Terminal device and base station device

Abstract

In a non-terrestrial network, the efficiency of movement control in wireless communication between a terminal device and a base station device is improved. The terminal device supports conditional switching and is provided with a receiving unit and a processing unit. The reception unit receives, from a base station device, a plurality of candidate cell settings corresponding to each of a plurality of candidate cells as handover destinations, first information indicating the type of event conditions for performing conditional handover, and second information indicating the order of the plurality of candidate cells. When switching from the first cell to the second cell is performed, the processing unit determines whether or not an event condition of the type indicated by the first information is satisfied and whether or not the second cell is a candidate cell corresponding to the order indicated by the second information. It is determined whether some of the plurality of candidate cell settings are deleted or all of the plurality of candidate cell settings are deleted.

Description

Technical Field

[0001] The present invention relates to a terminal device, a base station device, and a handover control method. Background Art

[0002] In the 3GPP (3rd Generation Partnership project), which is a standardization project, NR (New Radio (also known as "5G"), which is the fifth generation of mobile communications, is studying the technical specifications of the communication standard that meets the requirements of eMBB (Enhanced Mobile Broadband), Massive MTC (Machine Type Communications) and URLLC (Ultra-Reliable and Low Latency Communication).

[0003] 3GPP is studying technology that enables communications even in mountainous areas or offshore areas by applying NR to non-terrestrial networks (NTN) (for example, Non-Patent Document 1).

[0004] On the other hand, a handover procedure called conditional handover (condition-preset handover) has been proposed (for example, Non-Patent Documents 2 to 4).

[0005] In conditional handover (CHO: Conditional Handover), the base station device notifies the terminal device in advance of the cell setting information of the candidate cell that specifies the handover destination and the trigger condition of the handover (measurement event category (measurement event, measurement report event)). The trigger condition is also called an event condition. At this time, the base station device can set up to 8 candidate cells for the terminal device (that is, up to 8 conditional handover settings). The terminal device measures the serving cell and the surrounding cells. In addition, the terminal device evaluates the measurement event based on the trigger condition notified from the base station device. Then, when the notified trigger condition is met for the notified candidate cell, the terminal device applies the pre-notified cell setting as the cell setting of the handover destination and implements the handover. In this way, handover between cells can be implemented at a high speed.

[0006] In conditional handover, as described above, multiple cell settings are notified from the base station to the terminal device. Furthermore, after a successful conditional handover, the terminal device uses the cell settings corresponding to the destination cell. In other words, after a successful conditional handover, the cell settings corresponding to other cells are no longer necessary. Therefore, a terminal device that successfully completes a conditional handover autonomously deletes the cell settings corresponding to cells other than the destination cell.

[0007] Prior art literature

[0008] Non-patent literature

[0009] Non-Patent Document 1: 3GPP TR 38.821 V16.1.0 (2021-05)

[0010] Non-Patent Document 2: 3GPP TS 38.300 V17.2.0 (2022-09)

[0011] Non-Patent Document 3: 3GPP TS 38.331 V17.2.0 (2022-09)

[0012] Non-Patent Document 4: R2-2212449 Summary of the Invention

[0013] Problems to be solved by the invention

[0014] The application of conditional handover in non-terrestrial networks (NTNs) is under investigation. However, in NTNs (particularly those using artificial satellites), since the satellite orbits observed from Earth are approximately constant, multiple target cells (NTN cells) for a terminal device to move to can be easily estimated based on the terminal device's location information. Therefore, in NTNs, if the cell configuration information of unselected candidate cells is deleted after a successful conditional handover, the handover process efficiency will deteriorate.

[0015] An object of one aspect of the present invention is to improve the efficiency of mobility control in wireless communications between a terminal device and a base station device in a non-terrestrial network.

[0016] Means for solving problems

[0017] A terminal device according to one aspect of the present invention supports conditional handover. The terminal device includes: a receiving unit that receives, from a base station device, a plurality of candidate cell settings corresponding to a plurality of candidate cells of a handover destination, first information indicating a category of an event condition for executing the conditional handover, and second information indicating an order of the plurality of candidate cells; and a processing unit that, when performing handover from a first cell to a second cell, determines whether to delete a portion of the plurality of candidate cell settings or delete all of the plurality of candidate cell settings based on whether an event condition of the category indicated by the first information is satisfied and whether the second cell is a candidate cell corresponding to the order indicated by the second information.

[0018] A base station device according to one aspect of the present invention communicates with a terminal device that supports conditional switching. The base station device includes: a processing unit that generates a plurality of candidate cell settings corresponding to a plurality of candidate cells of the switching destination of the terminal device, first information indicating the category of an event condition for executing the conditional switching in the terminal device, and second information indicating the order of the plurality of candidate cells; and a sending unit that sends the plurality of candidate cell settings, the first information, and the second information to the terminal device so that when the terminal device switches from the first cell to the second cell, the terminal device determines whether to delete a part of the plurality of candidate cell settings or delete all of the plurality of candidate cell settings based on whether the event condition of the category indicated by the first information is satisfied and whether the second cell is a candidate cell corresponding to the order indicated by the second information.

[0019] Effects of the Invention

[0020] According to the above-described aspect, in a non-terrestrial network, the efficiency of mobility control in wireless communications between a terminal device and a base station device is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a diagram showing a configuration example of a wireless communication system according to an embodiment.

[0022] Figure 2 This is a diagram showing an example of the functional configuration of a terminal device according to an embodiment.

[0023] Figure 3 This is a diagram showing an example of the functional configuration of a base station apparatus according to an embodiment.

[0024] Figure 4 This is a diagram showing an example of a communication area of ​​a flying object in a non-ground network.

[0025] Figure 5An example of a conditional handover event in a non-terrestrial network is shown.

[0026] Figure 6 is a diagram illustrating another example of a conditional handover event in a non-terrestrial network.

[0027] Figure 7 This is a diagram showing an example of link information (CHO order) indicating the order in which multiple candidate cell configurations are applied.

[0028] Figure 8 This is a flowchart showing an example of processing of the terminal device.

[0029] Figure 9 This is a diagram showing an example of a switching sequence according to the first embodiment.

[0030] Figure 10 This is a diagram showing an example of a case where conditional switching is predicted to be successful.

[0031] Figure 11 This is a diagram showing an example of a case where an unpredicted handover is performed.

[0032] Figure 12 This is a diagram showing another example of link information.

[0033] Figure 13 This is a diagram showing another example of link information.

[0034] Figure 14 This is a flowchart showing an example of processing of the terminal device according to the second embodiment. DETAILED DESCRIPTION

[0035] The following describes embodiments of the present invention in detail with reference to the accompanying drawings. The topics and embodiments described in this specification are examples and do not limit the scope of the present invention. In particular, even if the descriptions are different, as long as they are technically equivalent, the technology of the present invention can be applied, and the scope of the present invention is not limited. Furthermore, the various embodiments can be appropriately combined within the scope of the processing content without contradiction.

[0036] In the wireless communication system of the embodiment of the present invention, well-known technologies may also be appropriately used. Applicable well-known technologies may be, for example, 5G (NR), Beyond 5G or other wireless communication methods. The wireless communication system of the embodiment of the present invention is based on NR, but is not limited to this. For example, the embodiment of the present invention can also be applied to LTE and LTE-Advanced. In addition, it can also be applied to a wireless communication system that uses NR as part of the wireless communication system. Moreover, the embodiment of the present invention can be applied to any wireless communication system that has at least a terminal device and a base station device, and can also be applied to future wireless communication systems. In the following description, LTE and LTE-Advanced are also referred to as E-UTRA (Evolved Universal Terrestrial Radio Access), but their meanings are the same.

