Terminal device, base station device, control method, and program for optimizing layer 1 / layer 2 triggered mobility (LTM)

Abstract

According to the present invention, a terminal device compliant with cellular communication standards of the Third Generation Partnership Project (3GPP) acquires, from a connected base station device, configuration information for measurements and reporting for handover based on Layer 1 / Layer 2 triggered mobility (LTM), the configuration information including a first piece of information that specifies a reference signal to be measured for beams of candidate cells for handover which are subject to Layer 1 (L1) radio quality measurements in the terminal device, and a second piece of information that indicates that an event defining a condition under which the L1 radio quality of the beams is to be reported. The terminal device performs L1 radio quality measurements of the reference signals for the beams, determines whether the measurement results satisfy the condition of the event, and when it is determined that the measurement results satisfy the condition, transmits a measurement report to the base station device.

Description

Terminal device, base station device, control method, and program for improving the efficiency of Layer 1 / Layer 2 Triggered Mobility (LTM)

[0001] The present invention relates to a technique for controlling measurement and reporting of wireless quality by a terminal device in a cellular communication system.

[0002] In cellular communication standards such as the fifth generation (5G) standard conforming to the Third Generation Partnership Project (3GPP (registered trademark)), a Layer 1 / Layer 2 Triggered Mobility (LTM) mechanism has been introduced to reduce the time required for handover.

[0003] In LTM, a terminal device reports the measurement result of wireless quality at Layer 1 to a base station device in accordance with an instruction from the base station device. In such a reporting procedure, it is possible that the efficiency of LTM may be reduced because the terminal device cannot report the measurement result of wireless quality without an instruction from the base station device.

[0004] The present invention provides techniques to improve the efficiency of Layer 1 / Layer 2 Triggered Mobility (LTM).

[0005] A terminal device according to one aspect of the present invention is a terminal device that complies with the cellular communication standard of the Third Generation Partnership Project (3GPP), and has: an acquisition means for acquiring from a connected base station device configuration information for measurement and reporting for handover by Layer 1 / Layer 2 Triggered Mobility (LTM), the configuration information including first information specifying a reference signal to be measured for a beam of a candidate cell that is a handover destination and for which the terminal device is to measure the wireless quality of Layer 1 (L1) in the terminal device; second information indicating an event that specifies the conditions for reporting the wireless quality of L1 of the beam; a measurement means for measuring the wireless quality of L1 of the reference signal for the beam; a determination means for determining whether the result of the measurement satisfies the condition of the event; and a transmission means for transmitting a measurement report to the base station device when it is determined that the result of the measurement satisfies the condition of the event.

[0006] A base station device according to one aspect of the present invention is a base station device that complies with the cellular communication standard of the Third Generation Partnership Project (3GPP), and has: a providing means for providing to a connected terminal device configuration information for measurement and reporting for handover by Layer 1 / Layer 2 Triggered Mobility (LTM), the configuration information including first information specifying a reference signal to be measured for a beam of a candidate cell as a handover destination that is the target of measurement of Layer 1 (L1) wireless quality in the terminal device, and second information indicating an event that specifies the conditions for reporting the L1 wireless quality of the beam; a receiving means for receiving from the terminal device a measurement report regarding the result of measurement of the L1 wireless quality based on the configuration information; and a transmitting means for transmitting to the terminal device a command to handover the terminal device based on the measurement report.

[0007] According to the present invention, the efficiency of Layer 1 / Layer 2 Triggered Mobility (LTM) can be improved.

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

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

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

[0011] (System Configuration) Fig. 1 shows an example of the configuration of a wireless communication system according to this embodiment. This wireless communication system is a cellular communication system conforming to the cellular communication standard of the Third Generation Partnership Project (3GPP (registered trademark)), and is configured to include base station devices (e.g., base station device 101, base station device 102) and terminal devices (e.g., terminal device 111). Note that it is assumed that the terminal device 111 is currently connected to the base station device 101, and then moves toward the base station device 102, and is in a state where it can execute a handover to the base station device 102. Note that, for the sake of simplicity, Fig. 1 shows only two base station devices and one terminal device, but it goes without saying that a large number of these devices may exist.

