Terminal equipment that improves connection destination change processing

Abstract

To improve efficiency in switching between cells to which a terminal device is connected. [Solution] When a terminal device has configuration information about a first other base station device, a base station device notifies the terminal device whether or not to delete the configuration information about the first other base station device in response to the terminal device connecting to a second other base station device different from the first other base station device due to handover or a change or addition of a secondary cell.

Description

[Technical Field]

[0001] The present invention relates to an advanced technology for connection destination change processing. [Background technology]

[0002] In cellular communication systems, handover techniques are used to ensure communication continuity by switching the connection destination of a terminal device in response to factors such as the movement of the terminal device. A standard handover technique involves initiating handover preparations and other processes on the core network side after the communication quality of the currently connected wireless link in the terminal device deteriorates, and then transmitting an instruction message from a base station device to the terminal device. However, this technique requires time for processing from the actual deterioration of communication quality until the transmission of the handover instruction, which can result in a prolonged period of time during which communication is unavailable or communication quality is insufficient. In response to this, a technique has been defined in which the preparations and other processes are performed in advance, and the terminal device switches the connection destination cell without receiving an instruction message from a base station device when certain conditions are met (see Non-Patent Document 1). The certain conditions include, for example, when the wireless quality of a neighboring cell becomes better than the wireless quality of the currently connected cell by a predetermined level or more, or when the wireless quality of the currently connected cell falls below a predetermined value. According to this method, preparation for handover is completed on the core network side before a deterioration in communication quality occurs that would require handover, and therefore the time during which communication is unavailable or communication quality is insufficient can be significantly reduced. This type of handover is called a conditional handover. Similarly, in multi-connectivity (MC) or the like in which a terminal device connects to multiple cells, preparation processes and the like can be performed in advance, and when a predetermined condition is met in the terminal device, the terminal device can add or change a secondary cell without receiving an instruction message from the base station device. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] 3GPP (registered trademark) TR38.874, V16.0.0, December 2018 Summary of the Invention [Problem to be solved by the invention]

[0004] In a conditional handover or the addition or change of a secondary cell, the pre-configured setting information in the terminal device is deleted after the terminal device connects to the new connection destination. Therefore, in an environment where the connection destination cell is frequently switched, such as an environment where small cells are used, the setting information is deleted and new pre-configuration is performed each time, which is inefficient. [Means for solving the problem]

[0005] The present invention provides a technique for improving the efficiency of switching between cells to which a terminal device is connected.

[0006] A base station device according to one embodiment of the present invention has configuration information about a first other base station device that provides a cell that is a pre-set candidate handover destination for a terminal device currently connected to the base station device, or that provides a cell that is a pre-set candidate destination for adding or changing a secondary cell for a terminal device currently connected to a cell provided by the base station device as a primary cell, the configuration information including conditions for the terminal device to connect to the first other base station device by handover or by changing or adding a secondary cell, and communication parameters when the terminal device connects to the first other base station device, and has a notification means for notifying the terminal device whether or not the configuration information about the first other base station device should be deleted in response to the terminal device connecting to a second other base station device different from the first other base station device by handover or by changing or adding a secondary cell.

[0007] A base station device according to another aspect of the present invention has an acquisition means for acquiring predetermined information about a second other base station device that is a candidate for connection upon handover from a first other base station device pre-configured for a terminal device or upon change or addition of a secondary cell, the predetermined information including at least one of conditions for the terminal device to connect to the second other base station device by handover or change or addition of a secondary cell, communication parameters when the terminal device connects to the second other base station device, and identification information corresponding to the combination of the conditions and the communication parameters, and a control means for controlling handover or change or addition of a secondary cell for the terminal device using the predetermined information about the second other base station device.

[0008] A terminal device according to one embodiment of the present invention comprises: a holding means for holding configuration information for a first other base station device that is a candidate for handover from a base station device to which the terminal device is currently connected, the configuration information including conditions for handing over to the first other base station device and communication parameters when handing over to the first other base station device; and a receiving means for receiving a notification from the base station device indicating whether or not the configuration information for the first other base station device should be deleted when the terminal device hands over to a second other base station device different from the first other base station device, wherein the holding means holds the configuration information for the first other base station device without deleting it when the terminal device hands over to a second other base station device different from the first other base station device in a state where the notification indicates that the configuration information for the first other base station device should not be deleted; and deletes the configuration information for the first other base station device when the terminal device hands over to a second other base station device different from the first other base station device in a state where the notification indicates that the configuration information for the first other base station device should be deleted.

[0009] A terminal device according to another aspect of the present invention comprises connection means capable of connecting in parallel to a first base station device that provides a primary cell and a second base station device that provides a secondary cell; holding means for holding configuration information for a first other base station device that provides a candidate cell to be changed to or added as the secondary cell when the secondary cell is changed or added while connected to the second base station device, the configuration information including conditions for the terminal device to connect to the first other base station device and communication parameters when connected to the first other base station device; and means for holding configuration information for the terminal device when the terminal device connects to a second other base station device different from the first other base station device and uses a cell provided by the second other base station device as the secondary cell. and a receiving means for receiving from the first base station device a notification as to whether the setting information for the first other base station device should be deleted when a secondary cell is added or when the secondary cell is changed from another cell, wherein the holding means holds the setting information for the first other base station device without deleting it when a handover is performed from the first base station device to a third other base station device in a state where the notification indicates that the setting information for the first other base station device should not be deleted, and deletes the setting information for the first other base station device when a handover is performed from the first base station device to the third other base station device in a state where the notification indicates that the setting information for the first other base station device should be deleted.

[0010] A terminal device according to yet another aspect of the present invention includes connection means capable of connecting in parallel to a first base station device that provides a primary cell and a second base station device that provides a secondary cell; holding means for holding configuration information about a first other base station device that provides a candidate cell to which the secondary cell is changed or to which the secondary cell is to be added when the secondary cell is changed or the secondary cell is added while connected to the second base station device, the configuration information including conditions for the terminal device to connect to the first other base station device and communication parameters when connected to the first other base station device; and holding means for holding configuration information when the terminal device connects to a second other base station device different from the first other base station device and adds a cell provided by the second other base station device as the secondary cell, and when the terminal device connects to the second other base station device different from the first other base station device and adds a cell provided by the second other base station device as the secondary cell, the configuration information including conditions for the terminal device to connect to the first other base station device and communication parameters when connected to the first other base station device. and a receiving means for receiving from the first base station device a notification of whether or not the configuration information for the first other base station device should be deleted when the secondary cell is changed, wherein the holding means holds the configuration information for the first other base station device without deleting it when the notification indicates that the configuration information for the first other base station device should not be deleted and when the addition or change of the secondary cell results in a connection to the second other base station device without connecting to the first other base station device, and deletes the configuration information for the first other base station device when the notification indicates that the configuration information for the first other base station device should be deleted and when the addition or change of the secondary cell results in a connection to the second other base station device without connecting to the first other base station device. [Effects of the Invention]

[0011] According to the present invention, it is possible to improve the efficiency of switching between cells to which a terminal device is connected. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a wireless communication system. [Figure 2]FIG. 2 is a diagram illustrating an example of the hardware configuration of a base station device and a terminal device. [Figure 3] FIG. 2 is a diagram illustrating an example of the functional configuration of a handover source base station device. [Figure 4] FIG. 2 is a diagram illustrating an example of the functional configuration of a base station device at a handover destination. [Figure 5] FIG. 2 is a diagram illustrating an example of a functional configuration of a terminal device. [Figure 6] FIG. 1 is a diagram illustrating an example of a flow of processing executed in a wireless communication system. [Figure 7] FIG. 1 is a diagram illustrating an example of a flow of processing executed in a wireless communication system. [Figure 8] FIG. 1 is a diagram illustrating an example of a flow of processing executed in a wireless communication system. [Figure 9] FIG. 1 is a diagram illustrating an example of a flow of processing executed in a wireless communication system. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention as claimed, and not all combinations of features described in the embodiments are necessarily essential to the invention. Two or more of the features described in the embodiments may be combined in any desired manner. Furthermore, the same reference numerals are used to designate identical or similar components, and redundant descriptions will be omitted.

