JP2023063394A - Terminal device, base station device, control method, and program for autonomous handover by terminal device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a terminal device to select an appropriate handover destination.

SOLUTION: A terminal device establishes a connection with a base station device, transmits information corresponding to a service requested by the terminal device, receives, by a radio resource control (RRC) message from a serving base station device, information on candidate base station devices for an autonomous handover of the terminal device from the serving base station device that has established the connection, acquires identification information on surrounding base station devices from wireless signals transmitted by the surrounding base station devices, and performs the handover to the candidate base station device corresponding to the identification information based on the information on the candidate base station device without relying on an instruction of the serving base station device when the identification information corresponds to identification information on any of the candidate base station devices, according to a condition related to the quality of the wireless signal from the serving base station device, after receiving the information on the candidate base station devices.

SELECTED DRAWING: Figure 5

COPYRIGHT: (C)2023,JPO&INPIT

Description

The present invention relates to terminal-initiated handover technology.

In next-generation cellular communication systems, it is expected that beams covering narrow areas (cells) will be formed to effectively utilize frequency resources. Such further miniaturization of cells may increase the frequency of handovers when terminal devices move. Therefore, it is important to shorten the service interruption time in one handover. In Non-Patent Document 1, there is a method in which a serving base station (serving cell) notifies in advance information for accessing a target cell candidate, an event dedicated to autonomous handover, etc. for a terminal device to perform autonomous handover. Are listed.

3GPP contribution, R2-1708840, August 2017

In the 5th generation cellular communication system, a network is created for each service such as voice call, video and music streaming, high-speed large-capacity communication, connection by many terminals, ultra-reliable low-delay communication, etc. Slicing is done. A terminal device can be provided with an appropriate service by, for example, connecting to a network slice corresponding to the requested service. On the other hand, the technology described in Non-Patent Document 1 does not consider such network slices, and it is conceivable that a terminal device may connect to an inappropriate network slice. As a result, the terminal device cannot receive appropriate service at the handover destination, and further handover may be required.

SUMMARY OF THE INVENTION An object of the present invention is to enable a terminal device to select an appropriate handover destination.

A terminal device according to an aspect of the present invention includes establishing means for establishing a connection with a base station device, transmitting means for transmitting information corresponding to a service requested by the terminal device, and a serving base with which the connection is established by the establishing means. Receiving means for receiving information of candidate base station devices for autonomous handover of the terminal device from the station device by means of a radio resource control (RRC) message from the serving base station device, and identification information of surrounding base station devices. from radio signals transmitted by the surrounding base station devices; When the identification information corresponds to the identification information of any one of the candidate base station apparatuses, the serving performs handover to the candidate base station apparatus to which the identification information corresponds based on the information of the candidate base station apparatus. and execution means for executing without depending on an instruction from the base station apparatus.

A base station apparatus according to an aspect of the present invention includes establishing means for establishing a connection with a terminal device, receiving means for receiving information corresponding to a service requested by the terminal device from the terminal device, and autonomy of the terminal device. selection means for selecting a candidate base station apparatus for selective handover; and transmission means for sending information on the candidate base station apparatus to the terminal apparatus by means of a radio resource control (RRC) message.

According to the present invention, a terminal device can select an appropriate handover destination.

