Method performed by node in a wireless communication system and node

Abstract

The disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. The present disclosure proposes a method performed by a node in a wireless communication system and the node. According to an embodiment, a method performed by a first node in a wireless communication system comprises: transmitting, to a second node, a first request message for requesting an identifier of an early random access channel (RACH) resource requester to which a candidate cell for a layer 1 / layer 2 triggered mobility (LTM) handover belongs; receiving, from the second node, a first response message including an identifier of the candidate cell and an identifier of the early RACH resource requester to which the candidate cell belongs, wherein the first node is a central unit (CU) of a source node and the second node is a CU of a candidate node; or the first node is a master node and the second node is a secondary node.

Description

METHOD PERFORMED BY NODE IN A WIRELESS COMMUNICATION SYSTEM AND NODE

[0001] The present disclosure relates to the field of wireless communication technology, and specifically to a method performed by a node in a wireless communication system and the node.

[0002] 5G mobile communication technologies define broad frequency bands such that high transmission rates and new services are possible, and can be implemented not only in “Sub 6GHz” bands such as 3.5GHz, but also in “Above 6GHz” bands referred to as mmWave including 28GHz and 39GHz. In addition, it has been considered to implement 6G mobile communication technologies (referred to as Beyond 5G systems) in terahertz (THz) bands (for example, 95GHz to 3THz bands) in order to accomplish transmission rates fifty times faster than 5G mobile communication technologies and ultra-low latencies one-tenth of 5G mobile communication technologies.

[0003] At the beginning of the development of 5G mobile communication technologies, in order to support services and to satisfy performance requirements in connection with enhanced Mobile BroadBand (eMBB), Ultra Reliable Low Latency Communications (URLLC), and massive Machine-Type Communications (mMTC), there has been ongoing standardization regarding beamforming and massive MIMO for mitigating radio-wave path loss and increasing radio-wave transmission distances in mmWave, supporting numerologies (for example, operating multiple subcarrier spacings) for efficiently utilizing mmWave resources and dynamic operation of slot formats, initial access technologies for supporting multi-beam transmission and broadbands, definition and operation of BWP (BandWidth Part), new channel coding methods such as a LDPC (Low Density Parity Check) code for large amount of data transmission and a polar code for highly reliable transmission of control information, L2 pre-processing, and network slicing for providing a dedicated network specialized to a specific service.

[0004] Currently, there are ongoing discussions regarding improvement and performance enhancement of initial 5G mobile communication technologies in view of services to be supported by 5G mobile communication technologies, and there has been physical layer standardization regarding technologies such as V2X (Vehicle-to-everything) for aiding driving determination by autonomous vehicles based on information regarding positions and states of vehicles transmitted by the vehicles and for enhancing user convenience, NR-U (New Radio Unlicensed) aimed at system operations conforming to various regulation-related requirements in unlicensed bands, NR UE Power Saving, Non-Terrestrial Network (NTN) which is UE-satellite direct communication for providing coverage in an area in which communication with terrestrial networks is unavailable, and positioning.

[0005] Moreover, there has been ongoing standardization in air interface architecture / protocol regarding technologies such as Industrial Internet of Things (IIoT) for supporting new services through interworking and convergence with other industries, IAB (Integrated Access and Backhaul) for providing a node for network service area expansion by supporting a wireless backhaul link and an access link in an integrated manner, mobility enhancement including conditional handover and DAPS (Dual Active Protocol Stack) handover, and two-step random access for simplifying random access procedures (2-step RACH for NR). There also has been ongoing standardization in system architecture / service regarding a 5G baseline architecture (for example, service based architecture or service based interface) for combining Network Functions Virtualization (NFV) and Software-Defined Networking (SDN) technologies, and Mobile Edge Computing (MEC) for receiving services based on UE positions.

[0006] As 5G mobile communication systems are commercialized, connected devices that have been exponentially increasing will be connected to communication networks, and it is accordingly expected that enhanced functions and performances of 5G mobile communication systems and integrated operations of connected devices will be necessary. To this end, new research is scheduled in connection with eXtended Reality (XR) for efficiently supporting AR (Augmented Reality), VR (Virtual Reality), MR (Mixed Reality) and the like, 5G performance improvement and complexity reduction by utilizing Artificial Intelligence (AI) and Machine Learning (ML), AI service support, metaverse service support, and drone communication.

[0007] Furthermore, such development of 5G mobile communication systems will serve as a basis for developing not only new waveforms for providing coverage in terahertz bands of 6G mobile communication technologies, multi-antenna transmission technologies such as Full Dimensional MIMO (FD-MIMO), array antennas and large-scale antennas, metamaterial-based lenses and antennas for improving coverage of terahertz band signals, high-dimensional space multiplexing technology using OAM (Orbital Angular Momentum), and RIS (Reconfigurable Intelligent Surface), but also full-duplex technology for increasing frequency efficiency of 6G mobile communication technologies and improving system networks, AI-based communication technology for implementing system optimization by utilizing satellites and AI (Artificial Intelligence) from the design stage and internalizing end-to-end AI support functions, and next-generation distributed computing technology for implementing services at levels of complexity exceeding the limit of UE operation capability by utilizing ultra-high-performance communication and computing resources.

[0008] The present disclosure relates to a method performed by a node for a mechanism of resource allocation in a wireless communication system and the node.

[0009] According to an aspect of an exemplary embodiment, there is provided a communication method in a wireless communication system.

[0010] Aspects of the present disclosure provide efficient communication methods in a wireless communication system.

[0011] The above and additional aspects and advantages of the present disclosure will become clearer and easier to understand through the following description given in combinaiton with the accompanying drawings. Here,

[0012] FIG. 1 is an exemplary system architecture of a system architecture evolution in various embodiments of the present disclosure;

[0013] FIG. 2 is an exemplary system architecture according to various embodiments of the present disclosure;

[0014] FIG. 3 is an exemplary flow diagram of a mobility mechanism between base stations according to the present disclosure;

[0015] FIG. 4 is another exemplary flow diagram of the mobility mechanism between base stations according to the present disclosure;

[0016] FIG. 5 is a flowchart of a method performed by a first node according to an exemplary embodiment of the present disclosure;

[0017] FIG. 6 is a flowchart of a method performed by a second node according to an exemplary embodiment of the present disclosure;

[0018] FIG. 7 is a flowchart of a method performed by a DU of a source node according to an exemplary embodiment of the present disclosure;

[0019] FIG. 8 is a flowchart of a method performed by a UE according to an exemplary embodiment of the present disclosure;

[0020] FIG. 9 illustrates an exemplary structure of each node applicable to the present disclosure;

[0021] FIG. 10 is a block diagram of a terminal or user equipment (UE) according to an embodiment of the disclosure;

[0022] FIG. 11 is a block diagram of a base station (BS) according to an embodiment of the disclosure; and

[0023] FIG. 12 is a block diagram of a network entity according to an embodiment of the disclosure.

[0024] According to an aspect of the present disclosure, a method performed by a first node in a wireless communication system is provided. The method comprises: transmitting, to a second node, a first request message for requesting an identifier of an early random access channel (RACH) resource requester to which a candidate cell for a layer 1 / layer 2 (L1 / L2) triggered mobility (LTM) handover belongs; receiving, from the second node, a first response message including an identifier of the candidate cell and an identifier of the early RACH resource requester to which the candidate cell belongs, wherein the first node is a central unit (CU) of a source node and the second node is a CU of a candidate node; or the first node is a master node and the second node is a secondary node.

[0025] According to an exemplary embodiment, the first response message may further comprise an identifier of a node to which the early RACH resource requester belongs.

[0026] According to an exemplary embodiment, the first request message may comprise the identifier of the candidate cell and Indication information for requesting the identifier of the early RACH resource requester, wherein the identifier of the early RACH resource requester is an identifier of an entity which indicates to request an early RACH resource.

[0027] According to an exemplary embodiment, the first request message may comprise at least one of: an Xn Setup Request message; an Xn Application Protocol (AP) Retrieve Early RACH Resource Requester IDentifier Request message; and an XnAP New Generation Radio Access Network Node Configuration Update message.

[0028] According to an exemplary embodiment, the first response message may comprise at least one of: an Xn Setup Response message; an Xn Application Protocol (AP) Retrieve Early RACH Resource Requester IDentifier Response message; and an XnAP New Generation Radio Access Network Node Configuration Update Acknowledge message.

[0029] According to an exemplary embodiment, the method may further comprise: receiving, from the second node, a second message comprising at least one of: timing advanced (TA)-related information of the candidate cell; the identifier of the early RACH resource requester; and an identifier of a node to which the early RACH resource requester belongs.

[0030] According to an exemplary embodiment, the method may further comprise: transmitting the TA-related information of the candidate cell to the node indicated by the identifier of the node to which the early RACH resource requester belongs or to a node indicated by the identifier of the early RACH resource requester.

[0031] According to an exemplary embodiment, the method may further comprise: receiving a second request message, wherein the second request message comprises information for requesting to configure an early RACH resource allocated to a node by the candidate cell based on a UE or based on a DU; and transmitting a second response message, wherein the second response message comprises information related to the early RACH resource allocated to the node by the candidate cell, configured based on the UE or based on the DU.

[0032] According to an exemplary embodiment, the second request message may comprise: the identifier of the candidate cell; and indication information for requesting to configure the early RACH resource allocated to the node by the candidate cell based on the UE or based on the DU.

[0033] According to an exemplary embodiment, the second response message may comprise: the identifier of the candidate cell; and Early Uplink Synchronization Configuration information.

[0034] According to an exemplary embodiment, the second request message may comprise at least one of: an Early RACH Resource Request message; a UE Context Modification Request; a UE Context Modification Required message; a Secondary Node (SN) Modification Required message; and an SN Modification Request message.

[0035] According to an exemplary embodiment, the second response message may comprise at least one of: an Early RACH Resource Request Acknowledge message; an Early RACH Resource Response message; a UE Context Modification Response message; a UE Context Modification Acknowledge message; an SN Modification Acknowledge message; and an SN Modification Request Acknowledge message.

[0036] According to another aspect of the present disclosure, a method performed by a second node in a wireless communication system is provided. The method comprises: receiving, from a first node, a first request message for requesting an identifier of an early random access channel (RACH) resource requester to which a candidate cell for a layer 1 / layer 2 triggered mobility (LTM) handover belongs; transmitting, to the first node, a first response message comprising an identifier of the candidate cell and an identifier of the early RACH resource requester to which the candidate cell belongs, wherein the first node is a central unit (CU) of a source node and the second node is a CU of a candidate node; or the first node is a master node and the second node is a secondary node.

[0037] According to an exemplary embodiment, the first response message may further comprise an identifier of a node to which the early RACH resource requester belongs.

[0038] According to an exemplary embodiment, the first request message may comprise the identifier of the candidate cell and Indication information for requesting the identifier of the early RACH resource requester, wherein the identifier of the early RACH resource requester is an identifier of an entity which indicates to request an early RACH resource.

[0039] According to an exemplary embodiment, the first request message may comprise at least one of: an Xn Setup Request message; an Xn Application Protocol (AP) Retrieve Early RACH Resource Requester IDentifier Request message; and an XnAP New Generation Radio Access Network Node Configuration Update message.

[0040] According to an exemplary embodiment, the first response message may comprise at least one of: an Xn Setup Response message; an Xn Application Protocol (AP) Retrieve Early RACH Resource Requester IDentifier Response message; and an XnAP New Generation Radio Access Network Node Configuration Update Acknowledge message.

[0041] According to an exemplary embodiment, the method may further comprise: transmitting, to the first node,a second message comprising at least one of: timing advanced (TA)-related information of the candidate cell; the identifier of the early RACH resource requester; and an identifier of a node to which the early RACH resource requester belongs.

[0042] According to an exemplary embodiment, the method may further comprise: transmitting a second request message, wherein the second request message comprises information for requesting to configure an early RACH resource allocated to a node by the candidate cell based on a UE or based on a DU; and receiving a second response message, wherein the second response message comprises information related to the early RACH resource allocated to the node by the candidate cell, configured based on the UE or based on the DU.

[0043] According to an exemplary embodiment, the second request message may comprise: the identifier of the candidate cell; and indication information for requesting to configure the early RACH resource allocated to the node by the candidate cell based on the UE or based on the DU.

[0044] According to an exemplary embodiment, the second response message may comprise: the identifier of the candidate cell; and Early Uplink Synchronization Configuration information.

[0045] According to an exemplary embodiment, the second request message may comprise at least one of: an Early RACH Resource Request message; a UE Context Modification Request; a UE Context Modification Required message; a Secondary Node (SN) Modification Required message; and an SN Modification Request message.

[0046] According to an exemplary embodiment, the second response message may comprise at least one of: an Early RACH Resource Request Acknowledge message; an Early RACH Resource Response message; a UE Context Modification Response message; a UE Context Modification Acknowledge message; an SN Modification Acknowledge message; and an SN Modification Request Acknowledge message.

[0047] According to an exemplary embodiment, the method further comprises: transmitting a second message to the first node, wherein the second message comprise at least one of: timing advanced (TA)-related information of the candidate cell; the identifier of the early RACH resource requester; and an identifier of a node to which the early RACH resource requester belongs.

[0048] According to another aspect of the present disclosure, a method performed by a distributed unit (DU) of a source node in a wireless communication system is provided. The method comprises: transmitting a second request message to a first node, wherein the second request message comprises information for requesting to configure an early RACH resource allocated to a node by a candidate cell based on a UE or based on the DU; and receiving a second response message from the first node, wherein the second response message comprises information related to the early RACH resource allocated to the node by the candidate cell, configured based on the UE or based on the DU.

[0049] According to an exemplary embodiment, the second request message may comprise: an identifier of the candidate cell; and indication information for requesting to configure the early RACH resource allocated to the node by the candidate cell based on the UE or based on the DU.

[0050] According to an exemplary embodiment, the second response message may comprise: the identifier of the candidate cell; and Early Uplink Synchronization Configuration information.

[0051] According to an exemplary embodiment, the second request message may comprise at least one of: an Early RACH Resource Request message; a UE Context Modification Request; a UE Context Modification Required message; a Secondary Node (SN) Modification Required message; and an SN Modification Request message.

[0052] According to an exemplary embodiment, the second response message may comprise at least one of: an Early RACH Resource Request Acknowledge message; an Early RACH Resource Response message; a UE Context Modification Response message; a UE Context Modification Acknowledge message; an SN Modification Acknowledge message; and an SN Modification Request Acknowledge message.

[0053] According to an exemplary embodiment, a first request message is transmitted by the first node, and the first request message is used to request an identifier of an early random access channel (RACH) resource requester to which a candidate cell for a layer 1 / layer 2 triggered mobility (LTM) handover belongs; and a first response message is transmitted by a second node, and the first response message comprises an identifier of the candidate cell and the identifier of the early RACH resource requester to which the candidate cell belongs, wherein the first node is a central unit (CU) of the source node and the second node is a CU of a candidate node; or the first node is a master node and the second node is a secondary node.

[0054] According to an exemplary embodiment, the first response message may further comprise an identifier of a node to which the early RACH resource requester belongs.

[0055] According to an exemplary embodiment, the first request message may comprise the identifier of the candidate cell and Indication information for requesting the identifier of the early RACH resource requester, wherein the identifier of the early RACH resource requester is an identifier of an entity which indicates to request an early RACH resource.

[0056] According to an exemplary embodiment, the first request message may comprise at least one of: an Xn Setup Request message; an Xn Application Protocol (AP) Retrieve Early RACH Resource Requester IDentifier Request message; and an XnAP New Generation Radio Access Network Node Configuration Update message.

[0057] According to an exemplary embodiment, the first response message may comprise at least one of: an Xn Setup Response message; an Xn Application Protocol (AP) Retrieve Early RACH Resource Requester IDentifier Response message; and an XnAP New Generation Radio Access Network Node Configuration Update Acknowledge message.

[0058] According to another aspect of the present disclosure, a method performed by a user equipment (UE) in a wireless communication system is provided. The method comprises: receiving a Radio Resource Control (RRC) Reconfiguration message; and transmitting an RRC Reconfiguration Complete message. A first request message is transmitted by a first node, and the first request message is used to request an identifier of an early random access channel (RACH) resource requester to which a candidate cell for a layer 1 / layer 2 triggered mobility (LTM) handover belongs.

[0059] A first response message is transmitted by a second node, and the first response message comprises an identifier of the candidate cell and an identifier of the early RACH resource requester to which the candidate cell belongs.

[0060] Here, the first node is a central unit (CU) of a source node and the second node is a CU of a candidate node; or the first node is a master node and the second node is a secondary node.

[0061] According to an exemplary embodiment, the first response message may further comprise an identifier of a node to which the early RACH resource requester belongs.

[0062] According to an exemplary embodiment, the first request message may comprise the identifier of the candidate cell and Indication information for requesting the identifier of the early RACH resource requester, wherein the identifier of the early RACH resource requester is an identifier of an entity which indicates to request an early RACH resource.

[0063] According to an exemplary embodiment, the first request message may comprise at least one of: an Xn Setup Request message; an Xn Application Protocol (AP) Retrieve Early RACH Resource Requester IDentifier Request message; and an XnAP New Generation Radio Access Network Node Configuration Update message.

[0064] According to an exemplary embodiment, the first response message may comprise at least one of: an Xn Setup Response message; an Xn Application Protocol (AP) Retrieve Early RACH Resource Requester IDentifier Response message; and an XnAP New Generation Radio Access Network Node Configuration Update Acknowledge message.

[0065] According to an exemplary embodiment, a second request message is transmitted by the second node, and a second response message is transmitted by the first node. The second request message comprises information for requesting to configure an early RACH resource allocated to a node by the candidate cell based on the UE or based on a DU; and the second response message comprises information related to the early RACH resource allocated to the node by the candidate cell, configured based on the UE or based on the DU.

[0066] According to an exemplary embodiment, the second request message may comprise: the identifier of the candidate cell; and indication information for requesting to configure the early RACH resource allocated to the node by the candidate cell based on the UE or based on the DU.

[0067] According to an exemplary embodiment, the second response message may comprise: the identifier of the candidate cell; and Early Uplink Synchronization Configuration information.

[0068] According to an exemplary embodiment, the second request message may comprise at least one of: an Early RACH Resource Request message; a UE Context Modification Request; a UE Context Modification Required message; a Secondary Node (SN) Modification Required message; and an SN Modification Request message.

[0069] According to an exemplary embodiment, the second response message may comprise at least one of: an Early RACH Resource Request Acknowledge message; an Early RACH Resource Response message; a UE Context Modification Response message; a UE Context Modification Acknowledge message; an SN Modification Acknowledge message; and an SN Modification Request Acknowledge message.

[0070] According to an exemplary embodiment, a second message is transmitted by the second node, and the second message comprises at least one of: timing advanced (TA)-related information of the candidate cell; the identifier of the early RACH resource requester; and an identifier of a node to which the early RACH resource requester belongs.

[0071] According to other aspects of the present disclosure, a first node, a second node, a DU of a source node and a user equipment (UE) that perform the above methods are further disclosed. According to another aspect of the present disclosure, a computer readable storage medium is further disclosed. The computer readable storage medium stores a computer executable instruction. When the computer executable instruction is executed by a processor, the processor performs the above method performed by the first node, the second node, the DU of the source node or the user equipment (UE).According to the implementations of the present disclosure, it is possible to determine which gNB-DU under the base station the candidate cell belongs to.

[0072] Hereinafter, embodiments of the disclosure will be described in detail with reference to the accompanying drawings.

[0073] In describing the embodiments, while numerous details are set forth for the purpose of illustration, it is understood that some aspects of the disclosure may be practiced with less than all of these details. Numerous variations and alternatives to the details provided herein are possible and are considered within the scope of the disclosure. In some instances, descriptions related to technical contents well-known in the art may be omitted so as to not obscure an understanding of the disclosure, and such omitted descriptions are understood to be within the scope of the disclosure.

[0074] For the same reason, in the accompanying drawings, some elements may be exaggerated, omitted, or schematically illustrated. Further, the size of each element does not completely reflect the actual size. In the drawings, identical or corresponding elements are provided with identical reference numerals or different reference numerals.

[0075] The advantages and features of the disclosure and ways to achieve them will be apparent by making reference to embodiments as described herein in detail in conjunction with the accompanying drawings. However, the disclosure is not limited to the embodiments set forth herein, but may be implemented in various different forms. Other features, aspects, and advantages of the subject matter described herein will become apparent from the disclosure. The following embodiments are merely examples to aid in an understanding of the disclosure and should not be construed to narrow the scope or spirit of the subject matter described herein in any way, but on the contrary, the disclosure covers all modifications, equivalents and alternatives falling within the spirit and scope of the subject matter as defined by the appended claims and equivalents thereof. Throughout the specification, the same or like reference numerals designate the same or like elements. Furthermore, terms which will be described herein are terms defined in consideration of the functions in the disclosure, and may be different according to users, intentions of the operators, or customs. Therefore, the definitions of the terms should be made based on the contents throughout the specification.

[0076] Herein, it will be understood that each block of flowchart illustrations, and combinations of blocks in the flowchart illustrations, may be performed based on computer program instructions. These computer program instructions may be loaded collectively onto at least one processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which perform through any one of, or in any combination of, the at least one processor of the computer or other programmable data processing apparatus, create means for performing the functions specified in the flowchart block(s). These computer program instructions may also be stored in a non-transitory computer usable or computer-readable memory that may direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer usable or computer-readable memory produce an article of manufacture including instruction means that perform the function specified in the flowchart block(s). The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable data processing apparatus to produce a computer executed process such that the instructions that perform on the computer or other programmable data processing apparatus provide steps for executing the functions specified in the flowchart block(s).

[0077] Further, each block may represent a module, segment, or portion of code, which includes one or more executable instructions for executing the specified logical function(s). It should also be noted that in some alternative implementations, the functions noted in the blocks may occur out of the order. For example, two blocks(or functions) shown in succession may in fact be performed substantially concurrently or the blocks may sometimes be performed in the reverse order, depending upon the functionality involved.

[0078] As used in embodiments of the disclosure, a “~unit / module” may refer to a software element or a hardware element, such as a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC), which performs a predetermined function. However, the term including the word “~unit / module” does not always have a meaning limited to software or hardware. The “~unit / module” may be constructed either to be stored in an addressable storage medium or to execute one or more processors. Therefore, the “~unit / module” includes, for example, software elements, object-oriented software elements, components such as class elements and task elements, processes, functions, properties, procedures, sub-routines, segments of a program code, drivers, firmware, micro-codes, circuits, data, database, data structures, tables, arrays, and parameters. The components and functions provided by the “~unit / module” may be either combined into a smaller number of components and a “~unit / module,” or divided into additional components and a “~unit / module.” Moreover, the components and “~units / modules” may be implemented to reproduce one or more central processing units (CPUs) within a device or a security multimedia card. Further, in the embodiments, the “~unit / module” may include one or more processors.

[0079] The entirety of the one or more computer programs may be stored in a single memory device or the one or more computer programs may be divided with different portions stored in different multiple memory devices.

[0080] Any of the functions or operations described herein can be processed by one processor or a combination of processors. The one processor or the combination of processors is circuitry performing processing and includes circuitry like an application processor (AP, e.g. a CPU), a communication processor (CP, e.g., a modem), a graphics processing unit (GPU), a neural processing unit (NPU) (e.g., an artificial intelligence (AI) chip), a Wi-Fi chip, a Bluetooth® chip, a global positioning system (GPS) chip, a near field communication (NFC) chip, connectivity chips, a sensor controller, a touch controller, a finger-print sensor controller, a display driver integrated circuit (IC), an audio CODEC chip, a universal serial bus (USB) controller, a camera controller, an image processing IC, microprocessors, microcontrollers, digital signal processors, FPGA, ASIC, a microprocessor unit (MPU), a system on chip (SoC), an IC, or the like. The one processor or the combination of processors executes instructions that can be stored in a memory, such as the operating system, in order to control the overall operation of the device. Also, the one processor or the combination of processors is also capable of executing other processes and programs resident in the memory, such as processes for the disclosure.

[0081] It will be appreciated that various embodiments of the disclosure according to the claims and description in the specification can be realized in the form of hardware, software or a combination of hardware and software.

