Terminal device and radio communications system

Abstract

To allow a terminal device to autonomously perform L1L2 triggered mobility (LTM) before receiving a Cell Switch command, thereby speeding up handover processing and shortening interruption times.SOLUTION: A terminal device that communicates with multiple base station devices while switching connection destinations acquires communication parameters and information on conditions for L1L2 triggered mobility (LTM) implementation associated with at least one candidate handover destination base station device, determines whether the conditions for LTM implementation associated with the candidate handover destination base station device are satisfied before receiving a Cell Switch Command from a source base station device that instructs a change of connection destination cell, and, transmits an RA preamble to the candidate handover destination base station device associated with the conditions for LTM implementation when the conditions for LTM implementation are satisfied.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present disclosure relates to a terminal device and a wireless communication system. [Background technology]

[0002] In a mobile communication system, as a terminal device moves, a handover is performed to switch the cell (base station device) to which the terminal device is connected. Conventionally, after receiving a handover instruction from the base station device, the terminal device performs a process of establishing a connection by performing a synchronization establishment and setting process in the cell to which the connection is to be switched. This process for switching the connection takes a certain amount of time, and the terminal device cannot communicate user data during the period in which this process is being performed. In contrast, in the method described in Non-Patent Document 1, the handover source base station device provides the terminal device with communication parameters in the radio resource control (RRC) layer for connection with another base station device at the handover destination before the handover is actually performed. Then, the handover source base station device transmits a layer 1 or layer 2 command to the terminal device to instruct the cell switching at the timing when the handover should be performed. In response to receiving the command, the terminal device executes a random access procedure with the handover destination base station device, thereby completing the handover without performing a setting process in the RRC layer thereafter. Such a cell switching technology is called LTM (L1L2 Triggered Mobility) and is intended to suppress deterioration of communication efficiency related to handover. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] 3GPP (registered trademark) Contribution, R2-2209255 Summary of the Invention [Problem to be solved by the invention]

[0004] In the handover process by LTM disclosed in Non-Patent Document 1, the terminal device needs to receive a Cell Switch command from the base station device. However, if the Cell Switch Command cannot be received, the terminal device cannot spontaneously start handover processing, and must execute cell search processing and reconnection processing after detecting RLF (Radio Link Failure). Therefore, the LTM technology of Non-Patent Document 1 has a problem that it cannot shorten the communication interruption time and cannot speed up the handover processing.

[0005] In view of such circumstances, the present disclosure proposes a technology that enables a terminal device to perform LTM before receiving a Cell Switch command, thereby speeding up handover processing and shortening the interruption time. [Means for solving the problem]

[0006] In order to solve the above problems, the present disclosure proposes, as an example, a terminal device that communicates with a plurality of base station devices while switching connection destinations, the terminal device including: a storage device that stores a program related to handover; and a processor that reads the program from the storage device and executes handover processing, wherein the processor executes the following processes: a process of acquiring communication parameters and information on conditions for LTM implementation associated with at least one handover destination candidate base station device from a connected handover source base station device; a process of determining whether the conditions for LTM implementation associated with the handover destination candidate base station device are satisfied before receiving a Cell Switch Command from the handover source base station device that instructs a change of connection destination cell; and a process of transmitting an RA preamble to the handover destination candidate base station device associated with the conditions for LTM implementation when the conditions for LTM implementation are satisfied.

[0007] Further features related to the present disclosure will become apparent from the description of the present specification and the accompanying drawings. Also, aspects of the present disclosure may be realized and realized by the elements and combinations of various elements and aspects of the following detailed description and the appended claims. The descriptions in this specification are exemplary and illustrative only and are not intended to limit the scope or application of the present disclosure in any way. Effect of the Invention

[0008] According to the technique disclosed herein, even if a terminal device cannot receive a Cell Switch command, it is possible to perform handover processing, thereby realizing faster processing and shorter interruption time. [Brief description of the drawings]

[0009] [Figure 1] 1 is a diagram illustrating an example of a schematic configuration of a wireless communication system according to an embodiment of the present invention. [Diagram 2] FIG. 1 is a diagram illustrating an example of a schematic configuration of a base station device 100 according to the present embodiment. [Diagram 3] FIG. 2 is a diagram illustrating an example of a schematic configuration of a terminal device 200 according to the present embodiment. [Figure 4] FIG. 11 is a diagram for explaining sequence example 1 of handover processing according to the present embodiment (in the case of contention-free RA). [Diagram 5] FIG. 11 is a diagram for explaining a second sequence example (in the case of contention-based RA) of handover processing according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] This embodiment discloses performing LTM to a candidate cell before a terminal device receives a Cell Switch Command from a handover source base station device. The technology according to this embodiment is not limited to this, but can be applied to, for example, wireless communication in the frequency band FR1 (410 MHz to 7125 MHZ). Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. In the accompanying drawings, functionally identical elements may sometimes be denoted by the same number. Although the accompanying drawings show specific embodiments in accordance with the principles of the present disclosure, these are for the purpose of understanding the present disclosure and are by no means used to limitatively interpret the present disclosure.

[0011] In this embodiment, although the description is in sufficient detail for those skilled in the art to implement the present disclosure, other implementations and forms are possible, and it is necessary to understand that changes in configuration and structure and replacement of various elements can be made without departing from the scope and spirit of the technical idea of the present disclosure. Therefore, the following description should not be construed as being limited thereto.

