User equipment, node, and communication method

Abstract

The user equipment is a user equipment that performs wireless communication with a master node and a secondary node using dual connectivity in a mobile communication system, receives first information indicating a neighboring cell from the master node, selects a secondary node to wake up based on the first information, and transmits second information indicating the neighboring cell that the user equipment wants to wake up to the master node.

Description

[Technical Field]

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

[0002] Cell-free Massive MIMO (Multi-Input Multi-Output) is a new mobile phone line configuration that is being considered to replace NR (New Radio), the fifth generation (5G) standard established by the Third Generation Partnership Project (3GPP (registered trademark; the same applies hereinafter)), a standardization project for mobile communications systems. Cell-free Massive MIMO is a configuration in which base stations are arranged more densely than before, and is a method that achieves both communication quality and power saving by operating only the minimum number of base stations that are most suitable for the communication requests of terminals.

[0003] On the other hand, mobile networks are required to have the characteristic of "quick connection, anytime, anywhere." In light of this, even if cell-free massive MIMO operates only the minimum number of base stations necessary, macro base stations that operate constantly and cover the entire area as before are expected to continue to exist in the future. Furthermore, the operation of these base stations is expected to be centrally managed by a central control unit (CU) in accordance with current standards.

[0004] In the above-mentioned situation settings, the procedure for activating small base stations that are normally asleep is as follows. First, a macro station that has been connected to a terminal in advance receives a request from the terminal for a high-quality link. Next, a search is made for small base stations and communication propagation paths that are suitable for communication with the terminal. As a result of the search, a link is established between the selected small base station and the terminal. Meanwhile, small base stations other than the selected small base station go back to sleep. As a result, only the selected small base station is activated.

[0005] When searching for small base stations and communication paths suitable for communication with a terminal, conventional methods (radiating reference signals) require each base station to be activated, even if only temporarily. Also, there is a possibility that reference signals may interfere with each other between closely spaced base stations. Therefore, there is a need for a technology that can complete the procedure of searching for a small base station and communication propagation path suitable for communication with a terminal in a power-saving and stable manner. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] 3GPP Technical Specification: TS38.401 V18.4.0(2024-12) Summary of the Invention

[0007] A user device according to a first aspect is a user device that performs wireless communication with a primary node and a secondary node using dual connectivity in a mobile communication system, receives first information indicating neighboring cells from the primary node, selects the secondary node to wake up based on the first information, and transmits second information indicating the neighboring cell that the user device wishes to wake up to the primary node.

[0008] A node according to a second aspect is a node operating in a mobile communication system in which a user device performs wireless communication using dual connectivity, the node transmitting first information to the user device indicating a neighboring cell, receiving second information from the user device indicating a neighboring cell that the user device wishes to wake up, and waking up the neighboring cell based on the received second information.

[0009] A communication method according to a third aspect is a communication method used by a user device that performs wireless communication with a primary node and a secondary node using dual connectivity in a mobile communication system, and includes the steps of receiving first information indicating a neighboring cell from the primary node, selecting a secondary node to wake up based on the first information, and transmitting second information indicating the neighboring cell that the user device wishes to wake up to the primary node.

[0010] A communication method according to a fourth aspect is a communication method used in a node that performs wireless communication with a user device using dual connectivity in a mobile communication system, and includes the steps of transmitting first information indicating a neighboring cell to the user device, receiving second information from the user device indicating a neighboring cell that the user device wishes to wake up, and waking up the neighboring cell based on the received second information. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a diagram illustrating a configuration example of a mobile communication system according to an embodiment. [Figure 2] FIG. 10 is a diagram illustrating an example of the configuration of a protocol stack of a U-plane radio interface that handles data. [Figure 3] FIG. 10 is a diagram illustrating an example of the configuration of a protocol stack of a C-plane wireless interface that handles signaling (control signals). [Figure 4] 1A and 1B are diagrams for explaining a terahertz (THz) wave cell according to an embodiment. [Figure 5] FIG. 2 is a diagram for explaining dual connectivity (DC) according to an embodiment. [Figure 6] FIG. 1 is a diagram illustrating a configuration example of a radio access network (RAN) according to an embodiment. [Figure 7] FIG. 2 is a diagram illustrating a configuration example of a UE (user equipment) according to the embodiment. [Figure 8] FIG. 2 is a diagram illustrating an example of the configuration of a node according to the embodiment. [Figure 9] FIG. 2 is a diagram illustrating an example of system operation according to the first embodiment. [Figure 10] FIG. 2 is a diagram illustrating an example of system operation according to the first embodiment. [Figure 11] FIG. 2 is a diagram illustrating an example of coordinated scheduling according to the first embodiment. [Figure 12] FIG. 2 is a diagram showing an example of the emission time of a synchronization signal block (SSB) beam according to the first embodiment. [Figure 13] FIG. 10 is a diagram showing another example of the emission time of a synchronization signal block (SSB) beam according to the first embodiment. [Figure 14] FIG. 10 is a diagram illustrating an example of system operation according to a modified example of the first embodiment. [Figure 15] FIG. 10 is a diagram illustrating an example of system operation according to a modified example of the first embodiment. [Figure 16] FIG. 10 is a diagram illustrating an example of system operation according to the second embodiment. [Figure 17] FIG. 10 is a diagram illustrating an example of system operation according to the second embodiment. [Figure 18] FIG. 10 is a diagram illustrating an example of system operation according to the third embodiment. [Figure 19] FIG. 10 is a diagram illustrating an example of system operation according to the third embodiment. [Figure 20] FIG. 10 is a diagram illustrating an example of system operation according to the fourth embodiment. [Figure 21] FIG. 10 is a diagram illustrating an example of system operation according to the fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] 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.

[0013] (1) First embodiment The first embodiment will be described with reference to FIGS.

[0014] (1.1) System configuration example 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.

[0015] 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 a 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).

[0016] The 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).

[0017] 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 are configured (i.e., functionally divided) with a CU (Central Unit), a DU (Distributed Unit), and an RU (Radio Unit), and the two units may be connected via a fronthaul interface. When the mobile communication system is 5GS, the nodes 200 are referred to as gNBs, the inter-node interfaces are referred to as Xn interfaces, and the fronthaul interfaces are referred to as F1 interfaces.

[0018] 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, etc. The term "cell" is used to indicate the smallest unit of a wireless communication area. The term "cell" is also used to indicate 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").

[0019] 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 forwarding. When the mobile communication system is 5GS, the C-plane device is called an AMF (Access and Mobility Management Function), the U-plane device is called a UPF (User Plane Function), and the interface between the node 200 and the CN device 300 is called an NG interface.

[0020] FIG. 2 is a diagram showing an example of the configuration of a protocol stack of a U-plane radio interface that handles data.

[0021] 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.

[0022] 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. CRC parity bits scrambled by the RNTI are added to the DCI transmitted from node 200.

[0023] 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 allocated to UE 100.

[0024] The RLC layer transmits data to the RLC layer on the receiving side using the functions of the MAC layer and 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.

