Terminal device, base station device, control method, and program for wireless quality measurement and report for improving handover efficiency

Abstract

This terminal device: receives, from a base station device being connected, configuration information that relates to measurement of wireless quality for each of a plurality of beams formed by another base station device and report of a result of the measurement, and that includes information of a group of beams composed of two or more beams among the plurality of beams and information specifying an event based on a statistical value of wireless quality for the group of beams; observes a reference signal transmitted from each of the plurality of beams on the basis of the configuration information and measures the wireless quality for each of the plurality of beams; identifies a statistical value of the wireless quality for the group on the basis of the wireless quality for each of the plurality of beams and the information of the group of beams; determines whether a designated event has occurred on the basis of the identified statistical value; and reports the statistical value to the base station device on the basis of the configuration information when it is determined that the event has occurred.

Description

Terminal device, base station device, control method, and program for measuring and reporting radio quality to improve handover efficiency

[0001] The present invention relates to a technique for measuring and reporting radio quality by a terminal device in a cellular communication system.

[0002] In cellular communication systems, handovers are performed in which a terminal device switches its connection cell or beam due to factors such as the terminal device's movement or changes in the communication environment. During handover, the terminal device measures each cell / beam, and the cell to which the terminal device connects is determined based on the measurement results. Non-Patent Document 1 describes that if the best value of the measured wireless quality is equal to or less than a predetermined threshold, the best value is treated as the quality of the cell corresponding to that beam. If there is a beam whose wireless quality exceeds the predetermined threshold, the linear average value of the wireless qualities of the beam is treated as the quality of the cell corresponding to that beam. That is, if the number of beams whose measured wireless quality exceeds the predetermined threshold is one or less, the measured quality of the best beam is treated as the quality of the cell corresponding to that beam. If the number of beams whose measured wireless quality exceeds the predetermined threshold is two or more, the linear average value of the qualities exceeding the threshold is treated as the quality of the cell corresponding to that beam. In one example, the terminal device notifies a base station device of the quality as the quality of candidate cells to be used as a handover destination, and the base station device transmits an instruction to the terminal device to handover to one of the cells.

[0003] 3GPP (registered trademark) TS 38.331

[0004] When using conventional standards, even if the quality of many beams of a cell is significantly below a threshold, the cell may be selected as a handover destination cell if the quality of a specific beam that exceeds the threshold is good. In this case, only a small number of beams may be able to communicate with good communication quality in the handover destination cell, which may result in a decrease in handover efficiency, such as an increase in the probability that another handover will be required in a short period of time when the terminal device is moving.

[0005] The present invention provides a technique for reporting radio quality measurement results that makes it possible to prevent a decrease in handover efficiency.

[0006] A terminal device according to one aspect of the present invention has: a receiving means for receiving, from a base station device to which it is connected, configuration information regarding measurement of wireless quality for each of a plurality of beams formed by another base station device and reporting of the results of the measurement, the configuration information including information on a group of beams consisting of two or more beams from the plurality of beams and information specifying an event based on a statistical value of wireless quality for the group of beams; a measuring means for observing a reference signal transmitted from each of the plurality of beams based on the configuration information and measuring the wireless quality for each of the plurality of beams; an identifying means for identifying a statistical value of wireless quality for the group based on the wireless quality for each of the plurality of beams and the information on the group of beams; a determining means for determining whether the specified event has occurred based on the identified statistical value; and a reporting means for reporting the statistical value to the base station device based on the configuration information when it is determined that the event has occurred.

[0007] A base station device according to one aspect of the present invention has a notification means for notifying a connected terminal device of configuration information regarding measurements of wireless quality for each of a plurality of beams formed by another base station device and reporting of the results of the measurements, the configuration information including information on a group of beams consisting of two or more beams from the plurality of beams and information specifying an event based on statistical values ​​of wireless quality for the group of beams; a receiving means for receiving from the terminal device, when it is determined that the event has occurred, a report of statistical values ​​of wireless quality determined from the wireless quality for each of the beams belonging to the group from the plurality of beams; and a decision means for deciding whether to hand over the terminal device to the other base station device based on the report.

[0008] According to the present invention, it is possible to prevent a decrease in handover efficiency caused by a measurement report of wireless quality.

[0009] 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.

[0010] The accompanying drawings are incorporated into and constitute a part of the specification, illustrate embodiments of the present invention, and are used, together with the description, to explain the principles of the present invention. FIG. 1 is a diagram illustrating an example of the configuration of a wireless communication system. FIG. 2 is a diagram illustrating an example of the flow of communication processing executed by the wireless communication system. FIG. 3 is a diagram illustrating an example of the flow of communication processing executed by the wireless communication system. FIG. 4 is a diagram illustrating an example of an event based on the wireless quality of each beam group. FIG. 5 is a diagram illustrating an example of the flow of communication processing executed by the wireless communication system. FIG. 6 is a diagram illustrating an example of an event based on the wireless quality of each beam group. FIG. 7 is a diagram illustrating an example of the flow of communication processing executed by the wireless communication system. FIG. 8 is a diagram illustrating an example of the flow of communication processing executed by the wireless communication system. FIG. 9 is a diagram illustrating an example of the flow of communication processing executed by the wireless communication system. FIG. 10 is a diagram illustrating an example of the hardware configuration of a base station device and a terminal device. FIG. 11 is a diagram illustrating an example of the functional configuration of a base station device. FIG. 12 is a diagram illustrating an example of the functional configuration of a terminal device.

[0011] 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.

[0012] Fig. 1 shows an example of the configuration of a wireless communication system according to this embodiment. The wireless communication system is, for example, a cellular communication system that complies with the 5th generation (5G) cellular communication standard of the 3rd Generation Partnership Project (3GPP), and is configured to include base station devices 101 to 102 and a terminal device 111. Note that Fig. 1 shows only two base station devices and one terminal device, but it goes without saying that many base station devices and many terminal devices may exist.

[0013] Base station device 101 is a base station device connected to terminal device 111. Base station device 102 is a candidate base station device for handover from base station device 101. Base station device 102 can form multiple beams and use some of the multiple beams to provide communication services to terminal device 111. Note that, like base station device 102, base station device 101 can also form multiple beams and use some of the beams to connect to terminal device 111 and provide communication services to terminal device 111.