[0082] Any such software may be stored in non-transitory computer readable storage media. The non-transitory computer readable storage media store one or more computer programs (software modules), the one or more computer programs include computer-executable instructions that, when executed by one or more processors of an electronic device individually or collectively, cause the electronic device to perform a method of the disclosure. Additionally, or alternatively, such software may be a computer program [product] comprising instructions which, when executed by one or more processors of an electronic device individually or collectively, cause the electronic device to perform a method of the disclosure.

[0083] Any such software may be stored in the form of volatile or non-volatile storage such as, for example, a storage device like read only memory (ROM), whether erasable or rewritable or not, or in the form of memory such as, for example, random access memory (RAM), memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a compact disk (CD), digital versatile disc (DVD), magnetic disk or magnetic tape or the like. It will be appreciated that the storage devices and storage media are various embodiments of non-transitory machine-readable storage that are suitable for storing a computer program or computer programs comprising instructions that, when executed, implement various embodiments of the disclosure. Accordingly, various embodiments of the present disclosure may provide a program comprising code for implementing apparatus or a method as claimed in any one of the claims of this specification and a non-transitory machine-readable storage storing such a program.

[0084] Hereinafter, the determination of priority between A and B in the present disclosure may refer to various actions such as selecting the one having a higher priority based on a predefined priority rule and performing an operation corresponding thereto, or omitting or dropping an operation corresponding to the one having a lower priority.

[0085] Hereinafter, "A or B" as described in the present disclosure may be understood as "A and / or B," which may include A, or B, or both A and B.

[0086] In addition, "at least one of A, B, and C" as described in the present disclosure may be understood to include A, or B, or C, or any combination of A, B, and C.

[0087] In addition, "at least one of A, B, or C" as described in the present disclosure may be understood to include A, or B, or C, or any combination of A, B, and C.

[0088] Furthermore, "A / B" as described in the present disclosure may be understood as "A and / or B," which may include A, or B, or both A and B.

[0089] Furthermore, "A, B" as described in the present disclosure may be understood as "A and / or B," which may include A, or B, or both A and B.

[0090] Furthermore, "A and B" as described in the present disclosure may be understood as "A and / or B," which may include A, or B, or both A and B.

[0091] Furthermore, “if condition A and condition B are satisfied,” as described in the present disclosure, may not be limited to a case where both condition A and condition B are satisfied, but may be understood to include a case where either condition A or condition B is individually satisfied, both condition A and condition B are satisfied, or one or more additional conditions are satisfied in combination.

[0092] Furthermore, throughout this disclosure, ordinal terms such as "first," "second," "third," etc., (and similar qualifiers) are used merely to distinguish between different instances, occurrences, configurations, messages, stages, elements or aspects of elements, operations, or information as described herein. Unless the context clearly dictates otherwise, the use of such ordinal terms does not itself require that the elements, operations, or information distinguished by these terms be structurally different, numerically distinct, or substantively dissimilar. For example, a "first signal" and a "second signal" may refer to instances of the same signal transmitted at different times or containing the same core information despite minor variations, or they may refer to signals with different content or characteristics, depending on the specific context. Similarly, a "first value" and a "second value" may represent the same magnitude but measured or applied in different circumstances, or they may represent different magnitudes. The interpretation should be guided by the specific technical context, function, and relationship described in the relevant portion of the specification and claims.

[0093] Furthermore, the terms “first ~”, “second ~”, etc., as described in the present disclosure with respect to various elements (e.g., information, objects, operation, sequences, or the like), should not limit those elements. These terms may only be intended to distinguish one element from another, and may not be intended to indicate a specific order. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element.

[0094] Furthermore, even if “first ~” and “second ~” are described in the present disclosure, it may be understood that element(s) referred to by “first ~” and “second ~” may be the same or different. For example, in case of element(s) being information, first information and second information may both be same information and, in some cases, are separate and different information.

[0095] In addition, the terms “if ~” and “in case that ~” as used in the disclosure or claims may be interpreted to include the meanings of “when (or upon) ~,” “in response to ~,” “based on ~,” or “according to ~,” and may be used interchangeably with these expressions. In addition, expressions other than those exemplified herein may also be used, as long as they have substantially the same meaning and do not impair the technical features of the present disclosure. If a method step (e.g. transmit a signal) is performed according to the disclosure of the application in connection with one of the above terms (such as “in case that ~” or the like), it may be interpreted to include the meanings (disclosure) of a prior determination that a feature has a specific state “~” (e.g. a bit length is above X), and then perform the method step in response to said determination.

[0096] For example, the physical layer signaling may be referred to as Layer 1 (L1) signaling and may include downlink control information (DCI). In addition, the higher layer signaling may include a medium access control (MAC) control message, a radio resource control (RRC) signaling message, a non-access stratum (NAS) signaling message, or an application layer message. The RRC signaling message may be referred to as L3 (layer 3) signaling. It should be noted, however, that the higher layer signaling is not limited to the aforementioned examples.

[0097] In addition, the term "not perform" as used in the present disclosure or claims may, in context, be understood to mean that the corresponding step is omitted or skipped. Such a term may be replaced with other terms having the same or substantially equivalent meaning.

[0098] In addition, "transmitting a message including A and B" as described in the present disclosure, may be understood as encompassing both (i) transmitting A and B in a single message, and (ii) transmitting A and B separately via multiple messages (e.g., transmitting a first message including A and a second message including B). This interpretation may also apply to messages that include two or more items (e.g., A, B, C), transmitted either together or separately.

[0099] In addition, "transmitting a message including A and transmitting a message including B" may also be interpreted as transmitting a message including A and B in a single message.

[0100] In the embodiments of the present disclosure described herein, terms or components included in the disclosure may be expressed in singular or plural form depending on the specific embodiments presented. However, such singular or plural expressions are selected appropriately for convenience of description, and the present disclosure is not limited to a singular or plural number of components. A component expressed in the plural form may be implemented as a single component, and a component expressed in the singular form may be implemented as multiple components.

[0101] The drawings or flowcharts described herein illustrate example methods that may be implemented according to the principles of the present disclosure, and various modifications may be made to the methods illustrated in the flowcharts of the present disclosure. For example, although illustrated as a series of steps, various steps in each drawing or flowchart may overlap, occur in parallel, occur in a different order, or be repeated. In other examples, any step may be omitted or replaced with another step.

[0102] The process of the flowchart may be performed by a device. One or more of the steps of the flowchart can be implemented by one or more processors / computer programs executing instructions to perform the noted functions.

[0103] The methods and apparatuses proposed in the embodiments of the present disclosure may be disclosed in connection with drawings disclosing flowcharts to illustrate example methods that may be implemented according to the principles of the present disclosure. Such flowcharts may contain different branches and / or sub-branches. It is understood that the principles of the present disclosure do not only contain the combination of all branches / sub-branches disclosed in the embodiment, but the present disclosure also contains at least one isolated branch / isolated sub-branch, in particular to a single branch / single sub-branch.

[0104] The methods and apparatuses proposed in the embodiments of the present disclosure are not limited to each embodiment individually, but may also be applied in combination of all or some of the embodiments proposed in the disclosure. Therefore, the embodiments of the present disclosure may be modified and applied without significantly departing from the scope of the present disclosure, as would be understood by those skilled in the art.

[0105] In this case, even if certain wordings are described differently across embodiments, they may be used interchangeably or in substitution or in combination if their underlying concepts are equivalent. For example, for the same or equivalent concept, even if one embodiment uses the expression "A" and another embodiment uses the expression "B", such expressions may be understood interchangeably, in substitution, or in combination.

[0106] The terms used in the following description to refer to access nodes, network entities, messages, interfaces between network entities, various types of identification information, and the like, are provided merely for the convenience of explanation by way of example. Therefore, the present disclosure is not limited to the terms describedherein, and other terms having equivalent technical meanings may also be used. Such terms may also be interchangeable with terms defined in any 3rd generation partnership project (3GPP) technical specifications (TS) or similar technical specifications, e.g., from the European telecommunications standards institute (ETSI), where appropriate.

[0107] Hereinafter, a base station (BS) is an entity that allocates resources to terminals, and may be at least one of a gNode B, an eNode B, a Node B, a wireless access unit, a BS controller, or a node on a network.

[0108] Furthermore, the base station of the present disclosure may include a split architecture comprising a central unit (CU) and a distributed unit (DU). In this structure, the CU is configured to process the higher layers of the control and user planes, while the DU is configured to process lower-layer radio resource functions. The embodiments of the present disclosure may be equally applicable to 5th generation (5G) base station architectures in which such CU and DU functional splits are implemented.

[0109] A terminal may include a user equipment (UE), a mobile station (MS), a cellular phone, a smartphone, a computer, a tablet, a wearable device, an Internet of Things (IoT) device, or any other device / system capable of performing communication functions.

[0110] In the disclosure, a downlink (DL) refers to a radio link through which a BS transmits a signal to a terminal, and an uplink (UL) refers to a radio link through which a terminal transmits a signal to a BS.

[0111] Furthermore, hereinafter, 5G mobile communication technologies (e.g., 5G new radio (NR)), 6th generation (6G) mobile communication technologies may be described by way of example, but the embodiments of the present disclosure may also be applied to other communication systems having similar technical backgrounds or channel types. For example, newly evolved mobile communication systems developed after 5G and 6G may be included. Furthermore, based on determinations by those skilled in the art, the embodiments of the present disclosure may also be applied to other communication systems (e.g., Wi-Fi systems) through some modifications without significantly departing from the scope of the present disclosure

[0112] In the following description, the terms physical channel and signal may be used interchangeably with data or control signal. For example, the term physical downlink shared channel (PDSCH) refers to a physical channel through which data is transmitted, but the term PDSCH may also be used to refer to the data itself. That is, in the present disclosure, the expression "transmit a physical channel" may be interpreted as being equivalent to the expression "transmit data or a signal via a physical channel."

[0113] Hereinafter, in the context of the present disclosure, higher layer signaling may refer to signaling corresponding to at least one or any combination of the following: master information block (MIB), system information block (SIB) or SIB M (M = 1, 2, ...), RRC, or MAC control element (CE), or a non-access stratum (NAS) signaling message, or an application layer message. The RRC signaling message may be referred to as Layer 3 (L3) signaling.

[0114] In addition, L1 signaling may refer to signaling corresponding to at least one or any combination of signaling techniques using the at least one or any combination of the following physical layer channels or signaling: physical downlink control channel (PDCCH), DCI, UE-specific DCI, group-common DCI, common DCI, scheduling DCI (e.g., DCI used for scheduling downlink or uplink data), non-scheduling DCI (e.g., DCI not used for scheduling downlink or uplink data) physical uplink control channel (PUCCH), or uplink control information (UCI). The L1 signaling message may be referred to as a physical layer signaling.

[0115] Hereinafter, the expression that information is configured by the BS, as used in the present disclosure or claims, may, in context, be understood to mean that the terminal receives the corresponding information from the BS via a physical layer signaling or a higher layer signaling. Such an expression may be replaced with other terms having the same or substantially equivalent meaning.

[0116] Hereinafter, the operational principle of the present disclosure will be described in detail with reference to the accompanying drawings.

[0117] In order to meet an increasing demand for wireless data communication services since a deployment of 4G communication system, efforts have been made to develop an improved 5G or pre-5G communication system. Therefore, the 5G or pre-5G communication system is also called “beyond 4G network” or “post LTE system”.

[0118] Wireless communication is one of the most successful innovations in modern history. Recently, a number of subscribers of wireless communication services has exceeded 5 billion, and it continues growing rapidly. With the increasing popularity of smart phones and other mobile data devices (such as tablet computers, notebook computers, netbooks, e-book readers and machine-type devices) in consumers and enterprises, a demand for wireless data services is growing rapidly. In order to meet rapid growth of mobile data services and support new applications and deployments, it is very important to improve efficiency and coverage of wireless interfaces.

[0119] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the present disclosure as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the various embodiments described herein can be made without departing from the scope and spirit of the present disclosure. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness.

[0120] The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the present disclosure. Accordingly, it should be apparent to those skilled in the art that the following description of various embodiments of the present disclosure is provided for illustration purpose only and not for the purpose of limiting the present disclosure as defined by the appended claims and their equivalents.

[0121] It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces.

[0122] The term “include” or “may include” refers to the existence of a corresponding disclosed function, operation or component which can be used in various embodiments of the present disclosure and does not limit one or more additional functions, operations, or components. The terms such as “include” and / or “have” may be construed to denote a certain characteristic, number, step, operation, constituent element, component or a combination thereof, but may not be construed to exclude the existence of or a possibility of addition of one or more other characteristics, numbers, steps, operations, constituent elements, components or combinations thereof.

[0123] The term “or” used in various embodiments of the present disclosure includes any or all of combinations of listed words. For example, the expression “A or B” may include A, may include B, or may include both A and B.

[0124] Unless defined differently, all terms used herein, which include technical terminologies or scientific terminologies, have the same meaning as that understood by a person skilled in the art to which the present disclosure belongs. Such terms as those defined in a generally used dictionary are to be interpreted to have the meanings equal to the contextual meanings in the relevant field of art, and are not to be interpreted to have ideal or excessively formal meanings unless clearly defined in the present disclosure.

[0125] Figs. 1 to 9 discussed below and various embodiments for describing the principles of the present disclosure in this patent document are only for illustration and should not be interpreted as limiting the scope of the disclosure in any way. Those skilled in the art will understand that the principles of the present disclosure can be implemented in any suitably arranged system or device.

[0126] Fig. 1 is an exemplary system architecture 100 of system architecture evolution (SAE). User equipment (UE) 101 is a terminal device for receiving data. An evolved universal terrestrial radio access network (E-UTRAN) 102 is a radio access network, which includes a macro base station (eNodeB / NodeB) that provides UE with interfaces to access the radio network. A mobility management entity (MME) 103 is responsible for managing mobility context, session context and security information of the UE. A serving gateway (SGW) 104 mainly provides functions of user plane, and the MME 103 and the SGW 104 may be in the same physical entity. A packet data network gateway (PGW) 105 is responsible for functions of charging, lawful interception, etc., and may be in the same physical entity as the SGW 104. A policy and charging rules function entity (PCRF) 106 provides quality of service (QoS) policies and charging criteria. A general packet radio service support node (SGSN) 108 is a network node device that provides routing for data transmission in a universal mobile telecommunications system (UMTS). A home subscriber server (HSS)109 is a home subsystem of the UE, and is responsible for protecting user information including a current location of the UE, an address of a serving node, user security information, and packet data context of the UE, etc.

[0127] Fig. 2 is an exemplary system architecture 200 according to various embodiments of the present disclosure. Other embodiments of the system architecture 200 can be used without departing from the scope of the present disclosure. User equipment (UE) 201 is a terminal device for receiving data. A next generation radio access network (NG-RAN) 202 is a radio access network, which includes a base station (a gNB or an eNB connected to 5G core network 5GC, and the eNB connected to the 5GC is also called ng-gNB) that provides UE with interfaces to access the radio network. An access control and mobility management function entity (AMF) 203 is responsible for managing mobility context and security information of the UE. A user plane function entity (UPF) 204 mainly provides functions of user plane. A session management function entity SMF 205 is responsible for session management. A data network (DN) 206 includes, for example, services of operators, access of Internet and service of third parties.

[0128] For ease of description, the following description of embodiments of the present disclosure involves terms and explanations as follows:

[0129] 1. LTM: Layer 1 / Layer 2 Triggered Mobility.

[0130] 2. SCPAC (subsequent CPAC): Subsequent Conditional PSCell Addition or Change, which is a conditional PSCell addition procedure or a PSCell change procedure is performed, after Primary Secondary Cell (PSCell) Addition, PSCell Change, Primary Cell (PCell) Change, or Secondary Cell Group (SCG) Release, based on subsequent CPAC configuration of a pre-configured candidate PSCell, without reconfiguring or restarting Conditional PSCell Change (CPC) and / or Conditional PSCell Addition (CPA).

[0131] 3. CHO: Conditional Handover, which, for example, is performed only when an evaluation condition is satisfied. Based on a measurement report from a UE, the network side pre-configures resources of multiple candidate cells (which may be located at the same base station or at different base stations), and transmits the corresponding resource and measurement configuration of each candidate cell to the UE in advance. Then, the UE saves the corresponding resource of each candidate cell and performs measurement to evaluate the condition. When a candidate cell is found to meet the conditions, the UE disconnects from a source cell and applies the corresponding configuration after successfully accessing the candidate cell that meets the condition (e.g., a target cell). The UE then releases all the configuration of the other candidate cells, while the base station (or a node) to which the target cell belongs notifies the source base station (or a node) selected by the candidate cell. Then, the network side performs the operation of releasing all the configuration of the other candidate cells.

[0132] 4. AMF: Access and Mobility Management Function, which is a network element of the 5G core network responsible for the access and mobility management of a 5G base station. The 5G base station is connected to the AMF through an NG-C interface.

[0133] 5. NG-RAN node: New Generation Radio Access Network node, e.g., 5G base station, including gNB or ng-eNB.

[0134] 6. gNB: next Generation Node B, e.g., 5G New Radio (NR) base station.

[0135] 7. gNB-DU: gNB-Distributed Unit, has functions such as Radio Link Control (RLC) protocol, Medium Access Control (MAC) and Physical Layer (PHY) protocol.

[0136] 8. gNB-CU: gNB-Central Unit, has functions such as Radio Resource Control (RRC), Service Data Adaptation Protocol (SDAP) and Packet Data Convergence Protocol (PDCP).

[0137] 9. NR-DC: NR-NR Dual Connectivity, or, NG-RAN Dual Connectivity.

[0138] 10. MN: Master Node.

[0139] 11. SN: Secondary Node.

[0140] 12. MCG: Master Cell Group, in MR-DC, a group of serving cells associated with the Master Node, comprising of the SpCell (PCell) and optionally one or more SCells.

[0141] 13. SCG: Secondary Cell Group, in MR-DC, a group of serving cells associated with the Secondary Node, comprising of the SpCell (PSCell) and optionally one or more SCells.

[0142] 14. SpCell: primary cell of a master or secondary cell group.

[0143] 15. SpCell: special cell, e.g., primary cell serving a UE, a primary cell in a master cell group or a secondary cell group.

[0144] 16. PSCell: Primary Secondary Cell, e.g., SpCell of a secondary cell group.

[0145] 17. PCell: Primary Cell, e.g., SpCell of a master cell group.

[0146] 18. MR-DC: Multi-Radio Dual Connectivity, dual connectivity between an E-UTRA node and an NR node, or between two NR nodes.

[0147] It should be understood that the message names in the present disclosure are only examples and other names may also be used. The information to be transmitted between interfaces may be defined by a separate new message, or by adding a new Information Element (IE) in an existing message using the corresponding existing interface specification.

[0148] Exemplary embodiments of the present disclosure are further described below with reference to the accompanying drawings.

[0149] The text and drawings are provided as examples only to help understand the present disclosure. They should not be interpreted as limiting the scope of the present disclosure in any way. Although certain embodiments and examples have been provided, based on the disclosure herein, it will be apparent to those skilled in the art that changes may be made to the illustrated embodiments and examples without departing from the scope of the present disclosure.

[0150] In the present disclosure, the entities and / or nodes may include: network entities or network logical units such as gNB, gNB Central Unit (gNB-CU), gNB Distributed Unit (gNB-DU), gNB-CU-Control Plane (gNB CU-CP), gNB-CU-User Plane (gNB CU-UP), en-gNB, eNB, ng-eNB, UE, Access and Mobility Management Function (AMF), Session Management Function (SMF), or Mobility Management Entity (MME).

[0151] In the present disclosure, the handover may include one or more of the following: handover, secondary node addition, secondary node change, master node change, etc.

[0152] In the present disclosure, the node may refer to a node or to a cell managed by a node.

[0153] In the present disclosure, the cell may refer to a cell or to a node where a cell is located.

[0154] In the present disclosure, the source node may refer to any source node during handover, such as a source node, a source secondary node, or a source master node.

[0155] In the present disclosure, the target node may also refer to a candidate target secondary node.

[0156] In the present disclosure, the target node may refer to any target node during handover, such as a target node, a target secondary node, a target master node, a candidate (alternative) target node, a candidate target source node, or a candidate target master node.

[0157] In the present disclosure, the target node may refer to one or more of the following: a target gNB-CU, a target gNB-DU, a target gNB CU-CP, a target gNB CU-UP, etc.

[0158] In the present disclosure, the source node may refer to one or more of the following: a source gNB-CU, a source gNB-DU, a source gNB CU-CP, a source gNB CU-UP, etc.

[0159] In the present disclosure, the master node is equivalent to the master base station. The secondary node is equivalent to the secondary base station. The source node is equivalent to the source base station. The target node is equivalent to the target base station. The candidate node is equivalent to the candidate base station. The source master node is equivalent to the source master base station. The target master node is equivalent to the target master base station. The candidate master node is equivalent to the candidate master base station. The source secondary node is equivalent to the source secondary base station. The target secondary node is equivalent to the target secondary base station. The candidate secondary node is equivalent to the candidate secondary base station.

[0160] In the present disclosure, the message names are only examples, and other message names may also be used.

[0161] In the present disclosure, “first”, “second”, etc., included in the message names are used only to distinguish one message from another and do not represent any order of execution or transfer.

[0162] In the present disclosure, detailed descriptions of steps irrelevant to the present disclosure are omitted.

[0163] In the present disclosure, the steps in each flowchart may be performed in combination with each other or individually. The steps and the sequence thereof in each flowchart are only examples, other possible steps and / or sequences are not excluded.

[0164] In the present disclosure, the base station may be a 6G base station, a 5G base station (such as gNB, ng-eNB), a 4G base station (such as eNB), a RAN node, or other types of access nodes.

[0165] Different embodiments of the above process are described below based on the addition or release of a secondary base station or the addition of the same secondary base station or different secondary base stations that may occur in an LTM scenario between base station nodes. The nodes involved in the scenario include the following nodes:

[0166] 1. Source master node: the base station of the PCell currently serving the UE.

[0167] 2. Source secondary node: the base station of the PSCell currently serving the UE.

[0168] 3. Candidate master node (or target master node): the serving base station of the candidate PCell or the serving base station of the target primary cell, which is prepared for the UE.

[0169] 4. Candidate secondary node (or target secondary node): the serving base station of the candidate PSCell or the serving base station of the target PSCell, which is prepared for the UE. Further, for a MCG LTM scenario without secondary node change, the secondary node serving the UE does not change during the preparation for candidate cell or target cell (that is, if the UE switches to the candidate cell, the source secondary node is still the secondary node serving the UE, in other words, the candidate secondary node or the target secondary node is as same as the source secondary node), but the PSCell serving the UE may or may not change.

[0170] In the following embodiments, considering that the candidate secondary node or the target secondary node is as same as the source secondary node, the “source secondary node” is used to refer to the base station of the secondary cell group serving the UE.

[0171] In order to reduce the handover latency of the UE, the LTM handover method uses an underlying signaling to trigger the handover of the UE. However, in this handover method, it is required to configure many different candidate cells and nodes for the UE. In order to reduce the impact of interruption on the services of the UE during an LTM handover process, an early synchronization process may be performed before the LTM is triggered, such that the UE may perform downlink synchronization with the candidate cell in advance and trigger an early uplink synchronization process to obtain the timing advanced (TA) value with the candidate cell in advance. Accordingly, the UE can perform an RACH-less access process. In this way, it is possible to reduce the time taken to access the target cell (the selected candidate cell is the target cell), thereby reducing the impact of interruption on the data transmission service.

[0172] For the early uplink synchronization process, it is required to use the random access resource of the candidate cell to indicate the UE for use. Since the random access resource of each cell is limited, how to achieve a reasonable or maximized resource utilization rate is a technical direction worthy of research.

[0173] In some embodiments, it is possible to allocate the random access resource of the candidate cell for an earyly TA acquisition based on a base station, a DU or a cell, to improve the resource utilization rate. In a resource allocation process, if all LTM base stations (source base station and candidate base station) have a CU-DU split architecture, the random access resource of the candidate cell for the early TA acquisition can be allocated based on different gNB-DUs. In this situation, the source base station can determine which base station a candidate cell under a non-source base station (i.e., the candidate base station) belongs to (e.g., based on the cell ID or CGI information in an L3 measurement report), but cannot determine which gNB-DU under the base station the candidate cell belongs to.

[0174] FIG. 3 is an exemplary flow diagram of a mobility mechanism between base stations according to the present disclosure. This embodiment includes the following steps.

