Communication system, base station device, and communication terminal device

Abstract

Provided is a high-speed communication system in NR (New Radio) and LTE, and the like. In a case where a secondary base station device detects a data-inactivation state in which downlink data to a communication terminal device is not activated for all bearers (ST802), the secondary base station device notifies the primary base station device of the occurrence of the data-inactivation state even if the secondary base station device is not inquired by the primary base station device (ST803). Upon receiving the notification of the occurrence of the data-inactivation state, the primary base station device transmits an instruction to transition from an RRC_CONNECTED state to an RRC_INACTIVE state to the communication terminal device (ST805). The communication terminal device transitions to the RRC_INACTIVE state in accordance with the instruction from the primary base station device (ST808).

Description

[0001] This invention application is a divisional application of the invention patent application with international application number PCT / JP2018 / 035876, international application date of September 27, 2018, and Chinese national phase application number 201880060306.2, entitled "Communication System, Base Station Device and Communication Terminal Device". Technical Field

[0002] The present invention relates to a communication system for wireless communication between a communication terminal device such as a mobile terminal device and a base station device. Background Technology

[0003] Within the 3GPP (3rd Generation Partnership Project), the standardization organization for mobile communication systems, a communication method known as Long Term Evolution (LTE) in terms of the radio domain and System Architecture Evolution (SAE) in terms of the overall system architecture including the core network and the radio access network (hereinafter collectively referred to as the network) has been studied (e.g., Non-Patent Documents 1-5). This communication method is also referred to as a 3.9G (3.9 Generation) system.

[0004] As an access method for LTE, the downlink uses OFDM (Orthogonal Frequency Division Multiplexing), and the uplink uses SC-FDMA (Single Carrier Frequency Division Multiple Access). Furthermore, unlike W-CDMA (Wideband Code Division Multiple Access), LTE does not include line switching; it is solely a packet communication method.

[0005] use Figure 1 Explain the decisions made in 3GPP concerning the frame structure of the LTE system as described in Non-Patent Document 1 (Chapter 5). Figure 1 This is an explanatory diagram showing the structure of the radio frame used in an LTE communication system. Figure 1In this system, a radio frame is 10ms long. A radio frame is divided into 10 equal-sized subframes. Each subframe is further divided into two equal-sized slots. The first and sixth subframes of each radio frame contain downlink synchronization signals. These synchronization signals consist of a primary synchronization signal (P-SS) and a secondary synchronization signal (S-SS).

[0006] Non-patent document 1 (Chapter 5) describes the decisions made by 3GPP regarding the channel structure of LTE systems. It is assumed that CSG (Closed Subscriber Group) cells also use the same channel structure as non-CSG cells.

[0007] The Physical Broadcast Channel (PBCH) is a downlink transmission channel from a base station (hereinafter sometimes referred to as "base station") to a mobile terminal device (hereinafter sometimes referred to as "mobile terminal") or other communication terminal device (hereinafter sometimes referred to as "communication terminal"). A BCH transport block is mapped to four subframes within a 40ms interval. There is no explicit signaling during the 40ms timing.

[0008] The Physical Control Format Indicator Channel (PCFICH) is a downlink transmission channel from the base station to the communication terminal. The PCFICH informs the communication terminal from the base station about the number of OFDM (Orthogonal Frequency Division Multiplexing) symbols used for PDCCHs. The PCFICH is transmitted per subframe.

[0009] The Physical Downlink Control Channel (PDCCH) is the downlink transmission channel from the base station to the communication terminal. The PDCCH notifies the recipients of resource allocation information for two transport channels: the Downlink Shared Channel (DL-SCH) and the Paging Channel (PCH), as well as HARQ (Hybrid Automatic Repeat reQuest) information related to the DL-SCH. The PDCCH also transmits uplink scheduling grants and response signals for uplink transmissions, namely Ack (Acknowledgement) and Nack (Negative Acknowledgement). The PDCCH is also known as the L1 / L2 control signal.

[0010] The Physical Downlink Shared Channel (PDSCH) is the downlink transmission channel from the base station to the communication terminal. The Downlink Shared Channel (DL-SCH), which serves as the transport channel, and the PCH, which also serves as the transport channel, are mapped to the PDSCH.

[0011] The Physical Multicast Channel (PMCH) is a downlink transmission channel from the base station to the communication terminal. The PMCH maps to the Multicast Channel (MCH), which serves as the transmission channel.

[0012] The Physical Uplink Control Channel (PUCCH) is the uplink transmission channel from the communication terminal to the base station. The PUCCH transmits response signals (ACK / Nack) for downlink transmissions. It also transmits CQI (Channel Quality Indicator) reports, which indicate the quality of received data or the quality of the communication line. The PUCCH also transmits scheduling requests (SRs).

[0013] The Physical Uplink Shared Channel (PUSCH) is the uplink transmission channel from the communication terminal to the base station. The Uplink Shared Channel (UL-SCH) is mapped to the PUSCH as one of the transmission channels.

[0014] The Physical Hybrid ARQ Indicator Channel (PHICH) is the downlink transmission channel from the base station to the communication terminal. PHICH transmits the Ack / Nack response signals to the uplink transmission. The Physical Random Access Channel (PRACH) is the uplink transmission channel from the communication terminal to the base station. PRACH transmits the random access preamble.

[0015] Downlink reference signals (RS) are known symbols in LTE communication systems. Five types of downlink reference signals are defined: Cell-specific Reference Signal (CRS), MBSFN reference signal, UE-specific reference signal (also known as Demodulation Reference Signal: DM-RS), Positioning Reference Signal (PRS), and Channel-State Information Reference Signal (CSI-RS). As a physical layer measurement of the communication terminal, the received power (RSRP) of the reference signal is also measured.

[0016] This describes the transport channel as described in Non-Patent Document 1 (Chapter 5). In the downlink transport channel, the broadcast channel (BCH) is broadcast to the entire coverage area of ​​its base station (cell). The BCH is mapped to the Physical Broadcast Channel (PBCH).

[0017] The Downlink Shared Channel (DL-SCH) utilizes HARQ (Hybrid ARQ) for retransmission control. DL-SCH can broadcast to the entire coverage area of ​​the base station (cell). DL-SCH supports dynamic or semi-static resource allocation. Semi-static resource allocation is also known as persistent scheduling. DL-SCH supports discontinuous reception (DRX) of communication terminals to reduce power consumption. DL-SCH is mapped to the Physical Downlink Shared Channel (PDSCH).

[0018] The Paging Channel (PCH) supports DRX (Device Response) of communication terminals to reduce power consumption. The PCH requires broadcasting across the entire coverage area of ​​the base station (cell). The PCH is mapped to physical resources such as the Physical Downlink Shared Channel (PDSCH), which can be dynamically utilized for traffic.

[0019] The Multicast Channel (MCH) is used to broadcast to the entire coverage area of ​​a base station (cell). The MCH supports SFN synthesis of MBMS (Multimedia Broadcast Multicast Service) services (MTCH and MCCH) in multi-cell transmission. The MCH supports quasi-static resource allocation. The MCH is mapped to the PMCH.

[0020] Retransmission control using HARQ (Hybrid ARQ) is applied to the Uplink Shared Channel (UL-SCH) in the uplink transport channel. UL-SCH supports dynamic or semi-static resource allocation. UL-SCH is mapped to the Physical Uplink Shared Channel (PUSCH).

[0021] The Random Access Channel (RACH) is restricted by control information. RACH is subject to collision risks. RACH is mapped to the Physical Random Access Channel (PRACH).

[0022] HARQ is explained below. HARQ is a technique that improves the communication quality of a transmission line by combining Automatic Repeat Request (ARQ) and Forward Error Correction. The advantage of HARQ is that even for transmission lines where communication quality changes, retransmission can effectively enable error correction. In particular, by combining the initial received result with the retransmitted result during retransmission, quality can be further improved.

[0023] Here's an example illustrating the retransmission method. If the receiving side cannot correctly decode the received data—in other words, if a CRC (Cyclic Redundancy Check) error occurs (CRC = NG)—a "Nack" is sent from the receiving side to the sending side. The sending side, upon receiving the "Nack," retransmits the data. If the receiving side can correctly decode the received data—in other words, if no CRC error occurs (CRC = OK)—a "ck" is sent from the receiving side to the sending side. The sending side, upon receiving the "Ack," sends the next data.

[0024] Explain the logical channel described in Non-Patent Document 1 (Chapter 6). The Broadcast Control Channel (BCCH) is a downlink channel used for broadcasting system control information. The BCCH, as a logical channel, is mapped to either the Broadcast Channel (BCH) as a transmission channel or the Downlink Shared Channel (DL-SCH).

[0025] The Paging Control Channel (PCCH) is a downlink channel used to transmit paging information and system information updates. The PCCH is used when the network does not know the cell location of the communicating terminal. The logical channel PCCH is mapped to the paging channel (PCH) as a transport channel.

[0026] The Common Control Channel (CCCH) is a channel used to transmit control information between a communication terminal and a base station. The CCCH is used when there is no RRC connection between the communication terminal and the network. In the downlink direction, the CCCH is mapped to the Downlink Shared Channel (DL-SCH) used as a transport channel. In the uplink direction, the CCCH is mapped to the Uplink Shared Channel (UL-SCH) used as a transport channel.

[0027] The Multicast Control Channel (MCCH) is a downlink channel used for point-to-multipoint transmission. The MCCH is used to send one or more MBMS control messages (MTCHs) from the network to the communication terminal. The MCCH is used only by the communication terminal receiving the MBMS. The MCCH is mapped to the multicast channel (MCH), which serves as the transport channel.

[0028] The Dedicated Control Channel (DCCH) is a channel used to transmit dedicated control information between a communication terminal and the network in a point-to-point manner. The DCCH is used when the communication terminal is in an RRC connection. In the uplink, the DCCH is mapped to the Uplink Shared Channel (UL-SCH), and in the downlink, it is mapped to the Downlink Shared Channel (DL-SCH).

[0029] A Dedicated Traffic Channel (DTCH) is a channel used to transmit user information and conduct point-to-point communication with individual terminals. DTCH exists in both the uplink and downlink. In the uplink, DTCH is mapped to the Uplink Shared Channel (UL-SCH), and in the downlink, it is mapped to the Downlink Shared Channel (DL-SCH).

[0030] The Multicast Traffic Channel (MTCH) is a downlink channel used to send service data from the network to communication terminals. The MTCH is used only by communication terminals receiving MBMS. The MTCH is mapped to the Multicast Channel (MCH).

[0031] CGI stands for Cell Global Identification. ECGI stands for E-UTRAN Cell Global Identifier. In LTE, LTE-A (Long Term Evolution Advanced) (described later), and UMTS (Universal Mobile Telecommunication System), CSG (Closed Subscriber Group) cells were introduced.

[0032] A CSG (Closed Subscriber Group) cell is a cell for a specific subscriber with designated access rights (hereinafter sometimes referred to as a "subscriber-specific cell"). A specific subscriber is permitted access to more than one cell within a PLMN (Public Land Mobile Network). The more than one cell that allows access to a specific subscriber is called a "CSG cell(s)". However, PLMNs have access restrictions.

[0033] A CSG cell is part of a PLMN that broadcasts a unique CSG identity (CSG ID) and uses a CSG indication to broadcast "TRUE". Members of a pre-registered and authorized joiner group access the CSG cell using the CSG ID from their access permission information.

[0034] CSGIDs are broadcast by the CSG cell or the cell itself. Multiple CSGIDs exist in LTE communication systems. Furthermore, the CSGID is used by the user terminal (UE) to facilitate access for CSG-associated members.

[0035] Location tracking of a communication terminal is performed on a unit consisting of one or more cells. Location tracking is used to enable the tracking of the communication terminal's location and to conduct conversations with it, even in standby mode; in other words, it is used to make calls to the communication terminal. The area used for location tracking of the communication terminal is called the tracking area.

[0036] In 3GPP, base stations referred to as Home-NodeB (Home-NB; HNB, home base station) and Home-eNodeB (Home-eNB; HeNB, home base station) have been studied. HNBs in UTRAN and HeNBs in E-UTRAN are, for example, base stations providing access services for homes, corporations, and businesses. Non-Patent Document 2 discloses three different modes for accessing HeNBs and HNBs. Specifically, it discloses Open access mode, Closed access mode, and Hybrid access mode.

[0037] Furthermore, within 3GPP, the Long Term Evolution Advanced (LTE-A) standard, version 10, is under continuous development (see Non-Patent Documents 3 and 4). LTE-A is based on the LTE radio inter-communication method, with some new technologies added to it.

[0038] In LTE-A systems, to support wider transmission bandwidths up to 100MHz, carrier aggregation (CA), which combines two or more component carriers (CCs), has been studied. CA is described in Non-Patent Literature 1.

[0039] In the case of a CA (Cybernetic Association), the UE has a unique RRC connection with the network (NW). Within the RRC connection, a serving cell provides NAS (Navigation Information and Security) input. This cell is called the Primary Cell (PCell). In the downlink, the carrier corresponding to the PCell is the Downlink Primary Component Carrier (DLPCC). In the uplink, the carrier corresponding to the PCell is the Uplink Primary Component Carrier (ULPCC).

[0040] Based on the UE's capabilities, secondary serving cells (SCells) are constructed, forming a group of serving cells with the Pcell. In the downlink, the carrier corresponding to the SCell is the Downlink Secondary Component Carrier (DLSCC). In the uplink, the carrier corresponding to the SCell is the Uplink Secondary Component Carrier (ULSCC).

[0041] For a UE, a group of serving cells consists of one PCell and one or more Scells.

[0042] Furthermore, as a new technology for LTE-A, it features technologies such as wideband extension and Coordinated Multiple Point Transmission and Reception (CoMP). CoMP, which 3GPP is researching for LTE-A, is documented in Non-Patent Literature 1.

[0043] In 3GPP, to cope with the massive traffic volume in the future, research has been conducted on small cell eNBs (sometimes referred to below as "small-scale base station devices") that form small cells. For example, research has been conducted on technologies that improve frequency utilization efficiency and increase communication capacity by setting up multiple micro eNBs and forming multiple small cells. Specifically, there are dual connectivity (DC) systems where the UE communicates by connecting to two eNBs. DC is described in Non-Patent Literature 1.

[0044] Sometimes one of the eNBs that perform dual connections (DC) is called the "primary eNB (MeNB)" and the other is called the "secondary eNB (SeNB)".

[0045] Mobile network traffic is trending upwards, and communication speeds are constantly increasing. With the official implementation of LTE and LTE-A, further increases in communication speeds are foreseeable.

[0046] Furthermore, regarding highly advanced mobile communications, discussions will focus on fifth-generation (hereinafter sometimes referred to as "5G") radio access systems aimed at providing services after 2020. For example, in Europe, the organization METIS is summarizing the requirements for 5G (see Non-Patent Document 5).

[0047] In 5G wireless access systems, for LTE systems, the following are the necessary conditions for achieving further low power consumption and low device cost: system capacity is 1000 times greater, data transmission speed is 100 times greater, data processing latency is 1 / 10th, and the number of simultaneous connections of communication terminals is 100 times greater.

[0048] To meet the above requirements, 3GPP is conducting 5G standard research as version 15 (see Non-Patent Documents 6-10). The technology for the 5G radio band is called "New Radio Access Technology" ("New Radio," abbreviated as "NR"), and several new technologies are being researched (see Non-Patent Document 11). For example, inactive control in UEs using DC is being studied. Furthermore, research on LTE standard extensions is also underway. For example, power control in UEs mounted on unmanned aerial vehicles is being studied (see Non-Patent Documents 12, 13).

[0049] Existing technical documents

[0050] Non-patent literature

[0051] Non-patent literature 1: 3GPPTS36.300V14.3.0

[0052] Non-patent document 2: 3GPPS1-083461

[0053] Non-patent literature 3: 3GPPTR36.814V9.2.0

[0054] Non-patent literature 4: 3GPPTR36.912V14.0.0

[0055] Non-patent literature 5: "Scenarios, requirements and KPIs for 5G mobile and wireless system", ICT-317669-METIS / D1.1

[0056] Non-patent literature 6: 3GPPTR23.799V14.0.0

[0057] Non-patent literature 7: 3GPPTR38.801V14.0.0

[0058] Non-patent literature 8: 3GPPTR38.802V14.1.0

[0059] Non-patent literature 9: 3GPPTR38.804V14.0.0

[0060] Non-patent literature 10: 3GPPTR38.912V14.0.0

[0061] Non-patent literature 11: 3GPPR2-1706892

[0062] Non-Patent Document 12: 3GPPRP-171050

[0063] Non-patent literature 13: 3GPPR1-1708433 Summary of the Invention

[0064] The technical problem that the invention aims to solve

[0065] In NR, control techniques related to the RRC_INACTIVE state are being explored as a means to reduce UE power consumption and enable rapid communication reconnection. RRC_INACTIVE state control in UEs using a DC architecture is also under investigation. To confirm whether there is data to be transmitted or received between the MgNB and SgNB, the MgNB queries the SgNB for data availability. However, the signaling used for this query between the MgNB and SgNB occupies bandwidth between base stations. This results in a decrease in communication speed between DC base stations, and consequently, a decrease in communication speed between the MgNB, SgNB, and UE.