[0012] <Schematic configuration example of the system> FIG. 1 is a diagram showing a schematic configuration example of a wireless communication system according to this embodiment. The wireless communication system is a cellular communication system configured according to a cellular communication standard such as the fifth generation (5G) of the 3rd Generation Partnership Project (3GPP (registered trademark)) and its successor standards. The wireless communication system includes a plurality of base station devices (base station devices 100_1, 100_2,...) and a terminal device 200.

[0013] In FIG. 1, the terminal device 200 is about to move from within the cell range formed by the base station device (handover source base station device) 100_1 to within the cell range formed by the base station device (handover destination base station device) 100_2. At this time, the terminal device 200 will perform a handover to switch the connected base station device from the handover source base station device 100_1 to the handover destination base station device 100_2. Although only the handover destination base station device 100_2 is shown as a handover destination candidate in FIG. 1, actually, there may be a plurality of handover destination candidates (handover destination base station devices 100_3, 100_4,..., 100_k,...).

[0014] <Regarding the conditions (events) for LTM implementation> In the LTM according to the present embodiment, the terminal device 200 starts connection processing and cell switching processing with the handover destination base station device 100_2 and other handover destination candidate base station devices (handover destination base station device 100_k: k=3, 4, . . . ) without receiving a command (Cell switch command) instructing cell switching from the handover source base station device 100_1. As an example, the terminal device 200 acquires, from the handover source base station device 100_1, information on a condition (event) for starting the cell switching processing and on a cell switching processing to be performed when the condition is determined to be met, and then determines whether the condition is met and performs the cell switching processing according to the condition. For example, it is assumed that the cell switching processing to the handover destination base station device 100_2 is associated with the condition 1, and the cell switching processing to another handover destination candidate base station device (handover destination base station device 100_3) is associated with the condition 2. In this case, when it is determined (confirmed) that condition 1 is met, the terminal device 200 executes a cell switching process to the base station device 100_2. On the other hand, when it is determined (confirmed) that condition 2 is met, the terminal device 200 starts a cell switching process to another handover destination candidate base station device (handover destination base station device 100_3). A plurality of pieces of information on the condition and the cell switching process are included in a message RRC Reconfiguration of an RRC (Radio Resource Control) layer, and a condition set for each candidate cell is included in condExecutionCond. In addition, a communication parameter used for communication with the handover destination candidate base station device is included in condLTMReconfig. These pieces of information are provided from the handover source base station device 100_1 to the terminal device 200.

[0015] <Specific examples of the above conditions (events)> As a condition (event) for performing LTM, for example, a condition related to the radio quality of a communicating cell or a candidate cell (CondEventA3, CondEventA4, CondEventA5, CondEventD1, CondEventT1) may be set. In this case, for example, RRC Reconfiguration includes information such as condExecutionCond=condEventA4 (threshold=threshold 1) and condLTMReconfig=communication parameters for candidate cell 1 for condReconfigId (condition setting identifier)=1, and condExecutionCond=condEventA4 (threshold=threshold 2) and condLTMReconfig=communication parameters for candidate cell 2 for condReconfigId=2, and this information is provided to the terminal device 200. Conventionally, it is considered that the base station device 100 sets information (MeasId) for setting a report of an event occurrence to the terminal device 200 in condExecutionCond. Here, MeasId is associated with an identifier measObjectId used by the terminal device to identify a measurement target of wireless quality and an identifier reportConfigId used by the terminal device to identify a report timing to the base station device. The identifier measObjectId is associated with an NR or LTE frequency to be measured by the terminal device 200. The identifier reportConfigId is associated with a report timing to the base station device 100, for example, an event of condEventA4 and a threshold value related to the event. In this way, the terminal device 200 can recognize an event of wireless quality to be determined from MeasId set in condExecutionCond.

[0016] <Internal configuration example of base station equipment> FIG. 2 is a diagram showing a schematic configuration example of the base station device 100. The base station device 100 includes, for example, a processor 101, a storage device 102, a ROM (Read Only Memory) 103, a RAM (Random Access Memory) 104, and a communication device 105. The processor 101 is a computer including 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 a program stored in the storage device 102 or the ROM 103. The ROM 103 is a read-only memory that stores information such as a program related to the processing executed by the base station device 100 and various parameters. The RAM 104 functions as a workspace when the processor 101 executes a program, and is a random access memory that stores temporary information. The storage device 102 is, for example, configured by a removable external storage device. The communication device 105 is, for example, configured by a circuit for wireless communication of 5G or its successor standard. Although one communication device 105 is shown in FIG. 2, the base station device 100 may include multiple communication devices. For example, the base station device 100 has wireless communication devices for 5G and its successor standards, and an antenna common to these devices. The base station device 100 may have separate antennas suitable for each standard. The base station device 100 may also have a wired communication device used when communicating with other base station devices or nodes of the core network. The base station device 100 may have separate communication devices 105 for each of a plurality of available frequency bands, or may have a common communication device 105 for at least some of these frequency bands.

[0017] The processor 101 reads a program related to handover stored in the memory device 102 or the ROM 103 and expands it into an internal memory (not shown), thereby generating an RRC setting unit 1011, an RA instruction unit 1012, a handover instruction unit 1013, an inter-base station communication unit 1014, a TA maintenance management unit 1015, and a PUCCH / PDCCH communication unit 1016.