[0175] In step 301, a UE transmits a Measurement Report message to a source NG-RAN node.

[0176] As an example, if the source NG-RAN node is in an architecture in which a gNB-CU and a gNB-DU are separate, the UE transmits the Measurement Report message (which includes an L3 measurement result) to a source gNB-DU. The L3 measurement result includes the measurement value of a neighbour cell. The source gNB-DU transmits an Uplink Radio Resource Control (UL RRC) Message Transfer message to transfer the received Measurement Report message to a source gNB-CU.

[0177] In step 302, the source NG-RAN node or the source gNB-CU determines to perform an LTM resource configuration.

[0178] As an example, the source NG-RAN node or the source gNB-CU receives the L3 measurement report reported by the UE and decides to perform an LTM configuration.

[0179] In step 303, the source NG-RAN node or the source gNB-CU transmits a Handover Request message to a candidate NG-RAN node or a candidate gNB-CU.

[0180] As an example, for each candidate cell, the source NG-RAN node or the source gNB-CU transmits the Handover Request message to the candidate NG-RAN node or the candidate gNB-CU to which the candidate cell belongs.

[0181] Optionally, the Handover Request message may include one or more of: LTM Triggering Indication information (LTM indication = initiation), a candidate cell ID, and Early Synchronization (Sync) Information Request information.

[0182] As an example, the candidate cell ID may indicate a candidate cell for the LTM handover. The candidate cell ID may be represented by a cell ID or an NR cell global ID (CGI).

[0183] As an example, the Early Sync Information Request information may include Early Sync Configuration Request Indication information. For example, when the Early Sync Configuration Request Indication information is Early Sync Configuration Request = true, it indicates that an early synchronization related parameter is requested to be configured.

[0184] For example, the Early Sync Information Request information may be used to request to allocate a random access resource of a candidate cell for an early TA acquisition based on a first rule.

[0185] In Example 1, the first rule may include: allocating the random access resource of the candidate cell for the early TA acquisition according to a base station to which the candidate cell belongs. The first rule may be simply referred to as Per-gNB. Optionally, the Early Sync Information Request information may include a gNB ID list or an early RACH resource list. For example, it may include a global gNB ID of one gNB (source gNB) or more gNBs (including the source gNB and candidate gNB(s)), indicating that the source NG-RAN node or the source gNB-CU requests the candidate NG-RAN node or the candidate gNB-CU to allocate, based on each LTM NG-RAN node, the random access resource of the candidate cell indicated by the candidate cell ID for the early TA acquisition process. Optionally, after an LTM gNB has acquired the early TA random access resource allocated by each candidate cell, if the LTM gNB is a base station with a CU-DU split architecture, the DU may acquire the early TA random access resource of the candidate cell through the following optional Examples 1-1 to 1-2.

[0186] In Example 1-1, the CU may actively allocate an appropriate resource to the DU or the UE based on an implementation. Optionally, the specific usage of the allocated resource is described in the following Examples 1-1-1 to 1-1-4.

[0187] In Example 1-1-1, the allocated resource is a DU dedicated resource. That is, the CU may allocate an appropriate resource based on the DU (for example, by using a non-UE-associated signaling). Different resources are allocated to different DUs, and a plurality of UEs on a DU may share the resource, thereby avoiding a resource conflict occurring when different DUs use the same resource. The early TA random access resource allocated by the candidate cell may be carried in a UE Context Modification Request to be transmitted to the DU. An indication (e.g., a dedicated resource indication) may be carried, indicating that the resource is a DU dedicated resource.

[0188] In Example 1-1-2, the allocated resource is a UE dedicated resource. That is, the CU may allocate an appropriate resource based on the UE (for example, by using a UE-associated signaling). Different resources are allocated to different UEs, and a dedicated resource is allocated to a UE on a DU, thereby avoiding a resource conflict occurring when different UEs use the same resource. Optionally, for a certain UE, the early TA random access resource allocated by the candidate cell may be carried in a UE Context Modification Request to be transmitted to the DU. An indication (e.g., a dedicated resource indication) may be carried, indicating that the resource is the UE dedicated resource.

[0189] In Example 1-1-3, the allocated resource is a DU one-time resource. That is, the CU may allocate an appropriate resource based on the DU (for example, by using a non-UE-associated signaling). Different resources are allocated to different DUs, and a plurality of UEs on a DU may share the resource, thereby avoiding a resource conflict occurring when different DUs use the same resource. The early TA random access resource allocated by the candidate cell may be carried in a UE Context Modification Request to be transmitted to the DU. An indication (such as a one-time resource indication) may be carried, indicating that the resource is a DU one-time resource. That is, after the random access resource of the candidate cell is used once for a certain UE (e.g., the DU successfully obtains the TA value of the UE for the candidate cell), the resource is automatically released and thus cannot be occupied. When the DU triggers the early TA acquisition process again to the candidate cell for the UE, if all resources have been used, the DU may apply for the random access resource of the candidate cell for the early TA acquisition again. The DU application mechanism refers to the scheme described in Example 1-2 below.

[0190] In Example 1-1-4, the allocated resource is a UE one-time resource. That is, the CU may allocate an appropriate resource based on the UE (for example, by using a UE-associated signaling). Different resources are allocated to different UEs, and a one-time resource is allocated to a UE on a DU, thereby avoiding a resource conflict occurring when different UEs use the same resource. Optionally, for a certain UE, the early TA random access resource allocated by the candidate cell may be carried in a UE Context Modification Request to be transmitted to the DU, and an indication (such as a one-time resource indication) may be carried, indicating that the resource is a UE one-time resource. That is, after the random access resource of the candidate cell is used once for this UE (e.g., the DU successfully obtains the TA value of the UE for the candidate cell), the resource is automatically released and thus cannot be occupied. When triggering the early TA acquisition process again to the candidate cell for the UE, the DU may apply for the random access resource of the candidate cell for the early TA acquisition again. The DU application mechanism refers to the scheme described in Example 1-2 below.

[0191] In Example 1-2, the DU requests the CU to allocate an appropriate resource based on the DU or the UE, and obtains the resource through the response information of the CU. For the base station with a CU-DU split architecture, the DU decides to trigger the early TA acquisition. Optionally, the specific usage of the allocated resource is described in the following Examples 1-2-1 to 1-2-4. The message involved in this process and the information that may be included therein may refer to the description of steps 317-1 and 317-2. Here, the early RACH resource requested by the DU or requested by the DU for a certain UE may be a DU dedicated resource or a DU one-time resource, or a UE dedicated resource or a UE one-time resource. Optionally, an indication (e.g., a dedicated resource indication) may be carried, indicating the type of the resource.

[0192] In Example 1-2-1, the allocated resource is a DU dedicated resource. That is, the DU requests the CU to allocate an appropriate resource based on the DU (for example, by using a non-UE-associated signaling). Different resources are allocated to different DUs, and a plurality of UEs on a DU may share the resource, thereby avoiding a resource conflict occurring when different DUs use the same resource.

[0193] In Example 1-2-2, the allocated resource is a UE dedicated resource. That is, the DU requests the CU to allocate an appropriate resource based on the UE (for example, by using a UE-associated signaling). Different resources are allocated to different UEs, and a dedicated resource is allocated to a UE on a DU, thereby avoiding a resource conflict occurring when different UEs use the same resource. The DU may reuse the dedicated resource allocated by the candidate cell for the UE, and may trigger the early TA acquisition process multiple times to the candidate cell for the UE, thereby improving the resource utilization rate.

[0194] In Example 1-2-3, the allocated resource is a DU one-time resource. That is, the DU requests the CUto allocate an appropriate resource based on the DU (for example, by using a non-UE-associated signaling). Different resources are allocated to different DUs, and a plurality of UEs on a DU may share the resource,thereby avoiding a resource conflict occurring when different DUs use the same resource. However, after the random access resource of the candidate cell is used once for a certain UE (e.g., the DU successfully obtains the TA value of the UE for the candidate cell), the resource is automatically released and thus cannot be occupied. When the DU triggers the early TA acquisition process again to the candidate cell for the UE, if all resources have been used, the DU may apply for the random access resource of the candidate cell for the early TA acquisition again.

[0195] In Example 1-2-4, the allocated resource is a UE one-time resource. That is, the DU requests the CUto allocate an appropriate resource based on the UE (for example, by using a UE-associated signaling). Different resources are allocated to different UEs, and a one-time resource is allocated to a UE on a DU, which can avoide a resource conflict occurring when different UEs use the same resource. After the random access resource of the candidate cell is used once for this UE (e.g., the DU successfully obtains the TA value of the UE for the candidate cell), the resource is automatically released and thus cannot be occupied. When triggering the early TA acquisition process again to the candidate cell for the UE, the DU may apply for the random access resource of the candidate cell for the early TA acquisition again.

[0196] In Example 2, the first rule may include: for a source base station, if the source gNB is a base station with a CU-DU split architecture, allocating a different resource to a different DU, and if the source gNB is a base station with a non-CU-DU split architecture, requesting the candidate cell to allocate an RACH resource according to the base station (this situation is the same as Example 1, and thus will not be repeatedly described here). This first rule is simply referred to as Per-DU in S-gNB+per-C-gNB. Optionally, for a candidate LTM gNB, no matter the candidate LTM gNB is a base station with a CU-DU split architecture or a base station with a non-CU-DU split architecture, a different resource is allocated to a different base station. After the candidate LTM gNB has acquired the early TA random access resource of each candidate cell, if the candidate LTM gNB is a base station with a CU-DU split architecture, a re-allocation may be performed for the CU and the DU according to the optional schemes involved in Example 1. The source base station can learn which gNB-DU a cell under the source base station belongs to. Optionally, the Early Sync Information Request information may include an early RACH resource list. For example, the early RACH resource list may include a gNB ID, and may further include Early RACH Resource Requester ID information. Here, the gNB ID may include the ID of a source gNB and / or a candidate gNB, and may be represented by a global gNB ID. There is a corresponding relationship between the Early RACH Resource Requester ID information and the gNB-DU ID, and the Early RACH Resource Requester ID information has the same value as the gNB-DU ID. The Early RACH Resource Requester ID information may be named as an ID having another name, indicating the ID of an entity requesting an early RACH resource, which is not limited in the present disclosure. Since the gNB-DU ID is not directly used (e.g., the early RACH resource list does not directly include the gNB-DU ID), it may be implemented that the architecture information of the base station is not exposed in the Xn interface specification. Optionally, this IE is included only when the source gNB indicated by the gNB ID is an gNB with a CU-DU split architecture. For example, the early RACH resource list includes the Early RACH Resource Requester ID information, which indicates the ID of the entity requesting the early RACH resource and implicitly indicates the gNB-DU ID.

[0197] In Example 3, the first rule may include: if all LTM base stations (source base station and candidate base stations) have a CU-DU split architecture, allocating the random access resource of the candidate cell for the early TA acquisition according to different gNB-DUs; and if all LTM base stations are a non-CU-DU split architecture, allocating the random access resource of the candidate cell for the early TA acquisition according to different base stations. In a situation where there are base stations having the two architectures (there is a base station with the CU-DU split architecture and a base station with the non-CU-DU split architecture), a combined approach is used. That is, for the base station with a CU-DU split architecture, the random access resource of the candidate cell for the early TA acquisition is allocated according to different DUs; and for the base station with the non-CU-DU split architecture, the random access resource of the candidate cell for the early TA acquisition is allocated according to different base stations. This first rule may be simply referred to as Per-gNB-DU. Optionally, the Early Sync Information Request information may include an early RACH resource list. As an example, the early RACH resource list may include a gNB ID, and may further include Early RACH Resource Requester ID information. For a specific implementation of the gNB ID and the Early RACH Resource Requester ID information, reference may be made to the specific implementation of the gNB ID and the Early RACH Resource Requester ID information in the above Example 2, and thus the details will not be repeatedly described here.

[0198] Based on the cell ID or CGI information in an L3 measurement report, the source base station can determine which base station a candidate cell under a non-source base station (i.e., the candidate base station) belongs to, but cannot determine which gNB-DU under the base station the candidate cell belongs to. Based on the Early RACH Resource Requester ID information, the source base station can learn which gNB-DU the candidate cell under the non-source base station (i.e., the candidate base station) belongs to. For the acquisition of the Early RACH Resource Requester ID information, reference may be made to the following steps 300-1 to 300-2, or to the following steps 302-1 to 302-2.

[0199] In step 300-1, the source NG-RAN node or the source gNB-CU transmits an Xn Setup Request message to the candidate NG-RAN node or the candidate gNB-CU. Alternatively, the source NG-RAN node or the source gNB-CU transmits an NG-RAN Node Configuration Update message to the candidate NG-RAN node or the candidate gNB-CU.

[0200] In step 300-2, the candidate NG-RAN node or the candidate gNB-CU transmits an Xn Setup Response message to the source NG-RAN node or the source gNB-CU. Alternatively, the candidate NG-RAN node or the candidate gNB-CU transmits an NG-RAN Node Configuration Update Acknowledge message to the source NG-RAN node or the source gNB-CU.

[0201] As an example, two neighbour NG-RAN nodes or gNB-CUs may exchange the Early RACH Resource Requester ID information associated with a cell, during the setup of an Xn interface (the Xn Setup Request message and / or the Xn Setup Response message) or during the configuration update of the NG-RAN node (the NG-RAN Node Configuration Update message and / or the NG-RAN Node Configuration Update Acknowledge message). Alternatively, during the setup of the Xn interface or during the configuration update of the NG-RAN node, a retrieval process may be triggered to the base station where the candidate cell is, to retrieve whether the candidate cell on the candidate base station has an associated gNB-DU ID information. For example, the Xn Setup Request message and / or the NG-RAN Node Configuration Update message may be used to request a retrieval for the Early RACH Resource Requester ID information or gNB-DU ID information associated with the candidate cell. Accordingly, if the information is retrieved successfully, the requested gNB-DU ID information assocaited with the candidate cell or information that implicitly maps the gNB-DU ID (e.g., the Early RACH Resource Requester ID information) is contained in the Xn Setup Response message and / or the NG-RAN Node Configuration Update Acknowledge message. If the information is not retrieved successfully, that is, the candidate base station is not a base station with a CU-DU split architecture, a failure message (an Xn Setup Failure message and / or an NG-RAN Node Configuration Update Failure message) may be returned, or the requested gNB-DU ID information associated with the candidate cell or the information that implicitly maps the gNB-DU ID is not contained in the Xn Setup Response message and / or the NG-RAN Node Configuration Update Acknowledge message. There is a corresponding relationship between the Early RACH Resource Requester ID information and the gNB-DU ID, and the Early RACH Resource Requester ID information has the same value as the gNB-DU ID. The Early RACH Resource Requester ID information may be named as another name, indicating the ID of an entity (which may be the gNB-DU) requesting an early RACH resource, or indicating the Early RACH Resource Requester ID. The Early RACH Resource Requester ID information may have another name such as a base station-sub level ID (gNB-Sub Level ID) or other names, which is not limited in the present disclosure.

[0202] Optionally, the Xn Setup Response message may include the Early RACH Resource Requester ID information. Optionally, the NG-RAN Node Configuration Update Acknowledge message may include the Early RACH Resource Requester ID information. The Early RACH Resource Requester ID information explicitly or implicitly identifies the gNB-DU ID information associated with the candidate cell under the non-source base station (i.e., the candidate base station).

[0203] Optionally, the Xn Setup Request message may include the Early RACH Resource Requester ID information. Optionally, the NG-RAN Node Configuration Update message may include the Early RACH Resource Requester ID information. The Early RACH Resource Requester ID information explicitly or implicitly identifies the gNB-DU ID information associated with the candidate cell under the base station initiating the message.

[0204] For example, the Early RACH Resource Requester ID information may be included in one or more of: Served Cell Information NR, Neighbour Information NR, and Neighbour Information E-UTRA. For example, the served NR cell information includes the Early RACH Resource Requester ID information, Neighbour Information NR includes the Early RACH Resource Requester ID information, and Neighbour Information E-UTRA includes the Early RACH Resource Requester ID information.

[0205] Here, Served Cell Information NR may include the gNB-DU ID information associated with the candidate cell under the non-source base station (i.e., the candidate base station) or ID information mapping the gNB-DU ID. Neighbour Information NR may include the gNB-DU ID information associated with the candidate cell under the non-source base station (i.e., the candidate base station) or the ID information mapping the gNB-DU ID. Neighbour Information E-UTRA may include the gNB-DU ID information associated with the candidate cell under the non-source base station (i.e., the candidate base station) or the ID information mapping the gNB-DU ID. Optionally, the ID information has the same value as the gNB-DU ID, that is, corresponds to the gNB-DU ID. Since the gNB-DU ID is not directly used, it may be implemented that the architecture information of the base station is not exposed in an Xn interface specification.

[0206] Thus, the Early RACH Resource Requester ID information indicates the gNB-DU ID associated with the candidate cell or the ID information mapping the gNB-DU ID. Then, when the gNB node is in an architecture in which the gNB-CU and the gNB-DU are separate, the gNB-CU can learn which gNB-DU under the neighbour gNB the neighbour cell belongs to.

[0207] In step 302-1, the source NG-RAN node or the source gNB-CU transmits an Identifier Request message to the candidate NG-RAN node or the candidate gNB-CU.

[0208] In step 302-2, the candidate NG-RAN node or the candidate gNB-CU transmits an Identifier Response message to the source NG-RAN node or the source gNB-CU.

[0209] Optionally, steps 302-1 and 302-2 may be performed after step 301 and before step 302, or may be performed after step 302 and before step 303.

[0210] The source gNB-CU receives the L3 measurement report transmitted by the UE. Then, before or after triggering an LTM configuration decision, the source gNB-CU first triggers a retrieval procedure to the base station where the candidate cell is before transmitting the Handover Request message to the candidate base station, to retrieve whether the candidate cell on the candidate base station has the gNB-DU ID information associated with the candidate cell. After receiving the Identifier Request message, the candidate gNB-CU or the candidate NG-RAN transmits an Identifier Response message to the source gNB-CU or the source NG-RAN.

[0211] Optionally, the Identifier Request message may be used to request a retrieval for the Early RACH Resource Requester ID associated with the candidate cell or the gNB-DU ID information associated with the candidate cell. The Identifier Request message may be a non-UE-associated message, and may be a new message named such as Retrieve Early RACH Resource Requester ID Request, or an existing message such as NG-RAN Node Configuration Update message.

[0212] As an example, the Identifier Request message may include one or more of: a candidate cell list, a candidate cell ID and Early RACH Resource Requester ID Request Indication information. Here, the candidate cell list may include one or more candidate cell ID information. The candidate cell ID may be represented by a cell ID or NR CGI. The Early RACH Resource Requester ID Request Indication information indicates to retrieve the gNB-DU ID information associated with the candidate cell indicated by the candidate cell ID or ID information that implicitly maps the gNB-DU ID associated with the candidate cell (for example, the Early RACH Resource Requester ID information or another name), indicating the ID of an entity (which may be the gNB-DU) requesting an early RACH resource, or indicating the Early RACH Resource Requester ID.

[0213] As an example, after receiving the Identifier Request message, the candidate gNB-CU or the candidate NG-RAN transmits the Identifier Response message to the source gNB-CU or the source NG-RAN. If the candidate base station is a base station with a CU-DU split architecture, the Identifier Response message may indicate a successful retrieval. The Identifier Response message may be a new message named such as Retrieve Early RACH Resource Requester ID Response, or an existing message such as the NG-RAN Node Configuration Update Acknowledge message. Optoinally, the Identifier Response message may include one or more of: a candidate cell list, a candidate cell ID, Early RACH Resource Requester ID information and a gNB ID. Here, the candidate cell list may include one or more candidate cell ID information. The candidate cell ID may be represented by a cell ID or NR CGI. The Early RACH Resource Requester ID information may be mapping ID information for implicitly indicating the gNB-DU ID associated with the candidate cell, or may have another name, indicating the ID of an entity (which may be the gNB-DU) requesting an early RACH resource, or indicating the Early RACH Resource Requester ID. The gNB ID may be the ID of the gNB to which the early RACH resource requester belongs. For example, the early RACH resource requester is a DU under the gNB indicated by the gNB ID.

[0214] If the candidate gNB is a base station with a CU-DU split architecture, the candidate gNB-CU can leran which gNB-DU under the gNB the candidate cell is on (through an F1 Setup Request message or a gNB-DU Configuration Update message transmitted by the gNB-DU to the gNB-CU). The candidate gNB-CU may return the gNB-DU ID information associated with the candidate cell or ID information that maps the gNB-DU ID (which may be Early RACH Resource Requester ID, or may have another name such as gNB-Sub Level ID). This ID may have the same value as the gNB-DU ID, and may correspond to the gNB-DU ID. Since the gNB-DU ID is not directly used, it may be implemented that the architecture information of the base station is not exposed in an Xn interface specification. This ID indicates the ID of an entity (which may be the gNB-DU) requesting an early RACH resource, or indicates the Early RACH Resource Requester ID.

[0215] If the candidate base station is a base station with a non-CU-DU split architecture, the candidate cell would not have an assocaited gNB-DU information. The Identifier Response message may indicate a retrieval failure. Retrieve Failure Indication information is returned, or information indicating that the candidate cell does not have an associated Early RACH Resource Requester ID is returned (or empty information is used to indicate that the candidate cell does not have an associated Early RACH Resource Requester ID), to indicate that the requested candidate cell does not have an associated gNB-DU information. Optionally, the Identifier Response message may be a new message named such as Retrieve Early RACH Resource Requester ID Failure, or an existing message such as the Xn Setup Failure message or the NG-RAN Node Configuration Update Failure message.

[0216] In Example 4, the first rule may include allocating the random access resource of the candidate cell for the early TA acquisition according to different other candidate cells (i.e., candidate cells other than the candidate cell indicated by the candidate cell ID). This first rule may be simply referred to as Per-Cell. For example, for the random access resource of one candidate cell for the early TA acquisition, a different resource is allocated to a different other candidate cell. A different resource is allocated to a different cell, and a plurality of UEs on a cell may share the resource, which can avoid a resource conflict occurring when different cells use the same resource. To support subsequent LTM, optionally, the Early Sync Information Request information may include a cell ID list or an early RACH resource list, which includes, for example, a cell ID or NR CGI of one cell (source cell) or more cells (including the source cell and a candidate cell), indicating that the source NG-RAN node or the source gNB-CU requests the candidate NG-RAN node or the candidate gNB-CU to allocate the random access resource for an early TA acquisition process according to different other candidate cells (i.e., the candidate cells other than the candidate cell indicated by the candidate cell ID).

[0217] In Example 5, the first rule may include allocating the random access resource of the candidate cell for the early TA acquisition according to the UE. This first rule may be simply referred to as Per-UE. UE-associated signalling may be used. In this way, a different resource is allocated to a different UE, which can avoid a resource conflict occurring when different UEs use the same resource. Optionally, the type of the resource requested to be allocated may indicated, such as a UE dedicated resource or a UE one-time resource. The specific usage is described in the following Example 5-1 or 5-2.

[0218] In Example 5-1, the resource type is the UE dedicated resource. By using a UE-associated signaling, it is possible to request the candidate cell to allocate an appropriate resource according to the UE. That is, different resources are allocated to different UEs, which can avoid a resource conflict occurring when different UEs use the same resource. The DU may reuse the dedicated resource allocated by the candidate cell to the UE, and may trigger the early TA acquisition process multiple times to the candidate cell for the UE, thereby improving the resource utilization rate.

[0219] In Example 5-2, the resource type is the UE one-time resource. By using a UE-associated signaling, it is possible to request the candidate cell to allocate a different one-time resource according to the UE. That is, a different one-time resource is allocated to a different UE, thereby avoiding a resource conflict occurring when different UEs use the same resource. After the random access resource of the candidate cell is used once for this UE (e.g., the DU successfully obtains the TA value of the UE for the candidate cell), the resource is automatically released and thus cannot be occupied. When triggering the early TA acquisition process again to the candidate cell for the UE, the DU may apply for the random access resource of the candidate cell for the early TA acquisition again.

