100 analyzing the uplink reference signal transmitted by the terminal device 200. In the TDD system, the CSI obtained by the terminal device 200 analyzing the downlink reference signal transmitted by the NW node 100 may be applied to the transmission parameter optimization of the uplink signal by using the reciprocity of the channel.

[0132] Here, as a main example of the uplink reference signal, there is a sounding reference signal (SRS). The NW node 100 estimates a channel state (CSI) by receiving and analyzing the SRS.

[0133] The CSI estimated by the NW node 100 mainly includes the following items. ・Channel coefficient ・Signal to noise ratio (SNR) ・Signal to interference plus noise ratio (SINR) ・Path loss ・Angle of Arrival (AoA) ・Delay spread ・Doppler spread

[0134] The uplink signal transmission parameter optimized on the basis of the CSI estimation result is indicated or notified to the terminal device 200 by the control device 300 or the NW node 100 mainly through downlink control information (DCI) in the PDCCH.

[0135] An example of the transmission parameter indicated to the terminal device 200 will be described below. ・Parameters for 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)

[0136] Furthermore, the control device 300 or the NW node 100 can designate a quasi co-location (QCL) relationship in the uplink by using a concept of a transmission configuration indication for uplink (TCI-UL) state and perform efficient beam management. This enables transmission in an appropriate beam direction particularly in communication in a high frequency band.

[0137] In a case where there are a large number of NW nodes 100 to be connected as in the cell-free communication, when the terminal device 200 transmits the uplink reference signal, a problem that the feedback amount increases occurs. Case 2 solves this problem.

[0138] Fig. 8 illustrates a sequence example of a procedure in Case 2. More particularly, Fig. 8 illustrates a sequence of CL-CSI estimation in a case where there is a plurality of NW nodes 100 (NW nodes 1 to N). The operation of this sequence is controlled by the control unit 150 of the network device 10 (the NW node 100 or the control device 300) and the control unit 250 of the terminal device 200. Fig. 9 illustrates an example of exchange of reference signals (downlink reference signal and uplink reference signal) between the terminal device 200 and each NW node 100 in a case where the procedure of Fig. 8 is applied.

[0139] Note that In the following description, a description of a portion overlapping with Case 1 will be omitted. That is, in the method of Case 2, the contents described in the method of Case 1 can be applied.

[0140] First, the control device 300 performs transmission configuration of the uplink reference signal and the downlink reference signal by RRC / MAC-CE / DCI or the like via at least one NW node 100 (S210). The transmission unit 151 of each NW node 100 transmits a downlink reference signal at a timing or a period according to the transmission configuration, and the reception unit 252 of the terminal device 200 receives these downlink reference signals (S220).

[0141] The control unit 250 of the terminal device 200 estimates the CSI on the basis of 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 state information according to the present disclosure.

[0142] The control unit 250 of the terminal device 200 determines the channel quality (the reception quality of the downlink reference signal) on the basis of 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 is to be transmitted (S240). That is, the terminal device 200 determines whether to use the CSI estimated from the downlink reference signal or the CSI estimated from the uplink reference signal as described later as the CSI estimation result applied to the transmission of the uplink signal (S290) as be described later. It is assumed that, even if the quality of the downlink reference signal received from the NW node 100 is poor (including a case where the downlink reference signal cannot be received), a situation (propagation path environment) is conceivable in which more suitable quality can be obtained at the time of uplink signal transmission.

[0143] As a specific processing example, whether or not the NW node 100 is a target for transmitting the uplink reference signal is determined for each NW node 100, on the basis of the channel quality of the downlink reference signal received from each NW node. Alternatively, the channel quality of the downlink reference signals received from all the NW nodes 100 are comprehensively determined, and the NW node 100 to which the uplink reference signal is to be transmitted is determined. As these detailed operation examples, a method similar to Case 1 can be used.

[0144] The transmission unit 251 of the terminal device 200 transmits the uplink reference signal to the NW node 100 (in the example of Fig. 8, NW nodes 1 and 2) determined in step S140 (S250). The NW node 100 that has received the uplink reference signal estimates the CSI of the uplink reference signal, and transmits (feeds back) an estimation result (the analysis result of the uplink reference signal) to the terminal device 200 (S270). The CSI estimated on the basis of the uplink reference signal in each NW node 100 corresponds to the second channel state information according to the present disclosure.

