User equipment, node, and communication method

Abstract

User equipment according to the present invention performs wireless communication with a node in a mobile communication system and comprises: a reception unit that receives a first reference signal transmitted by the node; a control unit that measures a first reference signal resource, calculates, on the basis of the measurement of the first reference signal resource, a precoder used for transmission of a physical uplink shared channel, and applies the precoder to the physical uplink shared channel; and a transmission unit that transmits, to the node, the physical uplink shared channel to which the precoder has been applied.

Description

User equipment, node, and communication method

[0001] The present invention relates to a user equipment, a node, and a communication method.

[0002] NR (New Radio), a fifth-generation (5G) standard formulated by the Third Generation Partnership Project (3GPP (registered trademark; the same applies hereinafter)), a standardization project for mobile communication systems, specifies codebook and non-codebook transmission methods for transmitting the physical uplink shared channel (PUSCH). In the non-codebook type, a precoder determined by the node is applied to the transmission of the PUSCH.

[0003] In the non-codebook type transmission method, there is a problem that it takes a long time for the precoder to be applied to the PUSCH. In the non-codebook type transmission method, after a node (also simply referred to as "node") of a network of a mobile communication system transmits CSI-RS to a user equipment (UE), two round trips of communication are performed between the node and the UE until the PUSCH to which the precoder is applied is received.

[0004] As a result, particularly in an environment where the propagation channel fluctuates significantly, the propagation channel may fluctuate significantly between the time the precoder is calculated and the time the precoder is applied, resulting in a non-optimal precoder. Examples of environments where the propagation channel fluctuates significantly include an environment where a UE moves at high speed, or an environment where wireless communication using a high frequency band such as millimeter waves or sub-terahertz waves is used. In the latter wireless communication using a high frequency band, the beam is sharper than in a low frequency band, so even a slight change in the environment can cause greater channel fluctuations. If the precoder becomes non-optimal, inter-stream interference in the received signal increases, degrading modulation accuracy and potentially reducing throughput.

[0005] 3GPP Technical Specification: TS 38.214 V18.0.0 (2023-09)

[0006] A user equipment according to a first aspect is a user equipment that performs wireless communication with a node in a mobile communication system, and includes: a receiving unit that receives a first reference signal transmitted by the node; a control unit that measures a resource of the first reference signal, calculates a precoder to be used for transmitting a physical uplink shared channel based on the measurement of the resource of the first reference signal, and applies the precoder to the physical uplink shared channel; and a transmitting unit that transmits the physical uplink shared channel with the precoder applied to the node.

[0007] A node according to a second aspect is a node that performs wireless communication with a user equipment in a mobile communication system, and includes: a transmitter that transmits a first reference signal to the user equipment; and a receiver that receives from the user equipment the physical uplink shared channel that has been transmitted by the user equipment and to which a precoder calculated based on measurement of resources of the first reference signal has been applied.

[0008] A communication method according to a third aspect is a communication method used by a user equipment (UE) that performs wireless communication with a node in a mobile communication system, and includes the steps of receiving a first reference signal transmitted by the node, measuring a resource of the first reference signal, calculating a precoder to be used for transmitting a physical uplink shared channel based on the measurement of the resource of the first reference signal, applying the precoder to the physical uplink shared channel, and transmitting the physical uplink shared channel with the precoder applied to the node.

[0009] A communication method according to a fourth aspect is a communication method used in a node that performs wireless communication with a user equipment in a mobile communication system, and includes the steps of: transmitting a first reference signal to the user equipment; and receiving, from the user equipment, the physical uplink shared channel that has been transmitted with a precoder calculated based on measurement of resources of the first reference signal applied thereto.

[0010] 1 is a diagram showing an example of the configuration of a mobile communication system according to an embodiment. FIG. 2 is a diagram showing an example of the configuration of a protocol stack of a radio interface of a U-plane that handles data. FIG. 3 is a diagram showing an example of the configuration of a protocol stack of a radio interface of a C-plane that handles signaling (control signals). FIG. 4 is a diagram showing a general procedure in which a precoder determined in a non-codebook type is applied to transmit a physical uplink shared channel. FIG. 5 is a diagram showing an example of the configuration of a UE (user equipment) according to an embodiment. FIG. 6 is a diagram showing an example of the configuration of a node according to an embodiment. FIG. 7 is a diagram showing an example of a system operation according to the first embodiment. FIG. 8 is a diagram showing an example of a system operation according to a modified example of the first embodiment. FIG. 9 is a diagram showing an example of a system operation according to the second embodiment. FIG. 10 is a diagram showing an example of a system operation according to the third embodiment. FIG. 11 is a diagram showing an example of a system operation according to the fourth embodiment. FIG. 12 is a diagram showing an example of a system operation according to the fifth embodiment. FIG. 13 is a diagram showing an example of a system operation according to a modified example of the fifth embodiment.

[0011] Hereinafter, a mobile communication system according to an embodiment will be described with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0012] (1) First Embodiment A first embodiment will be described with reference to FIGS. 1 to 7. FIG.

[0013] (1.1) System Configuration Example Fig. 1 is a diagram showing a configuration example of a mobile communication system according to an embodiment. The mobile communication system according to the embodiment is a system conforming to the 3GPP standard. For example, the mobile communication system according to the embodiment may be a fifth generation (5G) system or a sixth generation (6G) system.

[0014] The mobile communication system includes a network (NW) 1 and a user equipment (UE) 100. The UE 100 is a mobile communication device that performs wireless communication with the NW 1. The UE 100 may be any device used by a user, and may be, for example, a mobile phone terminal (including a smartphone), a tablet terminal, a notebook PC (Personal Computer), a communication module (including a communication card or chipset), a sensor or a device provided in a sensor, a vehicle or a device provided in a vehicle (Vehicle UE), or an aircraft or a device provided in an aircraft (Aerial UE).