[0018] Each processing unit generated in the processor 101 in FIG. 2 mainly corresponds to the function of the handover source base station device 100_1 to which the terminal device 200 is connected. The handover destination (candidate) base station device 100_2 is similar to the base station device 100_1 except that it does not transmit some signals of the RA procedure and may transmit some signals to the base station device 100_2, so it is not illustrated here. Also, FIG. 2 shows only functions particularly related to this embodiment, and other various functions that the base station device 100 may have are not illustrated. For example, the base station device 100 naturally has other functions that a base station device conforming to 5G or its successor standards generally has. Also, the functional blocks in FIG. 2 are shown in a schematic manner, and each functional block may be realized as an integrated unit, or may be further subdivided. Also, each function in FIG. 3 may be realized, for example, by the processor 101 executing a program stored in the ROM 103 or the storage device 102, or may be realized, for example, by a processor present in the communication device 105 executing predetermined software. Note that the details of the processes executed by each functional unit will not be described here, and only the general functions thereof will be outlined.

[0019] The RRC setting unit 1011 of the handover source base station device 100_1, for example, performs RRC layer setting for the connected terminal device 200. The RRC setting unit 1011 transmits a handover request to other candidate base station devices 100 (such as the handover destination base station device 100_2 and the handover destination base station device 100_3) that provide neighboring cells, acquires communication setting information (communication parameters) therefrom, and notifies the terminal device 200 of the communication setting information and the above-mentioned LTM implementation condition (communication parameters of each candidate cell and LTM implementation condition) by a message of the RRC layer. In this case, the above-mentioned communication setting information (communication parameters) also includes information required when the terminal device 200 executes a random access procedure (such as a sequence for generating an RA preamble and information on radio resources used for transmitting an RA preamble). In this embodiment, the message of the RRC layer is an RRC Configuration message. Then, the RRC setup section 1011 receives an RRC Configuration Complete message from the terminal device 200, and thereby performs connection processing setup between the terminal device 200 and another base station device 100 (handover destination base station device 100_2).

[0020] The RA instruction unit 1012 instructs the terminal device 200 for which the RRC layer setting has been completed to transmit an RA preamble to another base station device 100 (handover destination base station device 100_2) that is a candidate for the handover destination. Here, the instruction to transmit the RA preamble includes a sequence for generating an RA preamble specific to the terminal device 200 and a group of sequences that can also be used by other terminal devices 200 that are attempting to connect to the other base station devices 100, and also includes information on radio resources used to transmit the RA preamble. For example, the RA instruction unit 1012 can instruct the currently connected terminal device 200 to transmit an RA preamble to the handover destination base station device 100_2 (candidate 1) by a physical downlink control channel (PDCCH) order. In addition, the RA instruction unit 1012 can instruct the terminal device 200 to retransmit the RA preamble as necessary, or, when configured to repeatedly transmit the RA preamble, transmit an instruction to stop transmitting the RA preamble to the terminal device 200.

[0021] The handover instruction unit 1013 of the handover source base station device 100_1 instructs the terminal device 200 to execute handover. The handover instruction unit 1013 transmits, for example, a Cell switch command including information such as a cell identifier capable of identifying the handover destination base station device 100_2 to the terminal device 200. Note that, when a TA (Timing Advance) value used for uplink communication is determined by the transmission of an RA preamble by the terminal device, the TA value can be included in the command transmitted to the terminal device 200. This enables the terminal device 200 to transmit an uplink user data signal using the TA value immediately after handover.

[0022] The inter-base station communication unit 1014 of the base station device 100_1 communicates (for example, communication via a dedicated wired line) with each handover destination candidate base station device (handover destination base station device 100_2, 100_3, etc.). The inter-base station communication unit 1014 can, for example, notify the handover destination base station device 100_2, which is the transmission destination of the RA preamble, to cause the connected terminal device 200 to transmit the RA preamble. The inter-base station communication unit 1014 is also used, for example, to receive information for the RA procedure in the handover destination candidate base station device (handover destination base station device 100_2). The inter-base station communication unit 1014 can also receive, for example, a message (message 2 or message 4) to be transmitted from the handover destination base station device 100_2 to the terminal device 200 in the RA procedure. Furthermore, the handover source base station 100_1 can acquire the TA value calculated in the handover destination base station device 100_2 via the inter-base station communication unit 1014. Note that the signal received in the inter-base station communication unit 1014 is transferred to the terminal device 200 via, for example, the RA instruction unit 1012 or the like.

[0023] The TA maintenance management unit 1015 of the handover source base station 100_1 manages a TA value to be used when the terminal device 200 transmits an uplink signal to the handover destination base station device 100_2. The TA maintenance management unit 1015 can, for example, set an expiration date or an update period of the TA value, and instruct the terminal device 200 to retransmit an RA preamble so that the TA value is updated when the expiration date expires or the update period arrives. The TA maintenance management unit 1015 can also notify the terminal device 200 of an SRS setting in the handover destination base station device 100_2, and update the TA value by having the terminal device 200 transmit an SRS using the SRS setting. The terminal device 200 can acquire the TA value via the TA maintenance management unit 1015 of the handover destination base station device 100_2. In this case, the base station device 100_2 can transmit an instruction to transmit an RA preamble or an instruction to transmit an SRS to the terminal device 200.

[0024] The PUCCH / PDCCH / RA communication unit 1016 operates, for example, when the base station device 100 becomes the handover destination base station device 100_2. As described above, when the handover destination base station device 100_2 notifies the handover source base station device 100_1 of communication setting information (communication parameters), the handover destination base station device 100_2 can start receiving a PUCCH and transmitting a PDCCH and receiving an RA preamble between the terminal device 200. For example, as described above, when performing (continuing) a conditional handover, the PUCCH / PDCCH / RA communication unit 1016 can receive an RA preamble from the terminal device 200 and transmit an RA response to the terminal device 200 in order to execute an RA (random access) procedure.

