Base station apparatus advancing connection destination changing processing, terminal device, control method, and program

Abstract

To increase efficiency of switching between cells connected to a terminal device.SOLUTION: When a terminal device has setting information on first another base station apparatus, a base station apparatus notifies the terminal device of whether or not the setting information on the first another base station apparatus should be deleted, in response to connection of the terminal device to second another base station apparatus different from the first another base station apparatus by the change or addition of handover or a secondary cell.SELECTED DRAWING: Figure 6

Description

[Technical field]

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

[0002] In a cellular communication system, in order to ensure the continuity of communication, a handover technique is used to switch the connection destination of a terminal device according to the movement of the terminal device. In a standard handover method, after the communication quality of a connected wireless link in the terminal device deteriorates, a process such as handover preparation is started on the core network side, and an instruction message is transmitted from the base station device to the terminal device. However, in this method, since it takes time for the process from the actual deterioration of communication quality to the transmission of the handover instruction, the time during which communication is not possible or communication quality is insufficient may be prolonged. In response to this, a method is specified in which the process such as the preparation is performed in advance, and when a predetermined condition is satisfied in the terminal device, the connection destination cell is switched without receiving an instruction message from the base station device (see Non-Patent Document 1). The predetermined condition includes, for example, a case in which the wireless quality of an adjacent cell becomes better than the wireless quality of the connected cell by a predetermined level or more in the terminal device, or a case in which the wireless quality of the connected cell becomes equal to or lower than a predetermined value. According to this method, the 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 not possible or communication quality is insufficient can be significantly reduced. This type of handover is called a conditional handover. Similarly, in a multi-connectivity (MC) or the like in which a terminal device is connected to multiple cells, a preparation process or the like can be performed in advance, and when a certain condition is satisfied 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 addition or change of a secondary cell, the setting information previously set in the terminal device is deleted after connection to the changed 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-setting 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 cells to which terminal devices are 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-configured candidate for handover to a terminal device connected to the base station device, or that provides a cell that is a pre-configured candidate for adding or changing a secondary cell to a terminal device 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 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 embodiment of the present invention has an acquisition means for acquiring predetermined information about a second other base station device that is a candidate for a connection destination 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 under which the terminal device connects 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 a combination of the conditions and the communication parameters, and a control means for controlling the handover or change or addition of a secondary cell of 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 has a retaining means for retaining setting information for a first other base station device that is a candidate for a handover destination from a base station device to which the terminal device is currently connected, the setting information including conditions for the terminal device to hand over to the first other base station device and communication parameters when the terminal device hands over to the first other base station device, and a receiving means for receiving a notification from the base station device as to whether or not the setting 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 retaining means retains the setting information for the first other base station device without deleting it when the terminal device hands over to the second other base station device different from the first 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 the terminal device hands over to the second other base station device different from the first 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.

[0009] A terminal device according to another aspect of the present invention includes connection means capable of connecting in parallel to a first base station device providing a primary cell and a second base station device providing a secondary cell, and when the secondary cell is changed or the secondary cell is added while connected to the second base station device, configuration information about a first other base station device providing a candidate cell to be changed to or added as the secondary cell, the configuration information including conditions when the terminal device connects to the first other base station device and communication parameters when connected to the first other base station device, and a storage means for storing configuration information 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 a notification from the first base station device as to whether or not 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 embodiment of the present invention includes connection means capable of connecting in parallel to a first base station device providing a primary cell and a second base station device providing a secondary cell, and when the secondary cell is changed or the secondary cell is added while connected to the second base station device, configuration information about a first other base station device providing a candidate cell to be changed to or added as the secondary cell, the configuration information including conditions when the terminal device connects to the first other base station device and communication parameters when connected to the first other base station device, and 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 ... communication parameters when the terminal device connects to the second other base station device and adds a cell provided by the second other base station device as the secondary cell, the configuration information including communication parameters when the terminal device connects to the second other base station device and receives the secondary cell from another cell. and a receiving means for receiving a notification from the first base station device indicating whether or not the setting information for the first other base station device should be deleted when the first base station device has changed its secondary cell, wherein the holding means holds the setting information for the first other base station device without deleting it when the notification indicates that the setting 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 setting information for the first other base station device 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, in a state where the notification indicates that the setting information for the first other base station device should be deleted. Effect of the Invention

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

[0012] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a wireless communication system. [Diagram 2]FIG. 2 is a diagram illustrating an example of the hardware configuration of a base station device and a terminal device. [Diagram 3] 11 is a diagram illustrating an example of the functional configuration of a handover source base station device. [Figure 4] 11 is a diagram illustrating an example of the functional configuration of a handover destination base station device. [Diagram 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 PREFERRED EMBODIMENTS

[0013] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims, and not all combinations of features described in the embodiments are essential to the invention. Two or more features among the multiple features described in the embodiments may be arbitrarily combined. In addition, the same reference numbers are used for the same or similar configurations, and duplicated descriptions are omitted.