[0015] NW1 includes a radio access network (RAN) 10 and a core network (CN) 20. When the mobile communication system is a 5th generation system (5GS), the RAN 10 is referred to as a Next Generation Radio Access Network (NG-RAN), and the CN 20 is referred to as a 5G Core Network (5GC).

[0016] The RAN 10 includes a plurality of nodes 200 (nodes 200a to 200c in the illustrated example). The nodes 200 are connected to each other via inter-node interfaces. The nodes 200 are also referred to as base stations. The nodes 200 may be configured (i.e., functionally divided) with a CU (Central Unit) and a DU (Distributed Unit), and the two units may be connected by a fronthaul interface. When the mobile communication system is 5GS, the nodes 200 are referred to as gNBs, the inter-node interface is referred to as an Xn interface, and the fronthaul interface is referred to as an F1 interface.

[0017] Each node 200 manages one or more cells. The node 200 performs wireless communication with the UE 100 that has established a connection with its own cell. Each node 200 has a radio resource management (RRM) function, a routing function for user data (also simply referred to as "data"), a measurement control function for mobility control and scheduling, and the like. Note that "cell" is used as a term indicating the smallest unit of a wireless communication area. "Cell" is also used as a term indicating a function or resource for performing wireless communication with the UE 100. One cell belongs to one carrier frequency (also simply referred to as "frequency").

[0018] The CN 20 includes a CN device 300. The CN device 300 may include a C-plane device corresponding to the control plane (C-plane) and a U-plane device corresponding to the user plane (U-plane). The C-plane device performs various mobility controls and paging for the UE 100. The C-plane device communicates with the UE 100 using NAS (Non-Access Stratum) signaling. The U-plane device controls data transfer. When the mobile communication system is 5GS, the C-plane device is referred to as an AMF (Access and Mobility Management Function), the U-plane device is referred to as a UPF (User Plane Function), and the interface between the node 200 and the CN device 300 is referred to as an NG interface.

[0019] FIG. 2 is a diagram showing an example of the configuration of a protocol stack of a U-plane radio interface that handles data.

[0020] The U-plane radio interface protocol includes, for example, a physical (PHY) layer, a medium access control (MAC) layer, a radio link control (RLC) layer, a packet data convergence protocol (PDCP) layer, and a service data adaptation protocol (SDAP) layer.

[0021] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the PHY layer of UE 100 and the PHY layer of node 200 via a physical channel. The PHY layer of UE 100 receives downlink control information (DCI) transmitted from node 200 on a physical downlink control channel (PDCCH). Specifically, UE 100 performs blind decoding of the PDCCH using a radio network temporary identifier (RNTI) and acquires successfully decoded DCI as DCI addressed to the UE. The DCI transmitted from node 200 has CRC parity bits scrambled by the RNTI added.

[0022] The MAC layer performs data priority control and retransmission processing using Hybrid ARQ (HARQ). Data and control information are transmitted between the MAC layer of UE 100 and the MAC layer of node 200 via a transport channel. The MAC layer of node 200 includes a scheduler. The scheduler determines the uplink and downlink transport format (transport block size, modulation and coding scheme (MCS)) and the resources to be allocated to UE 100.

[0023] The RLC layer transmits data to the RLC layer on the receiving side by using the functions of the MAC layer and the PHY layer. Data and control information are transmitted between the RLC layer of the UE 100 and the RLC layer of the node 200 via logical channels.

[0024] The PDCP layer performs header compression / decompression, encryption / decryption, and the like.

[0025] The SDAP layer maps IP flows, which are units for QoS control by the CN 20, to radio bearers, which are units for QoS control by the AS (Access Stratum). Note that if the RAN is connected to the EPC, SDAP may not be required.

[0026] FIG. 3 is a diagram showing an example of the configuration of a protocol stack of a C-plane radio interface that handles signaling (control signals).

[0027] The protocol stack of the C-plane radio interface includes, for example, an RRC (Radio Resource Control) layer and an NAS (Non-Access Stratum) layer instead of the SDAP layer shown in FIG.

[0028] RRC signaling for various settings is transmitted between the RRC layer of UE100 and the RRC layer of node 200. The RRC layer controls logical channels, transport channels, and physical channels in accordance with the establishment, re-establishment, and release of radio bearers. When there is a connection (RRC connection) between the RRC of UE100 and the RRC of node 200, UE100 is in an RRC connected state. When there is no connection (RRC connection) between the RRC of UE100 and the RRC of node 200, UE100 is in an RRC idle state. When the connection between the RRC of UE100 and the RRC of node 200 is suspended, UE100 is in an RRC inactive state.

[0029] The NAS layer (also simply referred to as "NAS") located above the RRC layer performs session management, mobility management, etc. NAS signaling is transmitted between the NAS layer of the UE 100 and the NAS layer of the CN device 300. Note that the UE 100 also has an application layer in addition to the radio interface protocol. The layer below the NAS layer is referred to as the AS layer (also simply referred to as "AS").

[0030] FIG. 4 is a diagram illustrating a general procedure for transmitting a Physical Uplink Shared Channel (PUSCH) in a non-codebook manner.

[0031] In step S10, the node 200 transmits a resource configuration of an SRS (Sounding Reference Signal) to the UE 100. The UE 100 receives the resource configuration of the SRS. By this resource configuration, resources (frequency, time, antenna port) of the SRS are configured.

[0032] In step S20, the node 200 transmits the CSI-RS to the UE 100. The UE 100 receives the CSI-RS.

[0033] In step S30, the UE 100 measures the resource of the CSI-RS transmitted in step S20. The UE 100 calculates a precoder to be used for transmitting the SRS based on the measurement of the resource of the CSI-RS.

[0034] In step S40, the UE 100 applies the calculated precoder and transmits up to four SRSs to the node 200. For transmitting these SRSs, the SRS resources set by the resource configuration received in step S10 are used. Furthermore, one SRS antenna port is set for the SRS resource of each SRS.

[0035] In step S50, the node 200 determines one or more SRS Resource Indicators (SRIs) corresponding to the precoders used for transmitting the PUSCH, based on the received SRS.

