Terminal, base station device, and control method for improving handover performance using ai / ml

Abstract

To improve communication efficiency by enhancing handover processing.SOLUTION: Receiving, by a terminal, information on an event based on a probability of occurrence of at least one of a radio link failure (RLF) and a handover failure (HOF); Measuring radio quality of a signal transmitted from a base station apparatus, and performing, on a learned model acquired by machine learning in which the radio quality acquired for the signal transmitted from the base station apparatus in a learning phase is used as an input and a value indicating whether or not at least one of an RLF in a case where a handover process has not been performed and an HOF in a case where a handover process has been performed has occurred at a timing after a predetermined period from a timing at which the radio quality has been acquired is used as teacher data, An occurrence probability of at least one of an RLF and an HOF acquired by inputting radio quality measured in an inference phase is specified, and when the occurrence probability satisfies an event condition, a predetermined notification is transmitted to a base station device.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] In wireless communication systems that comply with the cellular communication standards of the Third Generation Partnership Project (3GPP (registered trademark)), handover processing is specified to switch 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 processing is performed, for example, when the wireless quality of a signal transmitted from a base station to which the 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. Summary of the Invention [Problem to be solved by the invention]

[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. [Means for solving the problem]

[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 radio quality of a signal transmitted from the base station device; an identifying means for inputting the radio quality acquired for the signal transmitted from the base station device in a learning phase, and identifying the probability of occurrence of at least one of the RLF and the HOF acquired by inputting the radio quality measured by the measuring means in an inference phase to a trained model acquired by machine learning using as training data a value indicating whether at least one of an RLF when no handover processing is performed within a predetermined period after the radio quality is acquired and an HOF when handover processing is performed; 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 the RLF and the HOF, obtained by inputting the wireless quality measured by the terminal device in an inference phase into a trained model obtained by machine learning using as input the wireless quality acquired for a signal transmitted from the base station device in a learning phase and a value indicating whether at least one of the RLF when a handover process is not performed within a predetermined period after the wireless quality is acquired and the HOF when a handover process is performed, as training data; 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. [Effects of the Invention]

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

[0008] [Figure 1] FIG. 1 is a diagram illustrating an example of the configuration of a wireless communication system. [Figure 2] FIG. 2 is a diagram illustrating an example of the hardware configuration of a base station device and a terminal device. [Figure 3] FIG. 2 is a diagram illustrating an example of a functional configuration of a terminal device. [Figure 4] FIG. 2 is a diagram illustrating an example of a functional configuration of a base station device. [Figure 5] FIG. 1 is a diagram illustrating an example of a flow of processing executed in a wireless communication system. DETAILED DESCRIPTION OF THE INVENTION

[0009] 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.

[0010] (System Configuration) FIG. 1 shows an example of the configuration of a communication system according to this embodiment. This communication system is a wireless communication system that complies with, for example, 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. For this reason, for example, the terminal device 111 executes 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 cell 122 and the cell 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.

[0011] Conventionally, the terminal device 111 measures the wireless quality of signals transmitted in 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 cellular communication standards. 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 for handing 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) instructing the terminal device 111 to perform the handover. Also, after the occurrence of an event in the terminal device 111, 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 by an RRC Reconfiguration message. Note that RRC is an abbreviation for Radio Resource Control.

[0012] Conventionally, handover processing is initiated in response to the wireless quality measured at that time in the terminal device 111 satisfying each of the above-mentioned events. In such a procedure, for example, the wireless quality of the connected cell (serving cell) deteriorates in event A2, event A3, etc., and a predetermined report is transmitted to the base station device 101 after the event occurs, and 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 occurrence of the event is detected in the terminal device 111 to when the handover instruction is transmitted from the base station device 101, the wireless quality may further deteriorate, and the handover instruction may not be received by the terminal device 111.

[0013] The terminal device 111 is supposed to start timer T310 when it is deemed that downlink synchronization with the base station device 101 cannot be established. 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 the occurrence of an event and the terminal device 111 is unable to receive the command, the terminal device 111 is unable to stop timer T310. As a result, the terminal device 111 is unable to perform handover processing, resulting in 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 the 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 and RLF.

[0014] 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 or not 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 or not RLF will occur when a handover process is not performed a predetermined period after the wireless quality is acquired as training data. When such a trained model is acquired, the terminal device 111 can obtain an estimated value of the probability of RLF occurring a predetermined period after the wireless quality is 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 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 the wireless quality of the cell 121 acquired in the learning phase as input and whether or not HOF occurs when handover processing is performed at a timing a predetermined period after the timing at which the wireless quality is acquired as training data. When such a trained model is acquired, the terminal device 111 can obtain an estimated value of the probability of HOF occurring at a timing a predetermined period after the timing at which the wireless quality is 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 provides 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 period is set arbitrarily, for example, to a period of several seconds. Note that this setting information can be notified in advance from the base station device 101 to the terminal device 111.