It is a figure which shows the structural example of a radio|wireless communications system. It is a figure which shows the hardware configuration example of an apparatus. It is a figure which shows the functional structural example of a base station apparatus. It is a figure which shows the functional structural example of a terminal device. FIG. 4 is a diagram showing a first example of the flow of processing executed in a wireless communication system; FIG. 5 is a diagram showing a second example of the flow of processing executed in the wireless communication system;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Configuration of wireless communication system)
FIG. 1 shows a configuration example of a wireless communication system according to this embodiment. The wireless communication system includes first base station apparatus 101 and second base station apparatus 102 and terminal apparatus 103 . The first base station apparatus 101 is a serving base station connected to the terminal apparatus 103 , and the second base station apparatus 102 is a non-serving base station not connected to the terminal apparatus 103 . Note that the first base station apparatus 101 can be configured to provide a plurality of cells (beams) by beamforming, for example. It acts as a serving base station in a serving cell) and as a non-serving base station in a second cell (non-serving cell) to which it is not connected. In the following, when one base station device provides both a serving cell and a non-serving cell, the portion of the base station device that provides the non-serving cell is treated as the second base station device 102, and the portion that provides the serving cell. is treated as the first base station apparatus 101 . Further, when the terminal device 103 switches the serving cell (handovers), the base station device that provides the serving cell after switching functions as the first base station device 101, and the handover source base station device functions as the second base station device. It becomes the base station device 102 . That is, the first base station apparatus 101 and the second base station apparatus 102 can be configured to differ only in whether they are connected to the terminal apparatus 103 or not. Note that FIG. 1 is only an example, and generally there are many base station devices and many terminal devices. The steps are performed individually.

In this embodiment, the terminal device 103 selects from the currently connected serving base station (first base station device 101) another base station device (for example, the second (102) is obtained in advance as information on candidate base station devices to be handover destinations. The information of the candidate base station apparatus can include, for example, cell identification information provided by the candidate base station apparatus and information used in the connection procedure with the candidate base station apparatus. Here, the identification information can be, for example, the NR Cell Global ID (NCGI) of the candidate base station apparatus. NCGI is a cell global ID determined by a combination of a Public Land Mobile Network ID (PLMN ID) and an NR Cell Identity (NCI). Also, the connection procedure is, for example, a random access procedure, and the information used in the connection procedure includes, for example, beam information formed by the candidate base station apparatus, routing information (Tracking Area ID (TAI)), frequency information, and the like. sell.

Then, the terminal device 103 communicates with the serving base station while holding the information of the candidate base station devices in this way, and while the communication environment with the serving base station is good, the terminal device 103 continues to communicate with the serving base station. communication can continue. Then, when the quality of the radio signal from the serving base station falls below a predetermined level, the identification information of the surrounding base station apparatus is acquired from the radio signal transmitted from the surrounding base station apparatus and held. It compares with the identification information of the candidate base station apparatus. Here, the identification information of the surrounding base station apparatuses can be, for example, Physical Cell ID (PCI). For example, when the identification information of the surrounding base station apparatus obtained from the radio signal received with radio quality equal to or higher than a predetermined level corresponds to the identification information (NCGI) of the candidate base station apparatus, the terminal apparatus 103 obtains the identification information. determines the corresponding candidate base station apparatus as the switching destination of the connection. When the identification information of a plurality of surrounding base station apparatuses corresponds to the identification information of the candidate base station apparatus, the terminal apparatus 103 selects the base station apparatus having the best radio quality among the surrounding base station apparatuses. , or by randomly selecting one base station apparatus from among the base station apparatuses whose radio quality exceeds the threshold level, or the like. Then, the terminal device 103 executes handover to the candidate base station device of the connection switching destination without going through the serving base station. For example, the terminal device 103 can establish a connection with a candidate base station device to switch connection to by executing a random access procedure. At this time, the terminal device 103 can transmit the context information (UE context) of the terminal device 103 to the candidate base station device to which the connection is to be switched. After that, the candidate base station device to which the connection is switched, notifies the switching source base station device (the former serving base station) that the terminal device 103 has autonomously executed the handover, and the data addressed to the terminal device 103. request the transfer of When the switching source base station apparatus receives the notification that the terminal apparatus 103 has handed over and the data transfer request, it transfers the data addressed to the terminal apparatus 103 to the connection switching destination candidate base station apparatus. Then, the transferred data addressed to the terminal device 103 is transmitted to the terminal device 103 from the candidate base station device to which the connection is switched. As a result, since the terminal device 103 can autonomously execute a handover without going through the serving base station, the terminal device 103 can quickly connect to the connection destination when the quality of the radio signal from the serving base station falls below a predetermined level. Switching of the base station apparatus is performed. As a result, the length of the period during which communication services cannot be provided to the terminal device 103 can be shortened. Note that the terminal device 103 may initiate autonomous handover in response to a trigger other than when the quality of the radio signal from the serving base station falls below a predetermined level. For example, an autonomous handover is initiated by another trigger such as the amount of delay in communication with the serving base station becoming larger than a predetermined value, or the amount of resources allocated from the serving base station being insufficient. may