[0025] The PDCP layer performs header compression / decompression, encryption / decryption, etc.

[0026] 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 an EPC (Evolved Packet Core), SDAP may not be required.

[0027] 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).

[0028] The protocol stack of the C-plane radio interface includes, for example, a Radio Resource Control (RRC) layer and a Non-Access Stratum (NAS) layer instead of the SDAP layer shown in FIG.

[0029] RRC signaling for various settings is transmitted between the RRC layer of UE 100 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 UE 100 and the RRC of node 200, UE 100 is in an RRC connected state. When there is no connection (RRC connection) between the RRC of UE 100 and the RRC of node 200, UE 100 is in an RRC idle state. When the connection between the RRC of UE 100 and the RRC of node 200 is suspended, UE 100 is in an RRC inactive state.

[0030] 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 UE 100 and the NAS layer of CN device 300. Note that UE 100 has an application layer and the like in addition to the radio interface protocol. Also, the layer below the NAS layer is referred to as the AS layer (also simply referred to as "AS").

[0031] (1.2) DC using a terahertz wave cell FIG. 4 is a diagram for explaining a terahertz (THz) wave cell according to an embodiment.

[0032] A mobile communication system according to an embodiment may be a 6G system. 6G is expected to utilize terahertz (THz) waves. A cell operated by THz waves is called a THz wave cell. Compared to millimeter waves (mmW), THz waves have a stronger tendency to propagate in a straighter direction, have a higher free space loss, and are more susceptible to the effects of the atmosphere and precipitation. Therefore, the THz wave cell may be an ultra-compact cell.

[0033] In the illustrated example, the diameter of the coverage area of ​​the THz-wave cell is approximately 10 [m], the diameter of the coverage area of ​​the mmW cell operated at mmW is approximately 100 [m], and the diameter of the coverage area of ​​the macrocell is approximately 1000 [m]. Under these assumptions, for example, a UE 100 moving at 60 [km / h] passes through the coverage area of ​​each THz-wave cell in approximately 599 [ms].

[0034] Dual connectivity (DC) is one method for stably controlling small cells in a mobile communication system. FIG. 5 is a diagram for explaining dual connectivity (DC) according to an embodiment. In the embodiment, it is assumed that a THz-wave cell is used as a cell of a secondary cell group (SCG). Furthermore, a THz-wave cell may be used as a secondary cell (SCell) of a master cell group (MCG). However, a mmW cell may be used instead of a THz-wave cell.

[0035] A DC may be set for the UE 100 in the RRC connected state. In the DC, the UE 100 performs radio communication with a master cell group (MCG) managed by a master node (MN) 200M and a secondary cell group (SCG) managed by a secondary node (SN). The MN 200M and the SN 200S are connected to each other via an inter-node interface. When there is no need to distinguish between the MN 200M and the SN 200S, they are simply referred to as the node 200. When the MN 200M is a 5G / NR node, it is also referred to as a master gNB (MgNB). When the SN 200M is a 5G / NR node, it is also referred to as a secondary gNB (SgNB).

[0036] For example, the MN 200M transmits a predetermined message (for example, an SN Addition Request message) to the SN 200S, and the MN 200M transmits an RRC Reconfiguration message to the UE 100, whereby the SCG is set in the UE 100 and DC is started. In DC, the UE 100 in the RRC connected state is assigned radio resources by the respective schedulers of the MN 200M and SN 200S, and performs radio communication using the radio resources of the MN 200M and the radio resources of the SN 200S.

[0037] The MN 200M may have a control plane connection with the CN 20. The MN 200M provides primary radio resources for the UE 100. The MN 200M manages the MCG, which is a group of serving cells associated with the MN 200M. The MCG has a primary cell (PCell) and optionally has one or more secondary cells (SCells). On the other hand, the SN 200S may not have a control plane connection with the CN 20. The SN 200S provides additional radio resources to the UE 100. The SN 200S manages the SCG, which is a group of serving cells associated with the SN 200S. The SCG has primary and secondary cells (PSCells) and optionally has one or more SCells. The PCell of the MCG and the PSCell of the SCG are sometimes referred to as special cells (SpCells).

[0038] The mobile communication system supports activation and deactivation of the SCG to enable reduction of power consumption of the UE 100 in which DC is configured. Activation / deactivation of the SCG can be instructed by an RRC Reconfiguration message from the MN 200M to the UE 100. While the SCG is deactivated, all SCG SCells are in an inactive state. While the SCG is deactivated, the UE 100 does not need to transmit a physical uplink shared channel (PUSCH), a sounding reference signal (SRS), or a channel quality indicator (CSI) report in the SCG. Also, while the SCG is deactivated, the UE 100 does not need to monitor a physical downlink control channel (PDCCH) or receive a downlink shared channel (DL-SCH) in the SCG. However, the UE 100 can continue radio link monitoring (RLM) and measurement reports for the PSCells. When activating the SCG, the UE 100 may skip the random access procedure if the timing advance (TA) with the PSCell is valid.

[0039] FIG. 6 is a diagram showing an example of the configuration of a RAN 10 according to this embodiment. The RAN 10 includes a MN 200M and one or more SNs 200S as multiple nodes 200. Note that FIG. 6 shows only one of the one or more SNs 200S. The MN 200M includes a CU 260, a macro station 270M, and a small station 270S. The macro station 270M included in the MN 200M is made up of a macro station DU and a macro station RU. The macro station 270M included in the MN 200M manages a PCell of an MCG. The small station 270S included in the MN 200M is made up of a small station DU and a small station RU. The small station 270S included in the MN 200M manages an SCell of an MCG.

[0040] Each of the one or more SNs 200S includes a CU 260 and a small station 270S (neither is shown). The small station 270S included in the SN 200S is made up of a small station DU and a small station RU. The small station 270S included in the SN 200S manages the PSCell and SCell of the SCG. Note that in DC, when the UE 100 connects to an SCG, the UE 100 connects to at least a PSCell. When the UE 100 connects to an SCG, it may connect to an SCell of the SCG as well as the PSCell.

[0041] In the DC according to this embodiment, the UE 100 performs radio communication with a PCell of an MCG managed by a macro station DU connected to the CU 260 included in the MN 200M, and a PSCell or SCell of an SCG managed by a small station DU included in the SN 200S. That is, the DC is performed using the PCell of the MCG and the PSCell or SCell of the SCG.

[0042] (1.3) Example of user device configuration FIG. 7 is a diagram illustrating a configuration example of a UE 100 (user equipment) according to the embodiment.

[0043] 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.

[0044] 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.

[0045] 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 under the control of the control unit 230. 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.

[0046] (1.4) Node configuration example 8 is a diagram illustrating a configuration example of a node 200 (base station) according to the embodiment. The node 200 may be an MN 200M or an SN 200S.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] The NW communication unit 240 is connected to adjacent nodes via an inter-node interface, and is connected to the CN device 300 via a node-CN interface.