[0015] As described above, the terminal device 111 can obtain the probability of RLF or HOF occurring at a predetermined timing in the future (a timing a predetermined period after the measurement value is obtained) by using AI / ML, 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 such circumstances, this embodiment provides a technique for performing handover processing based on predicted values ​​of RLF and HOF at appropriate timing.

[0016] In this embodiment, a new event based on the occurrence probability of at least one of RLF and HOF is defined. 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 necessary) into a trained model to acquire at least one of the occurrence probability of RLF and the occurrence probability of HOF. Here, the trained model can be acquired by machine learning using, as an input, the wireless quality of the cell 121 (or a neighboring cell such as cell 122 or cell 123 as necessary) acquired in the learning phase, as well as training data indicating whether or not at least one of RLF occurred when handover processing was not performed at a timing a predetermined period after the timing at which the wireless quality was acquired and HOF occurred at the timing at which 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, but a single trained model may also be generated by performing machine learning on these together. That is, machine learning may be performed using, as input, the measured value of the wireless quality of the cell 121, and both whether or not an RLF has occurred and whether or not an HOF has occurred a predetermined time after the measured value was obtained as training data, to acquire a trained model. Then, the terminal device 111 determines whether or not at least one of the probability of RLF occurrence and the probability of HOF occurrence in the future (at a predetermined time after the wireless quality is obtained), obtained as the output of the trained model, satisfies the event condition notified by the base station device 101. Then, 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 predetermined notification, the base station device 101 determines whether or not to execute a handover of the terminal device 111, and starts handover processing in response to the decision 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 RLF or HOF occurrence estimated by AI / ML, and makes it possible to handover the terminal device 111 to another cell at an appropriate timing.

[0017] The new event may include, for example, a first event that is determined to have occurred when the RLF occurrence probability exceeds a set 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 the predetermined value (threshold), information about a hysteresis value, and information about the length of time during which the RLF occurrence probability 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). Then, the terminal device 111 may determine that the condition of this first event has been released from being satisfied when the estimated value of the RLF occurrence probability has gone from being satisfied to being 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. The terminal device 111 may repeatedly transmit the predetermined notification to the base station device 101, for example, if the state in which the condition of the first event is satisfied continues thereafter. 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 the 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 the 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 terminated 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 that the first event has occurred 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.

[0018] The new event may also include a second event that is determined to have occurred when the probability of HOF occurrence exceeds a set 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 about the predetermined value (threshold), information about a hysteresis value, and information about 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 this second event is 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 this second event is no longer 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 of the second event remains satisfied for a period longer than the notified period. For example, if the condition of 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 related to 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 of 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 of 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.

[0019] 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 setting 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, when the terminal device 111 goes from a state in which the condition of the fourth event is satisfied to a state in which the signal strength 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 can determine that the state in which the condition of the fourth event is satisfied has been released. 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 maintained for a notified period of time. 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. Note that 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 related to 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 occurring is high but is higher than the probability of HOF occurring by a certain amount or more, a handover process 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.

[0020] 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 may be specified as, 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. Note that, in the predetermined notification, the terminal device 111 may notify the base station device 101 of information indicating the timing (for example, time) at which the event condition is satisfied.

[0021] Note that machine learning may be used to generate a trained model that inputs one or more wireless qualities 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.

[0022] 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 notify the base station device 101 in advance (for example, when establishing a connection) 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 the RLF-related or the HOF-related estimation. 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 (for example, 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 (for example, the first and fourth events described above).

[0023] 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 RLF or HOF actually occurs at a predetermined timing corresponding to the occurrence probability without transmitting a handover command to the terminal device. Then, the base station device 101 compares the actual measurement value of the occurrence probability of RLF or HOF with the notified estimated value of the occurrence probability of 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 the 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 becomes equal to or less than a predetermined level. Note that, if the terminal device 111 has generated a trained model, 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 in response to receiving a predetermined instruction from the base station device 101. This allows the trained model to be maintained in an appropriate state, and makes it possible to perform handover processing based on prediction at an appropriate timing.

[0024] (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 executes 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 executed 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 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 its successor standards. Although 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 its successor standard, and a common antenna for these circuits. The base station device 101 and the terminal device 111 may 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 the 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 multiple available frequency bands, or may have a common communication circuit 205 for at least some of these frequency bands.

[0025] FIG. 3 shows an example of the functional configuration of the terminal device 111. The terminal device 111 includes, for example, a capability information notifying unit 301, a setting information receiving unit 302, a quality measuring unit 303, an occurrence probability estimating unit 304, and a notifying unit 305. The terminal device 111 may also include a learning unit 306 as an option. 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 conforming to 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. 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. The details of the processes executed by each functional unit have been described above, so only the general functions of the terminal device 111 will be outlined here.

[0026] The capability information notifying unit 301 notifies the base station device 101 of capability information possessed by the terminal device 111 as UE Capability. 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 currently connected cell 121 (and other cells such as neighboring cells as necessary (e.g., cell 122, cell 123)) using AI / ML. Note that 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 currently connected cell and other cells such as neighboring cells as necessary. The measured wireless quality may be, for example, 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 occurrence probability 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.

