JP7442711B2 - Terminal device, base station device, control method, and program for autonomous handover by terminal device - Google Patents

Description

The present invention relates to a terminal device-driven handover technique.

In next-generation cellular communication systems, it is expected that beams will be formed to cover narrow areas (cells) and frequency resources will be used effectively. Due to such further miniaturization of cells, handovers may occur more frequently when a terminal device moves. Therefore, it is important to shorten the service interruption time during one handover. Non-Patent Document 1 describes a method in which a serving base station (serving cell) notifies information for accessing a target cell candidate, an event dedicated to autonomous handover, etc. in advance for a terminal device to autonomously handover. Are listed.

3GPP contribution, R2-1708840, August 2017

In the fifth generation cellular communication system, networks are created for each service such as voice calls, video and music streaming, and for each category such as high-speed large-capacity communication, connection with multiple terminals, and ultra-reliable low-latency communication. Slicing is performed. For example, a terminal device can receive an appropriate service by connecting to a network slice corresponding to the requested service. On the other hand, the technique described in Non-Patent Document 1 does not take such network slices into consideration, and it is conceivable that the terminal device connects to an inappropriate network slice. As a result, the terminal device may not be able to receive appropriate services at the handover destination, and further handover may become necessary.

The present invention has been made in view of the above problems, and 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 an establishing means for establishing a connection with a base station device, a transmitting means for transmitting information corresponding to a service requested by the terminal device, and a serving base to which a connection is established by the establishing means. Receiving means for receiving information on candidate base station apparatuses for autonomous handover of the terminal apparatus from the serving base station apparatus by a radio resource control (RRC) message, and identification information of surrounding base station apparatuses. an acquisition means for acquiring from a radio signal transmitted by the surrounding base station apparatus, and after receiving information on the candidate base station apparatus, according to conditions related to the quality of the radio signal from the serving base station apparatus, If the identification information corresponds to the identification information of any one of the candidate base station apparatuses, handover to the candidate base station apparatus to which the identification information corresponds is performed based on the information of the candidate base station apparatus. and an execution unit that executes the execution without depending on instructions from the base station device.

A base station device according to an aspect of the present invention includes: an 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; The terminal apparatus includes a selecting means for selecting a candidate base station apparatus for a typical handover, and a transmitting means for transmitting information on the candidate base station apparatus to the terminal apparatus by a radio resource control (RRC) message.

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

1 is a diagram illustrating a configuration example of a wireless communication system. It is a diagram showing an example of the hardware configuration of the device. FIG. 2 is a diagram illustrating an example of a functional configuration of a base station device. FIG. 2 is a diagram showing an example of a functional configuration of a terminal device. The figure which shows the 1st example of the flow of a process performed by a wireless communication system. The figure which shows the 2nd example of the flow of a process performed by a wireless communication system.

Embodiments of the present invention will be described below 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 a first base station device 101, a second base station device 102, and a terminal device 103. The first base station device 101 is a serving base station that is connected to the terminal device 103, and the second base station device 102 is a non-serving base station that is not connected to the terminal device 103. Note that the first base station device 101 can be configured to provide a plurality of cells (beams) by, for example, beamforming, and in this case, the first base station device 101 that is connected to the first cell (beam) of the plurality of cells In a second cell to which it is not connected (non-serving cell), it operates as a non-serving base station. In the following, when one base station apparatus provides both a serving cell and a non-serving cell, the part of the base station apparatus that provides the non-serving cell will be treated as the second base station apparatus 102, and the part that provides the serving cell will be treated as the second base station apparatus 102. is treated as the first base station device 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. This becomes the base station device 102. That is, the first base station apparatus 101 and the second base station apparatus 102 may be configured to differ only in whether or not they are connected to the terminal apparatus 103. Note that FIG. 1 is an example; in general, there are a large number of base station apparatuses and a large number of terminal apparatuses, and unless otherwise specified, the following explanation will be made between each base station apparatus and each terminal apparatus. Steps are executed individually.