[0145] The control unit 250 of the terminal device 200 determines, for every NW node 100, which one of the CSI estimation results of the uplink reference signal and the downlink reference signal is used (S280). That is, it is determined which CSI application result is applied to subsequent transmission of the uplink signal (S290). Basically, the CSI estimation result of the downlink reference signal is selected for the NW node 100 to which the uplink reference signal is not to be transmitted (that is, the NW node other than the NW node selected in step S240). The CSI estimation result of the uplink reference signal is selected for the NW node 100 to which the uplink reference signal is to be transmitted (that is, the NW node selected in step S240).

[0146] However, even for the NW node 100 to which the uplink reference signal is to be transmitted, in a case where there is a reason, for example, that feedback cannot be obtained from the NW node 100, the downlink reference signal may be selected also for the NW node 100. Furthermore, for the NW node 100 to which the uplink reference signal is to be transmitted, both the CSI estimation result of the uplink reference signal and the CSI estimation result of the downlink reference signal, for example, an average of both or the like, can be used as the CSI estimation result between the NW node 100 and the terminal device 200. Determining the CSI estimation result to be used for every NW node 100 in this manner may be referred to as CL-CSI estimation.

[0147] The transmission unit 251 of the terminal device 200 transmits the uplink signal by applying the determined CSI estimation result to each NW node 100 (S290). That is, the transmission unit 251 of the terminal device 200 transmits the uplink signal to the NW node selected in step S240 on the basis of the CSI estimation result of the uplink reference signal, and transmits the uplink signal to the NW node not selected in step S240 on the basis of the CSI estimation result of the downlink reference signal.

[0148] A specific example of the processing performed in step S240 described above may be similar to the specific example (Figs. 6 and 7) of step S140 described in detail in Fig. 4. In the description of the specific example of step S140 (Figs. 6 and 7), the uplink and the downlink are only required to be interchanged and read.

[0149] As an example, the control unit 250 of the terminal device 200 may select the NW node 100 in which the channel quality does not satisfy the quality condition. Alternatively, the control unit 250 of the terminal device 200 may determine whether or not the channel quality of the NW node 100 satisfies the quality condition for each of the plurality of frequency domains, and select the NW node 100 to which the uplink reference signal is to be transmitted, on the basis of the determination result for every frequency domain. For example, the control unit 250 of the terminal device 200 specifies a frequency domain in which none of the NW nodes 100 satisfies the quality condition, and selects the NW node 100 to which the uplink reference signal is to be transmitted, on the basis of the channel quality of the specified frequency domain for every NW node 100. For example, the control unit 250 of the terminal device 200 may select the NW node 100 with channel quality which is the highest or equal to or higher than the predetermined value in the specified frequency domain.

[0150] As described above, according to the sequence of Case 2, the terminal device 200 can estimate the CSI with each NW node 100 by using an appropriate reference signal (uplink reference signal or downlink reference signal).

[0151] According to the present embodiment, it is possible to estimate the channel state information obtained by using the uplink / downlink reference signals complementarily with each other, thereby efficiently estimating the channel state information.

[0152] (Another embodiment: reference signal transmission timing control by terminal device) In the existing standard, the transmission timing of the downlink reference signal and the transmission timing of the uplink reference signal are determined on the NW node 100 side, and are notified to the terminal device 200 via RRC / MAC-CE / DCI. The terminal device 200 side does not have a right to determine the transmission timing of the downlink reference signal and the transmission timing of the uplink reference signal. However, in the cell-free communication, it is important to reduce the transmission of the reference signal, and for this purpose, a mechanism for determining the transmission timing on the terminal device 200 side is considered to be effective.

[0153] As an example of such a mechanism, in particular, in the uplink reference signal, information (control information) indicating a basic period (for example, 5 ms period) may be transmitted from the transmission unit 151 of the control device 300 or the transmission unit 151 of the NW node 100 to the terminal device 200, and the terminal device 200 may allow the uplink reference signal to be freely transmitted at a multiple of the basic period (for example, 40 ms period). Such an 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.