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

[0015] In this embodiment, when the terminal device 121 establishes a connection with any base station device, or when the wireless quality with the currently connected base station device 101 deteriorates to a certain degree, the terminal device 121 performs pre-setting for handover. The state in which the pre-setting is performed here is a state in which the setting of parameters and the like in the case where the terminal device 121 connects to a candidate handover destination is completed, and the terminal device 121 does not actually switch the destination base station device. The pre-setting includes a condition for actually performing handover, and when the terminal device 121 determines that the condition is satisfied, it disconnects the connection with the currently connected base station device, establishes synchronization with the new destination base station device, and attempts to connect. A handover in which the terminal device 121 autonomously switches the destination using such pre-setting and autonomously switches the destination in response to determining that the condition is 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 the handover destination. Then, the base station device that is a candidate for the handover destination 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. Here, the base station device that is a candidate for the handover destination holds the transmitted information on parameters as pre-configured information. In addition, the currently connected base station device or the base station device that is a candidate for the handover destination determines a condition that should be satisfied when handing over to the base station device that is a candidate for the handover destination. Then, the currently connected base station device notifies the terminal device 121 of the pre-configured information including information on parameters to be used when handing over to the base station device that is a candidate for the handover destination and the handover condition. This notification can be performed, for example, by 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] When the terminal device 121 receives the pre-setting information, it holds the pre-setting information and starts monitoring whether the handover conditions are satisfied. When the conditions are satisfied, the terminal device 121 executes processes such as disconnecting the currently connected base station device and establishing synchronization with the handover destination base station device in order to actually switch the connection destination. There may be a plurality of base station devices that are candidates for the handover destination. For this reason, the pre-setting information is also set separately for each of one or more base station devices that are candidates for the handover destination, and therefore, the pre-setting information for each base station device may include handover identification information that identifies each of the pre-setting information. In addition, since one base station device may configure multiple cells, the pre-setting information may be set separately for the multiple cells. The terminal device 121 monitors whether the conditions for performing handover corresponding to each of the multiple pre-setting information are satisfied, and enables the pre-setting information including the satisfied conditions to perform handover. In this way, the terminal device 121 can complete the conditional handover, and accordingly communicates using communication parameters related to the base station device (cell) that is the connection destination after the handover.

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

[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 assumed that the terminal device 121 frequently performs handover. In such a case, the generation and deletion of the pre-configured information are frequently repeated, which is not efficient. For this reason, in this embodiment, the terminal device 121 is made to be able to reuse the pre-configured information. That is, after the completion of the conditional handover, the terminal device 121 holds the pre-configured information related to the base station device of the candidate handover destination that was not selected, without deleting it. Note that, in the following, the description will be given using terms such as "pre-configured information related to the base station device", but this "base station device" may be read as "cell". For example, when one base station device provides multiple cells, pre-configured information may be prepared for each of the multiple cells, and the pre-configured information may be held 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 the pre-configuration 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 should be held or deleted when the terminal device 121 is handed over to a device other than the first other base station device of the candidate. In addition, this base station device may also notify the terminal device 121 of whether the pre-configuration information that was previously set by another base station device to which the terminal device 121 was previously connected and that has been held without being deleted even after one or more handovers should be continued to be held or deleted. In addition, the base station device may perform pre-configuration for a conditional handover for a first other base station device for which the terminal device 121 does not hold corresponding pre-configuration information, and cause the terminal device 121 to hold the pre-configuration information. At this time, the base station device may notify the terminal device 121 of whether the pre-configuration information for the first other base station device to be newly held should be held even after handover to a second other base station device different from the first other base station device.

[0021] The terminal device 121 continues to hold the preset information held 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 a validity period may be set for the preset information, and in this case, the terminal device 121 may delete the preset information upon expiration of the validity period even in a state where handover is not actually performed. Then, the terminal device 121 continues to hold the preset information, which is in a state where it is indicated by a notification that it should not be deleted, among the preset information preset for each of one or more first other base station devices (cells) which are candidates for the handover destination from the currently connected base station device, without deleting it 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 the preset information, which is in a state where it is indicated by a notification that it should be deleted, among the preset information for the first other base station device, 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 pre-settings for handover for the terminal device 121 with respect to the base station device 102, the base station device 104, and the base station device 105 as candidates for the handover destination for the currently connected terminal device 121. Then, the base station device 101 notifies the terminal device 121 whether or not the pre-setting 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 hold the pre-setting information for the base station device 102 and the base station device 105, and notify the terminal device 121 that the pre-setting information for the base station device 104 should be deleted. At this time, 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 pre-setting information for the base station device 104 as before. Then, the terminal device 121 continues to hold the pre-setting 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 is handed over to the cell 112 of the base station device 102, the terminal device 121 connects to the base station device 102 using the pre-setting information of the base station device 102 as before. Then, the terminal device 121 deletes the pre-setting information of the base station device 104, and continues to hold the pre-setting information of the base station device 105 without deleting it. Note that when the terminal device 121 is handed over to the base station device 102, the base station device 102 may, for example, newly set the base station device 101, the base station device 103, and the base station device 106 as candidate base stations for the handover destination, and perform pre-setting for the terminal device 121 for handover to those base station devices. In this way, the terminal device 121 can continue to hold the pre-setting information within the necessary range, and as a result, it is possible to perform another handover immediately after the handover without repeating the pre-setting.

[0023] In addition, the base station device currently connected to the terminal device 121 may, after handover, instruct the terminal device 121 which pre-configured information should be deleted from among the pre-configured information for other base station devices other than the base station device of the handover destination, or may instruct the terminal device 121 which pre-configured information should be held without being deleted. In addition, when the terminal device 121 holds pre-configured information for multiple base station devices, the base station device may notify the terminal device 121 whether each of the pre-configured information should be held or deleted individually. In addition, the base station device may notify the terminal device 121 whether multiple pieces of pre-configured information should be held or deleted collectively. In addition, the base station device may instruct the terminal device 121 to change the operation of holding or deleting the pieces of pre-configured information depending on which base station device the handover process is executed for. For example, regarding holding of the pre-configured information for the base station device 104, it is possible to notify that the information should be held when a handover to the base station device 102 is executed, and that the information should be deleted when a handover to the base station device 105 is executed.