In this embodiment, the terminal device 103 switches from the serving base station to which it is connected (the first base station device 101) to another base station device (for example, the second base station device) that is a candidate for connection switching from the serving base station. information about the base station device 102) is obtained in advance as information about the handover destination candidate base station device. In one example, the information on the candidate base station device may include cell identification information provided by the candidate base station device and information used in a connection procedure with the candidate base station device. Here, the identification information may be, for example, the NR Cell Global ID (NCGI) of the candidate base station device. Note that NCGI is a global ID of a cell determined by a combination of Public Land Mobile Network ID (PLMN ID) and NR Cell Identity (NCI). Further, 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 device, routing information (Tracking Area ID (TAI)), frequency information, etc. sell.

Then, the terminal device 103 communicates with the serving base station while holding the information on the candidate base station device in this way, and as long as the communication environment with the serving base station is good, the terminal device 103 continues to communicate with the serving base station. communication can be continued. Then, in response to the quality of the wireless signal from the serving base station falling below a predetermined level, identification information of surrounding base station devices is acquired from the wireless signals transmitted from the surrounding base station devices and retained. The identification information of the candidate base station device is compared with that of the candidate base station device. Here, the identification information of surrounding base station devices may be, for example, Physical Cell ID (PCI). For example, when the identification information of surrounding base station apparatuses acquired from a radio signal received with radio quality equal to or higher than a predetermined level corresponds to the identification information (NCGI) of a candidate base station apparatus, the terminal apparatus 103 uses the identification information of the candidate base station apparatus (NCGI). determines the corresponding candidate base station device as the connection switching destination. Note that if the identification information of multiple surrounding base station devices corresponds to the identification information of a candidate base station device, the terminal device 103 selects the base station device with the best radio quality among the surrounding base station devices. , or by randomly selecting one base station apparatus from among the base station apparatuses whose wireless quality exceeds a threshold level, one candidate base station apparatus to switch to can be selected. The terminal device 103 then performs handover to the candidate base station device to which the connection is to be switched, without going through the serving base station. For example, the terminal device 103 can establish a connection with a candidate base station device to which connection is to be switched 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. Thereafter, the candidate base station device to which the connection is to be switched notifies the switching source base station device (previous serving base station) that the terminal device 103 has autonomously executed the handover, and transfers the data addressed to the terminal device 103 to the switching source base station device (former serving base station). request for transfer. When the switching source base station device receives the notification that the terminal device 103 has handed over and the data transfer request, it transfers the data addressed to the terminal device 103 to the candidate base station device to which the connection is to be switched. The transferred data addressed to the terminal device 103 is then transmitted to the terminal device 103 from the candidate base station device to which the connection is to be switched. As a result, the terminal device 103 can autonomously execute handover without going through the serving base station, so it can quickly change the connection destination in response to the quality of the wireless signal from the serving base station falling below a predetermined level. Base station equipment will now be switched. 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 start an autonomous handover in response to a trigger other than the fact that the quality of the wireless signal from the serving base station falls below a predetermined level. For example, an autonomous handover may be initiated due to another trigger such as the amount of communication delay with the serving base station becoming larger than a predetermined value or the amount of resources allocated from the serving base station being insufficient. It's okay.

In the fifth generation cellular communication system (NR, New Radio), a network slicing technique is used to define a network for each service. The network slices supported by each base station device may be different. In other words, some base station devices may support all network slices and provide all services, while other base station devices may support only some network slices and provide some services. We may not be able to provide such information. At this time, if the serving base station notifies the terminal device 103 of information on other base station devices in an adjacent relationship as candidate base station information regardless of the service requested by the terminal device 103, the terminal device 103 becomes autonomous. As a result of the handover, the candidate base station device to which the connection is to be switched may not be able to support the service requested by the terminal device 103.

