Terminal device, base station device, and control method for improving handover performance using artificial intelligence (AI) / machine learning (ML)

Abstract

This terminal device receives information of an event based on the probability of occurrence of at least either a radio link failure (RLF) or a handover failure (HOF) from a base station device being connected, measures radio quality for a signal transmitted from the base station device, inputs radio quality acquired for a signal transmitted from the base station device in a learning phase and, by inputting radio quality measured in an inference phase to a trained model acquired by machine learning in which is used as teaching data a value indicating at least which of an RLF when handover processing is not performed or an HOF when handover processing is performed has occurred at a timing a prescribed period after the timing at which said radio quality was obtained, identifies the probability of occurrence of at least either the RLF or the HOF acquired thereby. When the probability of occurrence satisfies a condition of the event, a prescribed notification is transmitted to the base station device.

Description

Terminal device, base station device, and control method for improving handover performance using artificial intelligence (AI) / machine learning (ML)

[0001] The present invention relates to an advanced handover technique in a cellular communication system.

[0002] In wireless communication systems compliant with the cellular communication standard of the Third Generation Partnership Project (3GPP (registered trademark)), a handover process is defined for switching the base station to which a mobile terminal device is connected, so that the mobile terminal device can continue to communicate with high quality. The handover process is performed, for example, when the wireless quality of a signal transmitted from a base station to which the mobile terminal device is currently connected falls below a predetermined level for a certain period of time, by transmitting a measurement result to the base station, and the base station then instructs the mobile terminal device to perform a handover.

[0003] For example, if the wireless quality of the terminal device further deteriorates during the time between when the wireless quality falls below a predetermined level and when a handover command is transmitted from the base station, the handover process may fail, resulting in a decrease in communication efficiency. Also, since it takes time for the terminal device to detect a more suitable base station to connect to and when a handover command is transmitted from the base station, an opportunity to improve communication efficiency may be missed.

[0004] The present invention provides a technique for enhancing handover processing and improving communication efficiency.

[0005] A terminal device according to one aspect of the present invention comprises: a receiving means for receiving, from a connected base station device, information on an event based on the probability of occurrence of at least one of a radio link failure (RLF) and a handover failure (HOF); a measuring means for measuring the wireless quality of a signal transmitted from the base station device; an identifying means for identifying the probability of occurrence of at least one of the RLF and the HOF obtained by inputting the wireless quality measured by the measuring means in the inference phase into a trained model obtained by machine learning using as input the wireless quality acquired for the signal transmitted from the base station device in the learning phase and a value indicating whether at least one of an RLF when handover processing is not performed within a predetermined period after the wireless quality was acquired and an HOF when handover processing is performed as training data; and a transmitting means for transmitting a predetermined notification to the base station device when the occurrence probability satisfies the condition of the event.

[0006] A base station device according to one aspect of the present invention comprises: a notification means for notifying a terminal device connected to a cell provided by the base station device of event information based on the probability of occurrence of at least one of a radio link failure (RLF) and a handover failure (HOF); a receiving means for receiving a predetermined notification transmitted from the terminal device based on the probability of occurrence of at least one of a radio link failure (RLF) and a handover failure (HOF), which is acquired by inputting the wireless quality acquired for a signal transmitted from the base station device in a learning phase and using as training data a value indicating whether at least one of an RLF when a handover process is not performed within a predetermined period after the wireless quality is acquired and an HOF when a handover process is performed, and which acquires the wireless quality measured by the terminal device in an inference phase and acquires the probability of occurrence of at least one of the RLF and the HOF, satisfying the conditions of the event; and a determination means for determining whether to hand over the terminal device from the cell to another cell in response to receiving the predetermined notification.

[0007] According to the present invention, the handover process can be enhanced to improve communication efficiency.

[0008] Other features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings, in which the same or similar elements are designated by the same reference numerals.

[0009] The accompanying drawings are incorporated in and constitute a part of the specification, illustrate embodiments of the present invention, and together with the description are used to explain the principles of the present invention. Figure 1 is a diagram showing an example of the configuration of a wireless communication system. Figure 2 is a diagram showing an example of the hardware configuration of a base station device and a terminal device. Figure 3 is a diagram showing an example of the functional configuration of a terminal device. Figure 4 is a diagram showing an example of the functional configuration of a base station device. Figure 5 is a diagram showing an example of the flow of processing executed in the wireless communication system.

[0010] Hereinafter, the embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the scope of the invention as claimed, and not all combinations of features described in the embodiments are necessarily essential to the invention. Two or more of the features described in the embodiments may be combined in any desired manner. Furthermore, the same reference numerals are used to designate identical or similar components, and redundant descriptions will be omitted.