[0012] In this embodiment, Layer 1 / Layer 2 Triggered Mobility (LTM) is used to shorten the handover time. In LTM, the base station device 101 notifies the base station device 102 of post-handover setting information between the terminal device 111 and the handover destination base station device 102 at a timing before the actual handover is performed. The base station device 101 transmits a HANDOVER REQUEST message to the base station device 102 for handover of the terminal device 111, and receives a HANDOVER REQUEST ACKNOWLEDGE message indicating acceptance of the handover. The HANDOVER REQUEST ACKNOWLEDGE message includes communication parameters to be used by the terminal device 111 after handover to the base station device 102. Then, based on that message, the base station device 101 can transmit a message (e.g., an RRC Reconfiguration message) including configuration information to be transmitted to the terminal device 111. This allows the terminal device 111 to complete configuration for performing communication with the base station device 102 based on the configuration information before receiving a handover instruction to the base station device 102. The terminal device 111 may also perform processes such as synchronization establishment for uplink and downlink with the base station device 102 in advance. For example, the terminal device 111 measures the radio quality at Layer 1 (L1) for the reference signal transmitted from the base station device 102 and reports the results to the base station device 101. Based on the report, the base station device 101 can determine whether to hand over the terminal device 111 to the base station device 102. L1 corresponds to the physical layer. After determining to hand over the terminal device 111 to the base station device 102, the base station device 101 can instruct the terminal device 111 to execute 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, it is possible to shorten the time from receiving the handover instruction until starting communication of user data with the base station device 102.

[0013] In this way, LTM can shorten the handover time, but the terminal device 111 performs L1 measurement and reporting according to instructions from the base station device 101. This measurement and reporting is performed according to a schedule determined by the base station device 101. For example, the base station device 101 performs periodic or semi-persistent reporting configuration for reporting L1 measurement results, or transmits aperiodic reporting configuration to the terminal device 111, so that the terminal device 111 transmits a report of the L1 measurement results to the base station device 101 at a specified timing. In this way, when measurement reporting is performed according to a schedule determined by the base station device 101, depending on the reporting period in the periodic or semi-persistent reporting configuration, the period from measurement to reporting may be long, and the measurement results may become outdated information. As a result, the terminal device 111 may not be handed over to an appropriate cell / beam, and communication efficiency in the system may be insufficient. On the other hand, for example, shortening the reporting period in a periodic or semi-persistent reporting configuration can shorten the period, but excessive resources may be reserved for the reporting, which may reduce the efficiency of communication throughout the system.Similarly, if a configuration is made such that aperiodic reporting is performed frequently, the efficiency of communication throughout the system may also be reduced.

[0014] In view of these circumstances, this embodiment introduces a mechanism in which the terminal device 111 spontaneously reports measurement results without receiving instructions from the base station device 101. This prevents the time between measurement and the reporting of the measurement results from becoming long, and also prevents excessive consumption of resources for reporting.

[0015] (Processing Flow) FIG. 2 shows an example of a processing flow according to this embodiment. Note that, in this embodiment, the terms "cell" and "beam" can be used interchangeably. That is, in the following description, an item described as a "cell" can be read as a "beam," and an item described as a "beam" can be read as a "cell." In this processing example, it is assumed that the terminal device 111 is initially in an RRC Connected state (i.e., connected) with the base station device 101. Note that RRC stands for Radio Resource Control. In this state, the terminal device 111 measures the received radio quality of reference signals transmitted in surrounding cells (beams) according to, for example, a conventional measurement procedure, and transmits a measurement report (S201). Here, measurement is performed, for example, in Layer 3 (L3). L3 corresponds, for example, to the RRC layer. The terminal device 111 holds a setting for measurement reporting in L3, for example, at the time of connection, and performs measurement reporting according to the setting. The configuration for the L3 measurement report may include information about an event indicating that the measurement result of the radio quality should be reported, for example, when at least one of the radio quality in the serving cell (the cell served by the currently connected base station device 101) and the radio quality in a neighboring cell (e.g., a cell served by the base station device 102 or a cell other than the serving cell served by the base station device 101) satisfies a predetermined condition. This event includes, for example, the radio quality of the neighboring cell becoming higher than the radio quality of the serving cell by a specific offset value (event A3), the radio quality of the neighboring cell exceeding a predetermined threshold (event A4), or the radio quality of the serving cell falling below a first threshold and the radio quality of the neighboring cell exceeding a second threshold (event A5). The terminal device 111 transmits the L3 measurement report to the base station device 101, for example, when the radio quality of the current serving cell falls below the predetermined threshold (event A2). The terminal device 111 may also transmit L3 measurement reports to the base station device 101, for example, periodically, semi-permanently, or in response to an instruction aperiodically.In response to receiving this measurement report, the base station device 101 starts preparing settings for candidate cells as the handover destination for handover by LTM (S202).

