Method and apparatus for controlling reduction of interruption time for a terminal configured with l3 handover and l1 / l2 triggered mobility (LTM) in a wireless communication system

Abstract

The disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate than a 4G communication system such as LTE. According to the disclosure, when L3 handover and LTM are configured for an arbitrary terminal, LTM preparation can be considered to perform L3 HO or LTM, and thus interruption time can be reduced.

Description

Technical Field

[0001] This disclosure relates to the operation of terminals and base stations in wireless or mobile communication systems. More specifically, this disclosure relates to the operation of terminals and base stations to address problems that may arise when L3 handover and LTM are configured simultaneously in a terminal. Background Technology

[0002] Given the successive generations of development in wireless communication, technologies have been developed primarily for human-oriented services such as voice calls, multimedia services, and data services. With the commercialization of 5G (fifth-generation) communication systems, the number of connected devices is expected to grow exponentially. These devices will increasingly connect to communication networks. Examples of connected things can include vehicles, robots, drones, home appliances, displays, smart sensors connected to various infrastructures, construction machinery, and factory equipment. Mobile devices are expected to evolve in various form factors, such as augmented reality glasses, virtual reality headsets, and holographic devices. Efforts are underway to develop improved 6G communication systems to provide a wide range of services by connecting hundreds of billions of devices and things in the 6G (sixth-generation) era. For these reasons, 6G communication systems are referred to as "beyond 5G" systems.

[0003] The 6G communication system, which is expected to be commercialized around 2030, will have peak data rates of terabytes per second (bps) and wireless latency of less than 100 microseconds, and will therefore be 50 times faster than 5G communication systems, with 1 / 10 of their wireless latency.

[0004] To achieve such high data rates and ultra-low latency, 6G communication systems have been considered for implementation in terahertz bands (e.g., the 95 GHz to 3 THz band). It is anticipated that, due to more severe path loss and atmospheric absorption in the terahertz band compared to the millimeter-wave bands introduced in 5G, technologies capable of ensuring signal transmission distance (i.e., coverage) will become even more critical. It is necessary to develop the following technologies as key technologies for ensuring coverage: radio frequency (RF) components, antennas, new waveforms with better coverage than orthogonal frequency division multiplexing (OFDM), beamforming and massive MIMO, full-dimensional MIMO (FD-MIMO), array antennas, and multi-antenna transmission technologies such as massive MIMO. Furthermore, new technologies for improving terahertz band signal coverage have been discussed in the industry, such as metamaterial-based lenses and antennas, orbital angular momentum (OAM), and reconfigurable smart surfaces (RIS).

[0005] In addition, to improve spectrum efficiency and overall network performance, the following technologies have been developed for 6G communication systems: full-duplex technology, enabling uplink and downlink transmissions to use the same frequency resources simultaneously; network technologies for integrated utilization of satellites, High Altitude Platform Stations (HAPS), etc.; improved network architecture to support mobile base stations and achieve network operation optimization and automation; dynamic spectrum sharing technology based on spectrum usage prediction to avoid collisions; the use of artificial intelligence (AI) in wireless communication to improve overall network operation by leveraging AI from the 6G development design phase and internalizing end-to-end AI support functions; and next-generation distributed computing technologies to overcome the limitations of UE computing capabilities through accessible ultra-high-performance communication and computing resources on the network, such as mobile edge computing (MEC) and the cloud. Furthermore, efforts are ongoing to enhance connectivity between devices, optimize networks, promote the software-defined networking of network entities, and increase the openness of wireless communication by designing new protocols for use in 6G communication systems, developing mechanisms for hardware-based secure environments and secure data usage, and developing technologies for maintaining privacy.

[0006] Research and development of 6G communication systems in hyper-connectivity, including human-to-machine (P2M) and machine-to-machine (M2M) technologies, is expected to enable next-generation hyper-connected experiences. Specifically, 6G communication systems are anticipated to provide services such as truly immersive extended reality (XR), high-fidelity mobile holograms, and digital twins. Furthermore, 6G communication systems will provide services such as remote surgery for enhanced safety and reliability, industrial automation, and emergency response, enabling the technology to be applied in various fields such as industry, healthcare, automotive, and home appliances.

[0007] At the same time, there is a need for solutions to address potential issues that may arise when Layer 3 (L3) handover and L1 / L2-triggered mobility (LTM) handover are configured simultaneously. Summary of the Invention

[0008] [Technical Issues]

[0009] This disclosure aims to provide a method and apparatus for addressing the problem of performing L3 HO without considering LTM preparation when L3 handover (HO) and LTM are configured for any terminal.

[0010] [Technical Solution]

[0011] According to embodiments of this disclosure, a method performed by a source distributed unit (DU) entity in a wireless communication system may include: receiving a measurement report message from a terminal, the measurement report message including information indicating whether at least one neighboring cell measured by the terminal is a Layer 1 (L1) / Layer 2 (L2) triggered mobility LTM candidate cell; sending the measurement report message to a centralized unit (CU) entity; receiving an LTM trigger request message from the CU entity based on the measurement report message; determining, based on the receipt of the LTM trigger request message, whether an LTM cell handover command media access control (MAC) element (CE) can be sent to the terminal; and when it is determined that the LTM cell handover command MAC CE can be sent, sending an LTM trigger response message to the CU entity.

[0012] Meanwhile, according to another embodiment of this disclosure, a method performed by a centralized unit (CU) entity in a wireless communication system may include: receiving a measurement report message from a source distributed unit (DU) entity; determining, based on the measurement report message, whether a target DU entity is a Layer 1 (L1) / Layer 2 (L2) triggered mobility (LTM) candidate cell; when the target DU entity is determined to be the LTM candidate cell, sending an LTM trigger request message to the source DU entity; and receiving an LTM trigger response message from the source DU entity based on the LTM trigger request message.

