Network node, mobile communication system, central unit, distributed unit, and communication method

Abstract

This network node has a central unit and a plurality of distributed units. The central unit transmits the transmission timing of a synchronization signal block to a second distributed unit.

Description

Network node, mobile communication system, central unit, distributed unit, and communication method

[0001] The present invention relates to a network node, a mobile communication system, a central unit, a distributed unit, and a communication method.

[0002] As a new form of mobile phone line replacing NR (New Radio), which is the fifth generation (5G) standard formulated by the 3rd Generation Partnership Project (3GPP (registered trademark, the same applies hereinafter)), a standardization project for mobile communication systems, a device configuration called cell-free massive MIMO (Multi Input Multi Output) is under study. Cell-free massive MIMO has a configuration in which base stations are arranged more densely than in the prior art, and is a system that achieves both communication quality and power saving by operating only the minimum necessary base stations that are most suitable for the communication requirements of terminals.

[0003] On the other hand, mobile lines are required to have the characteristic of being "connected anytime, anywhere, quickly". In view of this, even if cell-free massive MIMO is a system that operates only the minimum necessary base stations, it is expected that macro base stations that always operate as in the past and cover the entire area will continue to exist in the future. Furthermore, it is expected that the operation of these base stations will be collectively managed by a Central Unit (CU) in accordance with current standards.

[0004] Under the above-mentioned situation setting, the procedure for activating a small base station that is in sleep during normal times is as follows. First, a macro station pre-connected to a terminal is requested by the terminal for a high-quality line. Next, a small base station suitable for communication with the terminal and a communication propagation path are searched. As a result of the search, a link is established between the selected small base station and the terminal. On the other hand, small base stations other than the selected small base station are put back to sleep. As a result, only the selected small base station is activated.

[0005] In the procedure for searching for small base stations and communication propagation paths suitable for communication with terminals, conventional methods (radiation of reference signals) require the temporary activation of each base station. Furthermore, reference signals may interfere with each other in densely populated base stations. Therefore, there is a need for a technology that can complete the procedure for searching for small base stations and communication propagation paths suitable for communication with terminals in a power-efficient and stable manner.

[0006] 3GPP Technical Specification: TS38.401 V18.4.0 (2024-12)

[0007] The network node according to the first embodiment is a network node having a central unit and a plurality of distributed units, wherein the central unit transmits the transmission timing of the synchronization signal block to the second distributed unit.

[0008] The mobile communication system according to the second embodiment is a mobile communication system having a central unit and a plurality of distributed units, wherein the central unit transmits the transmission timing of a synchronization signal block to the second distributed unit.

[0009] The central unit according to the third embodiment is a central unit included in a mobile communication system having a central unit and a plurality of distributed units, which transmits the transmission timing of a synchronization signal block to the distributed units.

[0010] A distributed unit according to the fourth embodiment is a distributed unit included in a mobile communication system having a central unit and a plurality of distributed units, which receives the transmission timing of a synchronization signal block from the central unit and transmits the synchronization signal block based on the transmission timing.

[0011] The fifth aspect of the communication method is a communication method in a network node having a central unit and a plurality of distributed units, wherein the central unit transmits the transmission timing of a synchronization signal block to the second distributed unit.

[0012] This figure shows an example configuration of a mobile communication system according to an embodiment. This figure shows an example configuration of the protocol stack of a U-plane radio interface that handles data. This figure shows an example configuration of the protocol stack of a C-plane radio interface that handles signaling (control signals). This figure is for explaining a terahertz (THz) wave cell according to an embodiment. This figure is for explaining dual connectivity (DC) according to an embodiment. This figure shows an example configuration of a radio access network (RAN) according to an embodiment. This figure shows an example configuration of a UE (user equipment) according to an embodiment. This figure shows an example configuration of a node according to an embodiment. This figure shows an example of system operation according to the first embodiment. This figure shows an example of system operation according to the first embodiment. This figure shows an example of cooperative scheduling according to the first embodiment. This figure shows an example of the emission time of a synchronous signal block (SSB) beam according to the first embodiment. This figure shows another example of the emission time of a synchronous signal block (SSB) beam according to the first embodiment. This figure shows an example of system operation according to a modification of the first embodiment. This figure shows an example of system operation according to a modification of the first embodiment. This figure shows an example of system operation according to the second embodiment. This figure shows an example of system operation according to the second embodiment. This figure shows an example of system operation according to the third embodiment. This figure shows an example of system operation according to the third embodiment. This figure shows an example of system operation according to the fourth embodiment. This figure shows an example of system operation according to the fourth embodiment.

[0013] In the following, a mobile communication system according to an embodiment will be described with reference to the drawings. In the drawings, identical or similar parts are denoted by the same or similar reference numerals.

[0014] (1) The first embodiment will be described with reference to Figures 1 to 15.

[0015] (1.1) Example of System Configuration Figure 1 is a diagram showing an example of the configuration of a mobile communication system according to the embodiment. The mobile communication system according to the embodiment is a system that conforms 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.

[0016] The mobile communication system comprises a network (NW) 1 and a user device (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, such as 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 installed on a sensor, a vehicle or a device installed on a vehicle (Vehicle UE), or an aircraft or a device installed on an aircraft (Aerial UE).

[0017] NW1 includes a radio access network (RAN) 10 and a core network (CN) 20. When the mobile communication system is a fifth-generation system (5GS), RAN 10 is referred to as NG-RAN (Next Generation Radio Access Network) and CN 20 is referred to as 5GC (5G Core Network).

[0018] RAN10 includes a plurality of nodes 200 (nodes 200a to 200c in the illustrated example). The nodes 200 are interconnected via internode interfaces. Nodes 200 are also referred to as base stations. Nodes 200 consist of a CU (Central Unit), a DU (Distributed Unit), and a RU (Radio Unit) (i.e., functionally separated), 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 internode interfaces as Xn interfaces, and the fronthaul interfaces as F1 interfaces.

[0019] Each node 200 manages one or more cells. Nodes 200 perform wireless communication with UEs 100 that have established a connection with their own cell. Each node 200 has wireless resource management (RRM) functions, user data routing functions (also simply referred to as "data"), and measurement and control functions for mobility control and scheduling. 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 that performs wireless communication with a UE 100. One cell belongs to one carrier frequency (also simply referred to as "frequency").

[0020] CN20 includes CN device 300. 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 UE100. The C-plane device communicates with UE100 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 called AMF (Access and Mobility Management Function), the U-plane device is called UPF (User Plane Function), and the interface between node 200 and CN device 300 is called the NG interface.

[0021] Figure 2 shows an example of the protocol stack configuration for a U-plane radio interface that handles data.

[0022] A U-plane radio interface protocol includes, for example, a physical (PHY) layer, a MAC (Medium Access Control) layer, an RLC (Radio Link Control) layer, a PDCP (Packet Data Convergence Protocol) layer, and an SDAP (Service Data Adaptation Protocol) layer.