[0024] In addition, when notifying the terminal device 121 whether each of one or more pieces of preconfigured information held by the terminal device 121 should be held or deleted, the base station device may use identification information individually assigned to each piece of 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. In addition, the base station device may notify the terminal device 121 of identification information corresponding to preconfigured information that should not be deleted (should continue to be held) after handover. In addition, as the identification information of the preconfigured information, an identifier (physical cell identifier) ​​of a 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, which maps the cell identifier to a predetermined numerical range. In this case, the base station device may notify the terminal device 121 of whether the preconfigured information corresponding to the cell should be held or deleted using the cell identifier. For example, the base station device can notify the terminal device 121 of a list of identifiers of cells corresponding to preconfigured information that should be deleted and a list of identifiers of cells corresponding to preconfigured information that should not be deleted.

[0025] The base station device may also adjust the preset information so that the identification information corresponding to the preset information to be held is within a predetermined range. After the handover, the terminal device 121 may hold the preset information whose identification information has a value within the predetermined range, and delete the preset information corresponding to the identification information having a value other than the predetermined range. In this case, the base station device may notify the terminal device 121 of whether or not 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 preset information to be held or deleted. When performing the handover preconfiguration, the base station device sets the corresponding identification information of the preset information that should not be deleted so that the value of the corresponding identification information is included within the predetermined range. Similarly, when performing the handover preconfiguration, the base station device sets the corresponding identification information of the preset information to be deleted so that the value of the corresponding identification information is not included within the predetermined range. Furthermore, when the identification information of the preset information that has been held in the terminal device 121 before the handover to the base station device itself and that should be deleted is included in the predetermined range, the base station device may change the value of the identification information of the preset information to be reset 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 makes it possible to notify the terminal device 121 of whether to delete or hold the preset information without explicit signaling by the base station device.

[0026] The handover source base station notifies the handover destination base station that the terminal device 121 holds pre-setting information. This information makes it unnecessary for the handover destination base station to set the pre-setting information already held by the terminal device 121 again. If the pre-setting information needs to be changed, the handover destination base station may execute a procedure for changing the pre-setting. For example, the handover source base station notifies the handover destination base station of identification information associated with the pre-setting information. In one example, when performing pre-setting, the handover source base station may share the pre-setting information to be pre-set for the terminal device with each of the candidate handover destination base station devices. For example, in FIG. 1, when base station device 101 performs pre-settings for terminal device 121 when handing over to each of base station devices 102, 104, and 105 as candidates for handover destinations, pre-setting 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 base station device 102, base station device 104, and base station device 105, respectively, to acquire pre-setting information related to these base station devices, and to notify these base station devices of the acquired pre-setting information. In this case, for example, base station device 102 holds pre-setting information for base station device 104 and base station device 105 before 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, handover source base station device 101 may notify base station device 102 of, for example, 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 delete the information.On the other hand, base station device 102 may continue to hold the preset information of 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] Also, the base station device of the handover destination candidate may not hold the pre-configuration information of the other candidate base station devices before the handover is performed. In this case, the base station device of the handover source may notify the base station device of the handover destination of the pre-configuration information that the terminal device 121 continues to hold in response to the handover being performed. For example, the terminal device 121 deletes the pre-configuration information of the base station device 104, but continues to hold the pre-configuration information of the base station device 105. In this case, the base station device 101 may notify the base station device 102 of the pre-configuration 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 pre-configuration information of the base station device 104. This is because the pre-configuration 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] Also, the handover source base station may notify only one of the conditions for executing handover and the communication parameters among the preset information to be held. In this case, the handover destination base station may reset either the conditions for executing handover or the communication parameters that have not been acquired, or may acquire them from the candidate base station of the handover destination corresponding to the preset information. Also, the handover source base station may notify the handover destination base station of at least one of the above-mentioned identification information, the handover execution conditions, and the communication parameters, as well as information indicating which cell the information is for handover to. This information may be identification information that can identify a cell or a frequency, such as a PCI (physical cell identifier) ​​or an ARFCN-ValueNR (absolute radio frequency channel number). Note that these pieces of information may be included in the communication parameters of the preset information, but by notifying these pieces of information separately, the handover destination base station can recognize which cell or which frequency the preset information is related 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 may 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 device acquires from the handover source base station device, 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 preset information to be retained after handover from the handover source base station device, among preset information preset for one or more handover destination candidate base station devices in the terminal device 121. Then, the handover destination base station device controls the subsequent handover of the terminal device 121 to another base station device based on the acquired predetermined information.

[0030] In response to the terminal device 121 establishing a connection in a predetermined area (initial connection or handover), the connected base station device may execute pre-settings for the terminal device 121, including conditions to be satisfied when the terminal device 121 hands over to each of the multiple base station devices belonging to the predetermined area and settings of communication parameters to be used after the handover. Then, the base station device to which the terminal device 121 is connected shares the pre-setting information that has been pre-set with other base station devices in the predetermined area. In addition, the base station device to which the terminal device 121 is connected may also perform pre-settings in the case where a handover from another base station device to itself is performed, and may share the pre-setting information with other base station devices in the predetermined area. Then, the base station device in the predetermined area may delete the pre-setting information in response to the terminal device 121 handing over to outside the predetermined area. According to this, after the terminal device 121 establishes a connection in the predetermined area, the terminal device 121 can continuously execute a conditional handover in the predetermined area.