[0013] Meanwhile, according to another embodiment of this disclosure, a source distributed unit (DU) entity in a wireless communication system may include: a transceiver; and a controller, the controller controlling: receiving a measurement report message from a terminal via the transceiver, the measurement report message including information indicating whether at least one neighboring cell measured by the terminal is a Layer 1 (L1) / Layer 2 (L2) triggered mobility LTM candidate cell; sending the measurement report message to a centralized unit (CU) entity; receiving an LRM trigger request message from the CU entity based on the measurement report message; determining whether an LTM cell handover command media access control (MAC) element (CE) can be sent to the terminal based on the receipt of the LTM trigger request message; and sending an LTM trigger response message to the CU entity when it is determined that the LTM cell handover command MAC CE can be sent.

[0014] Meanwhile, according to another embodiment of this disclosure, a centralized unit (CU) entity in a wireless communication system may include: a transceiver; and a controller, the controller controlling: receiving a measurement report message from a source distributed unit (DU) entity via the transceiver; determining, based on the measurement report message, whether a target DU entity is a Layer 1 (L1) / Layer 2 (L2) triggered mobility LTM candidate cell; when the target DU entity is determined to be the LTM candidate cell, sending an LRM trigger request message to the source DU entity; and receiving an LTM trigger response message from the source DU entity based on the LTM trigger request message.

[0015] [Beneficial Effects]

[0016] According to this disclosure, when L3 handover and LTM are configured for any terminal, LTM preparation can be considered to perform L3 HO or LTM, thereby reducing downtime. Attached Figure Description

[0017] Figure 1 This is a graph showing the interruption time that may typically occur during a switching process.

[0018] Figure 2 This is a diagram illustrating a publicly available L3 handover process.

[0019] Figure 3 This is a diagram illustrating a publicly available LTM process.

[0020] Figure 4 This is a diagram used to illustrate potential problems in an environment where L3 HO and LTM are configured simultaneously using the proposed priority scheme, according to embodiments of this disclosure.

[0021] Figure 5 This is a diagram illustrating the LTM cell handover request process according to an embodiment of the present disclosure.

[0022] Figure 6 This is a diagram illustrating information, according to an embodiment of the present disclosure, indicating whether a neighboring cell measured by the UE is an LTM candidate cell (this information may be included in the L3 measurement report).

[0023] Figure 7 This is a diagram illustrating the specific content of the message presented in this disclosure.

[0024] Figure 8 This is a diagram illustrating the successful execution of an LTM trigger request process according to an embodiment of this disclosure.

[0025] Figure 9 This is a diagram illustrating a scenario where the LTM trigger request process fails according to an embodiment of this disclosure.

[0026] Figure 10 This is a diagram illustrating the message structure for sending "LTMCandidateCellFlag" according to an embodiment of this disclosure, in which...

[0027] Figure 11 This illustrates an embodiment of the present disclosure, where the UE transmits data including, for example, Figure 10 The figure shows an example of a successful LTM triggering process when the L3 measurement report of the "LTMCandidateCellFlag" IE is executed.

[0028] Figure 12 This illustrates another embodiment of the present disclosure, where the UE transmits data including, for example, Figure 10 The figure shows an example of a successful LTM triggering process when the L3 measurement report of the "LTMCandidateCellFlag" IE is executed.

[0029] Figure 13 This illustrates an embodiment of the present disclosure where, when the UE transmits data including... Figure 10 A diagram of an embodiment where the LTM triggering process fails (e.g., is unsuccessful) when the L3 measurement report of the disclosed “LTMCandidateCellFlag” IE is submitted.

[0030] Figure 14 This is a block diagram illustrating the structure of a terminal according to an embodiment of the present disclosure.

[0031] Figure 15 This is a diagram illustrating the structure of a base station according to an embodiment of the present disclosure. Detailed Implementation

[0032] The working principle of this disclosure will be described in detail below with reference to the accompanying drawings. In the following description, detailed descriptions of known techniques or configurations related to this disclosure will be omitted where it is determined that such detailed descriptions might unnecessarily obscure the essential points of this disclosure. Furthermore, the following terminology is defined in consideration of the functionality within this disclosure and may vary depending on the intent, practice, etc., of the user and operator. Therefore, its definitions should be interpreted based on the entirety of this specification.

[0033] Furthermore, detailed descriptions of known technologies or configurations related to this disclosure will be omitted where it is determined that such descriptions might unnecessarily obscure the essential points of this disclosure. Hereinafter, embodiments of this disclosure will be described with reference to the accompanying drawings.

[0034] In the following description, for ease of description, terms used to identify access nodes, to refer to messages, to refer to interfaces between access nodes, and to refer to various identification information are examples. Therefore, this disclosure is not limited to the terms described below, and other terms that refer to objects with equivalent technical meanings may be used.

[0035] For ease of description, this disclosure uses the terms and names defined in the 3GPP LTE standard. However, this disclosure is not limited to these terms and names and can be applied equivalently to systems conforming to other standards. In this disclosure, for ease of description, the term "eNB" may be used interchangeably with "gNB". For example, a base station described as an eNB may represent a gNB.

[0036] The wireless communication system supports various mobility management methods, including L3 handover, to support UE mobility. However, interruptions may occur during the handover process that supports UE mobility.

[0037] Figure 1 This is a graph showing the interruption time that may typically occur during a switching process. For example, Figure 1 This illustrates the potential downtime that a UE may experience during the handover process. Downtime can be defined as the time from when the UE receives the handover command message from the base station to when the UE first transmits uplink (UL) data to the target cell. In this case, as... Figure 1 As shown, the interruption time may include UE reconfiguration, downlink (DL) synchronization and UL synchronization (e.g., RACH procedure).

[0038] In wireless communication systems, methods have been proposed to reduce downtime that may occur when supporting mobility management methods, including handover. For example, a method such as Conditional Handover (CHO) has been proposed. However, since DL synchronization and UL synchronization account for a significant portion of downtime, the effectiveness of proposed methods for reducing downtime (such as CHO) may not be significant.

[0039] Therefore, L1 / L2 triggered mobility (LTM) was designed to reduce interrupt time.