[0066] In addition, techniques to reduce interference to surrounding base stations when communicating with UEs (hereinafter sometimes referred to as UAV-UEs) mounted on unmanned aerial vehicles are also under discussion. However, reducing the transmission power from the UAV-UE to minimize interference to surrounding base stations will result in a decrease in the receiving power of the serving cell, leading to a deterioration in the communication quality between the UAV-UE and the serving cell, and a reduction in communication speed.

[0067] In view of the above-mentioned problems, one of the objectives of this invention is to provide a high-speed communication system under NR and LTE.

[0068] Technical solutions adopted to solve technical problems

[0069] According to the present invention, a communication system is provided, which includes, for example, a communication terminal device and a plurality of base station devices configured to wirelessly communicate with the communication terminal device. The plurality of base station devices includes a primary base station device and a secondary base station device that constitute bearers for the communication terminal device. When the secondary base station device detects a data inactivity state for downlink data to the communication terminal device on all bearers, the secondary base station device notifies the primary base station device of the occurrence of the data inactivity state even without being queried by the primary base station device. Upon receiving the notification of the occurrence of the data inactivity state, the primary base station device sends an instruction to the communication terminal device to transition from the RRC_CONNECTED state to the RRC_INACTIVE state. The communication terminal device transitions to the RRC_INACTIVE state according to the instruction from the primary base station device.

[0070] According to the present invention, a base station device is provided, which is configured, for example, to wirelessly communicate with a communication terminal device. The base station device operates as a secondary base station device that, together with a primary base station device, serves as a bearer for the communication terminal device. When the base station device detects a data inactivity state for downlink data to the communication terminal device among all bearers, the base station device notifies the primary base station device of the occurrence of the data inactivity state even without being queried by the primary base station device.

[0071] According to the present invention, a base station device is provided, which is configured, for example, to wirelessly communicate with a communication terminal device. The base station device operates as a primary base station device, together with a secondary base station device, to bear the communication terminal device. When the secondary base station device detects a data inactivity state for downlink data to the communication terminal device on all bearers, the secondary base station device notifies the base station device of the occurrence of the data inactivity state even without being queried by the primary base station device. Upon receiving the notification of the occurrence of the data inactivity state, the base station device sends an indication to the communication terminal device to transition from the RRC_CONNECTED state to the RRC_INACTIVE state.

[0072] According to the present invention, a communication terminal device is provided, which is configured to wirelessly communicate with multiple base station devices. The multiple base station devices include a primary base station device and a secondary base station device that form a bearer for the communication terminal device. When the secondary base station device detects a data inactivity state where downlink data to the communication terminal device is inactive on all bearers, the secondary base station device notifies the primary base station device of the occurrence of the data inactivity state even without being queried by the primary base station device. When the primary base station device receives the notification of the occurrence of the data inactivity state, it sends an instruction to the communication terminal device to transition from the RRC_CONNECTED state to the RRC_INACTIVE state. The communication terminal device transitions to the RRC_INACTIVE state according to the instruction from the primary base station device.

[0073] Invention Effects

[0074] According to the present invention, a high-speed communication system in NR and LTE can be provided.

[0075] The objectives, features, form, and advantages of the present invention will become clearer from the following detailed description and accompanying drawings. Attached Figure Description

[0076] Figure 1 This is an explanatory diagram showing the structure of the radio frame used in an LTE communication system.

[0077] Figure 2 This is a block diagram showing the overall structure of a communication system 200 using the LTE method discussed in 3GPP.

[0078] Figure 3 This illustrates the communication terminal involved in the present invention. Figure 2 The diagram shows the structure of the mobile terminal 202.

[0079] Figure 4This illustrates the base station involved in the present invention. Figure 2 The diagram shows the structure of base station 203.

[0080] Figure 5 This is a block diagram illustrating the structure of the MME involved in this invention.

[0081] Figure 6 This is a flowchart illustrating the process of a communication terminal (UE) in an LTE communication system from cell search to standby mode.

[0082] Figure 7 This is a diagram illustrating the concept of cell structure when macro eNBs and micro eNBs are mixed.

[0083] Figure 8 This is a flowchart illustrating the actions of the UE transitioning to the RRC_INACTIVE state and returning to the RRC_CONNECTED state in Implementation 1.

[0084] Figure 9 This is a flowchart illustrating the actions of the UE transitioning to the RRC_INACTIVE state and returning to the RRC_CONNECTED state in Implementation 1.

[0085] Figure 10 This is a flowchart illustrating the action in Variation 1 of Implementation 1 where the transition of the UE to the RRC_INACTIVE state is interrupted by the RRC_INACTIVE state transition interruption indication from the MgNB.

[0086] Figure 11 This is a flowchart illustrating the action in Variation 1 of Implementation 1 where the transition of the UE to the RRC_INACTIVE state is interrupted by the generation of the uplink.

[0087] Figure 12 This is a flowchart illustrating the action of the UE in the RRC_INACTIVE state to determine the SgNB in ​​a variation 2 of Implementation 1.

[0088] Figure 13 This is a flowchart illustrating the action of the UE in the RRC_INACTIVE state to determine the SgNB in ​​a variation 2 of Implementation 1.

[0089] Figure 14 This is a flowchart illustrating the action of the UE in the RRC_INACTIVE state to determine the SgNB in ​​a variation 2 of Implementation 1.

[0090] Figure 15 This is a flowchart illustrating the action of the MgNB in ​​determining to communicate with the SgNB in ​​the RRC_INACTIVE state in a variation 2 of Implementation 1.

[0091] Figure 16 This is a flowchart illustrating the action of the MgNB in ​​determining to communicate with the SgNB in ​​the RRC_INACTIVE state in a variation 2 of Implementation 1.

[0092] Figure 17 This is a flowchart illustrating the action of the MgNB in ​​determining to communicate with the SgNB in ​​the RRC_INACTIVE state in a variation 2 of Implementation 1.

[0093] Figure 18 This is a flowchart illustrating the actions of the UE in the RRC_INACTIVE state to determine the moving target MgNB and the moving target SgNB in ​​a variation 2 of Implementation 1.

[0094] Figure 19 This is a flowchart illustrating the actions of the UE in the RRC_INACTIVE state to determine the moving target MgNB and the moving target SgNB in ​​a variation 2 of Implementation 1.

[0095] Figure 20 This is a flowchart illustrating the actions of the UE in the RRC_INACTIVE state to determine the moving target MgNB and the moving target SgNB in ​​a variation 2 of Implementation 1.

[0096] Figure 21 A flowchart illustrating small data transmission from the UE to the SgNB in ​​Implementation 2 is shown.

[0097] Figure 22 The flowchart illustrates the small data transmission from the UE to the MgNB and SgNB in ​​Implementation 2.

[0098] Figure 23 A flowchart illustrating the operation of using DC in the group copying of small data in Variation 1 of Implementation 2 is shown.

[0099] Figure 24 A flowchart illustrating the operation of using DC in the group copying of small data in Variation 1 of Implementation 2 is shown.

[0100] Figure 25 A flowchart illustrating the actions of using CA in the grouping and copying of small data in Variation 1 of Implementation 2 is shown.

[0101] Figure 26 This is a schematic diagram illustrating an example of using different frequency hopping modes for UAV-UE in each cell in Implementation 3.

[0102] Figure 27 This is a flowchart illustrating the action of the UAV-UE determining the communication mode in Implementation 5. Detailed Implementation

[0103] Implementation Method 1

[0104] Figure 2 This is a block diagram illustrating the overall structure of a communication system 200 using the LTE method discussed in 3GPP. Figure 2 The following explanation is provided. The radio access network is referred to as E-UTRAN (Evolved Universal Terrestrial Radio Access Network) 201. The communication terminal device, namely the mobile terminal device (hereinafter referred to as "Mobile Terminal (User Equipment): UE)") 202, can wirelessly communicate with the base station device (hereinafter referred to as "Base Station (E-UTRAN NodeB): eNB)") 203 and use wireless communication to transmit and receive signals.

[0105] Here, "communication terminal device" refers not only to mobile terminal devices such as mobile phone terminals, but also to stationary devices such as sensors. In the following description, "communication terminal device" may sometimes be abbreviated as "communication terminal".

[0106] If the control protocols for mobile terminal 202, such as RRC (Radio Resource Management) and user plane protocols (hereinafter sometimes also referred to as U-Plane), such as PDCP (Packet Data Convergence Protocol), RLC (Radio Link Control), MAC (Medium Access Control), and PHY (Physical layer), terminate at base station 203, then E-UTRAN consists of one or more base stations 203.

[0107] The control protocol RRC (Radio Resource Control) between mobile terminal 202 and base station 203 is used for broadcasting, paging, and RRC connection management. The states of base station 203 and mobile terminal 202 in the RRC are RRC_IDLE and RRC_CONNECTED.

[0108] In RRC_IDLE, PLMN (Public Land Mobile Network) selection, System Information (SI) broadcasting, paging, cell re-selection, and mobility are performed. In RRC_CONNECTED, the mobile terminal has an RRC connection and can send and receive data with the network. Furthermore, in RRC_CONNECTED, handover (HO) and neighbor cell measurement are performed.

[0109] Base station 203 is classified into eNB 207 and Home-eNB 206. Communication system 200 includes eNB group 203-1 containing multiple eNBs 207, and Home-eNB group 203-2 containing multiple Home-eNBs 206. The system consisting of EPC (Evolved Packet Core) as the core network and E-UTRAN 201 as the radio access network is called EPS (Evolved Packet System). Sometimes, EPC as the core network and E-UTRAN 201 as the radio access network are collectively referred to as the "network".

[0110] The eNB 207 connects to a Mobility Management Entity (MME), an S-GW (Serving Gateway), or an MME / S-GW unit (hereinafter sometimes referred to as "MME unit") 204 via the S1 interface, facilitating control information communication between the eNB 207 and the MME unit 204. Multiple MME units 204 can be connected to a single eNB 207. The eNBs 207s also connect to each other via the X2 interface, facilitating control information communication between them.

[0111] The Home-eNB 206 connects to the MME unit 204 via the S1 interface, and communication of control information between the Home-eNB 206 and the MME unit 204 is performed. One MME unit 204 can be connected to multiple Home-eNB 206s. Alternatively, the Home-eNB 206 connects to the MME unit 204 via the HeNBGW (Home-eNB Gateway) 205. The Home-eNB 206 and HeNBGW 205 are connected via the S1 interface, and the HeNBGW 205 and MME unit 204 are connected via the S1 interface.

[0112] One or more Home-eNB206s are connected to one HeNBGW205 and communicate via the S1 interface. The HeNBGW205 is connected to one or more MME units 204 and communicates via the S1 interface.

[0113] MME 204 and HeNBGW 205 are upper-level devices, specifically upper-level nodes, that control the connection between eNB 207 (as a base station) and Home-eNB 206 and mobile terminal (UE) 202. MME 204 constitutes the EPC (Engineering Process Control) as the core network. Base station 203 and HeNBGW 205 constitute E-UTRAN 201.

[0114] Furthermore, the following structure was studied in 3GPP. It supports the X2 interface between Home-eNBs 206. That is, Home-eNBs 206 are connected via the X2 interface and communicate control information between them. From the perspective of MME 204, HeNBGW 205 can be considered as a Home-eNB 206. From the perspective of Home-eNB 206, HeNBGW 205 can be considered as MME 204.

[0115] Whether the Home-eNB206 is connected to the MME unit 204 via the HeNBGW205 or directly to the MME unit 204, the interface between the Home-eNB206 and the MME unit 204 is always the S1 interface.

[0116] Base station 203 can constitute one cell or multiple cells. Each cell has a predetermined range as its coverage area, which enables communication with mobile terminal 202, and wireless communication is conducted with mobile terminal 202 within the coverage area. When a base station 203 constitutes multiple cells, each cell is configured to communicate with mobile terminal 202.

[0117] Figure 3 This illustrates the communication terminal involved in the present invention. Figure 2 The diagram shows the structure of the mobile terminal 202. Figure 3The transmission process of the mobile terminal 202 shown will be described. First, control data from the protocol processing unit 301 and user data from the application unit 302 are stored in the transmission data buffer unit 303. The data stored in the transmission data buffer unit 303 is transmitted to the encoding unit 304 for encoding processing such as error correction. Alternatively, data may be output directly from the transmission data buffer unit 303 to the modulation unit 305 without encoding processing. The data encoded by the encoding unit 304 is modulated in the modulation unit 305. The modulated data is converted into a baseband signal and then output to the frequency conversion unit 306, where it is converted into a wireless transmission frequency. Afterward, the transmission signal is transmitted from the antenna 307 to the base station 203.

[0118] Furthermore, the receiving process of the mobile terminal 202 is performed as follows: The antenna 307 receives the wireless signal from the base station 203. The received signal is converted from the wireless receiving frequency to a baseband signal by the frequency conversion unit 306, and demodulated in the demodulation unit 308. The demodulated data is transmitted to the decoding unit 309 for error correction and other decoding processes. Of the decoded data, control data is transmitted to the protocol processing unit 301, and user data is transmitted to the application unit 302. A series of processes of the mobile terminal 202 are controlled by the control unit 310. Thus, although in Figure 3 The details have been omitted, but the control unit 310 is connected to each of the units 301 to 309.

[0119] Figure 4 This illustrates the base station involved in the present invention. Figure 2 The diagram shows the structure of base station 203. Figure 4 The transmission processing of the base station 203 shown will be described. The EPC communication unit 401 handles data transmission and reception between base station 203 and EPC (MME unit 204, etc.), HeNBGW 205, etc. Other base station communication units 402 handle data transmission and reception with other base stations. The EPC communication unit 401 and other base station communication units 402 exchange information with the protocol processing unit 403. Control data from the protocol processing unit 403, as well as user data and control data from the EPC communication unit 401 and other base station communication units 402, are stored in the transmission data buffer unit 404.

[0120] The data stored in the transmit data buffer 404 is transmitted to the encoding unit 405 for encoding processing such as error correction. Alternatively, data may be output directly from the transmit data buffer 404 to the modulation unit 406 without encoding processing. The encoded data is modulated in the modulation unit 406. The modulated data is converted into a baseband signal and then output to the frequency conversion unit 407, where it is converted into a wireless transmission frequency. Afterward, the transmission signal is transmitted to one or more mobile terminals 202 using the antenna 408.

[0121] Furthermore, the reception processing of base station 203 is performed as follows. Wireless signals from one or more mobile terminals 202 are received by antenna 408. The received signal is converted from a wireless receiving frequency to a baseband signal by frequency conversion unit 407, and demodulated by demodulation unit 409. The demodulated data is transmitted to decoding unit 410 for error correction and other decoding processing. Of the decoded data, control data is transmitted to protocol processing unit 403, or EPC communication unit 401, or other base station communication units 402; user data is transmitted to EPC communication unit 401 and other base station communication units 402. A series of processes of base station 203 are controlled by control unit 411. Thus, although in Figure 4 The details have been omitted, but the control unit 411 is connected to each of the units 401 to 410.

[0122] Figure 5 This is a block diagram illustrating the structure of the MME involved in this invention. Figure 5 The above is shown in the middle. Figure 2 The structure of MME 204a included in MME 204 is shown. PDN GW communication unit 501 performs data transmission and reception between MME 204a and PDN GW. Base station communication unit 502 performs data transmission and reception between MME 204a and base station 203 via the S1 interface. When the data received from the PDN GW is user data, the user data is transmitted from PDN GW communication unit 501 to base station communication unit 502 via user plane communication unit 503, and then sent to one or more base stations 203. When the data received from base station 203 is user data, the user data is transmitted from base station communication unit 502 to PDN GW communication unit 501 via user plane communication unit 503, and then sent to PDN GW.

[0123] When the data received from the PDN GW is control data, the control data is transmitted from the PDN GW communication unit 501 to the control plane control unit 505. When the data received from the base station 203 is control data, the control data is transmitted from the base station communication unit 502 to the control plane control unit 505.

[0124] The HeNBGW communication unit 504, when HeNBGW 205 is present, performs data transmission and reception between MME 204a and HeNBGW 205 via an interface (IF) according to the information type. Control data received from the HeNBGW communication unit 504 is transmitted from the HeNBGW communication unit 504 to the control plane control unit 505. The processing results in the control plane control unit 505 are sent to the PDN GW via the PDNGW communication unit 501. Furthermore, the results processed by the control plane control unit 505 are sent to one or more base stations 203 via the base station communication unit 502 and the S1 interface, or to one or more HeNBGW 205 via the HeNBGW communication unit 504.

[0125] The control plane control unit 505 includes the NAS security unit 505-1, the SAE bearer control unit 505-2, and the Idle State mobility management unit 505-3, which performs all processing at the control plane (hereinafter sometimes referred to as C-Plane). The NAS security unit 505-1 is responsible for the security of NAS (Non-Access Stratum) messages. The SAE bearer control unit 505-2 manages the SAE (System Architecture Evolution) bearer. The Idle State Mobility Management unit 505-3 manages mobility in standby state (also known as Idle State; LTE-IDLE state, or simply idle), generates and controls paging signals in standby state, adds, deletes, updates, and retrieves tracking areas for one or more mobile terminals 202 within the coverage area, and manages the tracking area list.

[0126] MME204a distributes paging signals to one or more base stations 203. MME204a performs mobility control in the idle state. MME204a manages the tracking area list when the mobile terminal is in idle and active states. MME204a initiates the paging protocol by sending a paging message to cells belonging to the tracking area registered by the UE. The management of the CSG, CSGID, and whitelist of the Home-eNB206 connected to MME204a can be performed by the idle state mobility management unit 505-3.

