Terminal device, base station device, and handover control method

Abstract

The present invention improves the reduction efficiency of network power consumption by optimizing each of a method for controlling the movement of a terminal device and a base station device for supporting a network power reduction technology. The terminal device comprises a control unit that performs control corresponding to each of a first cell state which is a first mode and a second cell state which is different from the first mode. The terminal device also comprises a reception unit that receives, from the base station device, a first condition for determining that a first time has been exceeded and a second condition for determining that a second time at which a predetermined duration has elapsed since the first time has passed. The terminal device also comprises a processing unit that performs evaluation of an event condition for a conditional handover corresponding to the first cell state until the first condition is satisfied, performs evaluation of an event condition for a conditional handover corresponding to the second cell state when the first condition is satisfied, and starts a conditional handover procedure when the second condition is satisfied.

Description

Terminal device, base station device, and handover control method

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

[0002] The standardization project 3GPP (3rd Generation Partnership Project) (registered trademark) is studying technical specifications for communication standards that meet the requirements of NR (New Radio, also referred to as "5G"), which is fifth-generation mobile communications, including eMBB (Enhanced Mobile Broadband), MTC (Massive Machine Type Communications), and URLLC (Ultra-Reliable and Low Latency Communications).

[0003] In 3GPP, NES (Network Energy Savings) technology is being studied to reduce power consumption on the network side (that is, base station devices and core network devices) (Non-Patent Document 1).

[0004] One of the technologies under study for NES is Cell DTX / DRX, which is intended to realize discontinuous reception (DRX) and / or discontinuous transmission (DTX) on a cell-by-cell basis. Cell DTX / DRX is a technology in which a base station device sets an active period and an inactive period (or non-active period) on a cell-by-cell basis, and the base station device transmits and receives only during the active period and restricts transmission and reception during the inactive period, thereby reducing power consumption (Non-Patent Document 1).

[0005] Furthermore, a handover procedure called conditional handover (condition pre-set handover) has been proposed, which moves a terminal device to another cell when a cell transitions to a power saving mode (NES mode) (for example, Non-Patent Documents 1 to 3). The NES mode may refer to the state of a cell to which the above-mentioned Cell DTX / DRX is applied, or may refer to the state of a cell to which other technologies that contribute to power saving are applied. Note that cell shutdown (temporary or long-term cell power off), in which no cell transmission or reception is performed, is also considered to be one of the NES modes.

[0006] Conditional handover is a technique introduced to improve the robustness (stability) and success rate of handover. It is a handover procedure in which the target cell information and trigger conditions are set in advance. The terminal device evaluates the set trigger conditions and initiates the handover procedure to the target cell if the trigger conditions are met.

[0007] 3GPP TR 38.864 V18.0.0 (2022-12) R2-2305461R2-2306069

[0008] When a cell transitions to the energy saving mode (NES mode), the available radio resources are reduced compared to a conventional cell, resulting in a decrease in the total traffic volume of the cell or the total number of terminal devices that can be connected simultaneously. Therefore, when a cell transitions to the NES mode, the quality of service (QoS) requirements of the terminal device being executed may not be met, resulting in a degradation of the user experience. To mitigate this problem, it is preferable that a terminal device executing a low-latency service, such as a real-time service, perform handover to another cell before the cell transitions to the NES mode.

[0009] On the other hand, because the change to the NES mode is performed regardless of the cell quality (measurement result, cell quality) measured by the terminal device, there are cases where the terminal device cannot be moved to another cell using the normal handover procedure. For example, the measurement result of a terminal device located near the center of a serving cell is generally better than the measurement result of a neighboring cell, which means that there is a high possibility that a handover or a conditional handover based on a comparison of the quality of the serving cell with the quality of a neighboring cell will not be performed. Therefore, a forced handover procedure different from the normal one must be performed for each of these terminal devices, which causes a temporary increase in the amount of signaling of the base station device and a processing delay, preventing an immediate transition to the NES mode and reducing the power saving effect.

[0010] To address this problem, for example, Non-Patent Document 2 proposes a method of notifying the start of event evaluation for conditional handover using RRC signaling or a system information block (SIB). However, the method of Non-Patent Document 2 requires the addition of new signaling for notification, and the terminal device must constantly monitor this signaling. This complicates the operations of the base station device and the terminal device, but Non-Patent Document 2 neither discloses nor suggests a solution to this problem.

[0011] Furthermore, Non-Patent Document 3 proposes a method of performing a handover before switching to the NES mode by reusing a time-based conditional handover (CondEventT1). However, since the time-based conditional handover is performed without evaluating the quality of the candidate cell as the handover destination, there is a problem in that there is no way to confirm whether the cell as the handover destination is the best cell for the terminal device. However, Non-Patent Document 3 does not disclose or suggest a solution to this problem.

[0012] In view of these considerations, an object of one aspect of the present invention is to optimize the mobility control methods of base station devices and terminal devices that support network power saving technology (NES), thereby improving the efficiency of network power saving.

[0013] A terminal device according to one aspect of the present invention comprises a control unit capable of performing control corresponding to a first cell state which is a first mode and a second cell state which is a second mode different from the first mode; a receiving unit capable of receiving from a base station device a first condition for determining that a first time has been exceeded and a second condition for determining that a second time has passed, which is a predetermined duration from the first time; and a processing unit capable of evaluating a first event condition for conditional handover corresponding to the state of the first cell until the first condition is satisfied, and evaluating a second event condition for conditional handover corresponding to the state of the second cell when the first condition is satisfied, and starting a conditional handover procedure when the second condition is satisfied.

[0014] A base station device according to one aspect of the present invention comprises: a control unit capable of performing control corresponding to a first cell state, which is a first mode, and a second cell state, which is a second mode different from the first mode; a transmission unit capable of transmitting to a terminal device a first condition for determining that a first time has been reached and a second condition for determining that a second time, which is a predetermined duration from the first time, has passed; and a processing unit capable of causing the terminal device to evaluate a first event condition for conditional handover corresponding to the first cell state until the first condition is met, and, if the first condition is met, causing the terminal device to evaluate a second event condition for conditional handover corresponding to the second cell state, and, if the second condition is met, providing information for starting a conditional handover procedure.

[0015] According to the above-described aspects, it is possible to optimize the mobility control methods of base station devices and terminal devices that support network power saving technology (NES), and also to improve the efficiency of network power saving.

[0016] 1 is a diagram illustrating an example of the configuration of a wireless communication system according to an embodiment. FIG. 2 is a diagram illustrating an example of the functional configuration of a terminal device according to an embodiment. FIG. 3 is a diagram illustrating an example of the functional configuration of a base station device according to an embodiment. FIG. 4 is a diagram illustrating an example of a handover sequence according to an embodiment. FIG. 5 is a diagram illustrating an example of an event evaluation timing of conditional handover according to an embodiment. FIG. 6 is a diagram illustrating an example of the event evaluation timing of conditional handover according to an embodiment. FIG. 7 is a diagram illustrating an example of the event evaluation timing of conditional handover according to an embodiment. FIG. 8 is a diagram illustrating an example of time-based conditional handover. FIG. 9 is a diagram illustrating an example of the hardware configuration of a terminal device according to an embodiment. FIG. 10 is a diagram illustrating an example of the hardware configuration of a base station device according to an embodiment.

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The problems and embodiments in this specification are merely examples and do not limit the scope of the rights of the present application. In particular, even if the expressions used are different, the technology of the present application can be applied as long as they are technically equivalent, and do not limit the scope of the rights. Furthermore, each embodiment can be appropriately combined within the scope of the processing content.

[0018] Publicly known technologies may be used as appropriate in the wireless communication system according to the embodiment of the present invention. Applicable publicly known technologies may be, for example, 5G (NR), Beyond 5G, 5G-Advanced, or other wireless communication methods. The wireless communication system according to the embodiment of the present invention targets NR, but is not limited thereto. For example, the embodiment of the present invention can also be applied to LTE (Long Term Evolution) and LTE-Advanced. It can also be applied to a wireless communication system that uses NR as part of the wireless communication system.