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

Note that the serving base station can transmit information on candidate base station devices based on information on the service requested by the terminal device 103 through dedicated signaling to the terminal device 103. The individual signaling here can be performed by, for example, a radio resource control (RRC) message 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 the requested service information (NSSAI) in the registration request message when registering with the NR's RAN (Radio Access Network). . In this case, the base station device can obtain information on the service requested by the terminal device 103 by searching for information registered on the network side. That is, there is no need to newly transmit NSSAI from the terminal device 103 to the base station device. However, the terminal device 103 may transmit information on the requested service, such as NSSAI, to the base station device. For example, the terminal device 103 may include information on the requested service in a signal requesting information on candidates for connection switching destinations (for example, a message requesting a neighboring cell list) and transmit the signal to the serving base station. As a result, the serving base station does not need to search for information on the service requested by the terminal device 103 for the terminal device 103 requesting information on the candidate for connection switching destination, and can quickly retrieve information on the candidate base station device. The terminal device 103 can be notified.

Further, the serving base station can obtain information on services requested by each of the plurality of terminal devices 103, and group the terminal devices 103 so that, for example, terminal devices requesting the same service are grouped into the same group. The serving base station then selects a candidate base station apparatus for each group and transmits information on the selected candidate base station apparatus to one or more terminal apparatuses 103 belonging to the group by one signal. I can do it. This single signal transmission of information can be performed, for example, by broadcasting system information. Note that a multicast signal with a specified 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, the signal may include information specifying a target group or target service. Note that the plurality of terminal devices 103 may be grouped based on different criteria, such as whether or not they request the same service. 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. Thereby, the amount of radio resources used for notification of candidate base station devices can be reduced.

Below, examples of the configuration of each device and the flow of processing to be executed will be described.

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

Then, the base station device and the terminal device communicate with other devices by controlling the communication circuit 205 by, for example, the CPU 201. 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. Further, the communication circuit 205 of the base station device may be able to form one or more (plural) beams and perform wireless communication with the terminal device. Further, in this case, the communication circuit 205 of the terminal device can connect to the base station device and perform wireless communication via at least one of the beams formed by the communication circuit 205 of the base station device. configured. Note that in the configuration of FIG. 2, the base station device and the terminal device are schematically illustrated 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 may include a first communication circuit for wired communication with another base station device and a second communication circuit for wireless communication with a terminal device. Further, the terminal device may include, for example, a first communication circuit for NR and a second communication circuit for LTE (Long Term Evolution). Further, the terminal device may have a wireless communication circuit related to a standard other than cellular, such as a wireless LAN, or may further have a wired communication circuit used for wired connection such as a USB connection.

Note that the base station device and the terminal device may be equipped with dedicated hardware to execute each function, or a part may be executed by hardware and the other part may be executed by a computer running a program. . Alternatively, all functions may be performed by a computer and a program.

(Functional configuration)
FIG. 3 shows an example of a functional configuration of a base station device (first base station device 101 and second base station device 102). The base station device includes, 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. Further, the base station device may include a grouping section 306, for example, as an option.

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

The requested service acquisition unit 302 acquires information on the service requested by the terminal device 103. For example, the requested service acquisition unit 302 receives a message (registration request) requesting registration from an unregistered terminal device 103, and acquires the NSSAI in the message as information on the service requested by the terminal device 103. I can do it. Further, the requested service acquisition unit 302 can acquire, for the registered terminal device 103, information on a service requested by the terminal device 103, which is managed at a predetermined node in the network, from that predetermined node. Further, in some cases, when the terminal device 103 is handed over, the requested service acquisition unit 302 may acquire information on the service requested by the terminal device 103 from the handover source base station device.