[0127] Next, an example of a cell search method in a communication system is shown. Figure 6This is a flowchart illustrating the process of a communication terminal (UE) in an LTE communication system from cell search to standby operation. If the communication terminal starts cell search, in step ST601, the first synchronization signal (P-SS) and the second synchronization signal (S-SS) sent from the surrounding base stations are used to obtain the synchronization of time slot timing and frame timing.

[0128] P-SS and S-SS are collectively referred to as the Synchronization Signal (SS). The Synchronization Signal (SS) contains synchronization codes that correspond one-to-one with the PCIs assigned to each cell. The case with 504 PCIs is under investigation. These 504 PCIs are used to achieve synchronization, and the PCIs of synchronized cells are detected (determined).

[0129] Next, in step ST602, the reference signal (RS) sent from the base station to each cell after synchronization is achieved, i.e., the cell-specific reference signal (CRS), is measured, and the received power (RSRP) of the RS is determined. The reference signal (RS) uses a code that corresponds one-to-one with the PCI. This code can be used to obtain correlation and thus separate the cell from other cells. By deriving the RS code of the cell based on the PCI determined in step ST601, the RS can be detected, and the received power of the RS can be measured.

[0130] Next, in step ST603, the cell with the best RS reception quality is selected from one or more cells detected up to step ST602, for example, the cell with the highest RS reception power, i.e., the best cell.

[0131] Next, in step ST604, the PBCH of the best cell is received to obtain the broadcast information, i.e., the BCCH. The BCCH on the PBCH maps to the MIB (Master Information Block), which contains cell structure information. Therefore, by receiving the PBCH and obtaining the BCCH, the MIB can be obtained. Information in the MIB includes, for example, the DL (downlink) system bandwidth (also known as transmission bandwidth configuration), the number of transmit antennas, and the SFN (System Frame Number).

[0132] Next, in step ST605, based on the cell structure information of the MIB, the DL-SCH of the cell is received, and SIB (System Information Block) 1 in the broadcast information BCCH is obtained. SIB1 contains information related to accessing the cell, information related to cell selection, and scheduling information of other SIBs (SIBk; k≥2 integers). In addition, SIB1 contains the Tracking Area Code (TAC).

[0133] Next, in step ST606, the communication terminal compares the TAC of SIB1 received in step ST605 with the TAC portion of the Tracking Area Identity (TAI) in the tracking area list already saved by the communication terminal. The tracking area list is also called the TAI list. TAI is identification information used to identify the tracking area, consisting of the MCC (Mobile Country Code), MNC (Mobile Network Code), and TAC (Tracking Area Code). MCC is the country code. MNC is the network code. TAC is the tracking area code.

[0134] If the comparison result in step S606 is that the TAC received in step ST605 is the same as the TAC included in the tracking area list, the communication terminal enters standby mode in that cell. If the comparison result is that the TAC received in step ST605 is not included in the tracking area list, the communication terminal requests a change of tracking area from the core network (EPC) containing the MME, etc., through that cell to perform TAU (Tracking Area Update).

[0135] The apparatus constituting the core network (hereinafter sometimes referred to as "core network-side apparatus") updates the tracking area list based on the TAU request signal and the identification number (UE-ID, etc.) of the communication terminal sent from the communication terminal. The core network-side apparatus sends the updated tracking area list to the communication terminal. The communication terminal rewrites (updates) its own TAC list based on the received tracking area list. Afterward, the communication terminal enters standby mode in the cell.

[0136] With the widespread adoption of smartphones and tablets, traffic volume using cellular wireless communication systems has exploded, leading to concerns about insufficient wireless resources worldwide. To address this situation and improve frequency utilization efficiency, research is underway to advance cell miniaturization and spatial separation.

[0137] In the existing cell structure, cells composed of eNBs have a wide coverage area. Previously, cells were constructed by utilizing the wide coverage area of ​​multiple cells consisting of multiple eNBs to cover a specific area.

[0138] When miniaturizing cells, cells composed of existing eNBs have a narrower coverage area compared to cells composed of existing eNBs. Therefore, similar to existing technologies, to cover a certain area, a large number of miniaturized eNBs are needed compared to existing eNBs.

[0139] In the following explanation, as with conventional eNBs, cells with larger coverage areas are referred to as "macrocells," and the eNBs that make up macrocells are referred to as "macro eNBs." Furthermore, as with cells that have undergone miniaturization, cells with smaller coverage areas are referred to as "small cells," and the eNBs that make up small cells are referred to as "micro eNBs."

[0140] For example, a macro eNB can be a "wide area base station" as described in Non-Patent Document 7.

[0141] Micro eNBs can be, for example, low-power nodes, local nodes, and hotspots. Micro eNBs can be pico eNBs constituting pico cells, femto pico eNBs constituting femto pico cells, HeNBs, RRHs (Remote Radio Heads), RRUs (Remote Radio Units), RREs (Remote Radio Equipment), or RNs (Relay Nodes). An eNB can be a "Local Area Base Station" or a "Home Base Station" as described in Non-Patent Document 7.

[0142] Figure 7 This diagram illustrates the concept of a cell structure when macro eNBs and micro eNBs are mixed. Macro cells, composed of macro eNBs, have a relatively large coverage area 701. Small cells, composed of micro eNBs, have a smaller coverage area 702 compared to the coverage area 701 of the macro eNBs (macro cells).

[0143] In the case of multiple eNBs, the coverage area of ​​a cell consisting of one eNB may be included in the coverage area of ​​a cell consisting of other eNBs. Figure 7In the cell structure shown, as indicated by reference numerals "704" or "705", the coverage area 702 of the small cell composed of micro eNBs is sometimes included within the coverage area 701 of the macro cell composed of macro eNBs.

[0144] Furthermore, as indicated by reference numeral "705", there are also cases where the coverage areas 702 of multiple, for example, two small cells are included within the coverage area 701 of a macrocell. A mobile terminal (UE) 703, for example, is included within the coverage area 702 of the small cells and communicates via the small cells.

[0145] In addition, Figure 7 In the structure of the cell shown, as indicated by reference numeral "706", the following situation will occur: the coverage area 701 of the macro cell composed of macro eNBs and the coverage area 702 of the small cell composed of micro eNBs will overlap in a complex manner.

[0146] Furthermore, as indicated by reference numeral "707", the following situation will also occur: the coverage area 701 of macro cells composed of macro eNBs and the coverage area 702 of small cells composed of micro eNBs do not overlap.

[0147] Furthermore, as indicated by reference numeral "708", the following situation will also occur: the coverage area 702 of multiple small cells consisting of multiple micro eNBs will be within the coverage area 701 of a macro cell consisting of a macro eNB.

[0148] In NR, the UE receives an indication from the base station and transitions to the RRC_INACTIVE state. For UEs using the DC architecture, the MgNB issues the indication to transition to the RRC_INACTIVE state. The MgNB queries the SgNB to determine if data via SCG bearers and SCG fork bearers is inactive, i.e., data via these bearers is not being transmitted. The SgNB informs the UE of the inactivity status of data via all SCG bearers and SCG fork bearers. The MgNB uses this notification to instruct the UE to transition to the RRC_INACTIVE state. Thus, the MgNB can transition the UE to the RRC_INACTIVE state based on accurately reflecting the inactivity status of data via SCG bearers / SCG fork bearers.

[0149] Additionally, the base station sends a paging message to the UE in the RRC_INACTIVE state. The MgNB sends a paging message to the UE in the RRC_INACTIVE state that maintains the DC structure. The SgNB notifies the MgNB that data has been generated via the SCG bearer and / or SCG fork bearer. The UE requests the MgNB to restart the RRC connection. The MgNB instructs the UE to restart the RRC connection. The MgNB requests the SgNB to restart the RRC connection with the UE. The SgNB notifies the MgNB of the response to restarting the RRC connection with the UE. Thus, the MgNB can restore the UE from the RRC_INACTIVE state to the RRC_CONNECTED state by generating data via the SCG bearer and / or SCG fork bearer.

[0150] Using the above method leads to the following problems. For example, when data using SCG bearers and / or SCG fork bearers is continuously active, in response to the query sent from the MgNB to the SgNB, the SgNB notifies that the data using that bearer is active, thus the MgNB cannot transition the UE to the RRC_INACTIVE state. To ensure the MgNB accurately grasps the connectivity status of the data using that bearer and thus properly manages the UE state, it needs to repeatedly send the query to the SgNB. The SgNB also needs to repeatedly notify the MgNB of this status. This increases the signaling load on the inter-base station interface and the processing load in both the MgNB and SgNB.

[0151] The following are solutions to the above problems.

[0152] When communicating with a UE connected to the same SgNB, the SgNB notifies that data transmitted through the SgNB is inactive. This data can be carried using an SCG, an SCG fork, or an MCG fork. This notification can be sent when the data meets the inactivation condition. The notification can be sent once or multiple times. For example, the SgNB can send the notification multiple times when the data transitions between meeting and not meeting the inactivation condition. As another example, the SgNB can send the notification periodically.

[0153] The MgNB can query the SgNB to see if data passing through that SgNB is inactive. This can reduce signaling traffic, for example, at inter-base station interfaces.

[0154] The MgNB can also notify the SgNB of an instruction to begin evaluating inactive data passing through it. The SgNB can then use this instruction to begin evaluating inactive data passing through it. Alternatively, the MgNB may not notify the SgNB of the instruction to begin the evaluation. The SgNB can then begin the evaluation automatically. For example, the SgNB can begin the evaluation when the DC structure is established. This can reduce signaling traffic, such as at inter-base station interfaces.

[0155] Alternatively, the criteria for determining whether data passing through the SgNB is inactive can be pre-defined in the SgNB according to the standard.

[0156] As another example, this decision condition can be determined by the higher-level NW device and notified to the subordinate gNB. The aforementioned higher-level NW device can be, for example, an AMF (Access and Mobility Management Function) or an SMF (Session Management Function). This decision condition can be different for each UE or each gNB. Each UE or each gNB can be flexibly configured.

[0157] The decision condition determined by the upper-level NW device can also be notified to the MgNB by the upper-level NW device. The MgNB can then notify the SgNB of the decision condition. As another example, the decision condition can be determined by the upper-level NW device and notified to the subordinate gNB. The upper-level NW device can notify the MgNB and SgNB only of the decision condition, thus reducing the signaling volume between the upper-level NW device and the base station.

[0158] As another example, this judgment condition can be determined by the MgNB. The MgNB can then notify the secondary base station of the determined judgment condition. The MgNB's determination of this judgment condition and / or its notification of it to the SgNB can apply whether the MgNB makes the aforementioned inquiry to the SgNB or not. This judgment condition can be included in the signaling during the DC establishment process with the SgNB, or in an inquiry from the MgNB to the SgNB regarding whether data via SCG bearers and SCG fork bearers is inactive. It can also be included in the instruction to begin evaluating the inactivity of data via the SgNB, as described above.

[0159] As another example, this decision condition can be determined by the SgNB. For instance, it can reduce the signaling volume in the decision condition notification.

[0160] The above judgment criteria can also be based on time. For example, if the communication between the SgNB and the UE has not reached a certain time, the SgNB can determine that the data is not active. The aforementioned certain time can be given for each bearer. The aforementioned time can also be given based on the number of UEs in RRC_CONNECTED. Therefore, for example, when there are many UEs in RRC_CONNECTED, shortening the time until the data is determined to be inactive can improve the communication efficiency of the entire system.

[0161] The aforementioned time can also be determined using information related to the UE. For example, information indicating that it is an IoT UE can be used to set the aforementioned time shorter than that of a typical UE. As another example, information related to battery capacity can be used, allowing the aforementioned time to be set shorter for UEs with smaller battery capacities. This, for example, can suppress the power consumption of the UE.

[0162] The MgNB and / or SgNB can also pre-notify the UEAS context of the eNB / gNB within the paging-related RAN area. This UEAS context can contain information from a single MgNB / SgNB, or it can contain information from both the MgNB and SgNB. For example, only the MgNB may notify the base station within the paging-related RAN area of ​​the UEAS context containing information from both the MgNB and SgNB. As another example, the MgNB and SgNB may each notify the base station within the paging-related RAN area of ​​their own UEAS context containing information from their respective gNBs. Thus, for example, communication can be initiated quickly after paging when the UE moves.

[0163] As another example, the MgNB and SgNB can respectively notify the UEAS context containing information from both the MgNB and SgNB. This notification can also occur, for example, when the paging-related RAN areas of the MgNB and SgNB are different. Thus, UE state control can be implemented, for example, in the aforementioned scenarios.

[0164] The eNB / gNB can also query the UEAS context from other eNBs / gNBs within the paging-related RAN area. This query can also occur during random access processing between the UE and the eNB / gNB. Alternatively, the other eNBs / gNBs can notify the eNB / gNB of the UEAS context. The UEAS context can contain information about a single MgNB / SgNB, or information about both the MgNB and SgNB. This reduces the signaling load on the inter-base station interface.

[0165] The downlink data notification sent from the SgNB to the MgNB may also include information about the random access preamble used by the UE for random access processing with the SgNB. This SgNB random access preamble information in the downlink data notification can be sent together with the random access preamble notification in the DC structure. This random access preamble information may be different from or the same as the random access preamble information provided from the SgNB to the MgNB in ​​the DC structure. This allows for rapid random access processing between the UE and the SgNB, for example. Information related to the transmission power of the random access preamble from the UE may also be included. The same effect as described above can be achieved. Information related to the SgNB's beam used for communication between the SgNB and the UE may also be included. This allows for rapid beam capture of the SgNB in ​​the UE. Other information required for paging may also be included. For example, this could be information related to the UE's identifier, information related to the PDU session, or information related to QoS procedures. Information related to the RAN area used for paging to which the SgNB belongs may also be included.

[0166] The paging from the MgNB to the UE can include information indicating that data was generated in the SgNB. This information could be, for example, an identifier indicating that data was generated in the SgNB, or an identifier of the SgNB. It can also include the same information as the downlink data notification sent from the SgNB to the MgNB. The same effect as the information included in the downlink data notification can be achieved.

[0167] The paging from the MgNB to the UE may also include information indicating that data has been generated in the MgNB. This information may be the same as the information indicating that data has been generated in the SgNB. It may also include information related to the random access preamble used by the UE for random access processing with the MgNB. Thus, for example, random access processing between the UE and the MgNB can be performed quickly. It may also include information related to the transmission power from the UE of the random access preamble. The same effect as described above can be obtained. It may also include information related to the MgNB's beam used for communication between the MgNB and the UE. Thus, beam capture of the MgNB in ​​the UE can be performed quickly.

[0168] The UE can use this paging to initiate random access procedures with the MgNB. The UE can request an RRC connection restart from the MgNB. The UE can make this request after the MgNB responds with a random access response. The MgNB can instruct the UE to restart the RRC connection. This instruction can be given after the UE sends the request to the MgNB. The UE can use this instruction to return to the RRC_CONNECTED state.

[0169] The UE can initiate random access procedures to the SgNB. These procedures can be performed after the UE returns to the RRC_CONNECTED state. This avoids complicating the communication system design. Alternatively, they can be performed while the UE is in the RRC_INACTIVE state. For example, the UE can send a random access preamble to the SgNB without waiting for a random access response from the MgNB. As another example, the UE can wait for a random access response from the MgNB before sending the random access preamble to the SgNB. This allows the UE to quickly resume data transmission and reception with the SgNB, for example.

[0170] Figure 8 and Figure 9 This is a flowchart illustrating the actions of the UE transitioning to the RRC_INACTIVE state and returning to the RRC_CONNECTED state in this embodiment. Figure 8 and Figure 9 They are continuous at the position of boundary line BL0809. Figure 8 and Figure 9 The example shown is one where MgNB does not query SgNB to see if data passed through SgNB is inactive.

[0171] Figure 8 In step ST801, the UE is in the RRC_CONNECTED state. In step ST802, the SgNB determines that the data transmitted through this SgNB is not active. In step ST803, the SgNB notifies the MgNB that the data carried by the UE transmitted through this SgNB is not active.

[0172] Figure 8 In step ST805, the MgNB, utilizing the notification received from the SgNB in ​​step ST803 and the fact that the data carried by the MgNB is not active, instructs the UE to transition to the PPR_INACTIVE state. This instruction includes an identifier used for recovery to RRC_CONNECTED, such as a recovery ID. The instruction may also use RRC connection release signaling. RRC connection release signaling contains information indicating that the UE should transition to RRC_INACTIVE. Following step ST805, the UE transitions to the RRC_INACTIVE state in step S808.

[0173] Figure 8In the example shown, step ST805 uses RRC connection release signaling, but other RRC signaling can also be used. These other RRC signaling may also include the identifier used for recovery to RRC_CONNECTED, or information indicating a transition to RRC_NACTIVE for the UE.

[0174] Figure 8 In step ST806, the MgNB notifies the SgNB to terminate the connection with the UE. The SgNB terminates the connection with the UE using step ST806. Terminating the connection can be, for example, terminating the SCG side path of the SCG bearer and the SCG side path of the SCG fork bearer, or the SCG side path of the MCG fork bearer.

[0175] Figure 8 In step ST804, downlink data is sent from the UPF to the SgNB. In step ST807, the SgNB notifies the MgNB that downlink data to the UE has been generated. This notification may also include information about the random access preamble used by the UE and the SgNB for random access processing.