[0031] For example, it is assumed that the cell 111, the cell 112, the cell 114, and the cell 115 form a predetermined area, and the terminal device 121 establishes a connection with the base station device 101. At this time, for example, in response to the terminal device 121 establishing a connection or in response to an attempt to perform a handover from the base station device 101, the base station device 101 executes pre-setting for handover within the predetermined area. The base station device 101 transmits a handover request message to the base station device 102, the base station device 104, and the base station device 105, for example, and acquires information on communication parameters after the handover. In addition, the base station device 101 or a candidate base station device for the handover destination determines the handover conditions. Furthermore, the base station device 101 assigns identification information corresponding to a combination (pre-setting information) of the handover conditions and the communication parameters. Note that the base station device 101 may determine the identification information in advance and transmit the handover request message including the identification information. Then, the base station device 101 transmits the acquired pre-configuration information and identification information to the base station device 102, the base station device 104, and the base station device 105, which are candidates for the handover destination. The base station device 101 may also transmit pre-configuration information and identification information for when a handover is performed 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 pre-configuration 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 pre-configuration 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 pre-configuration information for the base station device 101, the base station device 102, and the base station device 104. Then, the base station device 101 also notifies the terminal device 121 of the pre-configured 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 pre-configured information should be deleted.For example, the pre-configured 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 having identification information different from the identification information of the area to which the currently connected base station device belongs, the pre-handover pre-configured information assigned with the identification information of the area to which the base station device before the handover belongs may be deleted.

[0032] The terminal device 121 may delete the preset information when, for example, the connected base station device explicitly notifies the deletion of the preset information or when the expiration date has passed, but 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, the terminal device 121 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 of the base station devices within the predetermined area to delete the preset information upon success of the handover (or upon disconnection of the connection with the base station device). For example, in response to terminal device 121 performing a handover 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] In addition, when the handover conditions or communication parameters need to be changed, the change may be made in the entire predetermined area, or only in some base station devices. 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 another area (for example, an area specific to the terminal device 121) may be defined. The predetermined area may be dynamically set, and for example, 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 response to the terminal device 121 handing over from the base station device 101 to the base station device 102. In this case, the base station device 102 executes a process such as transmitting a handover request message to the base station device 103 and the base station device 106, shares the pre-setting information with each base station device in the predetermined area, and notifies the terminal device 121 of the pre-setting information. Also, for example, in response to the handover of the terminal device 121 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 makes it possible to appropriately form a predetermined area according to the location of the terminal device 121 and appropriately prepare preconfigured information for conditional handover.

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

[0035] In the above description, the process when the terminal device 121 executes a conditional handover has been described, but the same method can be applied to the addition or change of 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 a pre-setting, the terminal device 121 usually deletes pre-setting information related to a base station device that provides a candidate for a secondary cell that was not selected as a connection destination. In contrast, in this embodiment, the terminal device 121 is enabled to hold this pre-setting information without deleting it. Also, even when there is a change in the primary cell (i.e., a handover), the terminal device 121 deletes pre-setting information related to a base station device that provides a candidate for a secondary cell. In contrast, in this embodiment, even when there is a handover regarding the primary cell, the terminal device 121 can hold pre-setting information related to a candidate for a secondary cell without deleting it.

[0036] The process of deleting the preset information may be performed in the same manner as the process at the time of the handover described above. For example, when a base station device providing a primary cell for the terminal device 121 connects to a new other base station device by changing or adding a secondary cell, the base station device 121 may notify the terminal device 121 of whether or not to continue to hold the preset information related to the 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 candidates for the secondary cell, the preset information is prepared for each of the multiple other base station devices that provide the multiple cells. Then, for each of the preset information for each of the multiple other base station devices, a setting of whether or not to delete the preset information when changing or adding a secondary cell to which the connection is made, and a notification of the setting to the terminal device 121 may be performed. In addition, the notification of whether or not to delete the preset information may include information indicating which of the multiple preset information should be deleted or which should not be deleted. In addition, information corresponding to the preset information that is not deleted in the terminal device 121 may be shared between the base station devices along with a change or addition of the connection destination of the terminal device 121. For example, when a change of the primary cell occurs (i.e., handover), the base station device providing the primary cell before the change may notify the base station device providing the primary cell after the change of information capable of identifying 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 a change of the secondary cell occurs, the base station device providing the secondary cell before the change may notify the base station device providing the secondary cell after the change of information capable of identifying preconfigured information that is not deleted and is held in the terminal device 121. Note that the base station device providing the secondary cell before the change may directly notify the base station device providing the secondary cell after the change, or the notification may be performed via the base station device providing the primary cell.This notification can be performed using a message such as UE CONTEXT MODIFICATION RESPONSE, UE CONTEXT RELEASE COMMAND, UE CONTEXT MODIFICATION REQUEST, etc. Also, this notification may be performed using a new Xn message.

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

[0038] In addition, In addition, processes similar to the processes related to the handover described above may be executed, 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 processes are similar to those of the processes during the handover described above, and therefore will not be repeated here.

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

[0040] In addition, as described above, the trigger for deleting the preset information related to the secondary cell candidate includes the addition and change of the secondary cell and the change (handover) of the primary cell. Here, when the primary cell is changed, for example, depending on which primary cell the handover is performed to, the secondary cell candidate for which the corresponding preset information is deleted or maintained can be determined. For example, depending on the available combination of the primary cell and the secondary cell, 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 the handover destination of the primary cell, and preset information related to other base station devices that provide them is held in the terminal device 121. It is also assumed that the fourth to seventh cells are set as candidates for the addition or change of the secondary cell, and preset information related to other base station devices that provide them is held in the terminal device 121. Here, it is assumed that only combinations of (first cell, fourth cell), (first cell, sixth cell), (first cell, seventh cell), (second cell, fourth cell), and (third cell, fifth cell) are available as combinations of primary cells and secondary cells. Note that information indicating such combinations of available 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 the secondary cell. For this reason, the terminal device 121 may delete preconfigured information related to the fifth cell. On the other hand, the terminal device 121 may maintain preconfigured information related to the fourth cell, sixth cell, and seventh cell without deleting them, since these cells can be used as secondary cells. Furthermore, when the terminal device 121 subsequently performs a handover from the first cell to the second cell, since the sixth and seventh cells cannot be used as secondary cells, 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, the terminal device 121 may delete all preconfigured information because the fourth cell, the sixth cell, and the seventh cell cannot be used as secondary cells.