[0051] The node 200M configured in this manner is a network node having a central unit and a plurality of distributed units. The central unit transmits the transmission timing of the synchronization signal block to the second distributed units. The CU 260 is an example of a central unit. The macro station 270M and the small station 270S are examples of a plurality of distributed units. The small station 270S is an example of a second distributed unit.

[0052] With the above configuration, the node 200M can transmit the transmission timing of the synchronization signal block to the second distributed unit, so that the procedure of searching for a small station 270S and a communication propagation path suitable for communication with the UE 100 can be completed in a power-saving and stable manner.

[0053] The mobile communication system according to this embodiment includes a central unit and a plurality of distributed units. The CU 260 is a central unit included in the mobile communication system.

[0054] The small station 270S is a distributed unit included in a mobile communication system having a central unit and a plurality of distributed units. The small station 270S receives the transmission timing of a synchronization signal block (SSB) from the central unit. The small station 270S transmits the SSB based on the transmission timing of the SSB.

[0055] (1.5) System operation example Fig. 9 is a diagram showing an example of system operation according to the first embodiment. The CU 260 shown in Fig. 9 is the CU 260 included in the SN 200S. The CU 260 included in the MN 200M is omitted in Fig. 9. The macro station 270M shown in Fig. 9 is the macro station 270M included in the MN 200M. In DC, when the CU 260 included in the SN 200S and the macro station 270M included in the MN 200M communicate with each other, the communication is performed via the CU 260 included in the MN 200M. The small station 270S shown in Fig. 9 is the small station 270S included in the SN 200S. In the system operation according to the first embodiment, the CU 260 included in the SN 200S transmits the SSB transmission timing to each of the plurality of small stations 270S included in the SN 200S.

[0056] In the following description, the CU 260 included in the SN 200S will be simply referred to as the "CU 260." The small station 270S included in the SN 200S will be simply referred to as the "small station 270S." The macro station 270M included in the MN 200M will be simply referred to as the "macro station 270M." In the following description, a "small station 270S" refers to any one of the small stations 270S-1 to 270S-N. A "multiple small stations 270S" refers to any two or more of the small stations 270S-1 to 270S-N.

[0057] In step S10, the UE 100 is previously connected to the PCell of the macro station 270M.

[0058] In step S20, each of the small stations 270S-1 to 270S-N is in sleep mode.

[0059] In step S30, the UE 100 transmits a request for radio quality conditions to the macro station 270M. The UE 100 transmits the request by including it in UCI to be transmitted on the PUCCH. Note that the UE 100 may transmit the request by including it in a PDCP Control PDU, an RRC message, or the like. The radio quality conditions include, for example, transmitting and receiving data at high throughput in each of the UL and DL. The macro station 270M receives the request for radio quality conditions from the UE 100. The request for radio quality conditions is an example of a notification transmitted from the UE 100 to the macro station 270M. Therefore, the UE 100 transmits the notification to the master node.

[0060] In step S40, the macro station 270M transmits a message notifying the CU 260 of the traffic congestion status. The macro station 270M transmits, for example, the traffic congestion status to the CU 260 by including the traffic congestion status in a Resource Status Request message. Therefore, the macro station 270M configuring the PCell notifies the CU 260 of information indicating the usage status of radio resources. The CU 260 receives the message notifying the traffic congestion status from the macro station 270M.

[0061] In step S50, the CU 260 instructs the small stations 270S to cancel sleep. Therefore, having received information indicating the usage status of radio resources, the CU 260 instructs the plurality of small stations 270S in the vicinity of the UE 100 to cancel sleep. The CU 260 selects small stations 270S located within a specific range based on the location information of the UE 100. The CU 260 instructs the selected small stations 270S from among the small stations 270S to cancel sleep. The selected small stations 270S receive the instruction to cancel sleep from the CU 260. Note that in Fig. 9, small stations 270S-1 to 270S-N are shown as the small stations 270S selected by the CU 260 as being located within a specific range.

[0062] The following describes in detail the process in which the CU 260 selects the small station 270S to instruct to cancel sleep based on the location information of the UE 100. For example, the CU 260 first selects the small station 270S that is close to the UE 100. In this case, the CU 260 may select the small station 270S that is a predetermined distance or less from the UE 100. The CU 260 may also select a predetermined number of small stations 270S from among the small stations 270S in order of shortest distance from the UE 100.

[0063] The CU 260 selects a set of small stations 270S that are unlikely to interfere with each other in the SSB search in step S120, which will be described later, from among the small stations 270S that are close to the UE 100. "Less likely to interfere with the SSB search" means that the signal power to interference ratio (SS-SIR) of the synchronization signal received by the UE 100 in the SSB search is unlikely to deteriorate. For example, the CU 260 selects small stations 270S that are close to the UE 100 and that use different frequency bands. The frequency bands used are the frequency bands of the cells that the small stations 270S use as the PSCell or SCell of the SCG. However, if interference between SSBs can be avoided by interference avoidance processing in the SSB search, which will be described later, small stations 270S that are close to the UE 100 and that use the same frequency band may be selected.

[0064] The CU 260 uses known techniques to determine the current location of the UE 100. The CU 260 determines the current location of the UE 100 based on, for example, Minimalization of Drive tests (MDT), Timing Advance, or Proximity Indication.

[0065] The processing capability of the UE 100 may be notified in advance from the UE 100 via the macro station 270M to the CU 260. In this case, the CU 260 may limit the number of small stations 270S to be selected as targets for issuing a command to cancel sleep, depending on the processing capability of the UE 100.

[0066] In step S60, in each of the small stations 270S-1 to 270S-N that have received the instruction to cancel sleep, both the DU and RU start up. The RU starts up its transmitter and receiver.

[0067] In step S70, the small stations 270S-1 to 270S-N each transmit a request for setting up operations to the CU 260. Each of the small stations 270S-1 to 270S-N transmits the request, for example, by including it in an F1 SETUP REQUEST message.

[0068] In step S80, the CU 260 transmits operation-related settings to each of the small stations 270S-1 to 270S-N. The CU 260 transmits the settings, for example, by including them in an F1 SETUP RESPONSE message.

[0069] In step S90, the CU 260 determines the SSB settings for each of the small stations 270S-1 to 270S-N. The SSB settings include an active SSB list and an SSB time order list.

[0070] The active SSB list is beam information indicating the SSB beams that transmit SSBs. The active SSB list includes an SSB index. The SSB index is an identifier that indicates the SSB beam that is requested to be activated. The SSB search direction is specified by the SSB index.

[0071] The SSB time order list indicates the SSB transmission timing. The SSB time order list indicates the time to start emitting SSB beams and the order in which the SSB beams are emitted. Therefore, in this embodiment, the SSB transmission timing is indicated by the time at which the first SSB to be transmitted among multiple SSBs starts transmitting and the order in which the multiple SSBs are transmitted. The CU 260 determines the SSB beam emission start time and the SSB beam emission order so that the SSBs do not interfere with each other between adjacent small stations 270S and the SS-SIR of the synchronization signal received by the UE 100 during SSB search does not decrease. Determining the SSB beam emission start time and the SSB beam emission order so that the SSBs do not interfere with each other between adjacent small stations 270S is referred to as coordinated scheduling. Coordinated scheduling will be described in detail later.