A fifth generation cellular communication system (NR, New Radio) uses a network slicing technique that defines a network for each service. And the network slices supported by each base station apparatus may differ. That is, some base station devices may support all network slices and provide all services, while some other base station devices may support only some network slices and provide some services. may not be provided. At this time, when the serving base station notifies the terminal device 103 of information of other base station devices in an adjacent relationship as information of candidate base station devices regardless of the service requested by the terminal device 103, the terminal device 103 autonomously As a result of performing a handover, the candidate base station apparatus to which the connection is switched may not be able to support the service requested by the terminal apparatus 103 .

On the other hand, in the present embodiment, the serving base station is the terminal device 103 among the other base station devices (for example, adjacent to the serving base station) that are candidates for connection switching from the serving base station. selects a candidate base station apparatus based on the information of the service requested by . Here, the service information requested by the terminal device 103 is, for example, Network Slice Selection Assistance Information (NSSAI). An NSSAI contains one or more Single-NSSAIs (S-NSSAIs), and each network slice is uniquely identified by an S-NSSAI. Note that a particular network slice only supports a particular Access and Mobility Management Function (AMF). For example, each base station device includes NCGI, beam information, routing information, and frequency information as information of other base station devices that are candidates for connection switching from its own device (for example, has an adjacent relationship with its own device). In addition, the AMF ID (or information of multiple S-NSSAIs) of the other base station apparatus can be managed. Each base station device acquires the NSSAI, which is information about the service requested by the terminal device 103, and selects the AMF ID corresponding to the acquired NSSAI among the other base station devices that are candidates for connection switching from the own device. Alternatively, another base station apparatus having the S-NSSAI information is selected as a candidate base station apparatus to switch connection. Then, the base station device transmits information on the selected candidate base station device to the terminal device 103 currently connected to the base station device. The information about the candidate base station apparatus transmitted here is the same as described above. After acquiring these pieces of information, the terminal device 103 can autonomously perform handover as described above in response to occurrence of a predetermined trigger. According to such a configuration, the terminal device 103 is provided with information on a base station device capable of providing the service requested by the terminal device 103 as information on the candidate base station device to which the connection is to be switched. It is possible to continue receiving the communication service more reliably after switching the connection.

Note that the serving base station can transmit information on candidate base station apparatuses based on information on services requested by the terminal apparatus 103 through dedicated signaling to the terminal apparatus 103 . Dedicated signaling here can be done, for example, by radio resource control (RRC) messages or on-demand system information (on-demand SI). In addition, the terminal device 103 can register the requested service on the network side by including requested service information (NSSAI) in a registration request message when registering with the NR RAN (Radio Access Network). . In this case, the base station apparatus can acquire information on the service requested by the terminal apparatus 103 by searching information registered on the network side. That is, the terminal device 103 does not have to newly transmit the NSSAI to the base station device. However, the terminal device 103 may transmit the requested service information such as the NSSAI to the base station device. For example, the terminal device 103 may transmit to the serving base station a signal requesting information on candidates for connection switching (for example, a message requesting a neighbor cell list) including information on the requested service. As a result, the serving base station does not need to search for information on the service requested by the terminal device 103 requesting information on the candidate of the connection switching destination, and quickly obtains the information on the candidate base station device. The terminal device 103 can be notified.