[0176] Figure 9 Steps ST809–ST813, ST816, and ST820 illustrate the steps for the MgNB and UE to transition from the RRC_INACTIVE state to the RRC_CONNECTED state. In step ST809, the MgNB sends a paging message to the UE. This paging message may contain the identifier of the SgNB. It may also include information about the random access preamble used for random access processing with both the MgNB and the SgNB.

[0177] Figure 9In step ST810, the UE sends a random access preamble to the MgNB. In step ST811, the MgNB notifies the UE of the random access response. In step ST812, the UE requests the MgNB to restore to the RRC_CONNECTED state. This request includes the identifier used in step ST805 when the MgNB notified the UE of the restoration to RRC_CONNECTED state. This request may use signaling such as an RRC Connection Resume Request. The MgNB uses the request from step ST812 and the identifier to determine whether to restore the UE to the RRC_CONNECTED state. In step ST813, the MgNB instructs the UE to restore to the RRC_CONNECTED state. In step ST816, the UE restores to the RRC_CONNECTED state. In step ST820, the UE notifies the MgNB that it has restored to the RRC_CONNECTED state. This notification may use signaling such as an RRC Connection Resume Complete.

[0178] Figure 9 In steps ST814 and ST815, the connection between the SgNB and the UE is restarted. This restart can be, for example, a restart of the SCG-side path of an SCG bearer and an SCG fork bearer, or a restart of the SCG-side path of an MCG fork bearer. In step ST814, the MgNB requests the SgNB to restart the connection with the UE. In step ST815, the SgNB notifies the MgNB that the connection with the UE has been restarted.

[0179] Figure 9 In steps ST817 and ST818, the UE and SgNB perform random access processing. In step ST817, the UE sends a random access preamble to the SgNB. This random access preamble can be the random access preamble notified to the UE by the MgNB in ​​step ST809. In step ST818, the SgNB notifies the UE of the random access response.

[0180] Figure 9 In step ST819, the SgNB sends downlink data to the UE, containing the data sent from the UPF to the SgNB in ​​step ST804. This restarts downlink communication via the SgNB.

[0181] Figure 8 and Figure 9An example of random access processing between the UE and the SgNB is shown in the RRC_CONNECTED state, but it can also be performed in the RRC_INACTIVE state. For example, steps ST817 and ST818 can be performed between steps ST809 and ST816. Step ST817 can be performed before, after, or after step ST810. Thus, for example, communication between the UE and the SgNB can be quickly restarted.

[0182] According to this embodiment 1, the inter-base station signaling volume associated with inactivity status queries and / or notifications for data using SCG bearers and SCG fork bearers can be reduced. Furthermore, even if data is generated via the SgNB, the MgNB can transition the UE to the RRC_CONNECTED state. This enables efficient communication using the DC.

[0183] According to embodiment 1, for example, the following structure is provided.

[0184] A communication system is provided, comprising a communication terminal device and multiple base station devices configured to wirelessly communicate with the communication terminal device. More specifically, the multiple base station devices include a primary base station device and a secondary base station device that constitute bearers for the communication terminal device. If the secondary base station device detects a data inactivity state (downlink data inactive to the communication terminal device) on all bearers, it will notify the primary base station device of the occurrence of the data inactivity state even without being queried by the primary base station device. Upon receiving the notification of the data inactivity state, the primary base station device sends an instruction to the communication terminal device to transition from the RRC_CONNECTED state to the RRC_INACIVE state. The communication terminal device transitions to the RRC_INACTIVE state according to the instruction from the primary base station device.

[0185] In this structure, at least one of the main base station device and the secondary base station device can retain information related to the connection with the communication terminal device even after the communication terminal device transitions to the RRC_INACTIVE state.

[0186] According to embodiment 1, the following structure is also provided, for example.

[0187] A communication system is provided, comprising a communication terminal device and multiple base station devices configured to wirelessly communicate with the communication terminal device. More specifically, the multiple base station devices include a primary base station device and a secondary base station device configured to carry out communication with the communication terminal device. When the secondary base station device detects downlink data generated to the communication terminal device which is in the RRC_INACTIVE state, the secondary base station device notifies the primary base station device of the occurrence of the downlink data. Upon receiving the notification of the downlink data generation, the primary base station device sends a paging message to the communication terminal device. Upon receiving the paging message, the communication terminal device requests the primary base station device to return to the RRC_CONNECTED state. Here, the paging message includes at least one of the following: connection-related information between the communication terminal device and the primary base station device, and connection-related information between the communication terminal device and the secondary base station device.

[0188] The above structure can be modified in various ways based on the disclosure and inspiration of this specification, including Embodiment 1. According to the above structure and its modifications, the above-mentioned technical problems can be solved and the above-mentioned technical effects can be obtained.

[0189] Variation 1 of Implementation Method 1

[0190] In UE state control using a DC architecture, the following problem arises: When downlink data for the UE is sent from the upper-level NW device to the MgNB or SgNB immediately after the MgNB has just notified the UE of the indication to transition to the RRC_INACTIVE state, the actions of the UE, MgNB, and SgNB are not yet defined. Therefore, for example, there is a problem where the UE, MgNB, and SgNB cannot understand the UE's state. The same problem occurs when uplink data is generated in the UE immediately after the MgNB has just notified the UE of the indication to transition.

[0191] The following are solutions to the above problems.

[0192] Once the UE transitions to the RRC_INACTIVE state, it returns to the RRC_CONNECTED state. The MgNB can also send an instruction to the UE to transition to the RRC_INACTIVE state.

[0193] The above actions also apply when downlink data is generated. That is, the MgNB can also send a paging message to the UE. Sending this paging message from the MgNB to the UE can immediately follow an indication of a transition to the RRC_INACTIVE state. The MgNB can also send this paging message to the UE when it receives downlink data from the upper-level NW device. Alternatively, it can send a paging message to the UE using a notification sent from the SgNB to the MgNB indicating the generation of downlink data. The SgNB can send this notification to the MgNB when it receives downlink data from the upper-level NW device.

[0194] The SgNB can also send a notification indicating the generation of downlink data to the MgNB before the MgNB notifies the SgNB of the UE connection termination. This reduces the processing load in the SgNB. Alternatively, the notification indicating the generation of downlink data can be sent after the UE connection termination notification, thus avoiding increased complexity in the communication system design.

[0195] The action of the UE returning to the RRC_CONNECTED state after transitioning to the RRC_INACTIVE state can also be applied during uplink data generation. That is, the UE can begin random access processing to the MgNB. Subsequent processing can be the same as during downlink data generation. Furthermore, during uplink data generation, the random access processing performed by the UE to the SgNB can be performed after the UE returns to the RRC_CONNECTED state, or it can be performed during the RRC_INACTIVE state. The random access processing performed by the UE to the SgNB can be performed either after waiting for a random access response from the MgNB, or it can be performed before the MgNB issues a random access response. The random access preamble can be sent from the UE to the SgNB before the UE sends the random access preamble to the MgNB. This achieves the same effect as during downlink data generation.

[0196] As an example of the process by which a UE returns to the RRC_CONNECTED state after transitioning to the RRC_INACTIVE state, it could be... Figure 8 Step ST804 is the procedure executed between steps ST803 and ST806. The procedure for the UE to return to the RRC_CONNECTED state after transitioning to the RRC_INACTIVE state can also be... Figure 8 Step ST807 can be a process executed before step ST806, or it can be a process executed after step ST806.

[0197] Other solutions are proposed. The UE interrupts the transition to the RRC_INACTIVE state. This could, for example, shorten the latency until data transmission between the UE and the SgNB resumes.

[0198] The MgNB may not notify the UE of the RRC Connection Release. This action can apply, for example, to situations where the DL data transmission from the UPF to the SgNB, or the downlink data notification from the SgNB to the MgNB, occurs before the MgNB sends the RRC Connection Release signaling to the UE. In these cases, the MgNB may also not notify the SgNB of the UE's connection termination indication. This allows, for example, a rapid resumption of communication between the UE and the SgNB.

[0199] Other examples are disclosed. A standby time can be set during the period from when the UE receives the RRC_INACTIVE state transition indication from the MgNB until the UE begins processing to transition to the RRC_INACTIVE state. The UE can interrupt the transition to the RRC_INACTIVE state using uplink data to the MgNB and / or SgNB generated during this standby time. It can also utilize the situation where downlink data is received from the MgNB and / or SgNB. It can also utilize the indication from the MgNB to interrupt the RRC_INACTIVE state transition. After the standby time has elapsed, the UE transitions to the RRC_INACTIVE state.

[0200] This standby time can also be set by the MgNB. The MgNB can interrupt the UE's transition to the RRC_INACTIVE state if downlink data is generated via MCG bearer or MCG fork bearer during this standby time. It can also interrupt the transition by utilizing downlink data notification received from the SgNB. Furthermore, it can interrupt the transition by utilizing information related to uplink data received from the UE, such as uplink data, SR, and BSR. The MgNB can determine that the UE has transitioned to the RRC_INACTIVE state after this standby time has elapsed.

[0201] This standby time can be set for both the UE and the MgNB. The standby times for the UE and the MgNB can be the same or different. The UE and / or the MgNB can set the standby time related to uplink data and the standby time related to downlink data separately. The standby time related to uplink data and the standby time related to downlink data can be the same or different. For example, regarding the standby time related to uplink data, the standby time set in the base station can be longer than the standby time set in the UE. As another example, regarding the standby time related to downlink data, the standby time set in the UE can be longer than the standby time set in the MgNB. Therefore, for example, if the standby time related to uplink data in the UE is exceeded during the HARQ retransmission period of uplink data, it is possible to prevent unclear identification between the UE and the MgNB related to the UE's RRC state.

[0202] The standby time can be determined according to standards, thus avoiding complicating the design of the communication system. As another example, it can be determined by the MgNB. The MgNB can notify the UE of the standby time. This notification can use signaling set during DC configuration. For example, the MgNB can include information related to the standby time in the RRC connection reset signaling to notify the UE.

[0203] The method for the UE to interrupt the transition to the RRC_INACTIVE state is disclosed. The MgNB can also notify the UE of an indication to interrupt the transition to the RRC_INACTIVE state. The UE can use this indication to interrupt the transition to the RRC_INACTIVE state. This indication can be RRC-specific signaling. Alternatively, a new signaling mechanism to cause an RRC connection release cancellation can be established as this RRC-specific signaling. The indication may include an identifier used for recovery to RRC_CONNECTED, such as a recovery ID.

[0204] Other signaling can also be used in addition to the aforementioned RRC-specific signaling. For example, RRC Connection Resume can be used. This RRC Connection Resume signaling can include information indicating the transition from interruption to the RRC_INACTIVE state. It can also include an identifier used for recovery to RRC_CONNECTED, such as a recovery ID. Thus, by suppressing the increase in the number of RRC signaling categories, system complexity can be avoided.

[0205] The MgNB can use the generation of downlink data through the MgNB during the aforementioned standby time to notify the UE of the interruption indication. Here, the downlink data through the MgNB can be downlink data carried using MCG, downlink data carried using an MCG fork, or downlink data carried using an SCG fork. The MgNB can use the receipt of downlink data notification from the SgNB during this standby time to notify the UE of the interruption indication.

[0206] Figure 10 This is a flowchart illustrating the action where the transition of the UE to the RRC_INACTIVE state is interrupted by the RRC_INACTIVE state transition interruption indication from the MgNB. Figure 10 and Figure 8 and Figure 9 Similarly, an example is shown where downlink data is sent from the UPF to the SgNB immediately after the SgNB notifies the MgNB that the SCG data is not active. Figure 10 The process shown includes and Figure 8 and Figure 9 The process shown has the same steps, so the same steps are labeled with the same step number, and common descriptions are omitted.

[0207] Figure 10 Steps ST801 to ST807 in the middle Figure 8 Since they are the same, the explanation is omitted.

[0208] Figure 10 In step ST807, when the downlink data notification is received by the MgNB within a certain period after the RRC_INACTIVE transition indication is sent in step ST805, in step ST901, the MgNB instructs the UE to interrupt the transition to RRC_INACTIVE. This indication includes an identifier used for recovery to RRC_CONNECTED, such as a recovery ID. The indication may also use signaling such as RRC Connection Release Cancel. The UE interrupts the transition to the RRC_INACTIVE state through step ST901, maintaining the RRC_CONNECTED state.

[0209] Figure 10In the example shown, step ST901 uses RRC connection release interrupt signaling, but other RRC signaling can also be used. These other RRC signaling can also include identifiers used for recovery to RRC_CONNECTED. For example, RRC connection resume can be used. The RRC connection resume signaling can include information indicating a transition from the interrupted state to RRC_INACTIVE.

[0210] Figure 10 Steps ST814 to ST815 in the middle Figure 9 Since they are the same, the explanation is omitted.

[0211] Figure 10 In this process, the UE maintains the RRC_CONNECTED state, therefore it differs from... Figure 8 and Figure 9 Random access processing with MgNB and SgNB is not performed.

[0212] Figure 10 Step ST819 and Figure 9 Since they are the same, the explanation is omitted.

[0213] Figure 10 In this process, the SgNB can send the downlink data notification shown in step ST807 to the MgNB without waiting for the UE connection stop indication shown in step ST806. The MgNB can also choose not to notify the SgNB of the UE connection stop indication. The action of the MgNB not notifying the SgNB of the UE connection stop indication can also apply to the situation where the SgNB sends the downlink data notification to the MgNB without waiting for the UE connection stop indication. The UE connection restart request and UE connection restart response can be the same as the aforementioned UE connection stop indication. Therefore, the signaling volume of the inter-base station interface can be reduced.

[0214] The MgNB can also send the UE connection stop indication to the SgNB only after a certain period of time has elapsed after receiving the SCG data inactivity notification. This certain period of time can, for example, be the same as the standby time set in the UE from the time it receives the RRC_INACTIVE state transition indication from the MgNB until the start of the process to transition to the RRC_INACTIVE state. Therefore, the SgNB can, for example, know the time until the UE transitions to RRC_INACTIVE, thus making UE control from the SgNB easier.

[0215] Other methods for the UE to interrupt the transition to the RRC_INACTIVE state are disclosed. The UE interrupts the transition to the RRC_INACTIVE state upon receiving downlink data. The MgNB can send downlink data to the UE immediately after the MgNB has given the UE the RRC_INACTIVE state transition indication. The SgNB can also send downlink data to the UE. The SgNB can send this downlink data immediately after the SCG data inactivity notification. The downlink data sent to the UE by the MgNB and / or SgNB can be data carried via the MCG bearer and / or MCG fork, or data carried via the SCG bearer and / or SCG fork. The SgNB can also send downlink data notification to the MgNB. Thus, the MgNB can easily manage the UE state. The MgNB can send a UE connection stop indication to the SgNB after the aforementioned standby time. Therefore, the SgNB can know the time until the UE transitions to RRC_INACTIVE, thus simplifying SgNB control.

[0216] Other methods for disclosing the UE's interruption of the transition to the RRC_INACTIVE state are provided. The UE interrupts the transition by sending uplink data to the MgNB and / or SgNB. Since it eliminates the need for the MgNB to send an indication of the interruption of the RRC_INACTIVE state transition to the UE, signaling load is reduced. This uplink data can be carried via the MCG and / or MCG forks, or via the SCG and / or SCG forks. An SR (Buffer Status Report) can also be used instead of uplink data. This SR can be sent to either the MgNB or the SgNB. A BSR can also be used. This BSR can be sent to either the MgNB or the SgNB. The MgNB and / or SgNB can determine that the UE's transition to the RRC_INACTIVE state has been interrupted by using the fact that the uplink data buffer in the BSR is not empty. The SgNB can send a notification to the MgNB indicating that uplink data has been received from the UE. The MgNB can monitor the status of uplink data transmitted via the SgNB, thus simplifying state control within the MgNB. The aforementioned uplink data notification can be sent from the SgNB to the MgNB when it receives the SR from the UE, or when it receives the BSR from the UE.

[0217] Figure 11 This is a flowchart illustrating the action of the UE's transition to the RRC_INACTIVE state being interrupted due to uplink data generation. Figure 11This example illustrates how the UE directly sends an uplink data transmission SR to the SgNB after the SgNB sends an SCG data inactivity notification to the MgNB. Figure 11 The process shown includes and Figure 8 and Figure 9 The process shown has the same steps, so the same steps are labeled with the same step number, and common descriptions are omitted.

[0218] Figure 11 Steps ST801, ST803, ST805, and ST806 in the process Figure 8 Since they are the same, the explanation is omitted.

[0219] Figure 11 In step ST1001, given that uplink data from the UE to the SgNB was generated immediately after receiving the UE connection stop indication in step ST806, the UE sends an SR to the SgNB. In step ST1002, the SgNB notifies the UE of permission to transmit uplink data, and in step ST1003, the SgNB sends an uplink data notification to the MgNB.

[0220] Figure 11 Steps ST814 to ST815 in the middle Figure 9 Since they are the same, the explanation is omitted.

[0221] Figure 11 During this process, the UE maintains the RRC_CONNECTED state. In step ST1004, the UE sends uplink data to the SgNB, and in step ST1005, the SgNB sends the uplink data to the UPF.

[0222] Figure 11 In the example shown, the RRC_CONNECTED state is maintained by sending an SR in step ST1001, but a BSR can also be used. Alternatively, the uplink data transmission itself can also be used. For example, the RRC_CONNECTED state can also be maintained for unlicensed uplink data transmission.