[0072] In step S100, the CU 260 transmits the SSB configuration determined in step S90 to each of the small stations 270S-1 to 270S-N. Accordingly, the CU 260 transmits the SSB transmission timing to each of the multiple small stations 270S. The CU 260 transmits the SSB configuration, for example, by including it in a gNB-CU CONFIGURATION UPDATE message. Each of the small stations 270S-1 to 270S-N receives the SSB configuration. If the received SSB configuration includes an activated SSB list, the small station 270S-i activates only the SSB beams indicated by the SSB indexes included in the activated SSB list.

[0073] As described above, in this embodiment, beam information indicating the SSB beams that transmit SSBs (for example, an active SSB list) is specified separately from the SSB transmission timings (for example, an SSB time order list). CU 260 transmits the beam information along with the SSB transmission timings to small station 270S. Note that the beam information and SSB transmission timings may be specified as a single piece of information. For example, because the SSB time order list specifies the transmission order for multiple SSBs, the SSB time order list includes information about the SSB beams that will be transmitted. Therefore, the beam information indicating the SSB beams and the SSB transmission timings may be specified by the SSB time order list. In this case, the active SSB list is omitted from the SSB settings.

[0074] In step S110, each of the small stations 270S-1 to 270S-N transmits a message indicating that the SSB beam indicated by the SSB index indicated by the SSB setting has been activated to the CU 260. Each of the small stations 270S-1 to 270S-N transmits the message, for example, by including it in a gNB-CU CONFIGURATION UPDATE ACKNOWLEDGE.

[0075] In step S120, the UE 100 performs an SSB search. Each of the small stations 270S-1 to 270S-N emits an SSB beam based on the time and order indicated by the SSB setting received from the CU 260 in step S100. Therefore, the multiple small stations 270S that have been woken up transmit SSBs based on the SSB transmission timing. Here, the small station 270S transmits SSBs based on the SSB transmission timing via an activated SSB beam among the SSB beams indicated by the beam information. The SSB includes, for example, a primary synchronization signal (PSS), a secondary synchronization signal (SSS), and a master information block (MIB).

[0076] The UE 100 receives SSBs from each of the small stations 270S-1 to 270S-N. The UE 100 measures the RSRQ (Reference Signal Received Quality) of the synchronization signal included in each SSB. The UE 100 selects the SSB with the largest measured RSRP from the received SSBs. The UE 100 determines that the small station 270S indicated by the Physical Cell Identity (PCI) detected based on the combination of the PSS and SSS included in the selected SSB is the optimal PSCell or SCell. The following describes an example of a case where the UE 100 determines that the small station 270S-1 of the small stations 270S-1 to 270S-N is the optimal PSCell or SCell. Note that even when the UE 100 receives multiple beams, it can perform the process of measuring the RSRQ in parallel as long as the frequency bands of the multiple beams are different from each other. The optimum PSCell or SCell is a PSCell or SCell that is suitable for communication with the UE 100.

[0077] In step S130, the UE 100 determines that the small station 270S-1 is the optimum PSCell or SCell, and transmits a Physical Random Access Channel (PRACH) to the small station 270S-1. The small station 270S-1 receives the PRACH from the UE 100. Upon receiving the PRACH, the small station 270S-1 transmits a random access response to the UE 100.

[0078] In step S140, the UE 100 connects to the small station 270S-1, using the cell of the small station 270S-1 as a PSCell or SCell. The UE 100 transmits an RRC connection request message to the small station 270S-1. The small station 270S-1 transmits an RRC connection message to the UE 100. Therefore, at least one of the multiple small stations 270S (small station 270S-1) receives the PRACH from the UE 100 and establishes a connection with the UE 100.

[0079] In step S150, the CU 260 instructs the small stations 270S (small stations 270S-2 to 270S-N) that were not connected to the UE 100 in step S140 to sleep. Therefore, the CU 260 instructs the small stations 270S that did not establish a connection with the UE 100, among the multiple small stations 270S, to sleep. The small stations 270S-2 to 270S-N each receive the instruction to sleep from the CU 260.

[0080] In step S160, the small stations 270S-2 to 270S-N that have received the sleep instruction each go to sleep again. Each of the small stations 270S-2 to 270S-N stops its transmitter and receiver.

[0081] In step S170, the small station 270S-1 transmits and receives data with the UE 100 at high throughput in both the UL and DL. The processing in step S170 includes, for example, the following processes: The small station 270S-1 transmits an SRS resource configuration to the UE 100. The small station 270S-1 transmits a channel state information reference signal (CSI-RS) to the UE 100. The UE 100 measures the CSI-RS resource and calculates a precoder to be used for transmitting the SRS based on the measurement of the CSI-RS resource. The UE 100 applies the calculated precoder and transmits the SRS to the small station 270S-1. The small station 270S-1 determines one or more SRS Resource Indicators (SRIs) corresponding to the precoders to be used for transmitting the PUSCH based on the received SRS. The small station 270S-1 transmits the determined one or more SRIs to the UE 100. The UE 100 transmits the PUSCH to the small station 270S-1 using the same antenna port as the antenna port for the SRS.

[0082] Here, the details of cooperative scheduling will be explained. Fig. 11 is a diagram showing an example of cooperative scheduling according to this embodiment. In the example shown in the figure, a small station 270S-1 and a small station 270S-2 are adjacent to each other and use the same frequency band.

[0083] The SSB index specifies the synchronization signal block beam (SSB beam), which is the beam that transmits the SSB. It is assumed that interference is likely to occur when the SSB with SSB index "i1" emitted by the small station 270S-1 and the SSB with SSB index "j1" emitted by the small station 270S-2 are emitted simultaneously. Similarly, it is assumed that interference is likely to occur when an SSB with SSB index "i2" and an SSB with SSB index "j2" are emitted simultaneously, an SSB with SSB index "i3" and an SSB with SSB index "j3" are emitted simultaneously, and an SSB with SSB index "i4" and an SSB with SSB index "j4" are emitted simultaneously. It is assumed that interference is unlikely to occur when the SSB index emitted by the small station 270S-1 and the SSB index emitted by the small station 270S-2 are emitted simultaneously other than the above.

[0084] The direction in which the SSB beam is emitted is predetermined for each base station. The CU260 knows in advance which small stations will cause interference if they simultaneously emit SSB beams.

[0085] In this embodiment, the order of the SSBs radiated by the small station 270S-1 and the order of the SSBs radiated by the small station 270S-2 are set as follows: This makes it possible to avoid interference between the SSBs radiated by the small station 270S-1 and the small station 270S-2, even if the adjacent small station 270S-1 and the small station 270S-2 use the same frequency band.