[0040] Specifically, Figure 2 It is a diagram illustrating a publicly available L3 handover process, and Figure 3 This is a diagram illustrating a publicly available LTM process.

[0041] To summarize the L3 handover process according to the embodiments, such as Figure 2 As shown, in S200, UE 200, which is in Radio Resource Control (RRC) connection state, can send an L3 measurement report to Source Distributed Unit (DU) 210 in S210. For example, UE 200 can perform measurements on at least one neighboring cell and report the measurement results.

[0042] In step S220, the L3 measurement report can be sent from the source DU 210 to the centralized unit (CU) 230.

[0043] In step S230, when CU 230 determines L3 switching based on the L3 measurement report, CU 230 can send an L3 HO request to the target DU 220 in S240. In S245, the target DU 220 can send an L3 HO confirmation to CU 230.

[0044] In step S250, CU 230 may send a UE context modification request to source DU 210, and in step S255, source DU 210 may send a UE context modification confirmation to CU 230.

[0045] In step S260, when the source DU 210 sends an RRC reconfiguration message to the UE 200, and in step S265, when the UE 200 sends an RRC reconfiguration completion message to the source DU 210, the RACH procedure can be executed in step S270. The RACH procedure in S270 may include the following steps: the UE 200 sending a PRACH preamble to the target DU 220, the UE 200 receiving MSG2 from the target DU 220, and the UE 200 sending MSG3 to the target DU 220, etc.

[0046] exist Figure 2 In L3 HO, when the UE performs DL synchronization and UL synchronization with the target DU after receiving the HO command based on the RRC reconfiguration message, the above-mentioned interruption time may occur.

[0047] Figure 3 This is a diagram illustrating the proposed LTM process for reducing downtime. The LTM process is based on... Figure 3 In summary, in S300, during step S305, the UE 300 in RRC connected state can send a measurement report to gNB 310. gNB 310 can be an nr gNB, such as a gNB. According to an embodiment, gNB 310 can be configured with one CU and multiple DUs (e.g., source DU and target DU).

[0048] In step S310, gNB 310 may perform an LTM candidate preparation procedure. Furthermore, in S315, gNB 310 may send information about the LTM candidate configuration via an RRC reconfiguration message. For example, gNB 310 may generate information about the LTM candidate configuration via the LTM candidate preparation procedure and send the generated information about the LTM candidate configuration to UE 300.

[0049] The UE 300 that receives the RRC reconfiguration message can send an RRC reconfiguration complete message to the gNB 310. In this case, steps S305 to S320 can be the LTM preparation process.

[0050] Step S325 is an early synchronization process in which UE 300 may perform DL / UL synchronization with at least one candidate cell. For example, UE 300 may identify at least one candidate cell based on the information about the LTM candidate configuration received from gNB 310 in S315, and perform DL / UL synchronization with the at least one candidate cell.

[0051] In step S330, UE 300 can send an L1 measurement report to gNB 310. When gNB 310 performs an LTM decision in step S335, gNB 310 can send a cell handover command to UE 300 using a Media Access Control (MAC) control element (CE). In this case, in step S345, UE 300, having received the MAC CE, can separate from the source and apply the target configuration. In step S350, UE 300 can perform a RACH procedure. Steps S330 to S350 can be LTM execution procedures.

[0052] LTM can be completed in S355 as part of the LTM completion process.

[0053] like Figure 3 As shown, in LTM, the early synchronization process allows UE 300 to achieve synchronization before receiving a cell handover command, thereby reducing downtime.

[0054] Furthermore, since cell handover commands are sent via MAC CE based on L1 measurement reports (e.g., since the command message is generated at the MAC layer), LTM also has the advantage of not requiring L3 layer processing compared to L3 HO.

[0055] Simultaneously, the network can configure both LTM and L3 handover for any UE. Since LTM and L3 handover are performed on the network side, priority management between LTM and L3 handover is required at the UE level. Typically, the priority between LTM and L3 handover can be configured in the following three scenarios: 1. When L3 handover is performed before LTM (e.g., when the UE receives the L3 handover command message before the gNB-DU sends the LTM cell handover command MAC CE), L3 handover has higher priority.

[0056] 2. When LTM is performed before L3 handover (e.g., when the UE receives an LTM notification message before the gNB-CU sends an L3 handover command message), LTM has a higher priority.

[0057] 3. When LTM and L3 handover are performed almost simultaneously (e.g., when the UE receives an L3 handover command message after sending an LTM cell handover command MACCE in gNB-DU), LTM has higher priority.

[0058] The proposed prioritization scheme essentially assigns higher priority to the handover message sent first, but when the L3 HO command and LTM cell handover MAC CE are sent simultaneously, a higher priority is assigned to LTM. However, the priority management scheme only covers the priority handling scheme between handover messages that occur after the HO command message is generated (e.g., L3 handover and LTM cell handover MAC CE). Furthermore, handover decisions can be performed based on the network-side implementation. In this case, even if the network is ready to support the UE's LTM, an L3 handover may still be performed, potentially rendering the benefits of LTM (e.g., significantly reduced downtime compared to L3 handover) meaningless.

[0059] Specifically, Figure 4 This is a diagram used to illustrate potential problems in an environment where L3 HO and LTM are configured simultaneously using the proposed priority scheme, according to embodiments of this disclosure.

[0060] For example, in S400, a UE 400 in RRC connected state can be a UE configured with both L3 HO and LTM.

[0061] In S405, UE 400 can send L3 measurement reports to source DU 410. Furthermore, in S410, source DU 410 can send L3 measurement reports to CU 430.

[0062] In S415, the LTM candidate preparation process can be performed between the source DU 410 and CU 430.

[0063] In S420, source DU 410 can send LTM configuration information to UE 400 via an RRC reconfiguration message. Furthermore, in S425, UE 400 can send an RRC reconfiguration complete message to source DU 410.