[0014] (System Configuration) 1 shows an example of the configuration of a wireless communication system according to this embodiment. In this wireless communication system, a plurality of base station devices 101 to 106 form cells 111 to 116, respectively, and a terminal device 121 moves across these cells. The base station devices 101 to 106 and the terminal device 121 are configured to operate, for example, in accordance with the Long Term Evolution (LTE) standard or the fifth-generation (5G) New Radio (NR) standard. Note that this is just one example, and the following discussion can be applied to any system in which the terminal device 121 communicates while switching its connection destination base station device by handover while moving. In this embodiment, it is assumed that the terminal device 121 is connected to the base station device 101, and then, upon moving into the range of a cell 112 or the like, a handover process is executed and the connection destination base station device is switched.

[0015] In this embodiment, pre-configuration for handover of the terminal device 121 is performed, for example, when the terminal device 121 establishes a connection with a base station device or when the wireless quality with the currently connected base station device 101 deteriorates to a certain degree. The pre-configuration state here refers to a state in which the terminal device 121 has completed configuration of parameters and the like for connecting to a candidate handover destination, but the terminal device 121 has not actually switched the destination base station device. The pre-configuration includes conditions for actually performing handover, and when the terminal device 121 determines that the conditions are satisfied, it disconnects from the currently connected base station device and attempts to establish synchronization with and connect to a new destination base station device. A handover in which the terminal device 121 autonomously switches the destination using such pre-configuration and when the terminal device 121 determines that the conditions are satisfied is called a conditional handover.

[0016] When a conditional handover is performed, the currently connected base station device transmits a handover request message (HANDOVER REQUEST) including information on parameters currently used by the terminal device 121 to another base station device that is a candidate for handover. The candidate base station device then transmits a response message (HANDOVER REQUEST ACKNOWLEDGE) to the message, including information on parameters to be used when the terminal device 121 is handed over, to the base station device to which the terminal device 121 is currently connected. The candidate base station device then retains the transmitted information on parameters as preconfigured information. The currently connected base station device or the candidate base station device determines conditions that must be satisfied when handing over to the candidate base station device. The currently connected base station device then notifies the terminal device 121 of the preconfigured information including information on parameters to be used when handing over to the candidate base station device that is a candidate for handover, and the handover conditions. This notification can be performed, for example, using a radio resource control (RRC) message. In one example, the pre-configuration information is notified to the terminal device 121 by an RRCReconfiguration message.

[0017] Upon receiving this preconfiguration information, the terminal device 121 stores the preconfiguration information and begins monitoring whether the handover conditions are satisfied. If the conditions are satisfied, the terminal device 121 performs processes such as disconnecting from the currently connected base station device and establishing synchronization with the handover destination base station device in order to actually switch the connection destination. Note that there may be multiple candidate base station devices as the handover destination. Therefore, the preconfiguration information is configured separately for each of one or more candidate base station devices as the handover destination. Therefore, the preconfiguration information for each base station device may include handover identification information that identifies the respective preconfiguration information. Furthermore, since one base station device may configure multiple cells, preconfiguration information may be configured separately for the multiple cells. The terminal device 121 monitors whether the conditions for executing a handover corresponding to each of the multiple preconfiguration information are satisfied, activates the preconfiguration information containing the satisfied conditions, and executes the handover. In this way, the terminal device 121 can complete the conditional handover and, accordingly, communicates using communication parameters related to the destination base station device (cell) after the handover.

[0018] Furthermore, the terminal device 121 deletes unused preset information from the preset information (i.e., preset information related to a base station device not selected as the handover destination). The handover source base station device also instructs other base station devices that are candidates for the handover destination and not selected as the handover destination to delete the preset information for handover of the terminal device 121. As a result, the preset information is deleted after the conditional handover is completed.

[0019] On the other hand, for example, when the terminal device 121 is moving at high speed or when the cells 111 to 116 are small cells, it is expected that the terminal device 121 will frequently perform handover. In such cases, the generation and deletion of preset information is frequently repeated, which is inefficient. For this reason, in this embodiment, the terminal device 121 is configured to be able to reuse preset information. That is, after completing a conditional handover, the terminal device 121 retains, rather than deletes, preset information related to base station devices that are not selected as handover destination candidates. Note that, in the following description, terms such as "preconfiguration information related to a base station device" are used, but this "base station device" may be read as "cell." For example, when one base station device provides multiple cells, preset information may be prepared for each of the multiple cells, and preset information may be retained or deleted for each cell.

[0020] In this embodiment, for example, a base station device currently connected to the terminal device 121 may notify the terminal device 121 whether to retain or delete preconfigured information for each of one or more first other base station devices (cells) that are candidates for a handover destination from the base station device 121 when the terminal device 121 is handed over to a device other than the candidate first other base station device. The base station device may also notify the terminal device 121 whether to continue to retain or delete preconfigured information that was preconfigured by another base station device to which the terminal device 121 was previously connected and that has been retained without being deleted even after one or more handovers. The base station device may perform preconfiguration for a conditional handover for a first other base station device for which the terminal device 121 does not retain corresponding preconfigured information, and cause the terminal device 121 to retain the preconfigured information. At this time, the base station device may notify the terminal device 121 whether to retain the preconfigured information for the newly retained first other base station device after handover to a second other base station device different from the first other base station device.

[0021] The terminal device 121 continues to retain the preset information retained before connecting to the currently connected base station device and the preset information preset by the currently connected base station device at least until handover from the currently connected base station device is performed. Note that an expiration date may be set for the preset information, and in this case, the terminal device 121 may delete the preset information upon expiration of the expiration date even if handover has not actually been performed. Then, the terminal device 121 continues to retain, without deleting, preset information that is in a state indicated by a notification not to be deleted among preset information preset for each of one or more first other base station devices (cells) that are candidates for handover from the currently connected base station device, even after handover to a second other base station device different from the first other base station device. On the other hand, the terminal device 121 deletes, among preset information for the first other base station device, preset information that is in a state indicated by a notification to be deleted, when handover is performed to a second other base station device different from the first other base station device.

[0022] For example, the base station device 101 performs preconfiguration for handover on the terminal device 121, currently connected to the base station device 102, the base station device 104, and the base station device 105, as candidate handover destinations. The base station device 101 then notifies the terminal device 121 whether the preconfiguration information for each of the base station device 102, the base station device 104, and the base station device 105 should be deleted when the terminal device 121 hands over to another base station device. For example, the base station device 101 may retain the preconfiguration information for the base station device 102 and the base station device 105, and notify the terminal device 121 that the preconfiguration information for the base station device 104 should be deleted. In this case, when the terminal device 121 hands over to the cell 114 of the base station device 104, the terminal device 121 connects to the base station device 104 using the preconfiguration information for the base station device 104 as before. The terminal device 121 then continues to retain the preconfiguration information of the base station device 102 and the base station device 105 without deleting it. On the other hand, when the terminal device 121 hands over to the cell 112 of the base station device 102, the terminal device 121 connects to the base station device 102 using the preconfiguration information of the base station device 102 as before. The terminal device 121 then deletes the preconfiguration information of the base station device 104, but continues to retain the preconfiguration information of the base station device 105 without deleting it. Note that when the terminal device 121 hands over to the base station device 102, the base station device 102 may, for example, newly designate the base station device 101, the base station device 103, and the base station device 106 as candidate base station devices for the handover destination, and may perform preconfiguration on the terminal device 121 for handover to these base station devices. In this way, the terminal device 121 can continue to retain preconfiguration information to the necessary extent, and as a result, it can perform another handover immediately after the handover without repeatedly performing preconfiguration.

[0023] After handover, the base station device currently connected to the terminal device 121 may instruct the terminal device 121 which preconfigured information for a base station device other than the handover destination base station device should be deleted, or may instruct the terminal device 121 which preconfigured information should be retained without being deleted. Furthermore, if the terminal device 121 retains preconfigured information for multiple base station devices, the base station device may notify the terminal device 121 whether to retain or delete each piece of preconfigured information individually. The base station device may also notify the terminal device 121 whether to retain or delete multiple pieces of preconfigured information collectively. Furthermore, the base station device may instruct the terminal device 121 to change the operation of retaining or deleting information depending on which base station device the handover process is to be performed on. For example, regarding retention of the preconfigured information for base station device 104, a notification may be issued to retain the information when a handover to base station device 102 is performed, and to delete the information when a handover to base station device 105 is performed.