[0011] (System Configuration) FIG. 1 shows an example configuration of a communication system according to this embodiment. This communication system is, for example, a wireless communication system conforming to the Long Term Evolution (LTE) or fifth generation (5G) cellular communication standards of the Third Generation Partnership Project (3GPP (registered trademark)), or their successor standards. This wireless communication system includes a base station device 101 and a terminal device 111. The terminal device 111 establishes a connection with the base station device 101 and performs wireless communication in a cell 121 provided by the base station device 101. The terminal device 111 is assumed to be, for example, portable by a user and to be mobile. If the terminal device 111 moves beyond the range of the cell 121, it will no longer be able to maintain communication in that cell 121. Therefore, for example, the terminal device 111 performs handover to another cell (cell 122 or cell 123) upon the occurrence of a predetermined event, such as a deterioration in communication quality in the currently connected cell 121. Note that the cells 122 and 123 may be provided by a base station device other than the base station device 101, or may be provided by the base station device 101. In other words, the base station device 101 may provide multiple cells.

[0012] Conventionally, the terminal device 111 measures the wireless quality of signals transmitted from the currently connected cell 121 and other adjacent cells (cells 122 and 123), and determines whether an event for initiating handover processing has occurred based on whether the wireless quality satisfies a predetermined condition. Events are defined in a cellular communication standard. Examples of events include event A2, which is determined to have occurred when the wireless quality of the currently connected cell falls below a predetermined threshold; event A3, which is determined to have occurred when the wireless quality of the adjacent cell becomes higher (by a predetermined offset) than the wireless quality of the currently connected cell; event A4, which is determined to have occurred when the wireless quality of the adjacent cell exceeds a predetermined threshold; and event A5, which is determined to have occurred when the wireless quality of the currently connected cell falls below a first predetermined threshold and the wireless quality of the adjacent cell exceeds a second predetermined threshold. When the terminal device 111 determines that any of the events set by the base station device 101 has occurred, it transmits a predetermined report to the base station device 101. Then, in response to receiving the predetermined report, the base station device 101 executes processing to hand over the terminal device 111 from the currently connected cell 121 to another cell (for example, cell 122 or cell 123). Note that the handover of the terminal device 111 can be performed, for example, by transmitting setting information for communication in a neighboring cell from the base station device 101 to the terminal device 111 before the occurrence of an event, and then transmitting a command (Handover command) from the base station device 101 to the terminal device 111 instructing the handover. Also, after the occurrence of an event, the handover processing can be started by transmitting setting information for communication in a neighboring cell of the handover from the base station device 101 to the terminal device 111 using an RRC Reconfiguration message. Note that RRC is an abbreviation for Radio Resource Control.

[0013] Conventionally, handover processing is initiated when the wireless quality measured at that time in the terminal device 111 satisfies one of the above-mentioned events. In this procedure, for example, the wireless quality of the connected cell (serving cell) deteriorates in event A2 or event A3, and a predetermined report is transmitted to the base station device 101 after the event occurs. Then, a handover instruction is transmitted from the base station device 101. Therefore, a certain period of time is required from the deterioration of wireless quality to the execution of handover. Then, during the period from when the terminal device 111 detects the occurrence of the event to when the base station device 101 transmits the handover instruction, the wireless quality may further deteriorate, and the handover instruction may not be received by the terminal device 111.

[0014] The terminal device 111 is supposed to start timer T310 when it is deemed unable to establish downlink synchronization with the base station device 101. More specifically, the terminal device 111 starts timer T310 when it receives N310 consecutive out-of-sync indications from the physical layer in the RRC layer. The terminal device 111 receives information on the number of N310 and the expiration time of T310 in advance as configuration information from the connected base station device 101. When timer T310 expires after being started, the terminal device 111 determines that a radio link failure (RLF) has occurred. Timer T310 is stopped when a handover command is received. However, as described above, if wireless quality deteriorates after an event occurs and the terminal device 111 is unable to receive the command, it cannot stop timer T310. As a result, the terminal device 111 is unable to execute handover processing, resulting in the occurrence of a handover failure (HOF). Furthermore, the terminal device 111 cannot start a connection re-establishment process (RRC Connection Re-establishment process) unless an RLF occurs after waiting until timer T310 expires. For this reason, in order to improve the efficiency of communication in a wireless communication system, it is important to reduce the probability of occurrence of HOF or RLF.