[0064] As mentioned above Figure 3 In step S430, UE 400 may perform DL / UL synchronization with at least one candidate cell as an early synchronization process. For example, UE 400 may identify at least one candidate cell based on LTM configuration information received from source DU410 in step S420, and perform DL / UL synchronization with said at least one candidate cell.

[0065] In S435, UE 400 can send an L3 measurement report triggered by event A3 to source DU 410. In S440, an L3 measurement report triggered by event A3 can be sent from source DU 410 to CU 430.

[0066] In S445, CU 430 can make L3 HO decisions based on L3 measurement reports triggered by event A3.

[0067] In step S450, CU 430 can send a UE context modification request to source DU 410, and in step S455, source DU 410 can send a UE context modification confirmation to CU 430.

[0068] In step S460, CU 430 may send an RRC reconfiguration message including the L3 HO command to UE 400.

[0069] Subsequently, in step S465, the RACH procedure can be executed. The RACH procedure in S465 may include the following steps: UE 400 sending a PRACH preamble to target DU 420, UE 400 receiving MSG2 from target DU 420, UE 400 sending MSG 3 to target DU 420, etc.

[0070] As described above, the network and UE can complete LTM support preparation through the LTM preparation phase (e.g., steps S415 to S430). Subsequently, when the UE sends an L3 measurement report to the gNB (e.g., the source DU), the source DU can pass the received L3 measurement report to the CU. Since the CU generates an L3 handover command based on the received L3 measurement report and passes the L3 handover command to the UE, the UE can perform L3 handover based on the aforementioned priority scheme instead of LTM.

[0071] Therefore, even if LTM preparation is performed, the UE should still need to perform the RACH procedure unnecessarily due to the execution of L3 HO, so the interruption time is not reduced.

[0072] Therefore, this disclosure proposes a method that allows the CU to consider whether to trigger LTM after receiving an L3 measurement report and determining whether handover is necessary, rather than immediately sending an L3 handover command. According to an embodiment, considering the DU state (LTM ready state), the CU can request the DU to send an LTM cell handover command MAC CE.

[0073] Figure 5 This is a diagram illustrating the LTM cell handover request process according to an embodiment of the present disclosure.

[0074] For example, in S500, a UE 500 in RRC connected state can be a UE configured with both L3 HO and LTM.

[0075] In S505, UE 500 can send L3 measurement reports to source DU 510. Furthermore, in S510, source DU 510 can send L3 measurement reports to CU 530.

[0076] In S515, the LTM candidate preparation process can be performed between the source DU 510 and CU 530.

[0077] In S520, source DU 510 can send LTM configuration information to UE 500 via RRC reconfiguration message. Furthermore, in S525, UE 500 can send an RRC reconfiguration complete message to source DU 510.

[0078] In S530, as an early synchronization process, UE 500 can perform DL / UL synchronization with at least one candidate cell. For example, UE 500 can identify at least one candidate cell based on the LTM configuration information received from source DU 510 in S520, and perform DL / UL synchronization with said at least one candidate cell.

[0079] In S535, UE 500 can send an L3 measurement report triggered by event A3 to source DU 510. In this case, UE 500 can include information (e.g., an information element (IE)) indicating whether the measured DU is an LTM candidate cell. The specific content of the information indicating whether the measured DU is an LTM candidate cell will be described later.

[0080] In S540, an L3 measurement report triggered by event A3 can be sent from source DU 510 to CU 530.

[0081] In S545, CU 530 can parse L3 measurement reports (MRs). For example, CU 530 can determine whether UE 500 needs a handover based on the received L3 measurement report. Furthermore, CU 530 can determine whether target DU 520 is an LTM candidate cell. For example, CU 530 can determine whether target DU 520 is an LTM candidate cell based on information included in the L3 measurement report that indicates whether the DU measured by UE 500 is an LTM candidate cell.

[0082] In step S550, CU 530 may send an LTM trigger request. For example, as a result of determination, when target DU520 is an LTM candidate cell, CU 530 may send an LTM trigger request to source DU 510.

[0083] In step S555, CU 530 may receive an LTM trigger response from source DU 510. For example, after receiving an LTM trigger request message, source DU 510 may determine that it is capable of sending an LTM cell handover command MAC CE. In this case, source DU 510 may send an LTM trigger response (LTM TRIGGERRESPONSE) to CU 530. In this case, the likelihood of source DU 510 sending the LTM cell handover command MAC CE can be determined based on whether source DU 510 is capable of including field values ​​(e.g., target configuration ID, TA command, TCI status ID, or BWP ID) within the MAC CE.

[0084] In S560, the source DU 510 can send LTM cell handover command MAC CE to UE 500.

[0085] at the same time, Figure 6 This is a diagram illustrating information (which may be included in the L3 measurement report) indicating whether a neighboring cell, as measured by the UE, is an LTM candidate cell according to an embodiment of this disclosure.

[0086] According to embodiments of this disclosure, the information indicating whether a neighboring cell measured by the UE is an LTM candidate cell can be "LTMCandidateCellFlag," which is an IE that can be included in the UL-DCCH message. This IE can be Boolean data. For example, when "LTMCandidateCellFlag" is "true," it can indicate that the neighboring cell measured by the UE is an LTM candidate cell. Conversely, a false value (e.g., false) can indicate that the measured neighboring cell is not an LTM candidate cell. This IE allows the CU to avoid a separate search operation when parsing the L3 measurement report to determine whether the neighboring cell measured by the UE is an LTM candidate cell. For example, the CU can identify whether a neighboring cell is an LTM candidate cell based on the "LTMCandidateCellFlag" IE without performing a separate search operation.

[0087] In addition, this disclosure discloses the signaling between CU and DU.

[0088] For example, the CU can send a message requesting the DU to send an LTM cell handover command MAC CE. This message could be an LTM TRIGGER REQUEST message. However, the LTM TRIGGER REQUEST message is just one example, and the specific message name can vary. An LTM TRIGGER REQUEST message is a message sent from the CU to the DU (e.g., the source DU) and is intended to request the DU to send an LTM cell handover command MAC CE to the UE.