The adjacent information storage unit 303 stores information about other base station devices that are adjacent to the own device. Here, the adjacent information storage unit 303 stores information regarding a base station device (cell) that is a candidate for a connection switching destination as information about another base station device in an adjacent relationship. In other words, other base station devices to be stored do not need to be directly adjacent to the base station device; for example, when switching connections using relays, other base station devices to be stored may be stored in cells that are not geographically adjacent to each other. information can be stored. Information on other base station devices may include, for example, NCGI, beam information, routing information, and AMF ID (or information on multiple S-NSSAIs). Note that the adjacent information storage unit 303 may have an automatic neighbor relation (ANR) function that automatically establishes an adjacent relationship when the number of adjacent base station devices increases or decreases.

The candidate base station selection unit 304 selects other base station apparatuses in an adjacent relationship based on the information on the service requested by the terminal device 103 acquired by the requested service acquisition unit 302 and the information stored in the adjacent information storage unit 303. Another base station device that can provide the requested service is selected as a candidate base station device to which the connection will be switched. For example, the candidate base station selection unit 304 selects the AMF ID or S- Another base station device having NSSAI information is selected as a candidate base station device to which connection is to be switched. Note that the selection of candidate base station devices does not need to be performed by the serving base station, and for example, this selection may be performed by a network node different from the serving base station.

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

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

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

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

The candidate information acquisition unit 402 acquires information on a candidate base station device to which the connection is to be switched, selected by the connected base station device (or other network node) according to the information on the service requested by the terminal device 103. do. The information on the candidate base station device here includes, for example, the identification information of the cell formed by the candidate base station device (e.g., NCGI), and the information used in the connection procedure with the candidate base station device (e.g., beam information, routing information, frequency information, etc.).

The trigger determination unit 403 determines, for example, that the amount of delay becomes larger than a predetermined value in response to the quality of the wireless signal from the serving base station falling below a predetermined level, or the load on the serving base station exceeding a predetermined value. The terminal device 103 determines a trigger for starting handover, such as that the amount of resources allocated from the serving base station is less than or equal to a predetermined amount. Note that the trigger determination unit 403 can determine any trigger for the terminal device 103 to autonomously start handover.

For example, when the trigger determination unit 403 detects a handover start trigger, the surrounding information acquisition unit 404 observes wireless signals from nearby base station devices that are not connected, and obtains identification information of those base station devices. (PCI). Note that the surrounding information acquisition unit 404 can also measure radio quality such as received power of radio signals from surrounding base station devices. Then, the peripheral information acquisition unit 404 determines whether there is any identification information of peripheral base station devices that corresponds to the identification information in the candidate base station information acquired by the candidate information acquisition unit 402. The surrounding information acquisition unit 404 determines a surrounding base station device having identification information that corresponds to the information of the candidate base station device as a handover target. Note that when the identification information of a plurality of peripheral base station apparatuses corresponds to the information of a candidate base station apparatus, the peripheral information acquisition unit 404 selects a base with the best radio quality among the plurality of peripheral base station apparatuses. One base station device randomly selected from among the station devices or those whose radio quality exceeds a predetermined standard can be determined as a handover target. Furthermore, before the trigger determination unit 403 detects the handover start trigger, the surrounding information acquisition unit 404 observes wireless signals from nearby base stations that are not connected and It is also possible to acquire identification information or measure received power. For example, the peripheral information acquisition unit 404 periodically observes radio signals from surrounding base station devices and holds the results, and when the trigger determination unit 403 detects a handover start trigger, , the handover target may be determined based on the held information. In addition, when observing radio signals from surrounding base station devices in advance, the surrounding information acquisition unit 404 determines whether the base station device corresponds to the identification information in the information on the candidate base station device acquired by the candidate information acquisition unit 402. It is also possible to retain only the results related to the above. According to this, the peripheral information acquisition unit 404 does not need to perform a process of extracting information regarding the candidate base station apparatus from the held information after the trigger determination unit 403 detects the handover start trigger. Thereby, the time required for processing after a handover start trigger is detected can be shortened.