[0036] In step S60, the node 200 transmits the determined one or more SRIs to the UE 100. Here, the one or more SRIs are transmitted by being included in downlink control information (DCI) transmitted on a physical downlink control channel (PDCCH). Here, the one or more SRIs are stored in an SRS resource indicator field within the field included in the DCI. The UE 100 receives the one or more SRIs. Also, in the non-codebook type transmission method, a TRI (Transmit Rank Indicator) is not notified from the node 200, but the UE 100 determines the TRI from the number of SRIs.

[0037] In step S70, the UE 100 transmits the PUSCH to the node 200 using the same antenna port as the antenna port of the SRS. The antenna port of the SRS is indicated by one or more received SRIs. As a result, the same precoder as that of the SRS of the SRS resource indicated by the received SRI is applied to the transmission of the PUSCH.

[0038] According to this procedure, two round trips of communication are made between the node 200 and the UE 100 from the time the node 200 transmits the CSI-RS to the UE 100 until the node 200 receives the PUSCH to which the precoder is applied. This poses a problem that the precoder may not be optimal, especially in an environment where the propagation channel fluctuates significantly. As a result, the throughput may decrease due to increased inter-stream interference and deterioration in modulation accuracy.

[0039] (1.2) Example of Configuration of User Equipment FIG. 5 is a diagram illustrating an example of the configuration of the UE 100 (user equipment) according to the embodiment.

[0040] The UE 100 includes a receiving unit 110, a transmitting unit 120, and a control unit 130. The receiving unit 110 and the transmitting unit 120 configure a wireless communication unit 140 that performs wireless communication with the node 200.

[0041] The receiving unit 110 performs various receptions under the control of the control unit 130. The receiving unit 110 includes an antenna and a receiver. The receiver converts a radio signal received by the antenna into a baseband signal (received signal) and outputs it to the control unit 130. The transmitting unit 120 performs various transmissions under the control of the control unit 130. The transmitting unit 120 includes an antenna and a transmitter. The transmitter converts a baseband signal (transmitted signal) output by the control unit 130 into a radio signal and transmits it from the antenna.

[0042] The control unit 130 performs various controls and processes in the UE 100. The operations of the UE 100 described above and below may be operations controlled by the control unit 130. The control unit 130 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used in the processing by the processor. The processor may include a baseband processor and a CPU (Central Processing Unit). The baseband processor performs modulation / demodulation and encoding / decoding of baseband signals. The CPU executes programs stored in the memory to perform various processes.

[0043] The UE 100 configured in this manner performs wireless communication with the node 200 in a mobile communication system. The receiver 110 receives a first reference signal transmitted by the node 200. The controller 130 measures the resource of the first reference signal, calculates a precoder to be used for transmitting the PUSCH based on the measurement of the resource of the first reference signal, and applies the precoder to the PUSCH. The transmitter 120 transmits the PUSCH to which the precoder has been applied to the node 200.

[0044] In this embodiment, the first reference signal is a downlink reference signal used to calculate a precoder to be applied to the transmission of PUSCH. The first reference signal is, for example, a CSI-RS in 3GPP, but may be other reference signals such as a DM-RS, a PT-RS, or a new reference signal introduced in the sixth generation. Below, an example will be described in which the first reference signal is a CSI-RS.

[0045] As a result, the UE 100 can transmit the PUSCH with fewer round trips of communication than in the procedure of Fig. 4. By reducing the number of round trips of communication, the UE 100 can suppress a decrease in throughput due to an increase in inter-stream interference and a deterioration in modulation accuracy, even in an environment in which the propagation channel fluctuates significantly.

[0046] Furthermore, in this embodiment, the control unit 130 determines the number of layers of the PUSCH based on measurement of the resources of the first reference signal. Furthermore, in this embodiment, the control unit 130 calculates a precoder to be used for transmitting the second reference signal based on measurement of the resources of the first reference signal, selects antenna ports corresponding to the determined number of layers of the PUSCH from the antenna ports of the second reference signal, and uses the selected antenna ports for the number of layers for transmitting the PUSCH. As a result, the part of the precoder applied to transmission of the second reference signal that is used for the second reference signal of the selected antenna port is used for transmitting the PUSCH.

[0047] In this embodiment, the second reference signal is an uplink reference signal used by the node 200 to receive the PUSCH. The second reference signal is, for example, a sounding reference signal (SRS) in 3GPP, but may be other reference signals such as a DM-RS, a PT-RS, or a new reference signal introduced in the sixth generation. An example of the case where the second reference signal is an SRS will be described below.

[0048] (1.3) Example of Node Configuration FIG. 6 is a diagram illustrating an example of the configuration of a node 200 (base station, gNB) according to an embodiment.

[0049] The node 200 includes a transmitting unit 210, a receiving unit 220, a control unit 230, and a NW communication unit 240. The transmitting unit 210 and the receiving unit 220 configure a wireless communication unit 250 that performs wireless communication with the UE 100.

[0050] The transmitting unit 210 performs various transmissions under the control of the control unit 230. The transmitting unit 210 includes an antenna and a transmitter. The transmitter converts a baseband signal (transmission signal) output by the control unit 230 into a radio signal and transmits it from the antenna. The receiving unit 220 performs various receptions under the control of the control unit 230. The receiving unit 220 includes an antenna and a receiver. The receiver converts a radio signal received by the antenna into a baseband signal (reception signal) and outputs it to the control unit 230.

[0051] The control unit 230 performs various controls and processes in the node 200. The operations of the node 200 described above and below may be operations under the control of the control unit 230. The control unit 230 includes at least one processor and at least one memory. The memory stores programs executed by the processor and information used in the processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation / demodulation and encoding / decoding of baseband signals. The CPU executes programs stored in the memory to perform various processes.

[0052] The NW communication unit 240 is connected to adjacent nodes via an inter-node interface, and to the CN device 300 via a node-CN interface.