[0086] The CU260 sets "i1, i2, i3, i4" as the SSB index for the small station 270S-1. Furthermore, the CU260 sets the SSB beam radiation start time to time t0 in the SSB time order list for the small station 270S-1, and sets the SSB beam radiation order to "i1, i2, i3, i4" using the SSB index. According to the SSB time order list, it is set that the SSB beams are radiated at a predetermined cycle in the order of "i1, i2, i3, i4" based on time t0. Time t0 is selected by the CU260 from among predetermined transmission times based on the SSB transmission cycle, for example. The SSB transmission cycle is set by the telecommunications carrier when the base station is installed. Note that time t0 may be specified by the CU260 without being selected from among the predetermined transmission times.

[0087] Meanwhile, the CU 260 sets "j1, j2, j3, j4" as the SSB index for the small station 270S-2. Furthermore, in the SSB time order list for the small station 270S-2, the CU 260 sets the SSB beam radiation start time to time t0, and sets the SSB beam radiation order to "j3, j4, j1, j2" using the SSB index. According to the SSB time order list, it is set that the SSB beams are radiated in a predetermined cycle in the order of "j3, j4, j1, j2" based on time t0.

[0088] FIG. 12 shows the radiation times of the SSB beams emitted from the RU of small station 270S-1 and the RU of small station 270S-2 when the radiation start times and radiation order of the SSB beams are set as described above.

[0089] Note that for an SSB index specified by the CU 260, the small station 270S may not activate all SSB beams specified by that SSB index. In other words, some SSB beams specified by the SSB index may not be activated. A DU may not activate an SSB beam specified by an SSB index due to, for example, a RU failure. As another example, the DU may know the location of the UE 100 in more detail and determine that it is not necessary to radiate an SSB beam in any direction other than the direction of the UE 100.

[0090] For example, if SSB indexes "j1, j2, j3, j4" are specified, small station 270S-2 may radiate only SSB beams with SSB indexes "j1, j2, j3." In other words, the SSB beam with SSB index "j4" is not radiated. In this case, the radiation times of the SSB beams radiated from the RU of small station 270S-1 and the RU of small station 270S-2 are shown in FIG. 13. Even if the DU does not activate the SSB beam specified by the SSB index, it is preferable not to place an SSB index in the section of SSB index "j4," which is not actually radiated, in order to avoid interference between SSB beams. If the section of SSB index "j4" is not left empty and the times at which SSB indexes "j1" and "j2" are radiated in that section are moved forward, coordination is disrupted, making SSB interference more likely.

[0091] Note that if the order of SSB beam emission is not set based on cooperative scheduling, and the SSB emission times are set so that the small stations 270S-1 and 270S-2 do not emit SSBs at the same time, the SSB search will take longer than if the SSBs are emitted at the same time. For example, if the small station 270S-2 emits four SSB beams after the small station 270S-1 has emitted four SSB beams, it will take longer than an SSB search based on cooperative scheduling. Note that it is sufficient to set the small stations 270S-1 and 270S-2 to emit at least one pair of SSBs at the same time. For the remaining SSBs, the small stations 270S-1 and 270S-2 may emit at different times.

[0092] The number of SSBs and the transmission period of the SSBs are set by the carrier when the base station is installed. In this embodiment, the number of SSBs is four, as described above. The transmission period is selected from, for example, 5 ms, 10 ms, 20 ms, 40 ms, 80 ms, or 160 ms.

[0093] In cooperative scheduling, the above-mentioned order of radiating SSB beams is one example, and any order may be used as long as interference is avoided. Also, although the above description has been given of a case where the number of small stations 270S is two, even if the number of small stations 270S is three or more, the order of radiating SSB beams may be any order as long as interference is avoided.

[0094] As described above, in cooperative scheduling, when the CU 260 instructs each of a plurality of small stations 270S that share the same frequency band to wake up, it transmits to each of the plurality of small stations 270S a transmission timing that prevents the SSB beams that transmit SSBs between the plurality of small stations 270S from interfering with each other. With this configuration, the UE 100 can perform an SSB search in a shorter time than when cooperative scheduling is not performed.

[0095] In this embodiment, an example has been described in which the SSB transmission timing is indicated by the time at which the first SSB transmitted among multiple SSBs starts (the SSB beam radiation start time) and the order in which multiple SSBs are transmitted, but this is not limited to this. An example has been described in which the SSB beam radiation start time and the radiation order are set, but this is not limited to this. The SSB transmission timing may be indicated only by the SSB transmission order. In this case, the SSB beam radiation start time is set in advance by the telecommunications carrier when the base station is installed, along with the SSB transmission period, etc. Therefore, the SSB transmission timing is indicated at least by the SSB transmission order. The SSB beam radiation time may also be specified as the SSB transmission timing.

[0096] (1.6) System Operation Example According to Modification of First Embodiment 14 and 15, an example of system operation according to a modification of the first embodiment will be described, focusing on differences from the first embodiment. In the above-described first embodiment, a case where both the DU and RU are activated in a small station 270S that has been instructed to cancel sleep has been described. In the example of system operation according to a modification of the first embodiment, a case where the RU is activated at a time different from the DU is described. Note that the processes from steps S210 to S250, steps S270 to S310, and steps S320 to S370 are the same as the processes from steps S10 to S50, steps S70 to S110, and steps S120 to S170 in FIGS. 9 and 10, and therefore descriptions thereof will be omitted.

[0097] In step S260a, the DU starts up in each of the small stations 270S-1 to 270S-N that received the instruction to cancel sleep. The RU does not start up. Then, the process of step S270 is carried out.

[0098] In step S315a, the RU in each of the small stations 270S-1 to 270S-N starts up. The RU starts up the transmitter and receiver. Then, in step S320, an SSB search is performed.

[0099] In the present embodiment, an example has been described in which a wake-up instruction, operation-related settings, and SSB settings are each transmitted from the CU 260 to the small station 270S, but this is not limiting. Two or more of the wake-up instruction, operation-related settings, and SSB settings may be included in a single message and transmitted from the CU 260 to the small station 270S.

[0100] (2) Second embodiment The second embodiment will be described, mainly focusing on differences from the first embodiment, with reference to Figures 16 and 17. In the second embodiment, the CU 260 transmits transmission frequency information indicating the transmission frequency of the PRACH to the second distributed unit to the UE 100 via the first distributed unit constituting the PCell. The macro station 270M is an example of the first distributed unit. The small station 270S is an example of the second distributed unit.

[0101] (2.1) Example of System Operation According to the Second Embodiment An example of system operation according to the second embodiment will be described, focusing on differences from the first embodiment, with reference to Figures 16 and 17. Note that the processes of steps S410 to S450, S470, S540, S570, and S580 are similar to the processes of steps S10 to S50, S70, S160, S140, and S170 in Figures 9 and 10, and therefore descriptions thereof will be omitted.

[0102] In step S460, in each of the small stations 270S-1 to 270S-N that received the instruction to cancel sleep, both the DU and RU start up. The RU starts up at least the receiver. The RU may start up the transmitter as well as the receiver. However, in order to reduce power consumption, it is preferable that when the small station 270S receives the instruction to cancel sleep, only the receiver starts up and the transmitter remains in the sleep state.