[0025] <Example of the internal configuration of a terminal device> FIG. 3 is a diagram showing a schematic configuration example of the terminal device 200. The terminal device 200 includes, for example, a processor 201, a storage device 202, a ROM (Read Only Memory) 203, a RAM (Random Access Memory) 204, a communication device 205, an input device 206, and an output device 207. The processor 201 is a computer including 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 a program stored in the storage device 202 or the ROM 203. The ROM 203 is a read-only memory that stores information such as programs and various parameters related to the processing executed by the terminal device 200. The RAM 204 functions as a workspace when the processor 201 executes a program, and is a random access memory that stores temporary information. The storage device 202 is, for example, configured by a removable external storage device. The communication device 205 is configured by, for example, a circuit for wireless communication of 5G or a successor standard. Although one communication device 205 is shown in FIG. 3, the terminal device 200 may include a plurality of communication devices. For example, the terminal device 200 has a wireless communication device for each of 5G and its successor standard, and an antenna common to those devices. The terminal device 200 may also have a communication device conforming to a wireless communication standard other than the cellular communication standard, such as a wireless local area network (LAN) or Bluetooth (registered trademark). Furthermore, the terminal device 200 may have a separate antenna suitable for each standard. The terminal device 200 may also have a separate communication device 105 for each of a plurality of available frequency bands, or may have a common communication device 205 for at least a part of those frequency bands.

[0026] The input device 206 can be configured, for example, by a touch panel or a numeric keypad, and is used when a user performs a predetermined operation or inputs desired information. The output device 207 can be configured, for example, by a display device, and in relation to this embodiment, displays information indicating the communication status, information indicating the success or failure of handover, and the like.

[0027] The processor 201 reads a program related to handover stored in the storage device 202 or the ROM 23, and develops it in an internal memory (not shown), thereby generating an RRC setting unit 2011, an RA (random access) execution unit 2012, an LTM implementation condition determination unit 2014, a handover processing unit 2013, and a timer control unit 2015. Note that FIG. 3 shows only functions particularly related to the present embodiment, and other various functions that the terminal device 200 may have are omitted from the illustration. For example, the terminal device 200 naturally has other functions that terminal devices conforming to 5G and its successor standards generally have. Also, the functional blocks in FIG. 3 are shown in a schematic manner, and each functional block may be realized as an integrated unit, or may be further subdivided.

[0028] The RRC setup unit 2011 performs a connection setup process with a handover destination base station device (candidate 1) 100_2 by receiving an RRC layer message from the connected handover source base station device 100_1. The RRC setup unit 2011 holds the setting of the connected handover source base station device 100_1 and the settings of a plurality of handover destination candidate base station devices (handover destination base station devices 100_k: k=2, 3, 4, . . . , n) in parallel.

[0029] The RA executor 2012 receives an instruction to transmit an RA preamble from the handover source base station device 100_1. The instruction to transmit the RA preamble is performed in the PDCCH order. The RA executor 2012 can also receive, for example, an instruction to retransmit the RA preamble or an instruction to stop transmitting the RA preamble. In response to receiving the instruction to transmit the RA preamble, the RA executor 2012 transmits the RA preamble to the handover destination (candidate 1) base station device 100_2. Here, a sequence for generating the RA preamble and information on radio resources for receiving the RA preamble in the handover destination base station device (candidate 1) 100_2 are acquired from the currently connected handover source base station device 100_1. The information on the sequence and radio resources may be acquired from system information transmitted by the handover destination base station device 100_2.

[0030] In response to receiving the Cell Switch command from the currently connected handover source base station device 100_1, the handover processing unit 2013 changes the connection destination to the handover destination base station device (candidate 1) 100_2. When the allocation of uplink radio resources in the handover destination base station device 100_2 is notified in the received Cell Switch command, the terminal device 200 can immediately transmit an uplink signal using the radio resources.

[0031] Meanwhile, the handover processing unit 2013 instructs the LTM execution condition determination unit 2014 to determine whether the above-mentioned LTM execution condition is met. That is, the LTM execution condition determination unit 2014 determines whether the LTM execution condition associated with the plurality of candidate cells notified from the handover source base station device 100_1 is met. If the condition is met, the handover destination to be executed is uniquely determined. For example, the LTM execution condition is determined such that a threshold included in the communication parameters is set low for a candidate cell with a good (not congested) communication situation, and a threshold is set high for a candidate cell with a bad (congested) communication situation.

[0032] When the LTM execution condition determination unit 2014 determines (confirms) that the conditions for LTM execution are met, the handover processing unit 2013 performs handover processing including RA execution processing on the candidate cell (handover destination base station apparatus 100_k) that satisfies the conditions (details will be described later). For example, when it is determined that the conditions for LTM execution associated with the handover destination base station apparatus 100_2 of candidate 1 are satisfied, the handover processing unit 2013 can spontaneously execute handover processing in the same manner as when the Cell Switch Command is received, even when the Cell Switch Command cannot be received. Therefore, it is not necessary to execute the reconnection process starting from cell search, and cell switching can be performed quickly.

[0033] The timer control unit 2015 controls the start and stop of various timers (such as T304) described later. For example, the timer (T304) starts when it is confirmed that the conditions for LTM execution are met and LTM execution is determined, and stops when the UE Contention Resolution Identity MAC CE or C-RNTI addressed PDCCH is received from the connected destination base station apparatus 100.