[0041] In addition, the terminal device 121 may be configured to delete all preconfigured information related to candidates for the secondary cell when the primary cell is changed to a cell other than the designated cell. In this case, for example, when the terminal device 121 changes the primary cell to the designated cell, preconfigured information to be maintained without being deleted may be specified 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 been performed 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 secondary cell that can be used in combination as a primary cell, the terminal device 121 may delete all preconfigured information related to candidates for the secondary cell. This is because it is assumed that the secondary cell cannot be set while the terminal device 121 is connected to such a primary cell. In addition, the terminal device 121 may maintain preconfigured information related to candidates for the secondary cell when the primary cell is changed to a designated cell. On the other hand, when the terminal device 121 changes the primary cell to a cell other than the designated cell, preconfigured information to be maintained without being deleted may be specified as described above.

[0042] Also, for example, when the terminal device 121 executes a reconnection process, the reconnection destination cell may instruct deletion of all or part of preconfigured information related to a secondary cell candidate. In this case, the terminal device 121 may retain or delete the preconfigured information according to an instruction from the reconnection destination cell. Also, the terminal device 121 may operate to retain the preconfigured information when reconnecting to a cell designated in advance, and to delete the preconfigured information when reconnecting to a cell not designated in advance.

[0043] In addition, when the terminal device 121 connects to a base station device (of a primary cell) or when requested by the base station device, the terminal device 121 can notify (to the network) the base station device of capability information (UE Capability) indicating whether or not the retained preconfigured information can be maintained at the time of handover or addition or change of a secondary cell. The base station device can execute the above-mentioned process when the capability information indicates that the terminal device 121 can maintain the preconfigured information. That is, 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-mentioned 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 addition or change of a secondary cell occurs.

[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 procedure as the above process may be used for handover to another cell (frequency) of the same base station device or addition or change as 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] In the following, a description will be given of 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.

[0046] (Device configuration) A hardware configuration example of the base station device and the terminal device will be described with reference to FIG. 2. In one example, the base station device and the terminal device are configured to 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 configured to include one or more processing circuits such as a general-purpose CPU (Central Processing Unit) or an ASIC (Application Specific Integrated Circuit), and executes the overall processing of the device and each of the above-mentioned processes by reading and executing a program 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 processing 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 configured, for example, by a removable external storage device. The communication circuit 205 is configured, for example, by a circuit for wireless communication of LTE or 5G. Note that, although one communication circuit 205 is illustrated in FIG. 2, the base station device and the terminal device may have multiple communication circuits. For example, the base station device and the terminal device may have a common antenna with the wireless communication circuits for LTE and 5G. The base station device and the terminal device may have an antenna for LTE and an antenna for 5G separately. The base station device may further have a wired communication circuit used when communicating with other base station devices or nodes of the core network. The terminal device may have a communication circuit for other wireless communication systems such as a wireless LAN. The base station device and the terminal device 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 the frequency bands.

[0047] FIG. 3 shows a functional configuration example of a first base station device which is a base station device providing a primary cell for setting a handover source base station device or a secondary cell change or addition. The first base station device has, for example, a conditional connection destination change setting unit 301, an information deletion necessity notification unit 302, an information provision unit 303, and an information sharing unit 304 as its functions. Note that FIG. 3 shows only functions particularly related to this embodiment, and other various functions that the first base station device may have are omitted from the illustration. For example, the first base station device naturally has other functions that LTE and 5G base station devices generally have. In addition, the functional blocks in FIG. 3 are shown in a schematic manner, and each functional block may be realized by being integrated, or may be further subdivided. In addition, each function 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 may be realized, for example, by a processor present inside 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 that is a handover destination base station device or a base station device that provides a secondary cell after an addition or change, as described later.

[0048] The conditional connection destination change setting unit 301 executes a setting process for conditional handover of the terminal device or addition or change of 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 of the conditional handover) to a base station device that is a candidate for the handover destination, and acquires information on communication parameters to be used after handover to the candidate base station device from the candidate base station device. In addition, 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 addition or change of a conditional secondary cell) to a base station device that provides a candidate cell for the secondary cell to be added or changed, and acquires information on communication parameters to be used after adding or changing the cell provided by the base station device as a secondary cell from the base station device that provides the candidate cell for the secondary cell. Then, the conditional connection destination change setting unit 301 notifies the terminal device of the communication parameters, and performs presetting of a conditional handover or a conditional addition or change of a secondary cell for the terminal device. Note that the conditions for executing the handover or the addition or change of the secondary cell may be acquired from a candidate base station device of the connection destination by the handover or the addition or change of the secondary cell, or may be determined by the conditional connection destination change setting unit 301.