[0024] Note that, when notifying the terminal device 121 whether each of one or more pieces of preconfigured information held by the terminal device 121 should be retained or deleted, the base station device may use identification information individually assigned to the preconfigured information. For example, the base station device may notify the terminal device 121 of identification information corresponding to preconfigured information that should be deleted after handover. The base station device may also notify the terminal device 121 of identification information corresponding to preconfigured information that should not be deleted (should continue to be held) after handover. Note that, as the identification information for the preconfigured information, an identifier (physical cell identifier) ​​of the cell to which the preconfigured information corresponds or a value corresponding to the identifier of the cell may be used. The value corresponding to the cell identifier may be, for example, CondReconfigId, and may be a value calculated as a result of inputting the cell identifier as an argument to a predetermined function. The predetermined function may be, for example, a modulo arithmetic function that maps the cell identifier to a predetermined numerical range. In this case, the base station device may use the cell identifier to notify the terminal device 121 of whether the preconfigured information corresponding to the cell should be retained or deleted. For example, the base station device can notify the terminal device 121 of a list of identifiers of cells corresponding to preset information that should be deleted and a list of identifiers of cells corresponding to preset information that should not be deleted.

[0025] Furthermore, the base station device may adjust the preset information so that the identification information corresponding to the preset information to be retained falls within a predetermined range. After handover, the terminal device 121 may retain preset information whose identification information has a value within the predetermined range, and delete preset information corresponding to identification information having a value outside the predetermined range. In this case, the base station device may notify the terminal device 121 of whether each piece of preset information should be deleted by notifying the terminal device 121 of information indicating the predetermined range. The predetermined range may also be fixed, and in this case, the base station device may not explicitly notify the terminal device 121 of the preset information to be retained or deleted. When performing handover preconfiguration, the base station device sets the corresponding identification information of preset information that should not be deleted so that the value of the corresponding identification information falls within the predetermined range. Similarly, when performing handover preconfiguration, the base station device sets the corresponding identification information of preset information that should be deleted so that the value of the corresponding identification information does not fall within the predetermined range. Furthermore, if the value of the identification information of preset information that was retained in the terminal device 121 before handover to the base station device itself and that should be deleted falls within the predetermined range, the base station device may change the value of the identification information of that preset information to reset it so that it is outside the predetermined range. In this way, the value of the identification information of the preset information can implicitly indicate whether the terminal device 121 should delete the preset information after handover. This allows the base station device to notify the terminal device 121 whether to delete or retain the preset information without performing explicit signaling.

[0026] The handover source base station notifies the handover destination base station that the terminal device 121 holds preconfiguration information. This information eliminates the need for the handover destination base station to reconfigure the preconfiguration information already held by the terminal device 121. If the preconfiguration information needs to be changed, the handover destination base station may execute a procedure for changing the preconfiguration. For example, the handover source base station notifies the handover destination base station of identification information associated with the preconfiguration information. In one example, when performing preconfiguration, the handover source base station may share the preconfiguration information to be preconfigured for the terminal device with each of the candidate handover destination base station devices. 1, when base station device 101 performs preconfiguration on terminal device 121 for handover to each of base station device 102, base station device 104, and base station device 105, which are candidate handover destinations, preconfiguration information may be shared among base station device 101, base station device 102, base station device 104, and base station device 105. That is, base station device 101 may be configured to transmit handover requests to each of base station device 102, base station device 104, and base station device 105, acquire preconfiguration information related to these base station devices, and notify these base station devices of the acquired preconfiguration information. In this case, for example, base station device 102 has stored the preconfiguration information of base station device 104 and base station device 105 since before the handover of terminal device 121. Here, when terminal device 121 is handed over to base station device 102, terminal device 121 deletes the preconfigured information of base station device 104 and continues to hold the preconfigured information of base station device 105. In this case, base station device 101, the handover source, may notify base station device 102, for example, of identification information corresponding to the preconfigured information of base station device 104. Based on this notification, base station device 102 may determine that the preconfigured information of base station device 104 should be deleted, and may delete the information.On the other hand, the base station device 102 may continue to hold the preset information of the base station device 105 without deleting it because the base station device 102 has not been notified of the corresponding identification information. Note that the base station device 102 may be notified of the identification information corresponding to the preset information to be deleted, or may be notified of the identification information corresponding to the preset information that should be continued to be held.

[0027] Furthermore, the base station device that is a candidate for the handover destination may not hold the preconfiguration information of the other candidate base station devices before the handover. In this case, the base station device that is the handover source may notify the base station device that is the target for the handover of the preconfiguration information that the terminal device 121 continues to hold in response to the handover. For example, the terminal device 121 deletes the preconfiguration information of the base station device 104 but continues to hold the preconfiguration information of the base station device 105. In this case, the base station device 101 may notify the base station device 102 of the preconfiguration information of the base station device 105 in response to the handover of the terminal device 121 to the base station device 102. Note that the base station device 101 does not notify the base station device 102 of the preconfiguration information of the base station device 104. This is because the preconfiguration information of the base station device 104 is deleted in the terminal device 121 in response to the handover of the terminal device 121 to the base station device 102.

[0028] Alternatively, the handover source base station may notify only the handover execution conditions and communication parameters from the preset information to be retained. In this case, the handover destination base station may reset either the handover execution conditions or communication parameters that it has not acquired, or may acquire them from the candidate handover destination base station corresponding to the preset information. The handover source base station may also notify the handover destination base station of at least one of the above-described identification information, handover execution conditions, and communication parameters, along with information indicating which cell the information is for handover to. This information may be, for example, identification information that can identify a cell or frequency, such as a PCI (Physical Cell Identifier) ​​or an ARFCN-ValueNR (Absolute Radio Frequency Channel Number). While these pieces of information may be included in the communication parameters of the preset information, notifying them separately allows the handover destination base station to recognize which cell or frequency the preset information relates to without analyzing the communication parameters in the preset information. In addition, the transmission of information from the handover source base station device to the handover destination base station device can be performed, for example, when the handover source base station device transfers the status of the sequence number in response to the handover destination base station device notifying the handover source base station device that the handover of terminal device 121 has been successful.

[0029] As described above, the handover destination base station acquires, from the handover source base station, predetermined information such as at least one of handover conditions, communication parameters, and identification information corresponding to a combination of the handover conditions and communication parameters, regarding the preset information to be retained after handover from the handover source base station, out of the preset information preset in advance for one or more handover destination candidate base station devices in the terminal device 121. Then, the handover destination base station controls the subsequent handover of the terminal device 121 to another base station based on the acquired predetermined information.

[0030] When the terminal device 121 establishes a connection in a predetermined area (initial connection or handover), the connected base station device may perform preconfiguration on the terminal device 121, including conditions to be satisfied when the terminal device 121 hands over to each of multiple base station devices belonging to the predetermined area and settings of communication parameters to be used after the handover. The base station device to which the terminal device 121 is connected shares the preconfiguration information with other base station devices in the predetermined area. The base station device to which the terminal device 121 is connected may also perform preconfiguration in the event that a handover from another base station device to the terminal device 121 is performed, and may share the preconfiguration information with other base station devices in the predetermined area. The base station device in the predetermined area may delete the preconfiguration information in response to the terminal device 121 handing over to a location outside the predetermined area. This allows the terminal device 121 to continuously perform conditional handover within the predetermined area after establishing a connection within the predetermined area.

[0031] For example, assume that cells 111, 112, 114, and 115 form a predetermined area, and that terminal device 121 has established a connection with base station device 101. At this time, for example, in response to terminal device 121 establishing the connection or in response to an attempt to perform handover from base station device 101, base station device 101 performs pre-configuration for handover within the predetermined area. For example, base station device 101 transmits a handover request message to base station device 102, base station device 104, and base station device 105, and acquires information on communication parameters after handover. In addition, handover conditions are determined by base station device 101 or a candidate base station device as the handover destination. Furthermore, base station device 101 assigns identification information corresponding to a combination of handover conditions and communication parameters (pre-configuration information). Note that base station device 101 may determine identification information in advance and transmit the identification information included in the handover request message. The base station device 101 then transmits the acquired preconfiguration information and identification information to the base station device 102, the base station device 104, and the base station device 105, which are candidate handover destinations. The base station device 101 may also transmit preconfiguration information and identification information for when a handover occurs from any of the base station device 102, the base station device 104, and the base station device 105 to the base station device 101. As a result, for example, the base station device 101 will hold preconfiguration information for the base station device 102, the base station device 104, and the base station device 105. The base station device 104 will hold preconfiguration information for the base station device 101, the base station device 102, and the base station device 105, and the base station device 105 will hold preconfiguration information for the base station device 101, the base station device 102, and the base station device 104. The base station device 101 then notifies the terminal device 121 of this preset information. Note that, when the terminal device 121 is handed over to a base station device outside a predetermined area, the terminal device 121 may be notified of information indicating that the preset information should be deleted.For example, the preset information may be assigned identification information indicating a specific area, and when the terminal device 121 performs a handover to a base station device belonging to an area with identification information different from the identification information of the area to which the currently connected base station device belongs, the preset information assigned with the identification information of the area to which the base station device before handover belongs may be deleted.