[0037] Hereinafter, embodiments of the base station apparatus, gateway, terminal apparatus, and wireless communication system disclosed in this application will be described with reference to the accompanying drawings. Note that the following embodiments do not limit the disclosed technology.

[0038] <Wireless Communication System>

[0039] Figure 1 A configuration example of a wireless communication system according to an embodiment of the present invention is shown. The wireless communication system according to the embodiment is composed of, for example, one or more terminal devices 10 , a base station device 20 , and a core network 30 .

[0040] The terminal device 10 may be, for example, a mobile phone, smartphone, PDA (Personal Digital Assistant), tablet computer, wearable terminal, personal computer (PC), vehicle, or any other device or equipment (e.g., sensor device) with wireless communication capabilities. The terminal device 10 may also be referred to as a wireless communication device, communication device, receiving device, mobile station, UE (User Equipment), or user device.

[0041] Wireless communication services are provided to terminal devices 10 by base stations 20 and a core network 30 in the wireless communication system. The core network 30 has functions such as managing service subscriber information, managing sessions such as voice calls, and managing the location registration of terminal devices 10. Furthermore, the core network 30 transmits control data and / or user data to the terminal devices 10 via the base stations 20.

[0042] The core network 30 can be the 5G Core (5G Core) in 5G (NR) or the Evolved Packet Core (EPC) in 4G (E-UTRA). Furthermore, the connection method between the core network 30 and the base station apparatus 20 can be either the NSA (Non-Stand Alone) method or the SA (Stand Alone) method.

[0043] The 5G base station device 20 connected to the 5GC is a gNB, and the 4G base station device 20 connected to the EPC is an eNB. Furthermore, 5G base station devices are connected via an Xn interface, and 4G base station devices are connected via an X2 interface.

[0044] The area (coverage area) formed by the base station apparatus 20 is sometimes referred to as a "cell." E-UTRA and 5G are cellular communication systems constructed from multiple cells. The wireless communication system according to the embodiment of the present invention can employ either TDD (Time Division Duplex) or FDD (Frequency Division Duplex), and different methods can be employed for each cell.

[0045] Base station apparatus 20 in the NTN includes an existing base station apparatus (i.e., a base station apparatus in a terrestrial network) and a service link provisioning system 220. In the following description, the base station apparatus in the terrestrial system network may be referred to as a "ground station 210." In other words, base station apparatus 20 is essentially implemented as a base station system comprising multiple devices.

[0046] The service link providing system 220 includes a gateway device (GW) 230 and an NTN payload unit 240. The gateway device 230 can communicate with a flying object 250. The flying object 250 is, for example, an unmanned aerial vehicle such as a HAPS (High Altitude Platform Station) or a space device such as an artificial satellite, and has at least an NTN payload unit 240. The flying object 250 can act as a repeater (Repeater, relay station). That is, the flying object 250 forwards the signal received from the gateway device 230 to the terminal device 10, and forwards the signal received from the terminal device 10 to the gateway device 230. In addition, the NTN payload unit 240 can also have some of the functions of the ground station 210. In addition, in the following description, artificial satellites are sometimes referred to as "satellites", but unless otherwise noted, their meanings, functions and effects are the same.

[0047] The communication path between the gateway 230 and the NTN payload unit 240 is sometimes referred to as a "feeder link." The communication path between the NTN payload unit 240 and the terminal device 10 is sometimes referred to as a "service link." The communication method used for the feeder link is not limited to NR; any communication method can be used.

[0048] The base station apparatus 20 may also be divided into a CU (Centralized Unit) and a DU (Distributed Unit). The CU is connected to the core network, and the DU is connected to the terminal apparatus 10. In this case, the communication path between the CU and the DU is implemented, for example, via a fronthaul interface (F1 interface). Alternatively, multiple DUs may be connected to a single CU.

[0049] exist Figure 1 In the example shown, data (DL data, downlink data) transmitted from core network 30 to terminal device 10 is transmitted from core network 30 to ground station 210 of base station device 20. Ground station 210 transmits the received data from gateway device 230 to aerial object 250 using a feeder link. Aircraft 250 transmits (forwards) the wireless signal received from ground station 210 to terminal device 10 using a serving link. In other words, aerial object 250 operates as a repeater.

[0050] Data (UL data, uplink data) transmitted from terminal device 10 to core network 30 is transmitted from terminal device 10 to aerial object 250 of base station device 20 using a serving link. Aircraft 250 operates as a repeater, transmitting (forwarding) received wireless signals to gateway device 230 using a feeder link. Gateway device 230 transmits the received wireless signals to ground station 210. Ground station 210 then transmits the received data to core network 30.

[0051] The terminal device 10 and the base station device 20 transmit and receive RRC messages (also called RRC signaling) in the Radio Resource Control (RRC) layer. In addition, the terminal device 10 and the base station device 20 transmit and receive MAC control elements (MACCE: MAC Control Element) in the Medium Access Control (MAC) layer. The RRC message is sent as an RRC PDU (Protocol Data Unit) and uses a common control channel (CCCH: Common Control Channel), a dedicated control channel (DCCH: Dedicated Control Channel), a paging control channel (PCCH: Paging Control Channel), a broadcast control channel (BCCH: Broadcast Control Channel), or a multicast control channel (MCCH: Multicast Control Channel) as a mapped logical channel (LCH: Logical Channel). The MAC CE is sent as a MAC PDU (or MAC subPDU). A MAC subPDU is equal to a service data unit (SDU: Service Data Unit) of the MAC layer plus, for example, an 8-bit header, and a MAC PDU contains one or more MACsubPDUs.

[0052] <Terminal Device>

[0053] Figure 2 An example of the functional configuration of the terminal device 10 according to the embodiment is shown. Figure 2 As shown, the terminal device 10 illustratively includes a processing unit 11, a control unit 13, a receiving unit 15, a transmitting unit 17, and a transmitting and receiving antenna unit 19. The processing unit 11 is configured to include, for example, a radio resource processing unit 111 and an NTN control information processing unit 113. Figure 2 The functional configuration shown is merely an example, and the functional divisions and names of the functional blocks may be different as long as the operations of the embodiment can be executed.

[0054] The processing unit 11 generates control information for controlling the receiving unit 15 and the transmitting unit 17, and outputs the control information to the control unit 13. The processing unit 11 performs processing related to the radio resource control layer, the packet data convergence protocol layer, the radio link control layer, and the media access control layer.

[0055] The radio resource processing unit 111 manages various configuration information (RRC parameters, information elements (IE)) of the terminal device 10. For example, the radio resource processing unit 111 generates information on each channel allocated in the physical uplink and outputs the information to the transmission unit 17.

[0056] The NTN control information processing unit 113 performs a series of control processes related to the NTN. For example, based on instructions from the radio resource processing unit 111 or instructions from the base station apparatus 20, the NTN control information processing unit 113 performs measurements of the serving cell and neighboring cells, starts and stops transmission and reception processing, starts the UL synchronization process, re-acquires system information, evaluates events related to handover, and performs a series of processes related to handover.

[0057] The control unit 13 performs various controls in the terminal device 10. For example, the control unit 13 generates control signals for controlling the receiving unit 15 and the transmitting unit 17 based on the control information from the processing unit 11. In addition, the control unit 13 controls wireless communication with the base station device 20 based on information on the control of the feeder link and the serving link.

[0058] The receiving unit 15 separates, demodulates, and decodes various signals received from the base station apparatus 20 via the transmitting and receiving antenna unit 19 based on a control signal supplied from the control unit 13. The receiving unit 15 passes the decoded information to the processing unit 11.