[0049] The information deletion necessity notification unit 302 notifies the terminal device whether the pre-configured information for each of the base station devices of the connection change destination candidates set by the conditional connection destination change setting unit 301 should be deleted or kept after connecting to another base station device different from the base station device. Whether the pre-configured information should be deleted may be set by the communication carrier, or may be determined according to a rule such as deleting the pre-configured information for a base station device with a small cell size, deleting the pre-configured information when the distance from the current location of the terminal device is a predetermined distance or more. Note that whether the pre-configured information should be deleted may be determined for each base station device (cell), but in one example, the pre-configured information to be deleted in relation to the connection change destination base station device may be specified. For example, when the terminal device 121 performs a handover or a secondary cell change from the base station device 101 to the base station device 102, the pre-configured information of the base station device 104 is deleted, but when the terminal device 121 performs a handover or a secondary cell change from the base station device 101 to the base station device 105, the pre-configured information of the 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 to delete the pre-configured information when notifying the terminal device of the pre-configured information, or may implicitly notify the necessity to delete the pre-configured information based on a predetermined rule, such as not deleting the pre-configured information if the value of the identification information corresponding to the pre-configured information is within a predetermined range.

[0050] When a terminal device that has been notified that one or more pieces of preconfigured information will continue to be held executes 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 a secondary cell, predetermined information including at least one of a condition for executing the handover or the addition or change of a secondary cell, communication parameters, and identification information corresponding to the condition and the communication parameters (preconfigured information), which correspond to the preconfigured information that will continue to be held. Note that the information providing unit 303 provides preconfigured information for a base station device different from the base station device connected by the handover or the addition or change of a secondary cell, out of the one or more pieces of preconfigured information.

[0051] For example, when preconfiguration information is shared among a plurality of base station devices including the own device belonging to a predetermined area, the information sharing unit 304 provides preconfiguration information for the own device and acquires preconfiguration information from base station devices other than the own device among the plurality of base station devices. In this case, the conditional connection destination change setting unit 301 provides the terminal device with the shared preconfiguration information (except for the preconfiguration information of the own device in some cases). At this time, the condition deletion necessity notifying unit 302 may explicitly notify that preconfiguration information for the base station device belonging to the predetermined area should be deleted when a handover or addition or change of a secondary cell is performed beyond the predetermined area. Note that a rule may be set in advance that preconfiguration information for the base station device belonging to the predetermined area should be deleted when a handover or addition or change of a secondary cell is performed beyond the predetermined area, and in this case, an explicit deletion instruction may not be transmitted. Note that the information sharing unit 304 may notify that preconfiguration information for the base station device belonging to the predetermined area should be deleted only when a change of a 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, for example, an information acquisition unit 401, a connection destination change control unit 402, an information sharing unit 403, and an information deletion unit 404 as its functions. Note that FIG. 4 shows only functions particularly related to this embodiment, and other various functions that the second base station device which is a handover destination base station device or a secondary cell after an addition or change may have are omitted from the illustration. For example, the second base station device naturally has other functions that LTE and 5G base station devices generally have. In addition, the functional blocks in FIG. 4 are shown in a schematic manner, and each functional block may be realized by being integrated, or may be further divided. In addition, each function 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 may be realized, for example, by a processor present inside the communication circuit 205 executing predetermined software. In addition, the details of the processes executed by each functional unit will not be described here, but only the general functions will be outlined. In addition, the second base station device can 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 when the terminal device is handed over to the terminal device itself or when the terminal device is connected to a cell provided by the terminal device as a secondary cell after change or addition, predetermined information corresponding to pre-setting information for changing the connection destination to another base station device (handover or addition or change of a secondary cell) that should be held in the terminal device. The predetermined information includes at least one of a condition that should be satisfied when the connection destination is changed, a communication parameter that should be used after the connection destination is changed, and identification information corresponding to the condition and the communication parameter. If the predetermined information is insufficient to execute the connection destination change control of the terminal device, the information acquisition unit 401 may acquire additional information for the 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 the control of the conditional handover or the conditional addition or change of the secondary cell based on the information acquired by the information acquisition unit 401. In addition, the connection destination change control unit 402 may execute the process of the conditional handover or the conditional addition or change of the secondary cell again in order to change the acquired information.

[0054] The information sharing unit 403 is the same as the above-mentioned information sharing unit 304. For example, when the pre-setting information is shared among a plurality of base station devices including the own device belonging to a predetermined area, the information sharing unit 403 provides the pre-setting information for the own device and acquires the pre-setting information from the base station devices other than the own device among the plurality of base station devices. For example, the information deleting unit 404 deletes the pre-setting information shared by the information sharing unit 403 in response to the terminal device moving out of the predetermined area. In addition, the information deleting unit 404 can delete the information acquired by the information acquiring unit 401 in response to the connection destination of the terminal device being changed to another base station device.

[0055] FIG. 5 shows an example of the functional configuration of the terminal device. The terminal device has, 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 as its functions. Note that FIG. 5 shows only functions particularly related to this embodiment, and various other functions that the terminal device may have are omitted. For example, the terminal device naturally has other functions that LTE and 5G terminal devices generally have. In addition, the functional blocks in FIG. 5 are shown in schematic form, and each functional block may be integrated and realized, or may be further subdivided. In addition, 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 may be realized, for example, by a processor present inside the communication circuit 205 executing a predetermined software. Note that the details of the processing performed by each functional unit will not be described here in detail, and only the rough functions will be outlined.

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

[0057] (Processing flow) Next, an example of the flow of processes executed in the wireless communication system will be described with reference to Fig. 6 and Fig. 7. Note that since the details of each process described here are as described above, only the outline of the processes will be described here, and the details will not be described.

