Base station equipment, terminal equipment, and control method for cell switching with carrier aggregation

Abstract

The present invention provides a terminal device and a control method thereof that enable a terminal using carrier aggregation (CA) communication to quickly resume communication using carrier aggregation even after a cell switchover. [Solution] In a mobile communication system, the received power of signals received from a first cell provided by a first base station connected to a terminal and a second cell provided by a second base station different from the first base station is measured. Based on the measurement results, it is determined that a first condition regarding received power is met, and based on the received power of each of the multiple second cells, it is determined that a second condition for performing communication using CA in the multiple second cells is met. Based on this, cell switching from the first cell to the multiple second cells and activation of CA between the second base station and the terminal are performed.

Description

[[Technical Field]]

[0001] The present invention relates to a cell switching technology for connecting a terminal in a mobile communication system. [[Background Art]]

[0002] In the 3rd Generation Partnership Project (3GPP (registered trademark)), LTM Cell Switch (L1 / L2 Triggered Mobility) is defined to more efficiently perform cell switching for a terminal to connect, compared with conventional layer 3 handover. LTM is an abbreviation for L1 / L2 Triggered Mobility. In cell switching by LTM, cell switching is performed at a lower layer compared with handover at layer 3, which enables fast cell switching. Non-Patent Document 1 describes a procedure for performing cell switching by LTM in a cellular communication standard.

[0003] Further, the 3GPP cellular communication standard describes communication using carrier aggregation. In communication using carrier aggregation, while a terminal is performing communication in a first cell configured by one base station, the terminal is enabled to perform communication in a second cell different from the first cell configured by the base station, and communication in the first cell and communication in the second cell are performed in parallel, thereby providing large-capacity communication to the terminal. [[Prior Art Documents]] [[Non-Patent Documents]]

[0004] [[Non-Patent Document 1]] 3rd Generation Partnership Project, "3GPP TS 38.300 V18.4.0 NR; NR and NG-RAN Overall description; Stage-2(Release 18)" [[Summary of the Invention]] [[Problem to be Solved by the Invention]]

[0005] If carrier aggregation is used in communication between a terminal and the serving base station to which the terminal is connected before cell switching, then carrier aggregation may also be used in communication between the terminal and the target base station to which the terminal is connected after cell switching. The present invention provides a technology that enables a terminal using carrier aggregation to quickly continue using carrier aggregation communication even after cell switching in a mobile communication system. [Means for solving the problem]

[0006] A base station device according to one aspect of the present invention is a terminal device that communicates with a base station device based on the cellular communication standard of the Third Generation Partnership Project (3GPP), and comprises: measuring means for measuring the received power of signals received from a first cell provided by a first base station device connected to the terminal device and a second cell provided by a second base station device different from the first base station device; and switching means for switching cells from the first cell to the second cell based on the result of the measurement that a first condition regarding received power has been met, wherein the first base station device and the terminal device When carrier aggregation (CA) is used in communication with the terminal device, and a single second base station device provides a plurality of second cells, a determination is made based on the received power of each of the plurality of second cells to determine whether a second condition for performing CA-based communication in the plurality of second cells is met. Based on the determination that the second condition is met in addition to the first condition, the switching means performs the cell switching from the first cell to the plurality of second cells and enables the CA between the second base station device and the terminal device.

[0007] A terminal device according to one aspect of the present invention is a base station device that communicates with a terminal device based on the cellular communication standard of the Third Generation Partnership Project (3GPP), and has control means that causes the terminal device to measure the received power of signals received from a first cell provided by the base station device and a second cell provided by another base station device, and based on the results of the measurement that a first condition regarding received power is met, causes the terminal device to perform cell switching from the first cell to the second cell, and when carrier aggregation (CA) is used in communication between the base station device and the terminal device, and when a plurality of the second cells are provided by a single other base station device, a determination is made based on the received power of each of the plurality of second cells to determine whether a second condition for performing communication using the CA in the plurality of second cells is met, and the control means causes the cell switching from the first cell to the plurality of second cells and the activation of the CA between the other base station device and the terminal device to be performed based on the determination that the second condition is met in addition to the first condition. [Effects of the Invention]

[0008] According to the present invention, in a mobile communication system, a terminal performing communication using carrier aggregation can quickly continue communication using carrier aggregation even after switching cells. [Brief explanation of the drawing]

[0009] [Figure 1] This is a diagram showing an example configuration of a mobile communication system. [Figure 2] This figure shows an example of a message sequence exchanged between communication devices. [Figure 3] This figure shows an example of a message sequence exchanged between communication devices. [Figure 4] This figure shows an example of the hardware configuration of a communication device. [Figure 5] This figure shows an example of the functional configuration of a base station. [Figure 6] This figure shows an example of the device's functional configuration. [Figure 7] This figure shows an example of a message sequence exchanged between communication devices. [Figure 8] This figure shows an example of a message sequence exchanged between communication devices. [Modes for carrying out the invention]

[0010] The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the invention as defined in the claims, and not all combinations of features described in the embodiments are essential to the invention. Two or more of the features described in the embodiments may be combined in any way. Furthermore, identical or similar configurations will be given the same reference numeral, and redundant descriptions will be omitted.

[0011] (System Configuration) Figure 1 shows an example configuration of a mobile communication system according to this embodiment. The mobile communication system of this embodiment is, for example, a cellular communication system compliant with the cellular communication standard of the Third Generation Partnership Project (3GPP®). The cellular communication standard may be Long Term Evolution (LTE), Fifth Generation Mobile Communication System (5G), Beyond 5G, 6G, etc. However, it is not limited to these, and the following discussion can be applied to a mobile communication system compliant with any wireless communication standard. This mobile communication system is composed of, for example, a base station 101, a base station 102, and a terminal 111. Base stations 101 and 102 may be referred to as base station 100 without distinction. Base station 100 exchanges wireless signals with terminal 111 via a wireless medium. Base station 100 includes, for example, gNB (next Generation Node B), eNB (evolved Node B), etc. Base station 100 is connected to a core network (not shown). The core network can be, for example, an Evolved Packet System (EPS) or a 5G Core Network (5GC). Terminal 111 is a terminal used by a user and exchanges radio signals with base station 100 via a wireless medium. Terminal 111 may be called User Equipment (UE). Terminal 111 includes, for example, smartphones, mobile phones, personal computers, tablet terminals, wearable devices, IoT (Internet of Things) terminals, etc. For example, base station 100 and terminal 111 can communicate using the connection established between terminal 111 and base station 100 in the cell provided by each base station 100. In Figure 1, base station 101 provides cell 121, and base station 102 provides cell 122. Note that one base station 100 can provide multiple cells. Figure 1 shows an example with two base stations 100 and one terminal 111, but in a mobile communication system, there may be three or more base stations 101 and two or more terminals 111. In this case, multiple terminals 111 may be connected to one base station 100, or one terminal 111 may be connected to multiple base stations 100.