[0089] Furthermore, the LTM TRIGGER RESPONSE message can be a message sent from the DU to the CU. The LTM TRIGGER RESPONSE message can also be a message notifying that the LTM trigger has been successfully executed. The LTM TRIGGER RESPONSE message is just one example, and specific message names can vary.

[0090] Additionally, an LTM trigger failure message can be a message sent from the DU to the CU. The LTM trigger failure message can be a notification that LTM triggering has failed. The LTM trigger failure message is just one example, and specific message names can vary.

[0091] Figure 7 This is a diagram illustrating the specific content of the messages presented in this disclosure. According to embodiments, the LTM TRIGGERREQUEST message, LTM TRIGGER RESPONSE message, and LTM TRIGGER FAILURE message may include at least one of a message type, gNB-CU UE F1AF ID, gNB-DU UE F1AP ID, and NR PCI. The message type is an IE that can indicate whether the sent message is an LTM TRIGGER REQUEST, LTM TRIGGER RESPONSE, etc. The gNB-CU UE F1AP ID and gNB-DU UE F1AP ID can be the UE identifiers (IDs) used by the CU and DU, respectively. The NR PCI can indicate the physical cell ID (PCI) of the target cell.

[0092] The LTM TRIGGER FAILURE message may additionally include a CAUSE IE. For example, a CAUSE IE may include an indication used to notify the CU of the reason for the LTM trigger failure.

[0093] Figure 8 This is a diagram illustrating the successful execution of an LTM trigger request process according to an embodiment of this disclosure.

[0094] In step S820, CU 800 may send an LTM TRIGGER REQUEST message to DU 810. In this case, DU 810, upon receiving the LTM TRIGGER REQUEST message, can determine whether it is capable of sending an LTM cell handover command MAC CE. For example, DU 810 can determine whether it can include (e.g., fill in field values) field values ​​(e.g., target configuration ID, TA command, TCI status ID, and BWP ID) within the LTM cell handover command MAC CE. As a result of this determination, if DU 810 can include the aforementioned field values, DU 810 can determine that it is capable of sending the LTM cell handover command MAC CE.

[0095] In step S830, DU 810 may send an LTM TRIGGER RESPONSE message to CU 800. For example, as a result of determination, when DU 810 determines that it is capable of sending the LTM cell handover command MAC CE, DU 810 may send an LTM TRIGGER RESPONSE message to CU 800.

[0096] at the same time, Figure 9 This is a diagram illustrating a scenario where the LTM trigger request process fails according to an embodiment of this disclosure.

[0097] In step S920, CU 900 may send an LTM TRIGGER REQUEST message to DU 910. In this case, DU 910, upon receiving the LTM TRIGGER REQUEST message, can determine whether it can send an LTM cell handover command MAC CE. For example, DU 910 can determine whether it can include (e.g., fill in field values) field values ​​(e.g., target configuration ID, TA command, TCI status ID, and BWP ID) in the LTM cell handover command MAC CE. As a result of this determination, if DU 910 cannot include the aforementioned field values, DU 910 can determine that it cannot send an LTM cell handover command MAC CE.

[0098] In step S930, when DU 910 determines that it cannot send the LTM cell handover command MAC CE, DU 910 can generate an LTM TRIGGER FAILURE message including CAUSE information and send the LTM TRIGGER FAILURE message to CU900.

[0099] According to an embodiment, when an abnormal condition such as a syntax error occurs, the DU 910 can operate as an unsuccessful operation.

[0100] at the same time, Figure 10 This is a diagram illustrating the message structure for sending "LTMCandidateCellFlag" according to an embodiment of this disclosure.

[0101] As described above, "LTMCandidateCellFlag" can be an IE indicating whether at least one neighboring cell measured by the UE is an LTM candidate cell. The "LTMCandidateCellFlag" IE can be included in the RRC reconfiguration message. For example, "LTMCandidateCellFlag" can be included as a Boolean value in the MeasResultNR of the RRC reconfiguration message. When "LTMCandidateCellFlag" is "true", it indicates that the neighboring cell measured by the UE is an LTM candidate cell. Conversely, if it is false, it indicates that the measured neighboring cell is not an LTM candidate cell. This IE allows the CU to avoid a separate search operation to determine whether the neighboring cell measured by the UE is an LTM candidate cell when parsing the L3 measurement report.

[0102] Figure 11 This illustrates an embodiment of the present disclosure where, when the UE transmits data including... Figure 10 The figure shows an example of a successful LTM triggering process when the L3 measurement report of the "LTMCandidateCellFlag" IE is executed.

[0103] As described in the above embodiments, in step S1140, any UE 1100 that has performed DL / UL synchronization with at least one candidate cell can send an L3 measurement report triggered by event A3 to the source DU 1110. In this case, UE 1100 may include information (e.g., an information element (IE)) indicating whether the measured DU is an LTM candidate cell. For example, as Figure 11 As shown, the MeasResultNR included in the RRC message sent by UE 1100 may include information related to the PCI of the target cell (e.g., Figure 11 The "physCellId": 205), and the "LTMCandidateCellFlag" is indicated as "true". In this disclosure, according to an embodiment, an L3 measurement report including "LTMCandidateCellFlag" is indicated as a modified L3 measurement report.

[0104] In S1145, the modified L3 measurement report triggered by event A3 can be sent from source DU 1110 to CU 1130.

[0105] In S1150, CU 1130 can parse the modified L3 Measurement Report (MR). For example, CU 1130 can determine whether UE 1100 needs a handover based on the received modified L3 Measurement Report. Furthermore, CU 1130 can determine whether the target DU1120 is an LTM candidate cell. For example, in Figure 11 In the illustrated embodiment, CU 1130 can identify the target DU 1120 with "physCellId" 205 as an LTM candidate cell based on the fact that the "LTMCandidateCellFlag" of the DU with "physCellId" 205, which is measured by UE 1100 and included in the modified L3 measurement report, is indicated as "true".