[0058] In FIG. 6, it is assumed that an initial connection is established between the terminal device 121 and the base station device 101. In this state, the base station device 101 decides to start preparation for a conditional handover by receiving, for example, a measurement report of wireless quality 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, for example, information such as communication parameters currently used in communication with the terminal device 121 and the type of communication service. The base station device that is a candidate for the handover destination may determine, for example, based on the information such as the communication parameters, whether or not it is possible to provide a communication service equivalent to that before the handover, and may reject the handover request if it is unable to provide such a communication service. In FIG. 6, it is assumed that all the 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). The base station device 101 may, for example, specify identification information of a conditional handover (i.e., identification information corresponding to preconfigured 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 the handover and transmit the conditions by including them in the handover request. When the conditions should be changed, the candidate base station device may present the changed conditions to the base station device 101 in response to the handover request. The base station device 101 may not determine conditions for executing the handover, and 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 each of the pieces of preconfiguration information corresponding to each of the candidate base station devices of the handover destination should be held or deleted even 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. It is assumed here that the notification has been transmitted to continue holding 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 executes the preconfiguration (S606).

[0060] Thereafter, the terminal device 121 is deemed to have satisfied the conditions for handing over to the base station device 102 (S607). The terminal device 121 disconnects the currently connected base station device 101 (not shown) and executes a connection process including establishing synchronization with the base station device 102 (S608). When the base station device 102 succeeds in connecting to the terminal device 121 and completes the handover, it transmits a notification of the success of the handover to the base station device 101, which is the handover source (S609). In response to the notification of the success of the handover, the base station device 101 notifies the base station device 102 of the state of the sequence number (S610). In this embodiment, the base station device 101 also transmits information on preset information that is preset in the terminal device 121 and is not 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 on the preset information may be the preset information itself, but may be, for example, 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, whose corresponding preset information is deleted in the terminal device 121, to delete the stored preset information (S611). This notification may be performed by, for example, 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 is handed over to a base station device other than the base station device 104, so the terminal device 121 deletes the preset information (S612). The base station device 101 notifies the base station device 104, whose 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 becomes able to notify the base station device 102 of the success of the handover.

[0061] Next, a process flow in which pre-configured information is shared in a predetermined area formed by the base station device 101, the base station device 102, the base station device 104, and the base station device 105 will be described with reference to FIG. 7. In this process, first, in response to the terminal device 121 being connected to the base station device 102 (S701), the base station device 102 starts the conditional handover process. Note that this is just an example, and the base station device 102 may start the conditional handover process when the wireless quality of the terminal device 121 satisfies a condition for starting the conditional handover process. The base station device 102 transmits a handover request for the conditional handover to other base station devices (the base station device 101, the base station device 104, and the base station device 105) in 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 the base station device 102 again after the terminal device 121 has handed over to the base station device, conditions under which the handover should be performed, and identification information, and provides pre-setting information of the base station device 102 to the other base station devices. The base station device 102 also provides the pre-setting information of the other base station devices that has been collected and obtained to the other base station devices. For example, the pre-setting information of the base station device 104 and the base station device 105 is provided to the base station device 101. Note that the pre-setting information of the base station device 101 may be provided to the base station device 101. The base station device 102 then transmits a message including the shared pre-setting information to the terminal device 121 (S707), and the terminal device 121 holds the pre-setting information and performs pre-setting (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 performs settings for a conditional handover to the base station device 103 outside the predetermined area for the terminal device 121 (S705 to S708). Then, it is assumed that the terminal device 121 decides to handover to the base station device 103, for example, when the handover condition for the base station device 103 is satisfied (S709). Then, in accordance with this decision, the terminal device 121 disconnects the connection with the currently connected base station device 102 and executes a connection process with the base station device 103 (S710). It is assumed that the handover to the base station device 103 is executed by a conditional handover, but this is not limited to the above. That is, the terminal device 121 may transmit a measurement report to the base station device 102, for example, when the wireless quality of the signal from the base station device 103 satisfies a predetermined condition, and the handover process 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 state 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 process flow of handling pre-configuration information related to secondary nodes will be described. FIG. 8 shows the process 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 switching of the connection destination (handover) is represented as S-MN (Source MN), and the MN after the switching of the connection destination is represented 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 represented as a secondary node (SN), and in FIG. 8, two SNs, SN1 and SN2, are shown. In this process, it is assumed that the S-MN first decides to start conditional secondary node addition and change (CPAC, Conditional PSCell Addition / Change) for setting the secondary cell of the connected terminal device (S801). The S-MN may start this process, for example, when the wireless quality in the terminal device satisfies the condition for starting the CPAC process. In addition, the S-MN may extract, for example, a base station device providing a cell in a frequency band that can be used together with the frequency band used by the own device as a candidate SN. Here, it is assumed that the S-MN extracts SN1 and SN2 as base station devices that provide cells that are candidates 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 the response (S803). Then, the S-MN 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). Note that here, it is assumed that the preconfiguration information of SN1 is specified to be retained even after a handover or a secondary cell is added or changed, and that the preconfiguration information of SN2 is specified to be deleted when a handover or a secondary cell is added or changed. Note that this is just an example, and for example, the preconfiguration information to be deleted and the preconfiguration information to be maintained may be configured to be different when a primary cell is changed (handover) from when a secondary cell is added or changed.Then, the terminal device holds 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 have been handed over to the T-MN by, for example, executing the above-mentioned conditional handover procedure or by executing the S-MN-led handover procedure (S807). At this time, the terminal device of this embodiment deletes only the preconfigured information to be deleted according to the setting in S805, triggered by the handover, 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 the secondary cell using the maintained preconfigured information (not shown). In addition, the S-MN may instruct the 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 and changing the secondary cell after the handover of the primary cell.