[0012] Base stations 101 and 102 may be interconnected by a network 131. Network 131 may be a wired or wireless network. For example, base stations 101 and 102 may communicate over network 131 using an X2 interface or an Xn interface. The X2 interface may be used for communication between eNBs. The Xn interface may be used for communication between gNBs. For example, when base station 101 causes a terminal 111 connected to its device to switch from a cell 121 provided by its device to a cell 122 provided by base station 102, it may exchange information necessary for the switch with base station 102 using an X2 interface or an Xn interface.

[0013] In 3GPP's cellular communication standards, LTM Cell Switching is defined as a cell switching method that switches cells at a lower layer than the conventional Layer 3 (L3) handover. LTM stands for L1 / L2 Triggered Mobility. LTM cell switching allows for efficient switching of the cell to which a terminal is connected. Figure 2 shows an example of the sequence exchanged between communication devices when performing LTM cell switching. In Figure 2, the source base station 101 connected to terminal 111 instructs terminal 111 to measure and report the radio quality of cell 121 and surrounding cells provided by its device. This instruction can be made via a setting using the Layer 3 RRC Reconfiguration message. RRC stands for Radio Resource Control. Terminal 111 makes a measurement report according to the setting by the source base station 101 (S201). This measurement report can also be made using the Layer 3 Measurement Report message. Based on the measurement report, the source base station 101 selects one or more candidate cells (LTM candidate cells) to be the switching destination for cell switching (S202). The source base station 101 notifies the terminal 111 of the selected LTM candidate cells (S203). This notification may include configuration information for the terminal 111 to communicate in the selected LTM candidate cells. The source base station 101 also notifies the terminal 111 of the settings for measuring and reporting the radio quality of each LTM candidate cell at the Layer 1 (L1) level. These notifications may be made using RRC reconfiguration messages. An LTM candidate cell may include multiple cells provided by a single base station 100. For example, a single base station 100 may configure cells at multiple different frequencies. Furthermore, each cell configured by each beam formed by a single base station 100 may be distinguishable.For example, in Figure 1, if the area of ​​cell 122 provided by base station 102 is covered by a set of multiple beams formed by base station 102, each of the distinguishable individual cells provided by each beam may be included in the LTM candidate cells as a distinct cell from one another. Thus, the term cell in this embodiment includes each cell provided by one base station at multiple different frequencies, and each distinguishable cell provided by each beam formed by one base station. Terminal 111 responds with an RRC reconfiguration complete message. This completes the preparation phase for performing LTM.

[0014] Terminal 111 performs synchronization processing for each cell notified as an LTM candidate cell (S205, S206). For example, as downlink (DL) synchronization, terminal 111 may perform processes such as activating the TCI state and synchronizing with the LTM candidate cell. TCI is an abbreviation for Transmission Configuration Indication. Terminal 111 prepares for communication with the LTM candidate cell by activating the TCI state corresponding to the candidate beam used for communication with the LTM candidate cell. Terminal 111 may also perform DL direction synchronization by receiving the synchronization signal transmitted by the LTM candidate cell. In addition, terminal 111 may perform processes such as TA adjustment as uplink (UL) synchronization. TA is an abbreviation for Timing Advance. TA adjustment can adjust the timing at which the signal transmitted by terminal 111 reaches the target base station 102 that provides the LTM candidate cell. In this way, pre-synchronization is performed between terminal 111 and the base station providing the LTM candidate cell, enabling efficient cell switching. This completes the Early Sync phase.

[0015] Terminal 111 measures the L1 level radio quality of each LTM candidate cell based on the settings notified by source base station 101 and sends a measurement report to source base station 101 (S207). In measuring the L1 level radio quality, the radio quality of each beam from which the signal is transmitted may be measured for each signal transmitted from each base station 100. In addition, each measured radio quality value may be reported in the report of the L1 level radio quality measurement. Reporting to source base station 101 may be done periodically or based on the fulfillment of predetermined conditions included in the settings. For example, predetermined conditions include the beam quality of the serving cell provided by source base station 101 falling below a threshold (event 2), the beam quality of the LTM candidate cell becoming higher than the beam quality of the serving cell by an offset value (event 3), the beam quality of the LTM candidate cell becoming higher than a threshold (event 4), and the beam quality of the serving cell falling below a first threshold and the beam quality of the LTM candidate cell becoming higher than a second threshold (event 5). Beam quality is, for example, received power. Values ​​indicating received power include RSRP, RSRQ, RSSI, SINR, etc. RSRP is an abbreviation for Reference Signal Received Power. RSRQ is an abbreviation for Reference Signal Received Quality. RSSI is an abbreviation for Received Signal Strength Indicator. SINR is an abbreviation for Signal to Interference plus Noise Ratio. Source base station 101 can set one or more of the above events 2 to 5 as predetermined conditions. Terminal 111 measures the radio quality of the beam of the serving cell or LTM candidate cell, uses the measured value to determine whether the predetermined condition notified by source base station 101 is met, and reports to source base station 101 if the predetermined condition is met. This reporting method, in which terminal 111 reports to source base station 101 when the predetermined condition indicated in the setting is met as a trigger, can be called event-triggered reporting.

[0016] When source base station 101 receives a measurement report from terminal 111, it decides whether or not to perform a cell switch (S208). If it is decided to perform a cell switch, source base station 101 notifies terminal 111 that a cell switch should be performed (S209). For example, source base station 101 may give instructions to terminal 111 by sending a MAC CE containing an LTM Cell Switch Command. MAC CE is an abbreviation for Medium Access Control Control Element. When terminal 111 receives the notification that a cell switch should be performed, it disconnects from source base station 101 and applies the settings for communication with target base station 102 (S210). Target base station 102 is a base station that provides the cell selected as the switch destination from among the LTM candidate cells. Terminal 111 establishes a connection with target base station 102 using a random access procedure (S211). This completes the LTM cell switch. Thus, by using LTM cell switching, procedures at Layer 3 become unnecessary, and the processing time during switching is shortened due to early synchronization with one or more LTM candidate cells, making it possible to perform cell switching efficiently.

[0017] On the other hand, cellular communication standards in 3GPP define communication using carrier aggregation (CA), in which communication via a plurality of cells is performed in parallel between one base station 100 and one terminal 111. As described above, the base station 100 can configure distinguishable cells on each of a plurality of different frequencies and each of a plurality of different beams. In communication using CA, one of the plurality of cells provided by the base station 100 is used as a primary cell (Pcell), and one or more of the other cells are used as secondary cells (Scell). When CA is used for communication between the base station 100 and the terminal 111, control information and user data are exchanged on the Pcell, and user data are exchanged on the Scell. Control information is not exchanged on the Scell, and control information that should be notified from the base station 100 on the Scell is notified to the terminal 111 via an RRC message on the Pcell. In communication between the base station 100 and the terminal 111, a connection is first established on the Pcell, and then Scell communication for CA is activated as needed. Therefore, among the plurality of cells configured by the base station 100, which cell serves as a Pcell and which cell serves as a Scell may vary depending on the terminal 111.