[0023] 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 UE100 and the PHY layer of Node 200 via a physical channel. The PHY layer of UE100 receives downlink control information (DCI) transmitted from Node 200 on the physical downlink control channel (PDCCH). Specifically, UE100 performs blind decoding of the PDCCH using the Radio Network Temporary Identifier (RNTI) and acquires the successfully decoded DCI as the DCI addressed to its own UE. The DCI transmitted from Node 200 has CRC parity bits scrambled by the RNTI added to it.

[0024] 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 UE100 and the MAC layer of node 200 via the transport channel. The MAC layer of node 200 includes a scheduler. The scheduler determines the transport format for the up and down links (transport block size, modulation and coding scheme (MCS)) and the resources to be allocated to UE100.

[0025] The RLC layer transmits data to the receiving RLC layer using the functions of the MAC layer and PHY layer. Data and control information are transmitted between the RLC layer of UE100 and the RLC layer of node 200 via a logical channel.

[0026] The PDCP layer performs header compression / decompression, encryption / decryption, etc.

[0027] The SDAP layer maps the IP flow, which is the unit for QoS control performed by CN20, to the wireless bearer, which is the unit for QoS control performed by AS (Access Stratum). Note that if the RAN is connected to the EPC (Evolved Packet Core), the SDAP is not required.

[0028] Figure 3 shows an example of the protocol stack configuration for a C-plane wireless interface that handles signaling (control signals).

[0029] The protocol stack of the C-plane wireless interface, for example, includes an RRC (Radio Resource Control) layer and a NAS (Non-Access Stratum) layer instead of the SDAP layer shown in Figure 2.

[0030] RRC signaling for various settings is transmitted between the RRC layer of UE100 and the RRC layer of Node 200. The RRC layer controls the logical channel, transport channel, and physical channel in response to the establishment, re-establishment, and release of the wireless bearer. If there is a connection (RRC connection) between the RRC of UE100 and the RRC of Node 200, UE100 is in the RRC connected state. If there is no connection (RRC connection) between the RRC of UE100 and the RRC of Node 200, UE100 is in the RRC idle state. If the connection between the RRC of UE100 and the RRC of Node 200 is suspended, UE100 is in the RRC inactive state.

[0031] The NAS layer (also simply referred to as "NAS"), located above the RRC layer, performs session management and mobility management, etc. NAS signaling is transmitted between the NAS layer of UE100 and the NAS layer of CN device 300. In addition to the wireless interface protocol, UE100 also has an application layer, etc. Furthermore, the layer below the NAS layer is called the AS layer (also simply referred to as "AS").

[0032] (1.2) DC using a terahertz wave cell Figure 4 is a diagram illustrating the terahertz (THz) wave cell according to the embodiment.

[0033] The mobile communication system according to this embodiment may be a 6G system. In 6G, it is envisioned that terahertz (THz) waves will be utilized. A cell that operates using THz waves is called a THz wave cell. Compared to millimeter waves (mmW), THz waves have even stronger directivity, higher free-space loss, and are more susceptible to atmospheric and rainfall influences. Therefore, THz wave cells can be ultra-small cells.

[0034] In the illustrated example, the diameter of the coverage area of ​​a THz wave cell is approximately 10 m, the diameter of the coverage area of ​​a mmW cell operating at mmW is approximately 100 m, and the diameter of the coverage area of ​​a macrocell is approximately 1000 m. Under these assumptions, for example, a UE100 moving at 60 km / h would pass through the coverage area of ​​each THz wave cell in approximately 599 ms.

[0035] Dual connectivity (DC) is one method for stably controlling small cells in a mobile communication system. Figure 5 is a diagram illustrating dual connectivity (DC) according to an embodiment. In this embodiment, it is assumed that a THz wave cell is used as a cell in a secondary cell group (SCG). Furthermore, a THz wave cell may also be used as a secondary cell (SCell) in a master cell group (MCG). However, a mmW cell may be used instead of a THz wave cell.

[0036] A UE100 in RRC connected state can be configured as a DC. In the DC, the UE100 communicates wirelessly with the master cell group (MCG) managed by the master node (MN) 200M and the secondary cell group (SCG) managed by the secondary node (SN). The MN200M and SN200S are connected to each other via an inter-node interface. When MN200M and SN200S are not distinguished, they are simply referred to as node 200. The MN200M is also called the master gNB (MgNB) when it is a 5G / NR node. The SN200M is also called the secondary gNB (SgNB) when it is a 5G / NR node.

[0037] For example, when MN200M sends a predetermined message (e.g., an SN Addition Request message) to SN200S, and MN200M sends an RRC Reconfiguration message to UE100, the SCG is set to UE100 and DC starts. In DC, UE100, in an RRC connected state, is allocated radio resources from the schedulers of MN200M and SN200S, and performs wireless communication using the radio resources of MN200M and SN200S.

[0038] The MN200M may have a control plane connection to the CN20. The MN200M provides the primary radio resources for the UE100. The MN200M manages the MCG, which is a group of serving cells associated with the MN200M. The MCG has a primary cell (PCell) and optionally one or more secondary cells (SCell). On the other hand, the SN200S does not have a control plane connection to the CN20. The SN200S provides additional radio resources to the UE100. The SN200S manages the SCG, which is a group of serving cells associated with the SN200S. The SCG has a primary and secondary cell (PSCell) and optionally one or more SCell. Note that the PCell of the MCG and the PSCell of the SCG are sometimes referred to as special cells (SpCell).

[0039] The mobile communication system supports the activation and deactivation of the SCG to reduce the power consumption of the UE100 when DC is set. Activation / deactivation of the SCG can be instructed by an RRC Reconfiguration message from the MN200M to the UE100. While the SCG is deactivated, all SCG SCells remain inactive. While the SCG is deactivated, the UE100 does not need to transmit Physical Uplink Shared Channel (PUSCH), Sounding Reference Signal (SRS), and Channel Quality Index (CSI) reports via the SCG. Furthermore, while the SCG is deactivated, the UE100 does not need to monitor the Physical Downlink Control Channel (PDCCH) or receive Downlink Shared Channel (DL-SCH) via the SCG. However, UE100 can continue wireless link monitoring (RLM) and measurement reporting for PSCell. When activating SCG, UE100 can skip the random access procedure if timing advance (TA) with PSCell is enabled.

[0040] Figure 6 shows an example configuration of RAN 10 according to this embodiment. RAN 10 includes MN200M as a plurality of nodes 200 and one or more SN200S. Note that only one of the one or more SN200S is shown in Figure 6. MN200M includes CU260, macro station 270M, and small station 270S. Macro station 270M included in MN200M consists of macro station DU and macro station RU. Macro station 270M included in MN200M manages the MCG's PCell. Small station 270S included in MN200M consists of small station DU and small station RU. Small station 270S included in MN200M manages the MCG's SCell.

[0041] 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 composed of a small station DU and a small station RU. The small station 270S included in the SN 200S manages the PSCell and the SCell of the SCG. Note that in DC, when the UE 100 connects to the SCG, the UE 100 connects to at least the PSCell. When connecting to the SCG, the UE 100 may connect to the SCell of the SCG together with the PSCell.