[0059] Based on the control signal provided by the control unit 13, the transmission unit 17 generates, for example, a physical uplink signal and encodes and modulates the physical uplink signal or physical uplink channel provided by the processing unit 11. The transmission unit 17 multiplexes the various signals and transmits them to the base station apparatus 20 via the transmitting and receiving antenna unit 19.

[0060] The processing unit 11 and the control unit 13 are implemented, for example, by a processor system including a processor and memory. In this case, the processor executes a program describing the operation of the terminal device 10, described later, thereby providing the functions of the processing unit 11 and the control unit 13. Furthermore, the processing unit 11 and the control unit 13 may be implemented by a single processor system or by multiple processor systems. Alternatively, the processing unit 11 and the control unit 13 may be implemented by a DSP or hardware circuitry.

[0061] <Base Station Device>

[0062] Figure 3 An example of the functional configuration of the base station apparatus 20 according to the embodiment is shown. Figure 3As shown, the base station device 20 illustratively includes a processing unit 21, a control unit 23, a receiving unit 25, a transmitting unit 27, and a transmitting and receiving antenna unit 29. The processing unit 21 is configured to include, for example, a radio resource processing unit 211 and an NTN control information processing unit 213. Figure 1 As shown, the base station apparatus 20 includes a service link providing system 220 .

[0063] like Figure 1 As shown, the base station device 20 also includes a gateway device 230, but in Figure 3 Can also be omitted in Figure 3 The gateway device 230 is logically constituted in the network. In addition, the gateway device 230 can also be realized by a part of the control unit 23, the receiving unit 25 and the sending unit 27. In addition, Figure 3 The functional configuration shown is merely an example, and the functional divisions and names of the functional blocks may be different as long as the operations of the embodiment can be executed.

[0064] The processing unit 21 generates, for example, control information for controlling the receiving unit 25 and the transmitting unit 27, and outputs the information to the control unit 23. The processing unit 21 performs, for example, processing related to the radio resource control layer, the packet data convergence protocol (PDCP) layer, the radio link control (RLC) layer, and the media access control layer.

[0065] The radio resource processing unit 211 generates, for example, downlink data, RRC messages, and MAC control elements to be allocated to the physical downlink shared channel PDSCH, and outputs the generated data to the transmitting unit 27. The radio resource processing unit 211 also manages various configuration information of the terminal device 10.

[0066] The NTN control information processing unit 213 performs a series of control processes related to the NTN. For example, based on instructions from the wireless resource processing unit 211 or notifications of signals or RRC messages from the terminal device 10, the NTN control information processing unit 213 performs the start and stop of the transmission and reception process, the start of the UL synchronization process, the update of system information, the adjustment of the transmission angle of the beam, the switching of the feeder link, the switching of the gateway device 230, the pre-setting of parameters related to the cell setting and measurement event category (measurement event) related to the handover, and the arrival prediction of the cell. In addition, the following "measurement event" includes not only measurement events corresponding to the previous measurement event ID (for example, measurement event A1), but also conditional events related to conditional handover corresponding to the conditional event ID.

[0067] The control unit 23 performs various controls in the base station device 20. For example, the control unit 23 generates control signals for controlling the receiving unit 25 and the transmitting unit 27 based on control information from the processing unit 21. The control unit 23 performs various controls on the gateway device 230 and the service link providing system 220.

[0068] Based on the control signal provided by the control unit 23, the receiving unit 25 separates, demodulates, and decodes various signals received from the terminal device 10 or the core network 30 via the transceiver antenna unit 29. The receiving unit 25 outputs the decoded information to the processing unit 21.

[0069] Based on the control signal provided by the control unit 23, the transmitting unit 27 generates, for example, a downlink reference signal. The transmitting unit 27 transmits a signal to the terminal device 10 via the transceiver antenna unit 29 by encoding, modulating, and multiplexing various information provided by the processing unit 21.

[0070] In addition, the transmitting unit 27 transmits data to the terminal device 10 or the core network 30. The transmitting unit 27 transmits, for example, information on the flying object 250 and the control of the service link. The receiving unit 25 receives data from the terminal device 10 and the core network 30. The receiving unit 25 receives, for example, information on the flying object 250, the power feeding link, and the control of the service link.

[0071] In addition, the processing unit 21 and the control unit 23 are implemented, for example, by a processor system including a processor and a memory. In this case, the processor provides the functions of the processing unit 21 and the control unit 23 by executing a program describing the operations of the base station device 20 described later. In addition, the processing unit 21 and the control unit 23 may be implemented by one processor system or by multiple processor systems. Alternatively, the processing unit 21 and the control unit 23 may also be implemented by a DSP or a hardware circuit, etc.

[0072] <NTN cell>

[0073] Figure 4 An example of the communication area (cell) of a flying object in a non-terrestrial network (NTN) is shown. In Figure 4 , the flying object 250 (250A to 250C) relays the radio signal received from the ground station 210 and transmits it as a beam to the ground. The terminal device 10 regards the area where it can receive the signal (beam) transmitted from the flying object 250 as a "service cell". In Figure 4In the example shown, cell 300A is the serving cell for terminal device 10. Here, when flying object 250 is a so-called non-geostationary satellite (NGSO: Non-Geostationary Satellite Orbit (also called an orbiting satellite)), such as a low-Earth orbit satellite (LEO) or a medium-Earth orbit satellite (MEO: Middle Earth Orbit), flying object 250 moves at high speed in a substantially fixed direction relative to the Earth's surface.

[0074] That is, the cells 300A to 300C formed by the beams from the flying objects 250A to 250C move at high speed in a substantially fixed direction over time. Therefore, the serving cell of the terminal device 10 changes over time. For example, in Figure 4 At a certain moment in time, the serving cell of terminal device 10 is cell 300A. Thereafter, when flying objects 250A to 250C each move, cell 300B formed by the beam from flying object 250B becomes the serving cell of terminal device 10. When flying objects 250A to 250C each move further, cell 300C formed by the beam from flying object 250C becomes the serving cell of terminal device 10.

[0075] As described above, in satellite-based NTN systems (particularly NGSO), the communicating cell or serving cell is constantly moving. Therefore, even if the terminal device 10 is stationary, it may become unable to use the current cell over time. Therefore, the base station device 20 needs to notify the terminal device 10 in advance of the time when the flying object 250 will pass overhead (i.e., the time when the terminal device 10 can communicate with the base station device 20 via the flying object 250). Therefore, in the NTN system, the base station device 20 includes this time information in NTN system information and notifies the terminal device 10. The terminal device 10 manages the measurement timing of the serving cell and neighboring cells based on this time information and performs measurements at appropriate times. The base station device 20 transmits a series of information related to satellite communications to the terminal device 10 using, for example, System Information Block Type 19 (SIB19). Furthermore, the NTN system information (SIB19) can also notify the terminal device 10 of orbital information (ephemeris information) of non-geostationary satellites and uplink adjustment values ​​(Common Timing Advance (Common TA)).

[0076] <Conditional Switch>

[0077] Figure 5 An example of a conditional handover event in a non-terrestrial network (NTN) is shown. Figure 5The conditional switching event shown is a distance-based measurement event, also called a conditional event D1 (Cont Event D1). Figure 5 In the example, the terminal device 10 (10A, 10B) measures the distance from a predetermined reference point r0 to the station. The terminal device 10 then compares the measured distance with a set threshold value to evaluate the handover event. The terminal device 10 also has a positioning function such as GPS.