[0018] FIG. 3 illustrates an example sequence of messages exchanged when the terminal 111 activates a Scell to perform communication using CA between the base station 100 and the terminal 111. In FIG. 3, it is assumed that the base station 100 and the terminal 111 have established a connection on the Pcell and are performing communication. First, the base station 100 instructs the terminal 111 to measure and report the radio quality of cells other than the Pcell provided by the base station 100 (S301). The base station 100 transmits a reference signal for the terminal 111 to measure radio quality in cells other than the Pcell configured by the base station 100 (S302). Although one cell other than the Pcell is illustrated in FIG. 3, a plurality of cells may be configured by the base station 100. In FIG. 3, one cell other than the Pcell is illustrated for convenience, and is referred to as a Scell candidate.

[0019] The terminal 111 measures the radio quality of the reference signal received from the Scell candidate, and reports the measurement result to the base station 100 (S303). For example, the terminal 111 may measure the reception power of the reference signal and report the measurement result to the base station 100. The base station 100 determines whether to perform communication using CA based on the measurement result. For example, when the measurement value of the radio quality of one or more Scell candidates exceeds a predetermined threshold in the measurement result, the base station 100 determines to use those Scell candidates as Scells and perform communication using CA. Further, when all the measurement values of the radio quality of the Scell candidates included in the measurement result are equal to or lower than the predetermined threshold, the base station 100 may determine not to perform communication using CA. When the base station 100 determines to perform communication using CA, the base station 100 notifies the terminal 111 of configuration information for performing communication in the Scell via the Pcell (S304). After completing the configuration of the configuration information for performing communication in the Scell, the terminal 111 sends a completion notification (S305). Then, the base station 100 notifies a message for activating the Scell configuration in the terminal 111 (S306). This message may be a MAC CE message. Through such message exchange, communication using CA based on communication in the Pcell and communication in the Scell can be performed between the base station 100 and the terminal 111 (S307).

[0020] Here, when terminal 111 is communicating with source base station 101 using CA, a cell switch from source base station 101 to target base station 102 may occur, for example, due to terminal 111's movement. For example, if terminal 111 is exchanging a large volume of traffic, CA-based communication may occur between terminal 111 and base station 100. In this case, if target base station 102 is capable of performing CA-based communication, it is highly likely that CA-based communication will continue even after terminal 111 switches to target base station 102. However, as shown in Figure 3, in order to perform CA-based communication, terminal 111 must first establish communication with target base station 102 in the Pcell, measure the radio quality of the Scell, and then activate the Scell ​​settings. Therefore, there is a possibility that terminal 111 may temporarily lack sufficient communication capacity between the time the cell switch is performed and the time the Scell ​​settings are activated.

[0021] In light of these circumstances, the terminal 111 in this embodiment performs cell switching from the source base station 101 to the target base station 102 and enables CA with the target base station 102 when the conditions for performing communication using CA are met based on the measured value of the received power of the target base station 102 before cell switching. For example, the terminal 111 measures the received power of signals received from the first cell provided by the source base station 101 and the second cell provided by the target base station 102, and performs cell switching from the first cell to the second cell based on whether the first condition regarding received power is met as a result of the measurement. The first condition may be, for example, one or more of the events 2 to 5 described above. When CA is used in communication between the source base station 101 and the terminal 111, and a single target base station 102 provides multiple second cells, a determination is made based on the received power of each of these multiple second cells to determine whether the second condition for performing communication using CA in these multiple second cells is met. Terminal 111, based on the determination that the second condition is met in addition to the first condition, switches from the first cell to multiple second cells and enables CA between the target base station 102 and itself. Source base station 101 instructs terminal 111 to measure the received power of the signals received from the first cell and the second cell, and, based on the measurement results, executes cell switching from the first cell to the second cell if the first condition is met. Furthermore, source base station 101, based on the determination that the second condition is met in addition to the first condition, executes cell switching from the first cell to multiple second cells and enables CA between the target base station 102 and terminal 111. The second condition may be that the received power of each of the multiple second cells meets the first condition. Furthermore, the second condition may be that, among the received powers of multiple second cells, at least one received power satisfies the first condition, and the other received powers are above a predetermined threshold.The second condition is not limited to these, and any method can be used to determine whether terminal 111 is capable of communicating with target base station 102 using CA. With this configuration, when terminal 111 switches from the first cell to the second cell, it is determined whether it is capable of communicating with target base station 102, which provides the second cell, using CA, and based on that determination, communication using CA is enabled at the time of cell switching. This makes communication using CA between terminal 111 and target base station 102 available immediately after cell switching.

[0022] Terminal 111 can send measurement results to source base station 101 and receive instructions from source base station 101 to switch cells from the first cell to the second cell. At this time, based on the fact that the instructions from source base station 101 include information indicating that a cell switch from the first cell to multiple second cells and the activation of CA between target base station 102 and terminal 111 should be performed, terminal 111 can perform a cell switch from the first cell to multiple second cells and the activation of CA between target base station 102 and terminal 111. For example, terminal 111 can determine whether the first and second conditions are met, and if it is determined that they are met, it can report to source base station 101. Based on receiving the report, source base station 101 can instruct terminal 111 to perform a cell switch from the first cell to multiple second cells and the activation of CA between target base station 102 and terminal 111. In this way, by configuring terminal 111 to determine the first and second conditions, the processing load on source base station 101 can be reduced. Terminal 111 can also determine whether the first condition is met, and if it is determined that the first condition is met, it can report this, and if it is determined that the second condition is met at source base station 101, it can receive instructions including information indicating that it should perform cell switching from the first cell to multiple second cells and enable CA between the second base station device and the terminal device. In this case, source base station 101 can determine whether the second condition is met based on the report, and if it is determined that the second condition is met, it can instruct terminal 111 to perform cell switching from the first cell to multiple second cells and enable CA between target base station 102 and terminal 111. In this way, by having source base station 101 and terminal 111 each perform the determination of the second and first conditions, the processing load can be distributed. Furthermore, the second condition can be flexibly set by the source base station 101 according to the wireless environment, etc.Furthermore, the source base station determines whether the first and second conditions are met based on the report from the terminal 111. Based on the determination that the first and second conditions are met, the source base station can instruct the terminal 111 to perform cell switching from the first cell to multiple second cells and enable CA between the other base station equipment and the terminal equipment. In this case, the terminal 111 receives instructions that indicate it should perform cell switching from the first cell to multiple second cells and enable CA between the second base station equipment and the terminal equipment if it is determined that the first and second conditions are met. By having the source base station 101 perform the determination of the first and second conditions in this way, the processing load on the terminal 111 can be reduced. In addition, the source base station 101 can flexibly set the first and second conditions. An example of the configuration and operation of the base station 101 and terminal 111 operating in this manner is described below.