[0032] The terminal device 121 may delete the preset information, for example, when it is explicitly notified by the base station device to which it is currently connected to delete the preset information or when the expiration date has passed, but it does not delete the preset information due to handover within a predetermined area. On the other hand, when the terminal device 121 moves beyond the predetermined area and hands over to another base station device that does not belong to the predetermined area, it deletes the preset information for the base station device that belongs to the predetermined area. In addition, the base station device that was connected to the terminal device 121 within the predetermined area immediately before the terminal device 121 hands over to a device outside the predetermined area may instruct each base station device within the predetermined area to delete the preset information upon success of the handover (or upon disconnection from the base station device). For example, in response to terminal device 121 handing over from base station device 102 to base station device 103, base station device 102 may notify base station device 101, base station device 104, and base station device 105 to delete pre-configured information shared among base station device 101, base station device 102, base station device 104, and base station device 105.

[0033] Note that when handover conditions or communication parameters need to be changed, the changes may be made throughout the entire predetermined area, or only some of the base station devices may make the changes. Note that the predetermined area may be, for example, an area corresponding to the same tracking area identifier (TAI), the same tracking area code (TAC), or the same system information area identifier, but a different area (for example, an area specific to the terminal device 121) may also be defined. The predetermined area may also be dynamically set. For example, when the terminal device 121 hands over from the base station device 101 to the base station device 102, the cell 113 and the cell 116 may be added to the predetermined area including only the cell 111, the cell 112, the cell 114, and the cell 115. In this case, the base station device 102 performs processing such as transmitting a handover request message to the base station device 103 and the base station device 106, shares the preconfigured information with each base station device in the predetermined area, and notifies the terminal device 121 of the preconfigured information. Furthermore, for example, when the terminal device 121 performs a handover from the base station device 102 to the base station device 103, the cells 111 and 114 may be deleted from the predetermined area. In this case, in response to the handover, the base station device 103 may instruct the base station device 101 and the base station device 104 to delete all preconfigured information for the terminal device 121, and may instruct the base station device 102, the base station device 105, and the base station device 106 to delete the preconfigured information for the base station device 101 and the base station device 104. Even when the predetermined area is defined in advance, one cell may be included in multiple predetermined areas. In this case, when the terminal device 121 connects to the base station device that provides this cell, preconfiguration may be performed for multiple predetermined areas including the cell. This allows the predetermined area to be appropriately formed according to the location of the terminal device 121, and the preconfiguration information for the conditional handover to be appropriately prepared.

[0034] In addition, when terminal device 121 ends communication, disconnects the connection, and enters a disconnected state, various pieces of information, such as pre-configured information related to terminal device 121, that are held in base station devices 101 to 106 and terminal device 121 as described above may be deleted.

[0035] In the above description, the processing when the terminal device 121 executes a conditional handover has been described. However, a similar method can also be applied to adding or changing a secondary cell when the terminal device 121 uses multi-connectivity (MC) or carrier aggregation (CA). That is, when the terminal device 121 autonomously adds or changes a secondary cell in response to determining that a condition is satisfied using preconfiguration, the terminal device 121 typically deletes preconfigured information related to a base station device that provides a secondary cell candidate that was not selected as a connection destination. In contrast, in this embodiment, the terminal device 121 is able to retain this preconfigured information without deleting it. Furthermore, even when a change of the primary cell occurs (i.e., a handover occurs), the terminal device 121 also deletes preconfigured information related to a base station device that provides a secondary cell candidate. In contrast, in this embodiment, even when a handover occurs regarding the primary cell, the terminal device 121 can retain preconfigured information related to a secondary cell candidate without deleting it.

[0036] Note that the process for deleting preconfigured information may be performed in the same manner as the process during handover described above. For example, when a base station device providing a primary cell for the terminal device 121 connects to a new base station device due to a change or addition of a secondary cell, the base station device may notify the terminal device 121 whether or not to continue to retain preconfigured information related to a base station device providing a cell that is a candidate for the other secondary cell that was not connected. For example, when there are multiple cells that are candidate for secondary cells, preconfigured information is prepared for each of the multiple base station devices that provide the multiple cells. Then, for each of the multiple other base station devices, a setting may be made as to whether or not to delete the preconfigured information when the secondary cell to which the terminal device 121 is connected is changed or added, and the setting may be notified to the terminal device 121. Furthermore, the notification as to whether or not to delete the preconfigured information may include information indicating which of the multiple preconfigured information should be deleted or which should not be deleted. Furthermore, information corresponding to the preconfigured information that is not deleted in the terminal device 121 may be shared between base station devices when the terminal device 121 changes or adds a connection destination. For example, when there is a change in the primary cell (i.e., a handover), the base station device that provided the primary cell before the change may notify the base station device that provides the new primary cell of information that can identify preconfigured information that is not deleted and is held in the terminal device 121. This notification may be performed using a message such as SN STATUS TRANSFER, EARLY STATUS TRANSFER, or RETRIEVE UE CONTEXT RESPONSE. This notification may also be performed using a new Xn message. When there is a change in the secondary cell, the base station device that provided the old secondary cell may notify the base station device that provides the new secondary cell of information that can identify preconfigured information that is not deleted and is held in the terminal device 121. Note that the base station device that provided the old secondary cell may directly notify the base station device that provides the new secondary cell, or this notification may be performed via the base station device that provides the primary cell.This notification can be made using a message such as UE CONTEXT MODIFICATION RESPONSE, UE CONTEXT RELEASE COMMAND, UE CONTEXT MODIFICATION REQUEST, etc. Alternatively, this notification may be made using a new Xn message.

[0037] Furthermore, this information sharing between base station devices may be performed only when a change of the primary cell (i.e., handover) occurs. In other words, if a change of the primary cell does not occur, the base station device providing the primary cell holds preconfigured information related to secondary cell candidates. The base station device of the primary cell takes the lead in the process of adding and changing the secondary cell, and it is assumed that the base station device of the changed secondary cell does not need to know the preconfigured information that is not deleted and is held in the terminal device 121. On the other hand, if a change of the primary cell occurs, the base station device of the changed primary cell needs to know which preconfigured information is held in the terminal device 121 for subsequent addition and change of the secondary cell. For this reason, information exchange between base station devices may be performed only when a change of the primary cell occurs. Note that, even when a secondary cell is added or changed, normal notifications such as transfer of transmission data and notification of frame numbers can naturally be performed. Note that, if the base station device providing the secondary cell uses information on which preconfigured information is held in the terminal device 121, that information may be shared between the base station devices of the secondary cells. In this case, even if the primary cell is not changed, information related to the pre-configuration information can be notified to the base station device providing the secondary cell after the change, for example, from the base station device providing the primary cell or the base station device providing the secondary cell before the change.

[0038] Furthermore, processing similar to the above-described handover-related processing may be performed, such as setting preconfiguration information related to a base station device that provides a cell corresponding to a predetermined area to which the terminal device 121 has become connected as preconfiguration information to be retained. However, the details of these processing are the same as those of the above-described handover processing, and therefore will not be repeated here.