Also, the serving base station may obtain information about the requested service for each of the plurality of terminals 103, and group the terminals 103 such that, for example, terminals requesting the same service are grouped together. Then, the serving base station selects a candidate base station device for each group and transmits information on the selected candidate base station device to one or more terminal devices 103 belonging to the group by one signal. I can. This transmission of information in one signal may be done, for example, by broadcasting system information. A multicast signal specifying a group may be transmitted, or a broadcast signal may be transmitted to all terminal devices. Note that when a broadcast signal is transmitted to all terminal devices, information designating a target group or target service may be included in the signal. Note that the grouping of the plurality of terminal devices 103 may be performed based on criteria different from whether or not the same service is requested. That is, when a plurality of services are processed in the same network slice, terminal devices that can be accommodated in the same network slice may be grouped together. This makes it possible to reduce the amount of radio resources used for notification of candidate base station apparatuses.

An example of the configuration of each device and the flow of processing to be executed will be described below.

(Hardware configuration)
FIG. 2 shows a hardware configuration example of the base station apparatus and the terminal apparatus. In one example, the base station apparatus and terminal apparatus have a hardware configuration as shown in FIG. In the base station apparatus and the terminal apparatus, the CPU 201 executes a program that is recorded in, for example, the ROM 202, the RAM 203, or the external storage device 204 and that implements each function of the base station apparatus and the terminal apparatus as described above.

Then, the base station apparatus and the terminal apparatus control the communication circuit 205 by, for example, the CPU 201 to communicate with other apparatuses. Note that the communication circuit 205 of the base station device can communicate with other base station devices and other network nodes, for example, through a wired line. Also, the communication circuit 205 of the base station apparatus may be capable of forming one or more (a plurality of) beams and performing wireless communication with the terminal apparatus. Also, in this case, the communication circuit 205 of the terminal device is connected to the base station device via at least one of the beams formed by the communication circuit 205 of the base station device so that wireless communication can be performed. Configured. In addition, in the configuration of FIG. 2, the base station apparatus and the terminal apparatus are shown schematically as having one communication circuit 205, but are not limited to this, and may have a plurality of communication circuits. For example, a base station device can have a first communication circuit for wired communication with other base station devices and a second communication circuit for wireless communication with a terminal device. Also, the terminal device may have, for example, a first communication circuit for NR and a second communication circuit for LTE (Long Term Evolution). Also, the terminal device may have a wireless communication circuit for standards other than cellular, such as wireless LAN, and may also have a wired communication circuit used for wired connection such as USB connection.

Note that the base station apparatus and the terminal apparatus may be provided with dedicated hardware for executing each function, or a part may be executed by hardware and the other part may be executed by a computer that operates a program. . Also, all functions may be performed by computers and programs.

(Function configuration)
FIG. 3 shows a functional configuration example of the base station apparatus (the first base station apparatus 101 and the second base station apparatus 102). The base station apparatus has, for example, a communication section 301 , a requested service acquisition section 302 , an adjacent information storage section 303 , a candidate base station selection section 304 and a candidate base station notification section 305 . Also, the base station apparatus may have grouping section 306 as an option, for example.

The communication unit 301 executes wired/wireless communication with other base station devices and wireless communication with the connected terminal device 103 .

A requested service acquisition unit 302 acquires information on a service requested by the terminal device 103 . For example, the requested service acquisition unit 302 receives a message (registration request) requesting registration from the unregistered terminal device 103, and acquires the NSSAI in the message as information on the service requested by the terminal device 103. I can. Further, the requested service obtaining unit 302 can obtain, from a predetermined node in the network, information about a service requested by the terminal device 103 managed by the registered terminal device 103 . In some cases, when the terminal device 103 performs handover, the requested service acquiring unit 302 may acquire information on the service requested by the terminal device 103 from the handover source base station device.