[0154] At that time, the NW node 100 or the control device 300 may notify the terminal device 200 of parameters related to the adjustment of the period in advance by RRC / MAC-CE / DCI. Here, the parameters are referred to as an adaptive periodicity range (ASPR). The ASPR parameters include, for example, following basic period, maximum period, maximum multiple, and minimum multiple in addition to the parameters of the existing periodicity. A set of each integer in a range from the minimum multiple to the maximum multiple and the basic period corresponds to a plurality of candidate values of the period available to the terminal device 200. ・Basic period: 5 ms, for example ・Maximum period: 40 ms, for example ・Maximum multiple: 8, for example ・Minimum multiple: 1, for example (same as basic period)

[0155] In the case of this example, the terminal device 200 can arbitrarily select a period from eight candidates of 5 ms, 10 ms, 15 ms, 20 ms, 25 ms, 30 ms, 35 ms, and 40 ms. The configuration of the period may be different for each NW node 100.

[0156] As described above, the terminal device 200 can autonomously adjust the transmission frequency of the uplink reference signal without receiving the control information (for example, RRC / MAC-CE / DCI) based on the downlink signal, as long as the transmission is performed in the period increased from the basic period by an arbitrary multiple within a range from the minimum multiple to the maximum multiple. Therefore, the number of times of transmission of the uplink reference signal can be efficiently reduced, and power consumption can be reduced. Reducing the number of times of transmission of the uplink reference signal is also effective in suppressing interference with other terminal devices and other NW nodes 100.

[0157] According to the present embodiment, the terminal device 200 can semi-autonomously control the transmission timing of the uplink reference signal without using the control information based on the downlink signal, and thus the number of times of transmission of the uplink reference signal can be reduced.

[0158] Note that the embodiment described above represents an example for embodying the present disclosure, and the present disclosure can be implemented in various other modes. For example, various modifications, replacements, omissions, or combinations thereof can be made without departing from the gist of the present disclosure. Such modifications, substitutions, omissions, and the like are also included in the scope of the present disclosure, and are similarly included in the technologies disclosed in the claims and the equivalents thereof.

[0159] Furthermore, the effects of the present disclosure described in the present specification are merely an example, and other effects may be achieved.