[0039] Note that a conditional change and addition of a secondary cell (Conditional PSCell Addition / Change) can be initiated by either a base station device (master node) that provides a primary cell or a base station device (secondary node) that provides a secondary cell. When a conditional change and addition of a secondary cell is initiated by a master node, the master node can instruct the terminal device 121 which preconfigured information should or should not be deleted. Furthermore, the master node can share information related to preconfigured information that is to be deleted or maintained without being deleted in the terminal device 121 with a secondary node that provides the secondary cell after the change / addition, using an S-NODE ADDITION REQUEST / S-NODE ADDITION REQUEST ACK, an S-NODE MODIFICATION REQUEST / S-NODE MODIFICATION REQUEST ACK, or the like. Furthermore, when a conditional change and addition of a secondary cell is initiated by a secondary node, the secondary node can instruct the terminal device 121 which preconfigured information should or should not be deleted. Furthermore, for example, the pre-change secondary node may share with the master node information related to preconfigured information that is to be deleted or maintained without being deleted in the terminal device 121, using S-NODE MODIFICATION REQUIRED / S-NODE MODIFICATION CONFIRM, etc. Then, the master node may share that information with the post-change secondary node, using S-NODE ADDITION REQUEST / S-NODE ADDITION REQUEST ACK, etc.

[0040] Furthermore, triggers for deleting preset information related to secondary cell candidates include, as described above, the addition or change of a secondary cell and the change (handover) of a primary cell. Here, when a change of the primary cell occurs, for example, depending on which primary cell a handover to has been performed, a secondary cell candidate for which corresponding preset information is deleted or maintained can be determined. For example, depending on available combinations of primary cells and secondary cells, the preset information to be maintained is determined. In one example, it is assumed that the first to third cells are set as candidates for a handover destination of the primary cell, and preset information related to other base station devices that provide these cells is held in the terminal device 121. It is also assumed that the fourth to seventh cells are set as candidates for an addition or change of a secondary cell, and preset information related to other base station devices that provide these cells is held in the terminal device 121. Here, it is assumed that only the following combinations of primary cells and secondary cells are usable: (first cell, fourth cell), (first cell, sixth cell), (first cell, seventh cell), (second cell, fourth cell), and (third cell, fifth cell). Note that information indicating such usable combinations of primary cells and secondary cells may be notified in advance from the base station device to the terminal device 121. In this case, when the primary cell is switched to the first cell, the terminal device 121 cannot use the fifth cell as a secondary cell. For this reason, the terminal device 121 may delete the preconfigured information related to the fifth cell. On the other hand, since the fourth cell, sixth cell, and seventh cell can be used as secondary cells by the terminal device 121, the preconfigured information related to these cells may be maintained without being deleted. Furthermore, if the terminal device 121 subsequently performs a handover from the first cell to the second cell, the sixth and seventh cells cannot be used as secondary cells, so the terminal device 121 may delete the preconfigured information for these cells and maintain the preconfigured information for the fourth cell, which can be used as a secondary cell.On the other hand, when the terminal device 121 performs a handover from the first cell to the third cell, it may delete all preconfigured information because none of the fourth cell, sixth cell, and seventh cell can be used as secondary cells.

[0041] Note that the terminal device 121 may be configured to delete all preconfigured information related to secondary cell candidates when the terminal device 121 changes the primary cell to a cell other than the designated cell. In this case, for example, when the terminal device 121 changes the primary cell to a designated cell, preconfigured information that should be maintained without being deleted may be designated as described above. For example, when the terminal device 121 performs a handover to a cell that does not hold corresponding preconfigured information, the terminal device 121 may determine that the handover has occurred to a cell other than the designated cell. For example, when the terminal device 121 connects to a base station device that provides a cell that does not have a usable secondary cell in combination as the primary cell, the terminal device 121 may delete all preconfigured information related to secondary cell candidates. This is because it is expected that a secondary cell cannot be configured while the terminal device 121 is connected to such a primary cell. Furthermore, when the terminal device 121 changes the primary cell to a designated cell, the terminal device 121 may maintain preconfigured information related to secondary cell candidates. On the other hand, when the terminal device 121 changes the primary cell to a cell other than the designated cell, preconfigured information that should be maintained without being deleted may be designated as described above.

[0042] Furthermore, for example, when the terminal device 121 executes a reconnection process, the reconnection destination cell may instruct the deletion of all or part of the preconfigured information related to the secondary cell candidate. In this case, the terminal device 121 may retain or delete the preconfigured information in accordance with the instruction from the reconnection destination cell. Furthermore, the terminal device 121 may operate to retain the preconfigured information when reconnecting to a predesignated cell, and to delete the preconfigured information when reconnecting to a cell that is not predesignated.

[0043] Note that the terminal device 121 can notify the base station device (network) of capability information (UE Capability) indicating whether or not the retained preconfigured information can be maintained when a handover or a secondary cell is added or changed, when the terminal device 121 connects to the base station device (of the primary cell) or when requested by the base station device. The base station device can execute the above-described process when the capability information indicates that the terminal device 121 can maintain the preconfigured information. In other words, when the base station device acquires capability information that does not indicate that the terminal device 121 can maintain the preconfigured information, the base station device can not execute the above-described process for the terminal device 121. In this case, the preconfigured information can be deleted in the terminal device 121 each time a handover or a secondary cell is added or changed.

[0044] In the above description, the terminal device 121 switches the base station device to which it is connected by handover or by changing or adding a secondary cell. However, the same procedures as those described above can also be used for handover to another cell (frequency) of the same base station device or for adding or changing a secondary cell. In this case, it can be said that one physical base station device includes multiple logical base station devices, and each of the logical base station devices provides a separate cell. Therefore, the base station device in this embodiment and the appended claims refers to a logical base station device, and "handover from a base station device to another base station device" and "changing or adding a secondary cell" also include handover and changing or adding a secondary cell within the same physical base station device. In this embodiment and the appended claims, "base station device" may be read as "cell."

[0045] Below, an example of the configuration of the base station devices (base station devices 101 to 106) and terminal device (terminal device 121) that execute the above-mentioned processing, and an example of the flow of the processing that is executed will be described.

[0046] (Device configuration) An example of the hardware configuration of a base station device and a terminal device will be described using FIG. 2. In one example, the base station device and the terminal device include a processor 201, a ROM 202, a RAM 203, a storage device 204, and a communication circuit 205. The processor 201 is a computer including one or more processing circuits, such as a general-purpose CPU (Central Processing Unit) or an ASIC (Application Specific Integrated Circuit), and performs overall processing of the device and each of the above-mentioned processes by reading and executing programs stored in the ROM 202 or the storage device 204. The ROM 202 is a read-only memory that stores information such as programs and various parameters related to the processes executed by the base station device and the terminal device. The RAM 203 functions as a workspace when the processor 201 executes a program and is a random access memory that stores temporary information. The storage device 204 is, for example, a removable external storage device. The communication circuit 205 is, for example, a circuit for LTE or 5G wireless communication. Although FIG. 2 illustrates one communication circuit 205, the base station device and the terminal device may have multiple communication circuits. For example, a base station apparatus and a terminal apparatus may have a common antenna as well as wireless communication circuits for LTE and 5G. The base station apparatus and the terminal apparatus may also have separate antennas for LTE and 5G. The base station apparatus may also have a wired communication circuit used when communicating with other base station apparatuses or nodes in the core network. The terminal apparatus may also have a communication circuit for other wireless communication systems, such as a wireless LAN. The base station apparatus and the terminal apparatus may have separate communication circuits 205 for each of a plurality of available frequency bands, or may have a common communication circuit 205 for at least some of these frequency bands.

[0047] FIG. 3 shows an example of the functional configuration of a first base station device, which is a base station device that provides a handover source base station device or a primary cell that performs settings for changing or adding a secondary cell. The first base station device has, as its functions, a conditional connection destination change setting unit 301, an information deletion necessity notification unit 302, an information providing unit 303, and an information sharing unit 304. Note that FIG. 3 only shows functions particularly related to this embodiment, and various other functions that the first base station device may have are omitted. For example, the first base station device naturally has other functions that LTE and 5G base station devices generally have. The functional blocks in FIG. 3 are shown schematically, and the respective functional blocks may be realized as an integrated unit or may be further subdivided. Furthermore, the functions in FIG. 3 may be realized, for example, by the processor 201 executing a program stored in the ROM 202 or the storage device 204, or by a processor within the communication circuit 205 executing predetermined software. The details of the processes executed by each functional unit will not be described here, but only the general functions will be outlined. The first base station device can also have the functions of a second base station device, which is a base station device that provides a handover destination or an added or changed secondary cell, as described below.