[0053] The node 200 configured in this manner performs wireless communication with the UE 100 in a mobile communication system. The transmitter 210 transmits a first reference signal to the UE 100. The receiver 220 receives a PUSCH from the UE 100. The PUSCH is a PUSCH transmitted by the UE 100 by applying a precoder calculated based on measurement of the resource of the first reference signal.

[0054] (1.4) System Operation Example Figure 7 is a diagram showing an example of system operation according to the first embodiment. The system operation according to the first embodiment is a method of transmitting a PUSCH to which a UE-determined precoder is applied, that is, a method of transmitting a PUSCH to which a precoder determined by UE 100 is applied. Note that duplicated explanations of operations similar to those in Figure 4 will be omitted.

[0055] In step S110, the node 200 transmits a PUSCH resource configuration and an SRS resource configuration to the UE 100. The node 200 transmits the resource configuration to the UE 100, for example, in an RRC layer. Note that the node 200 may transmit the resource configuration to the UE 100 in a MAC layer, or may transmit the resource configuration to the UE 100 by including it in DCI. The UE 100 receives the PUSCH resource configuration and the SRS resource configuration.

[0056] In step S120, the node 200 transmits the CSI-RS to the UE 100. The UE 100 receives the CSI-RS. Note that the node 200 may transmit the CSI-RS to the UE 100 before transmitting the above-described PUSCH resource configuration and SRS resource configuration. That is, the order in which the process of step S120 and the process of step S110 are performed may be reversed from the order shown in FIG. 7 .

[0057] In step S130, the UE 100 measures the resource of the CSI-RS transmitted in step S120. The UE 100 calculates a precoder to be applied to the transmission of the PUSCH and the SRS based on the measurement of the resource of the CSI-RS. The UE 100 determines the number of layers of the PUSCH based on the measurement of the resource of the CSI-RS.

[0058] The method by which the UE 100 calculates the precoder to be applied to the transmission of the PUSCH and SRS based on the measurement of the CSI-RS resource is, for example, a method based on singular value decomposition. The UE 100 expresses the result of the measurement of the CSI-RS resource as a matrix having rows corresponding to the number of antenna ports of the node 200 and columns corresponding to the number of antenna ports of the UE 100 (the maximum number of layers of the PUSCH). The UE 100 performs singular value decomposition on the matrix. The UE 100 determines whether the magnitude of the singular value obtained by the singular value decomposition is greater than a predetermined threshold. The UE 100 determines that the beam is transmittable when the magnitude of the singular value is greater than the predetermined threshold. The eigenvector corresponding to the singular value determined to be transmittable corresponds to the precoder weight of the beam (layer) determined to be transmittable, and the number of the eigenvectors corresponds to the number of transmittable layers. The method by which UE 100 calculates the precoder to be applied to the transmission of the PUSCH based on the measurement of the CSI-RS resource is not limited to the method based on singular value decomposition, and other methods may be used.

[0059] In step S140, UE 100 transmits the PUSCH to which the calculated precoder has been applied to node 200. Node 200 receives the PUSCH. Note that the timing at which UE 100 transmits the PUSCH to node 200 is scheduled by, for example, DCI. Also, UE 100 transmits the PUSCH to node 200 using the resources set in the PUSCH resource configuration received from node 200 in step S110.

[0060] UE 100 may transmit SRS to node 200 before transmitting PUSCH to node 200. UE 100 transmits SRS to node 200 using SRS resources for at least the number of layers described above. UE 100 selects an antenna port for the determined number of layers of PUSCH from the antenna ports for SRS, and uses the selected antenna port for transmitting PUSCH. As a result, PUSCH for the above number of layers is transmitted to node 200 by applying the same precoder as the precoder used for transmitting SRS from the selected antenna port.

[0061] Note that the transmission of the SRS and the PUSCH from the UE 100 to the node 200 in step S140 may be performed multiple times before the processing from step S110 to step S130 is performed next time. In addition, the number of times that the SRS and the PUSCH are transmitted may not be the same.

[0062] Here, in this embodiment, TDD (Time Division Duplex) is assumed in the PUSCH transmission method applying the UE-determined precoder shown in FIG. 7, that is, the PUSCH transmission method applying the precoder determined by the UE 100. The UE 100 can measure the CSI-RS received from the node 200 (that is, can perform channel estimation). The UE 100 uses channel reciprocity due to TDD to calculate the precoder to be used for transmitting the PUSCH based on the measurement of the CSI-RS, and also determines the number of layers of the PUSCH. In other words, the UE 100 has the ability to determine the precoder (beam) to be used for transmitting the PUSCH. The advantage of the PUSCH transmission method applying the UE-determined precoder is that the precoder to be used for transmission can be calculated from the received signal by using channel reciprocity due to TDD. That is, by executing a series of controls for transmitting the PUSCH in the UE 100 without communicating with the node 200, it is possible to determine the precoder in a shorter time than in the conventional procedure shown in FIG.

[0063] In the present embodiment, an example has been described in which the UE 100 (control unit 130) determines the number of layers of the PUSCH based on measurement of resources of the first reference signal (CSI-RS), but this is not limiting. The number of layers of the PUSCH does not have to be determined by the UE 100. In that case, for example, the node 200 determines the number of layers of the PUSCH, and the node 200 notifies the UE 100 of the determined number of layers. As another example, the number of layers of the PUSCH may be determined in advance, and the UE 100 may store the number of layers in advance.

[0064] In addition, in this embodiment, the UE 100 (control unit 130) calculates a precoder used for transmitting a second reference signal (SRS) based on measurement of the resource of the first reference signal (CSI-RS), selects an antenna port for the determined number of layers of the PUSCH from the antenna ports of the second reference signal (SRS), and transmits the PUSCH using the selected antenna port. However, this is not limited to this. The UE 100 may transmit the PUSCH using an antenna port other than the antenna port of the second reference signal (SRS).