[0034] <Operation at the time of RLF detection> As described above, for the conditions for LTM execution specified by the handover source base station apparatus 100_1, when the terminal device 200 determines (confirms) that the conditions are met, it starts the cell switching process. On the other hand, when the terminal device 200 detects an RLF (radio link failure), even if the conditions are not met, it may start the cell switching process.

[0035] When providing the terminal device 200 with the condition for performing LTM and information (communication parameters) related to the cell switching process associated with the condition for each candidate cell, the handover source base station device 100_1 also provides information of attemptCondReconfig=True / False. When detecting RLF (radio link failure), the terminal device 200 searches for and selects a cell to be used for communication. When attemptCondReconfig notified together with the information related to the cell switching process is True, the terminal device 200 determines whether the cell selected after the search is a candidate base station device (handover destination base station device 100_k) of the handover destination designated in the cell switching process. When it is determined that the cell is not the handover destination base station device designated in the cell switching process, the terminal device 200 performs reconnection processing as in the past. When the cell is the handover destination base station device designated in the cell switching process (any of the notified candidate cells), the terminal device 200 starts the cell switching process even if the condition is not met. This makes it possible to shorten the instantaneous interruption time.

[0036] <Example of handover processing sequence (in the case of contention-free RA)> FIG. 4 is a diagram for explaining a sequence example (in the case of contention-free RA) of handover processing executed when the condition for performing LTM is met without receiving a Cell Switch Command according to the present embodiment. The sequence shown in FIG. 4 is an example, and each procedure can be modified as described above. For example, FIG. 4 shows an example in which a unique sequence is notified to the terminal device 200 as a sequence for generating an RA preamble to be transmitted to the handover destination base station device 100_2, but it may be replaced with the above-mentioned procedure in which a group of sequences available to the multiple terminal devices 200 is notified. Note that in the example of FIG. 4, a connection is established between the handover source base station device 100_1 and the terminal device 200. In each step, the operation is performed by each processing unit (such as the RRC setting unit 1011), but since each processing unit is a function realized by the processor 101 or 201 of the base station device 100 or the terminal device 200, the processor 101 or 201 may be the operation unit. In the following description, the respective processing units of the handover source base station device 100_1 are represented as an RRC setting unit 1011_1, an RA instruction unit 1012_1, a handover instruction unit 1013_1, an inter-base station communication unit 1014_1, a TA maintenance management unit 1015_1, and a PUCCH / PDCCH communication unit 1016_1. The respective processing units of the handover destination base station device 100_2 are represented as an RRC setting unit 1011_2, an RA instruction unit 1012_2, a handover instruction unit 1013_2, an inter-base station communication unit 1014_2, a TA maintenance management unit 1015_2, and a PUCCH / PDCCH communication unit 1016_2. Furthermore, in each of the following steps, various communications are actually performed by the respective processing units of the base station device and the terminal device controlling the communication device 105 and the communication device 205.

[0037] (i) Step S401 The inter-base station communication unit 1014_1 of the handover source base station device 100_1 transmits a HANDOVER REQUEST message to the inter-base station communication unit 1014_2 of the handover destination base station device 100_2 that forms an adjacent cell and is a candidate for the handover destination of the terminal device 200, or to other base station devices (other candidate cells: the inter-base station communication unit 1014_k of the handover destination base station device 100_k (k=3, 4, ...)).

[0038] (ii) Step S402 When the inter-base station communication unit 1014_2 of the handover destination (candidate 1) base station device 100_2 receives the HANDOVER REQUEST message, it returns a HANDOVER REQUEST ACK message including information on communication parameters to be used when the terminal device 200 connects to the handover source base station device 100_1. The communication parameters include CG (Configured Grant) setting information including information on beam settings, parameters for executing a RA (Random Access) procedure, radio resources (frequency and time resources) to be used, etc. in the handover destination base station device 100_2. Other candidate cell base station devices similarly provide communication parameters to the handover source base station device 100_1.

[0039] (iii) Step S403 The RRC setting unit 1011_1 of the handover source base station device 100_1 notifies the terminal device 200 of an LTM Configuration message including the above-mentioned communication parameters acquired from the handover destination base station device 100_2. At this time, the RRC setting unit 1011_1 provides the terminal device 200 with a condition (event: condition for LTM implementation) enabling the implementation of LTM before the terminal device 200 receives a Cell Switch Command handover. With this process, the terminal device 200 does not need to perform an RRC layer configuration process after being instructed by the RA instruction unit 1012_1 to perform a handover to the handover destination base station device 100_2. Note that, although FIG. 4 shows a case where there is only one handover destination base station device, when there are multiple handover destination (candidate) base station devices, a similar configuration process is performed for each of them.

[0040] The RRC setting unit 2011 of the terminal device 200 receives, by the LTM Configuration message, for example, a measurement instruction for a synchronization signal (SS) / physical broadcast channel (PBCH) block (SSB: Synchronization Signal Block) transmitted from the handover destination base station device 100_2, an SSB index, CG (Configured grant) setting information related to uplink resources, and information associating uplink beam information. If the SSB index=1, the terminal device 200 uses the first CG setting information and beam information, and if the SSB index=2, the terminal device 200 uses the second CG setting information and beam information.