[0220] Accordingly, it is possible to allocate the random access resource of the candidate cell for the early TA acquisition according to the base station, the DU or the cell, or according to a combination of any two thereof. However, if there is not enough resource to be allocated, for example, if the resource allocated to a base station needs to be used by a plurality of DUs under the base station, there may be a situation where the resource is insufficient, that is, it is insufficient to allocate at least one resource to each DU, and thus, it is possible to consider requesting the candidate cell again to allocate more random access resources for the early TA acquisition according to the DU, the base station or the cell. The F1 and Xn interface signaling involved, which may be a new message or a reused existing message, may contain at least one of: a candidate cell ID, an Early Sync Information Request, and a base station list, a DU list or a cell list.

[0221] Here, the candidate cell ID may include at least one candidate cell ID information for indicating a request for a random access resource for an early TA acquisition from the candidate cell indicated by the candidate cell ID information.

[0222] The Early Sync Information Request may include a triggering indication, for example, a more resource indication, a resource extension indication, a resource insufficiency indication, a fewer resource indication, a resource reduction indication, or a resource oversufficiency indication.

[0223] The base station list at least contains a base station ID, the DU list at least contains a DU ID, and the cell list at least contains cell ID information, for indicating that the candidate cell indicated by the candidate cell ID is requested to allocate a corresponding appropriate amount of random access resources for the early TA acquisition according to the triggering indication.

[0224] After receiving the message containing the above information, the node at which the corresponding candidate cell is located performs a corresponding action. The candidate cell indicated by the candidate cell ID allocates a corresponding appropriate amount of random access resources for the early TA acquisition to the base station, the DU or the cell according to the triggering indication, and return the information to the requesting node such as the base station or the DU.

[0225] For the above different allocation principles of the random access resource of the candidate cell for the early TA acquisition, after the UE triggers the transmission of a preamble to a corresponding candidate cell by using the random access resource indicated by the DU, and the candidate DU calculates the TA information of the UE for the corresponding candidate cell, the TA information needs to be transmitted to the source DU through an interface signaling between network nodes. Since the transmission of the TA information may involve a non-UE-associated signaling, auxiliary information needs to be provided so that the source DU can identify which UE the received TA information of the candidate cell is for. The details are described in the following implementation.

[0226] Optionally, if the NG-RAN node is not in the architecture in which the gNB-CU and the gNB-DU are separate, the corresponding F1 Interface message and process will not be involved.

[0227] In step 304, the candidate gNB-CU transmits a UE Context Setup Request message to the gNB-DU to which the candidate cell belongs.

[0228] As an example, step 304 is optional, and if the candidate NG-RAN node is in an architecture in which the gNB-CU and the gNB-DU are separate, the candidate gNB-CU transmits the UE Context Setup Request message to the gNB-DU to which the candidate cell belongs.

[0229] Optionally, the UE Context Setup Request message may include one or more of: LTM Triggering Indication information, a candidate cell ID, and Early Sync Information Request information. As an example, the candidate cell ID may indicate a candidate cell for an LTM handover. The candidate cell ID may be represented by a cell ID or an NR cell global identifier (ID) (CGI).

[0230] As an example, the Early Sync Information Request information may include Early Sync Configuration Request Indication information. The Early Sync Information Request information may be used to request to allocate the random access resource of the candidate cell for the early TA acquisition based on the first rule. For a specific implementation of the Early Sync Information Request information and the Early Sync Configuration Request Indication information, reference may be made to the corresponding description in step 303 described above, and thus the details will not be repeatedly described here.

[0231] Corresponding to Example 1 in step 303, the Early Sync Information Request information may include a gNB ID list or an early RACH resource list, which includes, for example, a global gNB ID of one gNB (source gNB) or more gNBs (including the source gNB and the candidate gNB), indicating that the candidate gNB-CU requests the candidate cell indicated by the candidate cell ID under the candidate gNB-DU to allocate the random access resource (for an early TA acquisition process) of the candidate cell indicated by the candidate cell ID according to each LTM NG-RAN node.

[0232] Corresponding to Example 2 in step 303, the Early Sync Information Request information may include an early RACH resource list. For example, the early RACH resource list may include a gNB ID, and may further include a gNB-DU ID. Here, the gNB ID may include a source gNB and / or a candidate gNB, and may be represented by a global gNB ID. The gNB-DU ID corresponds to Xn interface information Early RACH Resource Requester ID information, and the Early RACH Resource Requester ID information is converted into the corresponding gNB-DU ID. If the early RACH resource list includes the gNB-DU ID, it indicates that the early RACH resource is allocated according to the gNB-DU indicated by the gNB-DU ID, and if the early RACH resource list does not include the gNB-DU ID, it indicates that the early RACH resource is allocated according to the gNB indicated by the gNB ID.

[0233] Corresponding to Example 3 in step 303, the Early Sync Information Request information may include an early RACH resource list. For example, the early RACH resource list may include a gNB ID, and may further include a gNB-DU ID (if the requested gNB is a base station with a CU-DU split architecture). Here, the gNB ID may include a source gNB and / or a candidate gNB, and may be represented by a global gNB ID. The gNB-DU ID corresponds to Xn interface information Early RACH Resource Requester ID information. If the early RACH resource list includes the gNB-DU ID, it indicates that the early RACH resource is allocated according to the gNB-DU indicated by the gNB-DU ID, and if the early RACH resource list does not include the gNB-DU ID, it indicates that the early RACH resource is allocated according to the gNB indicated by the gNB ID.

[0234] Corresponding to Example 4 in step 303, the Early Sync Information Request information may include a Cell ID list or an early RACH resource list, which includes, for example, a global Cell ID of one Cell (source Cell) or more Cells (including the source Cell and the candidate Cell), which may be represented by a cell ID or NR CGI. It indicates that the candidate NG-RAN node or the candidate gNB-CU requests the candidate gNB-DU to allocate the random access resource (for an early TA acquisition) of the candidate cell indicated by the candidate cell ID according to each different other candidate cell (i.e., a candidate cell other than the candidate cell indicated by the candidate cell ID).

[0235] Corresponding to Example 5 in step 303, the Early Sync Information Request information may be used to request to allocate the random access resource of the candidate cell for the early TA acquisition according to the UE. The Early Sync Information Request information may further be used to request a type of the allocated resource, for example, a UE dedicated resource or a UE one-time resource. For the details, reference may be made to the corresponding description in Example 5 in step 303, and thus the details will not be repeatedly described here.

[0236] In step 305, the candidate gNB-DU transmits a UE Context Setup Response message to the candidate gNB-CU.

[0237] As an example, if the candidate gNB-DU accepts an LTM configuration request, the candidate gNB-DU may transmit the UE Context Setup Response message to the candidate gNB-CU in response.

[0238] The UE Context Setup Response message may include one or more of: a candidate cell ID and Early Sync Information Response information. Here, the candidate cell ID may be represented by a cell ID or NR CGI. The Early Sync Information Response information may include Early Uplink Synchronization Configuration information, and the Early Uplink Synchronization Configuration information may include one or more of: RACH Configuration information and an early RACH resource list.

[0239] Here, the RACH Configuration information may be an Early Uplink Synchronization Configuration (EarlyUL-SyncConfig) IE contained and defined in TS 38.331, indicating a common part of allocated early RACH resources. The different part allocated to each node is indicated by preamble index information.

[0240] Corresponding to Example 1 in step 303, when the first rule is Per-gNB, the early RACH resource list may also be an LTM gNB list. The early RACH resource list may include one or more LTM gNB IDs and the corresponding allocated PRACH resources, for example, a preamble index list. Alternatively, the LTM gNB list may include one or more LTM gNB IDs and the corresponding allocated PRACH resources, for example, a preamble index list. Here, an LTM gNB ID may be a global gNB ID. The preamble index list may include one or more preamble indexes, indicating different parts of the PRACH resources allocated to the gNBs indicated by the LTM gNB IDs.

[0241] Corresponding to Example 2 in step 303, when the first rule is Per-DU in S-gNB+per-C-gNB, the early RACH resource list may include one or more of: a preamble index list, a gNB ID and a gNB-DU ID.

[0242] Here, the preamble index list may include one or more preamble indexes, indicating different parts of the PRACH resources allocated to the indicated gNB ID or gNB-DU ID. The gNB ID includes a source gNB ID and a candidate gNB ID, and may be represented by a global gNB ID. The gNB-DU ID may be optional. The gNB-DU ID corresponds to Xn interface information Early RACH Resource Requester ID information, and the Early RACH Resource Requester ID is converted into the corresponding gNB-DU ID. Optionally, if the early RACH resource list includes the gNB-DU ID, it indicates that the early RACH resource is allocated based on the gNB-DU indicated by the gNB-DU ID, and if the early RACH resource list does not include the gNB-DU ID, it indicates that the early RACH resource is allocated based on the gNB indicated by the gNB ID.

[0243] Corresponding to Example 3 in step 303, when the first rule is Per-gNB-DU, the early RACH resource list may include one or more of: a preamble index list, a gNB ID and a gNB-DU ID.

[0244] Similarly, the preamble index list may include one or more preamble indexes, indicating different parts of the PRACH resources allocated to the indicated gNB ID or gNB-DU ID. The gNB ID includes a source gNB ID and a candidate gNB ID, and may be represented by a global gNB ID. The gNB-DU ID may be optional. The gNB-DU ID corresponds to Xn interface information Early RACH Resource Requester ID information, and the Early RACH Resource Requester ID is converted into the corresponding gNB-DU ID. Optionally, if the early RACH resource list includes the gNB-DU ID, it indicates that the early RACH resource is allocated based on the gNB-DU indicated by the gNB-DU ID, and if the early RACH resource list does not include the gNB-DU ID, it indicates that the early RACH resource is allocated based on the gNB indicated by the gNB ID.

[0245] Corresponding to Example 4 in step 303, when the first rule is Per-Cell, the early RACH resource list may include one or more of: an LTM cell ID and a preamble index list. Here, the LTM cell ID may be a cell ID or NR CGI. The preamble index list may include one or more preamble indexes, indicating different parts of the PRACH resources allocated to the indicated gNB ID.

[0246] Corresponding to example 5 in step 303, when the first rule is Per-UE, the early RACH resource list may include LTM Early RACH Resource Configuration information, and the LTM Early RACH Resource Configuration information includes an RACH dedicated configuration (RACH-ConfigDedicated). Optionally, the early RACH resource list may include a preamble index, for example, a preamble index allocated in combination with the RACH configuration information.

[0247] In step 306, the candidate gNB or the candidate gNB-CU transmits a Handover Request Acknowledge message to the source gNB or the source gNB-CU.

[0248] As an example, for the requested candidate cell, the candidate gNB or the candidate gNB-CU returns the Handover Request Acknowledge message to the source gNB or the source gNB-CU. Optionally, the Handover Request Acknowledge message includes one or more of: a candidate cell ID and Early Sync Information Response information.

[0249] Here, the Early Sync Information Response information may include one or more of: RACH configuration information and an early RACH resource list. For a specific implementation of the RACH configuration information, reference may be made to the corresponding description in step 305, and thus the details will not be repeatedly described here.

[0250] Corresponding to Example 1 in Step 303, when the first rule is Per-gNB, for a specific implementation of the early RACH resource list, reference may be made to the corresponding description in step 305, and thus the details will not be repeatedly described here.

[0251] Corresponding to Example 2 in step 305, when the first rule is Per-DU in S-gNB+per-C-gNB, the early RACH resource list may include one or more of: a preamble index list, a gNB ID and Early RACH Resource Requester ID information. For a specific implementation of the preamble index list and the gNB ID, reference may be made to the corresponding description in step 305, and thus the details will not be repeatedly described here. The Early RACH Resource Requester ID information corresponds to the Early RACH Resource Requester ID information in the Xn Interface Handover Request message. If the early RACH resource list includes the Early RACH Resource Requester ID information, it indicates that the early RACH resource is allocated based on the gNB-DU mapped to the Early RACH Resource Requester ID information, and if the early RACH resource list does not include the Early RACH Resource Requester ID information, the early RACH resource is allocated based on the gNB indicated by the gNB ID.

[0252] Corresponding to example 3 in step 303, when the first rule is Per-gNB-DU, the early RACH resource list may include one or more of: a preamble index list, a gNB ID and Early RACH Resource Requester ID information. For a specific implementation of the preamble index list and the gNB ID, reference may be made to the corresponding description in step 305, and thus the details will not be repeatedly described here. For a specific implementation of the Early RACH Resource Requester ID information, reference may be made to the corresponding description (corresponding to Example 2 in step 303) in step 306.

[0253] Corresponding to Example 4 in step 303, when the first rule is Per-Cell, the early RACH resource list may include one or more of: an LTM cell ID and a preamble index list. For a specific implementation, reference may be made to the corresponding description in step 305, and thus the details will not be repeatedly described here.

[0254] Corresponding to Example 5 in step 303, when the first rule is Per-UE, the early RACH resource list may include LTM Early RACH Resource Configuration information, and the LTM Early RACH Resource Configuration information includes an RACH dedicated configuration (RACH-ConfigDedicated). Optionally, the early RACH resource list may include a preamble index, for example, a preamble index allocated in combination with the RACH configuration information.

[0255] In step 307, the source gNB-CU transmits a Context Modification Request message to the source gNB-DU.

[0256] Optionally, the Context Modification Request message includes RACH Configuration information, or the Context Modification Request message may be used to request an acquisition of an early RACH resource.

[0257] As an example, if the source gNB is in an architecture in which the gNB-CU and the gNB-DU are separate, the source gNB-CU may transmit a UE Context Modification Request message based on the RACH configuration allocated to the gNB by each candidate cell, to allocate the corresponding RACH configuration to the source gNB-DU or other candidate gNB-DUs under the gNB. Alternatively, the gNB-DU requests the gNB-CU to acquire the early RACH resource. For a specific implementation, reference may be made to the scheme in the above Example 1-2.

[0258] If the early RACH resource is an RACH resource allocated based on the DU, the cell or the UE, the source gNB may forward all RACH resources allocated by the candidate cell to the corresponding DU or cell or UE under the source gNB to the corresponding DU.

[0259] For the source cell, the source gNB-CU may transmit the UE Context Modification Request message to the source gNB-DU, to request the source cell to allocate the early RACH resource to another gNB, DU or cell or to the UE. The UE Context Modification Request message includes Early Sync Information Request information. For a specific implementation of the Early Sync Information Request information, reference may be made to step 304, and thus the details will not be repeatedly described here.

[0260] In step 308, the source gNB-DU transmits a UE Context Modification Response message to the source gNB-CU.

[0261] As an example, if the source gNB-DU accepts an LTM configuration request, the source gNB-DU transmits the UE Context Modification Response message in response. The UE Context Modification Response message includes Early Sync Information Response information. For a specific implementation of the Early Sync Information Response information, reference may be made to step 305, and thus the details will not be repeatedly described here.

[0262] In step 309, the source gNB or the source gNB-CU transmits an LTM Configuration Update message to the candidate gNB or the candidate gNB-CU.

[0263] As an example, to support subsequent LTM, the source gNB or the source gNB-CU may collect the LTM configuration information of all candidate cells accepted the LTM request and the early RACH resource information allocated by each candidate cell, and transmit the LTM configuration information and the early RACH resource information to each other candidate gNB or gNB-CU through an Xn interface message. The Xn interface message may be the LTM Configuration Update message.

[0264] Optionally, the LTM Configuration Update message includes one or more of: Early Synchronization (Sync) Candidate Cell Information List information, a candidate cell ID, a Transmission Channel Indication State Configuration List, and Early Uplink Synchronization Configuration information.

[0265] Here, the Early Sync Candidate Cell Information List information includes the Early Uplink Synchronization Configuration information allocated by one or more candidate cells to the corresponding gNB, the DU or cell under the gNB, or the UE.

[0266] The Transmission Channel Indication (TCI) State Configuration List may be the LTM-TCI-Info IE defined in TS 38.331.

[0267] For a specific implementation of the Early Uplink Synchronization Configuration information, reference may be made to the step 305, and thus the details will not be repeatedly described here.

[0268] In step 310, the candidate gNB-CU transmits a UE Context Modification Request message to the candidate gNB-DU.

[0269] As an example, if the candidate gNB is in an architecture in which the gNB-CU and the gNB-DU are separate, the candidate gNB-CU may transmit the UE Context Modification Request message based on the RACH configuration allocated to the gNB by each candidate cell, to allocate the corresponding RACH configuration to the candidate gNB-DU. Alternatively, the candidate gNB-DU requests the candidate gNB-CU to acquire the early RACH resource. For a specific implementation, reference may be made to the scheme in the foregoing Example 1-2.

[0270] If the early RACH resource is an RACH resource allocated based on the DU, the cell or the UE, the candidate gNB may forward all RACH resources allocated by the candidate cell to the corresponding DU or cell or UE under the candidate gNB to the corresponding DU.

[0271] In step 311, the candidate gNB-DU transmits a UE Context Modification Response message to the candidate gNB-CU.

[0272] In step 312, the candidate gNB or the candidate gNB-CU transmits an LTM Configuration Update Acknowledge message to the source gNB or the source gNB-CU.

[0273] For example, the candidate gNB or the candidate gNB-CU transmits a response message such as the LTM Configuration Update Acknowledge message to the source gNB or the source gNB-CU.

[0274] In step 313, the source gNB-CU transmits a Downlink RRC Message Transfer message to the source gNB-DU.

[0275] For example, after completing the LTM-related configuration, the network side performs an RRC reconfiguration process of the UE. The source gNB-CU transmits the Downlink (DL) RRC Message Transfer message to the source gNB-DU. Optionally, the DL RRC Message Transfer message includes an RRC Reconfiguration message, and the RRC Reconfiguration message includes an LTM configuration.

[0276] In step 314, the source gNB-DU transmits an RRC Reconfiguration message to the UE.

[0277] For example, the source gNB-DU forwards the received RRC Reconfiguration message to the UE.

[0278] In step 315, the UE transmits an RRC Reconfiguration Complete message to the source gNB-DU.

[0279] In step 316, the source gNB-DU transmits the RRC Reconfiguration Complete message to the source gNB-CU.

[0280] For example, the source gNB-DU forwards the RRC Reconfiguration Complete message to the source gNB-CU through an Uplink RRC Message Transfer message.

[0281] In step 317-1, the source gNB-DU transmits an Early RACH Resource Request message to the source gNB-CU, the source gNB-CU transmits the Early RACH Resource Request message to the candidate gNB-CU or to the candidate gNB, and the candidate gNB-CU transmits the Early RACH Resource Request message to the candidate gNB-DU.

[0282] In some embodiments, for the random access resource requested based on the UE for the early TA acquisition, except for the resource obtained and used during an LTM configuration preparation process as described above, for the one-time resource type, the resource is automatically released by the source gNB or the source gNB-DU after being used. It is possible that, after the TA expires and thus becomes invalid, the early TA acquisition process may be triggered for the UE again, or, after the UE performs the LTM once, a new source gNB or gNB-DU needs to trigger the early TA acquisition process for the UE. Optionally, the resource is requested again by using a UE-associated signaling.

[0283] In step 317-1, the source gNB-DU transmits, to the source gNB-CU, a message, for example, a new message named such as Early RACH Resource Request. Alternatively, the message may be an existing message such as a UE Context Modification Required message. Accordingly, the source gNB-CU transmits, to the candidate gNB or the candidate gNB-CU, a UE-associated message, for example, a new message named such as Early RACH Resource Request. Alternatively, the message may be an existing message such as the LTM Configuration Update message. If there is a DC scenario as shown in FIG. 4, the source SN may use an existing message such as an SN (S-NODE) Modification Required message, and the MN may use an SN (S-NODE) Modification Request message. Accordingly, the candidate gNB-CU transmits, to the candidate gNB-DU, a UE-associated message, for example, a new message named such as Early RACH Resource Request. Alternatively, the message may be an existing message such as the UE Context Modification Request message.

[0284] Optionally, the Early RACH Resource Request message may include one or more of: a candidate cell information list, a candidate cell ID, and Early Sync Information Request information. Similarly, the UE Context Modification Required message, the LTM Configuration Update message or the UE Context Modification Request message may also include these information.

[0285] The candidate cell information list includes ID information of one or more candidate cells. The Early Sync Information Request information may include Early Sync Configuration Request Indication information. For example, when the Early Sync Configuration Request Indication information is Early Sync Configuration Request = true, it indicates that an early synchronization related parameter is requested to be configured.

[0286] In step 317-2, the candidate gNB-DU transmits an Early RACH Resource Response message to the candidate gNB-CU, the candidate gNB-CU transmits the Early RACH Resource Response message to the source gNB-CU or the source gNB, and the source gNB-CU transmits the Early RACH Resource Response message to the source gNB-DU.

[0287] As an example, the candidate gNB-DU allocates a corresponding early RACH resource to the requested candidate cell for the UE, as described in step 317-2. The candidate gNB-DU transmits, to the candidate gNB-CU, a message, for example, a new message named such as Early RACH Resource Request Acknowledge or Early RACH Resource Response, or uses an existing message such as the UE Context Modification Response message.

[0288] Accordingly, the candidate gNB-CU transmits, to the source gNB-CU or the source gNB, a UE-associated message, for example, a new message named such as Early RACH Resource Request Acknowledge or Early RACH Resource Response, or uses an existing message such as the LTM Configuration Update Acknowledge message. If there is a DC scenario as shown in FIG. 4, the candidate SN may use an existing message such as an SN (S-NODE) Modification Request Acknowledge message, and the MN may use an SN (S-NODE) Modification Confirm message.

[0289] Accordingly, the source gNB-CU transmits, to the source gNB-DU, the UE-associated message, for example, a new message named such as Early RACH Resource Request Acknowledge or Early RACH Resource Response, or uses an existing message such as a UE Context Modification Confirm message.

[0290] After obtaining the early RACH resource allocated by a candidate cell for a certain UE, the gNB-DU or gNB may consider triggering an early TA acquisition process to the corresponding candidate cell for this UE.

[0291] Optionally, the Early RACH Resource Response message may include one or more of: a candidate cell information list, a candidate cell ID and Early Uplink Synchronization Configuration information. Here, the candidate cell information list includes the Early RACH Resource Configuration information allocated by one or more candidate cells. The Early Uplink Synchronization Configuration information may be indicated by the LTM Early RACH Resource Configuration information, or indicated by a combination of the RACH Configuration information and at least one allocated preamble index. Similarly, the UE Context Modification Response message, the LTM Configuration Update Acknowledge message or the UE Context Modification Confirm message may also include these information, and thus will not be repeatedly described one by one.

[0292] After obtaining the early RACH resource allocated by a candidate cell for a certain UE, the gNB-DU or gNB may consider triggering an early TA acquisition process to the corresponding candidate cell for this UE.

[0293] In step 318-1, the source gNB-DU transmits a PDCCH order instruction to the UE.

[0294] In step 318-2, the UE transmits a Random Access Request message to the candidate cell.

[0295] As an example, early synchronization is performed to obtain an early TA value. This process includes the following steps. After receiving the PDCCH order instruction transmitted by the gNB-DU currently serving the UE, the UE transmits the Random Access Request message to the candidate cell using the random access resource configuration indicated in the PDCCH order instruction. Here, the random access resource configuration in the PDCCH order instruction may be indicated by a parameter such as a Random Access Preamble index, a synchronization signal / PBCH block index (SSB index) and a PRACH occasion Mask index. After receiving the Random Access Request message, the candidate cell calculates a timing advanced (TA) value between the UE and the candidate cell.

[0296] In step 319, the candidate gNB-DU transmits a TA Information Transfer message to the candidate gNB-CU.

[0297] As an example, the candidate gNB-DU transmits the TA value and associated information to the candidate gNB-CU through a non-UE-associated DU-CU TA Information Transfer message.

[0298] For example, the DU-CU TA Information Transfer message may include one or more of: a TA information list, a candidate cell ID, a TA value, a preamble index, a random access-radio network temporary indentifier (RA-RNTI), and Resource Indication information.

[0299] Here, the TA information list may include TA values for one or more candidate cells and used RACH resource information. The same UE may have different TA values for different candidate cells, and different UEs may have different TA values for the same candidate cell.

[0300] The Resource Indication information may indicate that the RACH resource used by the UE was previously allocated to a corresponding node or cell by the candidate cell.

[0301] For different allocation principles, the information contained in the Resource Indication information may be as follows.

[0302] When the first rule is Per-gNB, the Resource Indication information includes an LTM gNB ID indicating a source gNB, and the gNB ID may be a global gNB ID.