[0014] The terminal device 111 measures the reception quality of a predetermined reference signal (e.g., a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) or a channel state information-reference signal (CSI-RS)) transmitted by another surrounding base station device (e.g., the base station device 102) while connected to the base station device 101. Each reference signal is associated with a transmission configuration (Transmission Configuration Indicator (TCI)) in the base station device. For example, in FIG. 1, TCI0 ​​to TCI8 are each associated with a different CSI-RS resource, and TCI9 to TCI11 are each associated with a different SSB index. Based on this information, the terminal device 111 can observe reference signals for each of multiple beams that are at least a portion of the many beams formed by base station devices other than the base station device 101, and measure wireless quality. In the following description, unless otherwise specified, "multiple beams" formed in another base station device refer to beams designated as measurement targets, and do not refer to all beams formed in the other base station devices. Here, wireless quality includes, for example, reference signal received power (RSRP), reference signal received quality (RSRQ), received signal strength, signal-to-noise ratio (SNR), signal-to-noise and interference ratio (SINR), interference power, etc. The terminal device 111 observes the resources of each reference signal, measures wireless quality, and reports the measurement results to the connected base station device 101. For example, when the base station device 101 receives information on the measurement results, it determines, based on the information, whether to hand over the terminal device 111 to a cell formed by another base station device.

[0015] Conventionally, for each cell formed by a base station device other than the currently connected base station device 101, if the number of reference signals (beams) whose wireless quality exceeds a predetermined threshold is one or less, the terminal device 111 notifies the base station device 101 of the best wireless quality. Here, the predetermined threshold is notified to the terminal device 111 in advance by the base station device 101, and can be given for SSB by the value absThreshSS-BlocksConsolidation and for CSI-RS by the value absThreshCSI-RS-Consolidation. Furthermore, if the number of reference signals (beams) whose wireless quality exceeds the predetermined threshold exceeds a predetermined number, the terminal device 111 notifies the base station device 101 of the average value of the number of measurement values ​​that does not exceed the predetermined number. Note that this predetermined number is notified in advance from the base station device 101 to the terminal device 111, and can be given for the SSB by the value nrofSS-BlocksToAverage and for the CSI-RS by the value nrofCSI-RS-ResourcesToAverage. Note that these values ​​are all set to a value of 2 or greater.

[0016] Based on such a report, the base station device 101 may handover the terminal device 111 to, for example, a cell having a beam with sufficiently good wireless quality. For example, the base station device 101 initiates a handover when the wireless quality of a neighboring cell measured by the terminal device 111 is better than the wireless quality of the cell formed by the terminal device 111 by a predetermined offset (Event A3), or when the wireless quality of the neighboring cell becomes better than a predetermined threshold (Event A4). However, if the wireless quality of the neighboring cell used as the reference at this time is determined as described above, it is expected that the efficiency of the handover will decrease. That is, in the conventional method, even if there is only one beam whose wireless quality exceeds the predetermined threshold, the terminal device 111 determines whether or not to perform a handover based on the wireless quality of that single beam. Here, if the wireless quality is accidentally very high but is good only under very limited conditions, the probability that the terminal device 111's state will deviate from that condition within a short period of time is high. If the terminal device 111 no longer satisfies these conditions, it may be necessary to perform a handover to another cell. In other words, with conventional methods, if a first cell exists in which the wireless quality is very good only for a specific beam, a handover to the first cell may be triggered even if a second cell exists that has multiple beams whose wireless quality is good on average but not better than that of the specific beam. As a result, the probability of a second handover being required within a short period of time may increase. The same applies when the wireless quality of only a few beams corresponding to significantly different geographical areas in the same cell exceeds a predetermined threshold. In other words, if the wireless quality of a target cell via one beam deteriorates after connecting to the target cell, it is possible that the terminal device 111 may find itself in a situation where there are no candidate beams to switch to in the vicinity. In this case, the terminal device 111 cannot switch to another beam with good quality without performing a handover, and it may be necessary to switch the target cell via a handover.

[0017] In this embodiment, in consideration of such circumstances, a plurality of beams are grouped, and statistical information such as the average value of the wireless quality in each group is reported from the terminal device 111 to the base station device 101. For example, in FIG. 1 , TCI0 ​​to TCI2 are grouped as a first group, TCI3 to TCI5 as a second group, and TCI6 to TCI8 as a third group. This grouping can be defined, for example, in relation to TCI9 to TCI11 corresponding to the SSB index. That is, as an example, it can be determined that a group of beams associated with CSI-RSs that cover a portion of an area covered by a beam corresponding to each SSB index belong to one group. After measuring the wireless quality of each beam, the terminal device 111 statistically processes the measured values ​​of the wireless quality for the beams belonging to each group and reports the statistical values ​​to the base station device 101. The terminal device 111 may report, for example, the (linear) average, variance, median, minimum value, etc. of the measurement values ​​to the base station device 101. The terminal device 111 may also report, for example, a weighted average of the measurement values ​​for multiple beams to the base station device 101. For example, if TCI0 ​​to TCI2 are grouped, a value such as (measurement value of TCI0) × 0.1 + (measurement value of TCI1) × 0.8 + (measurement value of TCI2) × 0.1 may be reported to the base station device 101. That is, weighted addition may be performed such that emphasis is placed on the measurement values ​​for beams in the group that correspond to the vicinity of the center of the range covered by those beams. Note that this is just one example, and any weight may be used. Note that, unless otherwise specified, the wireless quality for a group in the following description refers to the value after the above-described statistical processing has been performed on the wireless quality for the group.

[0018] By reporting such statistical values, the base station device 101 can grasp the trend of the wireless quality for each of the first to third groups described above, for example. The base station device 101 can then make a handover decision based on that trend. In other words, in the past, if the wireless quality of only one beam was significantly high, a decision to handover to that beam could be made based on that wireless quality. However, in this embodiment, the base station device 101 can decide not to handover to that beam if, for example, the statistical values ​​for multiple beams are not good enough to a certain extent. Note that this is just one example, and the base station device 101 can execute any control based on the acquired information.

[0019] In one example, the beam groups may be selected such that each beam is adjacent to at least one other beam in the group, as in the first to third groups described above. Furthermore, the beam groups may be configured such that every predetermined number of TCIs, such as TCI0, TCI2, TCI4, TCI6, and TCI8 in FIG. 1 are one group, and TCI1, TCI3, TCI5, and TCI7 are another group. Furthermore, the beam groups may be grouped based on any criteria, such as any TCI0, TCI1, TCI6, and TCI7 in one group, TCI2, TCI3, and TCI8 in another group, and TCI4 and TCI5 in yet another group. Furthermore, if the base station device 102 has multiple transmission / reception points (TRPs), a group may be set for each beam group belonging to the TRP. Furthermore, while the above example describes grouping of TCI0 ​​to TCI8, each associated with a separate resource of the CSI-RS, it is of course also possible to group beams associated with an SSB index, for example, by grouping TCI9 and TCI10 together.

[0020] By grouping multiple beams corresponding to adjacent or mutually close geographical areas (directions), it is expected that sufficient wireless quality can be ensured in the area corresponding to that group. Therefore, even if the communication quality of the terminal device 111 deteriorates after handing over to one of the beams belonging to that group, communication services with sufficient wireless quality can be provided to the terminal device 111 by changing the connection destination to another beam in the same group. Furthermore, by grouping beams covering non-adjacent geographical areas, if the wireless quality of the group is good, it is expected that a certain degree of good wireless quality can be obtained over a wide area formed by those beams. Therefore, by handing over the terminal device 111 to a base station device 102 that forms that beam group, even if the wireless quality of the connected beam deteriorates, communication services with sufficient wireless quality can be provided to the terminal device 111 by changing the connection destination to another beam formed by the base station device 102. As a result, unnecessary handovers can be prevented, and handover efficiency can be improved.