[0103] In step S470, each of the small stations 270S-1 to 270S-N transmits a request for settings related to operation to the CU 260. Here, each of the small stations 270S-1 to 270S-N transmits to the CU 260 a message indicating that it has started up and information about the frequency bands that it can receive, along with the request.

[0104] In step S480, the CU 260 transmits operation-related settings to each of the small stations 270S-1 to 270S-N. The CU 260 transmits transmission frequency information included in the settings. The transmission frequency information is information indicating the transmission frequency of the PRACH requested of the UE 100. The CU 260 transmits transmission frequency information common to the multiple small stations 270S to each of the multiple small stations 270S.

[0105] In step S490, the CU 260 transmits a system information block (SIB) (for example, SIB1) for each of the small stations 270S-1 to 270S-N to the UE 100 via the macro station 270M. The CU 260 includes transmission frequency information in the SIB and transmits it to the UE 100. Therefore, the CU 260 transmits the transmission frequency information to the UE 100 via the macro station 270M. Here, the transmission frequency information is the transmission frequency information transmitted to each of the small stations 270S-1 to 270S-N in step S480. Therefore, the transmission frequency information indicates the transmission frequency of the PRACH that can be received by each of the small stations 270S-1 to 270S-N. The UE 100 receives the SIB including the transmission frequency information. Therefore, the UE 100 receives information indicating the transmission frequency of the PRACH from the macro station 270M to the small station 270S.

[0106] Note that CU 260 may include the transmission frequency information in information other than the SIB and transmit the information to UE 100.

[0107] In step S500, the UE 100 transmits a PRACH that can be received by each of the plurality of small stations 270S to each of the plurality of small stations 270S. The small station 270S receives the PRACH from the UE 100. Here, each of the small stations 270S-1 to 270S-N receives the PRACH transmitted from the UE 100 without a precoder being applied. The transmission frequency of the PRACH is the transmission frequency indicated by the transmission frequency information. Transmitting the PRACH without applying a precoder (that is, without precoding) means, in other words, that the PRACH is radiated in all directions without forming a beam.

[0108] As described above, transmission frequency information indicating the transmission frequency of the PRACH is notified in advance to each of the small stations 270S-1 to 270S-N by the CU 260, so that as many small stations 270S as possible can receive the PRACH of the same frequency. This makes it possible to reduce the number of times the PRACH is transmitted by the UE 100.

[0109] In step S510, the small stations 270S-1 to 270S-N each notify the CU 260 of the reception result of the PRACH. Therefore, the small station 270S notifies the CU 260 of the reception result of the PRACH. The reception result of the PRACH is indicated by the reception power of the PRACH. The CU 260 receives the reception result of the PRACH from each of the small stations 270S-1 to 270S-N.

[0110] Here, the CU 260 determines whether or not to connect the small stations 270S-1 to 270S-N to the UE 100 based on the reception result. For example, the CU 260 determines the small station 270S to connect to the UE 100 based on the magnitude of the received power of the PRACH. The CU 260 determines to connect the small station 270S with the greatest received power of the PRACH to the UE 100.

[0111] As another example, the CU 260 may determine to connect a predetermined number of small stations 270S in descending order of received power to the UE 100. As another example, the CU 260 may determine to connect to the UE 100 small stations 270S whose received power is equal to or greater than a predetermined threshold.

[0112] Note that the CU 260 may determine the small station 270S to connect to the UE 100 based on machine learning. In this machine learning, a trained model is used that has been trained so that the ranking of the small stations 270S to connect to the UE 100 is output when the received power is input. The trained model is generated in advance and stored in the UE 100. Any type of machine learning may be used as the machine learning. An example of machine learning is deep learning. It is preferable to use a technique such as transfer learning in training the learning model for generating the trained model. The CU 260 may determine to connect a predetermined number of small stations 270S to the UE 100 in descending order of the rank output by the trained model.

[0113] An example of a case where the CU 260 determines that of the small stations 270S-1 to 270S-N, the small station 270S-1 should be connected to the UE 100, and determines that the small stations 270S-2 to 270S-N should not be connected to the UE 100 will be described below.

[0114] In step S520, the CU 260 starts up the small station 270S that it has determined will connect to the UE 100 (small station 270S-1), and instructs the small stations 270S that it has determined will not connect to the UE 100 (small stations 270S-2 to 270S-N) to sleep. Therefore, when the CU 260 determines that it will not connect to the UE 100 based on the reception result of the PRACH by the small station 270S, it instructs that small station 270S to sleep. The small station 270S-1 receives the start-up instruction from the CU 260. The small stations 270S-2 to 270S-N each receive a sleep instruction from the CU 260.

[0115] In step S530, the RU in the small station 270S-1 that received the startup instruction starts up its transmitter. Therefore, the transmitter and receiver of the RU are in an activated state. Note that if the transmitter is activated in step S460, the processing of step S530 is omitted.

[0116] In step S550, the UE 100 performs an SSB search. The small station 270S-1 that has not been instructed to sleep radiates an SSB beam. Therefore, if the small station 270S is not instructed to sleep, it transmits an SSB to the UE 100. Note that information (such as the transmission cycle and beam settings) that allows the small station 270S-1 to radiate an SSB beam is set in advance. The UE 100 receives the SSB from the small station 270S-1.

[0117] In step S560, the UE 100 determines that the cell of the small station 270S-1 is the optimum PSCell or SCell, and transmits a PRACH to the small station 270S-1. The small station 270S-1 receives the PRACH from the UE 100.

[0118] As described above, in the system operation example according to the second embodiment, the UE 100 transmits a PRACH in both step S500 and step S560. When transmitting the PRACH in step S500, the UE 100 has not acquired information (such as an SSB index) required for initial access processing to the small station 270S. Therefore, as initial access processing to the small station 270S, the UE 100 performs an SSB search and transmits a PRACH again in step S560. Note that while the PRACH in step S500 is transmitted without precoding as described above, the PRACH in step S560 is transmitted after precoding has been performed. That is, in step S560, the small station 270S-1 receives a PRACH to which a precoder has been applied from the UE 100 that has received the SSB.

[0119] (3) Third embodiment The third embodiment will be described, mainly focusing on differences from the second embodiment, with reference to Figures 18 and 19. In the third embodiment, the CU 260 requests the UE 100 to transmit a reference signal to a second distributed unit via a first distributed unit constituting a PCell. The macro station 270M is an example of a first distributed unit. The small station 270S is an example of a second distributed unit.

[0120] (3.1) Example of system operation according to the third embodiment An example of system operation according to the third embodiment will be described, focusing on differences from the second embodiment, with reference to Figures 18 and 19. Note that the processes from step S610 to step S670 and step S720 to step S780 are similar to the processes from step S410 to step S470 and step S520 to step S580 in Figures 16 and 17, and therefore descriptions thereof will be omitted. Furthermore, the process of step S680 is similar to the process of step S80 in Figure 9, and therefore descriptions thereof will be omitted.