Adjacent information storage section 303 stores information on other base station apparatuses that are adjacent to the own apparatus. Here, adjacent information storage section 303 stores information about base station apparatuses (cells) that are candidates for connection switching destinations as information about other base station apparatuses that are adjacent to each other. That is, the stored other base station apparatus does not have to be directly adjacent to the base station apparatus. of information can be stored. Other base station device information may include, for example, NCGI, beam information, routing information, and AMF ID (or information for multiple S-NSSAIs). Note that the neighbor information storage unit 303 may have an Automatic Neighbor relation (ANR) function that automatically establishes a neighbor relationship when the number of base station apparatuses in a neighbor relationship increases or decreases.

Candidate base station selection section 304 selects another base station apparatus having an adjacent relationship based on the information on the service requested by terminal apparatus 103 acquired by requested service acquisition section 302 and the information stored in adjacent information storage section 303. Another base station apparatus capable of providing the requested service is selected as a candidate base station apparatus to which connection is switched. For example, the candidate base station selection unit 304 selects an AMF ID or an S− Another base station apparatus having the NSSAI information is selected as a candidate base station apparatus to switch the connection. Note that the selection of candidate base station devices may not be performed by the serving base station, for example, the selection may be performed by a network node different from the serving base station.

Candidate base station notification section 305 notifies terminal apparatus 103 of the candidate base station apparatus selected by candidate base station selection section 304 . For example, the candidate base station notification unit 305 notifies the information of the candidate base station apparatus according to the service requested by the terminal device 103 by dedicated signaling to the terminal device 103 using an RRC message or on-demand system information. The information of the candidate base station apparatus notified here can include, for example, cell identification information provided by the candidate base station apparatus and information used in the connection procedure with the candidate base station apparatus, in one example. .

The grouping unit 306 groups the plurality of terminal devices 103 according to the requested service and the network slice required to execute the service. For example, among the terminal devices 103 currently connected to the base station device, groups are formed so that terminal devices requesting the same service or terminal devices to be connected to the same network slice belong to the same group. When the grouping unit 306 groups the terminal devices, the candidate base station selection unit 304 selects candidate base station devices for each group, and the candidate base station notification unit 305 sends one multicast signal to the terminal devices belonging to the group. or by one broadcast signal for all terminal devices, information on the candidate base station devices is transmitted.

FIG. 4 is a diagram showing a functional configuration example of the terminal device 103. As shown in FIG. The terminal device 103 has, for example, a communication unit 401, a candidate information acquisition unit 402, a trigger determination unit 403, a peripheral information acquisition unit 404, a handover execution unit 405, and a requested service notification unit 406.

The communication unit 401 performs wireless communication with the connected base station device (first base station device 101). Further, the communication unit 401 can receive a radio signal from a base station device to which it is not connected and acquire cell identification information (for example, PCI) included in the radio signal.

Candidate information acquisition section 402 acquires information about a candidate base station apparatus to switch connection to, which is selected in the currently connected base station apparatus (or another network node) in accordance with service information requested by terminal apparatus 103. do. The information of the candidate base station device here includes, for example, identification information (eg, NCGI) of the cell formed by the candidate base station device, and information (eg, beam information, routing information) used in the connection procedure with the candidate base station device. information, frequency information, etc.).

For example, the trigger determination unit 403 detects that the quality of the radio signal from the serving base station has fallen below a predetermined level, or that the load on the serving base station has exceeded a predetermined value, and the amount of delay is greater than a predetermined value. A trigger for the terminal device 103 to start handover is determined, such as that the amount of resources allocated from the serving base station is equal to or less than a predetermined amount. Note that the trigger determination unit 403 can determine any trigger for the terminal device 103 to start handover autonomously.