The handover execution unit 405 executes the handover to the handover target base station device determined by the surrounding information acquisition unit 404 without going through the serving base station. The handover execution unit 405 executes, for example, a random access procedure with the target base station device. Furthermore, 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 information on the service requested by the terminal device 103, for example, by including the NSSAI in a registration request message when the terminal device 103 registers with the NR. Further, the requested service notification unit 406 can transmit information on the service requested by the terminal device 103 in a request message when requesting information on a candidate base station device from a serving base station, for example. Note that the requested service notification unit 406 may notify the information of the service requested by the terminal device 103 to the network side via the serving base station using 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 device 101, which is the serving base station of the terminal device 103, acquires information on a service requested by the terminal device 103 (S501). Note that in FIG. 5, information on the service requested by the terminal device 103 is notified to the first base station device 101 in a message requesting information on a candidate base station device to which connection is to be switched from the terminal device 103. An example is shown. Note that when requesting registration to the network, the terminal device 103 may notify the network side of information about the service requested by the terminal device. In this case, the first base station device 101 This information can be obtained from other nodes (eg, other base station devices). Then, the first base station apparatus 101 selects candidate base station apparatuses capable of supporting the service requested by the terminal apparatus 103 from among other adjacent base station apparatuses, based on the information of the service requested by the terminal apparatus 103. is selected (S502). For example, the first base station device 101 obtains an NSSAI as information about a service requested by the terminal device 103, and selects a base station device that configures a network slice corresponding to the NSSAI as a candidate base station device. Note that if the information on the service requested by the terminal device 103 cannot be obtained, a base station device corresponding to the default AMF is selected as a candidate base station device. In addition, in consideration of the load on the candidate base station apparatus, the first base station apparatus 101 provides a terminal apparatus that requests the same service in order to prevent multiple terminal apparatuses from simultaneously handing over to the same candidate base station apparatus. Information on different candidate base station apparatuses may be selected for each base station. The first base station device 101 notifies the terminal device 103 of information about the selected candidate base station device (S503). At this time, the first base station apparatus 101 can notify information to the terminal apparatus 103 by individual signaling such as an RRC message or on-demand system information.

When the terminal device 103 receives information about candidate base stations, it holds the information. Then, the terminal device 103 continues to monitor whether a trigger that requires handover occurs during communication with the first base station device 101. Here, when the terminal device 103 detects a trigger such as the quality of the wireless signal from the first base station device 101 falling below a predetermined level (S504), it subsequently detects a trigger such as when the quality of the wireless signal from the first base station device 101 falls below a predetermined level (S504). Observe and obtain identification information of each base station device (cell provided by each base station device) from the radio signal. Then, the terminal device 103 compares the acquired identification information with the identification information of the candidate base station device, and detects surrounding base station devices having identification information that corresponds to any of the identification information of the candidate base station device. (S505). If the terminal device 103 detects a plurality of base station devices at this time, the terminal device 103 determines the base station device to be the handover target based on, for example, the quality of the radio signals from those base station devices. 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 device 103 can perform a random access procedure using, for example, the routing information (TAI) and beam information of the second base station device 102 determined as the handover target. Also, at this time, the terminal device 103 transmits context information (UE context) of the terminal device 103 to the second base station device 102.

Thereafter, the second base station apparatus 102 sends a notification that the terminal apparatus 103 has autonomously performed a handover and a request to transfer data addressed to the terminal apparatus 103 to the first base station apparatus 101 that 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), and also updates the status of the sequence number (SN), etc. Communication status information is transmitted to the second base station device 102 (S509). Through these steps, the handover is completed (S510), and thereafter, the second base station device 102 performs communication with the terminal device 103 as a serving base station. Then, the second base station device 102 executes the operation as the first base station device 101 in FIG. 5, for example.