[0019] Furthermore, the embodiments of the present invention are applicable to any wireless communication system including at least a terminal device and a base station device, and are also applicable 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 the meaning is the same.

[0020] Hereinafter, embodiments of a base station apparatus, a terminal apparatus, and a wireless communication system disclosed in the present application will be described with reference to the drawings. Note that the disclosed technology is not limited to the following embodiments.

[0021] <Wireless Communication System> Fig. 1 is a diagram showing an example of the configuration of a wireless communication system 1 according to an embodiment of the present invention. The wireless communication system 1 according to the embodiment is configured from, for example, a terminal device 10, base station devices 20A and 20B, and a core network 30. Note that when there is no need to distinguish between the base station devices 20A and 20B, they will simply be referred to as base station device 20. Furthermore, there may be multiple terminal devices 10.

[0022] The terminal device 10 may be a wireless terminal such as a mobile phone, a smartphone, a PDA (Personal Digital Assistant), a tablet, a wearable device, a personal computer, a vehicle, or any other device or equipment (sensor device, etc.) having a wireless communication function. The terminal device 10 may also be referred to as a wireless communication device, a communication device, a receiving device, a mobile station, a UE (User Equipment), a user device, etc.

[0023] A wireless communication service is provided to a terminal device 10 by a base station device 20 and a core network 30 in a wireless communication system 1. The core network 30 has functions such as managing service subscriber information, managing sessions such as voice calls, and managing location registration of the terminal device 10. The core network 30 also transmits control data and / or user data to the terminal device 10 via the base station device 20.

[0024] The core network 30 may be a 5G Core (5GC) in 5G (NR) or an Evolved Packet Core (EPC) in 4G (E-UTRA). The connection method between the core network 30 and the base station device 20 may be a Non-Stand Alone (NSA) method or a Stand Alone (SA) method.

[0025] 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. The 5G base station devices are connected to each other via an Xn interface, and the 4G base station devices are connected to each other via an X2 interface.

[0026] An area (coverage area) formed by a base station device 20 may be called a "cell." E-UTRA and 5G are cellular communication systems constructed by multiple cells. As a wireless communication system 1 according to an embodiment of the present invention, either a time division duplex (TDD) or a frequency division duplex (FDD) method may be applied, and different methods may be applied to different cells.

[0027] The base station device 20 may be configured, for example, as being divided into a CU (Centralized Unit), a DU (Distributed Unit), and an RU (Radio Unit). The CU is connected to a core network. The DU is connected to the terminal device 10 via the RU, for example. The communication path between the CU and the DU is realized by, for example, a fronthaul interface (F1 interface). Multiple DUs may be connected to one CU.

[0028] In the example shown in Figure 1, data (DL data, downlink data) transmitted from the core network 30 to the terminal device 10 is transmitted from the core network 30 to the base station device 20, and then transmitted (forwarded) from the base station device 20 to the terminal device 10.

[0029] Data (UL data, uplink data) transmitted from the terminal device 10 to the core network 30 is transmitted from the terminal device 10 to the base station device 20 and then transmitted (transferred) from the base station device 20 to the core network 30 .

[0030] The terminal device 10 and the base station device 20 transmit and receive RRC messages (also called RRC signaling) in a Radio Resource Control (RRC) layer. Also, the terminal device 10 and the base station device 20 transmit and receive MAC control elements (MAC CEs) in a Medium Access Control (MAC) layer.

[0031] The RRC message is transmitted as an RRC Protocol Data Unit (PDU), and the logical channel (LCH) to which it is mapped may be a common control channel (CCCH), a dedicated control channel (DCCH), a paging control channel (PCCH), a broadcast control channel (BCCH), a multicast control channel (MCCH), or the like.

[0032] The MAC CE is transmitted as a MAC PDU (or MAC subPDU). A MAC subPDU is equivalent to a service data unit (SDU) in the MAC layer plus, for example, an 8-bit header, and the MAC PDU includes one or more MAC subPDUs.

[0033] Next, the physical channels and physical signals according to the embodiment include at least a synchronization signal (Primary Synchronization Signal, Secondary Synchronization Signal), a physical broadcast channel (PBCH), a physical random access channel (PRACH), a physical downlink control channel (PDCCH), a channel state information-reference signal (CSI-RS), a physical uplink control channel (PUCCH), a physical downlink shared channel (PDSCH), a physical uplink shared channel (PUSCH), a scheduling reference signal (SRS), and a demodulation reference signal (DMRS), but detailed description thereof will be omitted.

[0034] <Terminal Device> Fig. 2 is a diagram showing an example of the functional configuration of the terminal device 10 according to the embodiment. As shown in Fig. 2, the terminal device 10 includes, for example, a processing unit 11, a control unit 13, a receiving unit 15, a transmitting unit 17, and a transmitting / receiving antenna unit 19. The processing unit 11 includes, for example, a radio resource processing unit 111 and an NES information processing unit 113. Note that the functional configuration of the terminal device 10 shown in Fig. 2 is merely an example, and the functional divisions and names of each functional block may be different as long as the operations according to the embodiment can be executed.

[0035] The processing unit 11 generates, for example, 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 executes processes related to, for example, a radio resource control layer, a packet data convergence protocol (PDCP) layer, a radio link control (RLC) layer, and a medium access control layer.

[0036] The radio resource processing unit 111 manages various setting information (RRC parameters, information elements (IEs)) of the terminal device 10. For example, the radio resource processing unit 111 generates information to be allocated to each channel of the physical uplink and outputs the information to the transmission unit 17. Furthermore, based on instructions from the base station device 20, the radio resource processing unit 111 performs measurements of the serving cell and surrounding cells, start and stop of transmission and reception processing, DL synchronization procedure (cell search), UL synchronization procedure (random access procedure), reacquisition of system information, event evaluation related to handover, a series of processes related to handover, and the like.

[0037] The NES information processing unit 113 performs processing procedures corresponding to the management of NES-related settings and parameters. For example, the NES information processing unit 113 performs processes such as determining whether to evaluate a measurement event taking the NES mode into consideration, determining the timing to apply parameters related to the NES mode, and triggering a condition handover taking the NES mode into consideration. The NES information processing unit 113 determines whether to perform each procedure and determines the timing based on the RRC parameters (information elements) provided via the radio resource processing unit 111, and provides the results to the radio resource processing unit 111 as control information.

[0038] The control unit 13 performs various controls in the terminal device 10. For example, the control unit 13 generates control signals or control data for controlling the receiving unit 15 and the transmitting unit 17 based on control information from the processing unit 11. The control unit 13 also controls uplink transmission to the base station device 20 and downlink reception from the base station device 20 based on information related to discontinuous transmission and reception.

[0039] The receiving unit 15 separates, demodulates, and decodes various signals received from the base station device 20 via the transmitting / receiving antenna unit 19 based on a control signal provided by the control unit 13. The receiving unit 15 outputs the decoded information to the processing unit 11.

[0040] The transmitter 17 generates, for example, a physical uplink signal based on a control signal provided from the controller 13, and performs encoding and modulation on the physical uplink signal or the physical uplink channel provided from the processor 11. The transmitter 17 multiplexes various signals and transmits them to the base station device 20 via the transmitter-receiver antenna unit 19.

[0041] The processing unit 11 and the control unit 13 are realized, for example, by a processor system including a processor and a memory. In this case, the processor provides the functions of the processing unit 11 and the control unit 13 by executing a program that describes the operation of the terminal device 10 (described later). The processing unit 11 and the control unit 13 may be realized by a single processor system or by multiple processor systems. Alternatively, the processing unit 11 and the control unit 13 may be realized by a DSP (Digital Signal Processor), a hardware circuit, or the like.