[0121] In step S690, the CU 260 requests the UE 100 to transmit an SRS to each of the small stations 270S-1 to 270S-N, specifying the frequency of the SRS, via the macro station 270M. The UE 100 accepts the request from the macro station 270M to transmit an SRS to each of the small stations 270S-1 to 270S-N. Note that the macro station 270M may transmit a message including this request to the UE 100 at any time.

[0122] Furthermore, the CU 260 requests the UE 100 to transmit an SRS to the macro station 270M via the macro station 270M. The UE 100 accepts a request to transmit an SRS from the macro station 270M to the macro station 270M. Note that the macro station 270M may transmit a message including the request to the UE 100 at any time.

[0123] In step S700, the UE 100 transmits an SRS to each of the small stations 270S-1 to 270S-N and to the macro station 270M. The UE 100 transmits an SRS to each of the small stations 270S-1 to 270S-N and an SRS to the macro station 270M at the same time. The UE 100 transmits an SRS to each of the small stations 270S-1 to 270S-N at a frequency designated for each of the small stations 270S-1 to 270S-N. The small stations 270S-1 to 270S-N each receive the SRS from the UE 100. The UE 100 transmits an SRS to the macro station 270M at a frequency designated for the macro station 270M. The macro station 270M receives the SRS.

[0124] Here, the request to transmit the SRS in step S690 is made before the connection between the UE 100 and the small station 270S is established. Therefore, the CU 260 requests the UE 100 to transmit the SRS to the small station 270S via the macro station 270M before the connection between the UE 100 and the small station 270S is established.

[0125] Furthermore, the transmission of the SRS in step S700 is performed before a connection is established between the UE 100 and the small station 270S. Therefore, the small station 270S is not yet synchronized with the UE 100, and even if the small station 270S receives the SRS, it is unable to accurately measure the distance between the UE 100 and the small station 270S (that is, the time difference between when the UE 100 transmits the SRS and when the small station 270S receives the SRS). Therefore, the UE 100 also transmits and receives the SRS with the macro station 270M with which a connection has already been established, and by sharing the SRS transmission time measured in the transmission and reception of the SRS with the CU 260, it becomes possible to calibrate the reception time of the SRS at the small station 270S.

[0126] In step S710, each of the small stations 270S-1 to 270S-N notifies the CU 260 of the result of receiving the SRS. In addition, the macro station 270M notifies the CU 260 of the result of receiving the SRS.

[0127] Here, the CU 260 determines whether or not to connect the small stations 270S-1 to 270S-N to the UE 100 based on the reception result. For example, the CU 260 determines the small station 270S to connect to the UE 100 based on the magnitude of the received power of the SRS. The CU 260 performs channel estimation based on the SRS received by each of the small stations 270S-1 to 270S-N, and determines that the small station 270S with the greatest received power of the SRS should be connected to the UE 100.

[0128] As another example, the CU 260 may determine to connect a predetermined number of small stations 270S in descending order of received power to the UE 100. As another example, the CU 260 may determine to connect to the UE 100 small stations 270S whose received power is equal to or greater than a predetermined threshold.

[0129] The CU 260 may determine the small station 270S to connect to the UE 100 based on machine learning, in the same manner as described in the second embodiment. The CU 260 may determine to connect a predetermined number of small stations 270S to the UE 100 in descending order of the rank output by the trained model.

[0130] In the process of step S720, if the CU 260 determines not to connect to the UE 100 based on the reception result of the SRS by the small station 270S, it instructs the small station 270S to go to sleep. An example of a case where the CU 260 determines that of the small stations 270S-1 to 270S-N, the small station 270S-1 should be connected to the UE 100, and determines that the small stations 270S-2 to 270S-N should not be connected to the UE 100 will be described below.

[0131] In step S750, the small station 270S-1 transmits SSB only in the direction in which it can be received most strongly by the UE 100. The small station 270S-1 determines this direction based on the reception result of the SRS received in step S700. The UE 100 receives the SRS from the small station 270S-1.

[0132] In the SSB search in step S750, SSB is transmitted only in the direction where UE 100 can receive the strongest signal, which is simpler than the conventional SSB search. This is because SRS has already been transmitted from UE 100 to small station 270S in step S700. The simplification of the SSB search means saving power and increasing the speed.

[0133] (4) Fourth embodiment The fourth embodiment will be described, mainly focusing on differences from the first embodiment, with reference to Figures 20 and 21. In the fourth embodiment, a UE 100 is a user equipment that performs wireless communication with a master node and a secondary node using dual connectivity in a mobile communication system, and receives first information indicating a neighboring cell from the master node. The UE 100 selects a secondary node to be woken up based on the first information. The UE 100 transmits second information indicating a neighboring cell that the UE 100 wishes to wake up to the master node. The macro station 270M is an example of a master node. The small station 270S is an example of a secondary node.

[0134] (4.1) Example of System Operation According to the Fourth Embodiment 20 and 21, an example of system operation according to the fourth embodiment will be described, focusing on differences from the first embodiment. Note that the processes of steps S810 to S840 and steps S930 to S950 are similar to the processes of steps S10 to S40, S130, S140, and S170 in Figures 9 and 10, and therefore descriptions thereof will be omitted. Furthermore, the process of step S920 is similar to the process of step S550 in Figure 17, and therefore descriptions thereof will be omitted.

[0135] In step S850, the CU 260 notifies the UE 100 of the first information via the macro station 270M. Accordingly, the CU 260 transmits the first information to the UE 100. The first information indicates small stations 270S in a sleeping state near the UE 100. Therefore, the first information is information about secondary nodes in a sleeping state. The small stations 270S in a sleeping state near the UE 100 are small stations 270S-1 to 270S-N. The UE 100 receives the first information from the macro station 270M.

[0136] Here, the transmission of the first information from the macro station 270M to the UE 100 is executed at a time after the UE 100 transmits a request for radio quality conditions to the macro station 270M in step S830. Therefore, the UE 100 receives the first information from the macro station 270M after the UE 100 requests high-throughput communication.

[0137] In step S860, the UE 100 selects the small station 270S to be woken up from the candidates. Here, the UE 100 selects the small station 270S to be woken up based on connection history information. In this embodiment, the UE 100 selects the small station 270S to be woken up based on machine learning, using the current location of the UE 100 and connection history information.

[0138] The connection history information is information that indicates the connection history of the UE 100 over a predetermined period of time in the past (for example, the most recent month or the like). The connection history information includes, for example, location and time information when the UE 100 connected to a small station 270S that it previously connected to, an identifier of the small station 270S that it previously connected to, and the communication quality when the UE 100 connected to the small station 270S that it previously connected to. The location when the UE 100 connected to the small station 270S that it previously connected to is acquired, for example, based on the Global Positioning System (GPS). The identifier of the small station 270S that it previously connected to is, for example, the cell ID of the cell of that small station 270S.

[0139] The connection history information may include a daily movement pattern of the UE 100. It is assumed that the movement pattern reflects the daily behavior of the user of the UE 100 and is a unique pattern for each day.