[0015] In recent years, the application of artificial intelligence (AI) / machine learning (ML) to cellular communication systems has been discussed. Using AI / ML, for example, it is possible to predict whether an RLF will occur in the future based on the wireless quality of the currently connected cell. For example, a trained model can be acquired by machine learning using the wireless quality of the cell 121 acquired in the learning phase as input and whether an RLF will occur if a handover process is not performed a predetermined period after the wireless quality is acquired as training data. Once such a trained model is acquired, the terminal device 111 can input the results of measuring the wireless quality of a signal transmitted from the cell 121 in the inference phase to obtain an estimated value of the probability that an RLF will occur a predetermined period after the wireless quality is acquired. Furthermore, the terminal device 111 provides the base station device 101 with the output of the trained model, enabling the base station device 101 to make the determination. Furthermore, for example, a trained model can be acquired by machine learning using, as input, the wireless quality of the cell 121 acquired in the learning phase and training data indicating whether or not a HOF occurred when a handover process was performed at a predetermined time after the wireless quality was acquired. When such a trained model is acquired, the terminal device 111 can obtain an estimated value of the probability of a HOF occurring at a predetermined time after the wireless quality was acquired by inputting the results of measuring the wireless quality of a signal transmitted from the cell 121 in the inference phase. Furthermore, the terminal device 111 can provide the base station device 101 with the output of the trained model, thereby enabling the base station device 101 to make this determination. Here, the predetermined time is set arbitrarily, for example, to a period of several seconds. This setting information can be notified in advance from the base station device 101 to the terminal device 111.

[0016] As described above, by using AI / ML, the terminal device 111 can obtain the probability of an RLF or HOF occurring at a predetermined timing in the future (a timing a predetermined period after the measurement value is obtained), but conventional standards do not assume that such probabilities will be obtained, and therefore there are no provisions on how to perform handover processing using these probabilities, and such handover processing cannot be performed. In view of these circumstances, this embodiment provides a technique for performing handover processing based on predicted values ​​of RLF and HOF at appropriate timing.

[0017] In this embodiment, a new event is defined based on the probability of occurrence of at least one of RLF and HOF. The base station device 101 notifies the connected terminal device 111 of configuration information of the newly defined event. The terminal device 111 receives the configuration information of the event. Then, the terminal device 111 inputs, for example, the wireless quality of the connected cell 121 (or a neighboring cell such as cell 122 or cell 123 as needed) into a trained model to acquire at least one of the probability of occurrence of RLF and the probability of occurrence of HOF. Here, as described above, the trained model can be acquired by machine learning using as input the wireless quality of the cell 121 (or a neighboring cell such as cell 122 or cell 123 as needed) acquired in the learning phase and training data indicating whether at least one of RLF occurred when handover processing was not performed at a predetermined time after the timing at which the wireless quality was acquired and HOF occurred at the time when handover processing was performed. Note that machine learning for the probability of RLF occurrence and the probability of HOF occurrence may be performed separately to generate separate trained models. However, these may also be combined and machine learning may be performed to generate a single trained model. That is, machine learning may be performed using the measured value of the wireless quality of the cell 121 as input and both the occurrence or non-occurrence of RLF and the occurrence or non-occurrence of HOF a predetermined time after the measurement value was obtained as training data to acquire a trained model. The terminal device 111 then determines whether at least one of the probability of RLF occurrence and the probability of HOF occurrence in the future (a predetermined period after the wireless quality was obtained) obtained as the output of the trained model satisfies the event condition notified by the base station device 101. If the condition is satisfied, the terminal device 111 transmits a predetermined notification, such as a conventional Measurement Report, to the base station device 101. Then, based on receiving the specified notification, the base station device 101 determines whether or not to execute a handover of the terminal device 111, and starts the handover process if it decides to execute the handover.Note that the base station device 101 may always decide to execute handover of the terminal device 111 when receiving a predetermined notification. This enables handover based on the probability of future occurrence of RLF or HOF estimated by AI / ML, and enables handover of the terminal device 111 to another cell at an appropriate timing.

[0018] The new event may include, for example, a first event that is determined to have occurred when the probability of RLF occurrence exceeds a predetermined value. The configuration information regarding the first event notified from the base station device 101 to the terminal device 111 may include, in addition to information about a predetermined value (threshold), information about a hysteresis value, and information about the length of time that the probability of RLF occurrence must continue to exceed the predetermined value to trigger a predetermined notification. For example, the terminal device 111 may determine that the condition of this first event has been satisfied when the estimated value of the RLF occurrence probability output from the trained model exceeds a predetermined value plus a hysteresis value (a value obtained by adding the hysteresis value to the predetermined value). The terminal device 111 may then determine that the condition of this first event has been released from being satisfied when the estimated value of the RLF occurrence probability falls below a predetermined value minus a hysteresis value (a value obtained by subtracting the hysteresis value from the predetermined value). The terminal device 111 transmits a predetermined notification to the base station device 101 when the state in which the condition of the first event is satisfied remains unchanged for a period longer than the notified period. For example, if the state in which the condition of the first event is satisfied continues thereafter, the terminal device 111 may repeatedly transmit the predetermined notification to the base station device 101. The predetermined notification transmitted to the base station device 101 may include information indicating an estimated value of the probability of RLF occurrence. Furthermore, the setting information regarding the first event may include information indicating whether or not to transmit a predetermined notification when the state transitions from a state in which the condition of the first event is satisfied to a state in which the condition is no longer satisfied. When this information indicates that a predetermined notification should be transmitted, for example, the terminal device 111 may transmit a predetermined notification to the base station device 101 indicating that the state in which the first event occurred has been resolved in response to a transition to a state in which the condition of the first event is no longer satisfied after transmitting a predetermined notification indicating the occurrence of the first event to the base station device 101. This allows the base station device 101 to recognize that the terminal device 111 is in a state where RLF is likely to occur in the future.