[0023] (Circuit configuration) An example configuration of the base station 101 and terminal 111 will be described. Figure 4 shows the hardware configuration of the base station 101 and terminal 111. In one example, the base station 101 and terminal 111 are configured to include a processor 401, ROM 402, RAM 403, storage device 404, and communication circuit 405. The processor 401 is a computer configured to include one or more processing circuits, such as a general-purpose CPU (Central Processing Unit) or ASIC (Application-Specific Integrated Circuit). The processor 401 performs the overall processing of the device and the above-mentioned processing by reading and executing programs stored in the ROM 402 and storage device 404. The ROM 402 is a read-only memory in which information such as programs and various parameters related to the processing performed by the base station 100 is recorded. The RAM 403 functions as a workspace when the processor 401 executes programs and is a random-access memory in which temporary information is recorded. The storage device 404 is configured, for example, by a removable external storage device. The communication circuit 405 includes, for example, circuits for wired or wireless communication between the base station 101 and the terminal 111. For example, the base station 101 can communicate with the terminal 111 using the communication circuit 405 for LTE or 5G and an antenna (not shown). The base station 101 can also communicate with other base stations and network equipment (not shown) using the communication circuit 405 for wired communication. The terminal 111 can communicate with the base station 101 using the communication circuit 405 for LTE or 5G and an antenna (not shown).

[0024] (Functional Configuration) Figure 5 shows an example of the functional configuration of base station 101. Base station 101 includes, for example, a cell switching control unit 501, a report receiving unit 502, and a condition determination unit 503 as its functions. Figure 5 shows the functional configuration of base station 101 in this embodiment, and omits, for example, the general configuration of base station 101. As an example, base station 101 may have a function unit that exchanges information necessary for cell switching and communication using CA with other base stations using an X2 interface or an Xn interface. These function units can be realized, for example, by a processor 401 executing a program stored in ROM 402 or storage device 404 and controlling the communication circuit 405 as needed. However, it is not limited to this, and for example, dedicated hardware for realizing each function may be provided.

[0025] The cell switching control unit 501 controls the cell switching of terminal 111. For example, the cell switching control unit can cause terminal 111 to measure the received power of signals received from its own device and signals received from surrounding cells. As an example, the cell switching control unit 501 can instruct terminal 111 to perform a measurement by notifying terminal 111 of an RRC message including measurement settings or an RRC message including LTM candidate settings. The cell switching control unit 501 can also instruct terminal 111 to perform a cell switch. For example, the cell switching control unit 501 can cause terminal 111 to perform a cell switch based on the fulfillment of the first condition described above. In addition, the cell switching control unit 501 can instruct terminal 111 to activate CA based on the fulfillment of the second condition described above, in addition to the fulfillment of the first condition. For example, an instruction to activate CA may be to disable the TCI state corresponding to other cells while keeping the TCI state corresponding to the cell targeted for CA activated. For example, the cell switching control unit 501 can initiate cell switching by notifying terminal 111 of a MAC CE containing an LTM Cell Switch Command message.

[0026] The report receiving unit 502 receives measurement result reports from the terminal 111. For example, the report receiving unit 502 may periodically receive reports from the terminal 111. The report receiving unit 502 may also receive reports from the terminal 111 based on the determination that the first condition has been met at the terminal 111. Furthermore, the report receiving unit 503 may receive reports from the terminal 111 based on the determination that both the first and second conditions have been met at the terminal 111.

[0027] The condition determination unit 503 determines whether or not to have terminal 111 perform a cell switch based on the measurement result report from terminal 111. For example, the condition determination unit 503 may determine whether the first and second conditions are met based on reports received periodically from terminal 111. In this case, the condition determination unit 503 may determine that terminal 111 should perform a cell switch based on the first condition being met. Furthermore, the condition determination unit 503 may determine that terminal 111 should continue communication using CA even after the cell switch, based on the second condition being met. On the other hand, if the condition determination unit 503 receives a measurement result report based on the determination that the first condition has been met at terminal 111, it may determine whether or not the second condition is met. In this case, the condition determination unit 503 may determine that terminal 111 should perform a cell switch based on the receipt of the report from terminal 111. Furthermore, the condition determination unit 503 may determine, based on the fulfillment of the second condition, that terminal 111 should continue communication using CA even after cell switching. On the other hand, if the condition determination unit 503 receives a report of measurement results based on the determination that terminal 111 has fulfilled both the first and second conditions, it may determine, based on the receipt of the report from terminal 111, that terminal 111 should switch cells and continue communication using CA even after cell switching. The condition determination unit 503 may also use methods other than these to determine whether terminal 111 should switch cells or perform communication using CA. For example, in addition to the first and second conditions, the condition determination unit 503 may make a determination based on the traffic situation at its own device and the target base station.

[0028] Figure 6 shows an example of the functional configuration of terminal 111. Terminal 111 includes, for example, a wireless quality measurement unit 601, a cell switching unit 602, a report transmission unit 603, an instruction reception unit 604, and a condition determination unit 605 as its functions. Figure 6 shows the functional configuration of terminal 111 in this embodiment, and omits, for example, the general configuration of terminal 111. These functional units can be realized, for example, by the processor 401 executing a program stored in the ROM 402 or storage device 404 and controlling the communication circuit 405 as needed. However, it is not limited to this, and for example, dedicated hardware may be provided to realize each function.

[0029] The wireless quality measurement unit 601 performs wireless quality measurements. For example, the wireless quality measurement unit 601 can measure the received power of signals received from the source base station 101 and the target base station 102. As an example, the wireless quality measurement unit 601 can perform measurements based on RRC messages containing measurement settings and RRC messages containing LTM candidate settings received from the source base station 101.

[0030] The cell switching unit 602 performs cell switching. For example, the cell switching unit 602 may perform cell switching based on instructions from the source base station 101. As an example, the cell switching unit 602 may perform cell switching based on an LTM Cell Switch Command message received from the source base station 101. Cell switching may, for example, involve enabling the TCI state corresponding to the cell specified in the LTM Cell Switch Command message while disabling the TCI state corresponding to other cells. Also, if the LTM Cell Switch Command message contains information indicating that CA should be enabled, the cell switching unit 602 enables CA. For example, enabling CA may involve enabling the TCI states corresponding to multiple cells while disabling the TCI state for other cells.

[0031] The report transmission unit 603 reports the results measured by the radio quality measurement unit 601 to the source base station 101. For example, the report transmission unit 603 may transmit reports periodically. The report transmission unit 603 may also transmit a report when the condition determination unit 605 determines that the first condition is met. Furthermore, the report transmission unit 603 may transmit a report when the condition determination unit 605 determines that both the first and second conditions are met.

[0032] The instruction receiving unit 604 receives instructions from the source base station 101. For example, the instruction receiving unit 604 may receive an instruction from the source base station 101 to perform radio quality measurements. The instruction receiving unit 604 may also receive an instruction from the source base station 101 to configure settings for communication with LTM candidate cells. For example, configuring settings for communication with LTM candidate cells may involve enabling the TCI state corresponding to each LTM candidate cell. The instruction receiving unit 604 may also receive instructions for cell switching or CA activation. For example, the instruction receiving unit 604 may receive an LTM Switch Command message.