[0016] For example, before the terminal device 111 actually performs handover, the base station device 101 transmits a HANDOVER REQUEST message and receives a HANDOVER REQUEST ACKNOWLEDGE message from the base station device 102, the HANDOVER REQUEST ACKNOWLEDGE message including communication parameters that the terminal device 111 should use after handover to the base station device 102. Then, the base station device 101 transmits to the terminal device 111 an RRC message (for example, an RRC reconfiguration message) including the communication parameters for the LTM candidate cell received from the base station device 102 (S203). Note that this RRC message may include configuration information for measurement and reporting for LTM. In response to receiving this RRC message, the terminal device 111 completes pre-configuration for the LTM candidate cell (S204). Then, the terminal device 111 establishes downlink synchronization by receiving a synchronization signal or the like of the candidate cell as needed (optionally), and establishes uplink synchronization by executing a random access procedure (S205). Thereafter, the terminal device 111 transmits the measurement results of the wireless quality on L1 to the base station device 101 (S206). Then, the base station device 101 determines to hand over the terminal device 111 to an adjacent cell based on the measurement results (S207), and transmits a handover command (Cell Switch Command) to the terminal device 111 (S208). The base station device 101 transmits, for example, the Cell Switch Command including information specifying the handover destination cell (beam). When a beam to be the handover destination is specified, an identifier (TCI-state ID) of a Transmission Configuration Indication (TCI) corresponding to the beam can be specified in the Cell Switch Command. Upon receiving this command, the terminal device 111 disconnects (detaches) from the serving cell (beam) and applies the communication parameters received in S203, thereby executing a handover to the cell (beam) to be the handover destination.

[0017] Here, conventionally, the terminal device 111 is supposed to transmit a report of the measurement results of the L1 wireless quality in S206 in accordance with an instruction from the base station device 101. That is, measurement report settings for LTM are provided in the RRC message transmitted from the base station device 101 to the terminal device 111 in S203, and the terminal device 111 transmits the measurement report in accordance with those settings. Here, conventional measurement reports for LTM only support periodic measurement reports, and no settings exist for performing event-based measurement reports. That is, as measurement report setting information for LTM, there is a reporting setting for CSI (Channel State Information) for LTM, and the parameters thereof are stored in LTM-CSI-ReportConfig-r18. LTM-CSI-ReportConfig-r18 includes LTM-CSI-ReportConfigId-r18, which is an identifier of this report configuration, reportConfigType-r18, which specifies the measurement timing, and pucch-CSI-ResourceList, which specifies which physical uplink control channel (PUCCH) resource should be used in the report. In this way, conventionally, measurement and reporting of radio quality for LTM is performed using the timing and PUCCH resource specified by the base station device 101, and the terminal device 111 is not able to report radio quality in a timely manner in a situation where handover is required.

[0018] For this reason, in this embodiment, the terminal device 111 is allowed to spontaneously report measurement results for LTM (without being restricted by the base station device 101 specifying resources for reporting). For example, in S203, the base station device 101 notifies the terminal device 111 of first configuration information for measuring the L1 radio quality and second configuration information for determining whether or not to report the measurement results to the base station device 101. In one example, the first configuration information is provided as LTM-Config, and the second configuration information is provided as LTM-CSI-ReportConfigToAddModList. The first configuration information includes a list of beams to be measured. Conditions under which measurement results should be reported are predefined, and an event ID is assigned to each of them, and the event ID can be included in the second configuration information. For example, events such as the radio quality of L1 of a connected first beam falling below a predetermined threshold, the radio quality of L1 of a handover destination candidate second beam exceeding a predetermined threshold, the radio quality of L1 of the second beam exceeding the radio quality of L1 of the first beam by a predetermined offset, and the radio quality of L1 of the first beam falling below the first threshold and the radio quality of L1 of the second beam exceeding a second threshold are defined as events, and an event ID is assigned to each of them. Information indicating which event, if any, should be met to report the measurement results is included in the second setting information as an event ID. Note that multiple events may be set in parallel. The terminal device 111 measures signals (e.g., synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB) or CSI reference signal (CSI-RS)) transmitted in the handover destination candidate beam and the connected beam, and determines whether an event corresponding to the notified event ID has occurred based on the measurement results. The threshold associated with the event can be notified from the network (base station device 101) to the terminal device 111. The threshold may be set individually for each candidate beam (cell) of the handover destination, or a common threshold may be set for multiple beams (cells).Furthermore, when the condition for each event continues to be satisfied for a predetermined period of time, the terminal device 111 may transmit a measurement report due to that event to the base station device 101. That is, even if the wireless quality based on a single measurement result satisfies the condition for the event, the terminal device 111 may not transmit a measurement report based on the event unless the condition is satisfied for a predetermined period of time. This predetermined period of time may be notified from the base station device 101 to the terminal device 111 as TimeToTrigger in EventTriggerConfig. TimeToTrigger may be specified, for example, for each event, or for each candidate beam (cell) for handover destination.