[0019] The new event may also include a second event whose occurrence is determined to have occurred when the probability of HOF occurrence exceeds a first predetermined value. The configuration information regarding the second event notified from the base station device 101 to the terminal device 111 may include, in addition to information regarding the predetermined value (threshold), information regarding a hysteresis value, and information regarding the length of time during which the probability of HOF occurrence must continue to exceed the predetermined value to trigger the predetermined notification. For example, the terminal device 111 may determine that the condition of the second event has been satisfied when the estimated value of the probability of HOF occurrence output from the trained model exceeds a predetermined value plus a hysteresis value (a value obtained by adding the hysteresis value to the predetermined value). The terminal device 111 may then determine that the condition of the second event has been released from being satisfied when the estimated value of the probability of HOF occurrence falls below a predetermined value minus a hysteresis value (a value obtained by subtracting the hysteresis value from the predetermined value). The terminal device 111 transmits a predetermined notification to the base station device 101 when the condition for the second event remains satisfied for a period longer than the notified period. For example, if the condition for the second event continues to remain satisfied thereafter, the terminal device 111 may repeatedly transmit the predetermined notification to the base station device 101. The predetermined notification transmitted to the base station device 101 may include information indicating an estimated value of the probability of HOF occurrence. Furthermore, the setting information regarding the third event may include information indicating whether or not to transmit a predetermined notification when a transition from a state in which the condition for the second event is satisfied to a state in which the condition is no longer satisfied. If this information indicates that a predetermined notification should be transmitted, for example, the terminal device 111 may transmit a predetermined notification indicating the occurrence of a third event to the base station device 101 in response to a transition from a state in which the condition for the second event is no longer satisfied after transmitting a predetermined notification indicating the occurrence of the second event to the base station device 101. Note that the terminal device 111 may be notified of a predetermined value or a hysteresis value that is different from the setting information of the second event as the setting information of the third event.This allows the base station device 101 to recognize that the terminal device 111 is in a state where HOF is likely to occur in the future or a state where HOF is unlikely to occur in the future.

[0020] The new event may also include a fourth event whose occurrence is determined to be a condition that the probability of occurrence of RLF exceeds a value obtained by adding a predetermined value (offset value) to the probability of occurrence of HOF. That is, a fourth event whose occurrence is determined to be a condition that the difference between the first occurrence probability of RLF and the second occurrence probability of HOF exceeds the predetermined value may be defined. The configuration information about the fourth event notified from the base station device 101 to the terminal device 111 may include, in addition to information about the predetermined value, information about a hysteresis value and information about the length of time during which the probability of occurrence of HOF must continue to exceed the predetermined value to trigger the predetermined notification. For example, the terminal device 111 may determine that the condition for the fourth event is satisfied when the difference between the estimated value of the first occurrence probability of RLF and the estimated value of the second occurrence probability of HOF output from the trained model exceeds a predetermined value plus a hysteresis value (a value obtained by adding the hysteresis value to the predetermined value). Then, the terminal device 111 may determine that the state in which the condition of the fourth event is satisfied has been released when the terminal device 111's signal level falls below a predetermined value minus a hysteresis value (a value obtained by subtracting the hysteresis value from the predetermined value). The terminal device 111 transmits a predetermined notification to the base station device 101 when the state in which the condition of the fourth event is satisfied remains unchanged for a period longer than the notified period. For example, if the state in which the condition of the fourth event is satisfied continues to be maintained thereafter, the terminal device 111 may repeatedly transmit the predetermined notification to the base station device 101. The predetermined notification transmitted to the base station device 101 may include information indicating an estimated value of the probability of RLF occurrence and information indicating an estimated value of the probability of HOF occurrence. Furthermore, the setting information regarding the fourth event may include information indicating whether or not to transmit a predetermined notification when the state in which the condition of the fourth event is satisfied transitions to a state in which the condition is not satisfied.When this information indicates that a predetermined notification should be made, for example, after transmitting a predetermined notification indicating that a fourth event has occurred to the base station device 101, in response to a transition to a state in which the condition of the fourth event is not satisfied, the terminal device 111 can transmit a predetermined notification indicating that the state in which the fourth event has occurred has been released to the base station device 101. As a result, when the probability of RLF occurrence is high but is higher than the probability of HOF occurrence by a certain amount or more, handover processing is executed, thereby making it possible to reduce the probability that the connection of the terminal device 111 is disconnected and to provide more stable communication to the terminal device 111.