[0078] In a distance-based measurement event, a reference point r0 (reference point) serving as a reference for ranging is set within the cell. The reference point r0 is notified from the base station device 20 to the terminal device 10. In addition, the base station device 20 notifies the terminal device 10 of the hysteresis Hys and the thresholds (TH1, TH2) as information related to the conditional event D1. The terminal device 10, which has set the conditional event D1 as a valid measurement event, measures the distance d between the position of the reference point r0 and the position of the own station. Then, when the value d1 obtained by subtracting the hysteresis Hys from the distance d is greater than the threshold TH1, and the value d2 obtained by adding the hysteresis Hys to the distance d is less than the threshold TH2, the terminal device 10 determines that the event establishment condition is satisfied. Figure 5 In the example shown, the terminal device 10B is located between the distance d1 and the distance d2, and the conditional event D1 is satisfied. In this case, the terminal device 10B determines that a conditional handover to a preset candidate cell should be performed.

[0079] On the other hand, when the value obtained by adding the hysteresis Hys to the distance d is greater than the threshold TH1 and the value obtained by subtracting the hysteresis Hys from the distance d is less than the threshold TH2, the terminal device 10 determines that the event establishment condition is not satisfied. Figure 5 In the example shown, the conditional event D1 is not satisfied in the terminal device 10A.

[0080] Figure 6 Another example of a conditional handover event in a non-terrestrial network (NTN) is shown. Figure 6 The conditional handover event shown is a time-based measurement event, also known as conditional event T1 (Cont Event T1). The terminal device 10 measures the time from a reference time to the current time. The terminal device 10 then evaluates the handover event by comparing the measured time with a set threshold.

[0081] exist Figure 6In the example shown, the terminal device 10 is located in the cell 300A. Furthermore, the base station device 20 (not shown) notifies the terminal device 10 of the time information (threshold value TH_t) and the event establishment time interval information (duration) that have elapsed since January 1, 1980 in the Gregorian calendar as information related to the conditional event T1. The elapsed time information is notified in units of 10 milliseconds. The terminal device 10, for which the conditional event T1 is set as a valid measurement event, measures the current moment in milliseconds and starts comparison with the notified elapsed time information (threshold value TH_t). Furthermore, when the current moment exceeds the notified threshold value TH_t, the terminal device 10 determines that the event establishment condition is satisfied.

[0082] When the current time exceeds the value obtained by adding the event establishment time interval information (duration) to the threshold value TH_t, the terminal device 10 determines that the event establishment condition is not satisfied. Figure 6 In the example shown, at time T1, conditional event T1 is not satisfied in terminal device 10. Later, at time Δt after time T1 (i.e., time T1 + Δt), conditional event T1 is satisfied. At this point, terminal device 10 performs conditional handover to a pre-set candidate cell (e.g., cell 300B).

[0083] In consideration of the above matters, the embodiments of the present invention are described in detail below with reference to the accompanying drawings. In addition, in the description of the embodiments of the present invention, if it is determined that the specific description of the known functions and structures associated with the embodiments of the present invention does not make the gist of the embodiments of the present invention clear, the detailed description thereof will be omitted.

[0084] <First embodiment>

[0085] A terminal device according to a first embodiment of the present invention receives, from a base station device, a plurality of candidate cell settings corresponding to a plurality of candidate cells as a handover destination, first information indicating the type of event condition for performing conditional handover, and second information indicating the order of the plurality of candidate cells. Furthermore, when performing handover from the first cell to the second cell, the terminal device determines whether to delete a portion of the plurality of candidate cell settings or delete all of the plurality of candidate cell settings based on whether the event condition of the type indicated by the first information is satisfied and whether the second cell is a candidate cell corresponding to the order indicated by the second information.

[0086] The base station device in the first embodiment generates a plurality of candidate cell settings corresponding to a plurality of candidate cells of the handover destination of the terminal device, first information indicating the category of the event condition for performing conditional handover in the terminal device, and second information indicating the order of the plurality of candidate cells. The base station device then transmits the generated plurality of candidate cell settings, the first information, and the second information to the terminal device. Thus, when handing over from the first cell to the second cell, the terminal device can determine whether to delete a portion of the plurality of candidate cell settings or delete all of the plurality of candidate cell settings based on whether the event condition of the category indicated by the first information is satisfied and whether the second cell is a candidate cell corresponding to the order indicated by the second information.

[0087] The second information indicating the order of multiple candidate cells is implemented, for example, by information (link information) indicating the order of application of the candidate cell setting information. The link information can use, for example, an ID (CondReconfigId) that identifies the conditional switching setting, or a physical cell ID (PCI: PhysCellId) contained in the conditional switching setting. In addition, the link information can use a report setting ID (ReportConfigId) that identifies the report setting containing the measurement event, or a measurement ID (MeasId) that indicates the correspondence between the report setting and the measurement object. In addition, if the conditional switching setting to be applied can be uniquely specified, other identification information can also be used. For example, an ID (LinkId) for linking corresponding IDs to each other can be added, or other new IDs can be added to the RRC message. In the following example, CondReconfigId is used as the information for identifying the conditional switching setting, but the same effect is achieved even if CondReconfigId is replaced by another ID.

[0088] In addition, when the cell (serving cell) in communication of the terminal device 10 is changed according to switching, one or more of the flying object 250, the gateway device 230, the ground station 210, and the base station device 20 may be changed.

[0089] Figure 7 An example of link information (CHO order) indicating the order in which multiple candidate cell configurations are applied is shown. In this embodiment, the link information indicates that the candidate cell configuration identified by "CondReconfigId: 0" is applied first, the candidate cell configuration identified by "CondReconfigId: 1" is applied second, and the candidate cell configuration identified by "CondReconfigId: 2" is applied third. Furthermore, each candidate cell configuration includes information specifying or identifying the target cell for handover.

[0090] The base station apparatus 20 determines (predicts or assumes) which satellites will arrive above the terminal apparatus 10 and in what order based on the terminal apparatus 10's location information, information indicating the orbits of satellites covering the terminal apparatus 10's location, cycle information, information indicating overhead time, and the like. Specifically, the base station apparatus 20 determines (predicts or assumes) in what order the cells formed by the various satellites will cover the terminal apparatus 10. The base station apparatus 20 then generates conditional handover settings containing cell setting information corresponding to each of the multiple predicted cells. The base station apparatus 20 then notifies the terminal apparatus 10 of the multiple conditional handover settings and link information (CHO sequence).

[0091] Furthermore, the base station apparatus 20 transmits the link information to the terminal apparatus 10 using an RRC message (for example, an RRC Setup message, an RRC Reconfiguration message, etc.). The terminal apparatus 10 acquires the link information from the received RRC message.

[0092] Figure 8 This is a flowchart illustrating an example of processing by the terminal device 10. It is assumed here that the terminal device 10 receives conditional handover settings and link information from the base station device 20. The conditional handover settings, for example, include information indicating candidate cells for handover destinations. Furthermore, the conditional handover settings may include information regarding handover triggering conditions (measurement event types or conditional event IDs). Alternatively, the handover triggering conditions may be notified to the terminal device 10 independently of the conditional handover settings.

[0093] In S1, the terminal device 10 determines the target cell for conditional handover based on the conditional handover setting received from the base station device 20. Then, the terminal device 10 starts evaluating the measurement event for the serving cell and / or the determined target cell. The target cell is determined based on the CHO order. Here, after receiving the conditional handover setting, when conditional handover has not yet been performed in the terminal device 10, processing is performed based on "CHO ​​order: 1". Figure 7 In the illustrated embodiment, the cell specified by the conditional handover setting corresponding to "CondReconfigId: 0" is regarded as the target cell. Similarly, when a conditional handover is performed once in the terminal device 10 and the conditional handover is successful, processing is performed based on "CHO ​​Order: 1". Figure 7 In the illustrated embodiment, the cell specified by the conditional handover configuration corresponding to "CondReconfigId: 1" is regarded as the target cell.