[0160] Note that the present disclosure can also have the following configuration. (1) A communication device comprising: circuitry configured to: receive downlink reference signals from a plurality of network nodes in a wireless network; estimate first channel state information based on the downlink reference signals received from the plurality of network nodes and determine channel quality for each network node; select a subset of network nodes of the plurality of network nodes to which an uplink reference signal is to be transmitted, based on the determined channel quality; transmit the uplink reference signal to the subset; receive feedback information including second channel state information estimated by the subset based on the uplink reference signal; and apply channel state information for communication with each network node of the plurality of network nodes based on at least one of the first channel state information and the second channel state information. (2) The communication device of (1), wherein the circuitry is configured to select the subset by identifying network nodes in which the channel quality does not satisfy a quality condition. (3) The communication device of (2), wherein the quality condition comprises comparing at least one of path loss, reference signal received power (RSRP), reference signal received quality (RSRQ), received signal strength indicator (RSSI), signal-to-interference-plus-noise ratio (SINR), signal-to-noise ratio (SNR), or signal-to-interference ratio (SIR) to a respective threshold. (4) The communication device of and of (1) to (3), wherein the circuitry is configured to evaluate the channel quality for each network node across a plurality of frequency domains and select the subset based on frequency domain-specific channel quality determinations. (5) The communication device of (4), wherein the circuitry is configured to: specify at least one frequency domain in which none of the plurality of network nodes satisfies a quality condition; and select network nodes for the subset based on having highest channel quality among the plurality of network nodes in the specified at least one frequency domain. (6) The communication device of any of (1) to (5), wherein the circuitry is configured to apply the channel state information by: using the first channel state information for communication with network nodes not included in the selected subset; and using the second channel state information for communication with network nodes included in the selected subset. (7) The communication device of (6), wherein the circuitry is configured to determine transmission parameters for uplink signals to each network node based on the respective channel state information, the transmission parameters including at least one of resource allocation, modulation and coding scheme (MCS), precoding matrix, transmission rank, or transmission power. (8) The communication device of and of (1) to (7), wherein the circuitry is configured to combine the first channel state information and the second channel state information for network nodes included in the selected subset to determine optimized communication parameters. (9) The communication device of and of (1) to (8), wherein the uplink reference signal comprises a sounding reference signal (SRS) and the downlink reference signals comprise at least one of channel state information reference signals (CSI-RS) or synchronization signal blocks (SSB). (10) The communication device of and of (1) to (9), wherein the first channel state information comprises at least one of a channel quality indicator (CQI), a precoding matrix indicator (PMI), a rank indicator (RI), a CSI resource indicator (CRI), layer 1 reference signal received power (L1-RSRP), or layer indicator (LI). (11) The communication device of and of (1) to (10), wherein the second channel state information comprises at least one of a channel coefficient, signal to noise ratio (SNR), signal to interference plus noise ratio (SINR), path loss, angle of arrival (AoA), delay spread, or Doppler spread. (12) The communication device of and of (1) to (11), wherein the circuitry is configured to receive transmission configuration information for the uplink reference signal and the downlink reference signals via at least one of RRC signaling, MAC-CE, or DCI. (13) The communication device of any of (1) to (12), wherein the feedback information includes transmission parameters optimized based on the second channel state information, the transmission parameters comprising at least one of transmitted precoding matrix indicator (TPMI), transmitted rank indicator (TRI), SRS resource indicator (SRI), modulation and coding scheme (MCS), or transmit power control (TPC) command. (14) The communication device of any of (1) to (13), wherein the circuitry is configured to dynamically adjust selection of the subset based on changes in the determined channel quality over time to adapt to varying channel conditions. (15) Infrastructure equipment comprising: circuitry configured to: acquire first channel state information based on uplink reference signal received from a communication device by each network node of a plurality of network nodes; select a subset of the plurality of network nodes to transmit a downlink reference signal to the communication device based on the first channel state information; cause the subset to transmit a downlink reference signal; acquire feedback information including second channel state information estimated by the communication device based on the downlink reference signal transmitted from the subset; and apply channel state information for communication with the communication device from each network node of the plurality of network nodes based on at least one of the first channel state information and the second channel state information. (16) The infrastructure equipment of (15), wherein the circuitry is configured to select the subset by determining which network nodes have channel quality indicated by the first channel state information that does not satisfy a quality condition. (17) The infrastructure equipment of (16), wherein the quality condition comprises comparing path loss indicated by the first channel state information for each network node to a threshold value. (18) The infrastructure equipment of any of (15) to (17), wherein the circuitry is configured to select the subset based on evaluation of the first channel state information from all network nodes of the plurality of network nodes. (19) The infrastructure equipment of (18), wherein the evaluation comprises: evaluating whether channel quality corresponding to the first channel state information of each network node satisfies a quality condition for each of a plurality of frequency domains; and selecting the subset based on evaluation results across the plurality of frequency domains. (20) The infrastructure equipment of (19), wherein the circuitry is configured to: identify at least one frequency domain in which none of the plurality of network nodes satisfies the quality condition; and select network nodes for the subset based on having highest channel quality among the plurality of network nodes in the identified at least one frequency domain. (21) The infrastructure equipment of (19), wherein the circuitry is configured to determine that no network nodes should be selected for the subset when channel quality equal to or higher than a threshold is obtained across all frequency domains by the plurality of network nodes. (22) The infrastructure equipment of any of (15) to (21) , wherein the circuitry is configured to apply the channel state information by: selecting the first channel state information for network nodes not included in the subset; and selecting the second channel state information for network nodes included in the subset. (23) The infrastructure equipment of (22), wherein the circuitry is configured to determine transmission parameters for each network node based on the selected channel state information, the transmission parameters including at least one of resource allocation, modulation and coding scheme (MCS), precoding matrix, transmission rank, or beamforming configuration. (24) The infrastructure equipment of any of (15) to (23), wherein the circuitry is configured to control transmission period of the downlink reference signal for each network node in the subset according to channel quality corresponding to the first channel state information. (25) The infrastructure equipment of any of (15) to (24), wherein the circuitry is configured to update a transmission configuration indication (TCI) state based on the first channel state information and cause notification of the updated TCI state to the communication device. (26) The infrastructure equipment of (25), wherein the updated TCI state includes a new QCL-Type defined by the uplink reference signal, the new QCL-Type including at least one of spatial RX / TX beam information, angle of arrival (AoA), delay spread, or Doppler shift / spread. (27) The infrastructure equipment of any of (15) to (26), wherein the infrastructure equipment is configured to control the plurality of network nodes, and each network node comprises at least one of a base station, a transmission and reception point (TRP), a radio unit (RU), a central unit (CU), a distributed unit (DU), an IAB node, or a relay terminal. (28) The infrastructure equipment of any of (15) to (27), wherein the circuitry is configured to coordinate selection and control functions across the plurality of network nodes via signaling interfaces. (29) The infrastructure equipment of any of (15) to (28), wherein the circuitry is configured to combine the first channel state information and the second channel state information for network nodes included in the subset to determine optimized communication parameters. (30] The infrastructure equipment of any of (15) to (29), wherein the circuitry is configured to control transmission of configuration information for the uplink reference signal and the downlink reference signal to the communication device via at least one of RRC signaling, MAC-CE, or DCI.