[0042] In the DC according to the present embodiment, the UE 100 performs wireless communication with the PCell of the MCG managed by the macro station DU connected to the CU 260 included in the MN 200M, and the PSCell or SCell of the SCG managed by the small station DU included in the SN 200S. That is, DC is performed using the PCell included in the MCG and the PSCell or SCell included in the SCG.

[0043] (1.3) Configuration Example of User Equipment Figure 7 is a diagram showing a configuration example of the UE 100 (user equipment) according to the embodiment.

[0044] 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 constitute a wireless communication unit 140 that performs wireless communication with the node 200.

[0045] The receiving unit 110 performs various types of reception under the control of the control unit 130. The receiving unit 110 includes an antenna and a receiver. The receiver converts a wireless signal received by the antenna into a baseband signal (received signal) and outputs the baseband signal to the control unit 130. The transmitting unit 120 performs various types of transmission 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 from the control unit 130 into a wireless signal and transmits the wireless signal from the antenna.

[0046] The control unit 130 performs various types of control and processing in the UE 100. The operations of the UE 100 described above and described 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 for processing by the processor. The processor may include a baseband processor and a CPU (Central Processing Unit). The baseband processor performs modulation / demodulation, encoding / decoding, and the like on baseband signals. The CPU executes programs stored in the memory to perform various types of processing.

[0047] (1.4) Configuration Example of Node FIG. 8 is a diagram showing a configuration example of a node 200 (base station) according to an embodiment. The node 200 may be an MN 200M or an SN 200S.

[0048] The node 200 includes a transmitting unit 210, a receiving unit 220, a control unit 230, and an NW communication unit 240. The transmitting unit 210 and the receiving unit 220 constitute a wireless communication unit 250 that performs wireless communication with the UE 100.

[0049] The transmitting unit 210 performs various types of transmission 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 from the control unit 230 into a wireless signal and transmits the wireless signal from the antenna. The receiving unit 220 performs various types of reception under the control of the control unit 230. The receiving unit 220 includes an antenna and a receiver. The receiver converts a wireless signal received by the antenna into a baseband signal (reception signal) and outputs the baseband signal to the control unit 230.

[0050] The control unit 230 performs various controls and processes at the node 200. The operation of the node 200 described above and below may be controlled by 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 for processing by the processor. The processor may include a baseband processor and a CPU. The baseband processor performs modulation, demodulation, encoding, and decoding of baseband signals. The CPU executes programs stored in memory and performs various processes.

[0051] The NW communication unit 240 is connected to an adjacent node via an inter-node interface. The NW communication unit 240 is connected to the CN device 300 via a node-CN interface.

[0052] Node 200M, configured in this way, is a network node having a central unit and multiple distributed units. The central unit transmits the transmission timing of the synchronization signal block to the second distributed unit. CU260 is an example of a central unit. Macro station 270M and small station 270S are examples of multiple distributed units. Small station 270S is an example of a second distributed unit.

[0053] With the above configuration, node 200M can transmit the transmission timing of the synchronization signal block to the second distributed unit, enabling the procedure of searching for a communication path with small station 270S, which is suitable for communication with UE100, to be completed in a power-efficient and stable manner.

[0054] The mobile communication system according to this embodiment is a mobile communication system having a central unit and a plurality of distributed units. Furthermore, CU260 is a central unit included in the mobile communication system having a central unit and a plurality of distributed units.

[0055] Furthermore, the small station 270S is a distributed unit included in a mobile communication system having a central unit and multiple distributed units. The small station 270S receives the transmission timing of the Synchronization Signal Block (SSB) from the central unit. The small station 270S transmits the SSB based on the SSB transmission timing.

[0056] (1.5) System Operation Example Figure 9 is a diagram showing a system operation example according to the first embodiment. The CU260 shown in Figure 9 is the CU260 included in SN200S. In Figure 9, the CU260 included in MN200M is omitted. The macro station 270M shown in Figure 9 is the macro station 270M included in MN200M. When the CU260 included in SN200S and the macro station 270M included in MN200M communicate in DC, the communication is performed via the CU260 included in MN200M. The small station 270S shown in Figure 9 is the small station 270S included in SN200S. In the system operation according to the first embodiment, the CU260 included in SN200S transmits the SSB transmission timing to each of the multiple small stations 270S included in SN200S.

[0057] In the following explanation, CU260 included in SN200S will be simply referred to as "CU260". Small station 270S included in SN200S will be simply referred to as "Small station 270S". Macro station 270M included in MN200M will be simply referred to as "Macro station 270M". Also, in the following explanation, "Small station 270S" refers to any one of Small station 270S-1 to Small station 270S-N. "Multiple small stations 270S" refers to two or more of Small station 270S-1 to Small station 270S-N.

[0058] In step S10, UE100 is pre-connected to the PCell of the macro station 270M.

[0059] In step S20, small stations 270S-1 through 270S-N are in sleep mode.

[0060] In step S30, UE100 transmits a request for radio quality conditions to macro station 270M. UE100 transmits this request in the UCI transmitted via PUCCH. Alternatively, UE100 may transmit this request in a PDCP Control PDU or RRC message. Radio quality conditions include, for example, high throughput data transmission and reception in both UL and DL. Macro station 270M receives the request for radio quality conditions from UE100. The request for radio quality conditions is an example of a notification transmitted from UE100 to macro station 270M. Therefore, UE100 transmits a notification to the master node.

[0061] In step S40, the macro station 270M sends a message to the CU 260 notifying it of the traffic congestion status. For example, the macro station 270M sends the traffic congestion status to the CU 260 in a Resource Status Request message. Thus, the macro station 270M, which constitutes PCell, notifies the CU 260 of information indicating the usage of radio resources. The CU 260 receives a message from the macro station 270M notifying it of the traffic congestion status.

[0062] In step S50, CU260 instructs the small station 270S to wake up. Therefore, having received information indicating the usage status of radio resources, CU260 instructs multiple small stations 270S near UE100 to wake up. Based on the location information of UE100, CU260 selects small stations 270S located within a specific range. CU260 instructs the selected small station 270S to wake up. The selected small station 270S receives the instruction to wake up from CU260. In Figure 9, small stations 270S-1 to 270S-N are shown as small stations 270S-1 to 270S-N selected by CU260 as being located within a specific range.

[0063] The details of the process by which CU260 selects a small station 270S to be woken from sleep mode based on the location information of UE100 are described below. For example, CU260 first selects a small station 270S that is close to UE100. In this case, CU260 may select a small station 270S whose distance from UE100 is less than or equal to a predetermined distance. Alternatively, CU260 may select a predetermined number of small stations 270S in order of their shortest distance from UE100.

[0064] CU260 selects a set of small stations 270S that are close to UE100, such that their SSB searches in step S120 (described later) are less likely to interfere with each other. Less interference in SSB searches means that the signal power to interference ratio (SS-SIR) of the synchronization signals received by UE100 during the SSB search is not likely to deteriorate. For example, CU260 selects small stations 270S that are close to UE100 and that use different frequency bands. The frequency band is the frequency band of the cell used by the small station 270S as a PSCell or SCell of the SCG. However, if interference between SSBs can be avoided by the interference avoidance process in the SSB search described later, a small station 270S that is close to UE100 and uses the same frequency band may be selected.