[0140] The current location of the UE 100 is determined based on, for example, the above-described MDT, Timing Advance, or Proximity Indication.

[0141] In the machine learning, a learning model is used that outputs a score for each small station 270S that will wake up when the current location of the UE 100 and connection history information are input. The learning model is generated in advance and stored in the UE 100. Any type of machine learning may be used as the machine learning. An example of the machine learning is deep learning. It is preferable to use a technique such as transfer learning in training the learning model to generate the trained model.

[0142] The UE 100 generates the second information by assigning a high rank to the small stations 270S to be woken up, starting with the small stations 270S that have the highest scores output by the learning model. The second information indicates the small stations 270S that the UE 100 wants to wake up, based on the rank of the small stations 270S.

[0143] In step S870, the UE 100 transmits second information indicating the small station 270S that the UE 100 wishes to wake up to the CU 260 via the macro station 270M. Therefore, the UE 100 transmits the second information indicating the small station 270S that the UE 100 wishes to wake up to the macro station 270M. The CU 260 receives the second information from the UE 100 via the macro station 270M.

[0144] In step S880, the CU 260 instructs the small stations 270S to cancel sleep. The CU 260 instructs the small stations 270S indicated by the second information to cancel sleep. The CU 260 determines whether or not startup is possible for the small stations 270S in order from the highest rank indicated by the second information. When the CU 260 determines that startup is possible for a small station 270S of a certain rank, it cancels this determination process for the remaining stations in the rank. Note that the CU 260 has previously acquired information indicating whether or not startup is possible for the small stations 270S. The CU 260 instructs the small stations 270S that it has determined to be able to start up to cancel sleep.

[0145] As described above, when the macro station 27 receives the second information from the UE 100, the second information is transmitted to the CU 260 via the macro station 270M, and the small station 270S is instructed to cancel sleep by the CU 260. Therefore, when the macro station 270M receives the second information, it starts up the small station 270S.

[0146] An example of a case where the CU 260 determines that of the small stations 270S-1 to 270S-N, the small station 270S-1 should be connected to the UE 100, and determines that the small stations 270S-2 to 270S-N should not be connected to the UE 100 will be described below.

[0147] In step S880, the CU 260 instructs the small station 270S-1 to wake up from sleep. Accordingly, the CU 260 wakes up the neighboring cell based on the second information received from the UE 100. The small station 270S-1 receives the instruction to wake up from sleep from the CU 260.

[0148] In step S890, the small station 270S-1 that has received the instruction to wake up from sleep starts both the DU and RU. The RU starts up its transmitter and receiver.

[0149] In step S900, the small station 270S-1 transmits a request for settings related to operation to the CU 260. The small station 270S-1 transmits the request by including it in an F1 SETUP REQUEST message, for example.

[0150] In step S910, the CU 260 transmits operation-related settings to the small station 270S-1. The CU 260 transmits the settings, for example, by including them in an F1 SETUP RESPONSE message.

[0151] In the fourth embodiment, an example of a case where machine learning is used in the process of selecting the small station 270S to wake up has been described, but the present invention is not limited to this. In this process, a table may be used instead of machine learning. As the table, for example, a table in which a set of the current location and connection history information of the UE 100 is associated with a set of scores for each small station 270S to wake up is used.

[0152] In the second, third, and fourth embodiments described above, an example has been described in which a sleep wake-up instruction and operation-related settings are respectively transmitted from the CU 260 to the small station 270S, but this is not limiting. The sleep wake-up instruction and operation-related settings may be included in a single message and transmitted from the CU 260 to the small station 270S.

[0153] In the system operation examples according to the above-described embodiments, an example has been described in which the macro station 270M is included in the MN 200M and the small station 270S is included in the SN 200S. That is, an example has been described in which the macro station 270M and the small station 270S belong to different cell groups, but this is not limiting. The macro station 270M and the small station 270S may belong to the same cell group. For example, the macro station 270M and the small station 270S may be included in the MN 200M. The system operation examples according to the above-described embodiments may be implemented in a case in which the macro station 270M and the small station 270S belong to the same cell group.

[0154] 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. The computer-readable medium can be used to install the program 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. Furthermore, circuits that execute the processes performed by the UE 100 or the node 200 may be integrated, and at least a part of the UE 100 or the node 200 may be configured as a semiconductor integrated circuit (chipset, system-on-chip (SoC)).

[0155] In the above-described embodiment, an example in which node 200 is an NR base station (gNB) has been described, but node 200 may be an LTE base station (eNB) or a 6G base station. Also, node 200 may be a relay node such as an IAB (Integrated Access and Backhaul) node. Node 200 may be a DU of an IAB node. Also, UE 100 may be an MT (Mobile Termination) of an IAB node.

[0156] Furthermore, the term "node" primarily refers to a base station, but may also refer to a core network device or part of a base station (CU, DU, or RU (Radio Unit)). A node may also be configured by a combination of at least part of a core network device and at least part of a base station.

[0157] 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. [Explanation of symbols]

[0158] 1. Network 10...RAN 20…CN 100…UE 110...Receiver 120...Transmitter 130...Control unit 140...Radio communication unit 200...nodes 210...Transmitter 220...Receiver 230...Control unit 240…Network Communications Department 250...Radio communication section 300…CN device

Claims

1. A user equipment (UE) that performs wireless communication with a master node and a secondary node using dual connectivity in a mobile communication system, receiving first information indicating neighboring cells from the master node; selecting the secondary node to be woken up based on the first information; transmitting second information to the master node indicating a neighboring cell from which the user equipment wishes to wake up; User equipment.

2. The first information is received from the master node after the user device requests high-throughput communication. The user device of claim 1 .

3. The first information is information about the secondary node that is in a sleep state. The user device of claim 1 .

4. The secondary node to be released from sleep mode is selected based on connection history information. The user device of claim 1 .

5. The connection history information is Location and time information when the user device previously connected to the secondary node; an identifier of the previously connected secondary node; and The communication quality when the user equipment connected to the previously connected secondary node is included.

5. A user device according to claim 4.

6. The master node starts the secondary node upon receiving the second information. The user device of claim 1 .

7. A node operating in a mobile communication system in which a user device performs wireless communication using dual connectivity, The node transmitting first information indicating a neighboring cell to the user equipment; receiving second information from the user equipment indicating a neighboring cell that the user equipment wishes to wake up; waking up the neighboring cell based on the received second information; node.

8. A communication method used in a user equipment that performs wireless communication with a master node and a secondary node using dual connectivity in a mobile communication system, comprising: receiving first information indicating neighboring cells from the master node; selecting a secondary node to wake up based on the first information; transmitting second information indicating a neighboring cell from which the user equipment wishes to wake up to the master node; Communication method.

9. A communication method used in a node that performs wireless communication with a user device using dual connectivity in a mobile communication system, comprising: transmitting first information indicating a neighboring cell to the user equipment; receiving second information from the user equipment indicating a neighboring cell from which the user equipment wishes to wake up; waking up the neighboring cell based on the received second information; A communication method comprising:

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