[0065] (1.5) Modification of First Embodiment With reference to FIG. 8 , a modification of the first embodiment will be described, focusing on differences from the first embodiment. In the modification of the first embodiment, when the receiving unit 110 receives the first information from the node 200, the transmitting unit 120 transmits the PUSCH using a PUSCH transmission method to which a UE-determined precoder is applied. In other words, when the receiving unit 110 receives the first information from the node 200, the transmitting unit 120 applies, to the transmission of the PUSCH, a precoder calculated by the control unit 130 based on measurement of the resource of the first reference signal. The first information is information indicating that the PUSCH transmission method to which a UE-determined precoder is applied is used to transmit the PUSCH.

[0066] Fig. 8 is a diagram showing an example of system operation according to a modification of the first embodiment. Note that the processes of steps S210, S230, and S240 are similar to the processes of steps S110, S130, and S140 in Fig. 7, and therefore descriptions thereof will be omitted.

[0067] In step S220, the node 200 transmits the CSI-RS to the UE 100. The first information is included in the CSI-RS. Here, the first information is included in the CSI-RS, which means that the CSI-RS is transmitted based on a sequence corresponding to the use of a PUSCH transmission method to which a UE-determined precoder is applied for the transmission of the PUSCH. That is, there are two types of CSI-RS: a CSI-RS indicating the use of a PUSCH transmission method to which a UE-determined precoder is applied, and a CSI-RS indicating that a PUSCH transmission method to which a UE-determined precoder is applied is not used. These two types of CSI-RS have different sequences for generating the CSI-RS.

[0068] When the UE 100 receives the first type of CSI-RS, it determines that it uses a PUSCH transmission method to which a UE-determined precoder is applied to transmit the PUSCH, that is, that it applies the precoder determined by the UE 100. On the other hand, when the UE 100 receives the second type of CSI-RS, it determines that it does not use a PUSCH transmission method to which a UE-determined precoder is applied to transmit the PUSCH, that is, that it uses a general Non-codebook type transmission method as shown in FIG.

[0069] When the UE 100 determines that the first information is included in the CSI-RS, it executes the processes of steps S230 and S240. On the other hand, when the UE 100 determines that the first information is not included in the CSI-RS, it executes the subsequent processes based on a general procedure in which a precoder determined in the non-codebook type is applied and PUSCH is transmitted (the processes after step S30 in FIG. 4).

[0070] In the modification of the first embodiment, an example in which the first information is included in the CSI-RS has been described, but the present invention is not limited to this. The first information may be included in the DCI transmitted from the node 200 to the UE 100, or may be transmitted in the RRC layer. Furthermore, the first information may be transmitted for all PUSCH transmissions to be transmitted thereafter, or may be transmitted for one PUSCH transmission.

[0071] Furthermore, when the control unit 130 determines that channel reciprocity between the uplink and the downlink is satisfied, the control unit 130 may use a PUSCH transmission method that applies a UE-determined precoder. In this case, the control unit 130 determines whether channel reciprocity is satisfied, for example, as follows. For example, the control unit 130 determines that channel reciprocity is satisfied when time division duplex (TDD) is used as the communication method and the uplink and downlink frequencies are the same or the difference is within a threshold. As another example, the control unit 130 determines that channel reciprocity is satisfied when the movement speed of the UE 100 is slow enough to realize channel model reciprocity.

[0072] Furthermore, the control unit 130 may determine whether to use time division duplex based on the frequency band to which the component carrier used by the UE 100 for communication with the node 200 belongs.

[0073] (2) Second Embodiment With reference to FIG. 9 , the second embodiment will be described, focusing mainly on differences from the first embodiment. In the first embodiment described above, the number of layers of the PUSCH transmitted by UE 100 is not shared between node 200 and UE 100. Therefore, node 200 must perform reception processing assuming the maximum number of layers. In other words, node 200 must perform blind decoding. Node 200 knows the number of its own antenna ports, or the number of antenna ports of UE 100, or the maximum number of layers within the capability of UE 100. However, node 200 does not know the number of layers determined by UE 100. Therefore, node 200 must perform reception processing based on the number of its own antenna ports, or the number of antenna ports of UE 100, or the maximum number of layers within the capability of UE 100. For example, even if UE 100 is transmitting with a layer count of 1, node 200 must perform reception processing assuming the number of layers is 8. This poses a problem that power consumption may worsen compared to when the node 200 knows the number of layers.

[0074] In this embodiment, the receiving unit 110 receives maximum layer number information from the node 200. The maximum layer number information is information indicating the maximum number of layers of the PUSCH transmitted by the transmitting unit 120. The control unit 130 controls the number of layers of the PUSCH to be equal to or less than the maximum value indicated by the maximum layer number information.

[0075] (2.1) System Operation Example A system operation example according to the second embodiment will be described, focusing on differences from the first embodiment, with reference to Fig. 9. Fig. 9 is a diagram showing a system operation example according to the second embodiment. Note that the processes of steps S310, S320, and S350 are similar to the processes of steps S110, S120, and S140 in Fig. 7, and therefore will not be described here.

[0076] In step S330, node 200 transmits maximum number of layers information to UE 100. The maximum value of the number of layers indicated by the maximum number of layers information is, for example, 2. Node 200 transmits the maximum number of layers information to UE 100, for example, by including it in DCI. Note that in 3GPP, in the case of a codebook-type transmission method, node 200 transmits the maximum number of layers information to UE 100 using a predetermined area in a predetermined format of DCI. On the other hand, in 3GPP, this area is not used in a non-codebook-type transmission method. Therefore, even in a transmission method of a PUSCH to which a UE-determined precoder is applied, the maximum number of layers information is transmitted using this area, thereby making effective use of DCI resources.

[0077] Alternatively, the information on the maximum number of layers may be transmitted in the MAC layer or in the RRC layer.

[0078] In this embodiment, the maximum number of layers information is transmitted after the CSI-RS is transmitted, but this is not limited to this. The maximum number of layers information may be transmitted before the CSI-RS is transmitted. In other words, the process of step S330 may be performed before the process of step S320.