[0021] In each group, beams to be used for processing such as calculating the radio quality of the group and determining handover may be determined, and beams not to be used for such processing may be determined. For example, if it is known in advance that the quality of a specific beam in the group is low due to the operating conditions of surrounding base station devices (e.g., when transmission is not performed using a specific beam), the measurement results for that beam may not be used for calculating the radio quality of the group and determining handover. Furthermore, for example, a beam whose measurement results tend to show a unique value (e.g., a value significantly higher or lower than that of other adjacent beams) may be determined not to be used for calculating the radio quality of the group. The number of beams to be considered in each group may also be set. For example, a minimum number of beams to be considered in each group may be set. According to this, for example, if a certain beam is suitable as a connection destination because the radio quality of multiple beams is good but the radio quality of other beams is low, the radio quality of (at least some of) the beams with low radio quality may not be considered in calculating the radio quality of the group. Therefore, by reducing the influence of the beam with low wireless quality, it is possible to prevent handover from becoming difficult to be performed to a base station device having a group suitable as a connection destination. In this case, since the statistical value of wireless quality for a minimum number of beams is calculated, even if the wireless quality of only one specific beam is high, the statistical value of wireless quality of the group to which that beam belongs will be reduced by the wireless quality of the other beams, so it is still possible to make it difficult to select that beam as a handover destination.

[0022] The base station device 101 transmits configuration information for causing the above-described report to be performed to the terminal device 111. For example, the base station device 101 transmits the above-described configuration information to the terminal device 111 using a Radio Link Control (RRC) message (e.g., an RRC Reconfiguration message). The configuration information includes measurement configuration (e.g., layer 1 or layer 3) (e.g., information specified by MeasObjectNR) and measurement result reporting configuration (e.g., information specified by ReportConfigNR). For example, the measurement configuration includes a list of beams including information identifying the beams to be measured (e.g., beam identifiers or TCI indexes). The reporting configuration includes, for example, information specifying reporting of radio quality information on a group-by-group basis, in addition to or instead of information similar to that in a conventional measurement report regarding radio quality measurement. Furthermore, at least one of the measurement configuration and the reporting configuration, or separately from these information, includes information indicating the group to which each beam included in the list belongs. The base station device 101 may notify the terminal device 111 of configuration information including information about a large number of beams and groups, and may activate or deactivate measurements and reports related to beams to be measured and reported, separately from the configuration information. For example, the base station device 101 may notify the terminal device 111 of information specifying some beams, of which the configuration information has been notified, that are to be used by the terminal device 111 to actually perform measurements and reports, separately from the configuration information. In one example, configuration information about a large number of beams corresponding to a wide geographical area may be notified by an RRC message as described above, and activation information specifying some beams to be used by the terminal device 111 may be transmitted via a medium access control element (MAC CE). In this way, the MAC CE of the MAC layer may activate or deactivate configuration information related to beams to be actually measured, depending on changes in the state of the terminal device 111, eliminating the need to transmit and receive RRC layer messages each time.

[0023] Based on the configuration information (and the activation information), the terminal device 111 measures beams formed by surrounding base station devices (e.g., the base station device 102) and calculates statistical values ​​of the measurement results for each group to which the beam belongs. The terminal device 111 may also transmit information on the measurement results for each beam to the base station device 101, as in the past. The terminal device 111 then transmits the statistical values ​​of the measurement results to the base station device 102. The terminal device 111 may periodically report the statistical values ​​of the measurement results to the base station device 101, or may transmit the statistical values ​​of the measurement results to the base station device 101 in response to receiving a predetermined instruction from the base station device 101. The base station device 101 may, for example, notify the terminal device 111 of an instruction to report a single measurement result or an instruction to report periodic measurement results as a reporting configuration. This instruction may be transmitted from the base station device 101 to the terminal device 111, for example, using downlink control information (DCI) or MAC CE. Furthermore, when a periodic measurement result report is instructed, the period can be specified together with the instruction. Note that information indicating the period may be notified to the terminal device 111 together with the above-mentioned setting information.

[0024] When the base station device 101 receives a report of the measurement result from the terminal device 111, the base station device 101 can determine whether to hand over the terminal device 111 to a cell provided by another base station device based on the result. In one example, the base station device 101 can determine to hand over the terminal device 111 to another base station device when a predetermined condition is met, such as the statistical value of the wireless quality for each group of beams formed by the other base station device (base station device 102) being higher than a predetermined level, as described above.

[0025] An example of the processing flow in this case will be described using Figures 2 and 3. The processing in this embodiment is performed in the same manner as conventional processing, except for changes to the processing related to measurement and reporting. That is, the base station device 101 connected to the terminal device 111 measures reference signals (SSB or CSI-RS) transmitted from surrounding base station devices (such as the base station device 102) and transmits cell identifiers of the surrounding base station devices and report setting information to the terminal device 111 so that the terminal device 111 reports the radio quality of the reference signals (S201). At this time, the base station device 101 also notifies the terminal device 111 of information on the identifiers of the beams to be measured, which are at least a portion of the multiple beams formed by the base station devices that provide the neighboring cells. Furthermore, in this embodiment, at least the multiple beams to be measured are grouped into one or more groups, and the base station device 101 notifies the terminal device 111 of information on the groups. Note that this information may be included in one or two of the measurement configuration of the communicating cell (information specified by, for example, servingcellMO), the measurement configuration of the candidate cell (information specified by, for example, MeasObjectNR), and the reporting configuration (information specified by, for example, ReportConfigNR), or may be included in all of them. Furthermore, information on groups may be prepared separately from these. In this case, at least one of the measurement configuration and the reporting configuration indicates that measurement reports of radio quality for each group should be performed. When the terminal device 111 receives configuration information including an instruction indicating that measurement reports of radio quality for each group should be performed, the terminal device 111 can refer to the information on the group and confirm the group of beams specified as the measurement target. Furthermore, when reporting measurement results, the measurement values ​​of the reference signals of the communicating cell measured for beam failure detection (BEAM FAILURE DETECTION) may be reused according to the measurement configuration of the communicating cell.