[0106] In step S1155, CU 1130 may send an LTM trigger request. For example, as a result of determination, when target DU1120 is an LTM candidate cell, CU 1130 may send an LTM trigger request message to source DU 1110. The LTM trigger request message may include at least one of the following: message type, gNB-CU UE F1AP ID, gNB-DU UE F1AP ID, and NR PCI (e.g., 205).

[0107] In step S1160, CU 1130 can receive an LTM trigger response from source DU 1110. For example, after receiving the LTMTRIGGER REQUEST message, source DU 1110 can determine that it is capable of sending an LTM cell handover command MAC CE. In this case, source DU 1110 can send an LTM TRIGGER RESPONSE to CU 1130. In this case, the likelihood of source DU 1110 sending the LTM cell handover command MAC CE can be determined based on whether source DU 1110 can include (padded) field values ​​(e.g., target configuration ID, TA command, TCI status ID, or BWP ID) within the MAC CE.

[0108] In S1165, source DU 1110 can send LTM cell handover command MAC CE to UE 1100.

[0109] at the same time, Figure 12 This illustrates another embodiment of the present disclosure, where the UE transmits data including, for example, Figure 10The figure shows an example of a successful LTM triggering process when the L3 measurement report of the "LTMCandidateCellFlag" IE is executed.

[0110] For example, in S1200, the UE 1200 in RRC connected state can be a UE configured with both L3 HO and LTM.

[0111] In S1205, UE 1200 can send L3 measurement reports to source DU 1210. Furthermore, in S1210, source DU 1210 can send L3 measurement reports to CU 1230.

[0112] In S1215, the LTM candidate preparation process can be performed between the source DU 1210 and CU 1230.

[0113] In S1220, source DU 1210 can send LTM configuration information to UE 1200 via an RRC reconfiguration message. Furthermore, in S1225, UE 1200 can send an RRC reconfiguration complete message to source DU 1210.

[0114] In S1230, as an early synchronization process, UE 1200 may perform DL / UL synchronization with at least one candidate cell. For example, UE 1200 may identify at least one candidate cell based on the LTM configuration information received from source DU 1210 in S1220, and perform DL / UL synchronization with said at least one candidate cell.

[0115] In step S1235, UE 1200 may send the L3 measurement report triggered by event A3 to source DU 1210. In this case, UE 1200 may include information indicating whether the measured DU is an LTM candidate cell (e.g., information element (IE)). For example, such as Figure 12 As shown, the MeasResultNR included in the RRC message sent by UE 1200 may include information related to the PCI of the target cell (e.g., Figure 12 The "physCellId": 205), and the "LTMCandidateCellFlag" is indicated as "true". In this disclosure, according to an embodiment, an L3 measurement report including "LTMCandidateCellFlag" is indicated as a modified L3 measurement report.

[0116] In S1240, a modified L3 measurement report triggered by event A3 can be sent from source DU 1210 to CU 1230.

[0117] In S1245, CU 1230 can parse the modified L3 Measurement Report (MR). For example, CU 1230 can determine whether UE 1200 needs a handover based on the received modified L3 Measurement Report. Furthermore, CU 1230 can determine whether the target DU1220 is an LTM candidate cell. For example, in Figure 12 In the illustrated embodiment, CU 1230 can identify the target DU 1220 with "physCellId" 205 as an LTM candidate cell based on the fact that the "LTMCandidateCellFlag" of the DU with "physCellId" 205, which is measured by UE 1200 and included in the modified L3 measurement report, is indicated as "true".

[0118] In step S1250, CU 1230 may send an LTM trigger request. For example, as a result of determination, when target DU 1220 is an LTM candidate cell, CU 1230 may send an LTM trigger request message to source DU 1210. The LTM trigger request message may include at least one of the following: message type, gNB-CU UE F1AP ID, gNB-DU UE F1AP ID, and NR PCI (e.g., 205).

[0119] In step S1255, CU 1230 can receive an LTM trigger response from source DU 1210. For example, after receiving the LTMTRIGGER REQUEST message, source DU 1210 can determine that it is capable of sending an LTM cell handover command MAC CE. In this case, source DU 1210 can send an LTM TRIGGER RESPONSE to CU 1230. In this case, the likelihood of source DU 1210 sending the LTM cell handover command MAC CE can be determined based on whether source DU 1210 can include (padded) field values ​​(e.g., target configuration ID, TA command, TCI status ID, or BWP ID) within the MAC CE.

[0120] In S1260, source DU 1210 can send LTM cell handover command MAC CE to UE 1200.

[0121] In addition, in S1265, the LTM cell handover notification procedure can be performed between the source DU 1210, the target DU 1220, and the CU 1230.

[0122] Based on the above process, when the target DU 1220 sends a UL authorization to the UE 1200 in S1270, the UE 1200 can send a PUSCH to the target DU 1220 in S1275.

[0123] at the same time, Figure 13 This illustrates an embodiment of the present disclosure where, when the UE transmits data including... Figure 10 A diagram of an embodiment where the LTM triggering process fails (e.g., is unsuccessful) when the L3 measurement report of the disclosed “LTMCandidateCellFlag” IE is submitted.

[0124] For example, in S1300, the UE 1300 in RRC connected state can be a UE configured with both L3 HO and LTM.

[0125] In S1305, UE 1300 can send L3 measurement reports to source DU 1310. Furthermore, in S1310, source DU 1310 can send L3 measurement reports to CU 1330.

[0126] In S1315, the LTM candidate preparation process can be performed between the source DU 1310 and CU 1330.

[0127] In S1320, source DU 1310 can send LTM configuration information to UE 1300 via an RRC reconfiguration message. Furthermore, in S1325, UE 1300 can send an RRC reconfiguration complete message to source DU 1310.

[0128] In S1330, as an early synchronization process, UE 1300 may perform DL / UL synchronization with at least one candidate cell. For example, UE 1300 may identify at least one candidate cell based on the LTM configuration information received from source DU 1310 in S1320, and perform DL / UL synchronization with said at least one candidate cell.