[0019] The events defined here may be similar to events based on conventional L3 measurement results. For example, the events may include an event determined to occur when the L1 radio quality of a handover destination candidate beam (or cell) exceeds a value indicating the L1 radio quality of the beam (or cell) to which the terminal device 111 is currently connected. The events may also include an event determined to occur when the L1 radio quality of a handover destination candidate beam (or cell) exceeds a value obtained by adding a predetermined offset value to the value indicating the L1 radio quality of the beam (or cell) to which the terminal device 111 is currently connected. The events may also include an event determined to occur when the L1 radio quality of a handover destination candidate beam (or cell) exceeds a predetermined threshold. The events may also include an event determined to occur when the L1 radio quality of the beam (cell) to which the terminal device 111 is currently connected falls below a first threshold and the L1 radio quality of the handover destination candidate beam (cell) rises above a second threshold. The L1 radio quality may be L1-RSRP, L1-SINR, filtered RSRP, or filtered SINR. RSRP is the reference signal received power, and SINR is the signal-to-interference-and-noise ratio. The radio quality value used here may be the measurement value itself (absolute value) or a differential value from a reference value (e.g., another measurement value such as a previous measurement value). While the conventional L3 event configuration is configured in reportConfig, the L1 event configuration is provided, for example, in the LTM candidate configuration in an RRC message, in association with the L1 measurement resource configuration. The event configuration may be configured for each candidate beam (cell) of the handover destination.

[0020] The setting of L1 measurement resources (setting of beams (to be measured) for evaluating events) will be described. Measurement targets for L1 radio quality are, for example, CSI-RS and SSB. Here, the SSB to be measured is specified as SSB-Index in setting information LTM-CSI-ResourceConfig corresponding to the identifier LTM-CSI-ResourceConfigId included in LTM-Config in the RRC message. Separately, SSB setting information is specified in LTM-SSB-Config in association with SSB-Index, and the SSB to be measured is identified by referring to the corresponding setting information using the SSB-Index. Note that a plurality of measurement target resources (reference signals to be measured) for each of a plurality of handover destination candidate beams (cells) can be notified to the terminal device 111 by the RRC message. Then, a medium access control element (MAC CE) may activate some of the multiple measurement targets. This eliminates the need to transmit an RRC message from the base station device 101 to the terminal device 111 every time a candidate beam (cell) for handover or a reference signal to be measured is changed. This allows the terminal device 111 to identify the reference signal to be measured and measure its radio quality based on the activated setting. Note that the terminal device 111 can measure the radio quality of the reference signal for the currently connected serving beam using setting information for that measurement, but may also use the radio quality measured for detecting a connection failure, for example, to determine an event.

[0021] Furthermore, in LTM-Config, candidateTCI-state for each candidate beam of the handover destination is provided. Each candidateTCI-state includes a TCI-state ID, which is an identifier of that TCI-state, and QCL-Info. QCL stands for Quasi Co-Location and is an index that defines the correlation between symbols transmitted from two different antenna ports. Then, in QCL-Info, an index of NZP (Non Zero Power)-CSI-RS-ResourceSetId for indicating the CSI-RS resource, or an index of SSB is specified. In addition, the resource of the SSB or CSI-RS to be measured can be specified using the parameter resourceForChannelMeasurement of CSIReportConfig included in LTM-CSI-ReportConfigToAddModList in the configuration information for reporting the measurement results. In this way, the TCI state is associated with the resource from which the reference signal (CSI-RS) is transmitted. The terminal device 111 can, for example, measure the reference signal associated with each TCI state.

[0022] Here, for example, when SSB and CSI-RS are used as reference signals to be measured, if the measurement results of the SSB for one beam are compared with the CSI-RS for the other beam, the comparison results may be inappropriate. For this reason, in this embodiment, the terminal device 111 is configured to compare common reference signals as much as possible. QCL-Info may further include information indicating the type of QCL (qcl-Type). The QCL type is defined by QCL-Type A to D. This may indicate the extent to which the reference signals associated with two TCIs are communicated via similar paths. For example, two TCIs that share a common Doppler shift, Doppler spread, average delay, and delay spread are defined as being in a relationship defined as QCL-Type A. Similarly, when the Doppler shift and Doppler spread are common, it is defined as QCL-Type B; when the mean delay and Doppler shift are common, it is defined as QCL-Type C; and when the spatial reception parameters are common, it is defined as QCL-Type D. In this embodiment, reference signals transmitted in two beams having any of these QCL-Type relationships can be mutually utilized. This makes it possible to identify other reference signals (referred to as QCL-RSs) having a QCL relationship for each reference signal. For example, when CSI-RS measurement results have been obtained for the currently connected beam (cell), the terminal device 111 also attempts to acquire CSI-RS measurement results for candidate beams (cells) for handover destinations. Here, even if the CSI-RS is not transmitted for the candidate beam (cell) of the handover destination, if the QCL-RS transmitted in a beam that has a QCL relationship with the beam (having a certain QCL-Type defined) is a CSI-RS, the terminal device 111 can determine an event using the measurement results of the CSI-RS. Similarly, for example, if the CSI-RS is not configured in the serving cell, the event determination may be performed based on the CSI-RS of another beam that has a QCL relationship.That is, instead of the CSI-RS of the serving beam, the CSI-RS of another beam to which a predetermined QCL relationship is specified may be regarded as the CSI-RS of the serving beam, and an event determination may be performed. Also, for example, if there is no other beam in a QCL relationship with the serving beam, or if the CSI-RS is not transmitted in the other beams, and the CSI-RS is not transmitted in the serving beam, an event determination may be performed based on the SSB in the serving beam. In this way, even if different types of reference signals are designated as measurement targets in the serving beam and the beam of the candidate cell for handover, the terminal device 111 can appropriately perform event determination by aligning the types of reference signals by using the QCL-RS as an alternative reference signal to be measured for one of those beams.