[0026] The base station device 101 may use an RRC message to notify the terminal device 111 of configuration information designating a large number of beams as candidates for measurement targets. The base station device 101 may then transmit, for example, via a MAC CE or DCI, information to enable some of the candidate beams as measurement targets to the terminal device 111. In this case, it is not necessary to transmit an RRC message again when the measurement targets are changed. Alternatively, the groups to which each beam belongs may be set in advance, and the information may be transmitted via an RRC message. Alternatively, the groups may be reorganized each time the beams to be measured are updated, and information about the groups may be transmitted using a MAC CE or the like, along with information enabling the beams to be measured. Furthermore, the beams to be enabled as measurement targets may be specified by information specifying a group. That is, when the relationship between groups and beams is set in advance (for example, via an RRC message), a specific group may be designated by a MAC CE or the like, and the terminal device 111 may be instructed to measure the radio quality of each beam belonging to the group.

[0027] Based on the received measurement and reporting settings, the terminal device 111 measures the reception quality of a predetermined reference signal (SSB or CSI-RS) transmitted from the beam targeted for measurement (S202). Then, the terminal device 111 uses the measurement results to identify the reception quality (statistical value) for each group (S203). Then, the terminal device 111 reports the identified reception quality for each group to the base station device 101 (S204). Note that the terminal device 111 may report the reception quality for each beam in addition to the reception quality for each group to the base station device 101. Upon receiving the report, the base station device 101 decides to perform a handover as necessary (S205) and transmits a handover instruction to the terminal device 111 (S206). In response to the instruction, the terminal device 111 executes a handover from the base station device 101 to another base station device (e.g., the base station device 102) (S207).

[0028] For example, after deciding to have the terminal device 111 execute a handover, the base station device 101 may transmit a HANDOVER REQUEST message to a handover destination base station device (e.g., the base station device 102), and upon receiving a HANDOVER REQUEST ACKNOWLEDGE message indicating acceptance of the handover, may transmit a message (e.g., an RRC Reconfiguration message) for initiating handover to the terminal device 111. In this case, communication parameters to be used by the terminal device 111 may be specified in the HANDOVER REQUEST ACKNOWLEDGE message, and the base station device 101 may transmit the communication parameters together with a handover instruction.

[0029] Note that this is just one example, and the base station device 101 may, for example, notify the terminal device 111 of post-handover configuration information between the terminal device 111 and the base station device of the handover destination at a timing before the actual handover is performed (e.g., at the time of S201 or at a timing earlier). Then, for example, before receiving a handover instruction to the base station device 102, the terminal device 111 may receive configuration information for communication with the base station device 102 and perform processes such as establishing synchronization of the uplink and downlink with the base station device 102 in advance. Then, for example, the terminal device 111 may measure the wireless quality at Layer 1 of the reference signal transmitted from the base station device 102 and report the results to the base station device 101. Based on the report, the base station device 101 may decide whether to hand over the terminal device 111 to the base station device 102. After determining to handover the terminal device 111 to the base station device 102, the base station device 101 can instruct the terminal device 111 to perform the handover without performing processing such as transmitting a HANDOVER REQUEST message to the base station device 102. In this case, since the connection setup between the terminal device 111 and the base station device 102 has already been completed, the time from receiving the handover instruction until starting communication of user data with the base station device 102 can be shortened. Note that a procedure for shortening such a handover period is called Layer 1 / Layer 2 Triggered Mobility (LTM). In one example, the measurement configuration for this LTM can be notified to the terminal device 111 by an information element called LTM-Config, and the reporting configuration can be notified by an information element called LTM-CSI-ReportConfigToAddModList.

[0030] In this embodiment, regardless of whether pre-configuration for handover is performed, the terminal device 111 identifies wireless quality information for a group of beams and reports it to the base station device 101. Then, depending on the result of the report, the base station device 101 may decide to execute a handover to another base station device with good wireless quality for the group, and not to execute a handover to another base station device with poor wireless quality for the group. That is, when a specific base station device forms multiple beams, if the wireless quality of only one or a few beams among the multiple beams is particularly high, it is assumed that the wireless quality of the group is not high. In this case, if the terminal device 111 moves slightly or the surrounding environment changes, another handover may be necessary within a short period after the handover. In contrast, the base station device 101 according to this embodiment may avoid a handover to a base station device with insufficient wireless quality for almost all of the multiple beams and encourage a handover to a base station device that forms multiple beams belonging to a group with good statistical wireless quality. This makes it possible to prevent handovers from being repeatedly performed within a short period of time due to changes in circumstances such as the movement of the terminal device 111 .

[0031] In the above example, the base station device 101 determines whether to cause the terminal device 111 to perform a handover. However, the terminal device 111 may also determine whether to perform a handover autonomously. That is, the terminal device 111 may perform a conditional handover. The processing flow in this case is shown in FIG. 3. The base station device 101 notifies the terminal device 111 of information indicating beams to be measured and the group to which each beam belongs (S301), similar to S201 in FIG. 2. In this case, configuration information for reporting does not need to be notified. For example, the base station device 101 transmits a HANDOVER REQUEST message to a candidate base station device (e.g., the base station device 102) as the handover destination, at a timing prior to S301, and receives a HANDOVER REQUEST ACKNOWLEDGE message including configuration information for the terminal device 111 after the handover. The base station device 101 then notifies the terminal device 111 of configuration information to be used after handover to the candidate base station device as a handover destination, for example, in a message at S301. FIG. 3 shows an example in which the configuration information for this conditional handover is notified from the base station device 101 to the terminal device 111 at S301 using an information element called “conditional LTM config.” Note that this configuration information may be notified before or after S301. The terminal device 111 retains configuration information for connection with the candidate base station device as a handover destination, and also performs pre-configuration, such as executing uplink and downlink synchronization establishment processing, as necessary (S302). The terminal device 111 then measures the wireless quality of predetermined reference signals transmitted from other surrounding base station devices (S303) and, similar to S203, identifies the wireless quality for each group (S304). Then, the terminal device 111 determines whether or not to perform a handover based on the wireless quality for each identified group (S305), and if it decides to perform a handover, it performs handover processing to the base station device to which the handover is to be performed (S306).

[0032] As described above, in this embodiment, when the decision on whether to perform handover is made in the base station device 101, the wireless quality for each group is reported to the base station device 101. When the decision is made in the terminal device 111, the wireless quality for each group is not transmitted to the base station device 101, and the terminal device 111 may independently decide to perform handover based on the wireless quality. In either case, by using the wireless quality for each group, the terminal device 111 can handover to a base station device having multiple beams with good wireless quality (due to the existence of a group with good statistical wireless quality) without handing over to a base station device having insufficient wireless quality in almost all of the multiple beams. This makes it possible to avoid a situation where there is no beam with good wireless quality among the beams formed by the connected base station device, even if the wireless quality significantly deteriorates in a short period after the terminal device 111 hands over, and to prevent unnecessary handovers from occurring.