[0033] The condition determination unit 605 can perform condition determinations based on the measurement results from the wireless quality measurement unit 601. For example, the condition determination unit 605 can determine whether or not a first condition is met. The condition determination unit 605 can also determine whether or not a second condition is met. If the measurement settings or LTM candidate settings notified by the source base station 101 include information indicating the first or second condition, the condition determination unit 605 can perform condition determinations based on this information.

[0034] (Process flow) (Example of processing in the first case) This section describes the operations of the source base station 101 and terminal 111 when terminal 111, which is communicating with source base station 101 using CA, performs cell switching to target base station 102. Figure 7 shows an example of the operations performed by each device when terminal 111, which is communicating with source base station 101 using CA, performs cell switching to target base station 102. In Figure 7, it is assumed that one or more LTM candidate cells for terminal 111 to perform LTM cell switching are identified in advance by source base station 101. For example, source base station 101 may identify LTM candidate cells based on the radio quality of signals received by terminal 111 from its own device and surrounding cells, as provided by terminal 111. In this case, source base station 101 may instruct terminal 111 to measure and report the radio quality of signals received from its own device and from surrounding cells. For example, source base station 101 may give instructions using measurement configuration (MeasConfig). In response, terminal 111 may perform measurements according to the measurement settings and transmit a Measurement Report (S702). The Measurement Report may include information indicating the received power of signals received by terminal 111 from source base station 101 and surrounding base stations. Based on the Measurement Report, source base station 101 may identify LTM candidate cells. In Figure 7, it is assumed that target base station 102 has cells configured at two different frequencies. For example, the cell configured by target base station 102 at the first frequency will be called the first LTM candidate cell. The cell configured by target base station 102 at the second frequency will be called the second LTM candidate cell. In Figure 7, two cells are shown as being configured by target base station 102, but target base station 102 may have three or more cells. Terminal 111 may measure the received power of signals transmitted at each of the first LTM candidate cell and the second LTM candidate cell and provide a Measurement Report. The signals used to measure received power may be, for example, synchronization signals or reference signals.The synchronization signal may be, for example, a Synchronization Signal block (SSB). The reference signal may be, for example, a Channel State Information Reference Signal (CSI-RS). The source base station 101 identifies LTM candidate cells based on the measurement report received from the terminal 111 (S703). For example, the source base station 101 may identify each cell in the measurement report that shows a received power exceeding a predetermined threshold as an LTM candidate cell. In this example, the source base station 101 identifies the surrounding cells, including the first and second LTM candidate cells, as LTM candidate cells.

[0035] The source base station 101 instructs terminal 111 to configure the LTM candidate (S704). This configuration can be done, for example, using information for configuring the LTM candidate included in the RRC Reconfiguration message. This information for configuring the LTM candidate may be called the LTM Candidate Configuration. For example, the LTM Candidate Configuration may include information that identifies the LTM candidate cell and communication parameters that terminal 111 should use for communication after switching to each LTM candidate cell. Each LTM candidate cell configuration may be assigned an identifier to identify it. For example, each LTM candidate cell configuration may be assigned a different target configuration ID. The target configuration ID may be used by the source base station 101 to specify the configuration that terminal 111 should apply when switching cells. For example, by receiving the LTM Candidate Configuration, terminal 111 may activate the TCI state corresponding to each LTM candidate cell. Furthermore, by receiving an LTM Cell Switch Command from the source base station 101, terminal 111 can disable TCI states corresponding to other cells and configuration information while keeping the TCI states corresponding to the cells and configuration information specified by the LTM Cell Switch Command enabled. The source base station 101 can also instruct terminal 111 to measure the Layer 1 radio quality of signals received from its own device or LTM candidate cells. This instruction to measure radio quality may be included in the LTM candidate configuration or notified as a separate message. Radio quality is, for example, received power. The measured value (L1 measured value) in the Layer 1 radio quality measurement may be a measured value that represents the individual radio quality measured. For example, the measured value that represents the individual radio quality may be so-called raw data. On the other hand, the measured value (L3 measured value) in the Layer 3 radio quality measurement may be a statistical value of the measured value that represents the individual radio quality measured. For example, the statistical value may be the mean, maximum, median, weighted mean, etc. The source base station 101 may include a first condition in the LTM candidate setting for determining whether or not to report a value indicating the measured radio quality.The first condition includes, for example, events 2 to 5 described above. Terminal 111 uses the measurement results to determine whether the first condition is met, and if it is determined that the first condition is met, it may report the measurement results. Note that source base station 101 does not have to notify terminal 111 of the first condition. In this case, terminal 111 may periodically notify source base station 101 of the measurement results. For example, terminal 111 may notify source base station 101 of the measurement results each time it performs a measurement.

[0036] Furthermore, the source base station 101 may include a second condition in the LTM candidate setting for determining whether communication using carrier aggregation is feasible. The second condition may be, for example, that the first condition described above is satisfied in each of the multiple LTM candidate cells composed of a single target base station 102. Alternatively, the second condition may be, for example, that the first condition described above is satisfied in one of the multiple LTM candidate cells composed of a single target base station 102, and that one or more of the other LTM candidate cells composed of this target base station 102 satisfy the conditions that an Scell ​​must satisfy. For example, the condition that an Scell ​​must satisfy may be that the received power is higher than a predetermined threshold. Alternatively, the condition that an Scell ​​must satisfy may be that events 2 to 5 described above are satisfied between the Scell ​​of the source base station 101 and the target base station 102. For example, in the case of event 3, if the received power of the beam formed in the Scell ​​of the target base station 102 is greater than the received power of the beam of the Scell ​​of the source base station 101 by an offset value, the condition that the Scell ​​must satisfy may be met. Terminal 111 may use the measurement results to determine whether the second condition is met, and if it is determined that the second condition is met, it may report the measurement results. Note that source base station 101 does not have to notify terminal 111 of the second condition. In this case, source base station 101 may use the measurement results that terminal 111 periodically notifies or the measurement results that terminal 111 notifies based on the first condition being met to determine whether the second condition is met. Note that if terminal 111 has received information from target base station 102 indicating whether target base station 102 is capable of performing communication using CA, terminal 111 may determine whether the second condition is met if target base station 102 is capable of performing communication using CA.

[0037] When terminal 111 receives instructions from source base station 101, it stores information about each of the LTM candidate cells included in the instructions and responds to source base station 101 (S705). For example, terminal 111 responds with an RRC reconfiguration complete message. This completes the preparation phase for executing LTM.

[0038] Terminal 111 performs synchronization processing for each cell notified as an LTM candidate (S706, S707). For example, as downlink (DL) direction synchronization, terminal 111 may perform processes such as activating the TCI state and synchronizing with LTM candidate cells. TCI is an abbreviation for Transmission Configuration Indication. Terminal 111 prepares for communication with LTM candidate cells by activating the TCI state corresponding to the candidate beam to be used with the LTM candidate cell. Terminal 111 can also perform DL direction synchronization by receiving the synchronization signal transmitted by the LTM candidate cell. Terminal 111 can also perform processes such as TA adjustment for UL synchronization. TA is an abbreviation for Timing Advance. This completes the Early Sync phase. In this way, by activating the TCI state for the first LTM candidate cell and the second LTM candidate cell, each composed of the target base station 102 included in the LTM candidate cell, terminal 111 can be ready to perform CA-based communication with the target base station 102.