[0042] <Base Station Device> Fig. 3 is a diagram showing an example of the functional configuration of the base station device 20 according to the embodiment. As shown in Fig. 3, the base station device 20 includes, for example, a processing unit 21, a control unit 23, a receiving unit 25, a transmitting unit 27, and a transmitting / receiving antenna unit 29. The processing unit 21 is illustratively configured to include a radio resource processing unit 211 and an NES information processing unit 213. Note that the functional configuration of the base station device 20 shown in Fig. 3 is merely an example, and the names of the functional divisions and functional blocks may be different as long as the operations according to the embodiment can be performed.

[0043] The processing unit 21 generates, for example, control information for controlling the receiving unit 25 and the transmitting unit 27, and outputs the control information to the control unit 23. The processing unit 21 executes processes relating to, for example, the radio resource control layer, the packet data integration protocol layer, the radio link control layer, and the medium access control layer.

[0044] The radio resource processing unit 211 generates, for example, downlink data, an RRC message, and a MAC control element to be allocated to the physical downlink shared channel PDSCH, and outputs these to the transmission unit 27. The radio resource processing unit 211 also generates a control signal or control data to be allocated to the physical downlink control channel PDCCH, and outputs this to the transmission unit 27. Furthermore, the radio resource processing unit 211 manages various setting information of the terminal device 10. Based on a signal from the terminal device 10 or a notification by an RRC message, the radio resource processing unit 211 executes start and stop of transmission and reception processing, start of a UL synchronization procedure (random access procedure), update of system information, adjustment of the beam transmission angle, cell setting related to handover, and pre-setting of parameters related to measurement event types (measurement event identifiers).

[0045] The NES information processing unit 213 performs processing procedures corresponding to the management of NES-related settings and parameters for the terminal device 10. For example, the NES information processing unit 213 performs processing such as determining whether to transition to the NES mode, generating parameters indicating an evaluation of a measurement event taking the NES mode into consideration, determining the application timing of parameters related to the NES mode, and generating measurement event parameters for condition handover taking the NES mode into consideration. The NES information processing unit 213 provides the determined timing and values ​​of various parameters to the radio resource processing unit 211 as RRC parameters (information elements).

[0046] The control unit 23 performs various controls in the base station device 20. For example, the control unit 23 generates control signals or control data for controlling the receiving unit 25 and the transmitting unit 27 based on control information from the processing unit 21. Furthermore, the control unit 23 controls downlink transmission to the terminal device 10 and uplink reception from the terminal device 10 based on information related to intermittent transmission and reception.

[0047] The receiving unit 25 separates, demodulates, and decodes various signals received from the terminal device 10 or the core network 30 via the transmitting / receiving antenna unit 29 based on a control signal provided by the control unit 23. The receiving unit 25 outputs the decoded information to the processing unit 21.

[0048] The transmitter 27 generates, for example, a downlink reference signal based on the control signal provided by the controller 23. The transmitter 27 encodes, modulates, multiplexes, and so on various pieces of information provided by the processor 21, and transmits the signal to the terminal device 10 via the transmitting / receiving antenna unit 29.

[0049] Furthermore, the transmitter 27 transmits data to the terminal device 10, another base station device 20, or the core network 30. The receiver 25 receives data from the terminal device 10, another base station device 20, or the core network 30.

[0050] The processing unit 21 and the control unit 23 are realized, 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 that describes the operation of the base station device 20, which will be described later. The processing unit 21 and the control unit 23 may be realized by a single processor system or by multiple processor systems. Alternatively, the processing unit 21 and the control unit 23 may be realized by a DSP, a hardware circuit, or the like.

[0051] <Measurement Configuration / Measurement Report> The base station device 20 causes the terminal device 10 to measure frequencies (e.g., NR and / or EUTRA frequencies) by notifying (setting, specifying, transmitting) a measurement configuration to the terminal device 10. Note that the measurement configuration is notified, for example, by an RRC message (e.g., RRCReconfiguration).

[0052] The measurement configuration includes at least the following parameters: (1) Measurement object(s) The measurement object(s) includes information about the object(s) on which the terminal device 10 performs measurements, and multiple objects can be set in list format. The base station device 20 can indicate intra-frequency measurements, inter-frequency measurements, and inter-RAT (Radio Access Technology) E-UTRA measurements as measurement objects. In the case of inter-system EUTRA measurements, the EUTRA frequency is set as the measurement object.

[0053] Furthermore, the base station device 20 can include a list of cells to which a cell-specific offset is assigned, a block cell list, and an allowed cell list in the measurement objects. The cell-specific offset is an offset value added to the measurement result during measurement, the block cell list is a list indicating cells that are not applicable (non-target) for event evaluation (described later) or measurement reporting, and the allowed cell list is a list indicating cells that are applicable (target) for event evaluation or measurement reporting. To manage measurement objects, the base station device 20 sets a measurement object identifier (measObjectId) for each measurement object.

[0054] (2) Reporting configuration(s) The reporting configuration includes information related to a measurement report, and one or more reporting configurations are set for each measurement target in a list format. To manage the reporting configurations, the base station device 20 sets a reporting configuration identifier (reportConfigId) for each reporting configuration.

[0055] (3) Measurement identity(ies) The measurement identifier (measId) is an identifier for linking (associating, relating) one measurement object identifier (measObjectId) with one reporting configuration identifier (reportConfigId). Multiple measurement identifiers can be set in a list format. The measurement identifier may link multiple reporting configurations to one measurement object, or multiple measurement objects may be linked to the same reporting configuration. The measurement identifier is transmitted in a measurement report to report an event that satisfies a trigger condition to the base station device 20.

[0056] Regarding measurement targets for NR, the terminal device 10 measures and reports on the serving cell (also referred to as the serving cell), listed cells, and detected cells. Listed cells are cells included in a list notified by the base station device 20. Detected cells refer to other cells that the terminal device 10 has independently detected.

[0057] The measurement event(s) to be evaluated by the terminal device 10 are specified by the base station device 20. The measurement event is specified in the report configuration and managed by an event identifier (eventId). When a measurement event is triggered (established), the terminal device 10 generates a measurement report message (Measurement Report) and transmits it to the base station device 20. The condition (measurement type) indicating the trigger for transmitting the measurement report message is either a periodic report or an event triggered report, and either one of them is specified by the base station device 20.

[0058] For each measurement event, an applicable cell to be evaluated is defined. For example, the applicable cell for event A1 is the serving cell. The applicable cell for event A3 is a cell (neighbor cell) detected at the frequency to be measured and linked to the reporting configuration including event A3.

[0059] The terminal device 10 initiates the measurement reporting procedure when the measurement type is an event trigger report and the measurement result meets the condition indicated by the measurement event. In other words, the measurement reporting procedure is initiated when the measurement result of the measurement target cell meets (is established) the event condition corresponding to the event identifier specified in the reporting configuration included in the measurement configuration. At this time, the terminal device 10 reports the measurement result of the cell corresponding to the measurement identifier that meets the event condition (trigger condition).

[0060] <Conditional Handover> A terminal device 10 in a communication state moves within a cell formed by a base station device 20 using handover or conditional handover (CHO). In conditional handover, cell setting information specifying a candidate cell (target cell) as a handover destination and a trigger condition for handover (conditional handover) (measurement event type (measurement event, measurement report event)) are notified to the terminal device 10 in advance from the base station device 20. The measurement event (trigger condition) specified in the conditional handover setting is also referred to as an event condition (Conditional Event).

[0061] At this time, the base station device 20 can configure a maximum of eight candidate cells (i.e., a maximum of eight candidate cell configurations) for the terminal device 10. The terminal device 10 measures the serving cell and neighboring cells. Furthermore, the terminal device 10 evaluates measurement events based on trigger conditions notified from the base station device 20. Hereinafter, one or more pieces of cell configuration information and trigger conditions are collectively referred to as a conditional handover configuration. The conditional handover configuration includes candidate cells and other necessary cell configurations, and is specified in the form of one or more lists. Here, the measurement target cell is a candidate cell included in the conditional handover configuration, and is identified by a physical cell identifier (PCI). In other words, the terminal device 10 considers a cell having a physical cell identifier specified in an RRC message (RRCReconfiguration) included in the conditional handover configuration to be the measurement target cell.