[0048] The conditional connection destination change setting unit 301 executes a setting process for a conditional handover of the terminal device or for adding or changing a conditional secondary cell. That is, the conditional connection destination change setting unit 301 transmits a handover request (including, for example, information indicating communication parameters currently used by the terminal device and identification information for the conditional handover) to a base station device that is a candidate for the handover destination, and acquires, from the candidate base station device, information on communication parameters to be used after handover to the candidate base station device. Furthermore, the conditional connection destination change setting unit 301 transmits a secondary cell addition request (including, for example, information indicating communication parameters currently used by the terminal device and identification information corresponding to the conditional addition or change of the secondary cell) to a base station device that provides a candidate cell for the secondary cell to be added or changed, and acquires, from the base station device that provides the candidate cell for the secondary cell, information on communication parameters to be used after adding or changing the cell provided by the base station device as a secondary cell. Then, the conditional connection destination change setting unit 301 notifies the terminal device of the communication parameters and performs pre-settings for a conditional handover or a conditional addition or change of a secondary cell for the terminal device. Note that the conditions for executing a handover or an addition or change of a secondary cell may be acquired from a base station device that is a candidate for a connection destination due to the handover or the addition or change of a secondary cell, or may be determined by the conditional connection destination change setting unit 301.

[0049] The information deletion necessity notifying unit 302 notifies the terminal device whether the preconfigured information for each of the candidate base station devices set by the conditional connection destination setting unit 301 should be deleted or retained after the terminal device connects to another base station device different from the candidate base station device. Whether the preconfigured information should be deleted may be set by a telecommunications carrier, or may be determined according to rules such as deleting the preconfigured information for a base station device with a small cell size, or deleting the preconfigured information if the distance from the current location of the terminal device is greater than a predetermined distance. While whether the preconfigured information should be deleted may be determined for each base station device (cell), in one example, the preconfigured information to be deleted may be specified in relation to the base station device to which the connection is to be changed. For example, it may be specified that when the terminal device 121 performs a handover or a secondary cell change from base station device 101 to base station device 102, the preconfigured information for base station device 104 is deleted, but when the terminal device 121 performs a handover or a secondary cell change from base station device 101 to base station device 105, the preconfigured information for base station device 104 is not deleted. In addition, the information deletion necessity notification unit 302 may, for example, explicitly notify the terminal device of the necessity of deleting the preset information when notifying the terminal device of the preset information, or may implicitly notify the necessity of deletion based on a predetermined rule, such as not deleting the preset information if the value of the identification information corresponding to the preset information is within a predetermined range.

[0050] When a terminal device that has been notified that it will continue to retain one or more pieces of preset configuration information performs a conditional handover or a conditional addition or change of a secondary cell, the information providing unit 303 provides, to a base station device connected by the handover or the addition or change of the secondary cell, predetermined information including at least one of a condition for performing the handover or the addition or change of the secondary cell, communication parameters, and identification information corresponding to the condition and communication parameters (preconfiguration information), which correspond to the preset configuration information that will be retained. Note that the information providing unit 303 provides, from the one or more pieces of preset configuration information, preset configuration information for a base station device different from the base station device connected by the handover or the addition or change of the secondary cell.

[0051] For example, when preconfiguration information is shared among multiple base station devices, including the base station device itself, belonging to a predetermined area, the information sharing unit 304 provides the preconfiguration information for the base station device itself and acquires preconfiguration information from base station devices other than the base station device itself among the multiple base station devices. In this case, the conditional connection destination change setting unit 301 provides the terminal device with the shared preconfiguration information (excluding the preconfiguration information of the base station device itself, as the case may be). At this time, the condition deletion necessity notifying unit 302 may explicitly notify the terminal device that preconfiguration information for the base station device belonging to the predetermined area should be deleted if a handover or addition or change of a secondary cell is performed beyond the predetermined area. Note that a rule may be established in advance that preconfiguration information for the base station device belonging to the predetermined area should be deleted if a handover or addition or change of a secondary cell is performed beyond the predetermined area. In this case, an explicit deletion instruction may not be transmitted. Note that the information sharing unit 304 may notify the terminal device that preconfiguration information for the base station device belonging to the predetermined area should be deleted only if a change of the primary cell is performed beyond the predetermined area.

[0052] FIG. 4 shows an example of the functional configuration of a second base station device, which is a base station device providing a handover destination base station device or a secondary cell after an addition or change. The second base station device has, as its functions, for example, an information acquisition unit 401, a connection change control unit 402, an information sharing unit 403, and an information deletion unit 404. Note that FIG. 4 only shows functions particularly related to this embodiment, and does not illustrate various other functions that may be possessed by the second base station device, which is a handover destination base station device or a base station device of a secondary cell after an addition or change. For example, the second base station device naturally has other functions that LTE and 5G base station devices generally have. The functional blocks in FIG. 4 are shown schematically, and the respective functional blocks may be realized as an integrated unit or may be further subdivided. Furthermore, the functions in FIG. 4 may be realized, for example, by the processor 201 executing a program stored in the ROM 202 or the storage device 204, or by a processor within the communication circuit 205 executing predetermined software. The details of the processes executed by each functional unit will not be described here, but only the general functions thereof will be outlined. The second base station device may naturally have the functions of the first base station device described above.

[0053] The information acquisition unit 401 acquires, from a base station device that is a source of connection change, predetermined information corresponding to preconfiguration information for changing the connection destination (handover or addition or change of a secondary cell) to another base station device that should be retained in the terminal device when the terminal device is handed over to the base station device itself or when the terminal device connects to a cell provided by the base station device as a changed or added secondary cell. The predetermined information includes at least one of conditions that must be satisfied when the connection destination is changed, communication parameters that should be used after the connection destination is changed, and identification information corresponding to the conditions and communication parameters. Note that, if the predetermined information is insufficient to execute connection destination change control for the terminal device, the information acquisition unit 401 may acquire additional information for connection destination change control from, for example, a corresponding base station device or a base station device that is a source of connection destination change, based on the predetermined information. The connection destination change control unit 402 executes control of a conditional handover or a conditional addition or change of a secondary cell based on the information acquired by the information acquisition unit 401. Note that, in order to change the acquired information, the connection destination change control unit 402 may execute a conditional handover or a conditional addition or change of a secondary cell again.

[0054] The information sharing unit 403 is similar to the above-described information sharing unit 304. For example, when sharing preconfiguration information among a plurality of base station devices including the terminal device itself that belong to a predetermined area, the information sharing unit 403 provides preconfiguration information about the terminal device itself and acquires preconfiguration information from base station devices other than the terminal device itself among the plurality of base station devices. For example, the information deletion unit 404 deletes the preconfiguration information shared by the information sharing unit 403 when the terminal device moves out of the predetermined area. Furthermore, the information deletion unit 404 can delete the information acquired by the information acquisition unit 401 when the terminal device changes its connection destination to another base station device.

[0055] FIG. 5 shows an example of the functional configuration of a terminal device. The terminal device has, as its functions, for example, a connection destination change processing unit 501, an information acquisition unit 502, an information storage unit 503, and a deletion necessity receiving unit 504. Note that FIG. 5 only shows functions particularly related to this embodiment, and various other functions that the terminal device may have are omitted from the illustration. For example, the terminal device naturally has other functions that LTE and 5G terminal devices generally have. The functional blocks in FIG. 5 are shown schematically, and each functional block may be realized by being integrated or further subdivided. Each function in FIG. 5 may be realized, for example, by the processor 201 executing a program stored in the ROM 202 or the storage device 204, or by a processor within the communication circuit 205 executing predetermined software. Details of the processes performed by each functional unit will not be described here, and only their general functions will be outlined.

[0056] The connection destination change processing unit 501 executes a configuration process for a conditional handover or a conditional addition or change of a secondary cell between the currently connected base station device and the currently connected base station device. For example, the connection destination change processing unit 501 measures a signal from the currently connected base station device (e.g., providing a primary cell or a secondary cell) and transmits the measurement result to the currently connected base station device (e.g., providing the primary cell). Then, in response to the decision of the currently connected base station device to execute a handover or an addition or change of a secondary cell, the connection destination change processing unit 501 receives a configuration message (e.g., an RRC message such as an RRC Reconfiguration message) including pre-configuration information regarding a base station device that is a candidate for the handover destination or a candidate for the secondary cell to be added or changed to. Then, when a condition for executing a handover is satisfied, the connection destination change processing unit 501 disconnects the currently connected base station device and autonomously executes processes such as establishing time synchronization with a base station device that satisfies the condition, establishes a connection, and completes the handover. Furthermore, when the conditions for adding or changing a secondary cell are satisfied, the connection destination change processing unit 501 disconnects the connection with the base station device that provides the secondary cell if a secondary cell is currently connected, and autonomously performs processing such as establishing time synchronization with the base station device that meets the conditions to establish a connection and complete the configuration of the secondary cell. The information acquisition unit 502 acquires preconfigured information from the message received by the connection destination change processing unit 501. The information holding unit 503 holds the acquired preconfigured information. The deletion necessity receiving unit 504 receives a notification indicating whether the acquired preconfigured information should be held even after a connection destination change due to a handover or the addition or change of a secondary cell, or whether it should be deleted after the connection destination change. Based on the notification, the information holding unit 503 deletes preconfigured information that should be deleted and continues to hold preconfigured information that should be continued to be held after the connection destination change processing unit 501 executes the connection destination change processing.