[0094] In S2, the terminal device 10 determines whether the set measurement event establishment condition is satisfied. Figure 5When the condition event D1 is shown, the terminal device 10 determines whether the measurement event is established based on the distance from the reference point r0. Figure 6 At the conditional event T1 shown, the terminal device 10 determines whether a measurement event has been established based on the elapsed time from the reference time.

[0095] If the measurement event does not occur (S2: No), the terminal device 10 continues the associated measurement and repeats the measurement event evaluation. That is, the terminal device 10 repeats the measurement event evaluation without performing a handover. If the measurement event occurs, that is, if the triggering condition for the measurement event is met (S2: Yes), the terminal device 10 proceeds to S3.

[0096] In S3, the terminal device 10 determines whether the link information has been notified from the base station device 20 and whether the measurement event established in S2 is a specified measurement event. Specifically, the terminal device 10 determines whether the conditional handover setting includes valid link information and whether the established measurement event is a measurement event associated with the NTN (i.e., conditional event D1 or conditional event T1). In addition, the base station device 20 may also add additional information such as an identifier to the report setting to determine whether it is a specified measurement event. Alternatively, the base station device 20 may also specify the category of the measurement event associated with the NTN.

[0097] When valid link information is not received and / or when the established measurement event is not the specified measurement event (S3: No), the terminal device 10 implements the existing conditional handover process (or existing handover process) in S5. In this case, after the conditional handover (or handover) is successful, the terminal device 10 removes (deletes) all conditional handover settings related to candidate cells other than the object cell (i.e., the target cell). For example, when the received radio wave strength of the terminal device 10 is lower than the threshold level, the processing of S5 is sometimes performed.

[0098] When valid link information is received and the measurement event that is established is the specified measurement event (S3: Yes), the terminal device 10 determines in S4 whether the object cell when the measurement event is established meets the conditions represented by the link information. Specifically, the terminal device 10 determines whether the object cell when the measurement event is established is consistent with the cell determined based on the link information. Then, when these cells are inconsistent (S4: No), the terminal device 10 determines not to perform conditional switching to the desired cell. Then, in S5, the terminal device 10 executes the existing conditional switching process (or the existing switching process). In this case, the terminal device 10 deletes all conditional switching settings related to candidate cells other than the object cell (i.e., the target cell).

[0099] On the other hand, if the target cell at the time of the measurement event is consistent with the cell determined based on the link information (S4: Yes), the terminal device 10 implements the conditional handover process according to the embodiment of the present invention in S6. In this case, after the conditional handover is successful, the terminal device 10 deletes the conditional handover settings related to the target cell (target cell) and maintains the conditional handover settings related to the other candidate cells without deleting them.

[0100] Here, the terminal device 10 receives Figure 7 The link information shown. In addition, it is assumed that the terminal device 10 has not yet performed conditional handover after receiving the conditional handover setting. In this case, the processing is performed based on "CHO ​​order: 1". That is, the processing is performed based on the conditional handover setting identified by "CondReconfigId: 0" associated with "CHO ​​order: 1". Moreover, when the conditional handover to the object cell specified by the conditional handover setting is successful, the terminal device 10 deletes the conditional handover setting corresponding to "CondReconfigId: 0", but maintains the conditional handover setting corresponding to "CondReconfigId: 1" and the conditional handover setting corresponding to "CondReconfigId: 2".

[0101] Note that when deleting the conditional handover setting related to the target cell, the terminal device 10 may also delete the conditional handover setting that was planned to be applied before the conditional handover setting. Figure 7 In the operational state indicated by "CHO ​​Order: 1" in the link information shown, conditional handover succeeded to the target cell corresponding to "CondReconfigId: 1" rather than the target cell corresponding to "CondReconfigId: 0." In this case, not only the conditional handover setting identified by "CondReconfigId: 1" but also the conditional handover setting identified by "CondReconfigId: 0" is deleted. However, even in this case, it is preferable to maintain the conditional handover setting identified by "CondReconfigId: 2."

[0102] In this way, the terminal device 10 deletes part or all of the pre-set candidate cell setting information based on the measurement event type information of the successful conditional handover, the target cell information, and the link information indicating the conditional handover order. Figure 8 The steps of the flowchart shown can also be appropriately changed in order to obtain the same effect. For example, the processing of S3 and the processing of S4 can be executed simultaneously, or their order can be changed to execute.

[0103] Figure 9 An example of a switching sequence of the first embodiment is shown. Figure 9 In FIG, the cell 300A is the serving cell of the terminal device 10. The cell 300B is a neighboring cell of the terminal device 10 and is a candidate cell of the handover destination. Figure 4 In the example shown, cell 300A and cell 300B are formed by flying object 250A and flying object 250B, respectively.

[0104] In cell 300A, terminal device 10 is connected to base station device 20 (not shown), which is composed of an aircraft, a gateway device, a ground station, etc. Then, in S11, terminal device 10 receives an RRC message (RRCReconfiguration) transmitted from base station device 20. Alternatively, base station device 20 may transmit an RRC Setup message or an RRC Restabulishment message instead of an RRC Reconfiguration message.

[0105] The RRC message sent from the base station device 20 in S11 includes conditional handover configuration and link information. Figure 9 In the example shown, the conditional switching setting identified by id0 and the conditional switching setting identified by id1 are provided to the terminal device 10. The link information indicates the order in which the conditional switching settings are applied. In this embodiment, the link information indicates that id0 is applied first and id1 is applied second.

[0106] The base station apparatus 20 also transmits information indicating the handover triggering condition to the terminal apparatus 10. The triggering condition includes the measurement event type for the conditional handover and the conditional event ID. The triggering condition may also be determined for each cell. The triggering condition may be transmitted along with the conditional handover setting in step S11, or may be transmitted separately from the conditional handover setting.

[0107] The terminal device 10 identifies the order of conditional handover settings to be applied based on the RRC message received from the base station device 20. Here, each conditional handover setting includes information indicating the candidate cell of the handover destination of the terminal device 10. That is, the terminal device 10 is able to identify the order of candidate cells to be accessed. Afterwards, the terminal device 10 generates a response message (RRC Reconfigration Complete: RRC reconfiguration completed) for the received RRC message in S12 and sends it to the base station device 20. It should be noted that the terminal device 10 can send an RRC establishment completion message or an RRC reconstruction completion message to the base station device 20 based on the received RRC message.

[0108] In S13, the terminal device 10 determines the target cell based on the received conditional handover setting, performs cell quality measurement, and starts evaluating the specified measurement event. Then, when the specified measurement event is established (triggered), the terminal device 10 performs the conditional handover process in S14. Figure 9 In the illustrated example, the terminal apparatus 10 attempts conditional handover to the cell 300B, which is a candidate cell of the handover destination corresponding to the triggered measurement event.

[0109] When conditional handover to the cell 300B is successful (i.e., when the random access procedure is successful in the cell setting of the cell 300B), in S15 , the terminal apparatus 10 generates an RRC message (RRC ReconfigrationComplete) indicating that the conditional handover is successful, and transmits it to the base station apparatus 20 .

[0110] In S16, the terminal device 10 determines whether the established measurement event is a measurement event specified by the base station device 20, and whether the target cell when the measurement event is established satisfies the application order specified by the link information. Figure 9 In the example shown, these requirements are assumed to be met. Furthermore, assume that the conditional handover setting identified by id0 is applied and conditional handover to cell 300B is successful. In this case, the terminal device 10 deletes the conditional handover setting identified by id0 but maintains the conditional handover setting identified by id1.