[0023] Although the use of SSB as a QCL-RS of a serving beam (cell) is not currently permitted, if such use is permitted in the future, SSB may be applied as a QCL-RS. That is, the terminal device 111 may acquire measurement results of the serving beam (cell) using SSB used as a QCL-RS and compare them with measurement results of SSB of a candidate beam (cell) of the handover destination. Furthermore, the terminal device 111 may compare measurement results of the SSB of the serving beam (cell) with measurement results of SSB of another beam used as a QCL-RS for the candidate beam (cell) of the handover destination to perform event determination. Note that if the QCL-RS of the serving beam (cell) is a CSI-RS, it can be said that the terminal device 111 can receive SSB in the serving beam (cell). In this case, if the measurement target of the candidate beam (cell) of the handover destination is SSB, the terminal device 111 can perform event determination based on the measurement results of the SSB and the measurement results of the SSB of the serving beam (cell). Also, if the QCL-RS of the serving beam (cell) is CSI-RS and the measurement target of the candidate beam (cell) of the handover destination is CSI-RS, the terminal device 111 can perform event determination based on the measurement results of the QCL-RS for the serving beam (cell) and the measurement results of the CSI-RS of the candidate beam (cell) of the handover destination. Note that it is possible to assume that a tracking reference signal (TRS) is designated as the QCL-RS. In this case, event determination can be performed, for example, based on SSB, without using TRS. At this time, for example, if the measurement target of the candidate beam (cell) for handover is CSI-RS, the terminal device 111 can use the measurement results of the SSB that has a QCL relationship with that beam as the measurement results for that beam.

[0024] Note that various settings and operations, including the use of QCL-RS, related to the beam (cell) to be measured may be used only for event determination, or may be used for other purposes. For example, the setting of the beam to be measured may be performed as described above when measuring for periodic, semi-persistent, or aperiodic reporting instructed by the base station device 101. Note that, assuming that QCL-RS can be used, setting information specifying which of SSB, CSI-RS, and TRS is to be measured may be notified from the base station device 101 to the terminal device 111. For example, when the reference signal to be reported is CSI-RS, for a beam that transmits only SSB, the terminal device 111 may measure the radio quality of CSI-RS transmitted in other beams that have a QCL relationship with that beam, and report the measurement results to the base station device 101. Note that setting information for periodic, semi-persistent, and aperiodic reporting and setting information based on an event may be notified to the terminal device 111 in parallel. That is, the terminal device 111 may make an L1 measurement report based on the occurrence of an event, and may also make an L1 measurement report based on instructions from the base station device 101 even if no event occurs.

[0025] Furthermore, as described above, among the multiple TCIs configured by the RRC message, there may be activated TCIs and inactivated TCIs, and the radio quality of the reference signal in the inactivated TCI may be measured. The terminal device 111 may then compare the L1 radio quality of the reference signal in the activated TCI with that in the inactivated TCI to perform event determination. That is, the terminal device 111 can use only activated TCIs when performing data communication, but may measure the radio quality of the inactivated TCIs to determine handover by LTM. Furthermore, for example, with regard to the reference signal for the inactivated TCI, only the reference signal of the TCI designated as the QCL-RS of the activated TCI may be measured.

[0026] In response to the provision of the handover destination candidate beam (cell) configuration by LTM, the terminal device 111 continues to monitor the configured handover destination candidate beam (cell).Then, the terminal device 111 measures the wireless quality of the reference signal (SSB or CSI-RS) associated with and specified in the handover destination candidate beam (cell).For example, the terminal device 111 performs measurement of the wireless quality of L1 using parameters specified in ltm-CSI-ReportConfigToAddModList-r18 of the LTM candidate configuration included in the RRC message received from the base station device 101 in S203. Then, when the measurement result of the L1 wireless quality satisfies the set event conditions (for example, for a predetermined period specified by TimeToTrigger), the terminal device 111 transmits information on the L1 measurement result to the base station device 101 based on the setting information for reporting the wireless quality notified in S203. Note that the terminal device 111 may transmit a report of the measurement result to another base station device (for example, the base station device 102) that provides a candidate beam (cell) for the handover destination. The terminal device 111 transmits this measurement result report to the base station device 101 (or, in some cases, the base station device 102) by an L1 measurement report.