[0027] 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 included in base station devices that comply with LTE, 5G, or subsequent standards. The functional blocks in FIG. 4 are shown schematically, and the respective functional blocks may be integrated or further subdivided. The functions in FIG. 4 may be implemented, 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. The details of the processes executed by each functional unit are as described above, so only the general functions of the base station device 101 will be outlined here.

[0028] The capability information receiving unit 401 receives, from the terminal device 111, capability information (UE Capability) including information indicating whether or not the terminal device 111 has the capability to estimate the occurrence probability of at least one of RLF and HOF by AI / ML. The setting 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 by AI / ML, whether or not to perform the estimation. Furthermore, the setting 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 by AI / ML, of setting 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 by the setting information notified to the terminal device 111 by the setting information notifying unit 402. Furthermore, as described above, the predetermined notification may include the value of the occurrence probability when the condition of the event is satisfied. In response to receiving a 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 executed in accordance with existing regulations.

[0029] 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. Note that 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, and it is not necessary for both to perform machine learning. Also, machine learning may be performed in a network node different from either the base station device 101 or the terminal device 111. 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 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. Note that 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.

[0030] (Processing flow) An example of the 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.

[0031] First, the terminal device 111 notifies the base station device 101 of its own device's capability information (S501). Here, the 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 by AI / ML is notified from the terminal device 111 to the base station device 101. In response to 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 by AI / ML, the base station device 101 notifies the terminal device 111 of configuration information regarding an event based on the estimated value of the occurrence probability, for example, by using an RRC Reconfiguration message. Note that the base station device 101 can instruct the terminal device 111 to estimate the probability of occurrence of RLF / HOF by AI / ML in the configuration information. Thereafter, the terminal device 111 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 occurrence probability of at least one of RLF and HOF (S505). Then, the terminal device 111 determines whether the estimated value satisfies the event condition indicated by the setting information notified in S502 (S506), and transmits a predetermined notification (report of the inference result) to the base station device 101 based on the determination that the event condition is satisfied (S507). Then, based on the predetermined notification, the base station device 101 determines whether to hand over the terminal device 111 from the currently connected cell to another cell (S508). Thereafter, the base station device 101 executes a predetermined handover process (not shown) in response to the determination to hand over the terminal device 111.

[0032] 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 occurrence of a future radio link failure (RLF) or handover failure (HOF). This makes it possible to determine whether to hand over at the present time according to the probability of a future RLF / HOF, rather than the current wireless quality of the terminal device 111, for example, and therefore to more reliably maintain the connection of the terminal device 111. This makes it possible to contribute to Goal 9 of the Sustainable Development Goals (SDGs) led by the United Nations, which is to "build resilient infrastructure, promote sustainable industrialization and foster innovation."

[0033] The invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope of the gist of the invention.

Claims

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

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

5. 2. 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, a notification means for notifying a terminal device connected to a cell provided by the base station device of event information based on the occurrence probability 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 occurrence probability of at least one of the RLF and the HOF, acquired by inputting the wireless quality measured by the terminal device in the inference phase, into a trained model acquired by machine learning using as input the wireless quality acquired for a signal transmitted from the base station device in the learning phase and a value indicating whether or not at least one of the RLF when handover processing is not performed and the HOF when handover processing is performed as training data, satisfying the condition of the event; 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; A base station device comprising:

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. 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 HOF exceeds a first predetermined value.

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

10. 7. 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 occurrence probability of at least one of a radio link failure (RLF) and a handover failure (HOF); measuring a radio quality of a signal transmitted from the base station device; a trained model acquired by machine learning using, as input, a wireless quality acquired for a signal transmitted from the base station device in a learning phase and a value indicating whether or not at least one of an RLF when a handover process is not performed at a timing a predetermined period after the timing at which the wireless quality is acquired and an HOF when a handover process is performed, has occurred, as training data, and the trained model is acquired by inputting the measured wireless quality in an inference phase to determine the occurrence probability of at least one of the RLF and the HOF acquired; transmitting a predetermined notification to the base station device when the occurrence probability satisfies the condition of the event; A control method comprising:

12. A control method executed by a base station device, notifying a terminal device connected to a cell provided by the base station device of event information based on the occurrence probability 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 occurrence probability of at least one of the RLF and the HOF acquired by inputting the wireless quality measured by the terminal device in the inference phase into a trained model acquired by machine learning using as input the wireless quality acquired for a signal transmitted from the base station device in the learning phase and a value indicating whether or not at least one of the RLF when handover processing is not performed at a timing a predetermined period after the timing at which the wireless quality is acquired and the HOF when handover processing is performed as training data; and In response to receiving the predetermined notification, determining whether to hand over the terminal device from the cell to another cell; A control method comprising:

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

14. A program for causing a computer provided in a base station device to execute the control method according to claim 12.

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