[0065] FIG. 9 shows a flow of processing 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. Here, SN1 to SN3 exist as base station devices that provide cells that are candidates for the secondary cell, and the terminal device deletes the preconfigured information of SN2 when a handover or addition or change of a secondary cell occurs, but maintains the preconfigured information of SN1 and SN3 without deleting it. After that, for example, the terminal device connects to SN1 with the cell provided by SN1 as a secondary cell (S907). In this case, the terminal device deletes only the preconfigured information that should be deleted according to the setting in S905, 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 SN3, which is not the connection destination, without deleting it (S908). Note that the terminal device does not delete the preconfigured information of SN1, since it uses it as the setting information of the secondary cell currently connected. Thereafter, the terminal device may, for example, add or change the secondary cell using the maintained preconfiguration information (not shown). In addition, 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 and changing the secondary cell even after the secondary cell is 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, either partially or entirely.

[0067] In this way, the pre-configuration information for conditional handover and conditional addition or change of secondary cell can be reused even after the connection destination is changed due to handover or addition or change of secondary cell. This makes it possible to reduce the load of pre-configuration processing for conditional handover under conditions where handovers occur frequently. This makes it possible to contribute to Goal 9 of the Sustainable Development Goals (SDGs) led by the United Nations, "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 in parallel to a first base station device providing a primary cell and a second base station device providing a secondary cell; a receiving means for receiving, from the first base station device, a notification including 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 a condition when the terminal device connects to the first other base station device and a communication parameter when connected to the first other base station device, and information indicating whether or not the configuration information for the first other base station device should be deleted when the terminal device changes or adds the secondary cell; an execution means for executing a change or addition of the secondary cell based on the condition included in the notification being satisfied; Based on the change or addition of the secondary cell being performed, When the notification indicates that the configuration information for the first other base station device should not be deleted, the configuration information for the first other base station device is retained without being deleted; When the notification indicates that the configuration information for the first other base station device should be deleted, the configuration information for the first other base station device is deleted. A holding means for controlling the 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 first other base station devices is pre-configured for the terminal device, the notification indicates whether or not the setting information for each of the plurality of the first other base station devices should be deleted.

3. The terminal device according to claim 1, characterized in that the setting information that is pre-configured for each of a plurality of first other base station devices that respectively provide a plurality of cells that are candidates for changing to or adding the secondary cell includes identification information, and in the notification, the identification information indicates whether or not to delete the setting information for each of the plurality of first other base station devices.

4. The terminal device according to claim 1, characterized in that the receiving means receives from the first base station device a second notification as to whether or not to delete the pre-configured configuration information for each of the first other base station devices that provide multiple cells that are candidates for changing or adding the secondary cell, when the terminal device performs a handover from the first base station device to another base station device to change the primary cell.

5. The terminal device according to claim 1, characterized in that the notification indicates configuration information to be deleted from the configuration information for each of the one or more first other base station devices that are pre-configured for the terminal device.

6. The terminal device according to claim 1, characterized in that the notification indicates configuration information that should not be deleted from the configuration information for each of the one or more first other base station devices that are pre-configured for the terminal device.

7. The terminal device according to claim 1, further comprising an acquisition means for acquiring the setting information for each base station device belonging to a specified area, the setting information being set to be deleted when the terminal device moves beyond the specified area in response to the terminal device being connected in the specified area.

8. 8. The terminal device according to claim 7, wherein the predetermined area is an area corresponding to an identical tracking area identifier, an identical tracking area code, or an identical system information area identifier.

9. 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 first other base station devices, and the notification indicates whether or not each of the first other base station devices should be deleted using the identification information.

10. The terminal device according to claim 9 , wherein the identification information is information corresponding to an identifier of a cell formed by the first other base station device.

11. The terminal device according to claim 9, characterized in that the holding means determines that the setting information for the first other base station device should not be deleted when a value indicated by the identification information assigned to the setting information for the first other base station device is within a predetermined range.

12. The terminal device according to claim 1, further comprising a notification means for, when a base station device to which the connection is to be 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 other than the changed destination can be maintained without being deleted.

13. 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.

14. A control method executed by a terminal device capable of connecting in parallel to a first base station device providing a primary cell and a second base station device providing a secondary cell, comprising: receiving, from the first base station device, a notification including 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 a condition when the terminal device connects to the first other base station device and a communication parameter when connected to the first other base station device, and information indicating whether or not the configuration information for the first other base station device should be deleted when the terminal device changes or adds the secondary cell; performing a change or addition of the secondary cell based on the condition included in the notification being satisfied; and Based on the change or addition of the secondary cell being performed, when the notification indicates that the configuration information for the first other base station device should not be deleted, holding the configuration information for the first other base station device without deleting it; deleting the configuration information about the first other base station device when the notification indicates that the configuration information about the first other base station device should be deleted; A control method comprising:

15. A computer provided in a terminal device capable of connecting in parallel to a first base station device providing a primary cell and a second base station device providing a secondary cell, receiving, from the first base station device, a notification including 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 a condition when the terminal device connects to the first other base station device and a communication parameter when connected to the first other base station device, and information indicating whether or not the configuration information for the first other base station device should be deleted when the terminal device changes or adds the secondary cell; performing a change or addition of the secondary cell based on the condition included in the notification being satisfied; Based on the change or addition of the secondary cell being performed, when the notification indicates that the configuration information for the first other base station device should not be deleted, causing the configuration information for the first other base station device to be retained without being deleted; when the notification indicates that the configuration information for the first other base station device should be deleted, causing the configuration information for the first other base station device to be deleted; Program for.

Images