[0041] For example, when the handover processing unit 2013 of the terminal device 200 measures a radio signal (e.g., SSB) transmitted from the handover destination base station device 100_2, it notifies the handover source base station device 100_1 of the measurement result of the SSB. Here, the inter-base station communication unit 1014_1 of the handover source base station device 100_1 may notify the inter-base station communication unit 1014_2 of the handover destination base station device 100_2 of the measurement result. In this case, the handover destination base station device 100_2 can specify a rough beam to be used for communication with the terminal device 200. Note that the handover instruction unit 1013 of the handover destination base station device 100_2 may transmit the CSI-RS and cause the terminal device 200 to measure in order to form a finer beam. In this case, the inter-base station communication unit 1014_1 of the handover destination base station device 100_2 transmits setting information of the CSI-RS to the handover source base station device 100_1. The handover instruction unit 1013_2 of the handover source base station device 100_1 can transfer the setting information to the terminal device 200. The terminal device 200 may measure the CSI-RS based on the setting information and report the measurement result to the connected handover source base station device 100_1. Then, the inter-base station communication unit 1014_1 of the handover source base station device 100_1 transfers the measurement result to the handover destination base station device 100_2. This enables the handover instruction unit 1013_2 of the handover destination base station device 100_2 to transmit a downlink signal using a fine beam immediately after the terminal device 200 is handed over to the handover destination base station device 100_2.

[0042] When a RLF (Radio Link Failure) occurs, the terminal device 200 measures the SSB of the candidate cell (handover destination base station device 100_2) and determines whether or not it is in a state where it can be connected. If it is determined that it can be connected, the terminal device 200 can identify the radio resource and the uplink beam to be used for uplink transmission from the SSB index using the information received in the LTM Configuration, and can start communication.

[0043] (iv) Step S404 The handover instruction unit 1013_1 of the handover source base station device 100_1 transmits a Cell Switch Command including the TA value of the handover destination base station device 100_ to the terminal device 200. The Cell Switch Command can be transmitted by using, for example, a medium access control element (MAC CE) or downlink control information (DCI).

[0044] When the handover processing unit 2013 of the terminal device 200 receives the Cell Switch Command, a PUSCH resource is allocated by the handover destination base station device 100_2. Then, the terminal device 200 becomes able to transmit user data to the handover destination base station device 100_2 by using the allocated PUSCH resource. Note that the terminal device 200 has already executed the RA procedure as described above. Therefore, when the terminal device 200 can receive the Cell Switch Command, it is not necessary to execute the RA procedure again, and the terminal device 200 can immediately transmit user data to the handover destination base station device 100_2 by using the designated radio resource.

[0045] Also, when the Cell Switch Command is received, the handover processing unit 2013 of the terminal device 200 may transmit an acknowledgement (Ack) or the like to the handover source base station device 100_1. Furthermore, when the Cell Switch Command is received, the handover processing unit 2013 may switch the connection destination to the handover destination base station device 100_2 and transmit an Ack, an RRCReconfigurationComplete, or the like to the handover destination base station device 100_2 by using the allocated uplink radio resource. Then, the inter-base station communication unit 1014 of the handover destination base station device 100_2 can transfer the acknowledgement to the handover source base station device 100_1. Thereby, the handover source base station device 100_1 can recognize that the terminal device 200 has switched the connection destination to the handover destination base station device 100_2, and can discard, for example, the context information of the terminal device 200.

[0046] (v) Step S405 After transmitting the RA preamble in step S405 (after executing RA), the LTM implementation condition determination unit 2014 of the terminal device 200 determines (confirms) whether the above-mentioned LTM implementation condition is met (satisfied). Specifically, the LTM implementation condition determination unit 3014 determines whether the LTM implementation condition corresponding to each candidate cell notified from the handover source base station device 100_1 is satisfied.

[0047] (vi) Step S406 When the LTM execution condition determination unit 2014 of the terminal device 200 confirms that the conditions for performing LTM are met, the handover processing unit 2013 decides to execute cell switching processing to the handover destination base station device 100_k of the candidate cell corresponding to the condition match. Note that, when there are multiple candidate cells that meet the conditions for performing LTM, for example, the candidate cell with the shortest distance between the terminal device 200 and each handover destination base station device 100_k may be selected as the switching destination, or the candidate cell with the lowest congestion degree may be selected as the switching destination.

[0048] (vii) Step S407 When it is confirmed that the conditions for implementing LTM are met, the timer control unit 2015 of the terminal device 200 starts a timer (T304).

[0049] (viii) Step S408 The RA execution unit 2012 of the terminal device 200 transmits an RA preamble to a handover destination base station device (for example, the handover destination base station device 100_2) designated in the cell switching process associated with the condition.

[0050] (ix) Step S409 When the PUCCH / PDCCH communication unit 1016_2 of the handover destination base station device 100_2 receives the RA preamble transmitted from the terminal device 200 on the PUCCH, it transmits an RA response (UL grant) on the PDCCH to the terminal device 200, and notifies the terminal device 200 of the TA value of the handover destination base station device 100_2 and information regarding the radio resources to be used for uplink transmission.

[0051] (x) Step S410 The handover processing unit 2013 of the terminal device 200 transmits an RRCReconfigurationComplete to the handover destination base station device 100_2 at the instructed transmission timing of a PUSCH (Physical Uplink Shared Channel).

[0052] (xi) Step S411 If the Random Access procedure is successful, the timer control unit 2015 of the terminal device 200 stops the timer (T304) started in step S407. However, the timer stopping operation when the Random Access procedure is successful differs depending on whether the case is contention-free or contention-based.

[0053] In the case of CFRA (contention free), the MAC that received the Random Access Response notifies the RRC of the successful completion of the Random Access procedure. When the RRC processing unit in the terminal device receives the successful completion of the Random Access procedure from the MAC processing unit in the terminal device, the timer control unit 2015 determines that the cell switching process is successful and stops T304.