[0062] The base station device 20 and the terminal device 10 each identify and manage conditional handover configurations using a handover condition reconfiguration identifier (CondReconfigId). The base station device 20 and the terminal device 10 can add, delete, or change each conditional handover configuration corresponding to a handover condition reconfiguration identifier. In addition, the handover condition reconfiguration identifier (CondReconfigId) can specify an event condition by linking it to a measurement identifier (measId) included in the measurement configuration.

[0063] When the trigger condition is met (the conditional handover condition is satisfied), the terminal device 10 applies the cell configuration of the candidate cell corresponding to the measurement event as the handover destination cell. That is, after the conditional handover is successful, the cell configuration corresponding to other cells becomes unnecessary. Therefore, the terminal device for which the conditional handover is successful autonomously deletes the cell configuration corresponding to cells other than the destination cell.

[0064] FIG. 9 is a diagram illustrating an example of a conditional handover event. The conditional handover event illustrated in FIG. 9 is a time-based measurement event and is also referred to as event condition T1 (ContEventT1). Event condition T1 is introduced as a measurement event for a non-terrestrial network (NTN). The terminal device 10 measures the time from a certain reference time to the current time. Then, the terminal device 10 evaluates the handover event by comparing the measured time with a set threshold.

[0065] In the example shown in FIG. 9 , the terminal device 10 is located within a cell 300A. A base station device 20 (not shown) notifies the terminal device 10 of elapsed time information (threshold value TH_t) since January 1, 1980 in the Gregorian calendar and duration information (duration) as information related to the event condition T1. The elapsed time information is notified in units of 10 milliseconds. The terminal device 10, for which the event condition T1 is set as a valid measurement event, starts measuring the current time (Mt) in milliseconds and comparing it with the notified elapsed time information (threshold value TH_t). The terminal device 10 determines that the event entering condition is satisfied when Equation 1 is satisfied, i.e., when the current time exceeds the notified threshold value TH_t.

[0066] [Formula 1] Mt>TH_t

[0067] The terminal device 10 determines that the event leaving condition is satisfied when Equation 2 is satisfied, that is, when the current time Mt exceeds the value obtained by adding the duration information (duration) to the threshold TH_t. In the example shown in FIG. 9, the event condition T1 is not satisfied in the terminal device 10 at time T1. After that, when time t0 has elapsed from time T1, the event condition T1 is satisfied (i.e., time T1 + t0 > threshold TH_t). In this case, the terminal device 10 performs a conditional handover to a pre-set candidate cell (e.g., cell 300B).

[0068] [Formula 2] Mt>TH_t+duration

[0069] Another example of a conditional handover event is a quality-based event condition Ax (event condition A3, event condition A4, or event condition A5). Hereinafter, when an event condition Ax is described, it means that at least one of the event condition A3, event condition A4, or event condition A5 is used.

[0070] Here, the measurement quality of the serving cell is defined as Mp, the measurement quality of the neighboring cell as Mn, the frequency offset corresponding to the serving frequency as Ofp, the frequency offset corresponding to the frequency of the neighboring cell as Offn, the cell-specific offset corresponding to the serving cell as Ocp, the cell-specific offset corresponding to the neighboring cell as Ocn, the event-specific offset value as Off, the hysteresis value as Hys, and the quality-based threshold as Thresh (Thresh1, Thresh2). The base station device 20 transmits these parameters as part of the measurement configuration to the terminal device 10 using an RRC message.

[0071] The terminal device 10 determines that the event entering condition of the event condition A3 is satisfied when the measurement result of the cell satisfies Equation 3. Similarly, the terminal device 10 determines that the event leaving condition of the event condition A3 is satisfied when the measurement result satisfies Equation 4.

[0072] [Formula 3] Mn + Ofn + Ocn - Hys > Mp + Ofp + Ocp + Off

[0073] [Formula 4] Mn+Ofn+Ocn+Hys<Mp+Ofp+Ocp+Off

[0074] Furthermore, the terminal device 10 determines that the event entering condition of the event condition A4 is satisfied when the measurement result of the cell satisfies Equation 5. Similarly, the terminal device 10 determines that the event leaving condition of the event condition A4 is satisfied when the measurement result satisfies Equation 6.

[0075] [Formula 5] Mn+Ofn+Ocn-Hys>Thresh

[0076] [Formula 6] Mn+Ofn+Ocn+Hys<Thresh

[0077] Furthermore, the terminal device 10 determines that the event entering condition of the event condition A5 is satisfied when the measurement result of the cell satisfies both Equation 7 and Equation 8. Similarly, the terminal device 10 determines that the event leaving condition of the event condition A5 is satisfied when the measurement result satisfies either Equation 9 or Equation 10.

[0078] [Formula 7] Mp+Hys<Thresh1

[0079] [Formula 8] Mn+Ofn+Ocn-Hys>Thresh2

[0080] [Formula 9] Mp-Hys>Thresh1

[0081] [Formula 10] Mn+Ofn+Ocn+Hys<Thresh2

[0082] When setting the event condition T1, the base station device 20 also sets the event condition Ax at the same time. In other words, the base station device 20 needs to set, as a handover condition reset identifier, a measurement identifier linked to the event condition T1 and the event condition Ax in the terminal device 10.

[0083] Taking the above into consideration, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Note that, in the description of the embodiments of the present invention, if a specific description of well-known functions or configurations related to the embodiments of the present invention is determined to obscure the gist of the embodiments of the present invention, the detailed description will be omitted.

[0084] <First Embodiment> A terminal device 10 according to a first embodiment of the present invention has the capability to perform conditional handover and the capability to measure the current time. Based on a time-based conditional handover establishment condition (first condition) and a release condition (second condition), the terminal device 10 changes parameters applied to a quality-based conditional handover from a conventional conditional handover setting (first setting) to a conditional handover setting (second setting) compatible with the NES mode. Note that a state in which the NES mode is off, i.e., a cell state in the normal mode, is an example of the first cell state. Also, a state in which the NES mode is on, i.e., a cell state in the NES mode, is an example of the second cell state. Also, the normal mode is an example of the first mode, and the NES mode is an example of the second mode.

[0085] The base station device 20 in the first embodiment has the capability to perform conditional handover, the capability (function) to enable a power saving function in NES mode, and the capability to generate a conditional handover setting corresponding to the NES mode and notify the terminal device 10. The base station device 20 determines parameters related to the establishment condition (first condition) and departure condition (second condition) of a time-based conditional handover, and determines a conventional conditional handover setting (first setting) and a conditional handover setting corresponding to the NES mode (second setting) as parameters to be applied to a quality-based conditional handover, and transmits them to the terminal device 10.

[0086] 4 is a diagram showing an example of a handover sequence according to the embodiment. A cell 300A is a cell in which the terminal device 10 is located, and a cell 300B is a neighboring cell of the terminal device 10 and is one of candidate cells (target cells) for handover.

[0087] The terminal device 10 is connected to a base station device 20 (not shown) via a cell 300A. The base station device 20 initiates a conditional handover procedure if necessary based on the measurement results received from the terminal device 10. Typically, the base station device 20 requests handover preparation from the base station device 20 to which the notified cell (cell 300B) belongs, and information for accessing cell 300B is exchanged between the base station devices 20. Then, the base station device 20 transmits an RRC message (RRCReconfiguration) including information necessary for the conditional handover to the terminal device 10 (step S100).

[0088] The terminal device 10 receives an RRC message (RRCReconfiguration message) transmitted from the base station device 20. The base station device 20 may use an RRCSetup message or an RRCReestablishment message instead of the RRCReconfiguration message.

[0089] The base station device 20 transmits an RRC message including a conditional handover configuration. In the example of Fig. 4, the base station device 20 transmits the conditional handover configuration including at least a trigger condition related to the NES mode and cell configuration information of the cell 300B as a candidate cell.