[0111] Note that the base station apparatus 20 recognizes, based on the RRC message received from the terminal apparatus 10, that the terminal apparatus 10 has applied the conditional handover configuration according to the link information. Therefore, in order to match the conditional handover configuration between the terminal apparatus 10 and the base station apparatus 20, the base station apparatus 20 similarly deletes the ID deleted by the terminal apparatus 10. In this example, the base station apparatus 20 also deletes id0.

[0112] Figure 10 An example of a case where the predicted conditional handover is successful is shown. In this example, the terminal device 10 is connected to the cell 300A. In addition, the base station device 20 (not shown) recognizes the following situation.

[0113] (1) The terminal device 10 is connected to the cell 300A.

[0114] (2) It is expected that the serving cell of the terminal device 10 will shift from the cell 300A to the cell 300B and then to the cell 300C.

[0115] Therefore, the base station apparatus 20 transmits CHO setting_id0 and CHO setting_id1 to the terminal apparatus 10 (in Figure 9In the example, S11 is used). CHO setting_id0 is a conditional handover setting including information indicating that the candidate cell for conditional handover is cell 300B. CHO setting_id1 is a conditional handover setting including information indicating that the candidate cell for conditional handover is cell 300C. At this time, the base station device 20 also sends link information together with the conditional handover setting to the terminal device 10. In this case, the link information includes information indicating that CHO setting_id0 is applied first and CHO setting_id1 is applied second. The conditional handover setting and link information are as follows: Figure 10 As shown in (a), it is stored in the memory of the terminal device 10. In addition, the base station device 20 notifies the terminal device 10 of a trigger condition including a measurement event type or a conditional event ID for conditional handover.

[0116] Assume that after receiving the above-mentioned conditional handover setting, the terminal device 10 has not yet performed conditional handover. At this time, the terminal device 10 performs cell measurement based on the conditional handover setting corresponding to "CHO ​​order: 1" of the link information ( Figure 8 (S1 in the example). The conditional handover configuration corresponding to "CHO ​​order: 1" (i.e., CHO configuration_id0) specifies cell 300B as the target cell. Therefore, terminal device 10 performs measurements on both cell 300A and cell 300B. Furthermore, terminal device 10 evaluates whether the measurement event specified by base station apparatus 20 (e.g., conditional event D1 or conditional event T1) has been met.

[0117] When a measurement event specified in the terminal device 10 is established, the cell to be connected is determined through the random access procedure. Figure 10 As shown in (b), it is assumed that the conditional handover to the cell 300B is successful. Here, the candidate cell specified by CHO setting_id0 is consistent with the actual handover destination cell. Therefore, the terminal device 10 estimates that the prediction of the base station device 20 is correct. In other words, the terminal device 10 estimates that the conditional handover setting of the next handover destination of the cell 300B is valid. Therefore, the terminal device 10 does not delete but maintains the conditional handover setting of the next handover destination of the cell 300B (i.e., CHO setting_id1). In addition, the conditional handover setting corresponding to the handover destination cell (i.e., CHO setting_id0) is deleted.

[0118] Afterwards, the terminal apparatus 10 continues the conditional handover process using the conditional handover setting corresponding to "CHO ​​order: 2" (i.e., CHO setting_id 1). Therefore, the terminal apparatus 10 can control the conditional handover from the cell 300B to the cell 300C without receiving a new conditional handover setting from the base station apparatus 20.

[0119] Figure 11In addition, the conditional handover setting and link information sent from the base station device 20 (not shown) to the terminal device 10 are shown in FIG. Figure 10 and Figure 11 That is, the memory of the terminal device 10 stores Figure 10 Conditional switching settings and link information shown in (a).

[0120] However, in Figure 11 In the illustrated scenario, terminal device 10 performs a handover not to cell 300B but to an unpredicted cell 301. Cell 301 is formed, for example, by a base station located on the ground. Furthermore, handover to cell 301 is performed, for example, because the received power of terminal device 10 falls below a threshold level.

[0121] At this time, the candidate cell specified by CHO setting_id0 does not match the actual handover destination cell. Therefore, the terminal device 10 determines that it is not preferable to continue the conditional handover predicted by the base station device 20. Figure 11 As shown, the terminal device 10 deletes the conditional switching setting stored in the memory. At this time, the link information may be invalidated.

[0122] Figure 12 Another example of link information is shown. Figure 7 The link information shown indicates the order in which the candidate cell setting information is applied, but Figure 12 In the link information shown, the ID (CondReconfigId) identifying the conditional handover configuration that has already been applied is associated with the ID (CondReconfigId) identifying the conditional handover configuration that is scheduled to be applied next. The base station apparatus 20 generates multiple conditional handover configurations including candidate cell configuration information indicating predicted candidate cells, and then links the IDs (CondReconfigId) identifying each conditional handover configuration in chronological order based on the order in which the cells arrive at the terminal apparatus 10, and notifies the terminal apparatus 10 of the results.

[0123] When the terminal device 10 has not yet implemented conditional switching, the terminal device 10 determines that its own state is "not applied (initial state)". Figure 12In the example shown, the terminal device 10 regards the cell specified by the conditional handover setting corresponding to "CondReconfigId: 0" as the target cell. When the conditional handover based on the prescribed measurement event for the target cell corresponding to "CondReconfigId: 0" is successful, the terminal device 10 implements the above-mentioned conditional handover process. That is, after the conditional handover is successful, the terminal device 10 deletes the conditional handover setting related to the target cell (target cell) and maintains the conditional handover setting related to other candidate cells. On the other hand, when the conditional handover (or handover) to other cells is successful, the terminal device 10 executes the existing conditional handover process (or handover process). In this case, the terminal device 10 can delete all conditional handover settings.

[0124] When the conditional handover setting (candidate cell setting information) corresponding to "CondReconfigId: 0" is applied in the terminal device 10, Figure 12 In the example shown, the cell indicated by the conditional handover setting corresponding to "CondReconfigId: 1" is regarded as the target cell. Similarly, when the conditional handover setting (candidate cell setting information) corresponding to "CondReconfigId: 1" is applied, Figure 12 In the example shown, the cell indicated by the conditional handover configuration corresponding to "CondReconfigId: 2" is regarded as the target cell.

[0125] Alternatively, the terminal device 10 may determine the validity or invalidity of the conditional handover configuration separately, without considering the cell indicated by the corresponding conditional handover configuration as the target cell. For example, if the applied conditional handover configuration is "CondReconfigId: 0," the terminal device 10 may consider the conditional handover configuration corresponding to "CondReconfigId: 2" to be invalid and not evaluate the corresponding measurement event.

[0126] Figure 13 Another example of link information is shown. Figure 12 In the link information shown in , a conditional handover setting is associated with a "next applicable conditional handover setting". Figure 13 In the link information shown in , one or more "next applicable conditional handover configurations" can be associated with a single conditional handover configuration. Base station apparatus 20 generates multiple conditional handover configurations including candidate cell configuration information indicating predicted candidate cells, and links the IDs (CondReconfigId) identifying each conditional handover configuration in chronological order based on the order in which the cells arrive at terminal apparatus 10, and notifies terminal apparatus 10 of the result.

[0127] If the terminal device 10 has not yet executed conditional switching, the terminal device 10 determines that its own state is "not used (initial state)". Figure 13 In the example shown, the terminal device 10 regards the cells indicated by the conditional switching settings corresponding to "CondReconfigId: 0" and "CondReconfigId: 1" as target cells, respectively. That is, two target cells are designated. Moreover, when the conditional switching based on the specified measurement event is successful for either of the two target cells, the terminal device 10 performs the above-mentioned conditional switching process. That is, after the conditional switching is successful, the terminal device 10 deletes the conditional switching settings related to the cell of the switching destination. In addition, the terminal device 10 also deletes the conditional switching settings related to the target cell specified together with the cell of the switching destination. However, the terminal device 10 maintains the conditional switching settings related to other candidate cells. Figure 13 In the illustrated embodiment, the conditional switching settings corresponding to "CondReconfigId: 0" and "CondReconfigId: 1" are deleted, but the conditional switching settings corresponding to "CondReconfigId: 2", "CondReconfigId: 3" and "CondReconfigId: 4" are maintained.