[0033] The terminal device 111 not only measures the wireless quality of a beam formed by another base station device (e.g., the base station device 102) other than the currently connected base station device 101, but also measures the wireless quality of a beam formed by the base station device 101. The terminal device 111 may then switch beams to use a beam that can provide better wireless quality than the beam currently in use. In one example, the terminal device 111 may determine a beam to use based on the measurement results and request communication using that beam from the base station device 101. Furthermore, the terminal device 111 may transmit, as control information, information indicating the TCI corresponding to the beam to be used to the base station device 101 when transmitting uplink user data, for example.

[0034] In the above-described embodiment, an example has been described in which the terminal device 111 transmits a measurement report to the base station device 101 periodically or in response to an instruction from the base station device 101. Alternatively, an event may be set for determining whether or not to report the measurement result of the wireless quality of a reference signal measured by the terminal device 111, based on the wireless quality of the reference signal. For example, as shown in FIG. 4 , Events A3a, A4a, and A5a similar to conventional Events A3, A4, and A5 may be defined. That is, in conventional Event A3, it is determined that an event has occurred when the wireless quality (q2) of a neighboring cell becomes better than the wireless quality (q1) of the currently connected cell by more than a predetermined offset (Offset) (q2≧q1+Offset), whereas in Event A3a, this is applied to a group of beams. That is, Event A3a can be defined so that an event is determined to have occurred when the statistical value of the wireless quality of any of the groups of beams of a neighboring cell exceeds a value obtained by adding a predetermined offset value to the statistical value of the wireless quality of the group of beams used in the connected cell (or the wireless quality value of one beam currently in use). Furthermore, while the conventional Event A4 requires the wireless quality of the neighboring cell to exceed a predetermined threshold, Event A4a requires the wireless quality of any of the groups of beams of a neighboring cell to exceed a predetermined threshold. Furthermore, while Event A5 requires the wireless quality of the currently connected cell to fall below a first threshold and the wireless quality of the neighboring cell to be better than a second threshold, Event A5a requires the wireless quality of the group of beams currently in use to fall below the first threshold and the wireless quality of any of the groups of beams of a neighboring cell to be higher than a second threshold. Here, the group of beams used to determine an event may be determined by the terminal device. For example, the terminal device performs measurements on all beams and determines the group of connected beams. In this case, if the measurement value of the reference signal in the terminal device changes, the group used to determine an event also changes.On the other hand, when the base station device determines the group to be used for determining the event, the group may be changed by the setting in the RRC layer. In this case, the group of the beam related to the cell in communication used for determining the event is not changed by the change in the measurement value. Note that these are just examples, and another event may be newly defined.

[0035] Furthermore, a condition (Time To Trigger) related to the period during which it has been determined that each event has occurred may be applied as a condition for making a report corresponding to each event. That is, the terminal device 111 may transmit a measurement report to the base station device 101 not at the time when any of the above-mentioned Events A3a, A4a, and A5a occurs, but at the time when the event has continued to occur from the first occurrence of the event until the time length indicated by Time To Trigger has elapsed.

[0036] An example of the processing flow in this case is shown in Figure 5. Note that Figure 5 illustrates an example of the processing flow when LTM is performed, but similar processing, except for processing related to LTM, can be performed when Layer 3 measurement reporting is performed. In this processing, first, the base station device 101 to which the terminal device 111 is currently connected notifies the terminal device 111 of setting information, measurement settings, reporting settings, group information, and event information related to a base station device (cell) that is a candidate for LTM handover (S501). Here, the setting information related to the candidate base station device that is a candidate for LTM handover includes setting information (e.g., RRC layer) for the terminal device 111 to communicate with the candidate base station device. After receiving this information, the terminal device 111, as necessary, performs uplink and downlink synchronization establishment processing with the candidate base station device in advance for LTM handover (S502). Note that the measurement settings and reporting settings here include information for measuring and reporting beams formed by the candidate base station device that is a candidate for LTM handover. Furthermore, group information may be included in these pieces of information or may be notified separately from these pieces of information. Event information may be transmitted, for example, included in a report setting. Note that information defining each event may be notified separately to the terminal device 111, and the report setting may include only an event ID for specifying which event is the basis for transmitting a measurement result report.

[0037] The terminal device 111 measures the (layer 1) wireless quality (e.g., L1-RSRP) of a reference signal transmitted from a candidate base station device as a handover destination (S503) and performs statistical processing of the wireless quality for each beam group (S504). Then, the terminal device 111 determines whether the event specified in S501 has occurred based on the wireless quality for each group (S505). If the terminal device 111 determines that an event has occurred, it reports information indicating the wireless quality for each group to the base station device 101. Then, the base station device 101 determines whether to perform a handover based on the report (S507) and transmits information instructing a handover to the terminal device 111, for example, by a Cell Switch Command (S508). In accordance with the instruction, the terminal device 111 disconnects from the currently connected base station device 101 and performs connection processing with the handover destination base station device (S509).

[0038] In this way, by specifying the conditions for transmitting measurement reports, reports are transmitted only in situations where there is a high probability that a handover will be required, thereby reducing overhead compared to when measurement reports are transmitted periodically.

[0039] In the above embodiment, an example has been described in which the terminal device 111 executes a handover in response to a handover instruction from the base station device 101. Alternatively, an event may be set for the terminal device 111 to determine whether or not to perform a handover on its own initiative, based on the radio quality of a reference signal measured by the terminal device 111. For example, as shown in FIG. 6 , CondEvents A3a, A4a, and A5a similar to the conventional CondEvents A3, A4, and A5 may be defined. That is, the conventional CondEvent A3 determines that an event has occurred when the radio quality (q2) of a neighboring cell becomes better than the radio quality (q1) of the currently connected cell by more than a predetermined offset (Offset) (q2≧q1+Offset), whereas CondEvent A3a applies this to a group of beams. That is, CondEvent A3a can be defined so that an event is determined to have occurred when the statistical value of the wireless quality of any of the groups of beams of a neighboring cell exceeds a value obtained by adding a predetermined offset value to the statistical value of the wireless quality of the group of beams used in the connected cell (or the wireless quality value of one beam currently in use). Furthermore, while the conventional CondEvent A4 sets the condition for an event occurrence as the wireless quality of the neighboring cell exceeding a predetermined threshold, CondEvent A4a sets the condition for an event occurrence as the wireless quality of any of the groups of beams of a neighboring cell exceeding a predetermined threshold. Furthermore, CondEvent A5 sets the event occurrence condition as the wireless quality of the currently connected cell falling below a first threshold and the wireless quality of the neighboring cell becoming better than a second threshold, whereas CondEvent A5a sets the event occurrence condition as the statistical value of the wireless quality of the connected beam group (or the wireless quality value for one beam in use) falling below the first threshold and the wireless quality of one of the neighboring cell beam groups becoming higher than a second threshold. Here, the group of beams used to determine the event may be determined by the terminal device. For example, the terminal device measures all beams and determines the group of connected beams. In this case, if the measurement value of the reference signal in the terminal device changes, the group used to determine the event also changes.On the other hand, when the base station device determines the group to be used for determining the event, the group may be changed by the setting in the RRC layer. In this case, the group of the beam related to the cell in communication used for determining the event is not changed by the change in the measurement value. Note that these are just examples, and another event may be newly defined.