[0079] Note that the UE 100 (control unit 130) may use a PUSCH transmission method to which a UE-determined precoder is applied, for transmitting the PUSCH, when the receiving unit 110 receives the maximum number of layers information from the node 200. That is, the UE 100 may use the maximum number of layers information as the above-described first information.

[0080] In step S340, the UE 100 executes the process of step S130 described above while controlling the number of layers of the PUSCH to be equal to or less than the maximum value indicated by the maximum layer number information.

[0081] UE 100 controls the number of layers of PUSCH to be equal to or less than the maximum value indicated by the maximum layer number information, for example, as follows: For example, if all four singular values ​​obtained as a result of singular value decomposition are greater than a predetermined threshold, the number of layers is 4. If the result of singular value decomposition indicates that the number of layers is 4, but the maximum value indicated by the maximum layer number information is 2, UE 100 sets the number of layers to 2, selects the two largest singular values ​​from the four singular values, and selects eigenvectors corresponding to the selected singular values.

[0082] When receiving the PUSCH in step S350, the node 200 performs the reception process assuming the maximum value indicated by the maximum layer number information as the number of layers.

[0083] (3) Third Embodiment With reference to FIG. 10 , the third embodiment will be described, focusing mainly on differences from the second embodiment. In the above-described second embodiment, the node 200 reduces deterioration of power consumption in reception processing by transmitting maximum layer number information to the UE 100. However, according to the control of the second embodiment, even if the amount of data of the PUSCH that the UE 100 intends to transmit increases, the number of layers cannot be increased beyond the maximum value indicated by the maximum layer number information, even if the uplink channel condition improves. For example, even in a situation where the PUSCH can actually be transmitted with six layers, if the maximum value indicated by the maximum layer number information is four, the number of layers can only be transmitted with four. As a result, the control of the second embodiment has the problem of being unable to make full use of the channel capacity.

[0084] In this embodiment, the transmitter 120 transmits desired number of layers information to the node 200. The desired number of layers information is information indicating a desired number of layers, which is the maximum number of layers desired by the UE 100. In this embodiment, the transmitter 120 transmits the desired number of layers information to the node 200 when the desired number of layers is greater than the maximum value indicated by the maximum number of layers information.

[0085] (3.1) System Operation Example A system operation example according to the third embodiment will be described with reference to FIG. 10, focusing on differences from the second embodiment. In FIG. 10, non-essential steps are indicated by dashed lines. FIG. 10 is a diagram showing a system operation example according to the third embodiment. Note that the processes of steps S410, S420, S430, S440, and S450 are similar to the processes of steps S310, S320, S330, S340, and S350 in FIG. 9, and therefore will not be described again.

[0086] In step S460, the UE 100 transmits desired number of layers information to the node 200. The desired number of layers indicated by the desired number of layers information is, for example, 4. The UE 100 determines the desired number of layers, for example, as follows.

[0087] When the UE 100 determines that the amount of data (buffer amount) to be transmitted using the PUSCH is equal to or greater than a predetermined amount of data, the UE 100 determines the desired number of layers to be a number greater than the current number of layers. In another example, the UE 100 may determine the number of layers of the PUSCH determined based on measurement of the CSI-RS resource as the desired number of layers. In another example, when the UE 100 determines that the amount of data (buffer amount) to be transmitted using the PUSCH is equal to or greater than a predetermined amount of data, the UE 100 may determine the number of layers of the PUSCH determined based on measurement of the CSI-RS resource as the desired number of layers.

[0088] In step S470, node 200 again transmits the maximum number of layers information to UE 100. The maximum value of the number of layers indicated by the maximum number of layers information is, for example, 4. Here, node 200 determines the maximum number of layers based on the desired number of layers information received from UE 100. Node 200 transmits maximum number of layers information indicating the determined maximum number of layers to UE 100. Note that, instead of again transmitting the maximum number of layers information to UE 100, node 200 may transmit to UE 100 a response (ACK) indicating that the desired number of layers indicated by the desired number of layers information is permitted as the maximum number of layers.

[0089] In step S460, instead of transmitting the desired number of layers, the UE 100 may transmit to the node 200 a request to increase the maximum number of layers or a request indicating the amount of increase.

[0090] The processes of steps S460 and S470 may be executed before the process of step S440, or before the process of step S450.

[0091] In step S480, UE 100 determines the number of layers based on the maximum number of layers information retransmitted from node 200 or the desired number of layers, and transmits PUSCH and SRS to node 200. If the maximum number of layers information is transmitted from node 200 to UE 100 in step S470, UE 100 determines the number of layers based on the maximum number of layers information. If a response indicating that the desired number of layers indicated by the desired number of layers information is permitted is transmitted from node 200 to UE 100 in step S470, UE 100 determines the desired number of layers as the maximum number of layers. Note that, similar to step S450 (step S140), UE 100 transmits SRS to node 200 before transmitting PUSCH to node 200.

[0092] The node 200 performs the reception process assuming the maximum value indicated by the retransmitted maximum number of layers information or the desired number of layers indicated by the desired number of layers information received from the UE 100 as the number of layers.

[0093] Note that, at a time after step S450 and before step S460, the node 200 may retransmit the CSI-RS to the UE 100. When the CSI-RS is retransmitted, in step S460, the UE 100 may determine the number of layers of the PUSCH determined based on measurement of the resources of the retransmitted CSI-RS as the desired number of layers.

[0094] (4) Fourth Embodiment With reference to FIG. 11 , the fourth embodiment will be described, focusing mainly on differences from the second embodiment. In the above-described second embodiment, the node 200 reduces deterioration of power consumption in the reception process by transmitting maximum layer number information to the UE 100. However, according to the control of the second embodiment, even when the amount of PUSCH data that the UE 100 is attempting to transmit decreases or when the uplink channel condition deteriorates, the node 200 must perform the reception process assuming the maximum value indicated by the maximum layer number information as the number of layers. As a result, the control of the second embodiment has a problem in that unnecessary power consumption may occur.