[0027] The number of beams for which the measurement results of wireless quality are to be reported may be variable. For example, the base station device 101 may notify the terminal device 111 of the number of beams for which the report is to be made as configuration information for the report, and the terminal device 111 may report information on the measurement results for the number of beams specified by the configuration information (or less than that number). In one example, assume that the terminal device 111 receives configuration information specifying "4" as the number of beams for which the report is to be made, and that the number of beams that satisfy the event conditions is "3." In this case, the terminal device 111 may transmit only a report on the three beams that satisfy the event conditions, or may transmit a report on four beams, including the three beams and one beam that does not satisfy the event conditions. The terminal device 111 may transmit a report of the measurement results based on the event, for example, via the MAC CE, DG (Dynamic Grant)-PUSCH / CG (Configured Grant)-PUSCH of the physical uplink shared channel (PUSCH). The terminal device 111 may also transmit a measurement report using uplink control information (UCI) on a physical uplink control channel (PUCCH). The terminal device 111 may also transmit a measurement report using a combination of the PUCCH and the PUSCH. For example, the terminal device 111 may transmit a small number of bits indicating whether an event has occurred using PUCCH format 0 / 1, and transmit detailed information related to the event using a subsequent PUSCH. The terminal device 111 may also transmit an L1 signal such as a scheduling request (SR) that is used only when an event has occurred, and transmit detailed information related to the event via a subsequent MAC CE. The detailed information may include information indicating a measurement value of the L1 radio quality. The detailed information may also include information identifying a beam for which the event condition is satisfied. The terminal device 111 may also transmit information indicating the L3 measurement results together with the L1 measurement results.

[0028] (Device Configuration) FIG. 3 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 301, a ROM 302, a RAM 303, a storage device 304, and a communication circuit 305. The processor 301 is a computer configured to include one or more processing circuits, such as a general-purpose CPU (Central Processing Unit) or an ASIC (Application Specific Integrated Circuit), and performs the overall processing of the device and each of the above-mentioned processes by reading and executing programs stored in the ROM 302 or the storage device 304. The ROM 302 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 303 functions as a workspace when the processor 301 executes a program and is also a random access memory that stores temporary information. The storage device 304 is configured, for example, by a removable external storage device. The communication circuit 305 is configured, for example, by a circuit for wireless communication of 5G or a successor standard. While FIG. 3 illustrates one communication circuit 305, the base station device 101 and the terminal device 111 may have multiple communication circuits. For example, the base station device 101 and the terminal device 111 may have wireless communication circuits for 5G and a successor standard, respectively, and a common antenna for these circuits. The base station device 101 and the terminal device 111 may also have separate antennas suitable for each standard. The base station device 101 may also have a wired communication circuit used when communicating with other base station devices or nodes in the core network. The terminal device 111 may also have a communication circuit compliant with a wireless communication standard other than a cellular communication standard, such as a wireless local area network (LAN) or Bluetooth (registered trademark). The base station device 101 and the terminal device 111 may have separate communication circuits 305 for each of the multiple available frequency bands, or may have a common communication circuit 305 for at least some of the frequency bands.

[0029] FIG. 4 shows an example of the functional configuration of the base station device 101. The base station device 101 includes, for example, a setting notification unit 401, a report receiving unit 402, and a communication control unit 403. Note that FIG. 4 only shows functions particularly related to this embodiment, and various other functions that the base station device 101 may have are omitted from the illustration. 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. 4 are shown schematically, and the respective functional blocks may be integrated or further subdivided. Each function in FIG. 4 may be realized, for example, by the processor 301 executing a program stored in the ROM 302 or the storage device 304, or by a processor within the communication circuit 305 executing predetermined software. The details of the processing performed by each functional unit will not be described here, and only their general functions will be outlined.

[0030] The setting notification unit 401 notifies the terminal device 111 of the measurement setting and reporting setting of the L1 wireless quality for LTM. For example, when connecting to the terminal device 111, the setting notification unit 401 provides the terminal device 111 with the measurement setting and reporting setting of the L3 wireless quality, and thereafter, in response to identifying a cell (beam) to be subjected to handover by LTM based on the measurement result at L3, the setting notification unit 401 can transmit L1 measurement and reporting setting information for LTM to the terminal device 111. This setting information includes, for example, event information specifying the conditions for reporting the measurement result. The event can include, for example, an event determined to be satisfied when the wireless quality (e.g., L1-RSRP) of the cell (beam) to be subjected to LTM exceeds a predetermined threshold. Furthermore, the event can include, for example, an event determined to be satisfied when the serving cell (beam) falls below a predetermined first threshold and the handover destination candidate cell (beam) exceeds a second threshold different from the first threshold. The setting notification unit 401 can also notify the terminal device 111 of parameters for communication with the handover destination cell (beam) by LTM. The report receiving unit 402 receives the measurement result of the wireless quality at L1 that the terminal device 111 performed based on the setting information notified by the setting notification unit 401. The report receiving unit 402 may receive the measurement result of the wireless quality at L3 prior to receiving the measurement result of the wireless quality at L1 or in parallel with receiving the measurement result. The communication control unit 403 decides to hand over the terminal device 111 to another cell (beam) based on the measurement report in the report receiving unit 402, and transmits a Cell Switch Command to the terminal device 111 to specify the handover destination cell (beam) and cause the terminal device 111 to perform the handover.