[0128] Alternatively, the terminal device 10 may delete the conditional handover setting related to the handover destination cell, the conditional handover setting related to other target cells, and the conditional handover setting associated with other target cells. Figure 13 In the example shown, it is assumed that the conditional handover to the cell corresponding to "CondReconfigId: 0" is successful. In this case, the conditional handover setting corresponding to "CondReconfigId: 0" is deleted. At this time, the conditional handover setting corresponding to "CondReconfigId: 1", which is another target cell, is also deleted. In addition, the conditional handover settings corresponding to "CondReconfigId: 3" and "CondReconfigId: 4" that are associated with the conditional handover setting corresponding to "CondReconfigId: 1" are also deleted. However, the conditional handover setting corresponding to "CondReconfigId: 2", which does not meet the above conditions, is maintained.

[0129] If conditional handover (or handover) is successful to a cell other than the candidate cell specified by the link information, the terminal device 10 performs the existing conditional handover procedure (or handover procedure). In this case, all conditional handover settings are deleted from the memory of the terminal device 10.

[0130] Alternatively, the base station apparatus 20 may attach link information including one or more IDs (CondReconfigId) indicating the next candidate cell configuration to each conditional handover configuration, and transmit the information in advance to the terminal apparatus 10. In this case, the link information includes the ID indicating the candidate cell configuration that is valid when the conditional handover succeeds.

[0131] In addition to the existing conditional handover setting (first conditional handover setting), the base station device 20 may also notify the terminal device 10 of a conditional handover setting (second conditional handover setting) containing an ID representing one or more candidate cell settings that become valid when the conditional handover is successful. The content of the second conditional handover setting may be the same as the first conditional handover setting. The terminal device 10 does not regard the cell notified by the second conditional handover setting as the target cell, nor does it perform evaluation of the measurement event. Moreover, when the conditional handover based on the first conditional handover setting is successful, the terminal device 10 deletes the first conditional handover setting and makes the second conditional handover setting valid.

[0132] The base station apparatus 20 may notify the terminal apparatus 10 of information for grouping the existing conditional switching settings into a first group regarded as a first conditional switching setting and a second group regarded as a second conditional switching setting. In this case, the terminal apparatus 10 evaluates the measurement event based on the settings included in the first group. Moreover, when the conditional switching for the object cell of the first group is successful, the terminal apparatus 10 deletes the conditional switching settings of the first group and makes the conditional switching settings of the second group valid. In addition, the base station apparatus 20 may also set more than three groups. In this case, the base station apparatus 20 may use the group ID to explicitly indicate the order of the groups to be applied, or may implicitly notify the order of the groups to be applied based on the group ID (for example, applying in descending or ascending order of the group ID).

[0133] To specify the ID of the valid conditional handover setting, the base station apparatus 20 may notify the terminal apparatus 10 of a MAC control element (MAC CE) in a bitmap format. The terminal apparatus 10 may also perform conditional handover only for measurement events or target cells related to the ID specified as valid.

[0134] As described above, according to the first embodiment, when a conditional handover is executed to a predicted cell, the configuration information for subsequent conditional handovers is stored in the terminal device. This allows the terminal device to continuously execute conditional handovers without receiving new configuration information from the base station device, enabling efficient mobility control in the NTN system.

[0135] Alternatively, the network can specify which cell setting information to retain for a terminal device that has successfully completed a conditional handover. However, in this case, the cell setting information must be updated each time a handover succeeds, increasing signaling. Furthermore, unnecessary cell setting information is retained in the terminal device before the network initiates the update process, leading to unnecessary measurement event evaluations for cells that are not candidate handover destinations, potentially reducing mobility control efficiency.

[0136] <Second embodiment>

[0137] The second embodiment will be described. The description of the common structures, functions, and processes in the first and second embodiments will be omitted. Specifically, the following description will focus on the differences from the first embodiment.

[0138] The terminal device of the second embodiment receives and maintains the conditional handover setting. Furthermore, when the cell in which the RRC reconnection process is successful is designated as the next candidate cell through link information, the terminal device deletes the candidate cell setting corresponding to the next candidate cell and maintains the candidate cell setting corresponding to the candidate cells other than the next candidate cell.

[0139] The base station device of the second embodiment transmits multiple candidate cell settings, the first information, and the second information to the terminal device in the same manner as in the first embodiment. Furthermore, the base station device transmits information indicating that the conditional handover setting can be used during the RRC reconnection process to the terminal device. Therefore, when the RRC reconnection process using the conditional handover setting is successful, the terminal device can delete some or all of the pre-set cell setting information based on the information (link information) indicating the order of the candidate cell setting information.

[0140] Figure 14 This is a flowchart showing an example of the processing of the terminal device of the second embodiment. In this embodiment, it is assumed that link information and information indicating that the conditional switching setting can be used in the RRC reconnection process are attached to the conditional switching setting received from the base station device. In addition, the flowchart shows the processing when the RRC reconnection process (RRC reconstruction) is started. In addition, the RRC reconnection process is implemented to recover the temporary loss of UL / DL synchronization caused by the deterioration of the downlink reception quality in the terminal device 10, the failure of random access, etc., or the momentary disconnection of the wireless link due to the expiration of the protection timer in the RRC. The RRC reconnection process is also called the RRC re-establishment process.

[0141] In S21, when the terminal device 10 determines that the RRC reconnection process is required, it searches for a cell that can be reconnected (reconnection destination cell) by performing a cell search. When the reconnection destination cell is detected through the search, in S22, the terminal device 10 determines whether the detected cell is a target cell for conditional handover. If the detected cell is not a target cell (S22: No), the terminal device 10 performs the existing RRC reconnection process in S25. In this case, after the RRC reconnection process is successful, the terminal device 10 deletes all the maintained conditional handover settings.

[0142] When the detected cell is the target cell (S22: "Yes"), the terminal device 10 determines in S23 whether the link information has been notified from the base station device 20 and whether the conditions for the establishment of the specified measurement event are met. Specifically, when the terminal device 10 includes link information with valid conditional switching settings and attempts the RRC reconnection process, it determines whether the set measurement event is a measurement event associated with the NTN (i.e., conditional event D1 or conditional event T1) and whether the measurement event is established. In addition, the base station device 20 may also append information such as an identifier to the report setting based on whether it is a specified measurement event. In addition, the base station device 20 may also specify the category of the measurement event associated with the NTN.

[0143] The determination of whether a measurement event has been established may also be based on the same criteria as the evaluation of the measurement event described above. If link information is not notified, or if the conditions for establishing a measurement event are not met (S23: No), the terminal device 10 performs the existing RRC reconnection process in S25.

[0144] If the link information is notified and the established measurement event is a specified measurement event (S23: Yes), the terminal device 10 determines in S24 whether the target cell at the time of the measurement event satisfies the conditions indicated by the link information. Specifically, the terminal device 10 determines whether the target cell (reconnection target cell) at the time of the measurement event is consistent with the cell determined based on the link information. If these cells do not match (S24: No), the terminal device 10 performs the existing RRC reconnection procedure in S25.

[0145] On the other hand, if the target cell at the time of the measurement event is the same as the cell determined based on the link information (S24: YES), the terminal device 10 performs the RRC reconnection procedure according to the embodiment of the present invention in S26. That is, after the RRC reconnection procedure is successful, the terminal device 10 deletes the conditional handover settings related to the target cell (target cell) and maintains the conditional handover settings related to the other candidate cells.