For example, when the trigger determination unit 403 detects a handover start trigger, the peripheral information acquisition unit 404 observes radio signals from nearby base station devices that are not currently connected, and obtains identification information of those base station devices. (PCI). Surrounding information acquisition section 404 can also measure radio quality such as received power of radio signals from surrounding base station apparatuses. Then, peripheral information acquisition section 404 determines whether or not there is identification information of the peripheral base station apparatus that corresponds to the identification information in the information of the candidate base station apparatus acquired by candidate information acquisition section 402 . The peripheral information acquisition unit 404 determines a peripheral base station device having identification information corresponding to the information of the candidate base station device as a handover target. When the identification information of a plurality of neighboring base station devices corresponds to the information of the candidate base station device, the neighboring information acquiring unit 404 obtains the base station device having the best radio quality among the plurality of neighboring base station devices. One base station device randomly selected from among the station devices or those whose radio quality exceeds a predetermined criterion can be determined as a handover target. In addition, before the trigger determination unit 403 detects a handover start trigger, the peripheral information acquisition unit 404 observes wireless signals from surrounding base station devices that are not currently connected and Acquisition of identification information and measurement of received power may be performed. For example, the surrounding information acquisition unit 404 periodically observes radio signals from surrounding base station devices and stores the results. , may determine the handover target based on the information it has held. In addition, when performing observation of radio signals from surrounding base station devices in advance, peripheral information acquisition section 404 obtains identification information in the candidate base station device information acquired by candidate information acquisition section 402 and the corresponding base station device. You may make it hold|maintain only the result about. This eliminates the need for peripheral information acquiring section 404 to extract information about the candidate base station apparatus from the held information after trigger determining section 403 detects the trigger for starting handover. As a result, it is possible to shorten the time required for processing after the trigger for starting handover is detected.

The handover execution unit 405 executes handover to the target base station apparatus of the handover determined by the surrounding information acquisition unit 404 without going through the serving base station. Handover executing section 405 executes, for example, a random access procedure with a target base station apparatus. Also, at this time, the handover execution unit 405 can transmit the context information of the terminal device 103 to the target base station device.

The requested service notification unit 406 notifies the network side of information on the service requested by the terminal device 103 . The requested service notification unit 406 notifies the network side of the service information requested by the terminal device 103, for example, by transmitting a registration request message including the NSSAI when the terminal device 103 registers with the NR. Also, the requested service notification unit 406 can transmit, for example, information on the service requested by the terminal device 103 in a request message when requesting the information on the candidate base station device from the serving base station. Note that the requested service notification unit 406 may notify the network side of the information of the service requested by the terminal device 103 via the serving base station by signaling other than these.

(Processing flow)
Next, an example of the flow of processing executed in the wireless communication network will be described. FIG. 5 shows an example of the flow of the first process.

In the process of FIG. 5, first, the first base station apparatus 101, which is the serving base station of the terminal apparatus 103, acquires information on the service requested by the terminal apparatus 103 (S501). In FIG. 5, in the message requesting the information of the candidate base station apparatus to which the connection is switched from the terminal apparatus 103, the information of the service requested by the terminal apparatus 103 is notified to the first base station apparatus 101. shows an example. When requesting registration with the network, the terminal device 103 may notify the network side of information about the service it requests. In this case, the first base station device 101 may This information can be obtained from other nodes (eg, other base station devices). Then, based on the information of the service requested by the terminal device 103, the first base station device 101 selects a candidate base station device capable of supporting the service from other adjacent base station devices. is selected (S502). For example, the first base station apparatus 101 acquires an NSSAI as information on the service requested by the terminal apparatus 103, and selects base station apparatuses that configure network slices corresponding to the NSSAI as candidate base station apparatuses. If the terminal device 103 cannot acquire the information of the service requested by the terminal device 103, the base station device corresponding to the default AMF is selected as the candidate base station device. In addition, the first base station apparatus 101 considers the load of the candidate base station apparatus, and in order to prevent a plurality of terminal apparatuses from handing over to the same candidate base station apparatus all at once, the terminal apparatus requesting the same service Information on different candidate base station apparatuses may be selected for . The first base station device 101 notifies the terminal device 103 of information on the selected candidate base station device (S503). At this time, the first base station apparatus 101 can notify the terminal apparatus 103 of information by dedicated signaling such as an RRC message or on-demand system information.