[0039] Terminal 111 measures the radio quality of each LTM candidate cell according to instructions from source base station 111 (S709). If terminal 111 has been notified of a first condition by source base station 101, it may report the measurement result to source base station 101 if the first condition is met (S710). If terminal 111 has not been notified of the first condition by source base station 101, it may periodically notify source base station 101 of the measurement result (S710). For example, terminal 111 may notify source base station 101 of the measurement result each time it performs a measurement. Furthermore, if terminal 111 has been notified of a second condition by source base station 101, it may determine whether the measurement result meets the second condition. For example, terminal 111 may report the measurement result to source base station 101 if the measurement result meets both the first and second conditions. Furthermore, if the measurement results satisfy the first condition, terminal 111 may provide a report that includes a determination of whether or not the second condition is met. The report from terminal 111 may include, for example, information that identifies LTM candidate cells that satisfy the first and second conditions.

[0040] The source base station 101 decides whether or not to have terminal 111 perform a cell switch based on the report from terminal 111 (S711). The source base station 101 may also decide whether or not to have terminal 111 perform communication using CA after the cell switch has been performed. For example, if the source base station 101 has determined that the first and second conditions are met at terminal 111, it decides to have terminal 111 perform a cell switch based on the report of the L1 measurement result from terminal 111. For example, if the source base station 101 has notified terminal 111 of the first and second conditions, it can determine that the first and second conditions are met by receiving the report from terminal 111. Also, if the report from terminal 111 includes a determination result indicating that the second condition is met, the source base station 101 can determine that the first and second conditions are met based on this determination result. In these cases, the source base station 101 may decide to have the terminal 111 perform a cell switch to the first LTM candidate cell and the second LTM candidate cell of the target base station 102, and to have the terminal 111 communicate using CA with these cells. On the other hand, if the report from the terminal 111 includes a determination result indicating that the second condition is not met, the source base station 101 may determine from this determination result that the first condition is met, but the second condition is not. In this case, the source base station 101 may decide to have the terminal 111 perform a cell switch to the cell among the first and second LTM candidate cells of the target base station 102 that was reported as satisfying the first condition, and not to have the terminal communicate using CA.

[0041] Furthermore, if the source base station 101 has determined that the first condition is met at terminal 111, and has not determined that the second condition is met at terminal 111, it may determine whether the second condition is met based on the report from terminal 111. For example, if the source base station 101 has notified terminal 111 of the first condition but not of the second condition, it may determine that the first condition is met upon receiving the report from terminal 111. Then, the source base station 101 may determine whether the second condition is met based on the measured value of the received power of the LTM candidate cell included in the report from terminal 111. If the source base station 101 determines that the second condition is met, it may decide to have terminal 111 switch cells to the first and second LTM candidates of the target base station 102 and have them communicate using CA with these cells. On the other hand, if it is determined that the second condition is not met, the source base station 101 may decide to have the terminal 111 perform a cell switch to the cell of the target base station 102 that satisfies the first condition among the first and second LTM candidates, and not to have communication using CA.

[0042] Furthermore, if the terminal 111 does not make a determination regarding the first or second condition, the source base station 101 may determine whether the first and second conditions are met in its own device based on a report from the terminal 111. For example, if the source base station 101 has not notified the terminal 111 of either the first or second condition, it may periodically receive reports from the terminal 111. The source base station 101 may determine whether the first and second conditions are met based on the measured value of the received power of the LTM candidate cell included in the report from the terminal 111. If the source base station 101 determines that the first and second conditions are met, it may decide to have the terminal 111 perform a cell switch to the first and second LTM candidate cells of the target base station 102 and perform communication using CA with these cells. Furthermore, if the source base station 101 determines that the first condition is met and the second condition is not met, the source base station 101 may decide not to have the terminal 111 perform a cell switch to the cell reported as satisfying the first condition among the first and second LTM candidate cells of the target base station 102, and not to have the terminal 111 perform communication using CA. If the source base station 101 determines that neither the first nor the second condition is met, it will not have the terminal 111 perform a cell switch.

[0043] Based on the determined result, the source base station 101 instructs the terminal 111 to switch cells. For example, the source base station 101 may send a MAC CE containing the determined result to the terminal 111. The MAC CE may include an LTM Cell Switch Command message. The LTM Cell Switch Command message may include information indicating the LTM candidate cell to which the cell switch will take place. For example, the source base station 101 may notify the terminal 111 of the LTM candidate cell to which the cell switch will take place by specifying the target setting ID notified in the LTM candidate setting. If the L1 measurement report from the terminal 111 includes information indicating the quality of each beam of each LTM candidate cell, the LTM Cell Switch Command message may include information indicating which beam corresponding to the LTM candidate cell to which the cell switch will take place should be used.

[0044] When terminal 111 receives an LTM Cell Switch Command message, it performs cell switching (S713, S714). For example, terminal 111 may disable the TCI state used for communication with source base station 101 and apply the TCI state to be used for communication with target base station 102 as indicated in the LTM Cell Switch Command message. If there are LTM candidate cells that are not subject to cell switching and the TCI states corresponding to these cells are enabled, terminal 111 may disable (deactivate) these TCI states. Then, terminal 111 performs a procedure to connect to the first LTM candidate of target base station 102 (S714). For example, terminal 111 may perform a random access procedure. Terminal 111 may decide whether to perform the connection procedure to the first LTM candidate cell or the second LTM candidate cell provided by target base station 102, or the source base station 101 may decide and notify terminal 111. For example, between the first and second LTM candidate cells, the cell with the higher received power may be selected as the Pcell that should perform the connection procedure. Furthermore, the source base station 101 may specify the Pcell that the terminal 111 should perform the connection procedure on using the LTM Cell Switch Command message.

[0045] Terminal 111 may request to perform CA-based communication during the connection procedure to the target base station 102. For example, if terminal 111 uses a 4-step random access procedure for connecting to the target base station 102, it may request CA-based communication using message 1 (Msg1), which includes a random access preamble. Similarly, terminal 111 may request CA-based communication using message 3 (Msg3), which is transmitted using radio resources permitted by the random access response (Msg2). Furthermore, if terminal 111 uses a 2-step random access procedure for connecting to the target base station 102, it may request CA-based communication using message A (MsgA), which includes a random access preamble. In addition, when requesting CA-based communication, terminal 111 may notify information specifying the Scell ​​for CA-based communication. For example, if terminal 111 executes the random access procedure at the first LTM candidate cell, it may designate the first LTM candidate cell as a Pcell and the second LTM candidate cell as an Scell. In this case, terminal 111 may notify target base station 102 of information designating the second LTM candidate cell as an Scell ​​during the random access procedure for the first LTM candidate cell. Based on the information designating the Scell ​​included in the request from terminal 111, target base station 102 may activate the designated cell as an Scell ​​to be used for communication with terminal 111. With the Scell ​​activated in both terminal 111 and target base station 102, CA-based communication becomes possible between terminal 111 and target base station 102. Thus, in the procedure for terminal 111 to switch cells from source base station 101 to target base station 102, a determination is made as to whether CA-based communication is possible in the cell configured by target base station 102, and with the Scell ​​activated in both terminal 111 and target base station 102, CA-based communication becomes possible between terminal 111 and target base station 102 immediately after the cell switch.Furthermore, terminal 111 may request the target base station 102 to perform CA-based communication after the random access procedure is completed. For example, terminal 111 may request CA-based communication using an RRC message. Even in this case, the determination of whether CA-based communication is possible and the activation of terminal 111's Scell ​​are performed during the cell switching procedure, enabling CA-based communication efficiently during cell switching.