[0090] The terminal device 10 determines that a trigger condition (measurement event) related to the NES mode exists based on the notified conditional handover configuration, and stores the corresponding candidate cell configuration. Then, the terminal device 10 generates a response message (RRCReconfigurationComplete message) to the received RRC message and transmits it to the base station device 20 (step S101). The terminal device 10 may use an RRCSetupComplete message or an RRCReestablishmentComplete message as a response based on the received RRC message.

[0091] Next, the terminal device 10 determines a target cell based on the received conditional handover configuration. The terminal device 10 starts measuring the handover candidate cell based on the measurement configuration included in the received RRC message. That is, the terminal device 10 regards the notified handover candidate cell as a measurement target cell (applicable cell(s)) and starts evaluating measurement events. The terminal device 10 starts evaluating the candidate cell at an appropriate timing according to a measurement event specified at the same time (described later). Then, when a set predetermined measurement event is established (triggered) (step S102), the terminal device 10 performs a conditional handover procedure.

[0092] The terminal device 10 attempts a conditional handover to the cell 300B, which is a candidate cell for the handover destination corresponding to the triggered measurement event (step S103). If the conditional handover is successful (i.e., if synchronization acquisition and the random access procedure are successful in the cell configuration of the applied cell 300B), the terminal device 10 generates an RRC message (RRCReconfigurationComplete message) indicating that the conditional handover was successful, and transmits the RRC message to the base station device 20 via the cell 300B (step S104).

[0093] After transmitting the RRC message (RRCReconfigurationComplete message), the terminal device 10 assumes that the conditional handover to the cell 300B has been successful. In this case, if there are conditional handover settings for cells other than the selected candidate cell (cell 300B), the terminal device 10 deletes all settings for the remaining candidate cells (step S105).

[0094] 5 is a diagram showing an example of the timing of event evaluation for conditional handover according to the embodiment. The horizontal axis of the diagram indicates the passage of time. The upper part of FIG. 5 shows the NES mode of the serving cell, and the lower part conceptually shows measurement events related to conditional handover applied by the terminal device 10. The NES mode of the serving cell starts from an NES mode off state (i.e., a normal cell), and at time T13, the NES mode is turned on (i.e., the cell state is in power saving mode).

[0095] Time T10 indicates the timing when the terminal device 10 receives an RRC message (e.g., an RRCReconfiguration message) from the base station device 20 of the serving cell. The RRC message includes at least a conditional handover configuration related to the NES mode and a candidate cell. Here, the base station device 20 sets a time-based event condition T1 and a cell quality-based event condition Ax (CondEventAx-1 and CondEventAx-2 in the figure) in the terminal device 10 as trigger conditions for the conditional handover configuration. The base station device 20 includes measurement identifiers specifying the event condition T1 and the event condition Ax in the conditional handover configuration identified by the same handover condition reconfiguration identifier.

[0096] The cell quality (reception quality) is calculated by measuring the synchronization signal block (SSB) or the channel state information reference signal (CSI-RS). The cell quality can be expressed using any of the following: Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), Received Signal Strength Indicator (RSSI), Signal to Interference plus Noise Ratio (SINR), and path loss.

[0097] The base station device 20 sets a measurement configuration to the terminal device 10 to report on the SSB identifier, the quality for each SSB, the cell quality based on the SSB, or the CSI-RS identifier, the quality for each CSI-RS resource, and the cell quality based on the CSI-RS resource.

[0098] The normal conditional handover setting applied to the event condition (trigger condition) is also referred to as the first setting, and the conditional handover setting corresponding to the NES mode applied to the event condition is also referred to as the second setting.

[0099] When the terminal device 10 receives the RRC message at time T10, it checks whether a trigger condition related to the NES mode is included (set) in the conditional handover configuration. More specifically, the terminal device 10 checks whether information triggered by a measurement event when a leaving condition of the measurement event is met is set in the set time-based conditional handover (CondEventT1) and / or whether an offset value corresponding to the NES mode is set for the set quality-based event condition Ax. The information that triggers CondEventT1 when a leaving condition of the measurement event is met is also referred to as leaving report information (ReportOnLeave).

[0100] Here, the report on leave information (ReportOnLeave) may be set as a parameter applicable only when the NES mode is supported, or may be set as a general-purpose parameter whose purpose includes changing the NES mode. Furthermore, the name of the parameter may be different.

[0101] If this information has been set, the terminal device 10 determines that the corresponding conditional handover configuration requires evaluation of a measurement event taking into account the NES mode of the serving cell. In other words, at time T10, the base station device 20 sets, for the time-based conditional handover (CondEventT1), information for triggering a measurement event when a leaving condition of the measurement event is met and / or sets an offset value corresponding to the NES mode for the quality-based event condition Ax, and transmits the set information to the terminal device 10.

[0102] Time T11 indicates the timing at which the terminal device 10 applies the trigger condition taking the NES mode into consideration. When the establishment condition (entering condition) of the set time-based conditional handover (CondEventT1) is satisfied, in other words, the terminal device 10 determines that the timing at which Equation 1 is satisfied is time T11. That is, the base station device 20 implicitly notifies the terminal device 10 of the timing at which the trigger condition taking the NES mode into consideration is applied by CondEventT1, leave report information (ReportOnLeave), and a related threshold (TH_t). Note that time T11 is an example of a first time.

[0103] The period between times T10 and T11 is a period in which trigger conditions taking the NES mode into consideration are not applied, and the terminal device 10 evaluates a normal event condition Ax (CondEventAx-1 in the figure) based on the measured cell quality. That is, the terminal device 10 performs quality-based event evaluation using conventional formulas 3 to 10 based on the set event condition. The normal event condition Ax (CondEventAx-1 in the figure) is an example of a first event condition.

[0104] The terminal device 10 applies a trigger condition that takes NES mode into consideration at time T11. Specifically, the base station device 20 applies an NES mode offset Off_nes, which is an additional parameter, to the event condition Ax, and starts evaluating the event condition Ax that takes NES mode into consideration (CondEventAx-2 in the figure). The terminal device 10 may start an RRC timer at time T11 to measure the time for applying the NES mode offset Off_nes. Here, the RRC timer is set to the same value as the parameter duration of the duration information related to CondEventT1. Note that the event condition Ax that takes NES mode into consideration (CondEventAx-2 in the figure) is an example of a second event condition.

[0105] For example, when event condition A3 is set, the terminal device 10 evaluates the measurement event using formulas 11 and 12 from time T11. When the measurement result satisfies formula 11, the terminal device 10 determines that the event entering condition of event condition A3 that takes NES mode into consideration is satisfied. Similarly, when the measurement result satisfies formula 12, the terminal device 10 determines that the event leaving condition of event condition A3 that takes NES mode into consideration is satisfied.

[0106] [Formula 11] Mn+Ofn+Ocn-Hys+Off_nes>Mp+Ofp+Ocp+Off

[0107] [Formula 12] Mn+Ofn+Ocn+Hys+Off_nes<Mp+Ofp+Ocp+Off

[0108] Furthermore, for example, when event condition A4 is set, the terminal device 10 evaluates the measurement event using formulas 13 and 14 from time T11. When the measurement result satisfies formula 13, the terminal device 10 determines that the event entering condition of event condition A4 that takes NES mode into consideration is satisfied. Similarly, when the measurement result satisfies formula 14, the terminal device 10 determines that the event leaving condition of event condition A4 that takes NES mode into consideration is satisfied.

[0109] [Formula 13] Mn+Offn+Ocn-Hys+Off_nes>Thresh

[0110] [Formula 14] Mn+Offn+Ocn+Hys+Off_nes<Thresh

[0111] Furthermore, for example, when event condition A5 is set, the terminal device 10 evaluates the measurement event using formulas 15 to 18 from time T11. When the measurement result satisfies both formulas 15 and 16, the terminal device 10 determines that the event entering condition of event condition A5 that takes NES mode into consideration is satisfied. Similarly, when the measurement result satisfies either formula 17 or formula 18, the terminal device 10 determines that the event leaving condition of event condition A5 that takes NES mode into consideration is satisfied.