[0021] The event setting information may include, as a condition for issuing a predetermined notification, that the conditions for each of the above-mentioned events are satisfied at a specified timing. The terminal device 111 may transmit a predetermined notification to the base station device 101 when the conditions for the above-mentioned events related to the probability of occurrence of at least one of RLF and HOF based on the radio quality at the specified timing are satisfied. The timing specification may be, for example, information such as "X milliseconds later," "X slots later," or "X periods later" based on a specified period such as the transmission period of an SSB (synchronization signal (SS) / physical broadcast channel (PBCH) block) from the current time. The event setting information may also include, as a condition for issuing a predetermined notification, that the conditions for each of the above-mentioned events are satisfied during a specified period. The terminal device 111 may transmit a predetermined notification to the base station device 101 when the conditions for the above-mentioned events related to the probability of occurrence of at least one of RLF and HOF based on the radio quality during the specified period continue to be satisfied. Furthermore, the terminal device 111 may transmit a predetermined notification to the base station device 101 when the above-described event condition related to the occurrence probability of at least one of RLF and HOF based on wireless quality is satisfied for a predetermined percentage of the specified period. In this case, the setting condition of the event may include information indicating the predetermined percentage. In addition, the terminal device 111 may notify the base station device 101 of information indicating the timing (e.g., time) when the event condition is satisfied in the predetermined notification.

[0022] Note that machine learning may be used to generate a trained model that uses one or more wireless qualities as input and outputs at least one of the RLF occurrence probability and the HOF occurrence probability at multiple timings. This allows the RLF / HOF occurrence probability at multiple future timings to be identified at once, and the terminal device 111 can determine the above-mentioned events based on the occurrence probabilities at the multiple timings.

[0023] Furthermore, the terminal devices present in the cell 121 may include a terminal device that is not capable of estimating at least one of the probability of RLF occurrence and the probability of HOF occurrence using a trained model. The terminal device may then notify the base station device 101 in advance (e.g., at the time of connection establishment) capability information indicating whether it is capable of estimating at least one of the probability of RLF occurrence and the probability of HOF occurrence using a trained model, and, if capable of estimating, whether it is capable of estimating RLF or HOF. Note that, if the terminal device is only capable of estimating the probability of RLF occurrence, the base station device 101 may not notify the base station device 101 of configuration information regarding events based on the probability of HOF occurrence (e.g., the second to fourth events described above). Also, if the terminal device is only capable of estimating the probability of HOF occurrence, the base station device 101 may not notify the base station device 101 of configuration information regarding events based on the probability of RLF occurrence (e.g., the first and fourth events described above).

[0024] Note that the performance evaluation of the trained model may be performed periodically, for example. For example, the base station device 101 may collect information on the occurrence probability of at least one of RLF and HOF estimated in some terminal devices, and observe whether or not an RLF or HOF actually occurs at a predetermined timing corresponding to the occurrence probability without transmitting a handover command to the terminal device. The base station device 101 then compares the actual measurement value of the occurrence probability of the RLF or HOF with the notified estimated value of the occurrence probability of the RLF or HOF, and calculates the difference (error) between the actual measurement value and the estimated value. If the error is equal to or greater than a predetermined value, the base station device 101 may evaluate that the trained model is not suitable for the real environment and decide to perform re-learning (additional learning). The base station device 101 may perform re-learning for a certain period of time, for example, and notify the terminal device 111 of the trained model after re-learning. The base station device 101 then receives from the terminal device 111 a notification of an estimated value of the probability of occurrence of RLF or HOF obtained by the trained model, and compares the estimated value with the actual measured value of the probability of occurrence of RLF or HOF again. The base station device 101 may terminate the re-learning when the error between the estimated value of the output of the trained model and the actual measured value falls below a predetermined level. Note that, if the terminal device 111 has generated a trained model itself, it may notify the base station device 101 that it will perform this re-learning. Alternatively, the terminal device 111 may notify the base station device 101 that re-learning is necessary and perform the re-learning upon receiving a predetermined instruction from the base station device 101. This allows the trained model to be maintained in an appropriate state, making it possible to perform handover processing based on prediction at an appropriate timing.