[0046] (Second example of processing) This processing example explains how the source base station 101 efficiently switches cells for terminal 111 by communicating with the target base station 102. Figure 8 shows an example of the operations performed by each device when terminal 111, which is communicating with source base station 101 using CA, switches cells to target base station 102. In Figure 8, operations similar to those in Figure 7 are given the same reference number and their explanation is omitted. First, LTM candidate cells are identified between source base station 101 and terminal 111 (S701~S703). Once an LTM candidate cell is identified, source base station 101 performs communication regarding preparations for communication using CA with target base station 102, which constitutes the identified LTM candidate cell. Source base station 101 may perform communication regarding preparations for communication using CA if it is communicating with terminal 111 using CA and target base station 102 constitutes multiple LTM candidate cells. For example, source base station 101 can determine whether target base station 102, which comprises multiple LTM candidate cells, is capable of performing CA-based communication by querying it. Furthermore, if target base station 102 has notified via a wireless medium that its device is capable of CA-based communication, source base station 101 can determine that target base station 102 is capable of CA-based communication through a report made by terminal 111. In this case, source base station 101 can instruct terminal 111 to report information in the measurement report indicating whether the detected base station is capable of CA-based communication. Communication between source base station 101 and target base station 102 can be performed using, for example, an X2 interface or an Xn interface.

[0047] The source base station 101 may communicate with the target base station 102 before notifying the terminal 111 of an RRC Reconfiguration message including the LTM candidate setting (S801). For example, the source base station 101 may notify the target base station 102 that the cell configured by the target base station 102 is an LTM candidate cell for terminal 111. As an example, the source base station 101 may send a notification that includes information identifying terminal 111 and information identifying an LTM candidate cell among the cells configured by the target base station 102. This allows the target base station 102 to identify other LTM candidate cells in its own device when terminal 111 attempts to connect to any of the cells configured by its device. For example, the target base station 102 may activate the identified LTM candidate cell as a cell to be used for CA with terminal 111.

[0048] Source base station 101 may request target base station 102 to transmit a reference signal in the LTM candidate cells. For example, source base station 101 may request that aperiodic CSI-RS be transmitted. Target base station 102 may allocate radio resources for transmitting aperiodic CSI-RS in each LTM candidate cell and notify source base station 101 of information identifying the allocated radio resources. Target base station 102 may then transmit aperiodic CSI-RS using the allocated radio resources. Source base station 101 may notify terminal 111 of the LTM candidate configuration, including information identifying the radio resources notified by target base station 102. This allows terminal 111 to perform measurements using aperiodic CSI-RS after performing DL synchronization in the LTM candidate cells. Unlike periodically transmitted synchronization signals, aperiodic CSI-RS can be transmitted at any time, allowing terminal 111 to shorten the measurement period.

[0049] The timing of the source base station 101's communication with the target base station 102 is not limited to before the source base station 101 notifies terminal 111 of an RRC Reconfiguration message including LTM candidate settings. For example, the source base station 101 may communicate with the target base station 102 after determining the cell to which terminal 111 will switch (S711) (S802). For example, the source base station 101 may request the target base station 102 to communicate with terminal 111 using CA. After the cell to which terminal 111 will switch is determined, a request regarding CA-based communication is made to the target base station 102 that provides that cell, eliminating the need for the source base station 101 to communicate with other base stations that constitute the LTM candidate cell. In this case, the source base station 101 may make a request to the target base station 102 that includes information identifying terminal 111 performing cell switching and information identifying the LTM candidate cell corresponding to the Scell ​​to be used for CA. Based on this request, the target base station 102 may prepare the cell corresponding to the specified Scell ​​for communication with terminal 111 using CA. For example, the target base station 102 may perform settings such as allocating radio resources to terminal 111 in the Scell ​​or notifying terminal 111 of control information in the Scell ​​via the Pcell.

[0050] Communication between the source base station 101 and the target base station 102 is not limited to the above. For example, the target base station 102 and the terminal 111 may perform part of the random access procedure via the source base station 101 before the cell switching decision is made. For example, after completing DL synchronization (S706), the terminal 111 may perform UL synchronization to obtain the TA value. At this time, the terminal 111 may send a random access preamble to the target base station 102 to obtain the TA value. For example, the terminal 111 may send a random access preamble to one or more LTM candidate cells configured by the target base station 102. The random access preamble may be sent using radio resources notified to the terminal 111 from the target base station 102 via the source base station 101. For example, in communication with the target base station 102 in S801, the source base station 101 may request the allocation of radio resources for the terminal 111 to send the random access preamble. When the target base station 102 receives a random access preamble transmitted by the terminal 111, it determines the TA value between the target base station 102 and the terminal 111 based on the random access preamble. For example, the longer the distance between the target base station 102 and the terminal 111, the larger the TA value that may be determined. The target base station 102 notifies the terminal 111 of the determined TA value via the source base station 101. This allows the terminal 111 to obtain the TA value that its device should use for communication with the target base station 102. The target base station 102 may also notify the terminal 111 of the radio resources that should be used for the connection establishment procedure via the source base station 101. For example, information identifying the TA value and radio resources may be included in the LTM Cell Switch Command message that the source base station 101 transmits to the terminal 111. If the terminal 111 has obtained the TA value to be used for communication with the target base station 102 before cell switching, it may establish a connection with the target base station 102 without performing random access.For example, terminal 111 may send a message to target base station 102 to establish a connection using the TA value and radio resources notified from target base station 102 via source base station 101. At this time, based on receiving terminal 111's TA value from target base station 102, source base station 101 may communicate with target base station 102 regarding preparation for CA-based communication. For example, source base station 101 may notify target base station 102 of information identifying the Scell ​​for CA-based communication with terminal 111. This allows target base station 102 to prepare the Scell ​​in advance for communication with terminal 111. In this way, information for CA-based communication with terminal 111 is exchanged between source base station 101 and target base station 102, enabling CA-based communication to be enabled quickly after terminal 111 performs a cell switch.