[0112] [Formula 15] Mp+Hys<Thresh1

[0113] [Formula 16] Mn+Ofn+Ocn-Hys+Off_nes>Thresh2

[0114] [Formula 17] Mp-Hys>Thresh1

[0115] [Formula 18] Mn+Ofn+Ocn+Hys+Off_nes<Thresh2

[0116] Note that the method of applying the parameters of the event condition Ax (CondEventAx-2) taking these NES modes into consideration may be a method other than that exemplified above, as long as it makes it easier to satisfy the event establishment condition than the conventional event condition Ax. For example, a negative offset that lowers the thresholds (Thresh, Thresh1, Thresh2) may be added, or a more relaxed threshold may be used to evaluate the event. For example, an offset Ocp_nes that is lower than Ocp may be applied instead of the cell-specific offset (Ocn, Ocp), or an offset Ocn_nes of a neighboring cell that is higher than Ocn may be applied instead. Furthermore, the above-mentioned parameter application methods may be appropriately combined.

[0117] If any of the event conditions Ax (CondEventAx-2) that take the NES mode into consideration is met, the terminal device 10 stops the RRC timer if it is timing the RRC timer, and at the same time stops evaluating the event condition T1 (CondEventT1).

[0118] Time T12 indicates the timing at which the leaving condition of the time-based event condition T1 is satisfied. When the leaving condition (entering condition) of the set time-based conditional handover (CondEventT1) is satisfied, in other words, the terminal device 10 determines that the timing at which Equation 2 is satisfied is time T12. Note that, if the RRC timer is being timed, the terminal device 10 may regard the time at which the RRC timer expires as time T12. At time T12, the terminal device 10 cancels the event condition Ax (CondEventAx-2) that takes the NES mode into consideration and triggers CondEventT1. Then, the terminal device 10 starts the conditional handover procedure based on the candidate cell setting corresponding to CondEventT1. Note that CondEventT1 is an example of a third event condition. Also, time T12 is an example of a second time.

[0119] 6 is a diagram showing another example of the event evaluation timing for conditional handover according to the embodiment. Below, the description of the parts common to Fig. 5 will be omitted, and the parts different from Fig. 5 will be described. The NES mode of the serving cell starts from the NES mode OFF state (i.e., a normal cell), and at time T23, the NES mode is turned ON.

[0120] Time T20 indicates the timing when the terminal device 10 receives an RRC message (e.g., an RRCReconfiguration message) from the base station device 20 of the serving cell. The RRC message includes at least a conditional handover configuration related to the NES mode and a candidate cell. Here, the base station device 20 sets a time-based event condition T1 and a cell quality-based event condition Ax (e.g., CondEventAx-2 in FIG. 6 ) in the terminal device 10 as trigger conditions for the conditional handover configuration. The base station device 20 includes measurement identifiers specifying the event condition T1 and the event condition Ax in the conditional handover configuration identified by the same handover condition reconfiguration identifier.

[0121] The procedure and method by which the terminal device 10 checks whether a trigger condition related to the NES mode is included (set) in the conditional handover configuration may be the same as those in Fig. 5. At time T20, the base station device 20 sets an offset value corresponding to the NES mode for the leave report information (ReportOnLeave) and / or the quality-based event condition Ax for the time-based conditional handover (CondEventT1), and transmits the set information to the terminal device 10.

[0122] Time T21 indicates the timing at which the terminal device 10 activates the trigger of the quality-based event condition Ax (CondEventAx-2) that takes the NES mode into consideration and determines that the conditional handover procedure can be performed. When the establishment condition (entering condition) of the set time-based conditional handover (CondEventT1) is satisfied, in other words, the terminal device 10 determines that the timing at which Equation 1 is satisfied is time T21. That is, the base station device 20 implicitly notifies the terminal device 10 of the timing at which the conditional handover procedure that takes the NES mode into consideration can be performed by CondEventT1, leave report information (ReportOnLeave), and a related threshold (TH_t).

[0123] At time T20, the terminal device 10 starts evaluating the event condition Ax (CondEventAx-2) that takes the NES mode into consideration. The terminal device 10 performs quality-based event evaluation based on the set event condition, for example, using Equations 11 to 18. However, the terminal device 10 determines not to start the conditional handover procedure even if the event Ax condition (CondEventAx-2) is satisfied (triggered) between times T20 and T21.

[0124] On the other hand, if the event condition Ax (CondEventAx-2) is satisfied (triggered) after time T21, the terminal device 10 determines that the conditional handover procedure may be performed. Note that the terminal device 10 may suspend the satisfied conditional handover procedure and resume it after time T21. Note that time T21 is an example of the first time.

[0125] Time T22 indicates the timing at which the leaving condition of the time-based event condition T1 is satisfied. When the leaving condition (entering condition) of the set time-based conditional handover (CondEventT1) is satisfied, in other words, the terminal device 10 determines that the timing at which Equation 2 is satisfied is time T22. At time T22, the terminal device 10 cancels the event condition Ax (CondEventAx-2) that takes the NES mode into consideration and triggers CondEventT1. Then, the terminal device 10 starts the conditional handover procedure based on the candidate cell setting corresponding to CondEventT1. Note that time T22 is an example of a second time.

[0126] Note that since the event condition T1 is a measurement event for a non-terrestrial network (NTN), the terminal device 10 notifies the base station device 20 of information indicating that it does not support NTN but supports the event condition T1 using the terminal device capability (UE capability). The terminal device 10 may also notify the base station device 20 of information indicating that it supports a modified event condition T1 (i.e., an evaluation is performed by applying report information on leaving (ReportOnLeave) to the event condition T1). This information may be implicitly indicated by notifying one-bit information indicating support for conditional handover taking NES mode into consideration. Furthermore, a terminal device 10 that supports conditional handover taking NES mode into consideration may impose a restriction that requires support for the event condition T1.

[0127] If the conditional handover fails, or if a radio link failure occurs due to a deterioration in the cell quality of the serving cell making it difficult to continue communication, and if the conditional handover configuration taking the NES mode into consideration has been notified, the terminal device 10 may attempt a re-establishment (RRC re-establishment) procedure excluding a specified cell that meets the conditions. The base station device 20 may transmit, to the terminal device 10, information indicating permission for an attempt at a re-establishment procedure excluding the specified cell as part of the conditional handover configuration.

[0128] When attempting a reconnection procedure, the terminal device 10 may exclude the serving cell before reconnection as the predetermined cell. Alternatively, the terminal device 10 may exclude the serving cell before reconnection after the establishment condition of the event condition T1 is satisfied as the predetermined cell. In other words, the terminal device 10 determines whether the serving cell before reconnection can be selected as the reconnection destination cell based on whether the establishment condition of the event condition T1 is satisfied.

[0129] Furthermore, when the leave report information (ReportOnLeave) is set, the terminal device 10 may exclude the serving cell before reconnection after satisfying the leave condition of the event condition T1 as the specified cell. In other words, the terminal device 10 determines whether the serving cell before reconnection can be selected as the reconnection destination cell based on whether the leave condition of the event condition T1 is satisfied. By applying these determinations to the reconnection procedure, the terminal device 10 can reuse the conditional handover setting and exclude cells in the NES mode that are not suitable for stay from the reconnection destination cells. Note that the terminal device 10 may delete the conditional handover setting corresponding to the specified cell instead of excluding the specified cell.

[0130] When the terminal device 10 selects a cell other than the excluded cell and that matches the cell (applicable cell) indicated in the conditional handover configuration as the reconnection destination cell, the terminal device 10 reuses the conditional handover configuration and starts the reconnection procedure. That is, the terminal device 10 regards the matching conditional handover configuration as the reconnection destination cell configuration.

[0131] Furthermore, the terminal device 10 may directly trigger a measurement event based on L1 signaling (e.g., PDCCH) or L2 signaling (e.g., MAC CE) that indicates the triggering of an event condition regardless of the current time (timer) or cell quality, or may activate a suspended measurement configuration or measurement report.