[0095] In this embodiment, the transmitting unit 120 transmits the desired number of layers information to the node 200 when the desired number of layers is smaller than the maximum value indicated by the maximum number of layers information.

[0096] (4.1) System Operation Example A system operation example according to the fourth embodiment will be described with reference to FIG. 11 , focusing on differences from the second embodiment. In FIG. 11 , non-essential steps are indicated by dashed lines. FIG. 11 is a diagram showing a system operation example according to the fourth embodiment. Note that the processes of steps S510, S520, S530, S540, and S550 are similar to the processes of steps S310, S320, S330, S340, and S350 in FIG. 9 , and therefore will not be described again.

[0097] In step S560, the UE 100 transmits desired number of layers information to the node 200. The desired number of layers indicated by the desired number of layers information is, for example, 1. The UE 100 determines the desired number of layers, for example, as follows.

[0098] When the UE 100 determines that the amount of data (buffer amount) to be transmitted using the PUSCH has become equal to or less than a predetermined amount of data, the UE 100 determines the desired number of layers to be a number smaller than the current number of layers. In another example, the UE 100 may determine the number of layers of the PUSCH determined based on measurement of the CSI-RS resource as the desired number of layers. In another example, when the UE 100 determines that the amount of data (buffer amount) to be transmitted using the PUSCH has become equal to or less than a predetermined amount of data, the UE 100 may determine the number of layers of the PUSCH determined based on measurement of the CSI-RS resource as the desired number of layers.

[0099] In step S570, node 200 retransmits the maximum number of layers information to UE 100. The maximum value of the number of layers indicated by the maximum number of layers information is, for example, 1. Here, node 200 determines the maximum number of layers based on the desired number of layers information received from UE 100. Node 200 transmits maximum number of layers information indicating the determined maximum number of layers to UE 100. Note that, instead of retransmitting the maximum number of layers information to UE 100, node 200 may transmit to UE 100 a response (ACK) indicating that the desired number of layers indicated by the desired number of layers information is permitted as the maximum number of layers.

[0100] In step S560, instead of transmitting the desired number of layers, the UE 100 may transmit to the node 200 a request to reduce the maximum number of layers or a request indicating the amount of reduction.

[0101] The processes of steps S560 and S570 may be executed before the process of step S540 or before step S550.

[0102] In step S580, UE 100 determines the number of layers based on the maximum number of layers information retransmitted from node 200 or the desired number of layers, and transmits PUSCH and SRS to node 200. If the maximum number of layers information is transmitted from node 200 to UE 100 in step S570, UE 100 determines the number of layers based on the maximum number of layers information. If a response indicating that the desired number of layers indicated by the desired number of layers information is permitted is transmitted from node 200 to UE 100 in step S570, UE 100 determines the desired number of layers as the maximum number of layers. Note that, similar to step S550 (step S140), UE 100 transmits SRS to node 200 before transmitting PUSCH to node 200.

[0103] The node 200 performs the reception process assuming the maximum value indicated by the retransmitted maximum number of layers information or the desired number of layers indicated by the desired number of layers information received from the UE 100 as the number of layers.

[0104] Note that, at a time after step S550 and before step S560, the node 200 may retransmit the CSI-RS to the UE 100. When the CSI-RS is retransmitted, in step S560, the UE 100 may determine the number of layers of the PUSCH determined based on measurement of the resources of the retransmitted CSI-RS as the desired number of layers.

[0105] (5) Fifth Embodiment The fifth embodiment will be described with reference to Fig. 12, focusing on differences from the second embodiment. In the second embodiment described above, the node 200 reduces deterioration of power consumption in the reception process by transmitting maximum layer number information to the UE 100. However, the control of the second embodiment has a problem in that the number of layers cannot be dynamically changed.

[0106] In this embodiment, the transmitting unit 120 transmits, to the node 200, layer number information indicating the number of layers of the PUSCH.

[0107] This allows UE 100 to dynamically change the number of layers, thereby increasing system capacity and reducing power consumption of node 200 even when channel conditions change rapidly in an environment where wireless communication using high frequency bands such as millimeter waves or sub-terahertz waves is used.

[0108] (5.1) System Operation Example A system operation example according to the fifth embodiment will be described with reference to Fig. 12, focusing on differences from the second embodiment. In Fig. 12, non-essential steps are indicated by dashed lines. Fig. 12 is a diagram showing a system operation example according to the fifth embodiment. Note that the processes of steps S610, S620, S630, and S660 are similar to the processes of steps S310, S320, S340, and S350 in Fig. 9, and therefore will not be described again.

[0109] In step S640, the UE 100 transmits the number of layers information to the node 200. The node 200 receives the number of layers information. Here, the UE 100 determines, for example, the number of layers of the PUSCH determined based on measurement of the CSI-RS resource, as the number of layers indicated by the number of layers information.

[0110] In step S650, the node 200 transmits a response (ACK) indicating that the node 200 has received the layer number information to the UE 100. For example, the node 200 may transmit the response by including it in DCI. Note that, if the node 200 has not received the layer number information in step S640, the node 200 may determine that the number of layers indicated by the layer number information last received from the UE 100 continues to be used for transmitting the PUSCH.

[0111] The processes of steps S670, S680, S690, S6100, and S6110 are similar to the processes of steps S620, S630, S640, S650, and S660, and therefore will not be described again. Thereafter, the processes of steps S670, S680, S690, S6100, and S6110 are repeatedly executed.

[0112] 12 has described an example in which the process consisting of steps S640 and S650 is executed once for one execution of the process of step S660. In other words, an example in which the transmission of the PUSCH and the process consisting of the transmission of the layer number information and the transmission of a response indicating that the layer number information has been received correspond one-to-one has been described, but this is not limiting. The process consisting of steps S640 and S650 may be executed once for multiple executions of the process of step S660. In other words, multiple executions of the PUSCH may correspond to one execution of the process consisting of the transmission of the layer number information and the transmission of a response indicating that the layer number information has been received.