[0031] FIG. 5 shows an example of the functional configuration of the terminal device 111. The terminal device 111 includes, for example, a setting acquisition unit 501, a measurement reporting unit 502, and a communication unit 503. Note that FIG. 5 only shows functions particularly related to this embodiment, and various other functions that the terminal device 111 may have are omitted from the illustration. For example, the terminal device 111 naturally has other functions that terminal devices compliant with 5G or subsequent standards generally have. The functional blocks in FIG. 5 are shown schematically, and the respective functional blocks may be integrated or further subdivided. Each function in FIG. 5 may be realized, for example, by the processor 301 executing a program stored in the ROM 302 or the storage device 304, or by a processor within the communication circuit 305 executing predetermined software. The details of the processes performed by each functional unit will not be described here, and only their general functions will be outlined.

[0032] The setting acquisition unit 501 acquires setting information for L1 measurement and reporting for LTM from the base station device 101. The setting acquisition unit 501 receives setting information including, for example, information specifying a cell (or beam) to be measured and setting information for reporting. The setting information may include event information specifying conditions for reporting. The setting acquisition unit 501 may also receive setting information for L3 measurement and reporting. The setting acquisition unit 501 also acquires, for example, communication parameters to be used when connecting to a cell that is a candidate for LTM handover. Based on the setting information acquired by the setting acquisition unit 501, the measurement reporting unit 502 performs L1 measurement of a reference signal transmitted in a cell (or beam) that is a candidate for LTM handover destination, and determines whether the measurement result satisfies the event condition. If the measurement reporting unit 502 determines that the event condition is satisfied, it reports the measurement result to the base station device 101. Note that, for example, when the measurement reporting unit 502 receives an instruction for periodic, semi-persistent, or aperiodic reporting from the base station device 101, it can report the L1 measurement results to the base station device 101 in accordance with the instruction, regardless of whether the event conditions are satisfied. The measurement reporting unit 502 can also perform L3 measurements and report the measurement results to the base station device 101. The communication unit 503 performs communication with a destination base station device. For example, when the communication unit 503 receives a Cell Switch Command from the base station device 101, it can disconnect from the currently connected cell and perform handover (switching of the destination cell) by applying communication parameters previously received for LTM.

[0033] As described above, according to the present embodiment, an event-based reporting method is provided for reporting radio quality measurements for handovers using Layer 1 / Layer 2 Triggered Mobility (LTM). This prevents the time between the acquisition of measurement results and their reporting from becoming too long, and also prevents excessive resources from being reserved for reporting. This improves the efficiency of LTM. This makes it possible to contribute to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs), which is to "build resilient infrastructure, promote sustainable industrialization and foster innovation."

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

[0035] This application claims priority to U.S. Provisional Patent Application No. 63 / 570,380, filed March 27, 2024, the entire contents of which are incorporated herein by reference.

Claims

1. A terminal device conforming to the cellular communication standard of the Third Generation Partnership Project (3GPP), comprising: an acquisition means for acquiring from a connected base station device configuration information for measurement and reporting for handover by Layer 1 / Layer 2 Triggered Mobility (LTM), the configuration information including first information specifying a reference signal to be measured for a beam of a candidate cell as a handover destination for which the terminal device is to measure the wireless quality of Layer 1 (L1) in the terminal device, and second information indicating an event that specifies the conditions for reporting the wireless quality of L1 of the beam; a measurement means for measuring the wireless quality of L1 of the reference signal for the beam; a determination means for determining whether the result of the measurement satisfies the condition of the event; and a transmission means for transmitting a measurement report to the base station device when it is determined that the result of the measurement satisfies the condition of the event.

2. The terminal device described in claim 1, characterized in that the second information includes information on an event in which the condition is determined to be met when the wireless quality of L1 of the beam formed by the base station device and to which the terminal device is connected falls below a first threshold and the wireless quality of L1 of the beam of the candidate cell to which the handover is to be performed exceeds a second threshold different from the first threshold.

3. The terminal device according to claim 1, characterized in that the second information includes information of an event in which a condition is determined to be met when the wireless quality of L1 of the beam of the candidate cell for handover exceeds a predetermined threshold.