[0223] in addition, Figure 11 In the example shown, the SgNB sends the uplink data notification to the MgNB after obtaining permission to use the uplink data, but it can also send the uplink data notification before obtaining permission. For example, the MgNB can quickly grasp the UE status.

[0224] Figure 11In this process, the SR transmission shown in step ST1001 and the uplink data notification shown in step ST1003 can also be performed before the UE connection stop indication shown in step ST806. The MgNB may also choose not to notify the SgNB of the UE connection stop indication shown in step ST806. This action of the MgNB not notifying the SgNB of the UE connection stop indication can also be applied, for example, when the uplink data notification sent from the SgNB to the MgNB is performed before the UE connection stop indication. Similarly, the MgNB may also choose not to notify the SgNB of the UE connection restart request shown in step ST814, and the SgNB may also choose not to notify the MgNB of the UE connection restart response shown in step ST815. Thus, for example, the signaling volume of the inter-base station interface can be reduced.

[0225] The MgNB can send a UE connection stop indication to the SgNB after the aforementioned standby time. The SgNB can know the time until the UE transitions to RRC_INACTIVE, thus simplifying SgNB control.

[0226] The method disclosed in this variation 1 can also be applied to base stations and UEs that do not employ a DC structure. A base station and UE that do not employ a DC structure can be, for example, a structure where the UE is connected to a single base station, or a multi-connectivity (MC) structure. The same effect as a DC structure can be achieved.

[0227] According to this variation 1, it is possible to prevent the UE from generating erroneous data transmission and reception immediately after receiving the RRC_INACTIVE transition indication from the MgNB, thereby enhancing the robustness of the system.

[0228] Variation 2 of Implementation Method 1

[0229] As a method for UE mobility in the RRC_INACTIVE state, a procedure is obtained by combining inter-gNB restart, MN (Master Node) handover, and SN (Secondary Node Change).

[0230] Using the above method leads to the following problem: For a UE in the RRC_INACTIVE state, it is unclear who determines the target SgNB. Therefore, a UE in the RRC_INACTIVE state may be unable to perform SgNB mobility operations.

[0231] The following are solutions to the above problems.

[0232] The UE determines the SgNB. The UE uses cell reselection when determining the SgNB. The UE selects the detected cell from the cell reselection process as the SgNB.

[0233] The UE can also periodically measure surrounding cells. This period can be determined according to standards, or it can be the same as the DRX period.

[0234] The UE can also determine the surrounding cells while receiving a paging call. This reduces the processing load of UEs in the RRC_INACTIVE state.

[0235] The UE notifies the MgNB of the information of the determined SgNB. This information may be, for example, the identifier of the SgNB, or the identifier of the cell belonging to the SgNB, such as the Physical Cell Identity of the PSCell. This information may be included in RRC-specific signaling from the UE to the MgNB, such as an RRC Connection Resume Request, or in small data that can be sent in the RRC_INACTIVE state.

[0236] Figures 12-14 This is a flowchart showing the action of a UE in the RRC_INACTIVE state to determine the SgNB. Figures 12-14 It is continuous at the positions of boundary lines BL1213 and BL1314. Figures 12-14 This example illustrates a UE using a DC structure that generates SgNB mobility in the RRC_INACTIVE state and switches from S-SgNB to T-SgNB. Figures 12-14 When downlink data is generated via SgNB, the UE recovers to RRC_CONNECTED. Figures 12-14 The process shown includes and Figure 8 and Figure 9 The process shown has the same steps, so the same steps are labeled with the same step number, and common descriptions are omitted.

[0237] Figure 12 In step ST1101, the UE is in the RRC_INACTIVE state. In step ST1102, the UE determines the SgNB of the moving target. Figures 12-14 In the example, the moving target's SgNB is T-SgNB. The UE can use cell reselection when determining the SgNB.

[0238] Figure 12In step ST1103, the UPF is unaware that the UE's SgNB has become a T-SgNB, therefore it sends downlink data to the mobile source SgNB, i.e., the S-SgNB. In step ST1104, the S-SgNB sends a downlink data notification to the MgNB. The downlink data notification in step ST1104 can be combined with... Figure 8 The steps are the same as in ST807.

[0239] Figure 12 Steps ST809 to ST811 and Figure 9 Since they are the same, the explanation is omitted.

[0240] Figure 12 In step ST1108, the UE requests recovery to RRC_CONNECTED from the MgNB. This request contains information about the mobile target SgNB determined by the UE. The UE can also notify this request using the RRC Connection Resume Request signaling.

[0241] Figure 13 In step ST1109, the MgNB requests the UE context from the S-SgNB. In step ST1110, the S-SgNB sends the UE context to the MgNB. In step ST1109, the MgNB may include information indicating that it requests secondary base station information within the UE context. In step ST1110, the SgNB may send only the secondary base station information within the UE context to the MgNB. This, for example, can reduce the signaling volume associated with UE context transmission.

[0242] Figure 13 In step ST1111, the MgNB notifies the S-SgNB of a secondary base station addition request (SN AdditionRequest). This request may contain the UE context obtained by the S-SgNB. Figures 12-14 In the example, the T-SgNB determines that it has received the request. In step ST1112, the T-SgNB notifies the S-SgNB of a positive response to the request (SN Addition Request ACK). In step ST1113, the MgNB notifies the S-SgNB of the SN Release Request.

[0243] Figure 13 Steps ST813, ST816, ST820 and Figure 9 Since they are the same, the explanation is omitted.

[0244] Figure 13In step ST1115, the MgNB requests connection settings with the UE from the T-SgNB. In step ST1116, the T-SgNB notifies the MgNB that the settings have been completed.

[0245] Figure 14 In steps ST1118 and ST1119, a random access process is performed between the UE and the T-SgNB. The processing of steps ST1118 and ST1119 is similar to... Figure 9 The steps shown in ST817 and ST818 are the same.

[0246] Figure 14 Steps ST1120 and ST1121 illustrate the process of forwarding the PDCP sequence number reception / delivery status from the S-SgNB to the T-SgNB via the MgNB. In step ST1120, the S-SgNB forwards the reception / delivery status of the PDCP sequence number used for transmission and reception with the UE to the MgNB. In step ST1121, the MgNB forwards this status, which was received by the S-SgNB in ​​step ST1120, to the T-SgNB.

[0247] Figure 14 Steps ST1123 and ST1124 illustrate the process of forwarding downlink transmission data stored in the S-SgNB's PDCP buffer to the T-SgNB via the MgNB. In step ST1123, the S-SgNB forwards the PDCPPDU stored in the PDCP buffer to the MgNB. In step ST1124, the MgNB forwards the PDCPPDU received by the S-SgNB in ​​step ST1123 to the T-SgNB. The data forwarded in steps ST1123 and ST1124 may include the data sent from the UPF to the S-SgNB in ​​step ST1103.

[0248] Figure 14 In step ST1125, the MgNB notifies the SMF of a PDU session modification request. The PDU session to be modified according to this request can be a PDU session via the SCG. In step ST1126, the SMF and UPF modify the PDU session included in the PDU session modification request of step ST1125. In step ST1126, the PDU session modification can also be performed between the AMF and UPF in the same manner as in step ST1125.

[0249] Figures 12-14In this invention, the SMF can also be an AMF. Alternatively, an SMF can be connected between the UPF and the AMF, and the AMF can be connected to each gNB, namely MgNB, T-SgNB, and S-SgNB. This, for example, can improve the flexibility of the communication system structure. The same applies to the following aspects in this invention.

[0250] Figure 14 In step ST1127, the final packet from the UPF, whose path has switched from S-SgNB to T-SgNB, is marked with an end tag and sent from the UPF to S-SgNB. In steps ST1128 and ST1129, the packet marked with the end tag is forwarded from S-SgNB to T-SgNB via MgNB. In step ST1128, the packet is forwarded from S-SgNB to MgNB, and in step ST1129, the packet is forwarded from MgNB to T-SgNB.

[0251] Figure 14 In step ST1130, the path of the packet sent from the UPF is switched from S-SgNB to T-SgNB, and the packet is sent from the UPF to S-SgNB. In step ST1131, the packet sent in step ST1130 is sent from T-SgNB to the UE.

[0252] Figure 14 In step ST1132, the SMF notifies the MgNB that the PDU session change has been completed. In step ST1133, the MgNB instructs the S-SgNB to release the UE context notified to the MgNB in ​​step ST1110, and the S-SgNB releases the UE context. Alternatively, in step ST1132, the AMF can perform this notification instead of the SMF, similar to steps ST1125 and ST1126.

[0253] Figures 12-14 In the example shown, the UE uses cell reselection to determine the moving target SgNB, but it can also utilize the measurement configuration notified by the MgNB. This measurement configuration can be the configuration obtained from the MgNB when the UE is in the RRC_CONNECTED state. This, for example, can improve the flexibility of the SgNB determination method.

[0254] When determining the SgNB, the UE can choose the first detected cell among those meeting pre-defined conditions as the SgNB. This allows for rapid SgNB detection. Alternatively, it can choose the cell with the best conditions as the SgNB, thus improving communication reliability.

[0255] Other solutions are proposed. The MgNB determines the SgNB. The MgNB uses the measurement results notified from the UE to determine the SgNB.

[0256] The UE can also perform this measurement periodically. This period can be determined according to standards, or it can be the same as the DRX period. Alternatively, the MgNB can notify the UE individually, or the MgNB can broadcast it to its subordinate UEs.

[0257] The UE can also perform this measurement when it receives a paging message. This reduces the processing load of UEs in the RRC_INACTIVE state.

[0258] The UE can also notify the MgNB of the measurement results. The UE can use small data packets that can be sent in the RRC_INACTIVE state to perform this notification, thus enabling rapid notification of the measurement results. As another example, the notification can be in the form of a measurement report. Alternatively, the measurement results can be included in the signaling of the RRC Connection Resume Request.

[0259] The MgNB can use cell reselection criteria when deciding on the SgNB. The UE can notify the MgNB of the determination results used for cell reselection.

[0260] Figures 15-17 This is a flowchart illustrating the action of the MgNB in ​​deciding to communicate with the UE in the RRC_INACTIVE state. Figures 15-17 It is continuous at the positions of boundary lines BL1516 and BL1617. Figures 15-17 This illustrates a scenario where the UE uses small amounts of data that it can send in the RRC_INACTIVE state to notify the MgNB of the measurement results. Figures 15-17 When downlink data is generated via SgNB, the UE recovers to RRC_CONNECTED. Figures 15-17 The process shown includes and Figure 8 , Figure 9 and Figures 12-14 The process shown has the same steps, so the same steps are labeled with the same step number, and common descriptions are omitted.

[0261] Figure 15 Steps ST1101, ST1103, ST1104 and Figure 12 Since they are the same, the explanation is omitted. Figure 15 and Figure 12 The difference is that it does not involve Figure 12 The UE determines SgNB as shown in step ST1102.

[0262] Figure 15Steps ST809 to ST812 and Figure 9 Since they are the same, the explanation is omitted.

[0263] Figure 15 In step ST1202 shown, the UE notifies the MgNB of the measurement results. Figure 15 In this example, the notification is contained in small data that can be sent in the RRC_INACTIVE state. The settings associated with this determination can be notified to the UE from the MgNB when the UE is in the RRC_CONNECTED state. In step ST1203, the MgNB determines the moving target SgNB. This determination can use the determination results notified by the UE in step ST1202. Figures 15-17 The example shows the case where the moving target SgNB is determined to be T-SgNB.

[0264] Figure 16 Steps ST1109 to ST1113 and Figure 13 Since they are the same, the explanation is omitted.

[0265] Figure 16 In step ST1204 shown, with Figure 13 Similarly, step ST813 in the UE transitions the instruction from MgNB to RRC_CONNECTED. The instruction in step ST1204 contains information about the mobile target SgNB determined by MgNB. This information can be, for example, an SgNB identifier, or a PSCell identifier, such as a physical cell identifier. The UE uses step ST1204 to identify that the mobile target SgNB is a T-SgNB.

[0266] Figure 16 and Figure 17 The process after step ST816 in the middle and Figure 13 and Figure 14 The same applies, so the explanation is omitted.

[0267] Other solutions are proposed. Two scenarios are defined: one where the MgNB determines the SgNB, and another where the UE determines the SgNB. Information regarding the entity determining the SgNB can be determined according to standards, or it can be notified to the UE by the MgNB, or it can be notified to the MgNB and / or the UE by a higher-level NW device such as the SMF or AMF.

[0268] As an example of determining the subject of decision-making for the SgNB based on a standard, it is possible to utilize whether there is movement of the MgNB in ​​the UE in the RRC_INACTIVE state. For example, when the MgNB moves, the UE can determine the SgNB; when the MgNB moves, the moving target MgNB can also determine the SgNB. In the above cases, the UE can also determine the movement of the MgNB.

[0269] When deciding on the SgNB, the UE can use, for example, cell reselection. Alternatively, it can use the measurement configuration notified by the MgNB in ​​the RRC_CONNECTED state.

[0270] When the UE determines the SgNB, it can, for example, use the first detected cell among cells that meet certain conditions as the moving target MgNB, or the second detected cell as the moving target SgNB. Thus, the UE can quickly determine the MgNB and SgNB.

[0271] As another example, the cell with the best conditions can be designated as the MgNB, and the cell with the second best conditions as the SgNB. This can improve communication reliability. Alternatively, the reverse can be true: the cell with the best conditions can be designated as the SgNB, and the cell with the second best conditions as the MgNB. For example, by allocating C-Plane communication to the MgNB and U-Plane communication to the SgNB, the transmission speed and reliability of U-Plane communication can be improved.

[0272] When the MgNB decides the SgNB, it can use, for example, the measurement configuration notified to the UE from the MgNB in ​​the RRC_CONNECTED state. Alternatively, it can use the measurement configuration used during cell reselection.

[0273] Figures 18-20 This is a flowchart illustrating the actions of a UE in the RRC_INACTIVE state in determining the moving target MgNB and the moving target SgNB. Figures 18-20 It is continuous at the positions of boundary lines BL1819 and BL1920. Figures 18-20 The example shows the cases where the moving source MgNB and the moving target MgNB are set as S-MgNB and T-MgNB respectively, and the moving source SgNB and the moving target SgNB are set as S-SgNB and T-SgNB respectively. Figures 18-20 When downlink data is generated via SgNB, the UE recovers to RRC_CONNECTED. Figures 18-20 In this context, S-MgNB and T-MgNB belong to the same RAN cell. Figures 18-20 The process shown includes and Figure 8 , Figure 9 and Figures 12-14 The process shown has the same steps, so the same steps are labeled with the same step number, and common descriptions are omitted.

[0274] Figure 18 Steps ST1101 to ST1103 and Figure 12 Since they are the same, the explanation is omitted.

[0275] Figure 18 In step ST1300 shown, the UE determines the moving target MgNB and the moving target SgNB as T-MgNB and T-SgNB, respectively.

[0276] Figure 18 In step ST1301, the S-SgNB notifies the S-MgNB that downlink data has been generated. In step ST1302, the S-MgNB notifies the T-MgNB, which belongs to the same RAN cell, of the paging information to the UE.

[0277] Figure 18 In step ST1303, the T-MgNB uses the paging information received in step ST1302 to send a paging message to the UE. In steps ST1304 and ST1305, the UE and T-MgNB perform random access processing. This random access processing is related to... Figure 9 The steps shown in ST810 and ST811 are the same.

[0278] Figure 18 In step ST1306, the UE notifies the T-MgNB of its request to return to the RRC_CONNECTED state. Step ST1306 can be combined with... Figure 9 Step ST812 in the process also utilizes the signaling of the RRC Connection Resume Request. Additionally, the notification in step ST1306 may include information indicating the mobile target MgNB and mobile target SgNB determined by the UE. Figure 18 The example includes information on T-MgNB and T-SgNB.

[0279] Figure 18 Steps ST1307 and ST1308 illustrate the forwarding process of the UE context for the MgNB. In step ST1307, the T-MgNB requests the UE context from the S-MgNB. In step ST1308, the S-MgNB sends the UE context to the T-MgNB. In step ST1307, the T-MgNB may include information indicating that it requests primary base station information within the UE context. In step ST1308, the S-MgNB may send only the primary base station information within the UE context to the T-MgNB. This, for example, reduces the signaling volume associated with UE context transmission.

[0280] Figure 19 Steps ST1309 to ST1311 illustrate the forwarding process of the UE context from the S-SgNB and the SgNB addition process. This UE context is forwarded from the S-SgNB to the T-SgNB via the T-MgNB. Steps ST1309 to ST1311 involve... Figure 13Steps ST1109 to ST1111 are performed identically. In step ST1312, T-SgNB sends an affirmative response to T-MgNB regarding the secondary base station addition request. In step ST1313, T-MgNB sends a secondary base station release request to S-SgNB.

[0281] Figure 19 In step ST1315 shown, the T-MgNB sends an indication to the UE to switch to RRC_CONNECTED. This indication can be combined with... Figure 9 The steps in ST813 are the same.

[0282] Figure 19 In step ST816, the UE transitions to RRC_CONNECTED. In step ST1318, the UE notifies the T-MgNB that the transition to RRC_CONNECTED has been completed.

[0283] Figure 19 The steps ST1316 and ST1317 shown are to... Figure 9 In steps ST814 and ST815, MgNB is replaced with T-MgNB, and SgNB is replaced with T-SgNB.