Upon receiving the information about the candidate base station, the terminal device 103 holds the information. Then, the terminal device 103 continues to monitor whether or not a trigger requiring handover occurs during communication with the first base station device 101 . Here, when the terminal device 103 detects a trigger such that the quality of the radio signal from the first base station device 101 has fallen below a predetermined level (S504), subsequently, the radio signals from the surrounding base station devices are The identification information of each base station device (cell provided by each base station device) is acquired from the radio signal. Then, the terminal device 103 compares the acquired identification information with the identification information of the candidate base station devices, and detects surrounding base station devices having identification information corresponding to any of the identification information of the candidate base station devices. (S505). If the terminal apparatus 103 detects a plurality of base station apparatuses at this time, the terminal apparatus 103 determines the target base station apparatus for handover, for example, based on the quality of radio signals from these base station apparatuses. Then, the terminal device 103 executes a random access procedure with the base station device (second base station device 102) determined as the handover target (S506). At this time, the terminal apparatus 103 can perform a random access procedure using, for example, routing information (TAI) and beam information of the second base station apparatus 102 determined as a handover target. At this time, the terminal device 103 also transmits the context information (UE context) of the terminal device 103 to the second base station device 102 .

After that, the second base station apparatus 102 notifies the terminal apparatus 103 that the terminal apparatus 103 autonomously performed handover and requests the transfer of data addressed to the terminal apparatus 103 to the first base station apparatus 101, which is the handover source. Send (S507). Then, the first base station device 101 transfers the buffered data and packets addressed to the terminal device 103 to the second base station device 102 (S508). Information on the communication state is transmitted to the second base station apparatus 102 (S509). With these procedures, the handover is completed (S510), after which the second base station apparatus 102 communicates with the terminal apparatus 103 as a serving base station. Then, the second base station device 102 performs the operation as the first base station device 101 in FIG. 5, for example.

As described above, in the present embodiment, the terminal device 103 is notified of the base station device capable of providing the service requested by the terminal device 103 as a handover destination candidate base station device. Then, the terminal device 103 can autonomously execute handover (without being instructed by the serving base station) using the information of this candidate base station device. As a result, the service interruption period is short, and erroneous connection to a base station apparatus that cannot provide the service requested by the terminal apparatus 103 can be prevented. As a result, the terminal device 103 can continue to receive service more reliably.

Next, FIG. 6 shows a second example of processing. Note that FIG. 6 shows the flow until the serving base station notifies the terminal device of the information of the candidate base station device, and the processing after the notification of the information is the same as the processing after S504 in FIG. Therefore, illustration is omitted.

In the process of FIG. 6, the first base station apparatus 101 acquires information on services requested by a plurality of connected terminal apparatuses (S601). This information is obtained through notification from the terminal device to the network side when each terminal device requests registration to the network or requests information on candidate base station devices for switching connection destinations. can be done. The first base station apparatus groups a plurality of connected terminal apparatuses based on the acquired information (S602). For example, grouping can be done according to criteria such as terminals requesting the same service belong to the same group, or terminals to be connected to the same network slice belong to the same group. . Then, the first base station apparatus 101 selects a candidate base station apparatus for each group (S603). Then, the first base station apparatus 101 transmits information on the selected candidate base station apparatus using one signal to one or more terminal apparatuses belonging to the group (S604). Information transmission may be performed by one multicast signal addressed to one or more terminal devices belonging to the group, or may be performed by one broadcast signal including information specifying the group. .