[0025] (Device Configuration) FIG. 2 shows an example of the hardware configuration of the base station device 101 and the terminal device 111 according to this embodiment. In one example, the base station device 101 and the terminal device 111 are configured to include a processor 201, a ROM 202, a RAM 203, a storage device 204, and a communication circuit 205. The processor 201 is a computer configured to include one or more processing circuits, such as a general-purpose CPU (Central Processing Unit) or an ASIC (Application Specific Integrated Circuit), and performs the overall processing of the device and each of the above-mentioned processes by reading and executing programs stored in the ROM 202 or the storage device 204. The ROM 202 is a read-only memory that stores information such as programs and various parameters related to the processing performed by the base station device 101 and the terminal device 111. The RAM 203 functions as a workspace when the processor 201 executes a program and is also a random access memory that stores temporary information. The storage device 204 is configured, for example, by a removable external storage device. The communication circuit 205 is configured, for example, by a circuit for wireless communication of 5G or a successor standard. While FIG. 2 illustrates one communication circuit 205, the base station device 101 and the terminal device 111 may have multiple communication circuits. For example, the base station device 101 and the terminal device 111 may have wireless communication circuits for 5G and a successor standard, respectively, and a common antenna for these circuits. The base station device 101 and the terminal device 111 may also have separate antennas suitable for each standard. The base station device 101 may also have a wired communication circuit used when communicating with other base station devices or nodes in the core network. The terminal device 111 may also have a communication circuit compliant with a wireless communication standard other than a cellular communication standard, such as a wireless local area network (LAN) or Bluetooth (registered trademark). The base station device 101 and the terminal device 111 may have separate communication circuits 205 for each of the multiple available frequency bands, or may have a common communication circuit 205 for at least some of the frequency bands.

[0026] FIG. 3 shows an example of the functional configuration of the terminal device 111. The terminal device 111 includes, for example, a capability information notification unit 301, a setting information receiving unit 302, a quality measurement unit 303, an occurrence probability estimation unit 304, and a notification unit 305. The terminal device 111 may also include, as an option, a learning unit 306. Note that FIG. 3 only shows functions particularly related to this embodiment, and does not illustrate various other functions that the terminal device 111 may have. For example, the terminal device 111 naturally has other functions that terminal devices compliant with LTE, 5G, or subsequent standards generally have. The functional blocks in FIG. 3 are shown schematically, and the respective functional blocks may be realized as an integrated unit or may be further subdivided. Furthermore, the functions in FIG. 3 may be realized, for example, by the processor 201 executing a program stored in the ROM 202 or the storage device 204, or by a processor within the communication circuit 205 executing predetermined software. Since the details of the processes executed by each functional unit have been described above, only the general functions of the terminal device 111 will be outlined here.

[0027] The capability information notifying unit 301 notifies the base station device 101 of the capability information possessed by the terminal device 111 as UE Capability. For example, the capability information notifying unit 301 notifies the base station device 101 of information indicating whether the terminal device 111 has the capability to estimate at least one of the probability of RLF occurrence and the probability of HOF occurrence from the measurement value of the wireless quality of the connected cell 121 (and, as necessary, other cells such as neighboring cells (e.g., cell 122, cell 123)) using AI / ML. The terminal device 111 may have the capability to estimate only the probability of RLF occurrence, or may have the capability to estimate only the probability of HOF occurrence. The setting information receiving unit 302 receives setting information related to communication from the base station device 101. As described above, the setting information includes information related to events related to at least one of the probability of RLF occurrence and the probability of HOF occurrence. The quality measuring unit 303 measures the wireless quality of the connected cell and, as necessary, other cells such as neighboring cells. The measured wireless quality may be information such as reference signal received power (RSRP), reference signal received quality (RSRQ), and signal-to-interference and noise ratio (SINR). The occurrence probability estimation unit 304 inputs the wireless quality measured by the quality measurement unit 303 into the trained model to estimate the probability of occurrence of at least one of RLF and HOF at a predetermined future timing. The notification unit 305 determines whether the occurrence probability estimated by the occurrence probability estimation unit 304 satisfies the event condition indicated by the setting information, and transmits a predetermined notification to the base station device 101 based on whether the condition is satisfied. When a trained model should be generated in the terminal device 111, the learning unit 306 generates the trained model by machine learning. Furthermore, the learning unit 306 may re-train the trained model, for example, in response to an instruction from the base station device 101.