[0132] As described above, according to the first embodiment, the start timing of event evaluation for conditional handover taking the NES mode into consideration can be notified by utilizing the establishment conditions of conventional time-based measurement events. Therefore, the terminal device 10 can execute conditional handover taking the NES mode into consideration at an appropriate timing without receiving a new signal related to timing notification from the base station device 20. The base station device 20 can prevent degradation of the user experience due to changes in the NES mode, and can efficiently perform mobility control for the terminal device 10. That is, the mobility control methods of the base station device 20 and the terminal device 10 that support NES can be optimized, respectively. Furthermore, the efficiency of NES can be improved.

[0133] <Second Embodiment> A second embodiment will be described. The second embodiment shows a method for performing a conditional handover that takes the NES mode into consideration without using a time-based event condition T1. Note that a description of configurations, functions, or procedures common to the first and second embodiments will be omitted. That is, the following mainly describes the differences from the first embodiment.

[0134] The terminal device 10 according to the second embodiment of the present invention has the capability to perform conditional handover and the capability to measure the current time. The terminal device 10 applies a conditional handover setting (second setting) corresponding to the NES mode based on the current time.

[0135] The base station device 20 in the second embodiment has the capability to perform conditional handover, the capability to enable a power saving function in NES mode, and the capability to generate a conditional handover setting corresponding to the NES mode and notify the terminal device 10. The base station device 20 determines parameters of the conditional handover setting (second setting) corresponding to the NES mode based on the time at which the cell state transitions to the NES mode, and transmits the parameters to the terminal device 10.

[0136] 7 is a diagram showing another example of the event evaluation timing for conditional handover according to the embodiment. Below, the description of the parts common to Fig. 5 will be omitted, and the parts different from Fig. 5 will be described. The NES mode of the serving cell starts from the NES mode OFF state (i.e., normal cell), and at time T33, the NES mode is turned ON.

[0137] Time T30 indicates the timing when the terminal device 10 receives an RRC message (e.g., an RRCReconfiguration message) from the base station device 20 of the serving cell. The RRC message includes at least a conditional handover setting related to the NES mode and a candidate cell. Here, the base station device 20 sets a cell quality-based event condition Ax in the terminal device 10 as a trigger condition for the conditional handover setting.

[0138] The terminal device 10 checks whether a trigger condition related to the NES mode is included (set) in the conditional handover configuration. More specifically, the terminal device 10 checks whether a time-based offset value corresponding to the NES mode and timing information for applying the offset value are set for the set quality-based event condition Ax. The timing for applying the time-based offset value may be, for example, information indicated in the Gregorian calendar, such as the event condition T1, or information indicating the elapsed time starting from time T30.

[0139] If this information is set, the terminal device 10 determines that the corresponding conditional handover configuration requires evaluation of the measurement event taking into account the NES mode of the serving cell. In other words, at time T30, the base station device 20 sets a time-based offset value corresponding to the NES mode separately for the quality-based event condition Ax and transmits the set value to the terminal device 10.

[0140] Time T31 indicates the timing at which the terminal device 10 applies a time-based trigger condition that takes NES mode into consideration. The terminal device 10 determines that the timing at which a specified time has elapsed is time T31. In other words, the base station device 20 notifies the terminal device 10 of timing information for applying the trigger condition that takes NES mode into consideration.

[0141] The period from time T30 to time T31 is a period in which the trigger condition considering the NES mode is not applied, and the terminal device 10 evaluates the normal event condition Ax (CondEventAx-1) based on the measured cell quality. That is, the terminal device 10 performs quality-based event evaluation using conventional formulas 3 to 10 based on the set event condition.

[0142] At time T31, the terminal device 10 applies a trigger condition that takes the NES mode into consideration. Specifically, the base station device 20 applies an additional parameter, the NES mode offset Off_nes, to the event condition Ax, and starts evaluating the event condition Ax (CondEventAx-2) that takes the NES mode into consideration. Note that time T31 is an example of a first time.

[0143] At time T31, the terminal device 10 starts evaluating the event condition Ax (CondEventAx-2) that takes the NES mode into consideration. Based on the set event condition, the terminal device 10 performs quality-based event evaluation using, for example, Equations 11 to 18.

[0144] Time T32 indicates the timing at which the application time of the NES mode offset Off_nes ends. At time T32, the terminal device 10 stops applying the event condition Ax (CondEventAx-2) that takes the NES mode into consideration. After time T32, the terminal device 10 may start evaluating the conventional event condition Ax (CondEventAx-1), or may forcibly trigger CondEventAx at the timing of time T32 and start a conditional handover procedure based on the candidate cell setting corresponding to CondEventAx. Note that time T32 is an example of a second time.

[0145] 8 is a diagram showing another example of the event evaluation timing for conditional handover according to the embodiment. Below, the description of the parts common to Fig. 5 will be omitted, and the parts different from Fig. 5 will be described. The NES mode of the serving cell starts from the NES mode OFF state (i.e., a normal cell), and at time T43, the NES mode is turned ON.

[0146] Time T40 indicates the timing when the terminal device 10 receives an RRC message (e.g., an RRCReconfiguration message) from the base station device 20 of the serving cell. The RRC message includes at least a conditional handover setting related to the NES mode and a candidate cell. Here, the base station device 20 sets a time-based event condition T2 in the terminal device 10 as a trigger condition for the conditional handover setting.

[0147] The event condition T2 is a time-based event condition T1 plus a condition related to the quality of neighboring cells. For example, if both Equation 1 and Equation 5 are satisfied, the terminal device 10 determines that the event entering condition of the event condition T2 taking the NES mode into consideration is satisfied. Similarly, if either Equation 2 or Equation 6 is satisfied, the terminal device 10 determines that the event leaving condition of the event condition T2 taking the NES mode into consideration is satisfied. Alternatively, the terminal device 10 may determine that the event leaving condition of the event condition T2 taking the NES mode into consideration is satisfied if Equation 2 is satisfied.

[0148] The terminal device 10 determines whether a trigger condition related to the NES mode is included (set) in the conditional handover setting based on whether the event condition T2 is set. The base station device 20 sets leave report information (ReportOnLeave) for the time-based conditional handover (CondEventT2 in the figure) at time T40 and transmits it to the terminal device 10.

[0149] When the terminal device 10 satisfies the entering condition of the set time-based conditional handover (CondEventT2), in other words, it determines that the timing at which Equation 1 and Equation 5 are satisfied is time T41. That is, the base station device 20 implicitly notifies the terminal device 10 of the timing at which the conditional handover procedure taking the NES mode into consideration can be executed by CondEventT2, leave report information (ReportOnLeave), and a related threshold (TH_t). Note that time T41 is an example of a first time.

[0150] Time T42 indicates the timing at which the leaving condition of the time-based event condition T2 is satisfied. When the leaving condition (entering condition) of the set time-based conditional handover (CondEvent T2) is satisfied, the terminal device 10 determines that the satisfying timing is time T42. The terminal device 10 triggers CondEvent T2 at time T42. Then, the terminal device 10 starts the conditional handover procedure based on the candidate cell setting corresponding to CondEvent T2. Note that time T42 is an example of a second time.

[0151] As described above, according to the second embodiment, the start timing of event evaluation for conditional handover taking the NES mode into consideration can be notified by using a time-based parameter or a time-based measurement event taking cell quality into consideration. Therefore, the terminal device 10 can execute conditional handover taking the NES mode into consideration at an appropriate timing without receiving a new signal related to timing notification from the base station device 20. The base station device 20 can prevent degradation of the user experience due to a change in NES mode, and can efficiently perform mobility control for the terminal device 10. That is, the mobility control methods of the base station device 20 and the terminal device 10 that support NES can be optimized, respectively. Furthermore, the efficiency of NES can be improved.