[0129] In step S1335, UE 1300 may send the L3 measurement report triggered by event A3 to source DU 1310. In this case, UE 1300 may include information indicating whether the measured DU is an LTM candidate cell (e.g., information element (IE)). For example, such as Figure 13 As shown, the MeasResultNR included in the RRC message sent by UE 1300 may include information related to the PCI of the target cell (e.g., Figure 13 The "physCellId": 205), and the "LTMCandidateCellFlag" is indicated as "true". In this disclosure, according to an embodiment, an L3 measurement report including "LTMCandidateCellFlag" is indicated as a modified L3 measurement report.

[0130] In S1340, a modified L3 measurement report triggered by event A3 can be sent from source DU 1310 to CU 1330.

[0131] In S1345, CU 1330 can parse the modified L3 Measurement Report (MR). For example, CU 1330 can determine whether UE 1300 needs to handover based on the received modified L3 Measurement Report. Furthermore, CU 1330 can determine whether the target DU1320 is an LTM candidate cell. For example, in Figure 13 In the illustrated embodiment, CU 1330 can identify the target DU 1320 with "physCellId" 205 as an LTM candidate cell based on the fact that the "LTMCandidateCellFlag" of the DU with "physCellId" 205, which is measured by UE 1300 and included in the modified L3 measurement report, is indicated as "true".

[0132] In step S1350, CU 1330 may send an LTM trigger request. For example, as a result of determination, when target DU1320 is an LTM candidate cell, CU 1330 may send an LTM trigger request message to source DU 1310. The LTM trigger request message may include at least one of the following: message type, gNB-CU UE F1AP ID, gNB-DU UE F1AP ID, and NR PCI (e.g., 205).

[0133] Upon receiving the LTM TRIGGER REQUEST message, source DU 1310 can determine whether it can send the LTM cell handover command MAC CE. For example, source DU 1310 can determine whether to send the command based on whether it can include (padded) field values ​​(e.g., target configuration ID, TA command, TCI status ID, and BWP ID) within the MAC CE. As a result of this determination, if source DU 1310 determines that it cannot send the LTM cell handover command MAC CE to UE 1300, source DU 1310 can send an LTM TRIGGER FAILURE message to CU 1330. For example, if source DU 1310 determines that it cannot include (padded) field values ​​within the LTM cell handover command MAC CE, source DU 1310 can determine that it cannot send the LTM cell handover command MAC CE. In this case, the LTM TRIGGER FAILURE message may include a CAUSE IE. For example, the CAUSE IE may include an indication for notifying the CU of the reason for the LTM triggering failure.

[0134] According to embodiments of this disclosure, when L3 handover and LTM are configured simultaneously, LTM can be performed as needed based on network conditions, thereby reducing UE downtime.

[0135] at the same time, Figure 14 This is a block diagram illustrating the structure of a terminal according to an embodiment of the present disclosure.

[0136] refer to Figure 14 The terminal may include a transceiver 1410, a controller 1420, and a memory 1430. In this disclosure, the controller may be defined as a circuit, an application-specific integrated circuit, or at least one processor.

[0137] Transceiver 1410 can send signals to and receive signals from other network entities. Transceiver 1410 can send, for example, measurement reports to the base station and send and receive RRC messages.

[0138] According to the embodiments presented in this disclosure, controller 1420 can control the overall operation of the terminal. For example, controller 1420 can control the signal flow between each module to perform operations according to the flowchart above. According to an embodiment, controller 1420 can generate a measurement report including the “LTMCandidateCellFlag” IE. Furthermore, controller 1420 can control the transmission of the measurement report including the “LTMCandidateCellFlag” IE to the base station.

[0139] The memory 1430 may store at least one of the following: information transmitted and received by the transceiver 1410, and information generated by the controller 1420.

[0140] Figure 15 This is a diagram illustrating the structure of a base station according to an embodiment of the present disclosure. Furthermore, according to the embodiment, Figure 15 It can be a CU or DU entity.

[0141] refer to Figure 15 The base station may include a transceiver 1510, a controller 1520, and a memory 1530. In this disclosure, the controller may be defined as a circuit, an application-specific integrated circuit, or at least one processor.

[0142] Transceiver 1510 can send signals to and receive signals from other network entities. Transceiver 1510 can send SR and UL authorizations to and receive SR and UL authorizations from terminals.

[0143] According to the embodiments presented in this disclosure, controller 1520 can control the overall operation of the base station. For example, controller 1520 can control the signal flow between each module to perform operations according to the flowchart above. Specifically, for the CU entity, controller 1520 can control the generation and transmission of LTM TRIGGER REQUEST messages according to embodiments of this disclosure. Furthermore, for the DU entity, controller 1520 can control the generation and transmission of LTM TRIGGER RESPONSE messages according to embodiments of this disclosure.

[0144] The memory 1530 may store at least one of the following: information transmitted and received by the transceiver 1510, and information generated by the controller 1520.

[0145] In the specific embodiments of this disclosure described above, the components included in this disclosure are represented in a singular or plural form according to the presented specific embodiments. However, for ease of description, singular or plural expressions are appropriately chosen for the presented context, and this disclosure is not limited to singular or plural components, and even if a component is represented in the plural form, the component may be configured in the singular, or even if a component is represented in the singular form, the component may be configured in the plural form.

[0146] Furthermore, the embodiments disclosed in this specification and accompanying drawings are merely specific examples presented for the purpose of readily describing the technical content of this disclosure and aiding in understanding it, and are not intended to limit the scope of this disclosure. That is, it will be apparent to those skilled in the art that other modifications based on the technical concept of this disclosure are possible. Moreover, each embodiment can be combined with each other and operated as needed. For example, embodiments of this disclosure and portions of another embodiment can be combined with each other to operate a base station and a terminal. Furthermore, other modifications based on the technical concept of the above embodiments can be implemented in various systems (e.g., FDD LTE systems, TDD LTE systems, 5G or NR systems).