[0054] After the cell switching, the terminal device 200 may hold information condLTMReconfig related to the cell switching process. By the terminal device 200 holding the information related to the cell switching process even after the cell switching, it is possible to eliminate the need to newly receive condLTMReconfig from the base station device after the cell switching. Also, information related to whether or not to hold the information condLTMReconfig related to the cell switching process may be notified to the terminal device 200 from the handover source base station device 100_1 before the cell switching. As an example, it may be notified to hold only information related to the cell switching process that has not been executed and to delete information related to the cell switching process that has been executed.

[0055] In this manner, it is possible to shorten the period (instantaneous interruption time) during which communication of user data cannot be performed when the terminal device 200 is handed over from the handover source base station device 100_1 to the handover destination base station device 100_2. This makes it possible to provide, for example, communication services that require low delay and high reliability. In addition, by shortening the period (instantaneous interruption time) during which communication of user data cannot be performed, it is possible to suppress a decrease in efficiency of wireless communication.

[0056] <Example of handover processing sequence (in the case of contention-based RA)> FIG. 5 is a diagram for explaining a sequence of handover processing (in the case of contention-based RA) that is executed when the conditions for implementing LTM are met without receiving a Cell Switch Command according to this embodiment.

[0057] (i) Steps S501 to S510 This is the same process as steps S401 to S410 in FIG. (ii) Step S511 In the case of CBRA (contention based), the handover processing unit 2013 of the terminal device 200 transmits its own ID (C-RNTI or Temporary C-RNTI) to the handover destination base station device 100_2. Thereafter, when the handover processing unit 2013 receives DCI transmitted on the PDCCH addressed to its own ID (C-RNTI or Temporary C-RNTI) from the handover destination base station device 100_2, it determines that the Contention Resolution is successful. When it determines that the Contention Resolution is successful, the MAC processing unit in the terminal device 200 notifies the RRC processing unit in the terminal device 200 of successful completion of the Random Access procedure. When the RRC processing unit in the terminal device 200 receives successful completion of the Random Access procedure from the MAC processing unit in the terminal device, it is determined that the cell switching process is successful, and the timer control unit 2015 stops the timer (T304).

[0058] <Summary of the embodiment> (i) The terminal device 200 acquires communication parameters and information on the condition for performing LTM associated with the handover destination base station device (handover destination candidate base station device) 100_k (k=2, 3, 4, . . . n) from the handover source base station device 100_1. Then, the handover source base station device 100_1 transmits a Cell Switch Command instructing the terminal device 200 to change the connection destination cell. Before receiving the Cell Switch Command, the terminal device 200 determines whether the condition for performing LTM associated with the handover destination base station device 100_2 is satisfied. If the condition for performing LTM is satisfied, the terminal device 200 transmits an RA preamble to the handover destination base station device 100_2 associated with the condition for performing LTM. In this way, the handover process is resumed without waiting for detection of RLF, so that the handover process can be accelerated and the instantaneous interruption time can be shortened.

[0059] The information on the conditions for performing LTM provided from the handover source base station device 100_1 to the terminal device 200 together with the communication parameters includes CondEventA3, CondEventA4, CondEventA5, CondEventD1, and CondEventT1, which are defined in the 3GPP standard. This makes it possible to realize the LTM according to the present embodiment by utilizing the current 3GPP standard.

[0060] (ii) Furthermore, when the terminal device 200 detects a radio link failure (RLF), even if it cannot confirm that the conditions for performing LTM are satisfied, if it can be confirmed that the cell to which the cell is switched by performing LTM has the minimum radio quality that can be used for communication (for example, if the cell to which the cell is switched satisfies the cell selection criterion S), the terminal device 200 determines to perform LTM and executes a process of transmitting an RA preamble to the corresponding handover destination base station device 100_k. On the other hand, when the terminal device 200 detects a radio link failure (RLF) and cannot confirm that the cell to which the cell is switched by performing LTM has the minimum radio quality that can be used for communication, it executes a reconnection process starting from a cell search. In this way, even if an RLF occurs, it is possible to avoid the execution of the reconnection process by using the LTM execution setting, and to realize an accelerated handover process and a shortened interruption time.

[0061] (iii) The functions of the present embodiment and each example can also be realized by software program code. In this case, a storage medium on which the program code is recorded is provided to a system or device, and the computer (or CPU or MPU) of the system or device reads the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-mentioned embodiment, and the program code itself and the storage medium on which it is stored constitute the present disclosure. Examples of storage media for supplying such program code include flexible disks, CD-ROMs, DVD-ROMs, hard disks, optical disks, magneto-optical disks, CD-Rs, magnetic tapes, non-volatile memory cards, and ROMs.

[0062] Also, an operating system (OS) running on a computer may perform all or a part of the actual processing based on the instructions of the program code, and the functions of the above-mentioned embodiments may be realized by the processing. Furthermore, after the program code read from a storage medium is written into a memory on a computer, a CPU of the computer may perform all or a part of the actual processing based on the instructions of the program code, and the functions of the above-mentioned embodiments may be realized by the processing.

[0063] Furthermore, the program code of the software that realizes the functions of the embodiments and each example may be distributed via a network and stored in a storage means such as a hard disk or memory of the system or device, or in a storage medium such as a CD-RW or CD-R, so that when used, the computer (or CPU or MPU) of the system or device reads out and executes the program code stored in the storage means or storage medium.