[0065] Furthermore, CU260 determines the current position of UE100 based on known technology. CU260 determines the current position of UE100 based, for example, on MDT (Minimization of Drive Tests), Timing Advance, or Proximity Indication.

[0066] Furthermore, the processing capacity of UE100 may be notified in advance from UE100 to CU260 via macro station 270M. In that case, CU260 may limit the number of small stations 270S selected as targets for instructing UE100 to wake from sleep mode, according to its processing capacity.

[0067] In step S60, both the DU and RU are activated in small stations 270S-1 through 270S-N, each of which has received an instruction to wake from sleep. The RU activates the transmitter and receiver.

[0068] In step S70, small station 270S-1 to small station 270S-N each send a request for operational settings to CU260. Small station 270S-1 to small station 270S-N each send this request, for example, in an F1 SETUP REQUEST message.

[0069] In step S80, CU260 transmits the operational settings to small station 270S-1 and small station 270S-N respectively. CU260 transmits these settings, for example, in an F1 SETUP RESPONSE message.

[0070] In step S90, CU260 determines the SSB settings for each of the small stations 270S-1 through 270S-N. The SSB settings include an activated SSB list and an SSB time sequence list.

[0071] The activated SSB list is beam information that indicates the SSB beams transmitting SSBs. The activated SSB list includes an SSB index. The SSB index is an identifier that indicates the SSB beam requested to be activated. The SSB search direction is specified by the SSB index.

[0072] The SSB time sequence list indicates the transmission timing of the SSBs. The SSB time sequence list indicates the time when the SSB beam radiation begins and the order in which the SSB beams are emitted. Therefore, in this embodiment, the transmission timing of the SSBs is indicated by the time when the first SSB to be transmitted among the multiple SSBs begins to be transmitted and the order in which the multiple SSBs are transmitted. CU260 determines the SSB beam radiation start time and the SSB beam radiation order so that the SSBs do not interfere with adjacent small stations 270S and the SS-SIR of the synchronization signal received by UE100 in SSB search does not decrease. Determining the SSB beam radiation start time and the SSB beam radiation order so that the SSBs do not interfere with adjacent small stations 270S is called cooperative scheduling. Details of cooperative scheduling will be described later.

[0073] In step S100, CU260 transmits the SSB settings determined in step S90 to each of the small stations 270S-1 through 270S-N. Therefore, CU260 transmits the SSB transmission timing to each of the multiple small stations 270S. CU260 transmits the SSB settings, for example, in a gNB-CU CONFIGURATION UPDATE message. Each of the small stations 270S-1 through 270S-N receives the SSB settings. If the received SSB settings include an activated SSB list, small station 270S-i activates only the SSB beams indicated by the SSB indices included in the activated SSB list.

[0074] As described above, in this embodiment, beam information indicating the SSB beam to transmit the SSB (for example, an activated SSB list) is specified separately from the SSB transmission timing (for example, an SSB time sequence list). CU260 transmits the beam information along with the SSB transmission timing to the small station 270S. Note that the beam information and the SSB transmission timing may be specified as a single piece of information. For example, since the SSB time sequence list specifies the transmission order for multiple SSBs, the SSB time sequence list includes information about the SSB beams to be transmitted. Therefore, the beam information indicating the SSB beam and the SSB transmission timing may be specified by the SSB time sequence list. In that case, the activated SSB list is omitted from the SSB settings.

[0075] In step S110, each of the small stations 270S-1 to 270S-N sends a message to the CU260 indicating that it has activated the SSB beam indicated by the SSB index indicated by the SSB setting. Each of the small stations 270S-1 to 270S-N sends this message, for example, in a gNB-CU CONFIGURATION UPDATE ACKNOWLEDGE.

[0076] In step S120, UE100 performs an SSB search. Small stations 270S-1 through 270S-N each emit an SSB beam based on the time and order indicated by the SSB settings received from CU260 in step S100. Thus, multiple small stations 270S that have been woken from sleep transmit SSB based on the SSB transmission timing. Here, small stations 270S transmit SSB based on the SSB transmission timing via the 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).

[0077] UE100 receives SSB signals from small stations 270S-1 through 270S-N. UE100 measures the RSRQ (Reference Signal Received Quality) for the synchronization signal contained in each SSB. UE100 selects the SSB with the highest measured RSRP from among the received SSBs. Based on the combination of PSS and SSS contained in the selected SSB, UE100 determines that the small station 270S indicated by the Physical Cell Identity (PCI) is the optimal PSCell or SCell. The following describes an example of when UE100 determines that small station 270S-1 is the optimal PSCell or SCell among small stations 270S-1 through 270S-N. Furthermore, even when the UE100 receives multiple beams, it can perform the RSRQ measurement process in parallel as long as the frequency bands of those beams are different from each other. The optimal PSCell or SCell is the PSCell or SCell suitable for communication with the UE100.

[0078] In step S130, UE100 determines that small station 270S-1 is the optimal PSCell or SCell and transmits a Physical Random Access Channel (PRACH) to small station 270S-1. Small station 270S-1 receives the PRACH from UE100. Upon receiving the PRACH, small station 270S-1 transmits a random access response to UE100.

[0079] In step S140, UE100 connects to small station 270S-1 by setting its cell as PSCell or SCell. UE100 sends an RRC Connection Request message to small station 270S-1. Small station 270S-1 sends an RRC connection message to UE100. Thus, at least one of the multiple small stations 270S (small station 270S-1) receives a PRACH from UE100 and establishes a connection with UE100.

[0080] In step S150, CU260 instructs the small stations 270S (from small station 270S-2 to small station 270S-N) that did not connect to UE100 in step S140 to go to sleep. Therefore, CU260 instructs the small stations 270S that did not establish a connection with UE100 to go to sleep. Small stations 270S-2 to 270S-N each receive a sleep instruction from CU260.

[0081] In step S160, small stations 270S-2 to 270S-N, having received a sleep command, go back to sleep. Small stations 270S-2 to 270S-N then shut down their transmitters and receivers, respectively.

[0082] In step S170, the small station 270S-1 performs high-throughput data transmission and reception with the UE100 in both UL and DL. The processing in step S170 includes, for example, the following: The small station 270S-1 transmits the SRS resource settings to the UE100. The small station 270S-1 transmits a channel status information reference signal (CSI-RS) to the UE100. The UE100 measures the CSI-RS resources and calculates the precoder used for transmitting the SRS based on the measurement of the CSI-RS resources. The UE100 applies the calculated precoder and transmits the SRS to the small station 270S-1. Based on the received SRS, the small station 270S-1 determines one or more SRIs (SRS Resource Indicators) corresponding to the precoder used for transmitting the PUSCH. Small station 270S-1 transmits one or more determined SRIs to UE100. UE100 transmits PUSCH to small station 270S-1 using the same antenna port as the SRS antenna port.

[0083] Here, we will explain the details of cooperative scheduling. Figure 11 is a diagram showing an example of cooperative scheduling according to this embodiment. In the illustrated example, small station 270S-1 and small station 270S-2 are adjacent to each other and use the same frequency band.