[0284] Figure 19 Steps ST1118 and ST1119 in the middle Figure 14 Since they are the same, the explanation is omitted.

[0285] Figure 20 The steps ST1321 to ST1327 shown are to... Figure 14 In steps ST1120 to ST1124 shown, MgNB is replaced with T-MgNB.

[0286] Figure 20 In the example, steps ST1321 and ST1325 involve directly forwarding the PDCP sequence number reception / delivery status and PDCPPDU from the S-SgNB to the T-MgNB, but forwarding can also be done via the S-MgNB. For example, even if no connection is established between the S-SgNB and the T-MgNB, switching can still be performed between the MgNB and the SgNB.

[0287] Figure 20In step ST1328, the T-MgNB requests a path switch request from the SMF. This request may include PDU session switching requests for both the MgNB and SgNB. In step ST1329, the communication path is switched between the SMF and UPF. Alternatively, a PDU session switch for either the MgNB or SgNB may be performed. In steps ST1328 and ST1329, the AMF may be used instead of the SMF.

[0288] Figure 20 The steps ST1330 to ST1332 shown are to... Figure 14 In steps ST1127 to ST1129, MgNB is replaced with T-MgNB. Step ST1331 can also be performed via S-MgNB in ​​the same way as steps ST1321 and ST1325.

[0289] Figure 20 Steps ST1130 and ST1131 in the process are related to Figure 14 Since they are the same, the explanation is omitted.

[0290] Figure 20 In step ST1336, the SMF notifies the T-MgNB that the path switchover is complete. In step ST1337, the T-MgNB indicates to the S-MgNB that the UE context towards the MgNB is released. In step ST1338, the T-MgNB indicates to the S-SgNB that the UE context towards the MgNB is released.

[0291] Figure 20 Step ST1338 illustrates an example of the T-MgNB notifying the SgNB of a UE context release, but this notification can also be made via the S-MgNB. Alternatively, the S-MgNB can notify the S-SgNB of the UE context release instruction directed to the SgNB. Step ST1337 may also include a UE context release instruction directed from the T-MgNB to the S-MgNB directed to the MgNB. This reduces the signaling load on the inter-base station interface.

[0292] Other solutions are proposed. The higher-level NW device determines the SgNB. The higher-level NW device can be either an AMF or an SMF. The higher-level NW device notifies the MgNB of the determined SgNB information. The MgNB notifies the UE of the SgNB information.

[0293] The higher-level NW device can also determine the SgNB based on the load status of its subordinate gNBs. This load status could be, for example, the load of the inter-base station interface, the processing load, the radio resource load, the number of UEs accommodated, or a combination of these factors. Therefore, the SgNB can be determined based on the gNB's load status, thus optimizing the communication system.

[0294] The MgNB and / or SgNB can also notify the eNB / gNB in ​​the paging-related RAN area in advance of the UEAS context. This notification can also be performed using the same method as in Implementation 1. Thus, for example, communication can be initiated quickly after paging when the UE moves.

[0295] Alternatively, the eNB / gNB can query the UEAS context from other eNBs / gNBs within the paging-related RAN area. This query can also occur during the random access process between the UE and the eNB / gNB. The other eNBs / gNBs can also notify the eNB / gNB of the UEAS context. The UEAS context can contain information about a single MgNB / SgNB, or information about both the MgNB and SgNB. This reduces the signaling load at the base station interface.

[0296] By using this variant example 2, SgNB can move in the UE in the RRC_INACTIVE state.

[0297] Implementation Method 2

[0298] A UE with a DC (Distributed Control) architecture sends small data to the MgNB in ​​the RRC_INACTIVE state. The MgNB can also change the bearer structure when the UE transitions to RRC_INACTIVE. For example, the bearer structure change could be from an SCG bearer to an MCG bearer. Another example is from an SCG bearer to an SCG fork bearer. Therefore, even if data was previously transmitted using an SCG bearer, low-latency communication can be achieved through small data transmission.

[0299] Using the above method will result in the following problem: When the UE switches to RRC_INACTIVE, the bearer structure changes, thus increasing the signaling volume between MgNB and SgNB.

[0300] The following are solutions to the above problems.

[0301] The UE sends small data to the SgNB. It can also send small data to the MgNB. That is, small data transmission under RRC_INACTIVE can also be applied to the DC structure. Therefore, there is no need to change the bearer between the MgNB and SgNB, thus reducing the signaling volume of the inter-base station interface.

[0302] This small data can be data carried by the SCG, data carried by an SCG fork, data carried by an MCG fork, or MCG data. For example, by sending small data carried by an MCG fork to the SgNB, small data can be sent quickly even when the radio channel conditions between the UE and the MgNB deteriorate.

[0303] The UE can use information about the bearer through which small data is transmitted to determine the target base station. For example, it can send small data using MCG bearers or MCG fork bearers to the MgNB. It can also send small data using SCG bearers or SCG fork bearers to the SgNB. For example, since the inter-base station interface does not need to be connected, small data notification from the UE to the upper-level NW device can be carried out quickly.

[0304] In the above, the UE can also use information from downlink signal measurement results to determine the target base station for transmission. For example, if the measurement results from the SgNB are better than those from the MgNB, the UE can send small data to the SgNB using either the MCG fork bearer or the SCG fork bearer. The downlink signal mentioned above can be, for example, a synchronization signal (SS). Additionally, the measurement result information can be, for example, RSRP or RSRQ. Therefore, by using a base station with higher communication quality for small data communication, the UE can improve communication reliability.

[0305] In the above description, the UE can combine information about the bearer through which small data is transmitted with information from downlink signal measurement results to determine the target base station. For example, it can send small data using MCG bearers to the MgNB, or small data using SCG bearers to the SgNB. The transmission target for small data using MCG fork bearers or SCG fork bearers can be determined by the UE using information from downlink signal measurement results. This achieves both rapid small data notification and improved reliability.

[0306] When a UE sends small data to the SgNB, the UE may send a random access preamble to the SgNB. The SgNB may then send a random access response to the UE. This random access response can be sent after the UE sends the random access preamble to the SgNB.

[0307] The UE can request a return to RRC_CONNECTED from the SgNB. This request can also be made after the SgNB sends a random access response to the UE.

[0308] The UE can include an identifier, such as a recovery ID, used for recovery to RRC_CONNECTED in the request. The UE can also include information representing the MgNB, such as the MgNB's identifier, in the request. This, for example, can prevent malfunctions caused by duplicate recovery IDs issued by the SgNB as the primary base station of other UEs. As another example, the UE can include its identifier in the request. This, for example, achieves the same effect as described above.

[0309] The SgNB can also send a query to the MgNB related to the identifier used for recovery. This query may include the UE's identifier.

[0310] The MgNB can notify the SgNB of the identifier used for restoration. This notification may include information representing the MgNB, or it may include the UE's identifier. This notification can be made after the SgNB has made the query to the MgNB, or it can be made in advance. The aforementioned advance notification can be included in the UE connection stop notification sent by the MgNB to the SgNB, or it can be made as separate signaling. The MgNB can notify the SgNB of the identifier used for restoration.

[0311] The SgNB can retain information about the identifier used for recovery. The SgNB can also retain this information in combination with information representing the MgNB, or in combination with the UE's identifier. This, for example, prevents malfunctions caused by duplicate recovery IDs issued by the SgNB as the primary base station for other UEs.

[0312] The UE can send small data to the SgNB. This transmission can occur after the UE recovers from the RRC_CONNECTED connection to the SgNB. This small data can be data carried via SCG, data carried via an SCG fork, or data carried via an MCG fork.

[0313] The SgNB can notify the UE of its response to a request to restore to RRC_CONNECTED. This response can be an indication that the UE maintains the RRC_INACTIVE state. The response may contain the identifier used for restoring to RRC_CONNECTED, information representing the MgNB, or the UE's identifier.

[0314] The SgNB may choose not to notify the UE of its response to the request to restore to RRC_CONNECTED. Alternatively, the SgNB may notify the UE of its response to the small data instead of the above response.

[0315] The identifier used for recovery in RRC_CONNECTED, such as the recovery ID, can contain information representing the MgNB. For example, a portion of the recovery ID can be the same as the MgNB's ID. Thus, the identifier used for recovery is unique among gNBs, thereby facilitating the control of MgNB and SgNB.

[0316] Figure 21 This is a flowchart illustrating the actions taken when the UE sends small data to the SgNB. Figure 21 The process shown includes and Figure 8 and Figure 9 The process shown has the same steps, so the same steps are labeled with the same step number, and common descriptions are omitted.

[0317] Figure 21 Steps ST801, ST803, ST805, and ST808 in the process Figure 8 Since they are the same, the explanation is omitted.

[0318] Figure 21 In step ST1401 shown, the MgNB notifies the SgNB that the UE connection has stopped. This notification includes a recovery ID and the MgNB's ID. As another example, it may also include a recovery ID, a portion of which contains the MgNB's ID. The SgNB retains both the recovery ID and the MgNB's ID.

[0319] Figure 21 In step ST1407 shown, uplink transmission data is generated by the UE to the SgNB. Figure 21 In steps ST817 and ST818 shown, the UE performs random access processing to the SgNB. Figure 21 Steps ST817 and ST818 in the process are Figure 9 same.

[0320] Figure 21 In step ST1410, the UE requests recovery to RRC_CONNECTED from the SgNB. This request may include a recovery ID or an identifier for the MgNB.

[0321] Figure 21 In step ST1416, the UE sends small data to the SgNB. This small data can be data carried using SCG, data carried through an SCG fork, or data carried through an MCG fork.

[0322] Figure 21 In step ST1419 shown, the SgNB notifies the UE of an indication to maintain the RRC_INACTIVE state. This indication may include the recovery ID or the identifier of the MgNB.

[0323] The UE can send small data to both the MgNB and SgNB. For example, it can send small data to the MgNB using an MCG bearer or an MCG fork bearer. It can also send small data to the SgNB using an SCG bearer or an SCG fork bearer.

[0324] Figure 22 This is a flowchart illustrating the actions taken when the UE sends small data to the MgNB and SgNB. Figure 22 The process shown includes and Figure 8 and Figure 9 , Figure 21 The process shown has the same steps, so the same steps are labeled with the same step number, and common descriptions are omitted.

[0325] Figure 22 The process of steps ST801 to ST1407 in the middle is the same as Figure 21 Since they are the same, the explanation is omitted.

[0326] Figure 22 In steps ST810 and ST811, the UE performs random access processing to the MgNB. In steps ST817 and ST818, the UE performs random access processing to the SgNB. Figure 22 Steps ST810, ST11, ST817, and ST818 in the series are related to... Figure 9 same.

[0327] Figure 22 Step ST812 and Figure 9 Same. In step ST1513, the UE sends small data to the MgNB. This small data can be data carried through the MCG, data carried through an MCG fork, or data carried through an SCG fork.

[0328] Figure 22 In step ST1410, the UE requests recovery to RRC_CONNECTED from the SgNB. This request may contain a recovery ID or an identifier for the MgNB. Alternatively, it may contain both. Or, it may contain a recovery ID, a portion of which includes the MgNB identifier.

[0329] Figure 22 In step ST1416, the UE sends small data to the SgNB. This small data can be data carried via SCG, data carried via an SCG fork, or data carried via an MCG fork.

[0330] Figure 22In step ST1518 shown, the MgNB notifies the UE of an indication to maintain the RRC_INACTIVE state. This indication may include the recovery ID.

[0331] Figure 22 In step ST1419 shown, the SgNB notifies the UE of an indication to maintain the RRC_INACTIVE state. This indication may include the recovery ID or the identifier of the MgNB.

[0332] Figure 21 and Figure 22 The example shown illustrates a UE maintaining the RRC_INACTIVE state, but the UE can also transition to RRC_CONNECTED. When the UE transitions to RRC_CONNECTED, the process shown in Implementation 1 can also be applied.

[0333] This second implementation method enables the transmission of small data to the SgNB. As a result, bearer changes are eliminated during RRC_INACTIVE transitions, reducing the signaling load on the inter-base station interface.

[0334] According to embodiment 2, for example, the following structure is provided.

[0335] A communication system is provided, comprising a communication terminal device and multiple base station devices configured to wirelessly communicate with the communication terminal device. More specifically, the multiple base station devices include a primary base station device and a secondary base station device that serve as bearers for the communication terminal device. The communication terminal device, in the RRC_INACTIVE state, performs random access processing with the secondary base station device. After the random access processing, the communication terminal device requests to return to the RRC_CONNECTED state from the secondary base station device. Before returning to the RRC_CONNECTED state, uplink data is sent to the secondary base station device in the form of small data that can be transmitted in the RRC_INACTIVE state.

[0336] In this structure, a communication terminal device in the RRC_INACTIVE state can also perform random access processing with the main base station device. After the random access processing, it can request to return to the RRC_CONNECTED state from the main base station device, and before returning to the RRC_CONNECED state, it can send uplink data to the main base station device in the form of small data.

[0337] The above structure can be modified in various ways based on the disclosure and inspiration of this specification, including Embodiment 2. According to the above structure and its modifications, the above-mentioned technical problems can be solved and the above-mentioned technical effects can be obtained.

[0338] Variation 1 of Implementation Method 2

[0339] For communication methods requiring low latency and high reliability, packet replication can be used. As a packet replication method, either a DC (Distributed Domain) structure or a CA (Content Acquisition Domain) structure can be used.

[0340] When the above method is applicable to low-frequency communications requiring low latency and high reliability, such as emergency communications during earthquakes or emergency control signals during autonomous driving, the following problems arise. In low-frequency communications, the UE transitions to the RRC_INACTIVE state. However, how packet replication is performed in the RRC_INACTIVE state is unclear. As a result, it becomes impossible to achieve low-frequency communications requiring low latency and high reliability.

[0341] The following are solutions to the above problems.

[0342] For small data transmissions that a UE in the RRC_INACTIVE state can perform, packet replication is applicable.

[0343] The small data grouping and replication described above can employ a DC structure. This structure can be the same as that in Implementation Method 2.

[0344] The MgNB can configure packet replication for both the UE and the SgNB. These configurations can, for example, be included in the DC structure settings. Therefore, for example, the configuration for packet replication during small data transmission can be omitted, allowing for rapid initiation of small data transmission.

[0345] In the above, the default action / stop status for group replication can be set to "Action". This allows, for example, the rapid initiation of small data communication.

[0346] The UE can perform random access processing on both the MgNB and SgNB. The random access processing on the SgNB can be performed either after the MgNB has responded with a random access response, or before the MgNB responds. The UE can send the random access preamble to the SgNB before sending it to the MgNB. This random access processing can occur during uplink data transmission.

[0347] Figure 23 and Figure 24 This is a flowchart illustrating the actions taken when using DC in grouped replication of small data. Figure 23 and Figure 24 They are continuous at the boundary line BL2324. Figure 23 and Figure 24 Grouped replication is performed using MCG fork carriers. Figure 23 and Figure 24 The process shown includes and Figure 8 , Figure 9 and Figure 21 , Figure 22 The process shown has the same steps, so the same steps are labeled with the same step number, and common descriptions are omitted.

[0348] Figure 23 The steps in ST801 to ST818 are the same as those in the previous steps. Figure 22 Since they are the same, the explanation is omitted.

[0349] Figure 24 In step ST1610 shown, the UE performs packet replication of uplink transmitted data.

[0350] Figure 24 The steps in ST812 to ST1410 are the same as those in the previous steps. Figure 22 Since they are the same, the explanation is omitted.

[0351] Figure 24 In step ST1416, the UE sends the packets from the duplicated packets obtained in step ST1610 that were not sent in step ST1513 to the SgNB as small data packets. In step ST1612, the SgNB forwards the uplink transmission data received by the UE in step ST1416 to the MgNB. In step ST1613, the MgNB detects the duplication of the uplink transmission data, removes and deletes one of the duplicate uplink transmission data.

[0352] Figure 24 Steps ST1518 and ST1419 in the process are similar to Figure 22 Since they are the same, the explanation is omitted.

[0353] Small data packet replication can also use the CA structure. The UE and gNB can also maintain connection-related information between the terminal and the base station, such as the UEAS context. This UEAS context can be maintained when the UE transitions to the RRC_INACTIVE state.

[0354] Similar to packet replication using the DC structure, a gNB can notify the eNB / gNB in ​​the paging-related RAN area of ​​the UEAS context in advance, and the eNB / gNB can also query the UEAS context from other eNB / gNBs in the paging-related RAN area.

[0355] The base station can configure the UE for packet replication. This configuration can be included, for example, in the configuration of the UE's CA structure. For instance, the configuration can be included in the signaling for resetting the UE's RRC connection. Therefore, for example, the configuration for packet replication during small data transmission can be omitted, allowing small data transmission to begin quickly.

[0356] In the above, the default action / stop status for group replication can be set to "Action". This allows, for example, the ability to quickly begin sending small amounts of data.

[0357] The UE can perform random access processing on the gNB's Pcell and SCell. The random access processing for the SCell can be performed either after waiting for a random access response from the PCell, or before the PCell sends a random access response. The UE can send the random access preamble to the SCell before sending it to the Pcell, enabling rapid data transmission using the SCell. Alternatively, it can be performed at different times. This random access processing can occur during uplink data transmission.

[0358] Figure 25 This is a flowchart illustrating the actions taken when using CA in grouped replication of small data. Figure 25 In the example, PCell and SCell are used for grouped replication. Additionally, in... Figure 25 In the example, the gNB uses the PCell to send signaling to the UE. Figure 25 The process shown includes and Figure 8 and Figure 9 , Figure 21 The process shown has the same steps, so the same steps are labeled with the same step number, and common descriptions are omitted.