[0040] The above-described events can also be applied to conditional handover. For example, as shown in FIG. 7 , the base station device 101 notifies the terminal device 111 of a conditional handover configuration (conditional LTM config), as well as measurement configuration, group information, and event information for the conditional handover (S701). The conditional handover configuration includes, for example, an RRC layer configuration for communication with candidate base station devices as the handover destination, and further includes information indicating that the terminal device 111 may autonomously switch the connection destination. The measurement configuration, group configuration, and event information are the same as those in S501. The terminal device 111 performs uplink and downlink synchronization establishment processing with the candidate base station devices as the handover destination, as necessary (S702). Furthermore, the terminal device 111 measures the radio quality of reference signals transmitted from at least some of the beams formed by each candidate base station device as the handover destination (S703). The terminal device 111 then identifies the radio quality for each group from the radio quality of the measured reference signal (S704), and determines whether to perform handover based on the radio quality for each group, depending on whether the event specified in S701 has occurred (S705). That is, if the terminal device 111 determines that an event has occurred, it performs handover to another base station device that is the target of the event (S706). In this way, by defining an event related to a group of beams for which conditional handover is to be performed, when the terminal device 111 performs handover, the terminal device 111 can reliably connect to a beam with good radio quality for each group. Note that the terminal device 111 may select a beam to use for communication with the currently connected base station device using the above-mentioned group-related event.

[0041] In the above-described embodiment, an example has been described in which, at the time of handover (or changing of beams within the same cell), the radio quality corresponding to a plurality of beams formed by a base station device that is a candidate for the handover destination is grouped, and the radio quality for each group is identified. However, this is merely an example, and, for example, when adding or changing a secondary cell, the connection destination may be determined based on the radio quality for each group of beams as described above.

[0042] Furthermore, in the above-described embodiment, an example has been described in which a group of beams is set and the radio quality for that group is identified. However, without specifying a group, for example, statistical values ​​for two or more of a plurality of beams formed by a specific base station device may be specified as the radio quality for that specific base station device. Conventionally, when there is one or fewer beams whose radio quality exceeds a predetermined value, it has been specified that the terminal device reports the measurement results for the beam with the best radio quality to the serving base station device. In contrast, in this embodiment, the base station device may notify the terminal device of configuration information instructing the terminal device to report the radio quality as a statistical value, such as an average value, for a predetermined minimum number of beams or more. For example, by setting this minimum number, the influence of the unique radio quality on the reported radio quality for a base station device that has only one beam corresponding to a uniquely good radio quality and the radio quality of the other beams is poor can be suppressed. In this way, by selecting a base station device to which a terminal device is to connect based on statistical values ​​of measurement results for a predetermined minimum number or more of beams formed by candidate base stations without specifying a group, the probability that the terminal device will have to change its connection destination again within a short period of time after connecting to that base station device can be reduced.

[0043] An example of the processing flow in this case is shown in Figure 8. Note that Figure 8 shows the processing flow in which the terminal device 111 reports measurement results to the base station device 101 in response to the occurrence of an event. In Figure 8, parts that perform the same processing as in Figure 5 are assigned the same reference numerals, and descriptions thereof will be omitted. In this processing, the base station device 101 notifies the terminal device 111 of information indicating the minimum number of beams to be measured or reported, in addition to setting information, measurement setting, reporting setting, and event information related to a base station device (cell) that is a candidate for handover by LTM (S801). Here, the information indicating the minimum number of beams may be included in, for example, only one of the measurement setting and the reporting setting, or may be included in both, as in the group information in the above-mentioned embodiment. Furthermore, the information indicating the minimum number of beams may be transmitted separately from the measurement setting and the reporting setting, and information such as an index for identifying the minimum number of beams may be included in at least one of the measurement setting and the reporting setting.

[0044] The terminal device 111 then observes reference signals transmitted from each of the multiple beams formed by the candidate base station device as the handover destination and measures the wireless quality (S503). The terminal device 111 then identifies statistical values ​​(such as average values) of the wireless quality for a number of beams equal to or greater than the notified minimum number (S802). Conventionally, the terminal device 111 notifies the base station device 101 of the best value of the wireless quality if there is one or fewer beams whose wireless quality exceeds a predetermined threshold, or of the linear average value of the wireless quality if there are multiple beams whose wireless quality exceeds the predetermined threshold. Therefore, if there is only one beam corresponding to an exceptionally high wireless quality and the wireless quality of the other beams is extremely low, the terminal device 111 may report the exceptionally high wireless quality. On the other hand, by specifying the minimum number of beams (two or more) as in this processing example, the wireless quality is identified taking into account not only the exceptionally high wireless quality but also the extremely low wireless quality of the other beams. The terminal device 111, for example, identifies the fewest number of beams designated in descending order of wireless quality and calculates statistical values ​​of the wireless qualities of reference signals transmitted from those beams. Note that, for example, if there are more than the minimum number of beams corresponding to wireless qualities exceeding a predetermined threshold, the terminal device 111 may calculate the statistical values ​​by considering all of those beams. In this case, as in the past, an upper limit on the number of beams to be considered may be specified, and beams exceeding that number may not be considered even if their corresponding wireless qualities exceed the predetermined threshold. Furthermore, for example, even if there are more than the minimum number of beams corresponding to wireless qualities exceeding the predetermined threshold, the terminal device 111 may calculate the statistical values ​​by considering only the fewest number of beams. The calculated statistical values ​​may be, for example, a linear average value or other statistical values ​​such as the median of the wireless qualities of the fewest number of beams in descending order of wireless quality. Furthermore, other calculation methods may be used, such as the average value of the wireless qualities of the fewest number of beams in descending order of wireless quality, excluding the highest value, among the fewest number of beams in descending order of wireless quality.

[0045] Thereafter, the terminal device 111 determines whether an event has occurred based on the radio quality determined for a number of beams equal to or greater than the specified minimum value (S803). If the terminal device 111 determines that an event has occurred, it reports the radio quality information determined in S802 to the base station device 101 (S506). Note that the event here is determined, for example, by treating the "number of beams equal to or greater than the minimum value" as a "group" of Events A3a, A4a, and A5a shown in FIG. 4 . That is, if the (statistical values ​​of) radio quality for a number of beams equal to or greater than the specified minimum value among multiple beams formed in a base station device providing a neighboring cell exceeds a value obtained by adding a predetermined offset value to the radio quality of the currently connected beam or the statistical value of radio quality for a group including that beam, it can be determined that Event A3a has occurred. Furthermore, if the statistical values ​​of radio quality for a number of beams equal to or greater than the specified minimum value among multiple beams formed in a base station device providing a neighboring cell exceed a predetermined threshold, it can be determined that Event A4a has occurred. Furthermore, if the wireless quality of the currently connected beam or the statistical value of the wireless quality of a group including that beam falls below a first predetermined threshold, and (the statistical value of) the wireless quality for a specified minimum number or more of beams formed in a base station device that serves a neighboring cell exceeds a second predetermined threshold, it may be determined that Event A5a has occurred. Note that the wireless quality of the currently connected base station device may take into account only the beams in use, or may be the statistical value of the wireless quality for a number of beams formed by the base station device that is equal to or greater than a specified minimum number. Furthermore, the terminal device 111 may report the wireless quality statistical value regardless of an event, for example, periodically or when receiving a predetermined instruction from the base station device 101, in response to the predetermined instruction.