[0084] The SSB index specifies the synchronous signal block beam (SSB beam), which is the beam that transmits SSB. It is assumed that interference is likely to occur if the SSB with SSB index "i1" radiated by small station 270S-1 and the SSB with SSB index "j1" radiated by small station 270S-2 are radiated simultaneously. Similarly, interference is likely to occur if the SSB with SSB index "i2" and SSB with SSB index "j2", SSB with SSB index "i3" and SSB with SSB index "j3", and SSB with SSB index "i4" and SSB with SSB index "j4" are radiated simultaneously. For combinations of SSB indices other than those mentioned above, interference is unlikely to occur even if they are radiated simultaneously.

[0085] 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.

[0086] In this embodiment, the order of SSB radiated by small station 270S-1 and the order of SSB radiated by small station 270S-2 are set to the following order. This prevents interference between the SSB radiated by small station 270S-1 and small station 270S-2, even if the operating frequency bands of adjacent small stations 270S-1 and 270S-2 are the same.

[0087] CU260 sets "i1, i2, i3, i4" as the SSB index for small station 270S-1. Furthermore, in the SSB time sequence list for small station 270S-1, CU260 sets the SSB beam emission start time to time t0 and the SSB beam emission order to "i1, i2, i3, i4" using the SSB index. According to this SSB time sequence list, the SSB beam is emitted at a predetermined cycle in the order of "i1, i2, i3, i4" relative to time t0. Time t0 is selected by CU260, for example, from among predetermined transmission times based on the SSB transmission cycle. The SSB transmission cycle is set by the telecommunications carrier when the base station is installed. Note that time t0 may be specified by CU260 instead of being selected from among the predetermined transmission times.

[0088] On the other hand, CU260 sets "j1, j2, j3, j4" as the SSB index for small station 270S-2. Also, in the SSB time sequence list for small station 270S-2, CU260 sets the start time of SSB beam emission to time t0 and sets the order of SSB beam emission to "j3, j4, j1, j2" by SSB index. According to this SSB time sequence list, the SSB beam is set to be emitted at a predetermined period in the order of "j3, j4, j1, j2" based on time t0.

[0089] As described above, when the SSB beam emission start time and emission order are set, Figure 12 shows the emission times of the SSB beams emitted from the RU of small station 270S-1 and the RU of small station 270S-2, respectively.

[0090] Furthermore, for an SSB index specified by CU260, the small station 270S does not have to activate all SSB beams specified by that SSB index. In other words, there may be SSB beams among those specified by the SSB index that are not activated. If the DU does not activate an SSB beam specified by the SSB index, for example, there may be a malfunction in the RU. Another example is when the DU knows the location of UE100 in more detail and determines that there is no need to radiate an SSB beam in any direction other than that of UE100.

[0091] For example, if the SSB indices "j1, j2, j3, j4" are specified, small station 270S-2 may only radiate the SSB beams for the SSB indices "j1, j2, j3". In other words, the SSB beam for the SSB index "j4" will not be radiated. In this case, Figure 13 shows the radiation times of the SSB beams radiated from the RU of small station 270S-1 and the RU of small station 270S-2, respectively. Even if the DU does not activate the SSB beams specified by the SSB index, in order to avoid interference between SSB beams, it is preferable not to place an SSB index in the section of SSB index "j4" which is not actually radiated. If the radiation times of SSB indices "j1" and "j2" are shifted forward in the section of SSB index "j4" without leaving a gap, coordination will be disrupted and SSB interference will be more likely.

[0092] Furthermore, if the timing of SSB beam emission is set so that SSB beams are not emitted simultaneously between small stations 270S-1 and 270S-2, without setting the order of SSB beam emission based on coordinated scheduling, the SSB search will take longer than if the SSB beams were emitted simultaneously. For example, if small station 270S-2 emits four SSB beams after small station 270S-1 has emitted four SSB beams, the SSB search will take longer than an SSB search based on coordinated scheduling. However, it is sufficient that small stations 270S-1 and 270S-2 are set to emit at least one set of SSB beams simultaneously. For the remaining SSB beams, the timing of emission between small stations 270S-1 and 270S-2 may differ.

[0093] The number of SSBs and the transmission cycle of the SSBs are set by the telecommunications carrier when the base station is installed. In this embodiment, the number of SSBs is four, as described above. The transmission cycle is selected from, for example, 5 ms, 10 ms, 20 ms, 40 ms, 80 ms, or 160 ms.

[0094] In cooperative scheduling, the above-described order of SSB beam emission is just one example; any order is acceptable as long as interference is avoided. Furthermore, although the above description described the case where there are two small stations 270S, similarly, even if there are three or more small stations 270S, any order of SSB beam emission is acceptable as long as interference is avoided.

[0095] As described above, in cooperative scheduling, when CU260 instructs each of the multiple small stations 270S with the same frequency band to wake up, it transmits to each of the multiple small stations 270S a transmission timing that prevents the SSB beams transmitting SSB among the multiple small stations 270S from interfering with each other. With this configuration, UE100 can perform an SSB search in a shorter time compared to when cooperative scheduling is not performed.

[0096] In this embodiment, an example has been described in which the SSB transmission timing is indicated by the time when the first SSB among multiple SSBs is transmitted (SSB beam emission start time) and the transmission order of multiple SSBs, but it is not limited to this. An example has been described in which the SSB beam emission start time and the emission order are set, but it is not limited to this. The SSB transmission timing may also be indicated by the transmission order of the SSBs alone. In that case, the SSB beam emission start time is set in advance by the telecommunications carrier along with the SSB transmission cycle, etc., when the base station is installed. Therefore, the SSB transmission timing is indicated by at least the transmission order of the SSBs. The SSB beam emission time may also be specified as the SSB transmission timing.

[0097] (1.6) System Operation Example According to Modification of the First Embodiment Referring to Figures 14 and 15, the system operation example according to the modification of the first embodiment will be explained, mainly focusing on the differences from the first embodiment. In the first embodiment described above, the case in which both the DU and RU are started up in the small station 270S that has been instructed to wake from sleep was explained. In the system operation example according to the modification of the first embodiment, the case in which the timing of the RU's startup differs from the timing of the DU's startup will be explained. Note that the processes from step S210 to step S250, from step S270 to step S310, and from step S320 to step S370 are the same as the processes from step S10 to step S50, from step S70 to step S110, and from step S120 to step S170 in Figures 9 and 10, so their explanation will be omitted.

[0098] In step S260a, the DU is activated in each of the small stations 270S-1 through 270S-N that have received the instruction to wake from sleep. The RU is not activated. Subsequently, the process in step S270 is performed.

[0099] In step S315a, the RU is activated in each of the small stations 270S-1 through 270S-N. The RU activates the transmitter and receiver. Then, in step S320, an SSB search is performed.

[0100] In this embodiment, an example has been described in which a sleep wake-up instruction, operational settings, and SSB settings are transmitted from CU260 to small station 270S, but it is not limited to this. Two or more of the sleep wake-up instruction, operational settings, and SSB settings may be included in a single message transmitted from CU260 to small station 270S.