[0113] The modification of the fifth embodiment will be described, focusing on differences from the fifth embodiment, with reference to Fig. 13. In the modification of the fifth embodiment, the transmitter 120 transmits, to the node 200, a PUSCH including layer number information indicating the number of layers of the PUSCH to be transmitted next.

[0114] (5.2) Modification of Fifth Embodiment Fig. 13 is a diagram showing an example of system operation according to a modification of the fifth embodiment. Note that the processes of steps S710, S720, S730, S750, and S760 are similar to the processes of steps S610, S620, S630, S670, and S680 in Fig. 12, and therefore description thereof will be omitted.

[0115] In step S740, UE 100 transmits layer number information indicating the number of layers of the PUSCH to be transmitted next, including the layer number information in the PUSCH transmission, to node 200. The PUSCH to be transmitted next is the PUSCH transmitted by UE 100 in step S770. Note that, similar to step S550 (step S140), UE 100 transmits an SRS to node 200 before transmitting a PUSCH to node 200.

[0116] The process of step S770 is the same as the process of step S740, and therefore a description thereof will be omitted. Thereafter, the processes of steps S750, S760, and S770 described above are repeatedly executed.

[0117] In this modification, an example has been described in which the layer number information indicating the number of layers of the PUSCH to be transmitted next is included in the PUSCH transmission, but this is not limiting. The UE 100 may transmit the layer number information indicating the number of layers of the PUSCH to be transmitted next to the node 200 by including it in the PUCCH transmission.

[0118] A program may be provided that causes a computer (UE 100, node 200) to execute the operations according to the above-described embodiments. The program may be recorded on a computer-readable medium. Using the computer-readable medium, the program can be installed on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM or a DVD-ROM.

[0119] One embodiment of the present invention has been described in detail above with reference to the drawings, but the specific configuration is not limited to that described above, and various design changes and the like are possible within the scope that does not deviate from the gist of the present invention.

[0120] 1 Network 10 RAN 20 CN 100 UE 110 Receiving unit 120 Transmitting unit 130 Control unit 140 Wireless communication unit 200 Node 210 Transmitting unit 220 Receiving unit 230 Control unit 240 NW communication unit 250 Wireless communication unit 300 CN device

Claims

1. A user equipment that performs wireless communication with a node in a mobile communication system, comprising: a receiving unit that receives a first reference signal transmitted by the node; a control unit that measures a resource of the first reference signal, calculates a precoder to be used for transmitting a physical uplink shared channel based on the measurement of the resource of the first reference signal, and applies the precoder to the physical uplink shared channel; and a transmitting unit that transmits the physical uplink shared channel with the precoder applied to the node.

2. The user equipment according to claim 1, wherein the control unit determines the number of layers of the physical uplink shared channel based on measurement of resources of the first reference signal.

3. The user equipment according to claim 2, wherein the control unit calculates a precoder to be used for transmitting a second reference signal based on measurement of resources of the first reference signal, selects an antenna port for the number of layers from the antenna ports of the second reference signal, and uses the selected antenna port for the number of layers for transmitting the physical uplink shared channel.

4. The user equipment according to claim 1, wherein the transmitter uses the precoder for transmitting the physical uplink shared channel when the receiver receives first information from the node indicating that the precoder is to be used for transmitting the physical uplink shared channel.

5. The user equipment according to claim 4, wherein the first information is included in the first reference signal.

6. The user equipment according to claim 4, wherein the first information is included in downlink control information transmitted from the node to the user equipment.

7. The user equipment according to claim 1, wherein the control unit uses the precoder for transmitting the physical uplink shared channel when it is determined that channel reciprocity between the uplink and the downlink is satisfied.

8. The user equipment according to claim 2, wherein the receiving unit receives maximum layer number information from the node indicating a maximum value of the number of layers to be transmitted by the transmitting unit, and the control unit controls the number of layers to be equal to or less than the maximum value indicated by the maximum layer number information.

9. The user equipment according to claim 8, wherein the control unit uses the precoder for transmitting the physical uplink shared channel when the receiving unit receives the maximum layer number information from the node.

10. The user equipment according to claim 8, wherein the transmitting unit transmits to the node desired number of layers information indicating a desired number of layers, which is a desired maximum number of layers.

11. The user equipment according to claim 10, wherein the transmission unit transmits the desired number of layers information to the node when the desired number of layers is greater than the maximum value indicated by the maximum number of layers information.

12. The user equipment according to claim 10, wherein the transmission unit transmits the desired number of layers information to the node when the desired number of layers is smaller than the maximum value indicated by the maximum number of layers information.

13. The user equipment according to claim 2, wherein the transmission unit transmits layer number information indicating the number of layers to the node.

14. The user equipment according to claim 13, wherein the transmitting unit transmits the layer number information, which indicates the number of layers of the physical uplink shared channel to be transmitted next, to the node, including the layer number information in the physical uplink shared channel.

15. A node that performs wireless communication with a user equipment in a mobile communication system, comprising: a transmitter that transmits a first reference signal to the user equipment; and a receiver that receives from the user equipment a physical uplink shared channel that the user equipment transmits by applying a precoder calculated based on measurement of resources of the first reference signal.

16. A communication method used by a user equipment that performs wireless communication with a node in a mobile communication system, comprising: a step of receiving a first reference signal transmitted by the node; a step of measuring a resource of the first reference signal, calculating a precoder to be used in transmitting a physical uplink shared channel based on the measurement of the resource of the first reference signal, and applying the precoder to the physical uplink shared channel; and a step of transmitting the physical uplink shared channel to which the precoder has been applied to the node.

17. A communication method used in a node that performs wireless communication with a user equipment in a mobile communication system, comprising: a step of transmitting a first reference signal to the user equipment; and a step of receiving from the user equipment a physical uplink shared channel that has been transmitted with a precoder calculated based on measurement of resources of the first reference signal applied thereto.

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