[0057] (Processing flow) Next, an example of the flow of processing executed in the wireless communication system will be described with reference to Figures 6 and 7. Since the details of each processing described here are as described above, only an overview of the processing will be described here, and detailed description thereof will be omitted.

[0058] In FIG. 6, it is assumed that an initial connection between the terminal device 121 and the base station device 101 has been established. In this state, the base station device 101 decides to start preparation for a conditional handover, for example, by receiving a wireless quality measurement report from the terminal device 121 (S601). In response to this decision, the base station device 101 transmits a handover request message to other base station devices (base station device 102, base station device 104, base station device 105) that are candidates for the handover destination (S602). This handover request message may include information such as communication parameters currently used in communication with the terminal device 121 and the type of communication service. The candidate base station device for the handover destination determines, for example, based on the information such as the communication parameters, whether it can provide communication services equivalent to those before the handover, and if it cannot provide such communication services, it can reject the handover request. Note that in FIG. 6, it is assumed that all candidate base station devices accept the handover request. In this case, the candidate base station device may transmit information on communication parameters to be used when the terminal device 121 is handed over to the candidate base station device 101 in response to the handover request (S603). Note that the base station device 101 may, for example, specify identification information for a conditional handover (i.e., identification information corresponding to preconfiguration information) and transmit the information using the handover request, and the candidate base station device may transmit the communication parameters to the base station device 101 in association with the identification information. The base station device 101 may also determine conditions for executing a handover and transmit the conditions together with the handover request. If the conditions need to be changed, the candidate base station device may present the changed conditions to the base station device 101 in response to the handover request. Alternatively, the base station device 101 may not determine the conditions for executing a handover, but the candidate base station device may determine the conditions and notify the base station device 101 in response to the handover request.

[0059] The base station device 101 generates a predetermined message (e.g., an RRCReconfiguration message) including preconfiguration information based on the information collected from each of the candidate base station devices, and transmits the message to the terminal device 121 (S604). At this time, the base station device 101 notifies the terminal device 121 whether the preconfiguration information corresponding to each of the candidate base station devices that is the handover destination should be continued to be retained or deleted after handover to another base station device. This notification may be transmitted to the terminal device 121 in S604, or may be transmitted to the terminal device 121 separately from this. Here, it is assumed that the notification has been transmitted to continue retaining the preconfiguration information of the base station device 102 and the base station device 105, and to delete the preconfiguration information of the base station device 104. When the terminal device 121 successfully receives the predetermined message for this configuration, it transmits a response message (e.g., an RRCReconfigurationComplete message) to the base station device 101 (S605) and performs preconfiguration (S606).

[0060] Thereafter, the terminal device 121 is deemed to have satisfied the conditions for handover to the base station device 102 (S607). The terminal device 121 disconnects the currently connected base station device 101 (not shown) and executes connection processing including establishing synchronization with the base station device 102 (S608). When the base station device 102 successfully connects to the terminal device 121 and completes the handover, it transmits a notification of the handover success to the source base station device 101 (S609). In response to this notification of the handover success, the base station device 101 notifies the base station device 102 of the status of the sequence number (S610). Furthermore, in this embodiment, the base station device 101 transmits information regarding preset information that has been preset in the terminal device 121 and will not be deleted to the base station device 102. Note that this information may be transmitted together with the information notification of S610, or may be transmitted separately. The information related to the preset information may be the preset information itself, or may be predetermined information including at least one of handover conditions, communication parameters, and identification information corresponding to a combination of the conditions and communication parameters. The base station device 101 notifies the base station device 104, for which the corresponding preset information is to be deleted in the terminal device 121, to delete the stored preset information (S611). This notification may be performed, for example, by a HANDOVER CANCEL message. The terminal device 121 is configured to delete the preset information of the base station device 104 when the terminal device 121 hands over to a base station device other than the base station device 104, and therefore deletes this preset information (S612). The base station device 101 notifies the base station device 104, for which the corresponding preset information is stored in the terminal device 121, that the terminal device 121 has handed over from the base station device 101 to the base station device 102. As a result, when the terminal device 121 subsequently performs a handover from the base station device 102 to the base station device 104, the base station device 104 can notify the base station device 102 that the handover was successful.

[0061] Next, using FIG. 7, a process flow for sharing preconfigured information in a predetermined area formed by base station device 101, base station device 102, base station device 104, and base station device 105 will be described. In this process, first, when terminal device 121 is connected to base station device 102 (S701), base station device 102 starts a conditional handover process. Note that this is just an example, and base station device 102 may start a conditional handover process when the wireless quality of terminal device 121 satisfies a condition for starting a conditional handover process. Base station device 102 transmits a handover request for a conditional handover to other base station devices (base station device 101, base station device 104, and base station device 105) within the predetermined area (S702) and receives a response thereto (S703). These processes are similar to S602 and S603 in FIG. 6. The base station device 102 notifies each base station device within a predetermined area of ​​communication parameters (e.g., currently used communication parameters) to be used when the terminal device 121 hands over to that base station device and then hands over to the base station device 102 again, conditions under which the handover should be performed, and identification information, thereby providing preconfiguration information of the base station device 102 to the other base station devices. The base station device 102 also provides the other base station devices with the preconfiguration information of the other base station devices that it has collected. For example, the preconfiguration information of the base station device 104 and the base station device 105 is provided to the base station device 101. The base station device 102 then transmits a message including this shared preconfiguration information to the terminal device 121 (S707), and the terminal device 121 retains this preconfiguration information and performs preconfiguration (not shown). The terminal device 121 then transmits a response message to the base station device 102 (S708).

[0062] In this example, it is assumed that the base station device 102 also configures the terminal device 121 for conditional handover to a base station device 103 outside a predetermined area (S705 to S708). Then, it is assumed that the terminal device 121 decides to hand over to the base station device 103, for example, when a handover condition for the base station device 103 is satisfied (S709). Then, in accordance with this decision, the terminal device 121 disconnects the currently connected base station device 102 and executes connection processing with the base station device 103 (S710). It is assumed that the case where the handover to the base station device 103 is executed as a conditional handover has been described, but this is not limiting. That is, the terminal device 121 may transmit a measurement report to the base station device 102 when the wireless quality of a signal from the base station device 103 satisfies a predetermined condition, and the handover processing may be executed under the control of the base station device 102. Thereafter, base station device 103 notifies base station device 102 of the success of the handover (S711), and base station device 102 notifies the status of the sequence number (S712). Furthermore, because terminal device 121 has moved outside the predetermined area, base station device 102 instructs each base station device within the predetermined area to delete preconfigured information (S713), and deletes its own preconfigured information (not shown). Furthermore, terminal device 121 also deletes the preconfigured information of base station device 101, base station device 102, base station device 104, and base station device 105 that belong to the predetermined area (S714).