As described above, in this embodiment, a base station apparatus that can provide a service requested by the terminal apparatus 103 is notified to the terminal apparatus 103 as a candidate base station apparatus as a handover destination. Then, the terminal device 103 can autonomously execute handover (without depending on instructions from the serving base station) using information about this candidate base station device. Thereby, the service interruption period is short, and it is possible to prevent the terminal device 103 from erroneously connecting to a base station device that cannot provide the requested service. As a result, the terminal device 103 can continue to receive services 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 candidate base station device information, and the processing after notification of that information is the same as the processing after S504 in FIG. 5. Therefore, illustration is omitted.

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

When multiple terminal devices request the same service or connect to the same network slice, those terminal devices will be notified of the same candidate base station device information, and each terminal device will be notified of the same candidate base station device information. When information is notified to terminal devices, the same signal will be transmitted for each terminal device. On the other hand, by grouping as shown in FIG. 6 and notifying terminal devices belonging to the group with information on candidate base station devices using one signal, wireless communication required to notify information on candidate base station devices is possible. It becomes possible to reduce resources.

Claims (12)

A terminal device,
Establishment means for establishing a connection with a base station device;
a transmitting means for transmitting information corresponding to a service requested by the terminal device;
Receiving means for receiving information on candidate base station apparatuses for autonomous handover of the terminal apparatus from the serving base station apparatus with which the connection has been established by the establishing means, from the serving base station apparatus by a radio resource control (RRC) message. and,
acquisition means for acquiring identification information of surrounding base station devices from wireless signals transmitted by the surrounding base station devices;
After receiving the information on the candidate base station apparatus, the identification information corresponds to the identification information of any one of the candidate base station apparatuses according to a condition related to the quality of a radio signal from the serving base station apparatus. In this case, execution means for executing handover to a candidate base station corresponding to the identification information based on information on the candidate base station without depending on an instruction from the serving base station;
A terminal device comprising: The condition includes, in addition to the quality of the radio signal from the serving base station being below a first predetermined level, the quality of the radio signal from the candidate base station being equal to or higher than a predetermined level. The terminal device according to claim 1, characterized in that: 3. The information on 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 claim 1, wherein the transmitting means transmits Network Slice Selection Assistance Information (NSSAI) as information corresponding to the service requested by the terminal device. The transmitting means transmits a signal requesting information on the candidate base station device including information corresponding to a service requested by the terminal device.
The terminal device according to any one of claims 1 to 4. When executing the handover, the execution means transmits context information of the terminal device to a base station device to which connection is to be switched by the handover.
The terminal device according to any one of claims 1 to 5. A base station device,
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;
Selection means for selecting a candidate base station device for autonomous handover of the terminal device;
Transmitting means for transmitting information about the candidate base station device to the terminal device using a radio resource control (RRC) message;
A base station device comprising: The base station apparatus according to claim 7, wherein the receiving means receives Network Slice Selection Assistance Information (NSSAI) as information corresponding to the service requested by the terminal apparatus. A control method executed by a terminal device, comprising:
an establishment step of establishing a connection with the base station device;
a transmitting step of transmitting information corresponding to a service requested by the terminal device;
a receiving step of receiving information on a candidate base station device for autonomous handover of the terminal device from the serving base station device with which a connection has been established in the establishment step, from the serving base station device using a radio resource control (RRC) message; and,
an acquisition step of acquiring identification information of surrounding base station devices from wireless signals transmitted by the surrounding base station devices;
After receiving the information on the candidate base station apparatus, the identification information corresponds to the identification information of any one of the candidate base station apparatuses according to a condition related to the quality of a radio signal from the serving base station apparatus. an execution step of executing handover to the candidate base station to which the identification information corresponds, based on information on the candidate base station, without depending on an instruction from the serving base station;
A control method characterized by comprising: A control method executed by a base station device, comprising:
an establishment step of establishing a connection with a 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 transmitting step of transmitting information on the candidate base station device to the terminal device by a radio resource control (RRC) message;
A control method characterized by 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 device according to claim 7 or 8.

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