[0101] (2) Second Embodiment The second embodiment will be described with reference to Figures 16 and 17, mainly focusing on the differences from the first embodiment. In the second embodiment, CU260 transmits transmission frequency information indicating the transmission frequency of PRACH to the second distributed unit via the first distributed unit constituting PCell to UE100. Macro station 270M is an example of the first distributed unit. Small station 270S is an example of the second distributed unit.

[0102] (2.1) System Operation Example According to the Second Embodiment Referring to Figures 16 and 17, the system operation example according to the second embodiment will be described, mainly focusing on the differences from the first embodiment. Note that the processes from step S410 to step S450, step S470, step S540, step S570, and step S580 are the same as the processes from step S10 to step S50, step S70, step S160, step S140, and step S170 in Figures 9 and 10, so their explanation will be omitted.

[0103] In step S460, both the DU and RU are activated in each of the small stations 270S-1 to 270S-N that have received an instruction to wake from sleep. The RU activates at least the receiver. The RU may also activate the transmitter along with the receiver. However, in order to reduce power consumption, it is preferable that when small station 270S receives an instruction to wake from sleep, only the receiver is activated and the transmitter remains in sleep mode.

[0104] In step S470, small station 270S-1 to small station 270S-N each send a request for operational settings to CU260. At this point, small station 270S-1 to small station 270S-N each send a message indicating that they have started up, along with information on the receivable frequency bands, to CU260, along with the request.

[0105] In step S480, CU260 transmits operational settings to each small station 270S-1 through 270S-N. CU260 includes transmission frequency information in these settings. The transmission frequency information indicates the transmission frequency of the PRAC to be requested from UE100. CU260 transmits common transmission frequency information to each of the multiple small stations 270S.

[0106] In step S490, CU260 transmits the system information block (SIB) (e.g., SIB1) for each small station 270S-1 to 270S-N to UE100 via macro station 270M. CU260 transmits the transmission frequency information to UE100, including it in the SIB. Therefore, CU260 transmits the transmission frequency information to UE100 via macro station 270M. This transmission frequency information is the same information transmitted to each small station 270S-1 to 270S-N in step S480. Thus, the transmission frequency information indicates the transmission frequencies of PRACH that each small station 270S-1 to 270S-N can receive. UE100 receives the SIB containing the transmission frequency information. Therefore, UE100 receives information indicating the transmission frequency of the PRACH from macro station 270M to small station 270S.

[0107] Furthermore, CU260 may include the transmission frequency information in information other than SIB and transmit it to UE100.

[0108] In step S500, UE100 transmits a PRACH to each of the multiple small stations 270S, which can be received by each of the multiple small stations 270S. The small stations 270S receive the PRACH from UE100. Here, small stations 270S-1 to 270S-N each receive the PRACH transmitted from UE100 without the application of a precoder. The transmission frequency of the PRACH is the transmission frequency indicated by the transmission frequency information. Transmitting the PRACH without the application of a precoder (i.e., without pre-recording) means, in other words, that the PRACH is radiated in all directions without the formation of a beam.

[0109] As described above, by having the transmission frequency information indicating the PRACH transmission frequency notified in advance from CU260 to each of the small stations 270S-1 and 270S-N, as many small stations 270S as possible can receive PRACH on the same frequency. This reduces the number of PRACH transmissions by UE100.

[0110] In step S510, small stations 270S-1 to 270S-N each notify CU260 of the PRACH reception result. Therefore, small station 270S notifies CU260 of the PRACH reception result. The PRACH reception result is indicated by the PRACH reception power. CU260 receives the PRACH reception results from small stations 270S-1 to 270S-N.

[0111] Here, CU260 determines whether to connect small stations 270S-1 through 270S-N to UE100 based on the reception results. For example, CU260 determines which small station 270S to connect to UE100 based on the magnitude of the received power of PRACH. CU260 determines that the small station 270S with the largest received power of PRACH will be connected to UE100.

[0112] As another example, CU260 may determine that it will connect a predetermined number of small stations 270S to UE100 in order of the highest received power. As yet another example, CU260 may determine that it will connect small stations 270S whose received power is above a predetermined threshold to UE100.

[0113] Furthermore, CU260 may determine which small stations 270S to connect to UE100 based on machine learning. In this machine learning, a pre-trained model is used that has been trained to output the ranking of the small stations 270S that should connect to UE100 when the received power is input. The training model is generated in advance and stored in UE100. Any type of machine learning may be used. One example of machine learning is deep learning. When training the training model for generating the pre-trained model, it is preferable to use a method such as transfer learning. CU260 may determine to connect a predetermined number of small stations 270S to UE100 in order of the ranking output by the pre-trained model.

[0114] The following describes an example where CU260 determines that small station 270S-1 is connected to UE100 from small station 270S-1 to small station 270S-N, but determines that small station 270S-2 to small station 270S-N is not connected to UE100.

[0115] In step S520, CU260 activates the small station 270S (small station 270S-1) that it has determined to connect to UE100, and instructs the small stations 270S (from small station 270S-2 to small station 270S-N) that it has determined not to connect to UE100 to go to sleep. Therefore, if CU260 determines, based on the PRACH reception result by the small station 270S, that it will not connect to UE100, it instructs the small station 270S to go to sleep. Small station 270S-1 receives an activation instruction from CU260. Small stations 270S-2 to 270S-N each receive a sleep instruction from CU260.

[0116] In step S530, the RU starts the transmitter at small station 270S-1, which has received the start command. Therefore, both the RU's transmitter and receiver are started. Note that if the transmitter is already started in step S460, the process in step S530 is omitted.

[0117] In step S550, UE100 performs an SSB search. Small station 270S-1, which was not instructed to sleep, emits an SSB beam. Therefore, if small station 270S is not instructed to sleep, it transmits SSB to UE100. The information for small station 270S-1 to emit an SSB beam (transmission cycle, beam settings, etc.) is set in advance. UE100 receives SSB from small station 270S-1.

[0118] In step S560, UE100 determines that the cell of small station 270S-1 is the optimal PSCell or SCell and transmits PRACH to small station 270S-1. Small station 270S-1 receives PRACH from UE100.

[0119] As described above, in the system operation example according to the second embodiment, UE100 transmits a PRACH in step S500 and step S560, respectively. When transmitting the PRACH in step S500, UE100 has not acquired the information necessary for the initial access processing to the small station 270S (such as the SSB index). Therefore, as the initial access processing to the small station 270S, a PRACH is transmitted again in step S560 along with an SSB search. Note that the PRACH in step S500 is transmitted without pre-recording as described above, whereas the PRACH in step S560 is transmitted with pre-recording. In other words, in step S560, the small station 270S-1 receives a PRACH with a pre-coder applied from UE100, which has received the SSB.

[0120] (3) Third Embodiment The third embodiment will be described with reference to Figures 18 and 19, mainly focusing on the differences from the second embodiment. In the third embodiment, CU260 requests UE100 to transmit a reference signal to the second distributed unit via the first distributed unit that constitutes PCell. Macro station 270M is an example of the first distributed unit. Small station 270S is an example of the second distributed unit.