[0146] In this way, during the RRC reconnection process, the terminal device 10 deletes part or all of the pre-set candidate cell setting information based on the measurement event type information of the conditional handover, the information indicating the cell of the reconnection destination, and the link information indicating the order of the conditional handover. Figure 14 The steps shown can also be appropriately reversed to obtain the same effect. For example, the processing of S22, S23, and S24 can be performed simultaneously or reversed.

[0147] In order to reduce the signaling amount of conditional handover, only the differential settings that are changed after the handover can be notified from the base station device to the terminal device. That is, the reference setting (reference configuration) that serves as the benchmark in a series of cell settings and the differential setting of each candidate cell can also be notified to the terminal device. In this case, the terminal device 10 can regard the cell setting applied after the conditional handover is successful as the reference setting (reference configuration). In addition, the link information can also indicate the order of application of the reference setting and each differential setting.

[0148] Furthermore, during or after conditional handover, or during or after an RRC reconnection process, security keys may be updated to strengthen or confirm security functions from a higher layer. In this case, the terminal device 10 may delete the stored conditional handover settings regardless of the order of the link information. Furthermore, the base station device 20 may also instruct the update of security keys.

[0149] As described above, according to the second embodiment, when RRC reconnection to the predicted cell is performed, the terminal device maintains the configuration information for subsequent conditional handover. Therefore, the terminal device can continuously perform conditional handover without receiving new configuration information from the base station device after the RRC reconnection process, enabling efficient mobility control in the NTN system.

[0150] Furthermore, in non-terrestrial networks, terminal devices and base stations can continuously perform conditional handovers, not just once. This allows for efficient mobility control in wireless communications between terminal devices and base stations in non-terrestrial networks.

[0151] The above-described embodiments are intended to facilitate understanding of the present invention and are not intended to limit the present invention. The present invention is susceptible to modification and improvement without departing from its spirit and encompasses equivalents. For example, "satellite" is not limited to artificial satellites but may also refer to high altitude satellites (HAPS) and other unmanned or manned aircraft.

[0152] Description of Reference Numerals

[0153] 10 Terminal Devices

[0154] 20 Base Station Equipment

[0155] 30 Core Network

[0156] 11, 21 Processing Department

[0157] 13, 23 Control Department

[0158] 15, 25 Receiving Department

[0159] 17, 27 Sending Department

[0160] 19, 29 Transceiver antenna unit

[0161] 111, 211 Wireless Resource Processing Department

[0162] 113, 213NTN Control Information Processing Department

[0163] 210 Ground Station

[0164] 220 Service Link Provisioning System

[0165] 230 Gateway Device

[0166] 240 NTN payload unit

[0167] 250 (250A~250C) flying objects

[0168] 300 (300A~300C) community

Claims

1. A terminal device supporting conditional switching, wherein: The terminal device includes: a receiving unit that receives, from a base station apparatus, a plurality of candidate cell settings corresponding to a plurality of candidate cells of a handover destination, first information indicating a type of an event condition for executing the conditional handover, and second information indicating an order of the plurality of candidate cells; and A processing unit that, when performing a switch from a first cell to a second cell, determines whether to delete a part of the multiple candidate cell settings or to delete all of the multiple candidate cell settings based on whether an event condition of the category represented by the first information is met and whether the second cell is a candidate cell corresponding to the order represented by the second information.

2. The terminal device according to claim 1, wherein The event condition is a time-based or distance-based event condition.

3. The terminal device according to claim 1, wherein When an event condition of the category represented by the first information is met and the second cell is designated as the next candidate cell by the second information, the processing unit deletes the candidate cell setting corresponding to the next candidate cell and maintains the candidate cell setting corresponding to candidate cells other than the next candidate cell.

4. The terminal device according to claim 1, wherein When the event condition of the category represented by the first information is met and the second cell is designated as the next candidate cell by the second information, the processing unit deletes the candidate cell setting corresponding to the next candidate cell and maintains the candidate cell setting corresponding to the candidate cell applied after the next candidate cell in the second information.

5. The terminal device according to claim 1, wherein When the cell in which the reconnection process succeeds is designated as the next candidate cell by the second information, the processing unit deletes the candidate cell setting corresponding to the next candidate cell and maintains the candidate cell setting corresponding to the candidate cells other than the next candidate cell. The terminal device according to claim 1 , wherein: In the second information, an identifier identifying a candidate cell configuration to be applied next is associated with each of the plurality of identifiers that respectively identify the plurality of candidate cell configurations.

7. A base station device that communicates with a terminal device that supports conditional handover, wherein: The base station device includes: a processing unit that generates a plurality of candidate cell settings corresponding to a plurality of candidate cells of a handover destination of the terminal device, first information indicating a type of an event condition for executing the conditional handover in the terminal device, and second information indicating an order of the plurality of candidate cells; and A sending unit that sends the multiple candidate cell settings, the first information, and the second information to the terminal device, so that when the terminal device switches from the first cell to the second cell, the terminal device determines whether to delete a part of the multiple candidate cell settings or delete all of the multiple candidate cell settings based on whether an event condition of the category represented by the first information is met and whether the second cell is a candidate cell corresponding to the order represented by the second information.

8. The base station device according to claim 7, wherein: The event condition is a time-based or distance-based event condition.

9. The base station device according to claim 7, wherein: The second information is information that causes the terminal device to delete the candidate cell configuration corresponding to the next candidate cell and maintain the candidate cell configuration corresponding to candidate cells other than the next candidate cell when the second cell is designated as the next candidate cell by the second information.

10. The base station device according to claim 7, wherein: The second information is information that causes the terminal device to delete the candidate cell setting corresponding to the next candidate cell when the second cell is designated as the next candidate cell by the second information, and maintain the candidate cell setting corresponding to the candidate cell applied after the next candidate cell in the second information.

11. The base station device according to claim 7, wherein: The second information is for the terminal device to delete the candidate cell setting corresponding to the next candidate cell when the cell in which the reconnection process is successful is designated as the next candidate cell by the second information, and to maintain the information of the candidate cell setting corresponding to the candidate cells other than the next candidate cell.

12. The base station device according to claim 7, wherein: In the second information, an identifier identifying a candidate cell configuration to be applied next is associated with each of the plurality of identifiers that respectively identify the plurality of candidate cell configurations.

13. A handover control method, the handover control method being executed in a terminal device supporting conditional handover, wherein: receiving, from a base station apparatus, a plurality of candidate cell settings corresponding to a plurality of candidate cells of a handover destination, first information indicating a type of an event condition for executing the conditional handover, and second information indicating an order of the plurality of candidate cells; When performing a switch from a first cell to a second cell, based on whether an event condition of the category represented by the first information is met and whether the second cell is a candidate cell corresponding to the order represented by the second information, a part of the multiple candidate cell settings is deleted, or all of the multiple candidate cell settings are deleted.

14. A handover control method, the handover control method being executed in a base station device communicating with a terminal device supporting conditional handover, wherein: generating a plurality of candidate cell settings corresponding to a plurality of candidate cells of a switching destination of the terminal device, first information indicating a type of an event condition for executing the conditional switching in the terminal device, and second information indicating an order of the plurality of candidate cells, The multiple candidate cell settings, the first information, and the second information are sent to the terminal device, so that when the terminal device switches from the first cell to the second cell, the terminal device determines whether to delete part of the multiple candidate cell settings or delete all of the multiple candidate cell settings based on whether the event condition of the category represented by the first information is met and whether the second cell is a candidate cell corresponding to the order represented by the second information.

Images