[0359] Figure 25 Step ST801 and Figure 8 Since they are the same, the explanation is omitted.

[0360] Figure 25 In step ST1702 shown, the gNB instructs the UE to switch to RRC_INACTIVE via the PCell. This instruction can be used in conjunction with... Figure 8 The steps are the same as those in ST805.

[0361] Figure 25 Steps ST808 and ST1407 in the process are related to Figure 21 Since they are the same, the explanation is omitted.

[0362] Figure 25 In steps ST1705 and ST1706, random access processing is performed between the UE and the Pcell. In steps ST1707 and ST1708, random access processing is performed between the UE and the SCell.

[0363] Figure 25 In step ST1709, the UE requests an RRC connection restart from the gNB via the PCell. This request can be... Figure 9 The steps in ST812 are the same.

[0364] Figure 25 In step ST1610, the UE performs packet replication of the uplink transmission data. In step ST1711, the UE sends one of the replicated uplink transmission data to the gNB in ​​small data format via PCell. In step ST1712, the UE sends the other replicated uplink transmission data to the gNB in ​​small data format via SCell. In step ST1713, the gNB detects the duplication of the uplink transmission data, removes and deletes one of the duplicate uplink transmission data.

[0365] Figure 25 In step ST1714, the MgNB notifies the UE of an indication to maintain the RRC_INACTIVE state. Step ST1714 could also be an indication to transition to the RRC_CONNECTED state.

[0366] According to this variation 1, low-frequency but low-latency and high-reliability communication can be achieved.

[0367] Implementation Method 3

[0368] For UEs mounted on unmanned aerial vehicles (UAVs), different transmit power control applies compared to ground terminals. For example, for UAV-UEs, a maximum transmit power limit can be set. As another example, the transmit power of the target-SIR ground terminal and the UAV-UE can be different. This can reduce uplink interference from the UAV-UE to the base station.

[0369] Using the above method will result in the following problem: the aforementioned transmit power control also reduces the transmit power to the serving cell, thus degrading the reception quality of the signal transmitted by the UAV-UE to the serving cell.

[0370] The following are solutions to the above problems.

[0371] Repetition applies to uplink transmissions.

[0372] This repetition can also be performed when the aforementioned transmission power reduction method is applied. Thus, for example, uplink interference power can be suppressed, ensuring the reliability of uplink transmission.

[0373] An example of the application of the aforementioned method of reducing transmission power could be the difference between a UAV-UE and a typical UE. For instance, a UAV-UE could employ a method of reducing transmission power.

[0374] As another example, the difference between a UE in ground mode and a UE in flight mode could be illustrated. For instance, a UE in flight mode could employ a method of reducing transmission power. The UE could be a UAV-UE or a regular UE.

[0375] As another example, the UE's altitude information can be used to determine whether a transmit power reduction method is applicable. For instance, if the UE is at a higher altitude, a transmit power reduction method may be applicable. The UE can be a UAV-UE or a regular UE.

[0376] As another example, information about the received interference level at the base station can be used to determine whether a transmit power reduction method is applicable. For instance, when communicating with a base station with a high received interference level, a UE transmit power reduction method can be applied. The UE can be a UAV-UE or a regular UE.

[0377] As an example of repeated channels and / or signals used in the uplink transmission, the following (1) to (5) are disclosed.

[0378] (1)PUSCH.

[0379] (2) PUCCH.

[0380] (3) PRACH.

[0381] (4)RS.

[0382] (5) The combination of (1) to (4) above.

[0383] The RS in (4) above can be DMRS, SRS, or both. The repetition of SRS can be achieved by shortening the SRS transmission period or by setting new symbols for repeated transmission.

[0384] UAV-UE can use frequency hopping to transmit to the base station on each repetition. UAV-UE can also change the RB of the uplink transmitted signal for each repetition number.

[0385] For the frequency hopping described above, the UAV-UE can transmit to the base station by hopping frequency on each repetition. The frequency hopping pattern can be given on a per-cell basis. For example, the frequency hopping pattern can be given using the cell ID, such as the PCI.

[0386] As an example of frequency hopping mentioned above, an offset can be set for the RBs transmitted by the UAV-UE at each repetition. This offset can be given on a per-cell basis. For example, the offset can also be determined using the cell ID, such as the PCI.

[0387] Figure 26This is a schematic diagram illustrating an example of different frequency hopping modes used for UAV-UE in each cell. Figure 26 An example of PUSCH is shown in the figure. Figure 26 The document also shows an example where the uplink transmission from the UAV-UE is repeated 3 times.

[0388] For use Figure 26 The example of Cell#1 will be used to illustrate this. During the initial PUSCH transmission, the UAV-UE uses RB1801 to send a message to the base station. During the first retransmission, the UAV-UE uses RB1802, which is 1 RB higher in frequency direction than the initial transmission, to send a message to the base station. The second and third retransmissions are similar; the UAV-UE uses RB1803 and RB1804, which are 1 RB higher in frequency direction than the first and second retransmissions, respectively, to send messages to the base station.

[0389] For use Figure 26 The example of Cell#2 illustrates this. During the initial PUSCH transmission, the UAV-UE uses RB1811 to send a message to the base station. During the first retransmission, the UAV-UE uses RB1812, which is 2 RB higher in frequency direction than the initial transmission, to send a message to the base station. The second and third retransmissions are similar; the UAV-UE uses RB1813 and RB1814, which are 2 RB higher in frequency direction than the first and second retransmissions, respectively, to send a message to the base station.

[0390] Figure 26 The example shown illustrates a frequency range of one RB used for each uplink transmission, but multiple RBs are also possible. These multiple RBs can be continuous or discontinuous in the frequency direction, for example, using a skipped frequency range.

[0391] Figure 26 The example shown illustrates how the frequency range used for each uplink transmission can be determined using the frequency directional deviation, but it can also be determined using the cumulative frequency directional deviation and the remainder of the entire frequency range available to the UAV-UE. For example, Figure 26 In the example, the frequency range of the PUSCH allocated to the UAV-UE is 10 RBs. Assuming a frequency deviation of 7 RBs for each transmission, the first transmission could utilize the last RB in the frequency direction, the first retransmission could utilize the 8th RB from the bottom, the second retransmission could utilize the 5th RB from the bottom, and the third retransmission could utilize the 2nd RB from the bottom. This, for example, increases the number of frequency hopping modes, thus increasing the number of UAV-UEs that can be accommodated.

[0392] As another example of providing this frequency modulation mode, it can be given for each UAV-UE. Thus, for example, the frequency mode can be distributed among other UAV-UEs. As a result, for example, the uplink interference power of the base station can be reduced.

[0393] The base station can notify the UE of the frequency hopping mode. This notification can also use, for example, L1 / L2 signaling. This allows the base station to quickly allocate frequency resources. As another example, MAC signaling can be used. This allows for highly reliable notifications via HARQ retransmission. As yet another example, RRC signaling can be used. This allows for the notification of large amounts of information.

[0394] The notification can be sent by the base station on each repetition of the frequency hopping mode, enabling flexible scheduling at the base station. Alternatively, the initial transmission and repetitions of the frequency hopping mode can be notified simultaneously, avoiding complicating the UE's processing.

[0395] The base station can broadcast frequency hopping patterns to its subordinate UEs, thereby reducing signaling load.

[0396] As another example, the frequency hopping mode can be predefined by the standard. For instance, the frequency hopping mode can be determined using the UE's identifier. This, for example, can reduce the signaling load between the base station and the UAV-UE.

[0397] In this third embodiment, uplink communication is disclosed, but it can also be applied to downlink communication. Therefore, for example, it is possible to reduce the downlink interference power from the base station to the UAV-UE. It also ensures the reliability of downlink communication.

[0398] The downlink communication described above can be, for example, PDSCH. The base station can also repeat PDSCH to the UAV-UE. Frequency hopping can also be performed.

[0399] As another example, the downlink communication described above can also be a PDCCH. The base station can also repeat the DCI contained in the PDCCH to the UAV-UE.

[0400] As another example, the downlink communication described above can also be E-PDCCH. The base station can also repeat the E-PDCCH to the UAV-UE. Frequency hopping can also be performed.

[0401] In this embodiment 3, a UAV-UE is shown, but it can also be applied to a regular UE. For example, the method shown in this embodiment 3 can also be applied to a regular UE using information indicating that the UE is at a higher altitude. Thus, for example, even when a regular UE is carried on a UAV during flight, interference power can be reduced and reception quality can be ensured in the same way as with a UAV-UE.

[0402] According to this embodiment 3, the received signal power of the base station and / or UAV-UE can be increased by repetition. Furthermore, by using frequency hopping to distribute frequency resources with other UAV-UEs, uplink and / or downlink interference power can be reduced. Therefore, the reception quality of communication between the base station and the UAV-UE can be improved.

[0403] According to embodiment 3, for example, the following structure is provided.

[0404] A communication system is provided, comprising a communication terminal device and a plurality of base station devices configured to wirelessly communicate with the communication terminal device. More specifically, when the height difference between the location of the communication terminal device and the location of the base station devices is greater than or equal to a threshold, at least one of the communication terminal device and the base station devices performs repetitive control to repeatedly transmit a transmission target. In this structure, the repetitive control may include control that causes the transmission frequency of the transmission target to hop.

[0405] The above structure can be modified in various ways based on the disclosure and inspiration of this specification, including Embodiment 3. According to the above structure and its modifications, the above-mentioned technical problems can be solved and the above-mentioned technical effects can be obtained.

[0406] Variation 1 of Implementation Method 3

[0407] Other methods for reducing uplink interference from UAV-UEs are disclosed.

[0408] The number of UEs that can multiplex PUCCH is limited. This multiplexing limit can be the number of UEs that can multiplex one RB of PDCCH.

[0409] For example, a typical UE and a UAV-UE can have different numbers of PUCCH multiplexing. For instance, the number of PUCCH multiplexing in a UAV-UE can be less than the number of PUCCH multiplexing in a typical UE.

[0410] As another example, UEs in ground mode and UEs in flight mode can have different numbers of PUCCH multiplexing. For instance, the number of PUCCH multiplexing in a flight mode UE can be less than the number of PUCCH multiplexing in a ground mode UE. The UE can be a UAV-UE or a regular UE.

[0411] As another example, the UE's height information can be used to vary the number of UE multiplexing operations on the PUCCH. For instance, the number of UE multiplexing operations on the PUCCH in a UE with a higher height can be less than the number of PUCCH multiplexing operations in a UE with a lower height. The UE can be a UAV-UE or a regular UE.

[0412] As another example, the number of UE multiplexing operations in the PUCCH can be varied by utilizing information about the base station's received interference level. For instance, when communicating with a base station with a high received interference level, the number of UE multiplexing operations in the PUCCH can be reduced; conversely, when communicating with a base station with a low received interference level, the number of UE multiplexing operations in the PUCCH can be increased. The UE can be a UAV-UE or a regular UE. This, for example, can ensure that the communication quality between the base station and the UE is above a certain level.

[0413] The number of UE multiplexing operations mentioned above can be predetermined according to the standard. For example, a new parameter can be set to represent the number of UE multiplexing operations for the PUCCH in a UAV-UE. As another example, a new parameter can be set to represent the number of UE multiplexing operations for the PUCCH in flight mode. This, for example, makes it easier for the base station to control the number of UE multiplexing operations.

[0414] As another example, the number of UE multiplexing operations can be determined by a higher-level NW device. This higher-level NW device can be, for example, an MME or an AMF. The higher-level NW device can notify the base station of the aforementioned number of UE multiplexing operations. Therefore, for example, interference power can be flexibly controlled based on the number of UEs accommodated.

[0415] As another example, the number of UE multiplexes described above can be determined by the base station. The base station can determine this using, for example, the number of beams. Thus, flexible control corresponding to the number of beams can be performed.

[0416] In this variation 1, a limited number of multiplexing can be prioritized over an unlimited number of multiplexing. For example, when the base station has both UAV-UEs and regular UEs among its connected UEs, a limited number of multiplexing can be used. Thus, even when UAV-UEs and regular UEs are mixed, the interference power of the base station can be suppressed.

[0417] As another example, an unlimited number of multiplexing operations can be prioritized over a limited number of multiplexing operations. For instance, when a base station has a mix of UAV-UEs and regular UEs among its connected UEs, it can use an unlimited number of multiplexing operations. This allows the base station to accommodate a large number of UEs.

[0418] According to this variation 1, the number of UEs multiplexed by each RB of the PUCCH can be reduced, thus mitigating uplink interference.

[0419] Implementation Method 4

[0420] UAV-UE uses RSRP (Real Segment Retention Rate) for serving cell selection. For example, during cell selection and / or cell reselection, the UAV-UE selects the cell with the highest RSRP. Alternatively, the UAV-UE reports the RSRP measurement result to the serving cell. The serving cell uses this measurement result to determine the handover target.

[0421] Using the above method will lead to the following problem: Since the RS transmission power of each cell is different, the uplink transmission power of the serving cell may not necessarily be reduced when the serving cell is determined based on the downlink RSRP measurement results.

[0422] The following methods are disclosed to solve the above problems. Path loss is used to select the serving cell. The UAV-UE measures the path loss of the cell.

[0423] Path loss can be used for cell selection and / or cell reselection. For example, path loss can be used as a threshold for cell selection and / or cell reselection.

[0424] The UAV-UE can switch between path loss conditions and RSRP conditions. For example, when the UAV-UE uses a different transmit power control than the ground control described in Embodiment 3, it can utilize the path loss conditions. Conversely, when using the same transmit power as the ground control, the UE can utilize the RSRP conditions. This avoids complicating the design of the UAV-UE.

[0425] This threshold can be determined in advance according to a standard, or it can be broadcast to the UE by the base station.

[0426] As another example, this threshold can be individually notified to the UE by the base station. This individual notification from the base station to the UE can occur when the UE is in the RRC_CONNECTED state. The UE can also use the threshold included in this notification when transitioning from the RRC_CONNECTED state to the RRC_IDLE or RRC_INACTIVE state. This allows each UE flexible cell reselection control.

[0427] During cell selection and / or cell reselection, path loss and RSRP can be combined. For example, the threshold used for cell selection and / or cell reselection can utilize path loss conditions, RSRP conditions, or a combination of both. As another example, a path loss threshold and an RSRP threshold can be used. For instance, the RSRP threshold can be used as the minimum requested RSRP value. This RSRP threshold can be applied to the UAV-UE. Thus, for example, the received power of the UAV-UE can be kept to a minimum while reducing uplink interference.

[0428] As a method for determining cell selection and / or reselection targets for the UAV-UE, the UAV-UE can select a cell with lower path loss. This cell can be the one with the lowest path loss. Thus, for example, by reducing the transmission power from the UAV-UE, interference from the cell can be mitigated.

[0429] As another example of the judgment method, a threshold can be set for path loss. The UAV-UE can select cells with path loss less than this threshold. This cell could be, for example, the first detected cell among cells with path loss less than this threshold. Thus, for example, it is possible to quickly select cells that can suppress the UAV-UE's transmission power below a certain value.

[0430] As another example of a judgment method, path loss and RSRP can also be used. For example, an RSRP threshold can be used. The UAV-UE can select, for example, a cell with lower path loss among cells above the RSRP threshold. This cell could be, for example, the cell with the lowest path loss. Thus, for example, it can ensure that the downlink received power of the UAV-UE is above a certain value, and by reducing the transmitted power from the UAV-UE, cell interference can be mitigated.

[0431] As another example of using both path loss and RSRP as a judgment method, a path loss threshold can be used. The UAV-UE can select, for example, a cell with a higher RSRP among cells below the path loss threshold. This cell could be, for example, the cell with the highest RSRP. Thus, for example, cell interference can be reduced to a certain extent while ensuring the downlink received power of the UAV-UE.

[0432] As another approach to solving the above problems, path loss can be used for switching.

[0433] UAV-UE can measure path loss. The UAV-UE can include the measured path loss information in the signaling sent to the base station as a Measurement Report. Alternatively, a new Measurement Report can be created to notify the path loss measurement results.

[0434] This measurement report can be used to add event triggers for path loss. Therefore, the UAV-UE can quickly notify the serving cell of the measurement results for cells that meet certain conditions related to path loss.

[0435] Alternatively, new parameters can be set for the aforementioned event triggers. These parameters could be, for example, a path loss threshold or the difference in path loss between the serving cell and neighboring cells. This parameter can be broadcast to the UE by the base station, or it can be notified individually to each UE. Alternatively, it can be notified individually to the UAV-UE.

[0436] The aforementioned event triggers can include path loss conditions. For example, path loss conditions can be added to existing event triggers. For instance, event triggers using RSRP, RSRQ, and path loss can be configured. This not only reduces interference to the cell but also ensures the UAV-UE's received power, thereby guaranteeing reception quality.

[0437] The UAV-UE can switch between and utilize event triggers that include path loss conditions and existing event triggers that include RSRP conditions. For example, when the UAV-UE uses a different transmission power control than the ground control described in Embodiment 3, it can utilize an event trigger that includes path loss conditions. Conversely, when using the same transmission power as the ground control, the UAV-UE can utilize an event trigger that includes RSRP conditions. This avoids complicating the design of the UAV-UE.