[0303] When the first rule is Per-DU in S-gNB+per-C-gNB, the Resource Indication information includes a gNB ID. If the source gNB is a base station with a CU-DU split architecture, the Resource Indication information may further include a gNB-DU ID. The gNB ID indicates a source gNB, and the gNB ID may be a global gNB ID.

[0304] When the first rule is Per-gNB-DU, the Resource Indication information includes a gNB ID. If the source gNB is a base station with a CU-DU split architecture, the Resource Indication information may further include a gNB-DU ID. The gNB ID indicates a source gNB, and the gNB ID may be a global gNB ID. If the gNB ID information is contained in an F1AP DU-CU TA Information Transfer message, the gNB-CU will forward this TA information to the gNB indicated by the gNB ID.

[0305] When the first rule is Per-Cell, the Resource Indication information includes an LTM cell ID, which may be a cell ID or NR CGI.

[0306] When the first rule is Per-UE, the Resource Indication information includes a gNB-CU UE F1AP ID and / or gNB-DU UE F1AP ID, or the TA information of the candidate cell is transmitted using a UE-associated message.

[0307] In step 320, the candidate gNB or the candidate gNB-CU transmits a TA Information Transfer message to the source gNB or the source gNB-CU.

[0308] As an example, the candidate gNB or the candidate gNB-CU forwards TA-related information to the corresponding source gNB or source gNB-CU through non-UE-associated and newly defined Xnap information (e.g., the TA Information Transfer message). The candidate gNB-CU can determine to which node to forward information through the above Resource Indication information.

[0309] Optionally, the TA Information Transfer message may include one or more of: a TA information list, a candidate cell ID, a TA value, a preamble index, a random access radio network temporary identifier, and Resource Indication information. The Resource Indication information may indicate that the RACH resource used by the UE was previously allocated to a corresponding node or cell by the candidate cell.

[0310] For different allocation principles, the information contained in the Resource Indication information may be as follows.

[0311] When the first rule is Per-gNB, the TA Information Transfer message may not include the Resource Indication information. For the early RACH resource allocated based on the principle of a gNB, if the base station is in a CU-DU split architecture, the gNB knowns which gNB-DU under the gNB the gNB-CU reallocates the obtained resource to (through the allocation scheme in the foregoing Example 1-1 or 1-2). If the base station is a base station with a non-CU-DU split architecture, the gNB can determine which UE the TA value of the candidate cell is for by using the RACH resource.

[0312] When the first rule is Per-DU in S-gNB+per-C-gNB, the Resource Indication information may include Early RACH Resource Requester ID information. The Early RACH Resource Requester ID information corresponds to the Early RACH Resource Requester ID information in an Xn interface Handover Request message.

[0313] When the first rule is Per-gNB-DU, the Resource Indication information may include Early RACH Resource Requester ID information. The Early RACH Resource Requester ID information corresponds to the Early RACH Resource Requester ID information in an Xn interface Handover Request message. If the gNB-DU ID or Early RACH Resource Requester ID information is contained in an XnAP TA Information Transfer message, the gNB-CU will forward this TA information to the gNB-DU indicated by the gNB-DU ID or Early RACH Resource Requester ID information.

[0314] When the first rule is Per-Cell, the Resource Indication information may include an LTM cell ID.

[0315] When the first rule is Per-UE, the Resource Indication information may include a source NG-RAN node UE XnAP ID and / or a target NG-RAN node UE XnAP ID, or the TA information of the candidate cell is transmitted using a UE-associated message.

[0316] In step 321, the source gNB-CU transmits a TA Information Transfer message to the source gNB-DU.

[0317] As an example, the source gNB-CU transmits candidate cell information, TA value information and Early RACH Resource information to the corresponding source gNB-DU through a non-UE-associated CU-DU TA Information Transfer message.

[0318] In some embodiments, the method provided in the embodiment of the present disclosure may be applicable in various scenarios. For example, in a scenario where an inter-CU LTM with SN kept / release / addition is supported, or in an inter-gNB continuous CHO scenario or an inter-gNB continuous CHO with SN kept / release / addition scenario, if there is an early TA acquisition process, the allocation of the early uplink synchronization RACH resources of the candidate cell described in embodiments of the present disclosure is still applicable.

[0319] In an embodiment, for the principle in the above Example 3, that is, for a base station with a CU-DU split architecturewith a CU-DU split architecture, the candidate cell allocates the random access resource for the early TA acquisition according to different DUs. A problem involved therein is that, based on the cell ID or CGI information in an L3 measurement report, the source base station can determine which base station a candidate cell under a non-source base station (i.e., the candidate base station) belongs to, but cannot determine which gNB-DU under the base station the candidate cell belongs to. Therefore, before the Handover Request message is triggered, it is required to learn which gNB-DU under the base station the candidate cell under the candidate base station belongs to or the corresponding Early RACH Resource Requester ID information. For the acquisition of the Early RACH Resource Requester ID information, reference may be made to the above steps 300-1 to 300-2, or to the above steps 302-1 to 302-2. However, the above schemes occur before the handover request, and are intended to perform an early RACH resource request for the DU and / or base station where a recommended other candidate cell is during a candidate cell resource request process, but the recommended other candidate cell may fail in the LTM resource request process and thus is not used as a candidate cell, that is, is not accepted as an accepted candidate cell by the candidate base station. This may result in unnecessary signaling and a signaling waste, as well as a waste in RACH resource allocation. That is, for the retrieved gNB-DU ID information or the corresponding Early RACH Resource Requester ID information, the candidate cell does not need to allocate an early RACH resource to the DU. In order to make an early RACH resource request only for the gNB-DU under the base station and / or the base station to which an accepted candidate cell belongs, and obtain the gNB-DU ID information associated with the accepted candidate cell or the corresponding Early RACH Resource Requester ID information, the candidate base station may provide the gNB-DU ID information associated with the accepted candidate cell or the corresponding Early RACH Resource Requester ID information during a handover request preparation process. The above scheme may be embodied through the following process:

[0320] The Handover Request message in step 303 carries one or more of: a candidate cell ID (or a target cell ID, which may be represented by a cell ID or NR CGI), and explicit or implicit indication information (e.g., an LTM Information Request IE or other LTM-related IEs), indicating to retrieve the gNB-DU ID information associated with the candidate cell indicated by the candidate cell ID or the implicit mapping ID information corresponding to the gNB-DU ID (which is, for example, the Early RACH Resource Requester ID information, or may have another name).

[0321] The Handover Request Acknowledge message in step 306 carries one or more of: an accepted LTM candidate cell ID (or a target cell ID, which may be represented by a cell ID or NR CGI), and, if the candidate gNB is a base station with a CU-DU split architecture, the gNB-DU ID information associated with the candidate cell or the implicit mapping ID information corresponding to the gNB-DU ID (which is, for example, the Early RACH Resource Requester ID information, or may have another name).

[0322] If the candidate base station is a base station with a non-CU-DU split architecture, the candidate cell does not have an associated gNB-DU information. Accordingly, the Handover Request Acknowledge message in step 306 carries Retrieve Failure Indication information or indication information indicating that the candidate cell does not have an associated gNB-DU or Early RACH Resource Requester ID (or empty information is used to indicate that the candidate cell does not have an associated gNB-DU or Early RACH Resource Requester ID, that is, no gNB-DU or Early RACH Resource Requester ID information associated with the candidate cell is returned), to indicate that the requested candidate cell does not have an associated gNB-DU information.

[0323] If the gNB-DU ID or Early RACH Resource Requester ID information associated with the candidate cell is contained in an XnAP Handover Request Acknowledge message, the gNB-CU will consider using this information in the subsequent early RACH resource request, to request, through an XnAP LTM Configuration Update message, the candidate cell to allocate an early RACH resource to the gNB-DU indicated by the gNB-DU ID or Early RACH Resource Requester ID information associated with the accepted candidate cell.

[0324] The source base station and each candidate base station respectively performs the handover request process, and finally obtains the information of each accepted candidate cell and the gNB-DU information under the candidate base station to which the accepted candidate cell belongs (if the candidate base station is a base station with a CU-DU split architecture).

[0325] In this way, in the subsequent process, it is possible to request, through the LTM configuration update process, one or more candidate cells on the candidate base station to allocate an early RACH resource to the gNB-DU to which the accepted candidate cell belongs (if the candidate base station is a base station with a CU-DU split architecture) and / or the base station to which the candidate cell belongs (if the candidate base station is not a base station with a CU-DU split architecture). This LTM configuration update process may be based on a candidate cell or based on a node. If the LTM configuration update process is based on the candidate cell, in an LTM configuration update process, a candidate cell on a candidate base station is requested to allocate an early RACH resource to the gNB-DU and / or base station to which another candidate cell belongs. If the LTM configuration update process is based on the node, in an LTM configuration update process, for a plurality of candidate cells on a candidate base station, each candidate cell is requested to allocate an early RACH resource to the gNB-DU and / or base station to which another candidate cell belongs.

[0326] Therefore, the LTM Configuration Update message in step 309 carries one or more of: the accepted LTM candidate cell ID (alternatively, a candidate LTM cell list, containing one or more candidate cell IDs, where each candidate cell ID may be represented by an NR CGI), and an Early Synchronization (Sync) Information Request IE. The Early Sync Information Request IE indicates that an LTM candidate cell is requested to allocate an early RACH resource to the gNB-DU (which may be represented by the gNB-DU ID or Early RACH Resource Requester ID information) and / or base station (which may be represented by a global gNB ID) to which another candidate cell belongs.

[0327] Accordingly, if the candidate base station is a base station with a CU-DU split architecture, the UE Context Modification Request message in step 310 carries the information in the LTM Configuration Update message in step 309 to provide an early RACH resource to the DU.

[0328] Accordingly, the UE Context Modification Response message in step 311 carries one or more of: one or more candidate cell IDs (alternatively, each candidate cell ID may be represented by an NR CGI), and the early RACH resource allocated by each candidate cell to the gNB-DU and / or base station to which another candidate cell belongs, which may be represented by an Early Synchronization (Sync) Information Response IE.

[0329] Accordingly, the LTM Configuration Update Acknowledge message in step 312 carries one or more of: one or more candidate cell IDs (optioanlly, each candidate cell ID may be represented by an NR CGI), and the early RACH resource allocated by each candidate cell to the gNB-DU and / or base station to which another candidate cell belongs, which may be represented by an Early Synchronization (Sync) Information Response IE or an Early Uplink (UL) Synchronization (Sync) Configuration IE.

[0330] The above mechanism in which the source base station requests the candidate cell to allocate the early RACH resource after obtaining the accepted candidate cell is also applicable to the mechanism in which the candidate cell allocates the early RACH resource based on the base station or based on the cell. It is possible to reduce the unnecessary allocation of early RACH resources to a recommended candidate cell or the DU and / or base station to which the recommended candidate cell belongs, when the recommended candidate cell did not accept the LTM request. Accordingly, a waste in early RACH resource allocation of the candidate cell is reduced.

[0331] FIG. 4 is another exemplary flow diagram of the mobility mechanism between base stations according to the present disclosure. This embodiment includes the following steps. The embodiment shown in FIG. 4 is similar to the embodiment in FIG. 3, but the involved node names and the corresponding message names are different. It relates to a scenario that a UE in a dual-connectivity configures an SN / MN triggered inter-SN (conditional) LTM or another similar scenario (e.g., a scenario of an S-CPAC with an early TA process). Here, the RACH resources for early TA of a candidate PSCell may be allocated based on Examples 1-5 in the embodiment shown in FIG. 3.

[0332] In step 401-1, a UE transmits an L3 measurement report to a source S-NG-RAN (SN) node or an MN.

[0333] As an example, the UE transmits the L3 measurement report to the source S-NG-RAN node, or the UE transmits the L3 measurement report to the MN and then the MN forwardeds the L3 measurement report to the source S-NG-RAN node. The L3 measurement report includes the cell ID or CGI of a neighbour primary secondary cell (PSCell) and measurement result information. For a scenario triggered by the MN, the L3 measurement report is directly transmitted to the MN, and then the MN makes an LTM configuration decision. At this time, step 402 is ignored.

[0334] In step 401-2, the source S-NG-RAN node or the MN determines to perform an LTM configuration.

[0335] In step 402, the source S-NG-RAN node or a source SN gNB-CU transmits a Secondary Node Change Required message to the MN.

[0336] As an example, the source S-NG-RAN node or the gNB-CU of a source SN receives the L3 measurement report reported by the UE, and triggers the LTM configuration decision. The source S-NG-RAN node or the source SN gNB-CU initiates an inter-SN LTM request to the MN, and transmits a Secondary Node (S-NODE) Change Required message to the MN. Optionally, if a candidate PSCell allocates an early RACH resource based on a gNB-DU, the Secondary Node Change Required message may contain the gNB-DU ID information corresponding to a source PSCell and a candidate PSCell under the source SN or information implicitly mapping the gNB-DU ID. There is a corresponding relationship between Early RACH Resource Requester ID information and the gNB-DU ID, and the Early RACH Resource Requester ID information has the same value as the gNB-DU ID. The Early RACH Resource Requester ID information may be named as another name, for example, a base station-sub level ID (gNB-Sub Level ID) or another name, which is not limited in the present disclosure. This ID indicates the ID of an entity (which may be the gNB-DU) requesting an early RACH resource, or indicates an Early RACH Resource Requester ID.

[0337] In step 403, an M-NG-RAN node or the gNB-CU of the MN transmits a Secondary Node Addition Request message to a candidate S-NG-RAN node.

[0338] As an example, the M-NG-RAN node or the gNB-CU of the MN initiates the Secondary Node (S-NODE) Addition Request message to different candidate S-NG-RAN nodes to which the candidate PSCells belong or the gNB-CUs of different candidate SNs to which the candidate PSCells belong, respectively. For the information included in the Secondary Node Addition Request message, reference may be made to the information carried in the Handover Request message in the embodiment shown in FIG. 3. The candidate cell is corresponding to the candidate PSCell, and the candidate base station is corresponding to the candidate SN, and thus the details will not be repeatedly described here.

[0339] For the allocation of the early RACH resource by the candidate PSCell to the SN-DU, similarly, the MN can learn the candidate SN to which each candidate PSCell belongs, but cannot determine which SN-DU under this candidate SN the candidate PSCell belongs to (if the SN is a base station with a CU-DU split architecture). The MN can learn which SN-DU under the candidate SN the candidate PSCell belongs to, based on the Early RACH Resource Requester ID information. For the acquisition of the Early RACH Resource Requester ID information, reference may be made to steps 300-1 to 300-2 or steps 302-1 to 302-2 in the embodiment shown in FIG. 3.

[0340] Similarly, reference is made to steps 300-1 to 300-2 in the embodiment shown in FIG. 3. The Early RACH Resource Requester ID information is exchanged during the setup of an Xn interface between the MN and each SN (an Xn Setup Request message and / or an Xn Setup Response message) or during the configuration update of an NG-RAN node (an NG-RAN Node Configuration Update message and / or an NG-RAN Node Configuration Update Acknowledge message). There is a corresponding relationship between the Early RACH Resource Requester ID information and the gNB-DU ID, and the Early RACH Resource Requester ID information has the same value as the gNB-DU ID. The Early RACH Resource Requester ID information may be named as another name, for example, a base station-sub level ID (gNB-Sub Level ID) or another name, which is not limited in the present disclosure.

[0341] Optionally, the Xn Setup Response message may include the Early RACH Resource Requester ID information. Optionally, the NG-RAN Node Configuration Update Acknowledge message may include the Early RACH Resource Requester ID information. The Early RACH Resource Requester ID information explicitly or implicitly identifies the gNB-DU ID associated with the candidate cell under a non-source base station (i.e., a candidate SN base station).

[0342] For example, the Early RACH Resource Requester ID information may be included in one or more of: Served Cell Information NR, Neighbour Information NR and Neighbour Information E-UTRA. For a specific implementation, reference may be made to the corresponding description in the embodiment shown in FIG. 3, and thus the details will not be repeatedly described here.

[0343] Similarly, reference is made to steps 302-1 to 302-2 in the embodiment shown in FIG. 3. Before triggering an SN Addition Request, the MN may initiate a retrieval process to the candidate SN (which may contain the source SN) corresponding to the candidate PSCell cell (which may contain the source PSCell), for example, by transmitting an Identifier Request message. The candidate SN returns an Identifier Response message.

[0344] The Identifier Request message may be a non-UE-associated message, and may be a new message named such as Retrieve Early RACH Resource Requester ID Request, or an existing message such as the NG-RAN Node Configuration Update message or a UE-associated signaling such as the SN Modification Request message. The information carried in the Identifier Request message is as described in step 302-1 in FIG. 3, and thus the details will not be repeatedly described here.

[0345] The Identifier Response message may indicate a successful retrieval, and may be a new message named such as Retrieve Early RACH Resource Requester ID Response, or an existing message such as the NG-RAN Node Configuration Update Acknowledge message or a UE-associated signaling such as the SN Modification Request Acknowledge message. The information carried in the Identifier Request message is as described in step 302-2 in FIG. 3, and thus the details will not be repeatedly described here.

[0346] When the candidate SN is a base station with a CU-DU split architecture, for the involved interaction process between the SN-CU and the SN-DU, reference may be made to steps 304 and 305 in the above embodiment. The Early Sync Information Request information in the involved UE Context Setup Request message may further carry the ID information of the MN. For example, for the scheme in which the first rule is Per-gNB in Example 1, the Early Sync Information Request information may include an SN list which includes a global gNB ID of one SN (source SN) or more gNBs (including the source SN and a candidate SN), indicating the MN ID information (represented by a global gNB ID) associated with SNs.

[0347] For example, for the scheme in which the first rule is Per-gNB-DU in Example 3, an early RACH resource list is carried. As an example, the early RACH resource list may include an SN ID, and may further include the gNB-DU ID of an SN and / or MN ID information. Here, the SN ID includes the IDs of a source SN and a candidate SN, and may be represented by a global gNB ID. The gNB-DU ID of the SN corresponds to the Early RACH Resource Requester ID information contained in an Xn Interface Information SN Addition Request message, and the Early RACH Resource Requester ID information may be converted into the corresponding gNB-DU ID. If the early RACH resource list includes the gNB-DU ID of the SN, it indicates that the early RACH resource is allocated based on the gNB-DU of the SN indicated by the gNB-DU ID of the SN. If the early RACH resource list does not include the gNB-DU ID of the SN, it indicates that the early RACH resource is allocated based on the SN indicated by the SN ID. The MN ID information indicates the MN ID information associated with the candidate SN, and may be represented by a global gNB ID. This MN ID may indicate the candidate SN to forward the TA Information Transfer message to the indicated MN during the subsequent transfer of the TA information.

[0348] The SN ID and / or MN ID may be represented in an implicit way. For example, the SN ID and / or MN ID may be mapped to IDs with different names, but the values thereof are still represented by global gNB IDs. This can avoid introducing the concepts of SN and / or MN in the F1 interface specification.

[0349] Accordingly, during the resource allocation, the above information, as well as allocated RACH resource information, may also be carried in a UE Context Setup Response message.

[0350] In step 404, the candidate S-NG-RAN node or a gNB-CU of a candidate SN transmits a Secondary Node Addition Request Acknowledge message to the M-NG-RAN node or the MN.

[0351] As an example, if the candidate S-NG-RAN node or the gNB-CU of the candidate SN determines that the requested one or more candidate PSCells have accepted an LTM configuration request, the resource of the corresponding candidate PSCell is prepared, and the Secondary Node Addition Request Acknowledge message is returned to the M-NG-RAN node or the MN.

[0352] For the information contained in the Secondary Node Addition Request Acknowledge message, reference may be made to the information carried in the Handover Request Acknowledge message in the embodiment shown in FIG. 3. The candidate cell is corresponding to the candidate PSCell, and the candidate base station is corresponding to the candidate SN, and thus the details will not be repeatedly described here.

[0353] For each candidate S-NG-RAN node, through the above steps 403 and 404, the M-NG-RAN node collects the LTM configuration information of each candidate PSCell that has accepted the LTM request and the allocated early UL synchronization configuration information.

[0354] In step 405, the M-NG-RAN node transmits a Secondary Node Modification Request message to the source S-NG-RAN node and each other candidate S-NG-RAN node.

[0355] As an example, in order to support continuous LTM, the M-NG-RAN node may transmit the collected LTM configuration information of each candidate PSCell and the collected early UL synchronization configuration information to each other candidate S-NG-RAN node, and also to the source S-NG-RAN node, for example, by using an LTM Configuration Update message or an SN (S-Node) Modification Request message. For the specific information contained in the LTM Configuration Update message or the SN Modification Request message, reference may be made to the step 309 in the embodiment shown in FIG. 3. The candidate cell is corresponding to the candidate PSCell, and the candidate base station is corresponding to the candidate SN, and thus the details will not be repeatedly described here. The LTM Configuration Update message or the SN Modification Request message may further carry the MN ID information. In this way, when the TA information is transmitted through a non-UE-associated signaling (TA Information Transfer message) in a later stage, the TA information may be transmitted from the candidate SN to the source SN via the MN. If there is no control plane connection between the source SN and the candidate SN, the control plane message cannot be directly transmitted therebetween, and thus needs to be forwarded via the MN.

[0356] In step 406, the candidate S-NG-RAN node transmits a Secondary Node Modification Request Acknowledge message to the M-NG-RAN node, and the source SN transmits a Secondary Node Modification Request Acknowledge message to the M-NG-RAN node.

[0357] As an example, after receiving the information, the candidate S-NG-RAN node (including the source SN) stores the information. Optionally, a corresponding message is returned to the M-NG-RAN node, which, for example, may be an LTM Configuration Update Acknowledge message or an SN Modification Request Acknowledge message.

[0358] As an example, if the candidate S-NG-RAN node (including the source SN) is a node with a CU-DU split architecture, the gNB-CU of the SN may transmit a UE Context Modification Request message based on the RACH configuration allocated to this gNB by each candidate PSCell cell, so as to allocate the corresponding RACH configuration to the candidate gNB-DU. Alternatively, the gNB-DU requests the gNB-CU to acquire the early RACH resource. For a specific implementation, reference may be made to the scheme in the above Example 1-2 in FIG. 3.

[0359] If the early RACH resource is an RACH resource allocated based on the DU, the cell or the UE, the source gNB may forward all RACH resources allocated by the candidate cell to the corresponding DU or cell or UE under the SN to the corresponding DU.

[0360] In step 407, the M-NG-RAN node transmits an MN RRC Reconfiguration message to the UE.

[0361] As an example, the M-NG-RAN node configures the UE by transmitting the MN RRC Reconfiguration message, and the MN RRC Reconfiguration message may include a Candidate SN RRC Reconfiguration message.

[0362] In step 408, the UE transmits an RRC Reconfiguration Complete message to the M-NG-RAN node.

[0363] In step 409, the M-NG-RAN node transmits a Secondary Node Change Confirm message to the source S-NG-RAN node.

[0364] Alternatively, the M-NG-RAN node may transmit the collected LTM configuration information of each candidate PSCell and the collected early UL synchronization configuration information to the source S-NG-RAN node. For the contained specific information, reference may be made to step 309 in the embodiment shown in FIG. 3. The candidate cell is corresponding to the candidate PSCell, and the candidate base station is corresponding to the candidate SN, and thus the details will not be repeatedly described here. The MN ID information may be further carried. In this way, when the TA information is transmitted through a non-UE-associated signaling (TA Information Transfer message) in a later stage, the TA information may be transmitted from the candidate SN to the source SN via the MN. If there is no control plane connection between the source SN and the candidate SN, the control plane message cannot be directly transmitted therebetween, and thus needs to be forwarded via the MN.

[0365] In step 410, the source S-NG-RAN node determines that the UE triggers an early TA acquisition process to the candidate PSCell.

[0366] As an example, before the UE triggers the LTM, in order for the UE to obtain a TA value with the candidate PSCell cell in advance and then perform an RACH-less fast access process during the execution of the LTM, the source SN on the network side needs to trigger the UE to perform an early TA acquisition process. The source SN or the gNB-DU of the source SN triggers the UE to transmit a preamble to the candidate PSCell cell by using a PDCCH order. Then, the candidate PSCell cell calculates TA information and transmits a TA Information Transfer message from the candidate SN to the MN through an inter-network node signaling, and then the MN transmits the TA Information Transfer message to the source SN (alternatively, if the candidate SN and the source SN have a CU-DU split architecture, on the candidate SN side, the candidate SN-DU transmits a DU-CU TA Information Transfer message to the candidate SN-CU, and on the source SN side, the source SN-CU transmits a CU-DU TA Information Transfer message to the source SN-DU). After the source SN or the source SN-DU receives the TA message of the candidate cell, when the LTM is triggered, the TA of a target cell is carried to the UE through a Cell Switch Command MAC Control Element (CE).