[0063] Next, the processing flow for handling preconfiguration information related to secondary nodes will be described. FIG. 8 shows the processing flow when the master node (MN), which is a base station device providing a primary cell, is changed. In FIG. 8, the MN before the change of connection destination (handover) is denoted as S-MN (Source MN), and the MN after the change of connection destination is denoted as T-MN (Target MN). In addition, the base station device providing a candidate cell for the secondary cell to be added or changed is denoted as a secondary node (SN), and FIG. 8 shows two SNs, SN1 and SN2. In this processing, it is assumed that the S-MN first decides to start conditional secondary node addition and change (CPAC, Conditional PSCell Addition / Change) for setting a secondary cell for a connected terminal device (S801). The S-MN may start this processing, for example, when the wireless quality of the terminal device satisfies the conditions for starting CPAC processing. In addition, the S-MN may extract, as SN candidates, base station devices providing cells in frequency bands that can be used together with the frequency band used by the own device. Here, it is assumed that the S-MN has extracted SN1 and SN2 as base station devices that provide candidate cells for the secondary cell. The S-MN transmits a request message (SgNB Addition Request) for conditional secondary cell addition to SN1 and SN2 (S802) and receives a response thereto (S803). The S-MN then transmits a message including the shared preconfiguration information to the terminal device (S804), and the terminal device transmits a response message to the S-MN (S805). It is assumed here that the preconfiguration information of SN1 is specified to be retained even after a handover or a secondary cell addition or change occurs, and that the preconfiguration information of SN2 is specified to be deleted in the event of a handover or a secondary cell addition or change. It is to be noted that this is just an example, and the preconfiguration information to be deleted and the preconfiguration information to be maintained may be configured to be different between when a primary cell is changed (handover) and when a secondary cell is added or changed.The terminal device then stores this pre-setting information, including the settings to be deleted or maintained, and performs pre-setting (S806).

[0064] Thereafter, the terminal device is assumed to be handed over to the T-MN by, for example, executing the conditional handover procedure as described above or by executing a handover procedure initiated by the S-MN (S807). At this time, the terminal device of this embodiment, triggered by the handover, deletes only the preconfigured information that should be deleted in accordance with the setting in S805, and does not delete the preconfigured information that should not be deleted (should be maintained). Here, the terminal device deletes the preconfigured information of SN2, while maintaining the preconfigured information of SN1 without deleting it (S808). Then, the terminal device may, for example, add or change a secondary cell using the maintained preconfigured information (not shown). Furthermore, the S-MN may instruct SN2, whose corresponding preconfigured information has been deleted in the terminal device, to delete the preconfigured information prepared for the terminal device in S802 (S809). This makes it possible to reuse the preconfigured information for adding or changing a secondary cell after the handover of the primary cell.

[0065] FIG. 9 shows a processing flow when the SN to which the terminal device is connected is changed. The processing of S901 to S906 is the same as S801 to S806. Note that, here, SN1 to SN3 exist as base station devices that provide cells that are candidates for the secondary cell, and when a handover or an addition or change of a secondary cell occurs, the terminal device deletes the preconfigured information of SN2 but maintains the preconfigured information of SN1 and SN3 without deleting it. After that, for example, it is assumed that the terminal device connects to SN1 using the cell provided by SN1 as a secondary cell (S907). In this case, in accordance with the setting in S905, the terminal device deletes only the preconfigured information that should be deleted, and does not delete the preconfigured information that should not be deleted (should be maintained). Here, the terminal device deletes the preconfigured information of SN2, but maintains the preconfigured information of SN3, which is not the connection destination, without deleting it (S908). Note that the terminal device does not delete the preconfigured information of SN1 because it is using it as the configuration information of the currently connected secondary cell. Thereafter, the terminal device may, for example, add or change the secondary cell using the maintained preconfiguration information (not shown). Furthermore, the MN may instruct the SN2, whose corresponding preconfiguration information has been deleted in the terminal device, to delete the preconfiguration information prepared for the terminal device in S902 (S909). This makes it possible to reuse the preconfiguration information for adding or changing a secondary cell even after the secondary cell has been added or changed.

[0066] It should be noted that the techniques according to the above-described embodiments can be used in combination with one another in part or in whole.

[0067] In this way, pre-configuration information for conditional handover and conditional secondary cell addition or change can be reused even after a change in connection destination due to a handover or secondary cell addition or change. This reduces the load of pre-configuration processing for conditional handover in conditions where handovers occur frequently. This can contribute to Goal 9 of the United Nations' Sustainable Development Goals (SDGs), which is to "Build resilient infrastructure, promote sustainable industrialization and foster innovation."

[0068] The invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope of the gist of the invention.

Claims

1. A terminal device, a connection means capable of connecting to a first base station device providing a first cell and a second base station device providing a second cell in parallel; a receiving means for receiving from the first base station device a notification including configuration information about a candidate base station device that provides a candidate cell to be changed to or added as the second cell when the second cell is changed or added while the terminal device is connected to the second base station device, the configuration information including conditions for changing or adding the second cell and communication parameters when the second cell is changed or added, and information indicating whether the terminal device should hold the configuration information about the candidate base station device when the terminal device changes or adds the second cell based on the conditions being satisfied; an execution means for executing the change or addition of the second cell based on the condition included in the notification being satisfied; a control means for controlling to delete the configuration information for the candidate base station device when the notification does not include an instruction to retain the configuration information for the candidate base station device, based on the change or addition of the second cell to the candidate base station device being performed based on the satisfaction of the condition; A terminal device comprising:

2. The terminal device according to claim 1, characterized in that, when the setting information for each of a plurality of the candidate base station devices is set for the terminal device, the notification indicates whether or not the setting information for each of the plurality of the candidate base station devices should be retained.

3. The terminal device according to claim 1, characterized in that the setting information set for each of a plurality of candidate base station devices that respectively provide a plurality of cells that are candidates to change to or add to the second cell includes identification information, and in the notification, the identification information indicates whether or not the setting information for each of the plurality of candidate base station devices should be retained.

4. The terminal device according to claim 1, characterized in that, when the terminal device performs a handover from the first base station device to another base station device to change the first cell, the receiving means receives from the first base station device a second notification indicating whether or not to retain the setting information set for each of a plurality of candidate base station devices that provide a plurality of cells that are candidates to change to or to add the second cell.

5. The terminal device according to claim 1, characterized in that identification information is assigned to the setting information for each of one or more of the candidate base station devices, and the notification indicates whether or not each of the setting information for each of the candidate base station devices should be retained using the identification information.

6. The terminal device according to claim 1, further comprising a notification means for, when a base station device to which the terminal device is connected is changed, notifying the currently connected base station device of capability information indicating whether or not the setting information for a base station device different from the changed destination can be retained.

7. 2. The terminal device according to claim 1, wherein the receiving means receives the notification transmitted from the first base station device by an RRCReconfiguration message.

8. A terminal device, a connection means capable of connecting to a first base station device providing a first cell and a second base station device providing a second cell in parallel; a receiving means for receiving from the first base station device a notification including configuration information for a candidate base station device that provides a candidate cell to be changed to or added as the second cell when the second cell is changed or the second cell is added while the terminal device is connected to the second base station device, the configuration information including conditions for the terminal device to connect to the candidate base station device and communication parameters when connected to the candidate base station device, and information indicating whether the configuration information for the candidate base station device should be deleted when the terminal device changes or adds the second cell based on the conditions being satisfied; an execution means for executing the change or addition of the second cell based on the condition included in the notification being satisfied; a control means for controlling the deletion of the configuration information for the candidate base station device when the notification indicates that the configuration information for the candidate base station device should be deleted; A terminal device comprising:

9. The terminal device according to claim 8, characterized in that, when the setting information for each of a plurality of the candidate base station devices is set for the terminal device, the notification indicates whether or not each of the setting information for the plurality of the candidate base station devices should be retained.

10. The terminal device according to claim 8, characterized in that the setting information set for each of a plurality of candidate base station devices that respectively provide a plurality of cells that are candidates to change to or add to the second cell includes identification information, and in the notification, the identification information indicates whether or not the setting information for each of the plurality of candidate base station devices should be retained.

11. The terminal device according to claim 8, characterized in that the receiving means receives from the first base station device a second notification as to whether or not to retain the setting information set for each of a plurality of candidate base station devices that respectively provide a plurality of cells that are candidates to change to or to add the second cell, when the terminal device performs a handover from the first base station device to another base station device to change the first cell.

12. The terminal device according to claim 8, characterized in that identification information is assigned to the setting information for each of one or more of the candidate base station devices, and the notification indicates whether or not each of the setting information for each of the candidate base station devices should be retained using the identification information.

13. The terminal device according to claim 8, further comprising a notification means for, when a base station device to which the connection is made is changed, notifying the currently connected base station device of capability information indicating whether or not the setting information for a base station device different from the changed destination can be retained.

14. 9. The terminal device according to claim 8, wherein the receiving means receives the notification transmitted from the first base station device by an RRCReconfiguration message.

Images