[0064] The processes and techniques described herein are not inherently related to any particular device, and may be implemented by a combination of components. Various types of general-purpose devices may also be added. A dedicated device may be constructed to execute the functions of the present embodiment and each example. Various functions may also be formed by appropriately combining multiple components disclosed in the present embodiment and each example. For example, some components may be deleted from all the components shown in the embodiment and each example, or components across different examples may be appropriately combined.

[0065] In this disclosure, specific examples are described, but they are in all respects for the purpose of explanation (understanding the technology of the present disclosure) and not for the purpose of limitation. It is understood by those skilled in the art that there are many combinations of hardware, software, and firmware suitable for implementing the technology of the present disclosure. For example, the described software can be implemented in a wide range of program or script languages, such as assembler, C / C++, perl, Shell, PHP, Java (registered trademark), etc.

[0066] Furthermore, in the above-described embodiment, the control lines and information lines are those that are considered necessary for the explanation, and not all of the control lines and information lines in the product are necessarily shown. All of the components may be connected to each other.

[0067] In addition, other implementations of the present disclosure will become apparent to those skilled in the art from consideration of the present embodiments and examples. The specification and examples are exemplary only, with the scope and spirit of the present disclosure being indicated by the following claims. [Explanation of symbols]

[0068] 100 Base station equipment 100_1 Handover source base station 100_2 Handover destination base station 200 Terminal Equipment 101, 201 processors 102, 202 Storage devices 103, 203 ROM 104, 204 RAM 105, 205 Communication devices 206 Input Devices 207 Output Devices 1011, 2011 RRC setting section 1012 RA instruction section 1013 Handover instruction unit 1014 Inter-base station communication unit 1015 TA Maintenance Department 1016 PUCCH / PDCCH / RA communication unit 2012 RA Executive Committee 2013 Handover processing unit 2014 LTM Execution Condition Judgment Department 2015 Timer control unit

Claims

1. A terminal device that communicates with a plurality of base station devices while switching connection destinations, a storage device for storing a program relating to handover; a processor that reads the program from the storage device and executes a handover process; The processor, A process of acquiring communication parameters and information on conditions for performing LTM associated with at least one handover destination candidate base station device from a connected handover source base station device; a process of determining whether a condition for performing the LTM associated with the handover destination candidate base station device is satisfied before receiving a Cell Switch Command from the handover source base station device instructing a change of a connection destination cell; When the condition for performing LTM is satisfied, a process of transmitting an RA preamble to the base station device that is a handover destination candidate associated with the condition for performing LTM; A terminal device that executes the above.

2. In claim 1, A terminal device, wherein the processor acquires information on specific events including CondEvent A3, CondEvent A4, CondEvent A5, CondEvent D1, and CondEvent T1, which are specified in the 3GPP standard, as conditions for implementing the LTM, for each of the at least one handover destination candidate base station device.

3. In claim 1, The terminal device, when the processor detects a radio link failure, when it cannot confirm that the conditions for implementing LTM are met, and when it confirms a specified radio quality that can be used for communication for the cell switching destination by implementing LTM, executes a process to determine that LTM is possible.

4. In claim 1, The terminal device, wherein when the processor detects a radio link failure and is unable to confirm a predetermined radio quality that can be used for communication at a cell switching destination by implementing LTM, executes a reconnection process starting from a cell search.

5. In claim 1, A terminal device in which the processor receives information for identifying a measurement target for wireless quality and a first identifier associated with the information, information for identifying a timing for reporting to a base station device and a second identifier associated with the information, information for associating a measurement target for wireless quality, a report target, and a reporting timing using the first identifier and the second identifier, and a third identifier associated with the information, and specifies conditions for implementing LTM using the third identifier.

6. In claim 5, The first identifier is a measObjectId, the second identifier is a reportConfigId, A terminal device, wherein the third identifier is a MeasId.

7. In claim 1, The processor of the terminal device deletes some or all of the first communication parameters and the first LTM implementation conditions of the first handover destination base station device, and the second communication parameters and the second LTM implementation conditions of the second handover destination base station device, upon instruction from the handover source base station device, if the cell switching process is successful after transmitting an RA preamble.

8. A wireless communication system including a plurality of base station devices and at least one terminal device, which executes a handover from a handover source base station device to a handover destination candidate base station device, The handover source base station device to which the terminal device is connected A process of transmitting, to the terminal device, communication parameters associated with at least one handover destination candidate base station device and information on a condition for performing LTM; a process of transmitting a Cell Switch Command to the terminal device, the Cell Switch Command instructing the terminal device to change a connection destination to the base station device that is a handover destination candidate; The terminal device a process of determining whether a condition for performing the LTM associated with the handover destination candidate base station device is satisfied before receiving the Cell Switch Command from the handover source base station device; When the condition for performing LTM is satisfied, a process of transmitting an RA preamble to the base station device that is a handover destination candidate associated with the condition for performing LTM is executed. Wireless communication system.

9. In claim 8, A wireless communication system in which the terminal device acquires information on specific events including CondEvent A3, CondEvent A4, CondEvent A5, CondEvent D1, and CondEvent T1, which are specified in the 3GPP standard, as conditions for implementing the LTM, for each of the at least one handover destination candidate base station device from the handover source base station device.

10. In claim 8, When the terminal device detects a radio link failure, and when it cannot confirm that the conditions for implementing LTM are met, and when it confirms a specified radio quality that can be used for communication for the cell switching destination by implementing LTM, it executes a process of determining that LTM is possible.

11. In claim 8, A wireless communication system in which, when the terminal device detects a wireless link failure, if it cannot confirm a specified wireless quality that can be used for communication at a cell switching destination by implementing LTM, it executes a reconnection process starting with a cell search.

Images