[0121] (3.1) System Operation Example According to the Third Embodiment Referring to Figures 18 and 19, the system operation example according to the third embodiment will be described, mainly focusing on the differences from the second embodiment. Note that the processes from steps S610 to S670 and from steps S720 to S780 are the same as the processes from steps S410 to S470 and from steps S520 to S580 in Figures 16 and 17, so their explanation will be omitted. Also, the process of step S680 is the same as the process of step S80 in Figure 9, so its explanation will be omitted.

[0122] In step S690, CU260 requests UE100 via macro station 270M to transmit SRS signals from small station 270S-1 to small station 270S-N, specifying the SRS frequency. UE100 accepts the request from macro station 270M to transmit SRS signals from small station 270S-1 to small station 270S-N. Macro station 270M may send a message containing this request to UE100 at any time.

[0123] Furthermore, CU260 requests UE100 to transmit SRS to macro station 270M via macro station 270M. UE100 accepts the request from macro station 270M to transmit SRS to macro station 270M. Macro station 270M may send a message containing this request to UE100 at any time.

[0124] In step S700, UE100 transmits an SRS from small station 270S-1 to small station 270S-N and to macro station 270M. UE100 transmits the SRS from small station 270S-1 to small station 270S-N and the SRS to macro station 270M simultaneously. UE100 transmits an SRS from small station 270S-1 to small station 270S-N at the frequency specified for each small station 270S-1 to small station 270S-N. Small stations 270S-1 to 270S-N each receive the SRS from UE100. UE100 transmits an SRS to macro station 270M at the frequency specified for macro station 270M. Macro station 270M receives the SRS.

[0125] Here, the request for SRS transmission in step S690 is made before the connection between UE100 and small station 270S is established. Therefore, CU260 requests UE100 to transmit SRS to small station 270S via macro station 270M before the connection between UE100 and small station 270S is established.

[0126] Furthermore, the transmission of the SRS in step S700 is performed before the connection between UE100 and small station 270S is established. Therefore, small station 270S is not yet synchronized with UE100, and even if small station 270S receives the SRS, it is not possible to accurately measure the distance between UE100 and small station 270S (i.e., the time difference between when UE100 transmits the SRS and when small station 270S receives the SRS). To address this, UE100 also transmits and receives SRS with macro station 270M, with which a connection has already been established, and shares the SRS transmission time measured during this transmission and reception with CU260, thereby enabling calibration of the SRS reception time at small station 270S.

[0127] In step S710, each of the small stations 270S-1 to 270S-N notifies CU260 of the SRS reception result. The macro station 270M also notifies CU260 of the SRS reception result.

[0128] Here, CU260 determines whether to connect small stations 270S-1 through 270S-N to UE100 based on the received results. For example, CU260 determines which small station 270S will connect to UE100 based on the magnitude of the received SRS power. CU260 performs channel estimation based on the SRS received by each small station 270S-1 through 270S-N, and determines that the small station 270S with the largest received SRS power will be connected to UE100.

[0129] As another example, CU260 may determine that it will connect a predetermined number of small stations 270S to UE100 in order of the highest received power. As yet another example, CU260 may determine that it will connect small stations 270S whose received power is above a predetermined threshold to UE100.

[0130] Furthermore, CU260 may determine which small stations 270S to connect to UE100 based on machine learning, as described in the second embodiment. CU260 may determine to connect a predetermined number of small stations 270S to UE100 in order of the highest rank output by the trained model.

[0131] In step S720, if CU260 determines, based on the SRS reception result by small station 270S, that it will not connect to UE100, it instructs small station 270S to go to sleep. Below, an example is described in which CU260 determines that small station 270S-1 will be connected to UE100 from small station 270S-1, and that small station 270S-N will not be connected to UE100 from small station 270S-2.

[0132] In step S750, the small station 270S-1 transmits SSB only in the direction from which UE100 can receive the signal most strongly. The small station 270S-1 determines this direction based on the SRS reception result received in step S700. UE100 receives the SRS from the small station 270S-1.

[0133] In step S750, the SSB search is simplified compared to conventional SSB searches, as SSB is transmitted only in the direction from which UE100 can receive the signal most strongly. This is because SRS has already been transmitted from UE100 to small station 270S in step S700. The simplification of the SSB search is intended to reduce power consumption and increase speed.

[0134] (4) Fourth Embodiment The fourth embodiment will be described with reference to Figures 20 and 21, mainly focusing on the differences from the first embodiment. In the fourth embodiment, UE100 is a user device 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 an adjacent cell from the master node. UE100 selects a secondary node to wake from sleep based on the first information. UE100 transmits second information to the master node indicating the adjacent cell that UE100 wants to wake from sleep. Macro station 270M is an example of a master node. Small station 270S is an example of a secondary node.

[0135] (4.1) System Operation Example According to the Fourth Embodiment With reference to Figures 20 and 21, the system operation example according to the fourth embodiment will be described, mainly focusing on the differences from the first embodiment. Note that the processes from steps S810 to S840 and from steps S930 to S950 are the same as the processes from steps S10 to S40, S130, S140, and S170 in Figures 9 and 10, and therefore their explanation will be omitted. Also, the process in step S920 is the same as the process in step S550 in Figure 17, and therefore its explanation will be omitted.

[0136] In step S850, CU260 notifies UE100 of the first information via macro station 270M. Therefore, CU260 transmits the first information to UE100. The first information indicates a nearby sleep-state small station 270S of UE100. Therefore, the first information is information about a secondary node in sleep state. The nearby sleep-state small stations 270S of UE100 are small stations 270S-1 to 270S-N. UE100 receives the first information from macro station 270M.

[0137] Here, the transmission of the first information from macro station 270M to UE100 occurs after UE100 has transmitted the radio quality condition request to macro station 270M in step S830. Therefore, UE100 receives the first information from macro station 270M after UE100 has requested high-throughput communication.

[0138] In step S860, UE100 selects a small station 270S to be woken from sleep mode from among the candidates. Here, UE100 selects the small station 270S to be woken from sleep mode based on connection history information. In this embodiment, UE100 selects the small station 270S to be woken from sleep mode based on machine learning using UE100's current location and connection history information.

[0139] Connection history information is information that shows the connection history of UE100 over a predetermined period in the past (for example, the most recent month). Connection history information includes, for example, location and time information when UE100 previously connected with a small station 270S, the identifier of the small station 270S previously connected, and the communication quality when UE100 connected with the small station 270S previously connected. The location when UE100 previously connected with a small station 270S is obtained, for example, based on the Global Positioning System (GPS). The identifier of the small station 270S previously connected is, for example, the cell ID of the cell of the small station 270S.

[0140] Furthermore, the connection history information may include the daily movement patterns of UE100. These movement patterns are expected to be unique to each day, reflecting the daily behavior of the UE100 user.

[0141] The current location of UE100 is determined, for example, based on the aforementioned MDT, Timing Advance, or Proximity Indication.

[0142] In machine learning, a learning model is used that, given the current location of the UE100 and connection history information as input, outputs a score for each small station 270S to be woken from sleep mode. The learning model is pre-generated and stored in the UE100. Any type of machine learning may be used. One example of machine learning is deep learning. When training the learning model to generate the pre-trained model, it is preferable to use methods such as transfer learning.