[0152] 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 may be modified or improved without departing from the spirit thereof, and the present invention also includes equivalents. For example, an event condition Ax (CondEventAx-2) that takes NES mode into consideration may not be set, or the applicable event condition may be switched to another linked event condition rather than switching the parameters of the event condition. Specifically, event condition A3 may be switched to event condition A4.

[0153] <Hardware Configuration of Each Device in Each Embodiment> The hardware configuration of each device in the wireless communication system 1 in each embodiment will be described with reference to FIGS. 10 and 11. FIG.

[0154] 10 is a diagram illustrating an example of the hardware configuration of the terminal device 10. As illustrated in FIG. 10, the terminal device 10 includes, as hardware components, a radio frequency (RF) circuit 32 including an antenna 31, a central processing unit (CPU) 33, and a memory 34. The terminal device 10 may further include a display device such as a liquid crystal display (LCD) connected to the CPU 33. The memory 34 includes at least one of a random access memory (RAM) such as a synchronous dynamic random access memory (SDRAM), a read only memory (ROM), and a flash memory, and stores programs, control information, and data signals.

[0155] The correspondence between the functional configuration of the terminal device 10 shown in Fig. 2 and the hardware configuration of the terminal device 10 shown in Fig. 10 will be described. The transmitting / receiving antenna unit 19, the transmitter 17, and the receiver 15 are realized by, for example, an RF circuit 32, or an antenna 31 and an RF circuit 32. The control unit 13 and the processing unit 11 are realized by, for example, a CPU 33, a memory 34, a digital electronic circuit (not shown), etc. Examples of the digital electronic circuit include an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), and a large scale integration (LSI).

[0156] Fig. 11 is a diagram illustrating an example of the hardware configuration of the base station device 20. As shown in Fig. 11, the base station device 20 has, as hardware components, an RF circuit 42 equipped with an antenna 41, a CPU 43, a DSP 44, a memory 45, and a network IF (Interface) 46. The CPU 43 is connected via a bus to enable input and output of various signals and data signals. The memory 45 includes at least one of a RAM such as an SDRAM, a ROM, and a flash memory, and stores programs, control information, and data signals.

[0157] The correspondence between the functional configuration of the base station device 20 shown in Fig. 3 and the hardware configuration of the base station device 20 shown in Fig. 11 will be described. The transmitting / receiving antenna unit 29, the transmitter 27, and the receiver 25 are realized by, for example, an RF circuit 42, or an antenna 41 and an RF circuit 42. The control unit 23 and the processing unit 21 are realized by, for example, a CPU 43, a DSP 44, a memory 45, a digital electronic circuit (not shown), etc. Examples of the digital electronic circuit include an ASIC, an FPGA, and an LSI.

[0158] 1 Wireless communication system 10 Terminal device 20 Base station device 30 Core network 11, 21 Processing unit 13, 23 Control unit 15, 25 Receiving unit 17, 27 Transmitting unit 19, 29 Transmitting and receiving antenna unit 31, 41 Antenna 32, 42 RF circuit 33, 43 CPU 34, 45 Memory 44 DSP 46 Network IF 111, 211 Wireless resource processing unit 113, 213 NES information processing unit 300 (300A to 300B) Cell

Claims

1. A terminal device that communicates with a base station device, comprising: a control unit capable of performing control corresponding to a first cell state that is a first mode, and a second cell state that is a second mode different from the first mode; a receiving unit capable of receiving from the base station device a first condition for determining that a first time has been exceeded, and a second condition for determining that a second time has passed, which is a predetermined duration from the first time, and a processing unit that evaluates a first event condition for a conditional handover corresponding to the first cell state until the first condition is satisfied, evaluates a second event condition for a conditional handover corresponding to the second cell state when the first condition is satisfied, and initiates a conditional handover procedure when the second condition is satisfied.

2. The terminal device according to claim 1, wherein the second cell state is a power saving mode that reduces power consumption of the cell.

3. A terminal device as described in claim 2, characterized in that the first condition is a condition indicating that a third event condition is met when the first time is exceeded, and the second condition is a condition indicating that the third event condition is no longer met when the second time is a predetermined duration after the first time.

4. The terminal device according to claim 3, characterized in that, when the first condition is satisfied, the processing unit is capable of evaluating the second event condition of the conditional handover by applying a parameter related to the second cell state to the first event condition of the conditional handover corresponding to the first cell state.

5. The terminal device according to claim 3, characterized in that the processing unit evaluates the second event condition of the conditional handover simultaneously with receiving the first condition and the second condition, does not start the conditional handover procedure even if the second event condition is met, and can start the conditional handover procedure when the first condition is satisfied and the second event condition is met.

6. The terminal device according to claim 2, characterized in that, when the processing unit is notified of information indicating permission of an RRC reconnection procedure based on a conditional handover setting corresponding to the second cell state, when performing an RRC reconnection procedure using the conditional handover setting, the processing unit is capable of performing the RRC reconnection procedure by excluding a specified cell.

7. A base station device that communicates with a terminal device, comprising: a control unit capable of performing control corresponding to a first cell state which is a first mode, and a second cell state which is a second mode different from the first mode; a transmission unit capable of transmitting to the terminal device a first condition for determining that a first time has been exceeded, and a second condition for determining that a second time has passed, which is a predetermined duration from the first time, and a processing unit capable of causing the terminal device to evaluate a first event condition for a conditional handover corresponding to the first cell state until the first condition is satisfied, causing the terminal device to evaluate a second event condition for a conditional handover corresponding to the second cell state when the first condition is satisfied, and providing information for starting a conditional handover procedure when the second condition is satisfied.

8. The base station device according to claim 7, wherein the second cell state is a power saving mode that reduces power consumption of the cell.

9. The base station device according to claim 8, characterized in that the first condition is a condition indicating that a third event condition is met when the current time exceeds a predetermined time, and the second condition is a condition indicating that the third event condition is no longer met when a predetermined duration has elapsed from the time of the first condition.

10. The base station device according to claim 9, characterized in that the transmitting unit can provide the terminal device with information for evaluating the second event condition of the conditional handover by applying a parameter related to the second cell state to the first event condition of the conditional handover corresponding to the first cell state when the first condition is satisfied.

11. The base station device according to claim 10, characterized in that the transmitting unit is capable of causing the terminal device to evaluate the second event condition of the conditional handover simultaneously with receiving the first condition and the second condition, while not initiating the conditional handover procedure even if the second event condition is established, and providing information for initiating the conditional handover procedure when the first condition is satisfied and the second event condition is established.

12. The base station device according to claim 8, characterized in that, when the transmitting unit causes the terminal device to perform an RRC reconnection procedure using the conditional handover setting, it can notify the terminal device of information indicating permission for an RRC reconnection procedure excluding a specified cell based on a conditional handover setting corresponding to the state of the second cell.

13. A handover control method executed in a terminal device communicating with a base station device, comprising the steps of: performing control corresponding to a first cell state which is a first mode; and a second cell state which is a second mode different from the first mode; receiving from the base station device a first condition for determining that a first time has been exceeded, and a second condition for determining that a second time which is a predetermined duration from the first time has passed; evaluating a first event condition for conditional handover corresponding to the state of the first cell until the first condition is satisfied, evaluating a second event condition for conditional handover corresponding to the state of the second cell when the first condition is satisfied, and starting a conditional handover procedure when the second condition is satisfied.

14. A handover control method for a base station device communicating with a terminal device, comprising: a step of performing control corresponding to a first cell state which is a first mode and a second cell state which is a second mode different from the first mode, respectively; a step of transmitting to the terminal device a first condition for determining that a first time has been exceeded and a second condition for determining that a second time which is a predetermined duration has elapsed from the time of the first condition has elapsed; and a step of causing the terminal device to evaluate a first event condition for conditional handover corresponding to the state of the first cell until the first condition is satisfied, and, if the first condition is satisfied, causing the terminal device to evaluate a second event condition for conditional handover corresponding to the state of the second cell, and, if the second condition is satisfied, providing information for starting a conditional handover procedure.

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