[0028] FIG. 4 shows an example of the functional configuration of the base station device 101. The base station device 101 includes a capability information receiving unit 401, a setting information notifying unit 402, a notification receiving unit 403, and a handover control unit 404. The base station device 101 may also include a learning unit 405 as an option. Note that FIG. 4 only shows functions particularly related to this embodiment, and does not illustrate various other functions that the base station device 101 may have. For example, the base station device 101 naturally has other functions that are generally possessed by base station devices compliant with LTE, 5G, or subsequent standards. The functional blocks in FIG. 4 are shown schematically, and the respective functional blocks may be realized as an integrated unit or may be further subdivided. The functions in FIG. 4 may be realized, for example, by the processor 201 executing a program stored in the ROM 202 or the storage device 204, or by a processor within the communication circuit 205 executing predetermined software. Since the details of the processes executed by each functional unit have been described above, only the general functions of the base station device 101 will be outlined here.

[0029] The capability information receiving unit 401 receives capability information (UE Capability) from the terminal device 111, including information indicating whether the terminal device 111 has the capability to estimate the occurrence probability of at least one of RLF and HOF using AI / ML. The configuration information notifying unit 402 can transmit information instructing the terminal device 111, which has the capability to estimate the occurrence probability of at least one of RLF and HOF using AI / ML, whether or not to perform such estimation. Furthermore, the configuration information notifying unit 402 notifies the terminal device 111, which has the capability to estimate the occurrence probability of at least one of RLF and HOF using AI / ML, of configuration information related to the above-mentioned events. The notification receiving unit 403 receives a predetermined notification from the terminal device 111. As described above, this predetermined notification is transmitted from the terminal device 111 when the occurrence probability of at least one of RLF and HOF satisfies the condition of the event indicated in the configuration information notified to the terminal device 111 by the configuration information notifying unit 402. Furthermore, the predetermined notification may include a value of the occurrence probability that the condition of the event is satisfied, as described above. In response to receiving the predetermined notification, the handover control unit 404 determines whether or not to hand over the terminal device 111 to another cell. Then, when the handover control unit 404 determines to hand over the terminal device 111 to another cell, it starts processing for handing over the terminal device 111. This processing can be performed in accordance with existing regulations.

[0030] The learning unit 405 performs machine learning to generate a trained model for estimating the occurrence probability of at least one of RLF and HOF. It is sufficient for either the learning unit 306 of the terminal device 111 or the learning unit 405 of the base station device 101 to perform machine learning; it is not necessary for both to perform machine learning. Furthermore, machine learning may be performed in a network node different from either the base station device 101 or the terminal device 111. When the difference between the estimated value and the actual measured value of the occurrence probability of at least one of RLF and HOF exceeds a predetermined value, either the learning unit 306 of the terminal device 111 or the learning unit 405 of the base station device 101 performs re-learning of the trained model. When machine learning is performed in a network node different from either the base station device 101 or the terminal device 111, the base station device 101 may notify the network node that re-learning should be performed.

[0031] (Processing Flow) An example of a processing flow according to this embodiment is shown in Fig. 5. Note that, since the details of the processing executed in the wireless communication system are as described above, only an overview of the processing flow will be given here, and the details will not be repeated.

[0032] First, the terminal device 111 notifies the base station device 101 of its own device capability information (S501). Here, the terminal device 111 notifies the base station device 101 of capability information including information indicating that the terminal device 111 is capable of estimating the probability of occurrence of at least one of RLF and HOF using AI / ML. Upon determining from the capability information that the terminal device 111 is capable of estimating the probability of occurrence of at least one of RLF and HOF using AI / ML, the base station device 101 notifies the terminal device 111 of configuration information regarding events based on the estimated values ​​of the occurrence probabilities, for example, by using an RRC Reconfiguration message. Note that the base station device 101 can instruct the terminal device 111 in the configuration information to execute estimation of the probability of occurrence of RLF / HOF using AI / ML. The terminal device 111 then measures the reference signal transmitted from the base station device 101 (S503, S504) and inputs the measurement value into the trained model to obtain an estimated value of the probability of occurrence of at least one of RLF and HOF (S505). The terminal device 111 then determines whether the estimated value satisfies the event condition indicated by the configuration information notified in S502 (S506). Based on the determination that the event condition is satisfied, the terminal device 111 transmits a predetermined notification (report of the inference result) to the base station device 101 (S507). Based on the predetermined notification, the base station device 101 then determines whether to hand over the terminal device 111 from the currently connected cell to another cell (S508). The base station device 101 then executes a predetermined handover process (not shown) in response to the determination that the terminal device 111 should be handed over.

[0033] As described above, according to the present embodiment, it is possible to determine whether to hand over the terminal device 111 based on an estimated value of the probability of a future radio link failure (RLF) or handover failure (HOF). This makes it possible to determine whether to hand over the terminal device 111 at the present time, not according to the current wireless quality of the terminal device 111 but according to the probability of a future RLF / HOF, thereby more reliably maintaining the connection of the terminal device 111. This makes it possible to contribute to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs), which is to "build resilient infrastructure, promote sustainable industrialization and foster innovation."

[0034] The invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope of the gist of the invention.