When a plurality of terminal devices request the same service or connect to the same network slice, those terminal devices are notified of the same candidate base station device information. , the same signal is transmitted as many times as the number of terminal devices. On the other hand, by grouping as shown in FIG. 6 and notifying the information of the candidate base station apparatus with one signal to the terminal apparatuses belonging to the group, the radio communication required for notifying the information of the candidate base station apparatus is reduced. Resources can be reduced.

Claims (12)

A terminal device,
Establishment means for establishing connection with a base station device;
a transmission means for transmitting information corresponding to a service requested by the terminal device;
Receiving means for receiving, from the serving base station apparatus with which connection has been established by the establishing means, information on candidate base station apparatuses for autonomous handover of the terminal apparatus from the serving base station apparatus using a radio resource control (RRC) message. and,
Acquisition means for acquiring identification information of a surrounding base station device from a radio signal transmitted by the surrounding base station device;
The identification information corresponds to the identification information of any one of the candidate base station devices according to a condition related to the quality of radio signals from the serving base station device after receiving the information of the candidate base station devices. execution means for executing handover to the candidate base station device corresponding to the identification information based on the information of the candidate base station device without depending on the instruction of the serving base station device;
A terminal device comprising: The conditions include that the quality of the radio signal from the serving base station apparatus falls below a first predetermined level, and that the quality of the radio signal from the candidate base station apparatus is equal to or higher than a predetermined level. The terminal device according to claim 1, characterized by: 3. The information of the candidate base station apparatus includes cell identification information provided by the candidate base station apparatus and information used in a connection procedure with the candidate base station apparatus. The terminal device described in . 4. The terminal device according to any one of claims 1 to 3, wherein said transmission means transmits Network Slice Selection Assistance Information (NSSAI) as information corresponding to a service requested by said terminal device. wherein the transmission means transmits a signal requesting information on the candidate base station apparatus including information corresponding to the service requested by the terminal apparatus;
5. The terminal device according to any one of claims 1 to 4, characterized in that: The executing means, when executing the handover, transmits context information of the terminal device to a base station device to which connection is switched due to the handover.
The terminal device according to any one of claims 1 to 5, characterized in that: A base station device,
establishing means for establishing a connection with a terminal device;
a receiving means for receiving information corresponding to a service requested by the terminal device from the terminal device;
selection means for selecting a candidate base station apparatus for autonomous handover of the terminal apparatus;
transmitting means for transmitting information on the candidate base station apparatus to the terminal apparatus by means of a radio resource control (RRC) message;
A base station device characterized by having: 8. The base station apparatus according to claim 7, wherein said receiving means receives Network Slice Selection Assistance Information (NSSAI) as information corresponding to the service requested by said terminal apparatus. A control method performed by a terminal device,
an establishment step of establishing a connection with a base station device;
a transmission step of transmitting information corresponding to a service requested by the terminal device;
A receiving step of receiving information of candidate base station devices for autonomous handover of the terminal device from the serving base station device with which connection has been established in the establishing step, from the serving base station device by means of a radio resource control (RRC) message. and,
an acquiring step of acquiring identification information of a surrounding base station device from a radio signal transmitted by the surrounding base station device;
The identification information corresponds to the identification information of any one of the candidate base station devices according to a condition related to the quality of radio signals from the serving base station device after receiving the information of the candidate base station devices. an executing step of executing handover to the candidate base station device corresponding to the identification information based on the information of the candidate base station device without an instruction from the serving base station device;
A control method comprising: A control method executed by a base station device, comprising:
an establishing step of establishing a connection with the terminal device;
a receiving step of receiving information corresponding to a service requested by the terminal device from the terminal device;
a selection step of selecting a candidate base station device for autonomous handover of the terminal device;
a transmission step of transmitting information on the candidate base station apparatus to the terminal apparatus by means of a radio resource control (RRC) message;
A control method comprising: A program for causing a computer to function as the terminal device according to any one of claims 1 to 6. A program for causing a computer to function as the base station apparatus according to claim 7 or 8.

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