[0143] The UE100 generates second-order information by assigning higher rankings to the small stations 270S that have higher scores output by the learning model, in order of which they should be woken from sleep mode. This second-order information indicates which small stations 270S the UE100 wants to wake from sleep mode based on their ranking.

[0144] In step S870, UE100 transmits second information to CU260 via macro station 270M indicating the small station 270S that UE100 wants to wake from sleep. Therefore, UE100 transmits second information to macro station 270M indicating the small station 270S that UE100 wants to wake from sleep. CU260 receives second information from UE100 via macro station 270M.

[0145] In step S880, CU260 instructs the small station 270S to wake up from sleep. CU260 instructs the small station 270S indicated by the second information to wake up from sleep. CU260 determines whether the small stations 270S can be started, starting with the highest-ranking small station 270S indicated by the second information. If CU260 determines that a small station 270S of a certain rank can be started, it stops the determination process for subsequent ranks. Note that CU260 has previously obtained information indicating whether the small station 270S can be started. CU260 instructs the small station 270S that it has determined can be started to wake up from sleep.

[0146] As described above, when macro station 27 receives the second information from UE 100, it transmits it to CU 260 via macro station 270M, and CU 260 instructs small station 270S to wake up from sleep mode. Therefore, when macro station 270M receives the second information, it starts up small station 270S.

[0147] The following describes an example where CU260 determines that small station 270S-1 is connected to UE100 from small station 270S-1 to small station 270S-N, but determines that small station 270S-2 to small station 270S-N is not connected to UE100.

[0148] In step S880, CU260 instructs small station 270S-1 to wake up from sleep. Therefore, CU260 wakes up the adjacent cell based on the second information received from UE100. Small station 270S-1 receives the instruction to wake up from sleep from CU260.

[0149] In step S890, when small station 270S-1 receives an instruction to wake from sleep mode, both the DU and RU are activated. The RU activates the transmitter and receiver.

[0150] In step S900, the small station 270S-1 sends a request for operational settings to the CU260. The small station 270S-1 sends this request, for example, in an F1 SETUP REQUEST message.

[0151] In step S910, CU260 transmits the operational settings to small station 270S-1. CU260 transmits these settings, for example, in an F1 SETUP RESPONSE message.

[0152] In the fourth embodiment, an example of a case in which machine learning is used in the process of selecting the small station 270S to be woken from sleep was described, but the invention is not limited to this. In this process, a table may be used instead of machine learning. For example, the table may be one in which a pair of the current location and connection history information of the UE 100 is associated with a pair of scores for each of the small stations 270S to be woken from sleep.

[0153] In the second, third, and fourth embodiments described above, an example was given in which a sleep wake-up instruction and an operation-related setting are transmitted from CU260 to the small station 270S, but the invention is not limited to this. The sleep wake-up instruction and the operation-related setting may be included in a single message and transmitted from CU260 to the small station 270S.

[0154] In the system operation examples of each embodiment described above, an example was explained in which the macro station 270M is included in MN200M and the small station 270S is included in SN200S. In other words, an example was explained in which the macro station 270M and the small station 270S belong to different cell groups, but it is not limited to this. 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 MN200M. The system operation examples of each embodiment described above may be implemented in which the macro station 270M and the small station 270S belong to the same cell group.

[0155] A program may be provided that causes a computer (UE 100, node 200) to perform the operations according to the above embodiment. The program may be recorded on a computer-readable medium. Using a computer-readable medium, it is possible to install the program on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transient recording medium. The non-transient recording medium is not particularly limited, but may be a recording medium such as a CD-ROM or DVD-ROM. Furthermore, the circuits that perform each process performed by UE 100 or node 200 may be integrated, and at least a part of UE 100 or node 200 may be configured as a semiconductor integrated circuit (chipset, system-on-a-chip (SoC)).

[0156] In the above embodiment, an example was described in which node 200 is an NR base station (gNB), but node 200 may be an LTE base station (eNB) or a 6G base station. Furthermore, 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.

[0157] Furthermore, the term "node" primarily refers to a base station, but may also refer to a core network device or a part of a base station (CU, DU, or RU (Radio Unit)). A node may also consist of a combination of at least a part of the core network device and at least a part of a base station.

[0158] Although one embodiment of this invention has been described in detail above with reference to the drawings, the specific configuration is not limited to that described above, and various design changes can be made without departing from the spirit of this invention.

[0159] 1...Network 10...RAN 20...CN 100...UE 110...Receiver 120...Transmitter 130...Control Unit 140...Wireless Communication Unit 200...Node 210...Transmitter 220...Receiver 230...Control Unit 240...NW Communication Unit 250...Wireless Communication Unit 300...CN Device

Claims

1. A network node having a central unit and a plurality of distributed units, wherein the central unit transmits the transmission timing of a synchronization signal block to a second distributed unit.

2. The network node according to claim 1, wherein the transmission timing is indicated by the transmission order of the synchronization signal blocks.

3. The network node according to claim 2, wherein the transmission timing is indicated by the time when the transmission of the first synchronization signal block to be transmitted among the plurality of synchronization signal blocks begins, and the order in which the plurality of synchronization signal blocks are transmitted.

4. The network node according to any one of claims 1 to 3, wherein beam information indicating a synchronization signal block beam for transmitting the synchronization signal block is specified separately from the transmission timing, and the central unit transmits the beam information together with the transmission timing to the second distributed unit.

5. The network node according to claim 4, wherein the second distributed unit transmits the synchronization signal block based on the transmission timing via the activated synchronization signal block beam among the synchronization signal block beams indicated by the beam information.

6. The network node according to any one of claims 2 to 5, wherein when the central unit instructs each of the plurality of second distributed units having the same frequency band to wake up, it transmits to each of the plurality of second distributed units a transmission timing such that the synchronization signal block beams transmitting the synchronization signal block among the plurality of second distributed units do not interfere with each other.

7. A network node according to any one of claims 1 to 6, wherein a first distributed unit constituting a primary cell notifies the central unit of information indicating the status of wireless resource usage; the central unit, upon receiving the notification, instructs a plurality of second distributed units near the user device to wake up; the central unit transmits the transmission timing of a synchronization signal block to each of the plurality of second distributed units; the plurality of second distributed units that have woken up transmit the synchronization signal block based on the transmission timing; at least one of the plurality of second distributed units receives a physical random access channel from the user device and establishes a connection with the user device; and the central unit instructs the second distributed units that have not established a connection with the user device to sleep.

8. A mobile communication system having a central unit and a plurality of distributed units, wherein the central unit transmits the transmission timing of a synchronization signal block to a second distributed unit.

9. A central unit included in a mobile communication system having a central unit and a plurality of distributed units, the central unit transmitting the transmission timing of a synchronization signal block to the distributed units.

10. A distributed unit included in a mobile communication system having a central unit and a plurality of distributed units, the distributed unit receiving the transmission timing of a synchronization signal block from the central unit and transmitting the synchronization signal block based on the transmission timing.

11. A communication method in a network node having a central unit and a plurality of distributed units, wherein the central unit transmits the transmission timing of a synchronization signal block to a second distributed unit.

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