Claims

1. A source distributed unit (DU) entity in a wireless communication system, the source DU entity comprising: transceiver; as well as The controller controls the receiving of measurement report messages from the terminal via the transceiver. The measurement report messages include information indicating whether at least one neighboring cell measured by the terminal is a Layer 1 L1 / Layer 2 L2 mobility LTM candidate cell. The measurement report message is sent to the centralized unit (CU) entity. Based on the measurement report message, an LRM trigger request message is received from the CU entity. Based on the receipt of the LTM trigger request message, it is determined whether the LTM cell handover command Media Access Control (MAC) element (CE) can be sent to the terminal, and When it is determined that the LTM cell handover command MAC CE can be sent, an LTM trigger response message is sent to the CU entity.

2. The source DU entity according to claim 1, further comprising: When it is determined that the LTM cell handover command MAC CE cannot be sent, an LTM trigger failure message is sent to the CU entity. The LTM trigger failure message includes at least one of the following: message type information, the ID of the terminal used in the CU entity, the ID of the terminal used in the source DU, the physical cell ID (PCI) of the target DU entity, and information about the reason for the LTM trigger failure.

3. The source DU entity according to claim 1, wherein, The controller determines that the LTM cell handover command MAC CE can be sent when at least one of the target configuration identifier ID, timing advance TA command, transmission configuration indicator TCI status ID, and bandwidth portion BWP ID included in the LTM cell handover command MAC CE can be configured.

4. The source DU entity according to claim 1, wherein, The LRM trigger request message and the LTM trigger response message include at least one of the following: message type information, the ID of the terminal used in the CU entity, the ID of the terminal used in the source DU, and the physical cell ID (PCI) of the target DU entity.

5. A centralized unit (CU) entity in a wireless communication system, the CU entity comprising: transceiver; as well as The controller controls the receiving of measurement report messages from the source distributed unit (DU) entity via the transceiver. Based on the measurement report message, determine whether the target DU entity is a mobility LTM candidate cell triggered by Layer 1 L1 / Layer 2 L2. When the target DU entity is determined to be the LTM candidate cell, an LRM trigger request message is sent to the source DU entity, and Based on the LTM trigger request message, an LTM trigger response message is received from the source DU entity.

6. The CU entity according to claim 5, wherein, The controller controls: based on the LRM trigger request message, to receive an LTM trigger failure message from the source DU entity, and The LTM trigger failure message includes at least one of the following: message type information, the ID of the terminal used in the CU entity, the ID of the terminal used in the source DU, the physical cell ID (PCI) of the target DU entity, and information about the reason for the LTM trigger failure.

7. The CU entity according to claim 5, wherein, The LTM trigger response message is received when at least one of the following included in the LTM cell handover command media access control (MAC) control element (CE), the target configuration identifier (ID), the timing advance (TA) command, the transmission configuration indicator (TCI) status ID, and the bandwidth portion (BWP) ID, can be configured.

8. The CU entity according to claim 5, wherein, The LRM trigger request message and the LTM trigger response message include at least one of the following: message type information, the ID of the terminal used in the CU entity, the ID of the terminal used in the source DU, and the physical cell ID (PCI) of the target DU entity.

9. A method performed by a source distributed unit (DU) entity in a wireless communication system, the method comprising: The terminal receives a measurement report message, which includes information indicating whether at least one neighboring cell measured by the terminal is a mobility LTM candidate cell triggered by Layer 1 L1 / Layer 2 L2. The measurement report message is sent to the centralized unit (CU) entity; Based on the measurement report message, receive an LTM trigger request message from the CU entity; Based on the receipt of the LRM trigger request message, determine whether the LTM cell handover command media access control (MAC) control element (CE) can be sent to the terminal. as well as When it is determined that the LTM cell handover command MAC CE can be sent, an LTM trigger response message is sent to the CU entity.

10. The method of claim 9, further comprising: When it is determined that the LTM cell handover command MAC CE cannot be sent, an LTM trigger failure message is sent to the CU entity. The LTM trigger failure message includes at least one of the following: message type information, the ID of the terminal used in the CU entity, the ID of the terminal used in the source DU, the physical cell ID (PCI) of the target DU entity, and information about the reason for the LTM trigger failure.

11. The method according to claim 9, wherein, In the determination, it is determined that the LTM cell handover command MAC CE can be sent when at least one of the target configuration identifier ID, timing advance TA command, transport configuration indicator TCI status ID, and bandwidth portion BWP ID included in the LTM cell handover command MAC CE can be configured. The LRM trigger request message and the LTM trigger response message include at least one of the following: message type information, the ID of the terminal used in the CU entity, the ID of the terminal used in the source DU, and the physical cell ID (PCI) of the target DU entity.

12. A method performed by a centralized unit (CU) entity in a wireless communication system, the method comprising: Receive measurement report messages from the source distributed unit (DU) entity; Based on the measurement report message, determine whether the target DU entity is a mobility LTM candidate cell triggered by Layer 1 L1 / Layer 2 L2; When the target DU entity is determined to be the LTM candidate cell, an LTM trigger request message is sent to the source DU entity; as well as Based on the LRM trigger request message, an LTM trigger response message is received from the source DU entity.

13. The method of claim 12, further comprising: Based on the LRM trigger request message, an LTM trigger failure message is received from the source DU entity. The LTM trigger failure message includes at least one of the following: message type information, the ID of the terminal used in the CU entity, the ID of the terminal used in the source DU, the physical cell ID (PCI) of the target DU entity, and information about the reason for the LTM trigger failure.

14. The method according to claim 12, wherein, The LTM trigger response message is received when at least one of the following included in the LTM cell handover command media access control (MAC) control element (CE), the target configuration identifier (ID), the timing advance (TA) command, the transmission configuration indicator (TCI) status ID, and the bandwidth portion (BWP) ID, can be configured.

15. The method according to claim 12, wherein, The LRM trigger request message and the LTM trigger response message include at least one of the following: message type information, the ID of the terminal used in the CU entity, the ID of the terminal used in the source DU, and the physical cell ID (PCI) of the target DU entity.

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