[0161] 1 NW node 2 NW node 3 NW node 4 NW node 10 Network device 100 NW node 110 Communication point 120 Wireless communication unit 121 Signal transmission unit 122 Signal reception unit 130 Network communication unit 140 Storage unit 150 Control unit 151 Transmission unit 152 Reception unit 200 Terminal device 300 Control device 210 Antenna 220 Wireless communication unit 221 Signal transmission unit 222 Signal reception unit 240 Storage unit 250 Control unit 251 Transmission unit 252 Reception unit

Claims

1. A communication device comprising: circuitry configured to: receive downlink reference signals from a plurality of network nodes in a wireless network; estimate first channel state information based on the downlink reference signals received from the plurality of network nodes and determine channel quality for each network node; select a subset of network nodes of the plurality of network nodes to which an uplink reference signal is to be transmitted, based on the determined channel quality; transmit the uplink reference signal to the subset; receive feedback information including second channel state information estimated by the subset based on the uplink reference signal; and apply channel state information for communication with each network node of the plurality of network nodes based on at least one of the first channel state information and the second channel state information.

2. The communication device of claim 1, wherein the circuitry is configured to select the subset by identifying network nodes in which the channel quality does not satisfy a quality condition.

3. The communication device of claim 2, wherein the quality condition comprises comparing at least one of path loss, reference signal received power (RSRP), reference signal received quality (RSRQ), received signal strength indicator (RSSI), signal-to-interference-plus-noise ratio (SINR), signal-to-noise ratio (SNR), or signal-to-interference ratio (SIR) to a respective threshold.

4. The communication device of claim 1, wherein the circuitry is configured to evaluate the channel quality for each network node across a plurality of frequency domains and select the subset based on frequency domain-specific channel quality determinations.

5. The communication device of claim 4, wherein the circuitry is configured to: specify at least one frequency domain in which none of the plurality of network nodes satisfies a quality condition; and select network nodes for the subset based on having highest channel quality among the plurality of network nodes in the specified at least one frequency domain.

6. The communication device of claim 1, wherein the circuitry is configured to apply the channel state information by: using the first channel state information for communication with network nodes not included in the selected subset; and using the second channel state information for communication with network nodes included in the selected subset.

7. The communication device of claim 6, wherein the circuitry is configured to determine transmission parameters for uplink signals to each network node based on the respective channel state information, the transmission parameters including at least one of resource allocation, modulation and coding scheme (MCS), precoding matrix, transmission rank, or transmission power.

8. The communication device of claim 1, wherein the circuitry is configured to combine the first channel state information and the second channel state information for network nodes included in the selected subset to determine optimized communication parameters.

9. The communication device of claim 1, wherein the uplink reference signal comprises a sounding reference signal (SRS) and the downlink reference signals comprise at least one of channel state information reference signals (CSI-RS) or synchronization signal blocks (SSB).

10. The communication device of claim 1, wherein the first channel state information comprises at least one of a channel quality indicator (CQI), a precoding matrix indicator (PMI), a rank indicator (RI), a CSI resource indicator (CRI), layer 1 reference signal received power (L1-RSRP), or layer indicator (LI).

11. The communication device of claim 1, wherein the second channel state information comprises at least one of a channel coefficient, signal to noise ratio (SNR), signal to interference plus noise ratio (SINR), path loss, angle of arrival (AoA), delay spread, or Doppler spread.