[0367] The candidate SN-DU transmits the TA value and associated information to the candidate SN-CU through a non-UE-associated DU-CU TA Information Transfer message.

[0368] For example, the DU-CU TA Information Transfer message may include one or more of: a TA information list, a candidate PSCell ID, a TA value, a preamble index, a random access-radio network temporary indentifier, and Resource Indication information.

[0369] Here, the TA information list may include TA values of one or more candidate cells and the corresponnding RACH resource information.

[0370] For different allocation principles, the information contained in the Resource Indication information may be as follows.

[0371] When the first rule is Per-gNB, the Resource Indication information includes an SN ID and / or MN ID information. Here, the SN ID indicates a source gNB, and may be represented by a global gNB ID. The MN ID information indicates the MN to which a candidate SN belongs.

[0372] When the first rule is Per-DU in S-gNB+per-C-gNB, the Resource Indication information includes an SN ID, and may further include the gNB-DU ID of an SN and / or MN ID information. Here, the SN ID indicates a source gNB, and may be represented by a global gNB ID. If the source gNB is a base station with a CU-DU split architecture, the Resource Indication information includes the gNB-DU ID of the SN. The MN ID information indicates the MN to which a candidate SN belongs.

[0373] When the first rule is Per-gNB-DU, the Resource Indication information includes an SN ID, and may further include the gNB-DU ID of an SN and / or MN ID information. Here, the SN ID indicates a source gNB, and may be represented by a global gNB ID. If the source gNB is a base station with a CU-DU split architecture, the Resource Indication information includes the gNB-DU ID of the SN. The MN ID information indicates the MN to which a candidate SN belongs. This MN ID may indicate the candidate SN to forward the TA Information Transfer message to the indicated MN.

[0374] When the first rule is Per-Cell, the Resource Indication information includes an LTM PSCell ID, where the LTM PSCell ID may be indicated by a cell ID or NR CGI.

[0375] When the first rule is Per-UE, the Resource Indication information includes a gNB-CU UE F1AP ID and / or gNB-DU UE F1AP ID. Alternatively, the TA information of the candidate cell is transmitted via a UE-associated message.

[0376] The SN ID and / or MN ID may be represented in an implicit way. For example, the SN ID and / or MN ID may be mapped to IDs with different names, but the values thereof are still represented by global gNB IDs. This avoids introducing the concept of an SN and / or MN in the F1 interface specification.

[0377] In step 411, the candidate SN or the candidate SN-CU transmits a TA Information Transfer message to the MN.

[0378] As an example, the candidate SN or the candidate SN-CU transmits TA-related information to the corresponding MN through a non-UE-associated and newly defined Xnap information (e.g., TA information transfer). The candidate SN may determine, according to the MN ID information, which MN node to forward information to, because the same candidate SN may be associated with different MNs for different UEs.

[0379] For example, the TA Information Transfer message may include one or more of: a TA information list, a candidate cell ID, a TA value, a preamble index, a random access radio network temporary identifier, and Resource Indication information. Here, the Resource Indication information may indicate that the RACH resource used by the UE was previously allocated to a corresponding node or cell by the candidate cell.

[0380] For different allocation principles, the information contained in the Resource Indication information may be as follows.

[0381] When the first rule is Per-gNB, the Resource Indication information may carry an LTM SN ID, which indicates a source SN and may be represented by the global gNB ID.

[0382] When the first rule is Per-DU in S-gNB+per-C-gNB, the Resource Indication information may include an SN ID, and may further include Early RACH Resource Requester ID information. The SN ID indicates a source gNB, and may be represented by a global gNB ID. There is a corresponding relationship between the Early RACH Resource Requester ID information and a gNB-DU ID, and the Early RACH Resource Requester ID information has the same value as the gNB-DU ID. The Early RACH Resource Requester ID information may be named as another name, which is not limited in the present disclosure. Since the gNB-DU ID is not directly used (e.g., the Resource Indication information does not directly include the gNB-DU ID), it may be implemented that the architecture information of the base station is not exposed in an Xn interface specification. This IE is included only when the source SN indicated by the SN ID has a CU-DU split architecture. For example, the early RACH resource list includes the Early RACH Resource Requester ID information, which may implicitly indicate the gNB-DU ID under the SN.

[0383] When the first rule is Per-gNB-DU, the Resource Indication information may include an SN ID, and may further include Early RACH Resource Requester ID information. The SN ID indicates a source gNB, and may be represented by a global gNB ID. This SN ID may indicate the MN to forward the TA Information Transfer message to the SN indicated by the SN ID. There is a corresponding relationship between the Early RACH Resource Requester ID information and a gNB-DU ID, and the Early RACH Resource Requester ID information has the same value as the gNB-DU ID. The Early RACH Resource Requester ID information may be named as another name, which is not limited in the present disclosure. Since the gNB-DU ID is not directly used (e.g., the Resource Indication information does not directly include the gNB-DU ID), it may be implemented that the architecture information of the base station is not exposed in an Xn interface specification. This IE is included only when the source SN indicated by the SN ID has a CU-DU split architecture. For example, the early RACH resource list includes the Early RACH Resource Requester ID information, which may implicitly indicate the gNB-DU ID under the SN. This ID indicates the ID of an entity (which may be the gNB-DU) requesting an early RACH resource, or indicates the Early RACH Resource Requester ID.

[0384] When the first rule is Per-Cell, the Resource Indication information includes an LTM PSCell ID, where the LTM PSCell ID may be indicated by a cell ID or NR CGI.

[0385] When the first rule is Per-UE, the Resource Indication information includes M-NG-RAN node UE XnAP and / or S-NG-RAN node UE XnAP ID. Alternatively, the TA information of the candidate cell is transmitted using a UE-associated message.

[0386] In step 412, the MN transmits the TA Information Transfer message to the source SN or the source SN-CU.

[0387] As an example, the MN transmits the TA-related information to the source SN or source SN-CU through the non-UE-associated and newly defined Xnap information (e.g., the TA Information Transfer message). The MN can determine which node to forward information to through the above Resource Indication information, because the same MN may have different SNs for different UEs.

[0388] The TA Information Transfer message includes one or more of: a TA information list, a candidate cell ID, a TA value, a preamble index, a random access radio network temporary identifier, and Resource Indication information. Here, the Resource Indication information may indicate that the RACH resource used by the UE was previously allocated to a corresponding node or cell by the candidate cell.

[0389] When the first rule is Per-gNB, the Resource Indication information may not carry information, or the TA Information Transfer message may not include the Resource Indication information.

[0390] When the first rule is Per-DU in S-gNB+per-C-gNB, the Resource Indication information may include Early RACH Resource Requester ID information. There is a corresponding relationship between the Early RACH Resource Requester ID information and a gNB-DU ID, and the Early RACH Resource Requester ID information has the same value as the gNB-DU ID. The Early RACH Resource Requester ID information may be named as another name, which is not limited in the present disclosure. Since the gNB-DU ID is not directly used (e.g., the Resource Indication information does not directly include the gNB-DU ID), it may be implemented that the architecture information of the base station is not exposed in an Xn interface specification. This IE is included only when the source SN indicated by the SN ID has a CU-DU split architecture. For example, the early RACH resource list includes the Early RACH Resource Requester ID information, which may implicitly indicate the gNB-DU ID under the SN.

[0391] When the first rule is Per-gNB-DU, the Resource Indication information may include Early RACH Resource Requester ID information. This Early RACH Resource Requester ID information may indicate that the SN continues to forward the TA Information to the SN gNB-DU indicated by the Early RACH Resource Requester ID. There is a corresponding relationship between the Early RACH Resource Requester ID information and a gNB-DU ID, and the Early RACH Resource Requester ID information has the same value as the gNB-DU ID. The Early RACH Resource Requester ID information may be named as another name, which is not limited in the present disclosure. Since the gNB-DU ID is not directly used (e.g., the Resource Indication information does not directly include the gNB-DU ID), it may be implemented that the architecture information of the base station is not exposed in an Xn interface specification. This IE is included only when the source SN indicated by the SN ID has a CU-DU split architecture. For example, the early RACH resource list includes the Early RACH Resource Requester ID information, which may implicitly indicate the gNB-DU ID under the SN. This ID indicates the ID of an entity (which may be the gNB-DU) requesting an early RACH resource, or indicates the Early RACH Resource Requester ID.

[0392] When the first rule is Per-Cell, the Resource Indication information includes an LTM PSCell ID, where the LTM PSCell ID may be represented by a cell ID or NR CGI.

[0393] When the first rule is Per-UE, the Resource Indication information includes M-NG-RAN node UE XnAP and / or S-NG-RAN node UE XnAP ID. Alternatively, the TA information of the candidate cell is transmitted using a UE-associated message.

[0394] Alternatively, the source SN-CU may transmit a candidate cell, TA value information and Early RACH Resource information to the corresponding source gNB-DU through a non-UE-associated CU-DU TA Information Transfer message.

[0395] In an embodiment, for the principle in the above Example 3, that is, for an SN base station with a CU-DU split architecture, the candidate PSCell allocates the random access resource for the early TA acquisition according to different DUs. The problem involved therein is that, based on the cell ID or CGI information in an L3 measurement report, the source SN or the MN can determine which candidate SN a candidate cell under a non-source SN (i.e., a candidate SN) belongs to, but cannot determine which gNB-DU under the candidate SN the candidate cell belongs to. Therefore, before the SN Addition Request message is triggered, it is required to learn which gNB-DU under the candidate SN the candidate cell under the candidate SN belongs to or the corresponding Early RACH Resource Requester ID information. For the acquisition of the Early RACH Resource Requester ID information, reference may be made to the above steps 300-1 to 300-2 (between the MN and the SN), or to the above steps 302-1 to 302-2 (between the MN and the SN). However, the above schemes occur before the SN Addition Request, and are intended to perform an early RACH resource request for the DU and / or base station where a recommended other candidate cell is during a candidate PSCell resource request process, but the recommended other candidate cell may fail in the LTM resource request process and thus may be not used as a candidate cell, that is, the candidate SN did not accept to be an accepted candidate PSCell. This may result in unnecessary signaling and a signaling waste, as well as a waste in RACH resource allocation. That is, the candidate PSCell does not need to allocate an early RACH resource to the DU associated with the retrieved gNB-DU ID information or the corresponding Early RACH Resource Requester ID information. In order to make an early RACH resource request only for the gNB-DU under the SN and / or the base station to which an accepted candidate PSCell belongs, and obtain the gNB-DU ID information associated with the accepted candidate PSCell or the corresponding Early RACH Resource Requester ID information, the candidate SN may provide the gNB-DU ID information associated with the accepted candidate PSCell or the corresponding Early RACH Resource Requester ID information during an SN Addition Request preparation process. The above scheme may be embodied through the following process:

[0396] The Secondary Node Addition Request message in step 403 carries one or more of: a candidate PSCell ID (or a target cell ID, which may be represented by a cell ID or NR CGI), and explicit or implicit Indication information (e.g., the request may also be indicated through an LTM Information Request IE or other LTM-related IEs) indicating to retrieve the gNB-DU ID information associated with the candidate PSCell indicated by the candidate PSCell ID, or implicit mapping ID information (which is, for example, the Early RACH Resource Requester ID information, or may have another name) corresponding to the gNB-DU ID associated with the candidate PSCell.

[0397] The Secondary Node Addition Request Acknowledge message in step 404 carries one or more of: an accepted LTM candidate PSCell ID (or a target cell ID, which may be represented by a cell ID or NR CGI), and the gNB-DU ID information associated with the candidate PSCell (if the candidate gNB is a base station with a CU-DU split architecture) or the implicit mapping ID information corresponding to the gNB-DU ID (which is, for example, the Early RACH Resource Requester ID information, or may have another name).

[0398] If the candidate SN is a base station with a non-CU-DU split architecture, the candidate PSCell does not have an associated gNB-DU information. Accordingly, the Secondary Node Addition Request Acknowledge message in step 404 carries Retrieve Failure Indication information. Alternatively, inidacation information indicating that the candidate PSCell does not have an assocaited gNB-DU or Early RACH Resource Requester ID is returned (or empty information is used to indicate that the candidate cell does not have an associated gNB-DU or Early RACH Resource Requester ID, that is, no gNB-DU or Early RACH Resource Requester ID information associated with the candidate PSCell is returned), to indicate that the requested candidate PSCell does not have an associated gNB-DU information.

[0399] If the gNB-DU ID or Early RACH Resource Requester ID information associated with the candidate PSCell is contained in an XnAP Secondary Node Addition Request Acknowledge message, the MN (master base station) may use this information in the subsequent early RACH resource request, for requesting, through an XnAP Secondary Node Modification Request message, the candidate PSCell to allocate an early RACH resource to the gNB-DU indicated by the gNB-DU ID or Early RACH Resource Requester ID information associated with the accepted candidate PSCell.

[0400] The MN (master base station) and each candidate SN base station respectively performs the secondary node addition request process, and finally obtains the information of each accepted candidate PSCell and the gNB-DU information under the candidate SN to which the accepted candidate PSCell belongs (if the candidate SN is a base station with a CU-DU split architecture).

[0401] In this way, in the subsequent process, it is possible to request, through a secondary node modification request process, one or more candidate PSCells on the candidate SN to allocate an early RACH resource to the gNB-DU to which the accepted candidate PSCell belongs (if the candidate SN is a base station with a CU-DU split architecture) and / or the SN base station to which the candidate PSCell belongs (if the candidate base station is not a base station with a CU-DU split architecture). This secondary node modification request process may be based on a candidate cell or based on a node. If the secondary node modification request process is based on the candidate cell, in a secondary node modification request process, for one candidate PSCell on a candidate SN base station, this candidate PSCell is requested to allocate an early RACH resource to the gNB-DU and / or SN base station to which another candidate PSCell belongs. If the secondary node modification request process is based on the node, in a secondary node modification request process, for a plurality of candidate PSCells on a candidate SN base station, each corresponding candidate PSCell is requested to allocate an early RACH resource to the gNB-DU and / or base station to which another candidate PSCell belongs.

[0402] Therefore, the Secondary Node Modification Request message in step 405 carries one or more of: the accepted LTM candidate PSCell ID (optionally, a LTM candidate PSCell list, containing one or more candidate cell IDs, where each candidate cell ID may be represented by an NR CGI), and an Early Synchronization (Sync) Information Request IE. The Early Sync Information Request IE indicates that an LTM candidate PSCell is requested to allocate an early RACH resource to the gNB-DU (which may be represented by the gNB-DU ID or Early RACH Resource Requester ID information) and / or base station (which may be represented by a global gNB ID) to which another candidate PSCell belongs.

[0403] Accordingly, if the candidate SN base station is a base station with a CU-DU split architecture, it is possible to transmit the UE Context Modification Request message that carries the information in the Secondary Node Modification Request message in step 405, to provide an early RACH resource to the DU.

[0404] Accordingly, the UE Context Modification Response message returned by the DU carries one or more of: one or more candidate PSCell IDs (optionally, each candidate cell ID may be represented by an NR CGI), and the early RACH resource allocated by each candidate PSCell to the gNB-DU and / or base station to which another candidate PSCell belongs, which may be represented by an Early Synchronization (Sync) Information Response IE.

[0405] Accordingly, the SN Modification Acknowledge message in step 406 carries one or more of: one or more candidate PSCell IDs (optionally, each candidate cell ID may be represented by an NR CGI), and the early RACH resource allocated by each candidate PSCell to the gNB-DU and / or base station to which another candidate PSCell belongs, which may be represented by an Early Synchronization (Sync) Information Response IE or an Early Uplink (UL) Synchronization (Sync) Configuration IE.

[0406] The above mechanism in which the master base station MN requests the candidate PSCell to allocate the early RACH resource after obtaining the accepted candidate PSCell is also applicable to the mechanism in which the candidate PSCell allocates the early RACH resource based on the SN base station or based on the PSCell cell. It is possible to reduce the unnecessary allocation of the early RACH resources to a recommended candidate PSCell or the DU and / or base station to which the recommended candidate PSCell belongs, when the recommended candidate PSCell did not accept the LTM request. Accordingly, the waste in early RACH resource allocation to the candidate PSCell is reduced.

[0407] For the UE handover between nodes, there are the following situations:

[0408] -a handover from a source NG-RAN node to a target NG-RAN node (each node may be a base station with a CU-DU split architecture);

[0409] -a handover from the source NG-RAN node to a target MN + SN (each node may be a base station with a CU-DU split architecture);

[0410] -a handover from a source MN + SN to the target MN + SN (SN unchanged) (each node may be a base station with a CU-DU split architecture);

[0411] -a handover from the source MN + SN to the target MN + SN (SN changed) (each node may be a base station with a CU-DU split architecture);

[0412] -a handover from the source MN + SN to the target NG-RAN node (each node may be a base station with a CU-DU split architecture); and

[0413] -a handover from an MN + a source SN to the MN + a target SN (SN changed, MN unchanged, MN or SN triggered) (each node may be a base station with a CU-DU split architecture).

[0414] For the above handover situations, as well as a conditional handover (CHO), a continuous CHO, an LTM handover or a conditional LTM handover, there may be a corresponding early RACH allocation. The allocation principles in the embodiments of the present disclosure and the schemes set forth herein are also applicable to the above handover situations, as well as the conditional handover, the continuous CHO, the LTM handover or the conditional LTM handover.

[0415] FIG. 5 illustrates a method performed by a first node in a wireless communication system according to an exemplary implementation of the present disclosure. The method may be adapted to be performed by the source NG-RAN node, the source gNB-CU and the MN described in FIGS. 3 to 4. For a specific implementation of each step, reference may be made to the corresponding description in FIGS. 3 to 4. According to the exemplary implementation, the method performed by the first node in the wireless communication system comprises the following steps:

[0416] Step 501, transmitting a first request message to a second node.

[0417] As an example, the first request message may be used to request an identifier of an early random access channel (RACH) resource requester to which a candidate cell for an LTM handover belongs.

[0418] For a specific implementation of step 501 and the first request message, reference may be made to the related description in the above step 302-1, and thus the details will not be repeatedly described here.

[0419] Step 502, receiving a first response message from the second node.

[0420] As an example, the first response message may comprise an identifier of the candidate cell and an identifier of the early RACH resource requester to which the candidate cell belongs. For example, the identifier of the early RACH resource requester to which the candidate cell belongs may be the identifier of the early RACH resource requester to which the candidate cell indicated by the identifier of the candidate cell belongs. Here, the first node is a central unit (CU) of a source node and the second node is a CU of a candidate node; or the first node is a master node and the second node is a secondary node.

[0421] For a specific implementation of step 502 and the first response message, reference may be made to the related description in the above step 302-2, and thus the details will not be repeatedly described here. For a specific implementation of the identifier of the early RACH resource requester, reference may be made to the Early RACH Resource Requester ID information in step 302-2. The Early RACH Resource Requester ID information may be mapping ID information for implicitly indicating the gNB-DU to which the candidate cell belongs, or may be another name indicating the ID of an entity requesting an early RACH resource.

[0422] In some embodiments, the first request message may comprise the identifier of the candidate cell and indication information for requesting the identifier of the early RACH resource requester, wherein the identifier of the early RACH resource requester may indicate an identifier of an entity requesting an early RACH resource. For a specific implementation of the first request message, reference may be made to the Identifier Request message in the above step 302-2, and for a specific implementation of the Indication information for requesting the identifier of the early RACH resource requester, reference may be made to the Early RACH Resource Requester ID Request Indication information in the above Identifier Request message, and thus the details will not be repeatedly described here.

[0423] In some embodiments, the first response message may further comprise an identifier of a node to which the early RACH resource requester belongs. Here, for a specific implementation of the identifier of the node to which the early RACH resource requester belongs, reference may be made to the gNB ID in step 302-2, and thus the details will not be repeatedly described here.

[0424] In some embodiments, the first request message may comprise at least one of: an Xn Setup Request message; an Xn Application Protocol (AP) Retrieve Early RACH Resource Requester IDentifier Request message; and an XnAP New Generation Radio Access Network Node Configuration Update message.

[0425] In some embodiments, the first response message may comprise at least one of: an Xn Setup Response message; an Xn Application Protocol (AP) Retrieve Early RACH Resource Requester IDentifier Response message; and an XnAP New Generation Radio Access Network Node Configuration Update Acknowledge message.

[0426] In some embodiments, the method may further comprise: receiving, from the second node, a second message,which may comprise at least one of: TA-related information of the candidate cell; the identifier of the early RACH resource requester; and an identifier of a node to which the early RACH resource requester belongs. When transmitting the TA-related information to an MN, a candidate SN may also transmit the identifier of the node to which the early RACH resource requester belongs, and the identifier of the node to which the early RACH resource requester belongs may be a source SN ID. For a specific implementation, reference may be made to the related description in the above step 320 or 411, and thus the details will not be repeatedly described here.

[0427] In some embodiments, the method may further comprise: transmitting the TA-related information of the candidate cell to the node indicated by the identifier of the node to which the early RACH resource requester belongs or to a node indicated by the identifier of the early RACH resource requester. For example, the second node transmits the TA-related information of the candidate cell to the gNB-DU to which the candidate cell belongs. The second node transmits the TA-related information of the candidate cell to the source SN to which the gNB-DU belongs.

[0428] In some embodiments, the method may further comprise: receiving a second request message, and transmitting a second response message. For a specific implementation, reference may be made to the corresponding description in the method shown in FIG. 3 or FIG. 4, for example, to the specific implementations of the above Examples 1-2-1 to 1-2-4 and steps 317-1 and 317-2, and thus the details will not be repeatedly described here. For a specific implementation of the second request message, reference may be made to the Early RACH Resource Request message in the above step 317-1, and thus the details will not be repeatedly described here. For a specific implementation of the second response message, reference may be made to the Early RACH Resource Response message in step 317-2, and thus the details will not be repeatedly described here.

[0429] Optionally, the second request message may comprise information for requesting to configure an early RACH resource allocated to a node by the candidate cell based on a UE or based on a DU, and the second response message may comprise information related to the early RACH resource allocated to the node by the candidate cell, configured based on the UE or based on the DU.

[0430] In some embodiments, the second request message may comprise: the identifier of the candidate cell; and indication information for requesting to configure the early RACH resource allocated to the node by the candidate cell based on the UE or based on the DU.

[0431] In some embodiments, the second response message may comprise: the identifier of the candidate cell; and Early Uplink Synchronization Configuration information.

[0432] In some embodiments, the second request message may comprise at least one of: an Early RACH Resource Request message; a UE Context Modification Request; a UE Context Modification Required message; a Secondary Node (SN) Modification Required message; and an SN Modification Request message. For example, a DU transmits the UE Context Modification Required message to a CU, a source SN transmits the SN Modification Required message to an MN, and the MN transmits an SN Modification Acknowledge message to a candidate SN. For a specific implementation, reference may be made to the corresponding description in the method shown in FIG. 3 or FIG. 4, and thus the details will not be repeatedly described here.

[0433] In some embodiments, the second response message may comprise at least one of: an Early RACH Resource Request Acknowledge message; an Early RACH Resource Response message; a UE Context Modification Response message; a UE Context Modification Acknowledge message; an SN Modification Acknowledge message; and an SN Modification Request Acknowledge message. For example, the CU transmits the UE Context Modification Acknowledge message to the DU, the MN transmits the SN Modification Acknowledge message to the source SN, and the candidate SN transmits the SN Modification Acknowledge message to the MN. For a specific implementation, reference may be made to the corresponding description in the method shown in FIG. 3 or FIG. 4, and thus the details will not be repeatedly described here.

[0434] FIG. 6 illustrates a method performed by a second node in a wireless communication system according to an exemplary implementation of the present disclosure. The method may be adapted to be performed by the candidate gNB-CU, the candidate NG-RAN node and the SN described in FIGS. 3 to 4. For a specific implementation of each step, reference may be made to the corresponding description in FIGS. 3 to 4. According to the exemplary implementation, the method performed by the second node in the wireless communication system comprises the following steps:

[0435] Step 601, receiving a first request message from a first node.