[0438] For handovers using path loss, the cell can derive the path loss. The UAV-UE can notify the serving cell of the RSRP from the serving cell and / or neighboring cells. The serving cell and neighboring cells can notify each other of their RS receive power between cells. The serving cell can use the RSRP notified by the UE and the RS transmit power notified between cells to derive the path loss. This reduces the processing load in the UE.

[0439] The serving cell can use path loss to determine the handover target for the UAV-UE. As a decision-making method, the serving cell can, for example, choose a cell with lower path loss. This can mitigate uplink interference from the UAV-UE.

[0440] The serving cell can switch the handover target determination method for the UAV-UE. For example, when the UAV-UE uses a different transmit power control than that described in Embodiment 3, the serving cell can use path loss to determine the handover target of the UAV-UE. Alternatively, when the UAV-UE uses the same transmit power as that of the ground, the serving cell can use RSRP to determine the handover target of the UAV-UE. Thus, for example, it is possible to avoid complicating the design of the communication system.

[0441] As another example, cells with path loss below a certain threshold can be identified. This cell could be, for example, the first cell detected by the serving cell among cells below that threshold. Cells that significantly reduce uplink interference from the UAV-UE can be quickly detected.

[0442] As another example, cells with lower path loss among those with RSRP above a certain threshold can be selected. This ensures that the UAV-UE has sufficient receive power while mitigating uplink interference from the UAV-UE.

[0443] As another example, a cell with a higher RSRP among cells with a certain path loss can be selected. This can reduce uplink interference from the UAV-UE to a certain extent while ensuring the UAV-UE's received power.

[0444] In this embodiment 4, a UAV-UE is shown, but it can also be applied to a regular UE. For example, the method shown in this embodiment 4 can also be applied to a regular UE using information indicating that the UE is at a higher altitude. Thus, for example, even when a regular UE is carried on a UAV during flight, interference power can be reduced and reception quality can be ensured in the same way as with a UAV-UE.

[0445] In this embodiment 4, the use of path loss is shown, but cell transmit power can also be used. For example, cells with transmit power below a certain threshold can be used as cell selection and / or reselection targets and / or handover targets. This, for example, can reduce the downlink interference power of the cell to other UEs.

[0446] According to implementation method 4, cells that can transmit with lower uplink transmission power can be detected. Cell selection and / or cell reselection utilize path loss, thereby enabling the selection of cells that can transmit from the UAV_UE at lower transmission power. Furthermore, by using path loss during handover, the serving cell can be switched to a cell where the UAV-UE can transmit at lower transmission power. As a result, the uplink interference power of the UAV-UE can be reduced.

[0447] According to embodiment 4, for example, the following structure is provided.

[0448] A communication system is provided, comprising a communication terminal device and a plurality of base station devices configured to communicate wirelessly with the communication terminal device. More specifically, when the height difference between the location of the communication terminal device and the location of the base station devices is greater than or equal to a threshold, at least one of cell selection, cell reselection, and handover target cell determination is performed using path loss information.

[0449] The above structure can be modified in various ways based on the disclosure and inspiration of this specification, including Embodiment 4. According to the above structure and its modifications, the above-mentioned technical problems can be solved and the above-mentioned technical effects can be obtained.

[0450] Variation 1 of Implementation Method 4

[0451] In the above-described implementation 4, for example, when switching to a cell with lower path loss, the following problem arises: the UAV-UE repeatedly performs handovers, increasing the likelihood of handover failure. Handover failures can render the UAV-UE uncontrollable, for example, causing the UAV-UE to fall while in flight.

[0452] The method for solving the above problem is disclosed in this variation 1.

[0453] As a method for determining the cell selection / cell reselection target in Implementation Method 4, for example, the UAV-UE can select a cell with a large path loss. This cell can be the cell with the highest path loss. Thus, for example, the UAV-UE can select a large range of cells.

[0454] As another example of the judgment method, a threshold can be set for path loss. The UAV-UE can select cells whose path loss is greater than this threshold. This cell could be, for example, the first detected cell among cells whose path loss is greater than this threshold. Thus, the UAV-UE can quickly select cells within a certain range.

[0455] As another example of the judgment method, path loss and RSRP can also be used. For example, an RSRP threshold can be used. The UAV-UE can select, for example, a cell with a larger path loss among cells above the RSRP threshold. This cell could be, for example, the cell with the largest path loss. Thus, for example, a larger range of cells can be selected that can ensure the UAV-UE's downlink received power is above a certain value.

[0456] As another example of using both path loss and RSRP as a determining factor, a path loss threshold can be used. The UAV-UE can select, for example, a cell with a higher RSRP among cells above the path loss threshold. This cell could be, for example, the cell with the highest RSRP. Thus, for example, it is possible to select cells within a certain range while ensuring the downlink received power of the UAV-UE.

[0457] Other solutions are disclosed. As a handover target selection method in Implementation Method 4, for example, the serving cell can determine the cell with the largest path loss. It is also capable of detecting cells with a large cell range.

[0458] As another example, cells with path loss exceeding a certain threshold can be identified. This cell could be, for example, the first cell detected by the serving cell among those exceeding the aforementioned threshold. This allows for the rapid detection of cells within a certain range.

[0459] As another example, cells with high path loss among those with RSRP above a certain threshold can be selected. This ensures that the UAV-UE has sufficient received power while also detecting cells with a large detection range.

[0460] As another example, cells with higher RSRP among those with a certain path loss can be selected. This allows for the detection of cells within a certain range while ensuring the received power of the UAV-UE.

[0461] Other solutions are disclosed. The cell that the UAV-UE needs to access can be different on the C-Plane and U-Plane. A DC structure can be adopted. This can improve the reliability of communication.

[0462] The selection methods for C-Plane and U-Plane cells described above can be modified. For example, the selection of C-Plane cells can use the method disclosed in Modification 1. The selection of U-Plane cells can use the method disclosed in Implementation 4. This ensures robust communication between the UAV-UE and the base station while reducing uplink interference power at the base station.

[0463] In this variation 1, a UAV-UE is shown, but it can also be applied to a regular UE. For example, the method shown in this variation 1 can also be applied to a regular UE using information indicating that the UE is at a higher altitude. Thus, for example, even when a regular UE is carried on a UAV during flight, it is possible to select a larger range of cells in the same way as with a UAV-UE.

[0464] In this variation 1, the cell's transmission power can be used in the same way as in embodiment 4. For example, cells with transmission power above a certain threshold can be used as cell selection and / or reselection targets and / or handover targets. Thus, for example, cells with a larger cell range can be selected, reducing the number of handovers. As a result, the possibility of handover failure can be reduced.

[0465] According to the method shown in this variation 1, the UAV-UE uses cells with higher path loss, thereby enabling the use of cells with larger cell ranges. By using cells with larger cell ranges, the number of handovers can be reduced, resulting in a lower probability of handover failures. Furthermore, by applying this variation 1 to cell selection / cell reselection, the situation where the UAV-VE extends beyond the cell radius can be mitigated.

[0466] Implementation Method 5

[0467] The communication between the UAV-UE and the base station will cause the following problems. That is, since the radio wave transmission environment changes with the altitude at which the UAV-UE communicates with the base station, the uplink interference to the base station changes with the altitude, and the methods described in Embodiment 3, Embodiment 3 Modification 1, Embodiment 4, and Embodiment 4 Modification 1 may be ineffective.

[0468] This embodiment 5 proposes a method to solve the above-mentioned problems.

[0469] A new communication mode is established in the UAV-UE. This communication mode can be, for example, the communication mode used by the UAV-UE in flight (hereinafter sometimes referred to as flight mode). In flight mode, the UAV-UE can communicate using parameter settings different from those of the previous communication mode, such as normal mode. The parameters in flight mode can be, for example, the parameters shown in Embodiment 3, Embodiment 3 Modification 1, Embodiment 4, and Embodiment 4 Modification 1. The base station can broadcast the parameters in flight mode to the UAV-UE. Parameters from normal mode can also be included. As an example of this broadcast, system information can be used.

[0470] Alternatively, the base station can notify the UAV-UE of parameters in flight mode. Parameters in normal mode can also be included. The base station can provide this notification to the UAV-UE in advance. This notification can utilize, for example, dedicated RRC signaling. This, for example, can reduce the amount of signaling from the base station to the UE.

[0471] The base station can send this notification to the UAV-UE multiple times. For example, each time a communication mode is switched, the base station can send the parameter for the new communication mode to the UAV-UE. This notification can be sent using, for example, dedicated RRC signaling. Within the same mode, the set parameter can be variable. Therefore, even within the same flight mode, operational flexibility can be improved based on the base station's radio wave environment at the time of mode switching.

[0472] As another example, if the UAV-UE is communicating in flight mode and the parameters in flight mode change, the base station can notify the UAV-UE of the changed flight mode parameters. The same applies in normal mode. Thus, the base station can flexibly change parameters, thereby improving the flexibility of the communication system.

[0473] UAV-UE can switch between normal mode and flight mode for communication. This allows for appropriate transmission power control during takeoff and landing, and during flight, for example.

[0474] The handover can be determined by the UAV-UE. The UAV-UE determines the handover and applies it within its own system. The UAV-UE can then notify the base station of the handover. This can, for example, reduce the processing load on the base station.

[0475] RRC signaling can be used in this notification. Because a large amount of data can be sent, it is possible to include information about the measurement results used in the handover. This, for example, makes proper control of the UAV-UE at the base station easier.

[0476] As another example of this notification, MAC signaling can be used. HARQ retransmission not only ensures high reliability but also enables rapid notification.

[0477] As another example of this notification, L1 / L2 signaling can be used, enabling even faster notification.

[0478] UAV-UEs can use RSRP (Responsive RSRP) to determine handover, or they can use path loss to determine handover, or they can combine the two. Each time this determination is made, thresholds for RSRP and / or path loss can be set. For example, a UAV-UE can determine a transition from normal mode to flight mode based on the detection that a specified number of cells meet the conditions for using the RSRP and path loss thresholds. Thus, for example, the UAV-UE can handover between normal mode and flight mode without using location information, thereby avoiding complicating the UAV-UE design.

[0479] The thresholds for RSRP and / or path loss in this judgment can be determined in advance according to standards, or they can be broadcast by the base station to the UAV-UE, or the base station can notify the UAV-UE individually. The number of the above-mentioned provisions can also be the same.

[0480] Figure 27 This is a flowchart illustrating the actions of the UAV-UE in determining the communication mode. Figure 27 This illustrates an example of a base station pre-notifying the UAV-UE of parameters in normal and flight modes. Figure 27 The example shows a UAV-UE switching from normal mode to flight mode and then back to normal mode. Additionally, Figure 27 In the example, the UAV-UE uses L1 / L2 signaling to notify the base station of the communication mode switch.

[0481] Figure 27 In step ST1901 shown, the base station notifies the UAV-UE of the RRC parameters. These RRC parameters include parameters for normal mode and flight mode.

[0482] Figure 27In step ST1902 shown, the UAV-UE performs downlink signal measurement. The measurement object can be RSRP, path loss, or a combination of both.

[0483] Figure 27 In step ST1903, the UAV-UE uses the result of step ST1902 to determine that the flight mode switching conditions are met. The UAV-UE switches to flight mode. The UAV-UE uses the flight mode parameters obtained in step ST1901 to perform uplink transmission. In step ST1904, the UAV-UE uses L1 / L2 signaling to notify the base station that it has switched to flight mode.

[0484] Figure 27 In step ST1905, the UAV-UE performs downlink signal measurement. The object being measured can be the same as in step ST1902.

[0485] Figure 27 In step ST1906, the UAV-UE uses the measurement results from step ST1905 to determine that the normal mode switching conditions are met. The UAV-UE switches to normal mode. The UAV-UE uses the normal mode parameters obtained in step ST1901 to perform uplink transmission. In step ST1907, the UAV-UE uses L1 / L2 signaling to notify the base station that it has switched to normal mode.

[0486] Figure 27 The diagram illustrates an example where parameters in normal mode and flight mode are notified to the UAV-UE in advance by the base station. However, the base station can also notify the UAV-UE of these parameters multiple times. For example, in step ST1901, the parameters notified to the UAV-UE by the base station could be parameters for normal mode. Alternatively, the base station can notify the UAV-UE of flight mode parameters after step ST1904. Similarly, the base station can notify the UAV-UE of normal mode parameters after step ST1907. Thus, for example, in UAV-UEs that switch between normal mode and flight mode less frequently, the signaling volume with the base station can be reduced. As another example, if the parameters in flight mode change during communication by the UAV-UE in the flight mode shown in step ST1903, the base station can notify the UAV-UE of the changed flight mode parameters. The same applies to the normal mode shown in step ST1906. Thus, for example, the base station can flexibly change the parameters, thereby improving the flexibility of the communication system.

[0487] As another example of this handover, it can be determined by the base station. The base station can indicate the handover to the UAV-UE. This, for example, simplifies the control of the UAV-UE by the base station.

[0488] This instruction can use RRC signaling. For example, this instruction can be included in other RRC signaling. It can reduce signaling volume.

[0489] As another example of this instruction, MAC signaling can be used. HARQ retransmission not only ensures high reliability but also provides rapid notification.

[0490] As another example of this instruction, L1 / L2 signaling can be used, enabling further rapid notification.

[0491] The base station can determine the handover using RSRP, path loss, or a combination of both. This determination by the base station can be the same as the determination in the UAV-UE described above.

[0492] The base station can determine the handover using the cell, the beam, or a combination of both. The cell and / or beam, for example, is one where interference needs to be mitigated when using flight mode. The base station can notify the UAV-UE of this cell and / or beam information. This information can be the identifier of the cell and / or beam. The UAV-UE can then use this cell and / or beam information to perform the handover. For example, if the UAV-UE is communicating with the base station using this cell and / or beam, it can switch from normal mode to flight mode. Thus, interference can be mitigated for cells and / or beams where it needs to be mitigated, while ensuring transmission and reception quality for other cells and / or beams, enabling such efficient use of the communication system.

[0493] The communication mode and communication mode switching disclosed in Embodiment 5 can also be applied to ordinary UEs. For example, the communication mode and this switching can also be applied to ordinary UEs located at high altitudes. The conditions for this switching applied to ordinary UEs can be the same as or different from those applied to UAV-UEs. Thus, for example, it is possible to control the interference of uplink transmission power emitted from ordinary UEs located at high altitudes such as building rooftops on the base station.

[0494] This embodiment 5 can also be applied to embodiment 3, embodiment 1 of embodiment 3, embodiment 4, and variation 1 of embodiment 4. That is, the UAV-UE in embodiment 3, variation 1 of embodiment 3, embodiment 4, and variation 1 of embodiment 4 can be a flight mode UE. This flight mode UE can be a UAV-UE or a normal UE. Thus, for example, for a UAV-UE in flight and / or a UE located at a high altitude, appropriate transmission power control can be performed.

[0495] According to this embodiment 5, appropriate power control can be performed based on the flight altitude of the UE.

[0496] According to embodiment 5, for example, the following structure is provided.

[0497] A communication system is provided, comprising a communication terminal device and multiple base station devices configured to communicate wirelessly with the communication terminal device. More specifically, the communication terminal device and the base station devices communicate by switching between multiple communication modes based on the height difference between the positions of the communication terminal device and the base station devices.

[0498] The above structure can be modified in various ways based on the disclosure and inspiration of this specification, including embodiment 5. According to the above structure and its modifications, the above-mentioned technical problems can be solved and the above-mentioned technical effects can be obtained.

[0499] The above-described embodiments and their modifications are merely examples of the present invention. Within the scope of the present invention, the embodiments and their modifications can be freely combined. Any constituent elements of the embodiments and their modifications can be appropriately changed or omitted.

[0500] For example, in the above embodiments and their variations, a subframe is an example of a communication time unit in a fifth-generation base station communication system. It can also be a scheduling unit. In the above embodiments and their variations, it can also be recorded as a TTI unit, a time slot unit, a sub-time slot unit, or a mini-time slot unit as a subframe unit.

[0501] The present invention has been described in detail, but the above description is merely illustrative of all aspects, and the invention is not limited thereto. Numerous variations not illustrated are to be understood as conceivable without departing from the scope of the invention.

[0502] Label Explanation

[0503] 200 Communication system; 202 Communication terminal device; 203, 800 Base station device.

Claims

1. A communication system comprising a terminal device and a plurality of base stations wirelessly communicating with the terminal device, wherein the plurality of base stations include a primary base station and a secondary base station forming a dual connection with the terminal device, characterized in that, The terminal device performs small data transmission to the secondary base station in the RRC_INACTIVE state.

2. The communication system as described in claim 1, characterized in that, Packet replication is applied in the small data transmission using the terminal device.

3. A terminal device, which is the terminal device in a communication system, the communication system comprising the terminal device and a plurality of base stations that wirelessly communicate with the terminal device, wherein the plurality of base stations in the communication system include a primary base station and a secondary base station that form a dual connection with the terminal device, the terminal device being characterized in that... The terminal device performs small data transmission to the secondary base station in the RRC_INACTIVE state.

4. A secondary base station, which is the secondary base station in a communication system, the communication system comprising a terminal device and a plurality of base stations respectively communicating wirelessly with the terminal device, wherein the plurality of base stations in the communication system include a primary base station and the secondary base station constituting dual connections with the terminal device, the secondary base station being characterized in that... The secondary base station receives small data sent from the terminal device in the RRC_INACTIVE state.

Images