[0051] As described above, according to this embodiment, terminal 111 performs cell switching from source base station 101 to target base station 102 and enables CA with target base station 102 when the conditions for performing CA-based communication are met based on the measured received power of target base station 102 before cell switching. This makes CA-based communication between terminal 111 and target base station 102 immediately available after cell switching. With this configuration, for example, even if cell switching occurs when terminal 111 is performing communication with a large amount of traffic, the usable communication capacity of terminal 111 will not decrease, and stable communication will be possible. Therefore, it is possible to contribute to Goal 9 of the United Nations Sustainable Development Goals (SDGs), "Build resilient infrastructure, promote sustainable industrialization and foster innovation."

[0052] The invention is not limited to the embodiments described above, and various modifications and changes are possible within the scope of the gist of the invention. [Explanation of Symbols]

[0053] 101: Base station, 102: Base station, 111: Terminal

Claims

1. A terminal device that communicates with base station equipment based on the cellular communication standard of the Third Generation Partnership Project (3GPP), A measuring means for measuring the received power of signals received from a first cell provided by a first base station device connected to the terminal device, and a second cell provided by a second base station device different from the first base station device. The system includes a switching means that switches from the first cell to the second cell based on the results of the measurement indicating that the first condition regarding the received power has been met, When carrier aggregation (CA) is used in communication between the first base station device and the terminal device, and a single second base station device provides a plurality of second cells, a determination is made based on the received power of each of the plurality of second cells to determine whether a second condition for performing CA-based communication in the plurality of second cells is met. Based on the determination that the second condition is met in addition to the first condition, the switching means performs cell switching from the first cell to the plurality of second cells and activates the CA between the second base station device and the terminal device. A terminal device characterized by the following features.

2. A reporting means for reporting the results of the measurement to the first base station device, The system further includes a receiving means for receiving an instruction from the first base station device to switch cells from the first cell to the second cell, The switching means performs the cell switching from the first cell to the plurality of second cells and the activation of the CA between the second base station device and the terminal device, based on the information that the instruction includes information indicating that the cell switching from the first cell to the plurality of second cells and the activation of the CA between the second base station device and the terminal device. The terminal device according to feature 1.

3. The system further includes determination means for determining whether the first condition and the second condition are met, The reporting means makes the report when it is determined that the first and second conditions are met. The terminal device according to feature 2.

4. In the first base station device, a determination is made based on the report as to whether the second condition is met. The aforementioned terminal device is The system further includes a determination means for determining whether or not the first condition described above is met, The reporting means makes the report when it is determined that the first condition is met. The receiving means receives the instruction, which includes information indicating that, if it is determined that the second condition is met, it should perform the cell switching from the first cell to the plurality of second cells and the activation of the CA between the second base station device and the terminal device. The terminal device according to feature 2.

5. In the first base station device, a determination is made based on the report as to whether the first condition and the second condition are met. The receiving means receives the instruction, which includes information indicating that, if it is determined that the first and second conditions are met, it should perform the cell switching from the first cell to the plurality of second cells and the activation of the CA between the second base station device and the terminal device. The terminal device according to feature 2.

6. The second condition includes that the received power of each of the plurality of second cells satisfies the first condition. The terminal device according to any one of claims 1 to 5.

7. The second condition includes that, of the received powers of each of the plurality of second cells, at least one received power satisfies the first condition, and the other received powers are above a predetermined threshold. The terminal device according to any one of claims 1 to 5.

8. A base station device that communicates with terminal devices based on the cellular communication standard of the Third Generation Partnership Project (3GPP), The terminal device has control means that causes it to measure the received power of signals received from a first cell provided by the base station device and a second cell provided by another base station device, and to perform cell switching from the first cell to the second cell based on whether a first condition regarding received power is met based on the results of the measurement. When carrier aggregation (CA) is used in communication between the base station device and the terminal device, and when a single other base station device provides a plurality of the second cells, a determination is made based on the received power of each of the plurality of second cells to determine whether a second condition for performing CA-based communication in the plurality of second cells is met. Based on the determination that the second condition is met in addition to the first condition, the control means causes the cell switching from the first cell to the plurality of second cells and the activation of the CA between the other base station device and the terminal device to be performed. A base station device characterized by the following features.

9. The device further includes a receiving means for receiving a report of the measurement results from the terminal device. The base station device according to feature 8.

10. The terminal device makes a determination as to whether the first condition and the second condition are met. The receiving means receives the report when the first and second conditions are met. Based on receiving the report, the control means causes the terminal device to perform the cell switching from the first cell to the plurality of second cells and to activate the CA between the other base station device and the terminal device. The base station device according to feature 9.

11. The terminal device makes a determination as to whether or not the first condition is met. The base station device is, The system further includes a determination means for determining whether the second condition is met based on the aforementioned report, The receiving means receives the report when the first condition is met. Based on the determination that the second condition is met, the control means causes the terminal device to perform the cell switching from the first cell to the plurality of second cells and to activate the CA between the other base station device and the terminal device. The base station device according to feature 9.

12. The system further includes determination means for determining whether the first and second conditions are met based on the aforementioned report. Based on the determination that the first and second conditions are met, the control means causes the terminal device to perform the cell switching from the first cell to the plurality of second cells and to activate the CA between the other base station device and the terminal device. The base station device according to feature 9.

13. The second condition includes that the received power of each of the plurality of second cells satisfies the first condition. The base station device according to any one of claims 8 to 12.

14. The second condition includes that, of the received powers of each of the plurality of second cells, at least one received power satisfies the first condition, and the other received powers are above a predetermined threshold. The base station device according to any one of claims 8 to 12.

15. A control method performed by a terminal device that communicates with a base station device based on the cellular communication standard of the Third Generation Partnership Project (3GPP), A measurement step of measuring the received power of signals received from a first cell provided by a first base station device connected to the terminal device, and a second cell provided by a second base station device different from the first base station device. The system includes a switching step of switching from the first cell to the second cell based on the results of the measurement indicating that the first condition regarding the received power has been met, When carrier aggregation (CA) is used in communication between the first base station device and the terminal device, and a single second base station device provides a plurality of second cells, a determination is made based on the received power of each of the plurality of second cells to determine whether a second condition for performing CA-based communication in the plurality of second cells is met. The switching process, based on the determination that the second condition in addition to the first condition is met, performs the cell switching from the first cell to the plurality of second cells and activates the CA between the second base station device and the terminal device. A control method characterized by the following:

16. A control method performed by a base station device that communicates with terminal devices based on the cellular communication standard of the Third Generation Partnership Project (3GPP), The terminal device has a control step of causing it to measure the received power of signals received from a first cell provided by the base station device and a second cell provided by another base station device, and to perform cell switching from the first cell to the second cell based on whether a first condition regarding received power is met based on the results of the measurement. When carrier aggregation (CA) is used in communication between the base station device and the terminal device, and when a single other base station device provides a plurality of the second cells, a determination is made based on the received power of each of the plurality of second cells to determine whether a second condition for performing CA-based communication in the plurality of second cells is met. Based on the determination that the second condition in addition to the first condition is met, the control process performs the cell switching from the first cell to the plurality of second cells and the activation of the CA between the other base station device and the terminal device. A control method characterized by the following:

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