[0436] As an example, the first request message is used to request an identifier of an early random access channel (RACH) resource requester to which a candidate cell for a layer 1 / layer 2 triggered mobility (LTM) handover belongs.

[0437] For a specific implementation of step 601 and the first request message, reference may be made to the related description in the above step 302-1, and thus the details will not be repeatedly described here.

[0438] Step 602, transmitting a first response message to the first node.

[0439] For a specific implementation of step 602 and the first response message, reference may be made to the related description in the above step 302-2, and thus the details will not be repeatedly described here.

[0440] As an example, the first response message may comprise an identifier of the candidate cell and an identifier of the early RACH resource requester to which the candidate cell belongs. For example, the identifier of the early RACH resource requester to which the candidate cell belongs may be the identifier of the early RACH resource requester to which the candidate cell indicated by the identifier of the candidate cell belongs. Here, the first node is a central unit (CU) of a source node and the second node is a CU of a candidate node; or the first node is a master node and the second node is a secondary node.

[0441] In some embodiments, the method may further comprise: transmitting a second message to the first node. For a specific implementation, reference may be made to the related description in the above step 320 or 411, and thus the details will not be repeatedly described here.

[0442] As an example, the second message may comprise at least one of: timing advanced (TA)-related information of the candidate cell; the identifier of the early RACH resource requester; and an identifier of a node to which the early RACH resource requester belongs.

[0443] In some embodiments, the method may further comprise: transmitting a second request message, wherein the second request message comprises information for requesting to configure an early RACH resource allocated to a node by the candidate cell based on a UE or based on a DU; and receiving a second response message, wherein the second response message comprises information related to the early RACH resource allocated to the node by the candidate cell and configured based on the UE or based on the DU.

[0444] According to an exemplary embodiment, the first response message may further comprise an identifier of a node to which the early RACH resource requester belongs. Here, for a specific implementation of the identifier of the node to which the early RACH resource requester belongs, reference may be made to the gNB ID in step 302-2, and thus the details will not be repeatedly described here.

[0445] As an example, the second message may comprise at least one of: timing advanced (TA)-related information of the candidate cell; the identifier of the early RACH resource requester; and an identifier of a node to which the early RACH resource requester belongs.

[0446] According to an exemplary embodiment, the first request message may comprise the identifier of the candidate cell and indication information for requesting the identifier of the early RACH resource requester, wherein the identifier of the early RACH resource requester indicates an identifier of an entity requesting an early RACH resource. For a specific implementation of the first request message, reference may be made to the Identifier Request message in the above step 302-2, and for a specific implementation of the Indication information for requesting the identifier of the early RACH resource requester, reference may be made to the Early RACH Resource Requester ID Request Indication information in the above Identifier Request message, and thus the details will not be repeatedly described here.

[0447] According to an exemplary embodiment, the first response message may further comprise an identifier of a node to which the early RACH resource requester belongs. Here, for a specific implementation of the identifier of the node to which the early RACH resource requester belongs, reference may be made to the gNB ID in step 302-2.

[0448] According to an exemplary embodiment, the first request message may comprise at least one of: an Xn Setup Request message; an Xn Application Protocol (AP) Retrieve Early RACH Resource Requester IDentifier Request message; and an XnAP New Generation Radio Access Network Node Configuration Update message.

[0449] According to an exemplary embodiment, the first response message may comprise at least one of: an Xn Setup Response message; an Xn Application Protocol (AP) Retrieve Early RACH Resource Requester IDentifier Response message; and an XnAP New Generation Radio Access Network Node Configuration Update Acknowledge message.

[0450] In some embodiments, the method may further comprise: transmitting the TA-related information of the candidate cell to the node indicated by the identifier of the node to which the early RACH resource requester belongs or to a node indicated by the identifier of the early RACH resource requester. For example, the second node transmits the TA-related information of the candidate cell to the gNB-DU to which the candidate cell belongs. The second node transmits the TA-related information of the candidate cell to the source SN to which the gNB-DU belongs.

[0451] In some embodiments, the method may further comprise: transmitting a second request message, and receiving a second response message. For a specific implementation, reference may be made to the corresponding description in the method shown in FIG. 3 or FIG. 4, for example, to the specific implementations of the above Examples 1-2-1 to 1-2-4 and steps 317-1 and 317-2, and thus the details will not be repeatedly described here. For a specific implementation of the second request message, reference may be made to the Early RACH Resource Request message in the above step 317-1, and thus the details will not be repeatedly described here. For a specific implementation of the second response message, reference may be made to the Early RACH Resource Response message in step 317-2, and thus the details will not be repeatedly described here.

[0452] Optionally, the second request message may comprise information for requesting to configure the early RACH resource allocated by the candidate cell to a node based on a UE or based on a DU, and the second response message may comprise information related to the early RACH resource allocated by the candidate cell to the node, configured based on the UE or based on the DU.

[0453] In some embodiments, the second request message may comprise: the identifier of the candidate cell; and indication information for requesting to configure the early RACH resource allocated to the node by the candidate cell based on the UE or based on the DU.

[0454] In some embodiments, the second response message may comprise: the identifier of the candidate cell; and Early Uplink Synchronization Configuration information.

[0455] In some embodiments, the second request message may comprise at least one of: an Early RACH Resource Request message; a UE Context Modification Request; a UE Context Modification Required message; a Secondary Node (SN) Modification Required message; and an SN Modification Request message. For example, a DU transmits the UE Context Modification Required message to a CU, a source SN transmits the SN Modification Required message to an MN, and the MN transmits an SN Modification Acknowledge message to a candidate SN. For a specific implementation, reference may be made to the corresponding description in the method shown in FIG. 3 or FIG. 4, and thus the details will not be repeatedly described here.

[0456] In some embodiments, the second response message may comprise at least one of: an Early RACH Resource Request Acknowledge message; an Early RACH Resource Response message; a UE Context Modification Response message; a UE Context Modification Acknowledge message; an SN Modification Acknowledge message; and an SN Modification Request Acknowledge message. For example, the CU transmits the UE Context Modification Acknowledge message to the DU, the MN transmits the SN Modification Acknowledge message to the source SN, and the candidate SN transmits the SN Modification Acknowledge message to the MN. For a specific implementation, reference may be made to the corresponding description in the method shown in FIG. 3 or FIG. 4, and thus the details will not be repeatedly described here.

[0457] FIG. 7 illustrates a method performed by a DU of a source node in a wireless communication system according to an exemplary implementation of the present disclosure. The method may be adapted to be performed by the DU of the source node described in FIGS. 3 to 4. For a specific implementation of each step, reference may be made to the corresponding description in FIGS. 3 to 4. According to the exemplary implementation, the method performed by the DU of the source node in the wireless communication system comprises the following steps:

[0458] Step 701, transmitting a second request message to a first node.

[0459] Step 702, receiving a second response message from the first node.

[0460] In some embodiments, the first node is a central unit (CU) of the source node. The first node may receive the second request message from the DU of the source node, and the first node transmits the second response message to the DU of the source node.

[0461] For specific implementations of steps 701-702, reference may be made to the specific implementations of the above Examples 1-2-1 to 1-2-4 and steps 317-1 and 317-2, and thus the details will not be repeatedly described here. For a specific implementation of the second request message, reference may be made to the Early RACH Resource Request message in the above step 317-1, and thus the details will not be repeatedly described here. For a specific implementation of the second response message, reference may be made to the Early RACH Resource Response message in step 317-2, and thus the details will not be repeatedly described here.

[0462] As an example, the second request message may comprise information for requesting to configure an early RACH resource allocated to a node by a candidate cell based on a UE or based on the DU, and the second response message may comprise information related to the early RACH resource allocated to the node by the candidate cell, configured based on the UE or based on the DU.

[0463] In some embodiments, the second request message may comprise: an identifier of the candidate cell; and indication information for requesting to configure the early RACH resource allocated to the node by the candidate cell based on the UE or based on the DU.

[0464] In some embodiments, the second response message may comprise: the identifier of the candidate cell; and Early Uplink Synchronization Configuration information.

[0465] In some embodiments, the second request message may comprise at least one of: an Early RACH Resource Request message; a UE Context Modification Request; a UE Context Modification Required message; a Secondary Node (SN) Modification Required message; and an SN Modification Request message. For example, the DU transmits the UE Context Modification Required message to a CU, a source SN transmits the SN Modification Required message to an MN, and the MN transmits an SN Modification Acknowledge message to a candidate SN. For a specific implementation, reference may be made to the corresponding description in the method shown in FIG. 3 or FIG. 4, and thus the details will not be repeatedly described here.

[0466] In some embodiments, the second response message may comprise at least one of: an Early RACH Resource Request Acknowledge message; an Early RACH Resource Response message; a UE Context Modification Response message; a UE Context Modification Acknowledge message; an SN Modification Acknowledge message; and an SN Modification Request Acknowledge message. For example, the CU transmits the UE Context Modification Acknowledge message to the DU, the MN transmits the SN Modification Acknowledge message to the source SN, and the candidate SN transmits the SN Modification Acknowledge message to the MN. For a specific implementation, reference may be made to the corresponding description in the method shown in FIG. 3 or FIG. 4, and thus the details will not be repeatedly described here.

[0467] In some embodiments, a first request message is transmitted by the first node, and the first request message may be used to request an identifier of an early random access channel (RACH) resource requester to which a candidate cell for a layer 1 / layer 2 triggered mobility (LTM) handover belongs. For a specific implementation, reference may be made to the related description in the above step 302-1, and thus the details will not be repeatedly described here.

[0468] A first response message is transmitted by a second node, and the first response message comprises an identifier of the candidate cell and an identifier of the early RACH resource requester to which the candidate cell belongs. Here, the first node is a central unit (CU) of the source node and the second node is a CU of a candidate node; or the first node is a master node and the second node is a secondary node. For a specific implementation, reference may be made to the related description in the method shown in FIG. 3 or FIG. 4, for example, to the related description in step 302-2, and thus the details will not be repeatedly described here.

[0469] A second message is transmitted by the second node, and the second message may comprise at least one of: timing advanced (TA)-related information of the candidate cell; the identifier of the early RACH resource requester; and an identifier of a node to which the early RACH resource requester belongs. For a specific implementation, reference may be made to the related description in the above step 320 or 411, and thus the details will not be repeatedly described here.

[0470] In some embodiments, the first request message may comprise the identifier of the candidate cell and Indication information for requesting the identifier of the early RACH resource requester, wherein the identifier of the early RACH resource requester indicates an identifier of an entity requesting an early RACH resource. For a specific implementation of the first request message, reference may be made to the Identifier Request message in the above step 302-2, and for a specific implementation of the Indication information for requesting the identifier of the early RACH resource requester, reference may be made to the Early RACH Resource Requester ID Request Indication information in the above Identifier Request message, and thus the details will not be repeatedly described here.

[0471] In some embodiments, the first response message may further comprise an identifier of a node to which the early RACH resource requester belongs. Here, for a specific implementation of the identifier of the node to which the early RACH resource requester belongs, reference may be made to the gNB ID in step 302-2, and thus the details will not be repeatedly described here.

[0472] In some embodiments, the first request message may comprise at least one of: an Xn Setup Request message; an Xn Application Protocol (AP) Retrieve Early RACH Resource Requester IDentifier Request message; and an XnAP New Generation Radio Access Network Node Configuration Update message.

[0473] In some embodiments, the first response message may comprise at least one of: an Xn Setup Response message; an Xn Application Protocol (AP) Retrieve Early RACH Resource Requester IDentifier Response message; and an XnAP New Generation Radio Access Network Node Configuration Update Acknowledge message.

[0474] FIG. 8 illustrates a method performed by a user equipment (UE) in a wireless communication system according to an exemplary implementation of the present disclosure. The method may be adapted to be performed by the UE described in FIGS. 3 to 4. For a specific implementation of each step, reference may be made to the corresponding description in FIGS. 3 to 4. According to the exemplary implementation, the method performed by the UE in the wireless communication system comprises the following steps:

[0475] Step 801, receiving an RRC Reconfiguration message.

[0476] Step 802, transmitting an RRC Reconfiguration Complete message.

[0477] A first request message is transmitted by a first node for requesting an identifier of an early random access channel (RACH) resource requester to which a candidate cell for a layer 1 / layer 2 triggered mobility (LTM) handover belongs. For a specific implementation, reference may be made to the related description in the method shown in FIG. 3 or FIG. 4, for example, to the related description in step 302-1, and thus the details will not be repeatedly described here.

[0478] A first response message is transmitted by a second node, and the first response message may comprise an identifier of the candidate cell and an identifier of the early RACH resource requester to which the candidate cell belongs. For example, the identifier of the early RACH resource requester to which the candidate cell belongs may be the identifier of the early RACH resource requester to which the candidate cell indicated by the identifier of the candidate cell belongs. Here, the first node is a central unit (CU) of a source node and the second node is a CU of a candidate node; or the first node is a master node and the second node is a secondary node. For a specific implementation, reference may be made to the related description in the method shown in FIG. 3 or FIG. 4, for example, to the related description in step 302-2, and thus the details will not be repeatedly described here.

[0479] A second message is transmitted by the second node, and the second message comprises at least one of: timing advanced (TA)-related information of the candidate cell; the identifier of the early RACH resource requester; and an identifier of a node to which the early RACH resource requester belongs. For a specific implementation, reference may be made to the related description in the above step 320 or 411, and thus the details will not be repeatedly described here.

[0480] In some embodiments, the first request message may comprise the identifier of the candidate cell and Indication information for requesting the identifier of the early RACH resource requester, wherein the identifier of the early RACH resource requester indicates an identifier of an entity requesting an early RACH resource. For a specific implementation of the first request message, reference may be made to the Identifier Request message in the above step 302-2, and for a specific implementation of the Indication information for requesting the identifier of the early RACH resource requester, reference may be made to the Early RACH Resource Requester ID Request Indication information in the above Identifier Request message, and thus the details will not be repeatedly described here.

[0481] In some embodiments, the first response message may further comprise an identifier of a node to which the early RACH resource requester belongs. Here, for a specific implementation of the identifier of the node to which the early RACH resource requester belongs, reference may be made to the gNB ID in step 302-2, and thus the details will not be repeatedly described here.

[0482] In some embodiments, the first request message may comprise at least one of: an Xn Setup Request message; an Xn Application Protocol (AP) Retrieve Early RACH Resource Requester IDentifier Request message; and an XnAP New Generation Radio Access Network Node Configuration Update message.

[0483] In some embodiments, the first response message may comprise at least one of: an Xn Setup Response message; an Xn Application Protocol (AP) Retrieve Early RACH Resource Requester IDentifier Response message; and an XnAP New Generation Radio Access Network Node Configuration Update Acknowledge message.

[0484] In some embodiments, a second request message is transmitted by the second node, and a second response message is transmitted by the first node. For a specific implementation, reference may be made to the corresponding description in the method shown in FIG. 3 or FIG. 4, for example, to the specific implementations of the above Examples 1-2-1 to 1-2-4 and steps 317-1 and 317-2, and thus the details will not be repeatedly described here. For a specific implementation of the second request message, reference may be made to the Early RACH Resource Request message in the above step 317-1, and thus the details will not be repeatedly described here. For a specific implementation of the second response message, reference may be made to the Early RACH Resource Response message in step 317-2, and thus the details will not be repeatedly described here.

[0485] Optionally, the second request message may comprise information for requesting to configure an early RACH resource allocated to a node by the candidate cell based on the UE or based on a DU, and the second response message may comprise information related to the early RACH resource allocated to the node by the candidate cell, configured based on the UE or based on the DU.

[0486] In some embodiments, the second request message may comprise: the identifier of the candidate cell; and indication information for requesting to configure the early RACH resource allocated to the node by the candidate cell based on the UE or based on the DU.

[0487] In some embodiments, the second response message may comprise: the identifier of the candidate cell; and Early Uplink Synchronization Configuration information.

[0488] In some embodiments, the second request message may comprise at least one of: an Early RACH Resource Request message; a UE Context Modification Request; a UE Context Modification Required message; a Secondary Node (SN) Modification Required message; and an SN Modification Request message. For example, a DU transmits the UE Context Modification Required message to a CU, a source SN transmits the SN Modification Required message to an MN, and the MN transmits an SN Modification Acknowledge message to a candidate SN. For a specific implementation, reference may be made to the corresponding description in the method shown in FIG. 3 or FIG. 4, and thus the details will not be repeatedly described here.

[0489] In some embodiments, the second response message may comprise at least one of: an Early RACH Resource Request Acknowledge message; an Early RACH Resource Response message; a UE Context Modification Response message; a UE Context Modification Acknowledge message; an SN Modification Acknowledge message; and an SN Modification Request Acknowledge message. For example, the CU transmits the UE Context Modification Acknowledge message to the DU, the MN transmits the SN Modification Acknowledge message to the source SN, and the candidate SN transmits the SN Modification Acknowledge message to the MN. For a specific implementation, reference may be made to the corresponding description in the method shown in FIG. 3 or FIG. 4, and thus the details will not be repeatedly described here.

[0490] The technical features related to one or more of the node name, the base station name, the message name, the information name, etc. in the description of the present disclosure may alternatively be replaced by names, and the changes in names all fall within the scope of the present disclosure.

[0491] The above is an exemplary description of the methods performed by the nodes according to the implementations of the present disclosure. It should be understood that the corresponding steps shown in FIGS. 3-8 and the information contained in the steps are also within the scope of the present disclosure. At the same time, the nodes performing the corresponding methods are also within the scope of the present disclosure.

[0492] FIG. 9 illustrates an exemplary structure of each node applicable to the present disclosure. The exemplary node shown in FIG. 9 includes a transceiver 910 and a processor 920 coupled to the transceiver 910. The transceiver 910 is configured to transmit and receive a signal. The processor 920 is configured to perform the method described in the present disclosure. The present disclosure may alternatively be implemented as a computer storage medium. The computer storage medium stores computer executable instructions. When the stored computer executable instructions are executed by a processor, the processor performs the method described in the present disclosure.

[0493] FIG. 10 is a block diagram of a terminal or user equipment (UE) 1000 according to an embodiment of the disclosure.

[0494] The terminal is an electronic device capable of wireless communication and having various form factors, examples of the terminal may include a UE, a mobile station (MS), a cellular phone, a smartphone, a computer, a tablet, a wearable device, an Internet of Things (IoT) device, or any other device / system capable of performing wireless communication with a base station (BS) and / or another terminal through a wireless channel.

[0495] Referring to FIG. 10, the UE 1000 may include at least one transceiver (hereinafter, referred to as simply “transceiver”) 1001, at least one processor (hereinafter, referred to as simply “processor”) 1002, and at least one memory (hereinafter, referred to as simply “memory”) 1003. According to at least one or a combination of methods corresponding to the embodiments described in the present disclosure, the transceiver 1001, the processor 1002, and the memory 1003 of the UE 1000 may operate. However, components of the UE 1000 are not limited to the example components illustrated in FIG. 10. In another embodiment, the UE 1000 may further include additional components in addition to the above-mentioned components, or some components may be omitted. Further, in some embodiments, any combination of the transceiver 1001, the processor 1002, or the memory 1003 may be integrated in the form of one component.

[0496] The transceiver 1001 may be a communication circuit or communication circuitry that enables the UE 1000 to perform wireless communication with a node or an entity of a network. For example, the transceiver 1001 may enable the UE 1000 to transmit or receive a signal to or from a BS through cellular communication, or to transmit or receive a signal to or from another UE through cellular communication. For example, the transceiver 1001 may support at least one of various cellular communication technologies including 3rd generation (3G), 4th generation (4G), long term evolution (LTE), 5th generation (5G) NR, 6th generation (6G), and various cellular wireless communication technologies supported by the transceiver (1001) may include all subsequent generations of evolved wireless communications.

[0497] According to an embodiment, the UE 1000 may include a plurality of transceivers. For example, in the case of supporting evolved-universal terrestrial radio access-new radio (E-UTRA-NR) dual connectivity (EN-DC), the UE 1000 may include a first transceiver supporting the 4G LTE wireless communication and a second transceiver supporting the 5G NR wireless communication. According to another embodiment, in the case of supporting NR-dual connectivity (NR-DC), the UE 1000 may include a plurality of transceivers supporting the 5G NR wireless communication. According to still another embodiment, in the case of supporting near field wireless communication, the UE 1000 may separately include a transceiver supporting at least one standard in the group of wireless communication protocol standards as defined in the protocol standards for Bluetooth®, wireless local area network (WLAN) network (including institute of electrical and electronics engineers (IEEE) 802.11-2016 standard or its amendments, e.g., 802.11ah, 802.11ad, 802.11ay, 802.11ax, 802.11az, 802.11ba, and 802.11be, without being limited thereto).

[0498] According to an embodiment, the transceiver 1001 may include various circuit structures used to transmit or receive signals to or from a BS through a wireless channel. The signals may include control information and data. For example, the transceiver 1001 may include a radio frequency (RF) transmitter for up-converting and amplifying the frequency of a transmitted signal and an RF receiver for low-noise-amplifying a received signal and down-converting the frequency thereof. The transceiver 1001 may output a signal received through a wireless channel to the processor 1002 and may transmit, through a wireless channel, a signal output from the processor 1002.

[0499] The processor 1002 may control general operations of the UE 1000 according to embodiments of the disclosure. The processor 1002 may be implemented by one or more integrated circuit (or circuitry) (IC) chips and may execute various data processing operations. The processor 1002 may include at least one electric circuit, and may execute instructions (or a program, codes, data, etc.) stored in the memory 1003, individually, collectively or in any combination thereof. Further, the processor 1002 may include a single-core processor or multi-core processor, and may include a processor assembly including a plurality of processing circuits (circuitry) according to a specific implementation scheme.

[0500] The processor 1002 may be electrically, operatively, and / or communicatively coupled to the transceiver 1001 to control the transceiver 1001.

[0501] The processor 1002 may include at least one processor (or processing circuitry), and the at least one processor may perform the following operations individually, collectively or in any combination thereof. For example, the processor 1002 may include a communication processor (CP) configured to control communication operations and an application processor (AP) configured to control execution of an upper layer (for example, an application layer). In a specific embodiment, at least a part of the processor 1002 may be included in one chip (or IC) and the other part of the processor 1002 may be included in another chip (or IC). Otherwise, at least one processor may be included in another component, for example, the transceiver 1001 or the memory 1003.

[0502] The processor 1002 may perform or control or cause an operation of the UE 1000 for executing at least one or a combination of methods according to embodiments of the disclosure. For example, the processor 1002 may control operations of the UE 1000 for processing a downlink signal received from a BS or generating and transmitting an uplink signal to a BS. To this end, the processor 1002 may execute a computer program, codes, or instructions stored in the memory 1003, so as to control other components of the UE 1000 to enable execution of various operations.

[0503] The memory 1003 corresponds to a hardware storage device capable of temporarily or permanently storing information and may include one or more storage media. For example, the memory 1003 may include a memory assembly including one or more storage media. For example, the one or more storage media may include permanent memory, such as a hard drive, flash memory, or read-only memory (ROM), semipermanent memory, such as random access memory (RAM), cache memory, or a combination thereof.

[0504] The memory 1003 may be electrically, operatively, and / or communicatively coupled to the processor 1002 and may be accessed by the processor 1002.

[0505] The memory 1003 may store a computer program, codes, or instructions executable by the processor 1002. According to an embodiment, a computer program, codes, or instructions executable by the processor 1002 may be either stored in a single memory device or separated and distributedly stored in two or more memory devices. By executing the instructions stored in the memory 1003, the processor 1002 may perform various functions according to an embodiment of the disclosure.

[0506] According to an embodiment of the disclosure, operations of the UE 1000 may be caused to be performed based on execution of instructions (or a computer program or codes) stored in the memory 1003 by at least one processor (or processing circuitry) configured to execute the same individually, collectively, or in any combination thereof, based on processing circuitry that is not configured to execute instructions, and / or based on components of processing circuitry that is not configured to execute instructions.

[0507] FIG. 11 is a block diagram of a base station (BS) 1100 according to an embodiment of the disclosure.

[0508] The BS 1100 may perform wireless communication with at least one user equipment (UE) located within the area of the BS 1100 through a wireless channel. The BS 1100 may perform communication with a node or an entity of a network through wired or wireless communication.