4. The terminal device according to claim 1, characterized in that the setting information includes information specifying other beams that are formed by the base station device and have a Quasi Co-Location (QCL) relationship with each of the first beam to which the terminal device is connected and the second beam of the handover destination candidate cell, and the determination means, when a first reference signal to be measured on the first beam and a second reference signal to be measured on the second beam are different types of reference signals, determines whether the condition for the event is satisfied by using the radio quality of L1 of a third reference signal that is transmitted on another beam that has a QCL relationship with the first beam and is of the same type as the second reference signal, instead of the radio quality of L1 of the first reference signal, or determines whether the condition for the event is satisfied by using the radio quality of L1 of a fourth reference signal that is transmitted on another beam that has a QCL relationship with the second beam and is the same type as the first reference signal, instead of the radio quality of L1 of the second reference signal.

5. The terminal device described in claim 1, characterized in that the measuring means further measures the wireless quality of Layer 3 (L3) for reference signals transmitted in beams that are not currently connected, the transmitting means transmits a report of the wireless quality of L3 to the base station device, and the setting information is provided from the base station device based on the fact that the base station device has started processing for handover by LTM based on the wireless quality of L3.

6. The terminal device according to claim 1, characterized in that the transmitting means transmits the measurement report to the base station device using at least one of a physical uplink control channel (PUCCH) and a physical uplink shared channel (PUSCH).

7. A base station device conforming to the cellular communication standard of the Third Generation Partnership Project (3GPP), comprising: a providing means for providing to a connected terminal device configuration information for measurement and reporting for handover by Layer 1 / Layer 2 Triggered Mobility (LTM), the configuration information including first information specifying a reference signal to be measured for a beam of a candidate cell as a handover destination for which the terminal device is to measure Layer 1 (L1) wireless quality, and second information indicating an event that specifies a condition for reporting the L1 wireless quality of the beam; a receiving means for receiving from the terminal device a measurement report regarding the result of measurement of the L1 wireless quality based on the configuration information; and a transmitting means for transmitting to the terminal device a command to hand over the terminal device based on the measurement report.

8. The base station device described in claim 7, characterized in that the second information includes at least one of information on an event in which a condition is determined to be met when the wireless quality of L1 of the beam formed by the base station device and to which the terminal device is connected falls below a first threshold and the wireless quality of L1 of the beam of the candidate cell for handover destination exceeds a second threshold different from the first threshold, and information on an event in which a condition is determined to be met when the wireless quality of L1 of the beam of the candidate cell for handover destination exceeds a predetermined threshold.

9. The base station device according to claim 7, characterized in that the setting information includes information specifying other beams that are formed by the base station device and have a Quasi Co-Location (QCL) relationship with each of the first beam to which the terminal device is connected and the second beam of the candidate cell to which the handover is to be performed.

10. The base station device described in claim 7, characterized in that the receiving means receives from the terminal device a report of Layer 3 (L3) wireless quality for a reference signal transmitted in a beam to which the terminal device is not connected, and the providing means initiates LTM handover processing for the terminal device based on the L3 wireless quality and provides the setting information to the terminal device.

11. The base station device according to claim 7, characterized in that the receiving means receives the measurement report from the terminal device via at least one of a physical uplink control channel (PUCCH) and a physical uplink shared channel (PUSCH).

12. A control method executed by a terminal device conforming to the cellular communication standard of the Third Generation Partnership Project (3GPP), comprising: acquiring, from a connected base station device, configuration information for measurement and reporting for handover by Layer 1 / Layer 2 Triggered Mobility (LTM), the configuration information including first information specifying a reference signal to be measured for a beam of a candidate cell as a handover destination for which the terminal device is to measure the wireless quality of Layer 1 (L1), and second information indicating an event that specifies a condition for reporting the wireless quality of L1 of the beam; measuring the wireless quality of L1 of the reference signal for the beam; determining whether the result of the measurement satisfies the condition of the event; and transmitting a measurement report to the base station device if it is determined that the result of the measurement satisfies the condition of the event.

13. A control method executed by a base station device compliant with the 3rd Generation Partnership Project (3GPP) cellular communication standard, comprising: providing, to a connected terminal device, configuration information for measurement and reporting for handover by Layer 1 / Layer 2 Triggered Mobility (LTM), the configuration information including first information specifying a reference signal to be measured for a beam of a candidate cell as a handover destination for measuring Layer 1 (L1) wireless quality in the terminal device, and second information indicating an event that specifies a condition for reporting the L1 wireless quality of the beam; receiving from the terminal device a measurement report regarding the result of measuring the L1 wireless quality based on the configuration information; and transmitting to the terminal device a command to handover the terminal device based on the measurement report.

14. A program for causing a computer provided in a terminal device conforming to the cellular communication standard of the Third Generation Partnership Project (3GPP) to execute the control method according to claim 12.

15. A program for causing a computer installed in a base station device conforming to the cellular communication standard of the Third Generation Partnership Project (3GPP) to execute the control method according to claim 13.

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