[0046] FIG. 9 shows the flow of processing when the terminal device 111 performs a conditional handover, autonomously changing the base station device to which it is connected in response to the occurrence of an event. In FIG. 9, parts that perform the same processing as in FIG. 7 are assigned the same reference numerals, and descriptions thereof are omitted. In this processing, the base station device 101 notifies the terminal device 111 of the conditional handover configuration, the measurement configuration for the conditional handover, event information, and information indicating the minimum number of beams to be measured or reported (S901). Here, the information indicating the minimum number of beams may be included in the measurement configuration, as in the group information in the above-described embodiment, or may be transmitted separately from the measurement configuration, and information such as an index for identifying the minimum number of beams may be included in the measurement configuration. Then, as in S802, the terminal device 111 calculates statistical values ​​of wireless quality for beams equal to or greater than the specified minimum number (S902) and determines whether an event has occurred based on the calculated values ​​(S903). If the terminal device 111 determines that an event has occurred, it executes a handover (S706).

[0047] As described above, even when groups are not formed, by specifying the minimum number of beams to be considered when obtaining measurement results, it is possible to prevent a base station device that obtains specifically high wireless quality only for one or a very small number of beams from being highly evaluated for its wireless quality.

[0048] FIG. 10 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 1001, a ROM 1002, a RAM 1003, a storage device 1004, and a communication circuit 1005. The processor 1001 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 1002 or the storage device 1004. The ROM 1002 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 1003 functions as a workspace when the processor 1001 executes a program and is also a random access memory that stores temporary information. The storage device 1004 is configured, for example, by a removable external storage device. The communication circuit 1005 is configured, for example, by a circuit for wireless communication of 5G or a successor standard. While FIG. 10 illustrates one communication circuit 1005, 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 (e.g., the base station device 102) 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 1005 for each of the multiple available frequency bands, or may have a common communication circuit 1005 for at least some of the frequency bands.

[0049] FIG. 11 shows an example of the functional configuration of a base station device 101. The base station device 101 includes, for example, a measurement setting unit 1101, a report setting unit 1102, a beam group setting unit 1103, a setting notification unit 1104, and a handover control unit 1105. Note that FIG. 11 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 base station devices compliant with 5G and subsequent standards generally have. The functional blocks in FIG. 11 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. 11 may be realized, for example, by the processor 1001 executing a program stored in the ROM 1002 or the storage device 1004, or may be realized, for example, by a processor within the communication circuit 1005 executing predetermined software. The details of the processes executed by each functional unit will not be described here, but only the general functions thereof will be outlined.

[0050] The measurement setting unit 1101 generates measurement setting information for causing the terminal device 111 to measure radio signals transmitted from beams formed by other base station devices. The report setting unit 1102 generates report setting information for the terminal device 111 to report results of measuring radio signals based on the measurement setting information by the measurement setting unit 1101. Note that the report setting unit 1102 may, for example, set event information for reporting the measurement results and include it in the report setting information. The beam group setting unit 1103, for example, groups beams to be measured. Furthermore, the beam group setting unit 1103 may, for example, determine the minimum number of beams to be considered when reporting the measurement results. Information on the groups of beams set by the beam group setting unit 1103 or the minimum number of beams to be considered is provided to the measurement setting unit 1101 or the report setting unit 1102, and the provided information may be included in at least one of the measurement setting information and the reporting setting information. Furthermore, setting information including information on the group of beams set by the beam group setting unit 1103 or the minimum number of beams to be considered may be generated separately from the measurement setting unit 1101 and the report setting unit 1102. The setting notification unit 1104 notifies the terminal device 111 of the setting information generated via the measurement setting unit 1101, the report setting unit 1102, and the beam group setting unit 1103.

[0051] The handover control unit 1105 executes control for handing over the terminal device 111 to another base station device. For example, the handover control unit 1105 receives measurement results for a group of beams from the terminal device 111, and determines to execute handover of the terminal device 111 when a predetermined condition is met, such as the wireless quality indicated by the measurement results being higher by a predetermined offset than the wireless quality of the beam to which the terminal device 111 is currently connected (or a group of beams including that beam). After making this determination, the handover control unit 1105 transmits and receives control messages for handover with other base station devices forming the group of beams with good wireless quality, and can notify the terminal device 111 of setting information for communication with other base station devices and instruct the handover. The handover control unit 1105 may also acquire communication setting information for candidate base station devices as the handover destination and notify the terminal device 111 of the communication setting information before receiving a measurement result report. Then, based on the measurement result, the handover control unit 1105 may notify the terminal device 111 of a cell switching command specifying a connection destination cell, and cause the terminal device 111 to perform handover. Also, the handover control unit 1105 may set a conditional handover.

[0052] FIG. 12 shows an example of the functional configuration of the terminal device 111. The terminal device 111 includes, for example, a setting receiving unit 1201, a quality measuring unit 1202, a beam group quality identifying unit 1203, a report transmitting unit 1204, and a handover processing unit 1205. Note that FIG. 12 only shows functions particularly related to this embodiment, and various other functions that the terminal device 111 may have are not shown. For example, the terminal device 111 naturally has other functions that terminal devices compliant with 5G or subsequent standards generally have. Furthermore, the functional blocks in FIG. 12 are shown schematically, and each functional block may be realized as an integrated unit or may be further subdivided. Furthermore, each function in FIG. 12 may be realized, for example, by the processor 1001 executing a program stored in the ROM 1002 or the storage device 1004, or may be realized, for example, by a processor present within the communication circuit 1005 executing predetermined software. The details of the processes executed by each functional unit will not be described here, but only the general functions thereof will be outlined.