12. The communication device of claim 1, wherein the circuitry is configured to receive transmission configuration information for the uplink reference signal and the downlink reference signals via at least one of RRC signaling, MAC-CE, or DCI.

13. The communication device of claim 1, wherein the feedback information includes transmission parameters optimized based on the second channel state information, the transmission parameters comprising at least one of transmitted precoding matrix indicator (TPMI), transmitted rank indicator (TRI), SRS resource indicator (SRI), modulation and coding scheme (MCS), or transmit power control (TPC) command.

14. The communication device of claim 1, wherein the circuitry is configured to dynamically adjust selection of the subset based on changes in the determined channel quality over time to adapt to varying channel conditions.

15. Infrastructure equipment comprising: circuitry configured to: acquire first channel state information based on uplink reference signal received from a communication device by each network node of a plurality of network nodes; select a subset of the plurality of network nodes to transmit a downlink reference signal to the communication device based on the first channel state information; cause the subset to transmit a downlink reference signal; acquire feedback information including second channel state information estimated by the communication device based on the downlink reference signal transmitted from the subset; and apply channel state information for communication with the communication device from each network node of the plurality of network nodes based on at least one of the first channel state information and the second channel state information.

16. The infrastructure equipment of claim 15, wherein the circuitry is configured to select the subset by determining which network nodes have channel quality indicated by the first channel state information that does not satisfy a quality condition.

17. The infrastructure equipment of claim 16, wherein the quality condition comprises comparing path loss indicated by the first channel state information for each network node to a threshold value.

18. The infrastructure equipment of claim 15, wherein the circuitry is configured to select the subset based on evaluation of the first channel state information from all network nodes of the plurality of network nodes.

19. The infrastructure equipment of claim 18, wherein the evaluation comprises: evaluating whether channel quality corresponding to the first channel state information of each network node satisfies a quality condition for each of a plurality of frequency domains; and selecting the subset based on evaluation results across the plurality of frequency domains.

20. The infrastructure equipment of claim 19, wherein the circuitry is configured to: identify at least one frequency domain in which none of the plurality of network nodes satisfies the quality condition; and select network nodes for the subset based on having highest channel quality among the plurality of network nodes in the identified at least one frequency domain.

21. The infrastructure equipment of claim 19, wherein the circuitry is configured to determine that no network nodes should be selected for the subset when channel quality equal to or higher than a threshold is obtained across all frequency domains by the plurality of network nodes.

22. The infrastructure equipment of claim 15, wherein the circuitry is configured to apply the channel state information by: selecting the first channel state information for network nodes not included in the subset; and selecting the second channel state information for network nodes included in the subset.

23. The infrastructure equipment of claim 22, wherein the circuitry is configured to determine transmission parameters for each network node based on the selected channel state information, the transmission parameters including at least one of resource allocation, modulation and coding scheme (MCS), precoding matrix, transmission rank, or beamforming configuration.

24. The infrastructure equipment of claim 15, wherein the circuitry is configured to control transmission period of the downlink reference signal for each network node in the subset according to channel quality corresponding to the first channel state information.

25. The infrastructure equipment of claim 15, wherein the circuitry is configured to update a transmission configuration indication (TCI) state based on the first channel state information and cause notification of the updated TCI state to the communication device.

26. The infrastructure equipment of claim 25, wherein the updated TCI state includes a new QCL-Type defined by the uplink reference signal, the new QCL-Type including at least one of spatial RX / TX beam information, angle of arrival (AoA), delay spread, or Doppler shift / spread.

27. The infrastructure equipment of claim 15, wherein the infrastructure equipment is configured to control the plurality of network nodes, and each network node comprises at least one of a base station, a transmission and reception point (TRP), a radio unit (RU), a central unit (CU), a distributed unit (DU), an IAB node, or a relay terminal.

28. The infrastructure equipment of claim 15, wherein the circuitry is configured to coordinate selection and control functions across the plurality of network nodes via signaling interfaces.

29. The infrastructure equipment of claim 15, wherein the circuitry is configured to combine the first channel state information and the second channel state information for network nodes included in the subset to determine optimized communication parameters.

30. The infrastructure equipment of claim 15, wherein the circuitry is configured to control transmission of configuration information for the uplink reference signal and the downlink reference signal to the communication device via at least one of RRC signaling, MAC-CE, or DCI.

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