[0035] This application claims priority based on Japanese Patent Application No. 2024-131181, filed August 7, 2024, the entire contents of which are incorporated herein by reference.

Claims

1. A terminal device comprising: a receiving means for receiving, from a connected base station device, event information based on the probability of occurrence of at least one of a radio link failure (RLF) and a handover failure (HOF); a measuring means for measuring the wireless quality of a signal transmitted from the base station device; an identifying means for identifying the probability of occurrence of at least one of the RLF and the HOF, acquired by inputting the wireless quality measured by the measuring means in an inference phase, to a trained model acquired by machine learning using as input the wireless quality acquired for the signal transmitted from the base station device in a learning phase and a value indicating whether at least one of an RLF when handover processing is not performed at a timing a predetermined period after the timing at which the wireless quality was acquired and an HOF when handover processing is performed, as training data; and a transmitting means for transmitting a predetermined notification to the base station device when the occurrence probability satisfies the condition of the event.

2. The terminal device according to claim 1, wherein the event includes an event that is determined to have occurred when the probability of occurrence of the RLF exceeds a predetermined value.

3. The terminal device according to claim 1, wherein the event includes an event that is determined to have occurred when the probability of occurrence of the HOF exceeds a first predetermined value.

4. The terminal device according to claim 3, wherein the event includes an event that is determined to have occurred when the probability of occurrence of the HOF exceeds the first predetermined value and then falls below a second predetermined value.

5. The terminal device according to claim 1, wherein the event includes an event that is determined to have occurred when a first occurrence probability of the RLF exceeds a value obtained by adding a predetermined value to a second occurrence probability of the HOF.

6. A base station device comprising: notification means for notifying a terminal device connected to a cell provided by the base station device of event information based on the probability of occurrence of at least one of a radio link failure (RLF) and a handover failure (HOF); receiving means for receiving a predetermined notification transmitted from the terminal device based on the probability of occurrence of at least one of a radio link failure (RLF) and a handover failure (HOF), which is acquired by inputting the wireless quality acquired for a signal transmitted from the base station device in a learning phase and using as training data a value indicating whether at least one of an RLF when handover processing is not performed at a timing a predetermined period after the timing at which the wireless quality was acquired and an HOF when handover processing is performed, satisfied the condition of the event; and determination means for determining whether to hand over the terminal device from the cell to another cell in response to receiving the predetermined notification.

7. The base station device according to claim 6, wherein the event includes an event that is determined to have occurred when the probability of occurrence of the RLF exceeds a predetermined value.

8. The base station device according to claim 6, wherein the event includes an event that is determined to have occurred when the probability of occurrence of the HOF exceeds a first predetermined value.

9. The base station device according to claim 8, wherein the event includes an event that is determined to have occurred when the probability of occurrence of the HOF exceeds the first predetermined value and then falls below a second predetermined value.

10. The base station device according to claim 6, wherein the event includes an event that is determined to have occurred when a first occurrence probability of the RLF exceeds a value obtained by adding a predetermined value to a second occurrence probability of the HOF.

11. A control method executed by a terminal device, comprising: receiving, from a connected base station device, event information based on the probability of occurrence of at least one of a radio link failure (RLF) and a handover failure (HOF); measuring the wireless quality of a signal transmitted from the base station device; determining the probability of occurrence of at least one of the RLF and the HOF obtained by inputting the measured wireless quality into a trained model obtained by machine learning in a learning phase, the trained model using as input the wireless quality obtained for the signal transmitted from the base station device and a value indicating whether at least one of an RLF when handover processing is not performed and an HOF when handover processing is performed at a timing a predetermined period after the timing at which the wireless quality was obtained, and transmitting a predetermined notification to the base station device when the occurrence probability satisfies the condition of the event.

12. A control method executed by a base station device, comprising: notifying a terminal device connected to a cell provided by the base station device of event information based on the probability of occurrence of at least one of a radio link failure (RLF) and a handover failure (HOF); receiving a predetermined notification transmitted from the terminal device based on the probability of occurrence of at least one of a radio link failure (RLF) and a handover failure (HOF), which is acquired by inputting the wireless quality acquired for a signal transmitted from the base station device in a learning phase and using, as training data, values ​​indicating whether at least one of an RLF when handover processing is not performed at a timing a predetermined period after the timing at which the wireless quality was acquired, and an HOF when handover processing is performed, and which is acquired by inputting the wireless quality measured by the terminal device in an inference phase, satisfying the condition of the event; and determining whether to handover the terminal device from the cell to another cell in response to receiving the predetermined notification.

13. A program for causing a computer installed in a terminal device to execute the control method according to claim 11.

14. A program for causing a computer installed in a base station device to execute the control method set forth in claim 12.

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