[0509] Referring to FIG. 11, the BS 1100 may include at least one transceiver (hereinafter, referred to as simply “transceiver”) 1101, at least one processor (hereinafter, referred to as simply “processor”) 1102, and at least one memory (hereinafter, referred to as simply “memory”) 1103. According to at least one or a combination of methods corresponding to the embodiments described in the present disclosure, the transceiver 1101, the processor 1102, and the memory 1103 of the BS 1100 may operate. However, components of the BS 1100 are not limited to the example components illustrated in FIG. 11. In another embodiment, the BS 1100 may further include additional components in addition to the above-mentioned components, or some components may be omitted. Further, in some embodiments, any combination of the transceiver 1101, the processor 1102, or the memory 1103 may be integrated in the form of one component.

[0510] The transceiver 1101 may be a communication circuit or communication circuitry that enables the BS 1100 to perform wireless communication with a node or an entity of a network. For example, the transceiver 1101 may enable the BS 1100 to transmit or receive a signal to or from the UE X00 through cellular communication, or to transmit or receive a signal to or from another network entity through wireless communication. For example, the transceiver 1101 may support various cellular communication technologies including 3rd generation (3G), 4th generation (4G), long term evolution (LTE), 5th generation (5G) NR, 6th generation (6G), and various cellular wireless communication technologies supported by the transceiver (1101) may include all subsequent generations of evolved wireless communications. According to an embodiment, the transceiver 1101 may include various circuit structures used to transmit or receive signals to or from a UE through a wireless channel. The signals may include control information and data. For example, the transceiver 1101 may include a radio frequency (RF) transmitter for up-converting and amplifying the frequency of a transmitted signal and an RF receiver for low-noise-amplifying a received signal and down-converting the frequency thereof. The transceiver 1101 may output a signal received through a wireless channel to the processor 1102 and may transmit, through a wireless channel, a signal output from the processor 1102.

[0511] Meanwhile, according to an embodiment of the present disclosure, the BS 1100 may perform communication with a node or an entity of a network through wired or wireless communication. For example, the BS 1100 may perform wired or wireless communication with an adjacent BS, or a node or an entity of a core network through a backhaul network. Although not illustrated in FIG. 11, when the BS 1100 performs wired communication, the BS 1100 may further include a separate network interface for wired communication in addition to the transceiver 1101. The network interface may be referred to as network interface circuitry or communication interface circuitry.

[0512] The processor 1102 may control general operations of the BS 1100 according to embodiments of the disclosure. The processor 1102 may be implemented by one or more integrated circuit (or circuitry) (IC) chips and may execute various data processing operations. The processor 1102 may include at least one electric circuit, and may execute instructions (or a program, codes, data, etc.) stored in the memory 1103, individually, collectively or in any combination thereof. Further, the processor 1102 may include a single-core processor or multi-core processor, and may include a processor assembly including a plurality of processing circuits (circuitry) according to a specific implementation scheme.

[0513] The processor 1102 may be electrically, operatively, and / or communicatively coupled to the transceiver 1101 to control the transceiver 1101.

[0514] The processor 1102 may include at least one processor (or processing circuitry), and the at least one processor may perform the following operations individually, collectively or in any combination thereof. In a specific embodiment, at least a part of the processor 1102 may be included in one chip (or IC) and the other part of the processor 1102 may be included in another chip (or IC). Otherwise, at least one processor may be included in another component, for example, the transceiver 1101 or the memory 1103.

[0515] The processor 1102 may perform or control or cause an operation of the BS 1100 for executing at least one or a combination of methods according to embodiments of the disclosure. For example, the processor 1102 may control operations of the BS 1100 for generating and transmitting a downlink signal to a UE or processing an uplink signal received from a UE. Otherwise, the BS 1100 may transmit or receive a signal to or from a neighboring BS, transfer a signal received from a UE to an upper node of the network, or transmit a signal transferred from an upper node of the network to a UE. To this end, the processor 1102 may execute a computer program, codes, or instructions stored in the memory 1103, so as to control other components of the BS 1100 to enable execution of various operations.

[0516] The memory 1103 corresponds to a hardware storage device capable of temporarily or permanently storing information and may include one or more storage media. For example, the memory 1103 may include a memory assembly including one or more storage media. For example, the one or more storage media may include permanent memory, such as a hard drive, flash memory, or read-only memory (ROM), semipermanent memory, such as random access memory (RAM), cache memory, or a combination thereof.

[0517] The memory 1103 may be electrically, operatively, and / or communicatively coupled to the processor 1102 and may be accessed by the processor 1102.

[0518] The memory 1103 may store a computer program, codes, or instructions executable by the processor 1102. According to an embodiment, a computer program, codes, or instructions executable by the processor 1102 may be either stored in a single memory device or separated and distributedly stored in two or more memory devices. By executing the instructions stored in the memory 1103, the processor 1102 may perform various functions according to an embodiment of the disclosure.

[0519] According to an embodiment of the disclosure, operations of the BS 1100 may be caused to be performed based on execution of instructions (or a computer program or codes) stored in the memory 1103 by at least one processor (or processing circuitry) configured to execute the same individually, collectively, or in any combination thereof, based on processing circuitry that is not configured to execute instructions, and / or based on components of processing circuitry that is not configured to execute instructions.

[0520] The UE or the base station may perform various communication procedures related to the control plane or the user plane by cooperating with one or more network entities based on wireless communication. For example, the UE may communicate with a network entity (for example, an Access and Mobility Management Function (AMF), a Session Management Function (SMF), rtc.) via the base station, or the base station may perform at least one communication procedure by directly transmitting and receiving signals to / from, or relaying signals between, the network entities.

[0521] The structure of the above-described network entity will be described in more detail with reference to the drawings.

[0522] FIG. 12 is a block diagram of a network entity 1200 according to an embodiment of the disclosure.

[0523] The network entity 1200 may include an entity (apparatus, device, or server, etc.) that performs one or more network functions (NFs) or a part of a network function constituting a core network (e.g., a 5th generation (5G) core (5GC)) in a communication system. In this case, multiple NFs may be implemented within a single network entity, or a single NF may be distributed and implemented across a plurality of network entities. In addition, when an NF is implemented within the network entity, the NF may be implemented in the form of software, and in such a case, a program for operating the NF may be stored in memory of the network entity 1200.

[0524] A single NF may be implemented by one or more instances, which may be deployed on the same network entity or distributed across multiple network entities to operate. The instance may be a software unit that logically executes a specific network function, and may be implemented in a form that is decoupled from physical hardware resources. Further, one or more NFs may be implemented in the form of one network slice to operate to satisfy specifications required by a particular service.

[0525] The NF may include at least one of an access and mobility management function (AMF), a session management function (SMF), a local session management function (L-SMF), a user plane function (UPF), a local user plane function (L-UPF), a policy control function (PCF), a unified data management (UDM), a unified data repository (UDR), a network exposure function (NEF), a network repository function (NRF), an application function (AF), a network slice selection function (NSSF), a network data analytics function (NWDAF), a network slice admission control function (NSACF), an authentication server function (AUSF), or a data network (DN), etc.

[0526] Referring to FIG. 12, the network entity 1200 may include at least one network interface 1201, at least one processor 1202 (hereinafter, “processor”), and at least one memory 1203 (hereinafter, “memory”). As described above, a NF may be implemented in the form of a physical device such as the network entity 1200, or may be virtualized and executed in the form of an instance. When implemented as an instance, the NF need not necessarily include physical components as illustrated in FIG. 12. In such a case, the instance may be logically represented as comprising one or more logical functional elements.

[0527] According to at least one or a combination of methods corresponding to the embodiments described in the present disclosure, the network interface 1201, the processor 1202, and the memory 1203 of the network entity 1200 may operate. However, components of the network entity 1200 are not limited to the example components illustrated in FIG. 12. In another embodiment, the network entity 1200 may further include additional components in addition to the above-mentioned components, or some components may be omitted. Further, in an embodiment, the network interface 1201, the processor 1202, or the memory 1203 may be integrated in the form of one component.

[0528] The network interface 1201 is a collective term for a transmitter part of the network entity 1200 and a receiver part of the network entity 1200, and may be a communication circuit for transmitting or receiving a signal to or from a user equipment (UE), a base station (BS), or another network entity. Here, the communication circuit may include both a communication circuit for wireless communication and a communication circuit for a wired communication. For example, the network interface 1201 may include a circuit, logic, hardware, etc., configured to exchange a control plane message or a user plane message with a UE, a BS, or other core network entities through wireless communication or wired communication. The network interface 1201 may operate using various protocols (e.g., non-access stratum (NAS) protocol). The network interface 1201 may also be referred to, for convenience of description or depending on implementation, as communication circuitry, network interface circuitry, or a communication interface circuitry.

[0529] The processor 1202 may control general operations of the network entity 1200 according to embodiments of the disclosure. The processor 1202 may be implemented by one or more integrated circuit (or circuitry) (IC) chips and may execute various data processing operations. The processor 1202 may include at least one electric circuit, and may execute instructions (or a program, codes, data, etc.) stored in the memory 1203, individually, collectively or in any combination thereof. Further, the processor 1202 may include a single-core processor or multi-core processor, and may include a processor assembly including a plurality of processing circuits (circuitry) according to a specific implementation scheme. Further, it should be noted that, according to another embodiment, in a case where NF is implemented in the form of an instance, the network function may be not necessarily configured by physical hardware.

[0530] According to an embodiment, the processor 1202 may be electrically, operatively, and / or communicatively coupled to the network interface 1201 to control the network interface 1201.

[0531] The processor 1202 may include at least one processor (or processing circuitry), and the at least one processor may perform the following operations individually, collectively or in any combination thereof. In a specific embodiment, at least a part of the processor 1202 may be included in one chip (or IC) and the other part of the processor 1202 may be included in another chip (or IC). Otherwise, at least one processor may be included in another component, for example, the network interface 1201 or the memory 1203.

[0532] The processor 1202 may perform or control or cause an operation of the network entity 1200 for executing at least one or a combination of methods according to embodiments of the disclosure. For example, the processor 1202 may control operations of the network entity 1200 for exchanging a control plane message or a user plane message with a UE, a BS, or other core network entities through wireless or wired communication, using various protocols (e.g., NAS protocol). To this end, the processor 1202 may execute a computer program, codes, or instructions stored in the memory 1203, so as to control other components of the network entity 1200 to enable execution of various operations.

[0533] The memory 1203 corresponds to a hardware storage device capable of temporarily or permanently storing information and may include one or more storage media. For example, the memory 1203 may include a memory assembly including one or more storage media. For example, the one or more storage media may include permanent memory, such as a hard drive, flash memory, or read-only memory (ROM), semipermanent memory, such as random access memory (RAM), cache memory, or a combination thereof.

[0534] The memory 1203 may be electrically, operatively, and / or communicatively coupled to the processor 1202 and may be accessed by the processor 1202.

[0535] The memory 1203 may store a computer program, codes, or instructions executable by the processor 1202. According to an embodiment, a computer program, codes, or instructions executable by the processor 1202 may be either stored in a single memory device or separated and distributedly stored in two or more memory devices. By executing the instructions stored in the memory 1203, the processor 1202 may perform various functions according to an embodiment of the disclosure.

[0536] According to an embodiment of the disclosure, operations of the network entity 1200 may be caused to be performed based on execution of instructions (or a computer program or codes) stored in the memory 1203 by at least one processor (or processing circuitry) configured to execute the same individually, collectively, or in any combination thereof, based on processing circuitry that is not configured to execute instructions, and / or based on components of processing circuitry that is not configured to execute instructions.

[0537] In one embodiment, a method performed by a first node in a wireless communication system is provided, the method comprises: transmitting, to a second node, a first request message for requesting an identifier of an early random access channel (RACH) resource requester to which a candidate cell for a layer 1 / layer 2 triggered mobility (LTM) handover belongs; receiving, from the second node, a first response message including an identifier of the candidate cell and an identifier of the early RACH resource requester to which the candidate cell belongs, wherein the first node is a central unit (CU) of a source node and the second node is a CU of a candidate node; or the first node is a master node and the second node is a secondary node.

[0538] In another embodiment, the first response message further comprises an identifier of a node to which the early RACH resource requester belongs.

[0539] In another embodiment, the first request message comprises the identifier of the candidate cell and indication information for requesting the identifier of the early RACH resource requester, wherein the identifier of the early RACH resource requester is an identifier of an entity which indicates to request an early RACH resource.

[0540] In another embodiment, the first request message comprises at least one of: an Xn Setup Request message; an Xn Application Protocol (AP) Retrieve Early RACH Resource Requester Identifier Request message; and an XnAP New Generation Radio Access Network Node Configuration Update message.

[0541] In another embodiment, the first response message comprises at least one of: an Xn Setup Response message; an Xn Application Protocol (AP) Retrieve Early RACH Resource Requester IDentifier Response message; and an XnAP New Generation Radio Access Network Node Configuration Update Acknowledge message.

[0542] In another embodiment, the method further comprises: receiving, from the second node, a second message comprising at least one of: timing advanced (TA)-related information of the candidate cell; the identifier of the early RACH resource requester; and an identifier of a node to which the early RACH resource requester belongs.

[0543] In another embodiment, the method further comprises: transmitting the TA-related information of the candidate cell to a node indicated by the identifier of the node to which the early RACH resource requester belongs or to a node indicated by the identifier of the early RACH resource requester.

[0544] In one embodiment, a method performed by a second node in a wireless communication system is provided, the method comprises: receiving, from a first node, a first request message for requesting an identifier of an early random access channel (RACH) resource requester to which a candidate cell for a layer 1 / layer 2 triggered mobility (LTM) handover belongs; transmitting, to the first node, a first response message comprising an identifier of the candidate cell and an identifier of the early RACH resource requester to which the candidate cell belongs, wherein the first node is a central unit (CU) of a source node and the second node is a CU of a candidate node; or the first node is a master node and the second node is a secondary node.

[0545] In another embodiment, the first response message further comprises an identifier of a node to which the early RACH resource requester belongs.

[0546] In another embodiment, the first request message comprises the identifier of the candidate cell and Indication information for requesting the identifier of the early RACH resource requester, wherein the identifier of the early RACH resource requester is an identifier of an entity which indicates to request an early RACH resource.

[0547] In another embodiment, the method further comprises: transmitting, to the first node,a second message comprising at least one of: timing advanced (TA)-related information of the candidate cell; the identifier of the early RACH resource requester; and an identifier of a node to which the early RACH resource requester belongs.

[0548] In one embodiment, a method performed by a user equipment (UE) in a wireless communication system is provided, the method comprises: receiving a Radio Resource Control (RRC) Reconfiguration message; transmitting an RRC Reconfiguration Complete message, wherein a first request message is transmitted by a first node for requesting an identifier of an early random access channel (RACH) resource requester to which a candidate cell for a layer 1 / layer 2 triggered mobility (LTM) handover belongs, wherein a first response message is transmitted by a second node, and the first response message comprises an identifier of the candidate cell and an identifier of the early RACH resource requester to which the candidate cell belongs, wherein the first node is a central unit (CU) of a source node and the second node is a CU of a candidate node; or the first node is a master node and the second node is a secondary node.

[0549] In one embodiment, a node is provided, the node comprises: a transceiver, configured to transmit and receive a signal; and a processor, coupled to the transceiver, and configured to perform the method according to any one of the embodiments of the disclosure.

[0550] In one embodiment, a user equipment (UE) is provided, the UE comprises: a transceiver, configured to transmit and receive a signal; and a processor, coupled to the transceiver and configured to perform the method according to the embodiments of the disclosure.

[0551] In one embodiment, a computer readable storage medium is provided, the computer readable storage medium stores a computer executable instruction, wherein when the computer executable instruction is executed by a processor, the processor performs the method according to any one of the embodiments of the disclosure.

[0552] The various illustrative logical blocks, modules and circuits described in the present disclosure may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or　other programmable logic devices, a discrete gate or transistor logic, a discrete hardware component, or any combination thereof designed to perform the functions described herein. The general purpose processor may be a microprocessor, but in an alternative scheme, the processor may be any conventional processor, controller, microcontroller, or state machine. The processor may alternatively be implemented as a combination of computing devices, for example, a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in collaboration with a DSP core, or any other such configuration.

[0553] The steps of the method or algorithm described in the present disclosure may be embodied directly in hardware, in a software module executed by the processor, or in a combination of the two. The software module may reside in a RAM memory, a flash memory, a ROM memory, an EPROM memory, an EEPROM memory, a register, a hard disk, a removable disk, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor, to enable the processor to read information from / write information to the storage medium. In an alternative scheme, the storage medium may be integrated to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In an alternative scheme, the processor and the storage medium may reside as discrete components in a user terminal.

[0554] In one or more exemplary designs, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in the software, the functions may be stored on or transmitted over a computer readable medium as one or more instructions or codes. The computer readable medium includes both a computer storage medium and a communication medium, the communication medium including any medium that facilitates the transfer of a computer program from one place to another. The storage medium may be any available medium that can be accessed by a general purpose or special purpose computer.

[0555] Example methods and apparatuses are described in combination with the accompanying drawings in the description set forth herein, and do not represent all the examples that may be implemented or that are within the scope of the claims. The term “example” used herein means “serving as an example, instance, or illustration,” rather than “preferred” or “advantageous over other examples.” The detailed description includes specific details for the purpose of providing an understanding of the described techniques. These techniques, however, may be practiced without these specific details. In some cases, well-known structures and devices are shown in the form of a block diagram in order to avoid obscuring the concepts of the described examples.

[0556] This specification contains many specific implementation details, but the implementation details should not be construed as a limitation to the scope of any disclosure or the scope claimed, but rather as a description for specific features in a specific embodiment of the specific disclosure. Certain features described in the context of separate embodiments in this specification may alternatively be implemented in combination in a single embodiment. Rather, the various features described in the context of a single embodiment may be implemented separately in a plurality of embodiments or implemented in any suitable sub-combination. Furthermore, the features may be described as functioning in certain combinations in the context, and even initially so claimed, but in some cases one or more features in a claimed combination may be deleted from the combination, and the claimed combination may be directed to a sub-combination or the variation of the sub-combination.

[0557] It should be understood that the specific order or hierarchy of steps in the method in the present disclosure is an illustration for an exemplary process. Based on design preferences, it may be understood that the specific order or hierarchy of the steps in the method may be rearranged to achieve the functions and effects disclosed in the present disclosure. The accompanying method claims present the elements of various steps in example order, but are not intended to be limited to the specific order or hierarchy presented, unless specifically stated otherwise. Furthermore, although an element may be described or claimed in a singular form, the plural can also be expected unless the limitation to the singular is explicitly stated. Thus, the present disclosure is not limited to the examples shown, and any apparatus for performing the functions described herein is included in the aspects of the present disclosure.

[0558] It can be understood that “at least one” described in the present disclosure includes any and / or all possible combinations of the listed items, the various embodiments described in the present disclosure and the various examples in the embodiments may be varied and combined in any suitable form, and “ / ” described in the present disclosure represents “and / or.”

[0559] The text and drawings are provided as examples only to help readers understand the present disclosure. The text and drawings are not intended to limit and should not be interpreted as limiting the scope of the present disclosure in any way. Although certain embodiments and examples have been provided, based on the content disclosed herein, it is obvious to those skilled in the art that modifications to the illustrated embodiments and examples can be made without departing from the scope of the present disclosure.

[0560] Meanwhile, although specific embodiments of the present disclosure have been described in detail, various modifications may be made without departing from the scope of the present disclosure. Therefore, the scope of the present disclosure should not be limited to the described embodiments, but should be defined by the claims and equivalents thereof.

Claims

1. A method performed by a first node in a wireless communication system, the method comprising:transmitting, to a second node, a first request message for requesting an identifier of an early random access channel (RACH) resource requester to which a candidate cell for a layer 1 / layer 2 triggered mobility (LTM) handover belongs; andreceiving, from the second node, a first response message including an identifier of the candidate cell and an identifier of the early RACH resource requester to which the candidate cell belongs,wherein the first node is a central unit (CU) of a source node and the second node is a CU of a candidate node; or the first node is a master node and the second node is a secondary node.2.The method according to claim 1, wherein the first response message further comprises an identifier of a node to which the early RACH resource requester belongs.3.The method according to claim 1, wherein the first request message comprises the identifier of the candidate cell and indication information for requesting the identifier of the early RACH resource requester,wherein the identifier of the early RACH resource requester is an identifier of an entity which indicates to request an early RACH resource.4.The method according to claim 1, wherein the first request message comprises at least one of:an Xn Setup Request message;an Xn Application Protocol (AP) Retrieve Early RACH Resource Requester Identifier Request message; andan XnAP New Generation Radio Access Network Node Configuration Update message.5.The method according to claim 1, wherein the first response message comprises at least one of:an Xn Setup Response message;an Xn Application Protocol (AP) Retrieve Early RACH Resource Requester IDentifier Response message; andan XnAP New Generation Radio Access Network Node Configuration Update Acknowledge message.6.The method according to claim 1, further comprising:receiving, from the second node, a second message comprising at least one of:timing advanced (TA)-related information of the candidate cell;the identifier of the early RACH resource requester; andan identifier of a node to which the early RACH resource requester belongs.7.The method according to claim 6, further comprising:transmitting the TA-related information of the candidate cell to a node indicated by the identifier of the node to which the early RACH resource requester belongs or to a node indicated by the identifier of the early RACH resource requester.8.A method performed by a second node in a wireless communication system, the method comprising:receiving, from a first node, a first request message for requesting an identifier of an early random access channel (RACH) resource requester to which a candidate cell for a layer 1 / layer 2 triggered mobility (LTM) handover belongs; andtransmitting, to the first node, a first response message comprising an identifier of the candidate cell and an identifier of the early RACH resource requester to which the candidate cell belongs,wherein the first node is a central unit (CU) of a source node and the second node is a CU of a candidate node; or the first node is a master node and the second node is a secondary node.9.The method according to claim 8, wherein the first response message further comprises an identifier of a node to which the early RACH resource requester belongs.10.The method according to claim 8, wherein the first request message comprises the identifier of the candidate cell and indication information for requesting the identifier of the early RACH resource requester,wherein the identifier of the early RACH resource requester is an identifier of an entity which indicates to request an early RACH resource.11.The method according to claim 8, wherein the first request message comprises at least one of:an Xn Setup Request message;an Xn Application Protocol (AP) Retrieve Early RACH Resource Requester Identifier Request message; andan XnAP New Generation Radio Access Network Node Configuration Update message.12.The method according to claim 8, wherein the first response message comprises at least one of:an Xn Setup Response message;an Xn Application Protocol (AP) Retrieve Early RACH Resource Requester IDentifier Response message; andan XnAP New Generation Radio Access Network Node Configuration Update Acknowledge message.13.The method according to claim 8, further comprising:transmitting, to the first node, a second message comprising at least one of:timing advanced (TA)-related information of the candidate cell;the identifier of the early RACH resource requester; andan identifier of a node to which the early RACH resource requester belongs.14.A method performed by a user equipment (UE) in a wireless communication system, the method comprising:receiving a Radio Resource Control (RRC) Reconfiguration message; andtransmitting an RRC Reconfiguration Complete message, wherein a first request message is transmitted by a first node for requesting an identifier of an early random access channel (RACH) resource requester to which a candidate cell for a layer 1 / layer 2 triggered mobility (LTM) handover belongs,wherein a first response message is transmitted by a second node, and the first response message comprises an identifier of the candidate cell and an identifier of the early RACH resource requester to which the candidate cell belongs,wherein the first node is a central unit (CU) of a source node and the second node is a CU of a candidate node; or the first node is a master node and the second node is a secondary node.15.A user equipment (UE), comprising:at least one transceiver;at least one processor communicatively coupled to the at least one transceiver; andat least one memory, communicatively coupled to the at least one processor, storing instructions executable by the at least one processor individually or in any combination to cause the UE to:receive a Radio Resource Control (RRC) Reconfiguration message, andtransmit an RRC Reconfiguration Complete message, wherein a first request message is transmitted by a first node for requesting an identifier of an early random access channel (RACH) resource requester to which a candidate cell for a layer 1 / layer 2 triggered mobility (LTM) handover belongs,wherein a first response message is transmitted by a second node, and the first response message comprises an identifier of the candidate cell and an identifier of the early RACH resource requester to which the candidate cell belongs,wherein the first node is a central unit (CU) of a source node and the second node is a CU of a candidate node; or the first node is a master node and the second node is a secondary node.

Images