[0053] The setting receiver 1201 receives setting information generated via the measurement setting unit 1101, the report setting unit 1102, and the beam group setting unit 1103 from the base station device 101. The setting receiver 1201 may also receive, from the base station device 101, pre-setting information for conditional handover settings and communication with a base station device that is a candidate for handover for LTM. Based on the measurement setting information received by the setting receiver 1201, the quality measurement unit 1202 observes radio signals (reference signals) transmitted by base station devices other than the candidate base station device 101 and measures radio quality. The quality measurement unit 1202 observes reference signals transmitted from each of multiple beams formed by the other base station devices and measures the radio quality of each beam. The quality measurement unit 1202 may also measure the radio quality of one or more beams formed by the base station device 101, including the currently connected beam, as necessary. The beam group quality specifying unit 1203 calculates statistical values ​​of wireless quality obtained for a group of beams or for more than the minimum number of beams, based on beam group information (information indicating a group of beams or a minimum number of beams to be considered) received by the setting receiving unit 1201. The report transmitting unit 1204 reports the calculated statistical values ​​of wireless quality (and, if necessary, wireless quality measurement results for individual beams) to the base station device 101 based on the report setting information. Note that if an event is specified in the report setting information, the report transmitting unit 1204 reports the statistical values ​​to the base station device 101 when it determines that an event based on the statistical values ​​of wireless quality has occurred. For example, when the handover processing unit 1205 receives a handover instruction from the base station device 101, it executes handover from the base station device 101 to another base station device in accordance with the instruction. Furthermore, when the setting receiving unit 1201 receives a setting for a conditional handover, the handover processing unit 1205 autonomously executes a handover when a predetermined condition is satisfied, without relying on an instruction from the base station device 101. Note that the handover processing unit 1205 may autonomously change the destination beam from the currently connected beam to another beam, for example, without changing the destination base station device, based on the same criteria as in the case of a handover.

[0054] As described above, in this embodiment, the determination of whether to perform a handover is based on the statistical values ​​of wireless quality for at least two groups of beams, rather than on the individual wireless quality of each of the multiple beams formed by the candidate base station device as the handover destination (i.e., the beam designated as the measurement target among the many beams formed by the base station device). This reduces the probability that a terminal device will handover to a base station device that provides exceptionally high wireless quality for a very small number of beams. This increases the probability that a base station device that reduces the probability of a re-handover occurring even if the environment in which the terminal device is located changes is selected as the handover destination. This improves the stability of communication in the terminal device and prevents a decrease in handover efficiency in the wireless communication system. This contributes to Goal 9 of the United Nations' Sustainable Development Goals (SDGs), "Build resilient infrastructure, promote sustainable industrialization, and foster innovation."

[0055] 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.

[0056] This application claims priority based on Japanese Patent Application No. 2024-028913, filed February 28, 2024, the entire contents of which are incorporated herein by reference.

Claims

1. A terminal device having: a receiving means for receiving, from a connected base station device, configuration information regarding measurement of wireless quality for each of a plurality of beams formed by another base station device and reporting of the results of the measurement, the configuration information including information on a group of beams consisting of two or more beams from the plurality of beams and information specifying an event based on a statistical value of wireless quality for the group of beams; a measuring means for observing a reference signal transmitted from each of the plurality of beams based on the configuration information, and measuring the wireless quality for each of the plurality of beams; an identifying means for identifying a statistical value of wireless quality for the group based on the wireless quality for each of the plurality of beams and the information on the group of beams; a determining means for determining whether the specified event has occurred based on the identified statistical value; and a reporting means for reporting the statistical value to the base station device based on the configuration information when it is determined that the event has occurred.

2. The terminal device of claim 1, wherein the event includes an event that is determined to have occurred when a statistical value of wireless quality for the group exceeds a value indicating the wireless quality for the beam to which the terminal device is currently connected or a value obtained by adding a predetermined offset value to the statistical value of wireless quality for the group including the currently connected beam.

3. The terminal device according to claim 1 or 2, wherein the event includes an event that is determined to have occurred when a statistical value of wireless quality for the group exceeds a predetermined threshold.

4. A terminal device as described in any one of claims 1 to 3, wherein the event includes an event that is determined to have occurred when a value indicating the wireless quality of a beam to which the terminal device is currently connected or a statistical value of wireless quality for a group including the currently connected beam becomes lower than a first threshold and a statistical value of wireless quality for the group becomes higher than a second threshold.

5. A terminal device according to any one of claims 1 to 4, wherein the wireless quality is a layer 1 wireless quality.

6. A base station device having: a notification means for notifying a connected terminal device of setting information regarding measurement of wireless quality for each of a plurality of beams formed by another base station device and reporting of the results of the measurement, the setting information including information on a group of beams consisting of two or more beams from the plurality of beams and information specifying an event based on statistical values ​​of wireless quality for the group of beams; a receiving means for receiving from the terminal device, when it is determined that the event has occurred, a report of statistical values ​​of wireless quality identified from the wireless quality for each of the beams belonging to the group from the plurality of beams; and a decision means for deciding whether to hand over the terminal device to the other base station device based on the report.

7. The base station device of claim 6, wherein the event includes an event that is determined to have occurred when the statistical value of wireless quality for the group exceeds a value indicating the wireless quality for the beam to which the terminal device is currently connected or a value obtained by adding a predetermined offset value to the statistical value of wireless quality for the group including the currently connected beam.

8. The base station device according to claim 6 or 7, wherein the event includes an event that is determined to have occurred when a statistical value of wireless quality for the group exceeds a predetermined threshold.

9. A base station device as described in any one of claims 6 to 8, wherein the event includes an event that is determined to have occurred when a value indicating the wireless quality of a beam to which the terminal device is currently connected or a statistical value of the wireless quality for a group including the currently connected beam becomes lower than a first threshold and a statistical value of the wireless quality for the group becomes higher than a second threshold.

10. The base station device according to any one of claims 6 to 9, wherein the wireless quality is a layer 1 wireless quality.

11. A control method executed by a terminal device, comprising: receiving, from a connected base station device, configuration information regarding measurement of wireless quality for each of a plurality of beams formed by another base station device and reporting of the results of the measurement, the configuration information including information on a group of beams consisting of two or more beams from the plurality of beams and information specifying an event based on a statistical value of wireless quality for the group of beams; observing a reference signal transmitted from each of the plurality of beams based on the configuration information, and measuring the wireless quality for each of the plurality of beams; identifying a statistical value of wireless quality for the group based on the wireless quality for each of the plurality of beams and the information on the group of beams; determining whether the specified event has occurred based on the identified statistical value; and when it is determined that the event has occurred, reporting the statistical value to the base station device based on the configuration information.

12. A control method executed by a base station device, comprising: notifying a connected terminal device of configuration information regarding measurement of wireless quality for each of a plurality of beams formed by another base station device and reporting of the results of the measurement, the configuration information including information on a group of beams consisting of two or more beams from the plurality of beams and information specifying an event based on statistical values ​​of wireless quality for the group of beams; receiving from the terminal device, when it is determined that the event has occurred, a report of statistical values ​​of wireless quality identified from the wireless quality for each of the beams from the plurality of beams belonging to the group; and determining, based on the report, whether to hand over the terminal device to the other base station device.

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 installed in a base station device to execute the control method set forth in claim 12.

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